WEBVTT 00:00:00.000 --> 00:00:02.640 align:middle line:84% The following content is provided under a Creative 00:00:02.640 --> 00:00:04.000 align:middle line:90% Commons license. 00:00:04.000 --> 00:00:06.400 align:middle line:84% Your support will help MIT OpenCourseWare 00:00:06.400 --> 00:00:10.080 align:middle line:84% continue to offer high-quality educational resources for free. 00:00:10.080 --> 00:00:13.320 align:middle line:84% To make a donation or view additional materials 00:00:13.320 --> 00:00:17.280 align:middle line:84% from hundreds of MIT courses, visit MIT OpenCourseWare 00:00:17.280 --> 00:00:19.497 align:middle line:90% at ocw.mit.edu. 00:00:19.497 --> 00:00:21.080 align:middle line:84% DIERDRE TOOLE: Today we're going to be 00:00:21.080 --> 00:00:23.260 align:middle line:84% talking about the global phosphorus cycle. 00:00:23.260 --> 00:00:24.760 align:middle line:84% And I'm going to start out by saying 00:00:24.760 --> 00:00:26.218 align:middle line:84% I think that it's actually probably 00:00:26.218 --> 00:00:28.500 align:middle line:84% the simplest of the biogeochemical cycles, 00:00:28.500 --> 00:00:32.840 align:middle line:84% because there isn't really a gaseous form of phosphorus. 00:00:32.840 --> 00:00:36.622 align:middle line:84% So a nutshell, what the cycle is, is this first slide. 00:00:36.622 --> 00:00:38.580 align:middle line:84% I mean, we can't just leave it here, obviously. 00:00:38.580 --> 00:00:41.800 align:middle line:84% But basically, what happens is we have phosphorus minerals 00:00:41.800 --> 00:00:45.600 align:middle line:84% and varied phosphorus in the continental crust. 00:00:45.600 --> 00:00:47.375 align:middle line:90% This is leached and eroded. 00:00:47.375 --> 00:00:49.000 align:middle line:84% It ends up in the terrestrial biosphere 00:00:49.000 --> 00:00:51.300 align:middle line:84% where it's processed a variety of different ways. 00:00:51.300 --> 00:00:53.880 align:middle line:90% 00:00:53.880 --> 00:00:56.660 align:middle line:84% Once you have the different components 00:00:56.660 --> 00:00:58.160 align:middle line:84% in the terrestrial biosphere they're 00:00:58.160 --> 00:01:00.896 align:middle line:84% transported by rivers to estuaries and then 00:01:00.896 --> 00:01:02.070 align:middle line:90% in the oceans. 00:01:02.070 --> 00:01:04.910 align:middle line:84% There's also some physical transport via wind 00:01:04.910 --> 00:01:06.370 align:middle line:90% into the ocean. 00:01:06.370 --> 00:01:07.450 align:middle line:90% It gets to the ocean. 00:01:07.450 --> 00:01:09.090 align:middle line:90% It's cycled by the marine biota. 00:01:09.090 --> 00:01:12.270 align:middle line:84% It's buried, becomes part of the marine sediments, 00:01:12.270 --> 00:01:15.390 align:middle line:84% and then those sediments are subducted and then ultimately 00:01:15.390 --> 00:01:17.350 align:middle line:90% uplifted to continental crust. 00:01:17.350 --> 00:01:21.330 align:middle line:84% So that's it in a nutshell, small little nutshell, 00:01:21.330 --> 00:01:22.455 align:middle line:90% the phosphorus cycle. 00:01:22.455 --> 00:01:23.830 align:middle line:84% But what I'm going to do today is 00:01:23.830 --> 00:01:27.590 align:middle line:84% I'm going to go through each of the biogeochemical cycling 00:01:27.590 --> 00:01:30.710 align:middle line:84% and the different reservoirs and look at some of the inventories, 00:01:30.710 --> 00:01:34.670 align:middle line:84% just so we get an idea of the different scales we're talking 00:01:34.670 --> 00:01:38.910 align:middle line:84% about and some of the timescales in terms of turnover times 00:01:38.910 --> 00:01:41.290 align:middle line:84% and reservoirs, and then a little bit at the end, 00:01:41.290 --> 00:01:45.710 align:middle line:84% interactions with other biogeochemical cycles. 00:01:45.710 --> 00:01:48.370 align:middle line:90% So why phosphorus? 00:01:48.370 --> 00:01:49.010 align:middle line:90% Why phosphate? 00:01:49.010 --> 00:01:49.990 align:middle line:90% Why do we care? 00:01:49.990 --> 00:01:54.510 align:middle line:84% And what I'm showing here these are world ocean 00:01:54.510 --> 00:01:59.130 align:middle line:84% atlas surface distributions of phosphate 00:01:59.130 --> 00:02:01.430 align:middle line:84% in millimoles of phosphate per cubic meter, 00:02:01.430 --> 00:02:03.610 align:middle line:84% and sea surface nitrate in millimoles 00:02:03.610 --> 00:02:06.210 align:middle line:90% of nitrogen per cubic meter. 00:02:06.210 --> 00:02:08.930 align:middle line:84% And what some models have suggested 00:02:08.930 --> 00:02:10.650 align:middle line:84% and various individuals have suggested 00:02:10.650 --> 00:02:13.370 align:middle line:84% is that phosphate is a limiting nutrient 00:02:13.370 --> 00:02:15.150 align:middle line:90% on geological timescales. 00:02:15.150 --> 00:02:19.310 align:middle line:84% It's also really a limiting nutrient for biology. 00:02:19.310 --> 00:02:22.075 align:middle line:84% Without it, they can't do primary production. 00:02:22.075 --> 00:02:23.450 align:middle line:84% And so given that, we really need 00:02:23.450 --> 00:02:27.708 align:middle line:84% to constrain the phosphate budget globally. 00:02:27.708 --> 00:02:29.250 align:middle line:84% And to do that, we need to understand 00:02:29.250 --> 00:02:34.170 align:middle line:84% the factors that influence its oceanic inventory. 00:02:34.170 --> 00:02:38.890 align:middle line:84% And so just to address the age-old question 00:02:38.890 --> 00:02:43.470 align:middle line:84% are oceanic phytoplankton phosphate or nitrate limited. 00:02:43.470 --> 00:02:48.810 align:middle line:84% And that's something you'll hear people argue about ad nauseam. 00:02:48.810 --> 00:02:50.190 align:middle line:90% I think the jury's still out. 00:02:50.190 --> 00:02:54.290 align:middle line:84% It depends on timescales and it depends on environments. 00:02:54.290 --> 00:02:58.180 align:middle line:84% But there's two general viewpoints I would call them. 00:02:58.180 --> 00:03:01.040 align:middle line:84% And the first is the geochemist viewpoint. 00:03:01.040 --> 00:03:04.240 align:middle line:84% And essentially this consists of the fact that nitrogen, 00:03:04.240 --> 00:03:07.200 align:middle line:84% your loading of nitrogen, it can be topped off. 00:03:07.200 --> 00:03:08.660 align:middle line:84% If you don't have enough nitrogen, 00:03:08.660 --> 00:03:10.160 align:middle line:84% you can have diazotrophs, which can 00:03:10.160 --> 00:03:13.880 align:middle line:84% fix inorganic dianitrogen into organic forms, which 00:03:13.880 --> 00:03:15.720 align:middle line:90% are bioavailable. 00:03:15.720 --> 00:03:18.880 align:middle line:84% And phosphorus doesn't really have a comparable source 00:03:18.880 --> 00:03:21.000 align:middle line:84% like that because we don't have any gaseous forms 00:03:21.000 --> 00:03:24.220 align:middle line:84% and there aren't really the same of biological pathways. 00:03:24.220 --> 00:03:29.440 align:middle line:84% So geochemists tend to think of it as phosphate limitation. 00:03:29.440 --> 00:03:32.920 align:middle line:84% But the biologists' viewpoint, which is primarily 00:03:32.920 --> 00:03:35.600 align:middle line:84% observationalist and experimentalist, when 00:03:35.600 --> 00:03:38.600 align:middle line:84% they go out in the field and they look at field data 00:03:38.600 --> 00:03:41.160 align:middle line:84% and they do nutrient addition type experiments and bottle 00:03:41.160 --> 00:03:44.587 align:middle line:84% additions on deck at sea, they generally 00:03:44.587 --> 00:03:46.920 align:middle line:84% find when they're working with these natural assemblages 00:03:46.920 --> 00:03:49.880 align:middle line:84% that phytoplankton are more nitrogen 00:03:49.880 --> 00:03:51.960 align:middle line:84% stressed than phosphate stressed, 00:03:51.960 --> 00:03:54.740 align:middle line:84% and they respond better to nitrate additions 00:03:54.740 --> 00:03:57.020 align:middle line:90% than phosphate additions. 00:03:57.020 --> 00:04:01.380 align:middle line:84% And so to give a little bit of information 00:04:01.380 --> 00:04:04.020 align:middle line:84% on why some of these hypotheses started, 00:04:04.020 --> 00:04:07.980 align:middle line:84% this is the Levitus climatological data. 00:04:07.980 --> 00:04:12.800 align:middle line:84% And we have phosphate at the surface, at various depths. 00:04:12.800 --> 00:04:15.780 align:middle line:84% You can see the depths of the different colors indicated 00:04:15.780 --> 00:04:20.740 align:middle line:84% with these, I guess brownish spots being the shallowest, 00:04:20.740 --> 00:04:23.820 align:middle line:84% and then the pink being the deepest, 00:04:23.820 --> 00:04:25.520 align:middle line:90% versus nitrate concentrations. 00:04:25.520 --> 00:04:29.597 align:middle line:84% And this is the Redfield ratio line, the 16-to-1 ratio line. 00:04:29.597 --> 00:04:31.180 align:middle line:84% And you can see that in a lot of cases 00:04:31.180 --> 00:04:33.620 align:middle line:90% they do fall below that line. 00:04:33.620 --> 00:04:37.482 align:middle line:84% So that actually the nitrate is drawn down before the phosphate. 00:04:37.482 --> 00:04:39.940 align:middle line:84% And so there have been various modeling exercises that have 00:04:39.940 --> 00:04:42.300 align:middle line:90% been trying to address this. 00:04:42.300 --> 00:04:44.380 align:middle line:84% And one of the ones that I particularly like 00:04:44.380 --> 00:04:50.420 align:middle line:84% is Tyrrell 1999, where their final conclusion was 00:04:50.420 --> 00:04:53.530 align:middle line:90% that nitrate can be limiting. 00:04:53.530 --> 00:04:57.730 align:middle line:84% When you look at the ocean right now, nitrate can be limiting. 00:04:57.730 --> 00:05:00.120 align:middle line:84% But on the longer time scales, phosphate 00:05:00.120 --> 00:05:01.650 align:middle line:90% is ultimately limiting. 00:05:01.650 --> 00:05:03.850 align:middle line:84% Because when you change the amount of nitrate 00:05:03.850 --> 00:05:05.530 align:middle line:84% through nitrogen fixation, you also 00:05:05.530 --> 00:05:07.510 align:middle line:84% are going to change the comparable pathways, 00:05:07.510 --> 00:05:09.450 align:middle line:90% the loss pathways. 00:05:09.450 --> 00:05:12.310 align:middle line:84% Whereas phosphate, you can't do that. 00:05:12.310 --> 00:05:14.780 align:middle line:84% So if you change the amount of phosphate loading, 00:05:14.780 --> 00:05:16.530 align:middle line:84% you're going to directly change the amount 00:05:16.530 --> 00:05:18.490 align:middle line:90% of oceanic productivity. 00:05:18.490 --> 00:05:22.010 align:middle line:84% So it's really important for us in long term carbon 00:05:22.010 --> 00:05:25.970 align:middle line:84% dioxide, organic carbon export, to understand the inventories 00:05:25.970 --> 00:05:29.090 align:middle line:90% of phosphate and how it cycles. 00:05:29.090 --> 00:05:34.090 align:middle line:84% And so this is a figure that's going to come up a lot today. 00:05:34.090 --> 00:05:36.170 align:middle line:84% I'm going to say right off the bat 00:05:36.170 --> 00:05:38.850 align:middle line:84% that there's a lot of uncertainties 00:05:38.850 --> 00:05:40.290 align:middle line:90% in the numbers in this figure. 00:05:40.290 --> 00:05:44.130 align:middle line:84% Right now, if you look at it, import balances export, 00:05:44.130 --> 00:05:45.390 align:middle line:90% and it looks very clean. 00:05:45.390 --> 00:05:49.010 align:middle line:84% But we do have, and I'll talk about this a little bit today, 00:05:49.010 --> 00:05:53.560 align:middle line:84% estimates that don't make these estimates look as clean as they 00:05:53.560 --> 00:05:54.580 align:middle line:90% do in this figure. 00:05:54.580 --> 00:05:57.560 align:middle line:84% So that's just something to keep in mind. 00:05:57.560 --> 00:06:00.720 align:middle line:84% These are just estimates at the time this figure was made. 00:06:00.720 --> 00:06:03.600 align:middle line:84% And so again, just to reiterate that the atmosphere is not 00:06:03.600 --> 00:06:07.200 align:middle line:84% a significant reservoir of phosphorus at all. 00:06:07.200 --> 00:06:10.880 align:middle line:84% We do have an atmospheric box here. 00:06:10.880 --> 00:06:14.540 align:middle line:84% But that will correspond to aeolian dust input, 00:06:14.540 --> 00:06:16.560 align:middle line:90% which I'll talk about later. 00:06:16.560 --> 00:06:18.680 align:middle line:84% And we should know that phosphate only 00:06:18.680 --> 00:06:20.860 align:middle line:90% occurs in one oxidation state. 00:06:20.860 --> 00:06:24.600 align:middle line:84% And that's the +5 oxidation state which is orthophosphate 00:06:24.600 --> 00:06:27.440 align:middle line:90% which is PO4 3-minus. 00:06:27.440 --> 00:06:30.360 align:middle line:84% And so as far as this figure is concerned, 00:06:30.360 --> 00:06:33.940 align:middle line:84% all the inventories are in 10 to the 12th moles, 00:06:33.940 --> 00:06:38.040 align:middle line:84% and they tend to be in the bold where the arrows correspond 00:06:38.040 --> 00:06:43.360 align:middle line:84% to fluxes which are 10 to the 12 moles per year. 00:06:43.360 --> 00:06:47.560 align:middle line:84% And so we're going to start out with the lithosphere 00:06:47.560 --> 00:06:51.060 align:middle line:84% and follow the cycle all the way around. 00:06:51.060 --> 00:06:55.320 align:middle line:84% And so what we know right now is that, as with carbon, 00:06:55.320 --> 00:06:59.620 align:middle line:84% the lithosphere is the largest reservoir of phosphate. 00:06:59.620 --> 00:07:02.700 align:middle line:84% It happens to be about the 10th most abundant element 00:07:02.700 --> 00:07:08.100 align:middle line:84% in the lithosphere, and is about 0.1% by weight of the crust. 00:07:08.100 --> 00:07:12.340 align:middle line:84% And within this reservoir, most of the phosphate 00:07:12.340 --> 00:07:16.140 align:middle line:84% is in these phosphate minerals known as apatites. 00:07:16.140 --> 00:07:19.260 align:middle line:84% And this is their chemical formula. 00:07:19.260 --> 00:07:22.380 align:middle line:84% And they're either a fluorine, which 00:07:22.380 --> 00:07:28.360 align:middle line:84% is a fluorapatite, an OH ion which is hydroxyapatite, 00:07:28.360 --> 00:07:32.580 align:middle line:84% or the chlorine ion, which is the chlorapatite. 00:07:32.580 --> 00:07:33.860 align:middle line:90% This is their pure form. 00:07:33.860 --> 00:07:36.360 align:middle line:84% But their most common form when you look in the lithosphere, 00:07:36.360 --> 00:07:39.060 align:middle line:84% actually is this carbonate fluorapatite 00:07:39.060 --> 00:07:43.100 align:middle line:84% in which carbonate partially substitutes for phosphate. 00:07:43.100 --> 00:07:47.300 align:middle line:84% And the way this works is that just 00:07:47.300 --> 00:07:51.450 align:middle line:84% rather than having the phosphate ions, the ortho phosphate ions, 00:07:51.450 --> 00:07:54.130 align:middle line:84% you have carbonate ions substitute in their place 00:07:54.130 --> 00:07:55.610 align:middle line:90% in their crystal structure. 00:07:55.610 --> 00:07:57.290 align:middle line:84% But the one thing that's of interest 00:07:57.290 --> 00:08:00.690 align:middle line:84% is that the more carbonate ions you have, 00:08:00.690 --> 00:08:02.690 align:middle line:84% the more fluorine ions you're actually 00:08:02.690 --> 00:08:09.010 align:middle line:84% going to need relative to the phosphate ions 00:08:09.010 --> 00:08:11.250 align:middle line:90% to balance out the charges. 00:08:11.250 --> 00:08:13.130 align:middle line:84% And so these are just examples of what 00:08:13.130 --> 00:08:18.010 align:middle line:90% some really nice pure apatites. 00:08:18.010 --> 00:08:20.690 align:middle line:84% But they're really interesting because these apatites are not 00:08:20.690 --> 00:08:23.210 align:middle line:90% only in these rocks. 00:08:23.210 --> 00:08:26.850 align:middle line:84% There's actually quite a bit cycled biologically 00:08:26.850 --> 00:08:29.670 align:middle line:84% and cycled anthropogenically at this point. 00:08:29.670 --> 00:08:31.690 align:middle line:90% So it's important to know those. 00:08:31.690 --> 00:08:33.830 align:middle line:84% And the first is the hydroxyapatite, 00:08:33.830 --> 00:08:35.590 align:middle line:90% which is the OH version. 00:08:35.590 --> 00:08:37.630 align:middle line:90% It's produced by biota. 00:08:37.630 --> 00:08:40.890 align:middle line:84% So we have it in our teeth and we have it in our bones. 00:08:40.890 --> 00:08:42.850 align:middle line:90% So there's a lot of it around. 00:08:42.850 --> 00:08:48.230 align:middle line:84% There's also this fluorapatite, which 00:08:48.230 --> 00:08:51.598 align:middle line:84% is currently used in fluoridated water in toothpaste. 00:08:51.598 --> 00:08:53.390 align:middle line:84% And basically the reason the way that works 00:08:53.390 --> 00:08:58.230 align:middle line:84% is that you can exchange any OH ions in your teeth 00:08:58.230 --> 00:08:59.950 align:middle line:90% for the fluorine ion. 00:08:59.950 --> 00:09:02.353 align:middle line:84% So if you think about the amount of residential cities 00:09:02.353 --> 00:09:03.770 align:middle line:84% that are fluoridating their water, 00:09:03.770 --> 00:09:07.150 align:middle line:84% there's actually a fair amount of this stuff floating around. 00:09:07.150 --> 00:09:09.950 align:middle line:84% They also mine a lot of the sedimentary deposits 00:09:09.950 --> 00:09:12.650 align:middle line:84% of these apatites, and they get phosphorite out, 00:09:12.650 --> 00:09:16.070 align:middle line:84% which can be 18 to 40% of phosphorus by weight. 00:09:16.070 --> 00:09:17.610 align:middle line:90% And they use that in fertilizer. 00:09:17.610 --> 00:09:20.190 align:middle line:84% So a lot of tobacco fields are fertilized with this 00:09:20.190 --> 00:09:22.910 align:middle line:84% because I guess it changes the way it tastes, 00:09:22.910 --> 00:09:25.010 align:middle line:84% but essentially, as with most fertilizers, 00:09:25.010 --> 00:09:26.910 align:middle line:84% there's always that runoff issue, which 00:09:26.910 --> 00:09:28.855 align:middle line:84% is going to change the input to the ocean. 00:09:28.855 --> 00:09:30.230 align:middle line:84% So we have to be aware that there 00:09:30.230 --> 00:09:33.870 align:middle line:84% are some significant anthropogenic sources here. 00:09:33.870 --> 00:09:35.830 align:middle line:84% AUDIENCE: There's also a large anthropogenic-- 00:09:35.830 --> 00:09:37.910 align:middle line:84% there's a lot of phosphorus in detergents. 00:09:37.910 --> 00:09:40.390 align:middle line:84% DIERDRE TOOLE: Yeah, detergents have a lot. 00:09:40.390 --> 00:09:42.620 align:middle line:84% There's just a lot of phosphorus floating around 00:09:42.620 --> 00:09:44.340 align:middle line:84% anthropogenically, these are just 00:09:44.340 --> 00:09:45.720 align:middle line:84% in terms of the apatite minerals. 00:09:45.720 --> 00:09:52.700 align:middle line:84% But yeah, there's a huge influx from just urban runoff. 00:09:52.700 --> 00:09:54.580 align:middle line:84% AUDIENCE: Has there been a push to get rid 00:09:54.580 --> 00:09:56.020 align:middle line:90% of the phosphorus in detergents? 00:09:56.020 --> 00:09:57.980 align:middle line:90% I thought I heard-- 00:09:57.980 --> 00:10:02.040 align:middle line:84% AUDIENCE: Well, it's hard to do residential. 00:10:02.040 --> 00:10:03.900 align:middle line:90% People have been pushing it. 00:10:03.900 --> 00:10:05.780 align:middle line:84% The environmental groups are pushing a lot 00:10:05.780 --> 00:10:08.900 align:middle line:84% for using non-phosphorus detergents 00:10:08.900 --> 00:10:11.140 align:middle line:84% when you go camping and out in the wilderness. 00:10:11.140 --> 00:10:14.678 align:middle line:84% But I don't think it's been very successful for replacing it 00:10:14.678 --> 00:10:16.220 align:middle line:84% for industrial and residential usage. 00:10:16.220 --> 00:10:17.060 align:middle line:90% DIERDRE TOOLE: Yeah. 00:10:17.060 --> 00:10:19.000 align:middle line:84% Yeah, I mean, camping ones exist. 00:10:19.000 --> 00:10:21.480 align:middle line:84% I mean, there's all those camp suds. 00:10:21.480 --> 00:10:24.360 align:middle line:84% AUDIENCE: But for a lot of freshwater bodies, 00:10:24.360 --> 00:10:26.680 align:middle line:84% phosphorus eutrophication is a big problem. 00:10:26.680 --> 00:10:28.055 align:middle line:84% DIERDRE TOOLE: It's a huge issue. 00:10:28.055 --> 00:10:30.340 align:middle line:84% AUDIENCE: I know that local councils and stuff are 00:10:30.340 --> 00:10:34.245 align:middle line:84% trying to push it to that's a really small-- 00:10:34.245 --> 00:10:36.120 align:middle line:84% DIERDRE TOOLE: Yeah, it's just like anything. 00:10:36.120 --> 00:10:39.620 align:middle line:84% I mean, it takes a lot of momentum and development 00:10:39.620 --> 00:10:43.130 align:middle line:84% of actual good products to replace our current ones. 00:10:43.130 --> 00:10:44.850 align:middle line:84% But again, it's just something to be 00:10:44.850 --> 00:10:48.890 align:middle line:84% aware of that it is a very significant source of phosphorus 00:10:48.890 --> 00:10:49.590 align:middle line:90% to the ocean. 00:10:49.590 --> 00:10:53.510 align:middle line:84% And it's also going to very much throw all our nice inventories, 00:10:53.510 --> 00:10:55.710 align:middle line:84% which are a nice balance right now in these figures, 00:10:55.710 --> 00:10:56.430 align:middle line:90% out of whack. 00:10:56.430 --> 00:11:00.136 align:middle line:90% 00:11:00.136 --> 00:11:04.250 align:middle line:84% So once we have all this phosphate in the lithosphere 00:11:04.250 --> 00:11:07.750 align:middle line:84% and it's uplifted, so it's on land and it's exposed, 00:11:07.750 --> 00:11:10.130 align:middle line:84% it's going to be subjected to weathering processes, which 00:11:10.130 --> 00:11:12.290 align:middle line:84% is what we talked about on Tuesday. 00:11:12.290 --> 00:11:15.730 align:middle line:84% And the weathering and erosion of these uplifted rocks 00:11:15.730 --> 00:11:20.130 align:middle line:84% produce dissolved, reactive phosphorus phases, 00:11:20.130 --> 00:11:23.670 align:middle line:84% and particulate inert forms of phosphate. 00:11:23.670 --> 00:11:27.090 align:middle line:84% And this is when those phosphate minerals are acted on 00:11:27.090 --> 00:11:29.810 align:middle line:90% by the acidic compounds. 00:11:29.810 --> 00:11:32.530 align:middle line:84% And a way to think about it is that the particulate, really 00:11:32.530 --> 00:11:34.650 align:middle line:84% the inert forms of phosphorus, they're not 00:11:34.650 --> 00:11:36.930 align:middle line:90% going to be cycled by biology. 00:11:36.930 --> 00:11:41.150 align:middle line:84% They're just going to be subjected to physical transport 00:11:41.150 --> 00:11:44.230 align:middle line:84% processes, which will ultimately deposit them in the ocean. 00:11:44.230 --> 00:11:46.230 align:middle line:84% But it's really the dissolved phosphorus 00:11:46.230 --> 00:11:48.910 align:middle line:84% that we're more interested in the reactive form. 00:11:48.910 --> 00:11:51.030 align:middle line:84% And basically dissolved phosphorus, 00:11:51.030 --> 00:11:55.670 align:middle line:84% it occurs almost exclusively in this tetrahedral phosphate ions, 00:11:55.670 --> 00:11:58.670 align:middle line:84% and it has an acid base equilibria 00:11:58.670 --> 00:12:01.150 align:middle line:84% that it undergoes depending on the pH of the environment 00:12:01.150 --> 00:12:02.190 align:middle line:90% it's in. 00:12:02.190 --> 00:12:04.950 align:middle line:84% And so it cycles between four primary phases 00:12:04.950 --> 00:12:08.670 align:middle line:84% which range from phosphoric acid, dihydrogen 00:12:08.670 --> 00:12:12.910 align:middle line:84% phosphate, hydrogen phosphate, and then orthophosphate. 00:12:12.910 --> 00:12:16.710 align:middle line:84% And so what I have here is a diagram 00:12:16.710 --> 00:12:20.350 align:middle line:84% of the percent of total inorganic phosphate, 00:12:20.350 --> 00:12:22.990 align:middle line:84% and as a function of its chemical form, 00:12:22.990 --> 00:12:25.350 align:middle line:90% as a function of pH. 00:12:25.350 --> 00:12:28.030 align:middle line:84% So if we look, for example, at freshwater systems, which 00:12:28.030 --> 00:12:31.350 align:middle line:84% we were just talking about, their pH 00:12:31.350 --> 00:12:34.590 align:middle line:84% generally tends to range from about 6 to 7. 00:12:34.590 --> 00:12:39.940 align:middle line:84% So you can see that the primary phosphorus form is going 00:12:39.940 --> 00:12:41.660 align:middle line:90% to be the dihydrogen phosphate. 00:12:41.660 --> 00:12:43.680 align:middle line:84% And that's in contrast to the ocean, 00:12:43.680 --> 00:12:46.080 align:middle line:84% which has a slightly higher pH on the order of 8.2. 00:12:46.080 --> 00:12:48.740 align:middle line:84% But there we're going to have primarily the hydrogen phosphate 00:12:48.740 --> 00:12:49.320 align:middle line:90% ions. 00:12:49.320 --> 00:12:57.540 align:middle line:90% 00:12:57.540 --> 00:13:01.660 align:middle line:84% The dissolved phosphate is very reactive 00:13:01.660 --> 00:13:04.900 align:middle line:84% and it's taken up and cycled by the terrestrial biota. 00:13:04.900 --> 00:13:07.820 align:middle line:84% And it's extremely key for some of the most 00:13:07.820 --> 00:13:11.197 align:middle line:84% key functions of higher life forms, 00:13:11.197 --> 00:13:12.280 align:middle line:90% and life forms in general. 00:13:12.280 --> 00:13:16.020 align:middle line:84% I mean, it produces these organophosphates and phosphate 00:13:16.020 --> 00:13:17.082 align:middle line:90% esters. 00:13:17.082 --> 00:13:18.540 align:middle line:84% And the most important of those are 00:13:18.540 --> 00:13:19.940 align:middle line:84% things that are very obviously we 00:13:19.940 --> 00:13:26.500 align:middle line:84% know that are DNA and RNA or ATP in the phospholipids. 00:13:26.500 --> 00:13:29.920 align:middle line:84% And just to stress how important phosphate in these, for example, 00:13:29.920 --> 00:13:33.900 align:middle line:84% DNA, the backbones of the chain, which 00:13:33.900 --> 00:13:36.520 align:middle line:84% is what the nucleotides actually connect to, 00:13:36.520 --> 00:13:43.040 align:middle line:84% are these alternating chains of like deoxyribose 00:13:43.040 --> 00:13:44.760 align:middle line:90% with a phosphate. 00:13:44.760 --> 00:13:48.200 align:middle line:84% And so these form the backbones of the chains of DNA. 00:13:48.200 --> 00:13:49.140 align:middle line:90% RNA is the same. 00:13:49.140 --> 00:13:53.320 align:middle line:84% It's just a ribose and then the phosphate ion. 00:13:53.320 --> 00:13:54.860 align:middle line:90% So they're pretty key to life. 00:13:54.860 --> 00:13:58.160 align:middle line:84% I mean you can't have primary production, and reproduction, 00:13:58.160 --> 00:14:00.680 align:middle line:84% and higher life forms without these. 00:14:00.680 --> 00:14:06.680 align:middle line:84% It's also a key element in ATP, just so you guys know, 00:14:06.680 --> 00:14:11.100 align:middle line:84% it's a chemical currency of energy in life forms. 00:14:11.100 --> 00:14:14.860 align:middle line:84% And you see you have your sugar group and your ribose group. 00:14:14.860 --> 00:14:18.260 align:middle line:84% But then you have your three adenosine triphosphate. 00:14:18.260 --> 00:14:20.960 align:middle line:84% You have your three phosphates at the end. 00:14:20.960 --> 00:14:23.420 align:middle line:84% They're also really important in phospholipids, 00:14:23.420 --> 00:14:26.360 align:middle line:84% which are an important constituent of cell membranes. 00:14:26.360 --> 00:14:28.720 align:middle line:84% And basically, you have these phosphate esters which 00:14:28.720 --> 00:14:31.960 align:middle line:90% are produced with fatty acids. 00:14:31.960 --> 00:14:35.790 align:middle line:84% They're these hydrophobic phobic carbon chains. 00:14:35.790 --> 00:14:38.330 align:middle line:84% And then on the end, they have polar head groups. 00:14:38.330 --> 00:14:41.210 align:middle line:84% I think if you've seen pictures of cell membranes, 00:14:41.210 --> 00:14:43.110 align:middle line:84% you have the polar head groups, and then 00:14:43.110 --> 00:14:46.590 align:middle line:84% you have the fatty acid chains all pointing in. 00:14:46.590 --> 00:14:50.970 align:middle line:84% And phosphates is a key element in the polar head group. 00:14:50.970 --> 00:14:54.647 align:middle line:90% 00:14:54.647 --> 00:14:56.730 align:middle line:84% But just trying to understand what they happen to, 00:14:56.730 --> 00:14:58.188 align:middle line:84% and we're still going back to where 00:14:58.188 --> 00:15:00.430 align:middle line:84% we were talking about in terms of we 00:15:00.430 --> 00:15:02.510 align:middle line:90% have the uplift and erosion. 00:15:02.510 --> 00:15:05.990 align:middle line:84% And so we have these exposed minerals. 00:15:05.990 --> 00:15:08.950 align:middle line:84% And then they've been by various weathering processes turned 00:15:08.950 --> 00:15:10.930 align:middle line:84% into dissolved phosphate concentrations. 00:15:10.930 --> 00:15:13.668 align:middle line:84% We need to know what happens to that dissolved phosphate. 00:15:13.668 --> 00:15:15.710 align:middle line:84% And we know that actually the dissolved phosphate 00:15:15.710 --> 00:15:18.630 align:middle line:84% concentrations in soil are really low. 00:15:18.630 --> 00:15:23.790 align:middle line:84% And that's because there's a lot of iron and aluminum in soil. 00:15:23.790 --> 00:15:27.230 align:middle line:84% And the dissolved phosphate will actually adsorb onto these, 00:15:27.230 --> 00:15:30.790 align:middle line:84% forming iron and aluminum oxides, which will essentially 00:15:30.790 --> 00:15:33.500 align:middle line:84% it traps them and precipitates them out 00:15:33.500 --> 00:15:36.580 align:middle line:84% so they're no longer available for biology. 00:15:36.580 --> 00:15:38.420 align:middle line:84% And because of this, the terrestrial systems 00:15:38.420 --> 00:15:41.020 align:middle line:90% are often phosphate limited. 00:15:41.020 --> 00:15:43.960 align:middle line:84% But terrestrial plants have a way to get around this. 00:15:43.960 --> 00:15:47.420 align:middle line:84% They can increase the availability of that phosphate. 00:15:47.420 --> 00:15:50.500 align:middle line:84% They have these chelating compounds in their roots. 00:15:50.500 --> 00:15:54.100 align:middle line:84% What they do is they leach these chelating compounds, which 00:15:54.100 --> 00:15:57.020 align:middle line:84% can actually dissolve the iron oxides and aluminum 00:15:57.020 --> 00:15:59.540 align:middle line:84% oxides of phosphate and other salts 00:15:59.540 --> 00:16:02.940 align:middle line:84% to return that phosphate to a dissolved form that can then 00:16:02.940 --> 00:16:04.540 align:middle line:90% take up. 00:16:04.540 --> 00:16:08.980 align:middle line:84% And so we know that the carbon-to-phosphate ratio, 00:16:08.980 --> 00:16:11.660 align:middle line:84% the moles-to-moles ratio in marine organisms 00:16:11.660 --> 00:16:14.220 align:middle line:90% is often around Redfield. 00:16:14.220 --> 00:16:15.920 align:middle line:84% That's a whole other lecture in itself. 00:16:15.920 --> 00:16:18.580 align:middle line:90% But it's on the order of 106. 00:16:18.580 --> 00:16:20.820 align:middle line:84% But in terrestrial plants, we find that this ratio 00:16:20.820 --> 00:16:23.980 align:middle line:90% is much greater than 106. 00:16:23.980 --> 00:16:27.140 align:middle line:84% And so they're able to survive with much less phosphorus 00:16:27.140 --> 00:16:29.500 align:middle line:84% because of this availability issue. 00:16:29.500 --> 00:16:33.440 align:middle line:84% And terrestrial plants contain less phosphate per mole carbon 00:16:33.440 --> 00:16:36.840 align:middle line:84% due to the high proportion of structural, carbon-rich and 00:16:36.840 --> 00:16:39.200 align:middle line:84% phosphate-poor molecules, and examples of those 00:16:39.200 --> 00:16:44.560 align:middle line:84% are just carbohydrates, and ligands, and that type. 00:16:44.560 --> 00:16:47.540 align:middle line:84% So going back to our original figure, 00:16:47.540 --> 00:16:53.000 align:middle line:84% again, we want to try to get an idea of the turnover times 00:16:53.000 --> 00:16:57.040 align:middle line:84% and retention times in the land, the land soil 00:16:57.040 --> 00:16:59.520 align:middle line:90% reservoir for phosphorus. 00:16:59.520 --> 00:17:01.300 align:middle line:84% And so looking at the turnover time, 00:17:01.300 --> 00:17:06.520 align:middle line:84% we know that our inventory is 100 times 10 to the 12th or 10 00:17:06.520 --> 00:17:10.280 align:middle line:84% to the 14th moles of phosphorus in that land biota, 00:17:10.280 --> 00:17:14.760 align:middle line:84% and that it recycles with the back and forth between 00:17:14.760 --> 00:17:17.200 align:middle line:84% the biota, to the land, to the biota, 00:17:17.200 --> 00:17:19.984 align:middle line:84% on the order of times 10 to the 12th moles per year. 00:17:19.984 --> 00:17:21.359 align:middle line:84% So that gives you a turnover time 00:17:21.359 --> 00:17:27.240 align:middle line:84% of about 50 years for phosphate in a terrestrial environment. 00:17:27.240 --> 00:17:29.390 align:middle line:84% And if we want to think about the retention 00:17:29.390 --> 00:17:33.170 align:middle line:84% time of the reactive and eroded phosphate on land, 00:17:33.170 --> 00:17:36.710 align:middle line:84% so basically, once it's reactive, how long will 00:17:36.710 --> 00:17:38.630 align:middle line:90% it stay there? 00:17:38.630 --> 00:17:41.830 align:middle line:84% We have our inventory again, which is 6.5 times 10 00:17:41.830 --> 00:17:44.830 align:middle line:90% to the 15th moles. 00:17:44.830 --> 00:17:47.092 align:middle line:84% And then if you want to consider, 00:17:47.092 --> 00:17:48.550 align:middle line:84% and again, this is a rough estimate 00:17:48.550 --> 00:17:54.950 align:middle line:84% because we're trying to consider the various export pathways. 00:17:54.950 --> 00:17:57.910 align:middle line:84% You can have this pathway, which is just 00:17:57.910 --> 00:17:59.290 align:middle line:90% to the deep ocean and burial. 00:17:59.290 --> 00:18:02.510 align:middle line:84% And that's for the particulate, the inert forms of phosphate. 00:18:02.510 --> 00:18:05.170 align:middle line:84% And we also have the pathway to the surface ocean, 00:18:05.170 --> 00:18:09.670 align:middle line:84% and that's the more biologically labile forms of phosphate. 00:18:09.670 --> 00:18:13.985 align:middle line:84% You get a flux on the order of 0.7 times 10 to the 12 moles per 00:18:13.985 --> 00:18:16.110 align:middle line:84% year, which gives you a retention time on the order 00:18:16.110 --> 00:18:18.030 align:middle line:90% of 9,000 years. 00:18:18.030 --> 00:18:19.490 align:middle line:84% So once they're in the sediments, 00:18:19.490 --> 00:18:21.070 align:middle line:90% they tend to stay there. 00:18:21.070 --> 00:18:23.690 align:middle line:84% The phosphate tends to stay there for a fair amount of time. 00:18:23.690 --> 00:18:27.060 align:middle line:90% 00:18:27.060 --> 00:18:33.620 align:middle line:84% So given this turnover time of 50 years and the 9,000-year 00:18:33.620 --> 00:18:36.780 align:middle line:84% retention time, we need to understand the processes 00:18:36.780 --> 00:18:39.638 align:middle line:84% by which these the phosphate actually makes it to the ocean, 00:18:39.638 --> 00:18:42.180 align:middle line:84% because that's obviously what we're primarily concerned about 00:18:42.180 --> 00:18:45.180 align:middle line:84% because of the nutrient limitation. 00:18:45.180 --> 00:18:48.980 align:middle line:84% And there's two primary processes, the aeolian input 00:18:48.980 --> 00:18:52.460 align:middle line:84% of dust, which I'll talk about first which is a small input, 00:18:52.460 --> 00:18:56.000 align:middle line:84% and then fluvial inputs, which is really the primary input 00:18:56.000 --> 00:18:58.020 align:middle line:90% which I'll talk about second. 00:18:58.020 --> 00:18:59.840 align:middle line:84% And again, just to reiterate the point, 00:18:59.840 --> 00:19:02.760 align:middle line:84% there's no gaseous forms of phosphate. 00:19:02.760 --> 00:19:06.140 align:middle line:84% So this small source due to aeolian dust 00:19:06.140 --> 00:19:07.840 align:middle line:90% is the only atmospheric source. 00:19:07.840 --> 00:19:09.340 align:middle line:84% This is the only non-river source 00:19:09.340 --> 00:19:12.140 align:middle line:90% of phosphate to the ocean. 00:19:12.140 --> 00:19:17.740 align:middle line:84% And so if we want to estimate the total aeolian phosphate 00:19:17.740 --> 00:19:22.420 align:middle line:84% flux, we basically take an estimate of the total dust flux. 00:19:22.420 --> 00:19:26.480 align:middle line:84% And this is a map here from Natalie Mahowald's paper 00:19:26.480 --> 00:19:27.880 align:middle line:90% in 2005. 00:19:27.880 --> 00:19:32.000 align:middle line:84% And it's just a dust deposition estimate 00:19:32.000 --> 00:19:34.640 align:middle line:84% in grams per meter squared per year. 00:19:34.640 --> 00:19:39.480 align:middle line:84% So if we take this overall estimate of dust deposition, 00:19:39.480 --> 00:19:42.440 align:middle line:84% and then a mean concentration we expect a phosphate 00:19:42.440 --> 00:19:46.160 align:middle line:84% in those aerosols, and then an estimate 00:19:46.160 --> 00:19:48.520 align:middle line:84% of solubility, that will tell us how 00:19:48.520 --> 00:19:52.880 align:middle line:84% much actual aeolian phosphate flux 00:19:52.880 --> 00:19:56.320 align:middle line:84% makes it to the ocean in a reactive form. 00:19:56.320 --> 00:19:58.500 align:middle line:84% If we get things that are completely not soluble, 00:19:58.500 --> 00:20:00.500 align:middle line:84% they're just going to sink out and they're never 00:20:00.500 --> 00:20:02.600 align:middle line:90% going to be bioavailable. 00:20:02.600 --> 00:20:05.640 align:middle line:84% So in terms of this source, it's to remember 00:20:05.640 --> 00:20:07.680 align:middle line:84% that dust input to the ocean is highly 00:20:07.680 --> 00:20:09.960 align:middle line:90% variable in space and time. 00:20:09.960 --> 00:20:14.255 align:middle line:84% It varies seasonally with rainfall and transport patterns. 00:20:14.255 --> 00:20:15.880 align:middle line:84% Like we talked about last week, there's 00:20:15.880 --> 00:20:18.600 align:middle line:84% huge glacial interglacial cycles. 00:20:18.600 --> 00:20:20.680 align:middle line:84% And it's also very episodic based on wind speed 00:20:20.680 --> 00:20:23.950 align:middle line:90% or other physical processes. 00:20:23.950 --> 00:20:28.070 align:middle line:84% So again, bringing our equation along, 00:20:28.070 --> 00:20:32.230 align:middle line:84% we can use some literature values for solubility. 00:20:32.230 --> 00:20:35.590 align:middle line:84% Current estimates are that the solubility of dust phosphorus 00:20:35.590 --> 00:20:39.470 align:middle line:84% ranges from 21% to 51% which is actually enormous 00:20:39.470 --> 00:20:40.370 align:middle line:90% compared to iron. 00:20:40.370 --> 00:20:42.950 align:middle line:84% If you remember, it was a very small percentage. 00:20:42.950 --> 00:20:46.310 align:middle line:84% So there's quite a bit of soluble phosphate. 00:20:46.310 --> 00:20:51.110 align:middle line:84% And these are literature estimates of the actual input 00:20:51.110 --> 00:20:54.990 align:middle line:84% of phosphate in 10 to the ninth grams per year, 00:20:54.990 --> 00:21:00.950 align:middle line:84% and so if you just convert that you get 0.01 to 0.02 times 10 00:21:00.950 --> 00:21:03.910 align:middle line:90% to the 12th moles per year. 00:21:03.910 --> 00:21:10.430 align:middle line:84% And so you can see this is small input relative to the fluvial 00:21:10.430 --> 00:21:13.890 align:middle line:84% and relative to a lot of the turnover. 00:21:13.890 --> 00:21:17.270 align:middle line:84% So again, it's a fairly insignificant pathway. 00:21:17.270 --> 00:21:18.870 align:middle line:84% And it's important to know that even 00:21:18.870 --> 00:21:20.670 align:middle line:84% though the solubility of phosphate 00:21:20.670 --> 00:21:24.590 align:middle line:84% is so high, that even in the oligotrophic gyres, 00:21:24.590 --> 00:21:26.810 align:middle line:84% which are extremely nutrient limited, 00:21:26.810 --> 00:21:30.090 align:middle line:84% that the estimates of the input account for less than 1% 00:21:30.090 --> 00:21:31.650 align:middle line:90% of new production. 00:21:31.650 --> 00:21:33.570 align:middle line:84% The rest is attributed to upwelling 00:21:33.570 --> 00:21:35.730 align:middle line:90% of phosphate or vertical mixing. 00:21:35.730 --> 00:21:37.630 align:middle line:84% And again, this is in contrast to iron, 00:21:37.630 --> 00:21:40.130 align:middle line:84% where a small influx of iron can really 00:21:40.130 --> 00:21:43.070 align:middle line:84% increase your productivity fairly rapidly. 00:21:43.070 --> 00:21:45.890 align:middle line:90% 00:21:45.890 --> 00:21:49.750 align:middle line:84% So going back to the primary source of transfer to the ocean, 00:21:49.750 --> 00:21:53.970 align:middle line:84% it's fluvial processes, so transport and incorporation 00:21:53.970 --> 00:21:56.770 align:middle line:84% of these phosphate minerals in the particulate in dissolved 00:21:56.770 --> 00:22:01.090 align:middle line:84% forms to rivers via estuaries to the ocean. 00:22:01.090 --> 00:22:05.010 align:middle line:84% And what we do know is that a huge percentage, probably 00:22:05.010 --> 00:22:10.070 align:middle line:84% 90% to 95%, of the phosphorus in rivers is in particles. 00:22:10.070 --> 00:22:12.850 align:middle line:84% Very little of it's in the actual dissolved bioavailable 00:22:12.850 --> 00:22:14.130 align:middle line:90% form. 00:22:14.130 --> 00:22:15.930 align:middle line:84% And these are, again, the inert minerals 00:22:15.930 --> 00:22:18.890 align:middle line:84% which are eroded directly from the continental crust. 00:22:18.890 --> 00:22:22.520 align:middle line:84% And some of those iron and aluminum 00:22:22.520 --> 00:22:26.600 align:middle line:84% oxides where the reactive P was actually adsorbed onto the clay, 00:22:26.600 --> 00:22:28.120 align:middle line:90% those come too. 00:22:28.120 --> 00:22:32.860 align:middle line:84% But what happens is when these rivers dump into the estuaries, 00:22:32.860 --> 00:22:36.320 align:middle line:84% you can start having chemical changes within the estuaries 00:22:36.320 --> 00:22:36.980 align:middle line:90% themselves. 00:22:36.980 --> 00:22:40.040 align:middle line:84% You can think of them as being processing areas. 00:22:40.040 --> 00:22:47.440 align:middle line:84% And so in these estuaries, You can actually have the reactive P 00:22:47.440 --> 00:22:50.040 align:middle line:90% desorb from the iron oxides. 00:22:50.040 --> 00:22:53.320 align:middle line:84% And so then it becomes bioavailable. 00:22:53.320 --> 00:22:57.440 align:middle line:84% It can be processed, taken up by the Marine Freshwater biota, 00:22:57.440 --> 00:23:00.840 align:middle line:84% and turned into organic phosphorus compounds 00:23:00.840 --> 00:23:05.300 align:middle line:84% such as the DNA, the RNA, a lot of the intracellular components. 00:23:05.300 --> 00:23:09.280 align:middle line:84% And this can be removed from estuaries via sinking out, 00:23:09.280 --> 00:23:12.240 align:middle line:84% or also there's some salinity-induced flocculation 00:23:12.240 --> 00:23:15.063 align:middle line:84% with humics and irons in the river. 00:23:15.063 --> 00:23:16.480 align:middle line:84% But the important thing to know is 00:23:16.480 --> 00:23:22.150 align:middle line:84% that because the reactive P pool is so small 00:23:22.150 --> 00:23:25.950 align:middle line:84% relative to the particulate pool, a really small change 00:23:25.950 --> 00:23:29.890 align:middle line:84% amount in the partitioning between these two pools, 00:23:29.890 --> 00:23:32.230 align:middle line:84% so the amount of P adsorbed to the clays, 00:23:32.230 --> 00:23:35.350 align:middle line:84% it can greatly change our estimates of the fluvial input 00:23:35.350 --> 00:23:37.830 align:middle line:90% of bioavailable phosphate. 00:23:37.830 --> 00:23:39.870 align:middle line:84% And again, right now our estimates 00:23:39.870 --> 00:23:42.750 align:middle line:84% have a pretty large range, but currently they're 00:23:42.750 --> 00:23:46.610 align:middle line:84% about 0.03 to 0.15 times 10 to the 12 moles per year. 00:23:46.610 --> 00:23:50.510 align:middle line:90% 00:23:50.510 --> 00:23:56.310 align:middle line:84% And so once we have this and we have the estuaries draining out 00:23:56.310 --> 00:23:59.750 align:middle line:84% to the ocean, and some of this reactive dissolved phosphate 00:23:59.750 --> 00:24:02.030 align:middle line:84% making its way to the ocean, we need 00:24:02.030 --> 00:24:06.430 align:middle line:84% to understand some of the turnover processes and chemical 00:24:06.430 --> 00:24:08.590 align:middle line:90% components of it in the ocean. 00:24:08.590 --> 00:24:10.830 align:middle line:84% And so again, just going back to this figure, which 00:24:10.830 --> 00:24:14.590 align:middle line:84% we saw earlier, which is the percent of inorganic phosphate 00:24:14.590 --> 00:24:17.650 align:middle line:84% in the various chemical forms as a function of pH, 00:24:17.650 --> 00:24:23.290 align:middle line:84% remember in the ocean that the primary dissolved inorganic 00:24:23.290 --> 00:24:27.730 align:middle line:84% phosphorus form is hydrogen phosphate. 00:24:27.730 --> 00:24:30.250 align:middle line:84% And what tends to happen is that ion pairs 00:24:30.250 --> 00:24:33.030 align:middle line:84% are formed with a major cations in seawater. 00:24:33.030 --> 00:24:34.770 align:middle line:90% So you have a lot of these. 00:24:34.770 --> 00:24:37.690 align:middle line:84% You have some of your free hydrogen phosphate, 00:24:37.690 --> 00:24:41.690 align:middle line:84% but you also have sodium, calcium, and magnesium versions 00:24:41.690 --> 00:24:45.850 align:middle line:90% of these floating around. 00:24:45.850 --> 00:24:49.228 align:middle line:84% And so just to take a step back, because if you guys do 00:24:49.228 --> 00:24:51.770 align:middle line:84% any reading, I'm going to post some additional readings to do 00:24:51.770 --> 00:24:52.650 align:middle line:90% on this. 00:24:52.650 --> 00:24:54.530 align:middle line:84% There's a lot of jargon out there 00:24:54.530 --> 00:24:59.210 align:middle line:84% in terms of how people refer to the different phosphorus pools. 00:24:59.210 --> 00:25:03.090 align:middle line:84% And right now most of the dissolved phosphorus 00:25:03.090 --> 00:25:05.930 align:middle line:84% or the bioavailable bioreactive phosphorus, 00:25:05.930 --> 00:25:08.410 align:middle line:84% it's fairly much operationally defined. 00:25:08.410 --> 00:25:12.170 align:middle line:84% So basically we run these experiments and the results 00:25:12.170 --> 00:25:19.420 align:middle line:84% tell us which reservoir they should be put in. 00:25:19.420 --> 00:25:22.980 align:middle line:84% For example, the soluble reactive phosphorus, 00:25:22.980 --> 00:25:26.372 align:middle line:84% which people call SRP, is measured in filtered seawater, 00:25:26.372 --> 00:25:28.080 align:middle line:84% and it's a fraction of the phosphate that 00:25:28.080 --> 00:25:31.920 align:middle line:84% can be measured directly by the colorimetric phosphomolybdate 00:25:31.920 --> 00:25:33.360 align:middle line:90% method. 00:25:33.360 --> 00:25:36.240 align:middle line:84% And so basically we're not saying 00:25:36.240 --> 00:25:38.100 align:middle line:90% that it's just the particles. 00:25:38.100 --> 00:25:41.280 align:middle line:84% It's basically the results of this colorimetric method are 00:25:41.280 --> 00:25:45.440 align:middle line:84% what we're going to deem the soluble reactive phosphorus. 00:25:45.440 --> 00:25:48.160 align:middle line:84% And this fraction is believed to consist mostly 00:25:48.160 --> 00:25:50.120 align:middle line:90% of the inorganic phosphate. 00:25:50.120 --> 00:25:54.120 align:middle line:84% But it also encompasses a few acid labile organic compounds. 00:25:54.120 --> 00:25:57.880 align:middle line:84% So again, the partitioning isn't as clean as we'd like. 00:25:57.880 --> 00:26:01.280 align:middle line:84% There's also the total dissolved phosphate. 00:26:01.280 --> 00:26:04.000 align:middle line:84% And that's measured by the same method in filtered seawater 00:26:04.000 --> 00:26:07.440 align:middle line:84% after treating it with a strong oxidizing agent. 00:26:07.440 --> 00:26:10.840 align:middle line:84% And then there's the soluble non-reactive phosphate. 00:26:10.840 --> 00:26:13.980 align:middle line:84% And it's calculated by difference between these two 00:26:13.980 --> 00:26:14.520 align:middle line:90% methods. 00:26:14.520 --> 00:26:16.740 align:middle line:84% And it's generally thought to consist mainly 00:26:16.740 --> 00:26:21.600 align:middle line:84% of the dissolved organic phosphates and polyphosphates. 00:26:21.600 --> 00:26:24.940 align:middle line:84% So essentially your soluble reactive phosphorus 00:26:24.940 --> 00:26:28.780 align:middle line:84% can be considered your dissolved inorganic phosphate. 00:26:28.780 --> 00:26:30.940 align:middle line:84% Your total dissolved phosphate is obviously 00:26:30.940 --> 00:26:34.520 align:middle line:84% your total dissolved inorganic and dissolved organic phosphate, 00:26:34.520 --> 00:26:36.540 align:middle line:90% the sum of the two. 00:26:36.540 --> 00:26:38.900 align:middle line:84% And your soluble nonreactive phosphate 00:26:38.900 --> 00:26:41.100 align:middle line:84% can be considered first order approximation 00:26:41.100 --> 00:26:42.845 align:middle line:84% your dissolved organic phosphate. 00:26:42.845 --> 00:26:45.220 align:middle line:84% So just so if you see some of these terms floating around 00:26:45.220 --> 00:26:49.020 align:middle line:84% in the papers, people are going to use different nomenclature 00:26:49.020 --> 00:26:53.620 align:middle line:84% depending on the problem they're actually looking at. 00:26:53.620 --> 00:26:56.740 align:middle line:84% And so the soluble nonreactive phosphate 00:26:56.740 --> 00:26:59.820 align:middle line:84% or the dissolved organic phosphate, 00:26:59.820 --> 00:27:03.380 align:middle line:84% it's a large percentage of the total dissolved phosphate 00:27:03.380 --> 00:27:05.120 align:middle line:90% in surface oligotrophic waters. 00:27:05.120 --> 00:27:08.260 align:middle line:84% So a lot of it's in the organic form. 00:27:08.260 --> 00:27:10.570 align:middle line:84% But again, because it is bio-limiting 00:27:10.570 --> 00:27:14.010 align:middle line:84% and the concentrations are almost undetectable in some 00:27:14.010 --> 00:27:18.290 align:middle line:84% of these oligotrophic gyres in the subtropics, most of this 00:27:18.290 --> 00:27:22.870 align:middle line:84% is found as components within phytoplankton cells, so the DNA, 00:27:22.870 --> 00:27:25.890 align:middle line:90% RNA, the phospholipids. 00:27:25.890 --> 00:27:29.610 align:middle line:84% But as with carbon, we know that this dissolved organic phosphate 00:27:29.610 --> 00:27:32.770 align:middle line:84% can be converted back to inorganic phosphate 00:27:32.770 --> 00:27:36.430 align:middle line:84% via enzymatic and microbial remineralization processes. 00:27:36.430 --> 00:27:40.350 align:middle line:84% So it's going to cycle through the biota, the phytoplankton. 00:27:40.350 --> 00:27:45.050 align:middle line:84% and the bacteria loop, fairly much like carbon cycles through. 00:27:45.050 --> 00:27:48.850 align:middle line:84% So again, going back to this figure, 00:27:48.850 --> 00:27:51.050 align:middle line:84% we can see that the ocean biota reservoir 00:27:51.050 --> 00:27:54.050 align:middle line:84% is much smaller than the land reservoir 00:27:54.050 --> 00:27:56.370 align:middle line:90% by maybe a factor of 25. 00:27:56.370 --> 00:28:00.770 align:middle line:84% But the fluxes between the reactive people and the biota 00:28:00.770 --> 00:28:02.690 align:middle line:90% are much larger. 00:28:02.690 --> 00:28:05.690 align:middle line:84% You see, if you see here we have fluxes 00:28:05.690 --> 00:28:07.810 align:middle line:84% on the order of 2 times 10 to the 12. 00:28:07.810 --> 00:28:10.880 align:middle line:84% Here we have fluxes on the order of 33. 00:28:10.880 --> 00:28:12.880 align:middle line:84% I mean, they're not balanced with the difference 00:28:12.880 --> 00:28:18.500 align:middle line:90% being export to the deep ocean. 00:28:18.500 --> 00:28:22.840 align:middle line:84% We don't have that same lack of balance on the land side. 00:28:22.840 --> 00:28:25.280 align:middle line:84% So we want to look at a turnover time. 00:28:25.280 --> 00:28:28.280 align:middle line:84% Again, you can take the reservoir size, 00:28:28.280 --> 00:28:31.120 align:middle line:84% 4 times 10 to the 12th, and divide it by the flux. 00:28:31.120 --> 00:28:35.680 align:middle line:84% And it gives us a turnover time on the order of 0.12 years. 00:28:35.680 --> 00:28:38.040 align:middle line:84% And if you remember, the turnover time we had on land 00:28:38.040 --> 00:28:38.980 align:middle line:90% was 50 years. 00:28:38.980 --> 00:28:43.080 align:middle line:84% So there's a significantly faster cycling 00:28:43.080 --> 00:28:46.040 align:middle line:84% of organic phosphorus in the ocean than on land. 00:28:46.040 --> 00:28:48.640 align:middle line:84% And this tends to be due to the dominance 00:28:48.640 --> 00:28:51.818 align:middle line:84% of single-cell organisms with really short lifetimes. 00:28:51.818 --> 00:28:53.360 align:middle line:84% So they're just they're processing it 00:28:53.360 --> 00:28:55.900 align:middle line:84% through their lifetime really rapidly, 00:28:55.900 --> 00:28:58.220 align:middle line:84% so the growth-death bacterial processing. 00:28:58.220 --> 00:29:01.080 align:middle line:90% 00:29:01.080 --> 00:29:11.580 align:middle line:84% So it hasn't been easy to measure phosphorus cycling 00:29:11.580 --> 00:29:12.520 align:middle line:90% in seawater. 00:29:12.520 --> 00:29:15.060 align:middle line:90% 00:29:15.060 --> 00:29:20.240 align:middle line:84% A method that people have used and was published recently, 00:29:20.240 --> 00:29:22.820 align:middle line:84% I guess not so recently, in 1999, 00:29:22.820 --> 00:29:26.020 align:middle line:84% is that they tried to study phosphorus cycling using 00:29:26.020 --> 00:29:29.700 align:middle line:84% two natural radioactive phosphate isotopes. 00:29:29.700 --> 00:29:32.880 align:middle line:90% And this is P32 and P33. 00:29:32.880 --> 00:29:36.500 align:middle line:84% And these are cosmogenic isotopes from argon. 00:29:36.500 --> 00:29:40.020 align:middle line:84% So basically argon gets hit with cosmic rays. 00:29:40.020 --> 00:29:42.700 align:middle line:90% 00:29:42.700 --> 00:29:45.860 align:middle line:84% It forms these secondary isotopes. 00:29:45.860 --> 00:29:48.380 align:middle line:84% And the way that these are delivered to the ocean 00:29:48.380 --> 00:29:50.740 align:middle line:84% is that they're rapidly removed onto aerosols 00:29:50.740 --> 00:29:54.140 align:middle line:84% in the atmosphere, which are rained out via wet deposition 00:29:54.140 --> 00:29:55.085 align:middle line:90% processes. 00:29:55.085 --> 00:29:56.460 align:middle line:84% So again, that's something that's 00:29:56.460 --> 00:30:01.300 align:middle line:84% going to be subjected to a fairly spatially and temporally 00:30:01.300 --> 00:30:03.540 align:middle line:90% variable distribution. 00:30:03.540 --> 00:30:09.250 align:middle line:84% But what we do know is that P33 to P32 in rainwater 00:30:09.250 --> 00:30:10.970 align:middle line:90% varies very little. 00:30:10.970 --> 00:30:13.670 align:middle line:84% If you look at the activity ratio, the measurements. 00:30:13.670 --> 00:30:16.570 align:middle line:84% They have done, it's within a very small range. 00:30:16.570 --> 00:30:19.650 align:middle line:84% And that the P33 to P32 ratio actually 00:30:19.650 --> 00:30:21.850 align:middle line:84% will increase with time, and that's 00:30:21.850 --> 00:30:24.730 align:middle line:84% a function of their different half lives. 00:30:24.730 --> 00:30:26.690 align:middle line:84% So if you see P33 has a half life 00:30:26.690 --> 00:30:35.550 align:middle line:84% in the order of 14 days where that of P32 is 25 days. 00:30:35.550 --> 00:30:38.970 align:middle line:90% 00:30:38.970 --> 00:30:43.050 align:middle line:84% So what we know is that when we take 00:30:43.050 --> 00:30:48.410 align:middle line:84% in a sample of organic matter and look at this ratio, 00:30:48.410 --> 00:30:54.610 align:middle line:84% the higher the P33-to-P32 ratio, the older the phosphate pool, 00:30:54.610 --> 00:30:59.610 align:middle line:84% and older being essentially when the biota take up, 00:30:59.610 --> 00:31:01.590 align:middle line:84% assuming there's no isotopic fractionation, 00:31:01.590 --> 00:31:04.990 align:middle line:84% when the biota to take up these isotopes, 00:31:04.990 --> 00:31:07.990 align:middle line:84% they're essentially fixed within them, 00:31:07.990 --> 00:31:10.210 align:middle line:84% and then they're just subjected to radioactive decay. 00:31:10.210 --> 00:31:12.168 align:middle line:84% So you can see how long it's been since they've 00:31:12.168 --> 00:31:15.663 align:middle line:90% taken up isotopes. 00:31:15.663 --> 00:31:17.830 align:middle line:84% AUDIENCE: That ratio seems to go the wrong way given 00:31:17.830 --> 00:31:18.690 align:middle line:90% the half lives. 00:31:18.690 --> 00:31:21.390 align:middle line:90% 00:31:21.390 --> 00:31:22.960 align:middle line:90% P33 has a faster half life. 00:31:22.960 --> 00:31:27.190 align:middle line:84% DIERDRE TOOLE: Faster half life, so that should go down. 00:31:27.190 --> 00:31:28.670 align:middle line:84% AUDIENCE: I don't have those two. 00:31:28.670 --> 00:31:30.790 align:middle line:84% I don't have those two in my brain. 00:31:30.790 --> 00:31:34.870 align:middle line:84% DIERDRE TOOLE: Yeah, I might have mistaken the 32 is 14. 00:31:34.870 --> 00:31:37.650 align:middle line:84% Oh, I put the half lives backwards. 00:31:37.650 --> 00:31:38.290 align:middle line:90% I'm sorry. 00:31:38.290 --> 00:31:42.050 align:middle line:84% P32 is the 14 days and P33 is 25.3 days. 00:31:42.050 --> 00:31:42.990 align:middle line:90% Sorry. 00:31:42.990 --> 00:31:44.830 align:middle line:90% So, yeah. 00:31:44.830 --> 00:31:52.910 align:middle line:84% But it is the higher, so P32 is going to disappear faster 00:31:52.910 --> 00:31:53.690 align:middle line:90% for a given time. 00:31:53.690 --> 00:31:56.790 align:middle line:84% You're going to have less P32 than P33. 00:31:56.790 --> 00:32:00.390 align:middle line:84% So then you'll know that it's an older phosphorus pool. 00:32:00.390 --> 00:32:01.160 align:middle line:90% Thanks, Scott. 00:32:01.160 --> 00:32:01.660 align:middle line:90% Sorry. 00:32:01.660 --> 00:32:04.220 align:middle line:90% 00:32:04.220 --> 00:32:06.900 align:middle line:84% And so, again, what they did in this study, 00:32:06.900 --> 00:32:12.260 align:middle line:84% this is Benitez-Nelson and Buesseler in Nature in 1999. 00:32:12.260 --> 00:32:13.700 align:middle line:84% And what they did is they measured 00:32:13.700 --> 00:32:17.140 align:middle line:84% the phosphorus isotopic ratio in the different pools. 00:32:17.140 --> 00:32:19.030 align:middle line:84% So again, the inorganic phosphorus, 00:32:19.030 --> 00:32:20.780 align:middle line:84% the dissolved organic phosphorus, but then 00:32:20.780 --> 00:32:23.520 align:middle line:84% also within different size fractionations of the seawater. 00:32:23.520 --> 00:32:26.740 align:middle line:84% So you can get the phytoplankton class zooplankton. 00:32:26.740 --> 00:32:28.540 align:middle line:84% And from this they were able to estimate 00:32:28.540 --> 00:32:31.660 align:middle line:90% the age of the phosphorus. 00:32:31.660 --> 00:32:35.060 align:middle line:84% And they also could estimate the turnover of phosphate 00:32:35.060 --> 00:32:37.260 align:middle line:84% within the pools and the pathways 00:32:37.260 --> 00:32:39.400 align:middle line:84% through the various levels of the food chain. 00:32:39.400 --> 00:32:42.920 align:middle line:90% 00:32:42.920 --> 00:32:44.420 align:middle line:84% The crux of all of this, is that you 00:32:44.420 --> 00:32:50.920 align:middle line:84% need to be able to constrain the P33-to-P32 ratio of rainwater, 00:32:50.920 --> 00:32:53.300 align:middle line:84% because essentially, that's your starting point. 00:32:53.300 --> 00:32:55.100 align:middle line:84% And everything is going to be leveraged 00:32:55.100 --> 00:32:58.120 align:middle line:84% and compared to that starting point, so you need to know that. 00:32:58.120 --> 00:33:01.410 align:middle line:84% And so it's really crucial to understand 00:33:01.410 --> 00:33:02.910 align:middle line:90% the variability of that. 00:33:02.910 --> 00:33:06.690 align:middle line:84% And they found, again, that it's not very variable spatially. 00:33:06.690 --> 00:33:08.690 align:middle line:84% And preliminary results from these studies 00:33:08.690 --> 00:33:12.610 align:middle line:84% is that the DOP turnover rates vary widely in space and time, 00:33:12.610 --> 00:33:16.210 align:middle line:84% suggesting that there's a pretty large range of bioavailability 00:33:16.210 --> 00:33:19.550 align:middle line:84% of these DOP that it's not all considered the same. 00:33:19.550 --> 00:33:22.490 align:middle line:90% 00:33:22.490 --> 00:33:25.850 align:middle line:84% So going back to the same figure again, 00:33:25.850 --> 00:33:28.930 align:middle line:84% I should just put it up on the board somewhere. 00:33:28.930 --> 00:33:34.410 align:middle line:84% Surface seawater, phosphorus turnover time, again, 00:33:34.410 --> 00:33:38.390 align:middle line:84% taking the inventory divided by the flux. 00:33:38.390 --> 00:33:42.770 align:middle line:84% We have a turnover time on the order of 2.7 years. 00:33:42.770 --> 00:33:48.450 align:middle line:84% And so we do know that a relatively small fraction 00:33:48.450 --> 00:33:50.210 align:middle line:90% of this is exported. 00:33:50.210 --> 00:33:52.550 align:middle line:84% But again, there's very few direct measurements. 00:33:52.550 --> 00:33:57.590 align:middle line:84% They primarily consist of the isotopic ratio type measurements 00:33:57.590 --> 00:33:59.708 align:middle line:90% that I was just discussing. 00:33:59.708 --> 00:34:01.750 align:middle line:84% The current estimates are that the mean residence 00:34:01.750 --> 00:34:04.190 align:middle line:84% time and surface waters for phosphate 00:34:04.190 --> 00:34:06.550 align:middle line:90% is on the order of 9 years. 00:34:06.550 --> 00:34:10.389 align:middle line:84% And so because we don't have these direct estimates 00:34:10.389 --> 00:34:13.670 align:middle line:84% of P export flux, we're often left estimating it 00:34:13.670 --> 00:34:15.790 align:middle line:84% with quantities that we feel like we 00:34:15.790 --> 00:34:19.469 align:middle line:84% have a better understanding of and ability to constrain. 00:34:19.469 --> 00:34:22.489 align:middle line:84% And one of those is carbon export. 00:34:22.489 --> 00:34:23.989 align:middle line:84% And there's a lot of different ways, 00:34:23.989 --> 00:34:26.530 align:middle line:84% and people obviously use sediment traps and the like. 00:34:26.530 --> 00:34:30.830 align:middle line:84% But you can get global estimates based on satellite observations. 00:34:30.830 --> 00:34:35.429 align:middle line:84% So if you want to calculate your rate of your organic phosphorus 00:34:35.429 --> 00:34:37.550 align:middle line:84% export, what you could do is you can 00:34:37.550 --> 00:34:40.989 align:middle line:84% take some of carbon export data set 00:34:40.989 --> 00:34:44.870 align:middle line:84% and then a mean phosphate-to-carbon ratio 00:34:44.870 --> 00:34:46.989 align:middle line:84% in the organic matter that's being 00:34:46.989 --> 00:34:51.989 align:middle line:84% exported to calculate your export of organic phosphate. 00:34:51.989 --> 00:34:55.739 align:middle line:84% And so literature values from Laws et al, 00:34:55.739 --> 00:34:58.460 align:middle line:84% suggest that the global carbon export production 00:34:58.460 --> 00:35:02.460 align:middle line:84% is on the order of 10 to 15 moles of carbon per year, 00:35:02.460 --> 00:35:04.780 align:middle line:90% and that the average-- 00:35:04.780 --> 00:35:08.720 align:middle line:84% we'll get back to this a little later these C-to-P ratios. 00:35:08.720 --> 00:35:15.300 align:middle line:84% But the average C-to-P ratio is on the order of 117. 00:35:15.300 --> 00:35:20.340 align:middle line:84% And so this would suggest an average export of phosphate from 00:35:20.340 --> 00:35:23.780 align:middle line:84% the surface waters on the order of 10 to the 13th moles 00:35:23.780 --> 00:35:25.980 align:middle line:90% of phosphate per year. 00:35:25.980 --> 00:35:28.580 align:middle line:84% And I just want to address this so there's not any confusion 00:35:28.580 --> 00:35:32.560 align:middle line:84% later that this number is 10 to the 13th. 00:35:32.560 --> 00:35:37.860 align:middle line:84% So 10 times 10 to the minus 12th is significantly different than 00:35:37.860 --> 00:35:40.700 align:middle line:84% this 0.3 that we have in the original figure 00:35:40.700 --> 00:35:41.860 align:middle line:90% we're discussing. 00:35:41.860 --> 00:35:46.380 align:middle line:84% And as with anything, we're constantly updating estimates 00:35:46.380 --> 00:35:51.220 align:middle line:84% as we have better constraints on the different parameters. 00:35:51.220 --> 00:35:53.420 align:middle line:84% Again, there's a lot of uncertainty 00:35:53.420 --> 00:35:57.440 align:middle line:84% by factors of 2 to 3, up to factors of 10, obviously, 00:35:57.440 --> 00:35:58.700 align:middle line:90% within our flux estimates. 00:35:58.700 --> 00:36:00.325 align:middle line:84% So it's just something to keep in mind. 00:36:00.325 --> 00:36:04.480 align:middle line:84% I mean, we're looking at broad-scale comparisons 00:36:04.480 --> 00:36:08.760 align:middle line:84% between the various turnovers and the various reservoirs. 00:36:08.760 --> 00:36:14.660 align:middle line:84% So once we know that we have this export, 00:36:14.660 --> 00:36:18.262 align:middle line:84% this particulate organic that's leaving, 00:36:18.262 --> 00:36:20.720 align:middle line:84% again, if we want to divide it to first order approximation 00:36:20.720 --> 00:36:23.640 align:middle line:84% into our surface ocean, our deep ocean box, 00:36:23.640 --> 00:36:27.160 align:middle line:84% once we have this organic phosphorus that's 00:36:27.160 --> 00:36:29.880 align:middle line:84% leaving that box, the surface ocean, 00:36:29.880 --> 00:36:33.000 align:middle line:84% we need to understand how much of that's 00:36:33.000 --> 00:36:34.600 align:middle line:84% actually making it to the sea floor. 00:36:34.600 --> 00:36:39.360 align:middle line:84% Because that's what's going to help us complete our loop 00:36:39.360 --> 00:36:42.240 align:middle line:84% and get it back available to land. 00:36:42.240 --> 00:36:45.680 align:middle line:84% So literature estimates suggest that the global organic carbon 00:36:45.680 --> 00:36:49.360 align:middle line:84% delivery rate to the sea floor below 1,000 meters is estimated 00:36:49.360 --> 00:36:53.830 align:middle line:84% to be equivalent to an oxygen consumption of 54.4 times 10 00:36:53.830 --> 00:36:55.670 align:middle line:90% to the 12th moles per year. 00:36:55.670 --> 00:36:57.870 align:middle line:84% And so again, we don't have direct measurements 00:36:57.870 --> 00:37:00.250 align:middle line:84% of the phosphorus delivery to the sea floor. 00:37:00.250 --> 00:37:03.510 align:middle line:84% So we're going to use carbon and oxygen estimates, 00:37:03.510 --> 00:37:06.630 align:middle line:84% and try to back it out from those. 00:37:06.630 --> 00:37:11.510 align:middle line:84% And again, another literature estimate demonstrated that 00:37:11.510 --> 00:37:16.150 align:middle line:84% in this organic matter that below 1,000 meter, 00:37:16.150 --> 00:37:19.830 align:middle line:84% the ratio of oxygen and phosphorus in the organic 00:37:19.830 --> 00:37:22.930 align:middle line:84% matter, this is of the particles sinking to the deep sea, 00:37:22.930 --> 00:37:30.950 align:middle line:90% is on the order of 170. 00:37:30.950 --> 00:37:36.390 align:middle line:84% So again, if we want to estimate the phosphorus 00:37:36.390 --> 00:37:41.710 align:middle line:84% delivery to the sea floor, we can just do a simple conversion. 00:37:41.710 --> 00:37:47.010 align:middle line:84% And using the ratio and the flux, 00:37:47.010 --> 00:37:50.780 align:middle line:84% and we come up with 0.32 times 10 to the 12th moles 00:37:50.780 --> 00:37:52.420 align:middle line:90% of phosphorus for a year. 00:37:52.420 --> 00:37:55.100 align:middle line:84% And so just to put that into perspective, that's about 3% 00:37:55.100 --> 00:37:56.860 align:middle line:90% of the export flux. 00:37:56.860 --> 00:38:00.880 align:middle line:84% So I mean it's what you'd expect. 00:38:00.880 --> 00:38:02.380 align:middle line:90% It's a reasonable number. 00:38:02.380 --> 00:38:05.740 align:middle line:84% But let's just to keep in mind then that most of it, 97% of it, 00:38:05.740 --> 00:38:09.860 align:middle line:84% is remineralized and recycled within the ocean. 00:38:09.860 --> 00:38:12.740 align:middle line:84% And so the actual getting delivered to the sea floor 00:38:12.740 --> 00:38:15.260 align:middle line:84% for some of the next processes we're going to talk about 00:38:15.260 --> 00:38:18.740 align:middle line:90% is fairly small. 00:38:18.740 --> 00:38:21.620 align:middle line:84% And so again, now we have that 3% of the export flux 00:38:21.620 --> 00:38:24.460 align:middle line:84% from the surface hitting the sea floor. 00:38:24.460 --> 00:38:26.620 align:middle line:84% And we need to figure out how much of that 00:38:26.620 --> 00:38:29.140 align:middle line:84% that hits the sea floor is actually buried 00:38:29.140 --> 00:38:31.100 align:middle line:84% and how much of it is actually rereleased out 00:38:31.100 --> 00:38:32.400 align:middle line:90% into the water column. 00:38:32.400 --> 00:38:36.340 align:middle line:84% And so the degradation of organic phosphorus 00:38:36.340 --> 00:38:38.460 align:middle line:84% and sediments, it decreases with the amount 00:38:38.460 --> 00:38:41.400 align:middle line:90% of organic phosphorus buried. 00:38:41.400 --> 00:38:44.500 align:middle line:84% And this is because there's extensive phosphorus recycling 00:38:44.500 --> 00:38:48.220 align:middle line:84% due to remineralization processes within the oxic layer 00:38:48.220 --> 00:38:50.080 align:middle line:90% in the sediments. 00:38:50.080 --> 00:38:51.840 align:middle line:84% And what this serves to do is it actually 00:38:51.840 --> 00:38:54.720 align:middle line:84% increases the pore water phosphate concentrations, which 00:38:54.720 --> 00:38:57.040 align:middle line:84% can actually end up that you have as a diffusive 00:38:57.040 --> 00:39:00.880 align:middle line:84% flux out of the sediments where the sediment concentration is 00:39:00.880 --> 00:39:03.660 align:middle line:84% higher than the concentration in the overlying water. 00:39:03.660 --> 00:39:07.355 align:middle line:84% So you'll actually have a flux out. 00:39:07.355 --> 00:39:08.980 align:middle line:84% And again, this is from the literature. 00:39:08.980 --> 00:39:12.720 align:middle line:84% But deep sea sediment flux extrapolated to the global ocean 00:39:12.720 --> 00:39:14.880 align:middle line:84% actually suggests, like I said, that you 00:39:14.880 --> 00:39:18.080 align:middle line:84% do see an efflux of phosphate from the sediments that's 00:39:18.080 --> 00:39:22.400 align:middle line:84% greater than or equal to the rate of delivery of P 00:39:22.400 --> 00:39:24.520 align:middle line:90% from the surface export. 00:39:24.520 --> 00:39:28.320 align:middle line:84% So again, just to bring home the point 00:39:28.320 --> 00:39:31.200 align:middle line:84% here is that much of the organic carbon 00:39:31.200 --> 00:39:34.920 align:middle line:84% and the organic phosphorus is going to be remineralized 00:39:34.920 --> 00:39:36.960 align:middle line:90% in the water column. 00:39:36.960 --> 00:39:39.080 align:middle line:84% And that the actual thing we're trying 00:39:39.080 --> 00:39:41.480 align:middle line:84% to estimate at this point, which is burial, 00:39:41.480 --> 00:39:45.640 align:middle line:84% is it's the difference between the delivery to the seafloor 00:39:45.640 --> 00:39:48.150 align:middle line:84% and the efflux out, both of which 00:39:48.150 --> 00:39:49.810 align:middle line:90% are pretty poorly constrained. 00:39:49.810 --> 00:39:51.350 align:middle line:84% And again, it's an issue where we're 00:39:51.350 --> 00:39:52.890 align:middle line:90% subtracting two large numbers. 00:39:52.890 --> 00:39:56.110 align:middle line:84% So we need some more work done on that before we 00:39:56.110 --> 00:39:57.770 align:middle line:90% can be entirely quantitative. 00:39:57.770 --> 00:40:01.110 align:middle line:90% 00:40:01.110 --> 00:40:03.330 align:middle line:84% To do the same type of thing that we did with export, 00:40:03.330 --> 00:40:05.910 align:middle line:84% but rather just with burial in this case, 00:40:05.910 --> 00:40:10.030 align:middle line:84% we can estimate the rate of organic burial as a function 00:40:10.030 --> 00:40:15.310 align:middle line:84% of a measured or estimated organic carbon burial rate times 00:40:15.310 --> 00:40:19.150 align:middle line:84% the mean carbon-to-phosphate ratio in the buried sedimentary 00:40:19.150 --> 00:40:24.950 align:middle line:84% material, and the organic carbon burial rates at depths greater 00:40:24.950 --> 00:40:27.990 align:middle line:84% than 1,000 meters, are approximately 1.25 times 10 00:40:27.990 --> 00:40:30.310 align:middle line:90% to the 12th moles per year. 00:40:30.310 --> 00:40:32.870 align:middle line:84% And so that's less than 3% of the delivery. 00:40:32.870 --> 00:40:35.910 align:middle line:84% So we have 3% of the surface export reaching 00:40:35.910 --> 00:40:40.373 align:middle line:84% the sea floor, and then 3% of that actually getting buried. 00:40:40.373 --> 00:40:41.790 align:middle line:84% So you can see most of it is going 00:40:41.790 --> 00:40:47.010 align:middle line:84% to be recycled within the biota within the ocean. 00:40:47.010 --> 00:40:48.650 align:middle line:84% We do know though, if we're not going 00:40:48.650 --> 00:40:50.290 align:middle line:84% to look at such deep depths, if we 00:40:50.290 --> 00:40:52.170 align:middle line:84% want to focus more on the continental margins 00:40:52.170 --> 00:40:56.650 align:middle line:84% or the shallower regions, that there's much larger 00:40:56.650 --> 00:40:59.330 align:middle line:84% amounts of phosphorus are actually buried. 00:40:59.330 --> 00:41:01.350 align:middle line:84% So when we want to do global estimates, 00:41:01.350 --> 00:41:04.203 align:middle line:84% we have to keep in mind that the processes are going 00:41:04.203 --> 00:41:06.370 align:middle line:84% to be a little different in terms of their magnitude 00:41:06.370 --> 00:41:08.530 align:middle line:90% depending on where you are. 00:41:08.530 --> 00:41:13.330 align:middle line:84% But if we assume a Redfield ratio, again 106-to-1, 00:41:13.330 --> 00:41:21.690 align:middle line:84% in sediments deposited at depths greater than 1,000 meters, 00:41:21.690 --> 00:41:26.330 align:middle line:84% the maximum burial rate of organic phosphate is about 1.25 00:41:26.330 --> 00:41:29.270 align:middle line:84% times 10 to the 12 moles per year divided by 106, 00:41:29.270 --> 00:41:32.650 align:middle line:84% which ended up as 1.1 times 10 to the 10th moles per year. 00:41:32.650 --> 00:41:38.170 align:middle line:84% So that's a very small flux overall in the phosphorus cycle. 00:41:38.170 --> 00:41:43.600 align:middle line:84% But these flux estimates, they are getting adjusted upwards 00:41:43.600 --> 00:41:45.160 align:middle line:90% over the last decade. 00:41:45.160 --> 00:41:47.940 align:middle line:84% And a lot of that is because people, the investigators, 00:41:47.940 --> 00:41:50.440 align:middle line:84% are starting to take into account the shallower sediments 00:41:50.440 --> 00:41:53.720 align:middle line:84% and the higher deposition rates and burial 00:41:53.720 --> 00:41:57.080 align:middle line:84% rates in these continental margin regions. 00:41:57.080 --> 00:42:00.360 align:middle line:84% And so now, the current understanding is that these 00:42:00.360 --> 00:42:05.280 align:middle line:84% estimates actually range from 4.1 to 18.5 times 10 to the 10th 00:42:05.280 --> 00:42:08.600 align:middle line:90% moles per year. 00:42:08.600 --> 00:42:17.280 align:middle line:84% And so, once these organic materials land in the sea floor 00:42:17.280 --> 00:42:21.320 align:middle line:84% and start to get buried, we need to understand 00:42:21.320 --> 00:42:24.360 align:middle line:84% the effect of the organic matter degradation. 00:42:24.360 --> 00:42:26.880 align:middle line:84% So any bacterial processes within the sediments 00:42:26.880 --> 00:42:31.280 align:middle line:84% of the overlying waters, how that's going 00:42:31.280 --> 00:42:33.260 align:middle line:90% to affect the C-to-P ratio. 00:42:33.260 --> 00:42:35.600 align:middle line:84% Because I mean, all of our budgeting so far 00:42:35.600 --> 00:42:37.920 align:middle line:84% we've done based on these ratios. 00:42:37.920 --> 00:42:40.600 align:middle line:84% And so we don't really have a good assessment 00:42:40.600 --> 00:42:44.870 align:middle line:84% of how the bacterial processing will change these ratios, which 00:42:44.870 --> 00:42:47.910 align:middle line:90% are key to understand. 00:42:47.910 --> 00:42:51.850 align:middle line:84% What I have plotted here is from the literature. 00:42:51.850 --> 00:42:56.870 align:middle line:84% It's a mole-to-mole plot of phosphorus 00:42:56.870 --> 00:42:59.010 align:middle line:90% to carbon in organic matter. 00:42:59.010 --> 00:43:01.030 align:middle line:84% It's times 10 to the third because we've 00:43:01.030 --> 00:43:02.650 align:middle line:84% done rather than carbon to phosphorus, 00:43:02.650 --> 00:43:05.510 align:middle line:84% phosphorus to carbon, as a function 00:43:05.510 --> 00:43:10.563 align:middle line:84% of the percent of organic carbon in the sediments. 00:43:10.563 --> 00:43:12.230 align:middle line:84% And what you can see, a couple of things 00:43:12.230 --> 00:43:15.830 align:middle line:84% are immediately obvious that coming up 00:43:15.830 --> 00:43:20.050 align:middle line:84% with an average C-to-P, it's a pretty hard task. 00:43:20.050 --> 00:43:23.070 align:middle line:84% And it's obviously something that's going to vary spatially. 00:43:23.070 --> 00:43:25.670 align:middle line:90% It's highly variable. 00:43:25.670 --> 00:43:30.350 align:middle line:84% But you do see that the P-to-C ratio, C-to-P, it 00:43:30.350 --> 00:43:33.950 align:middle line:84% varies systematically with the percent of organic carbon 00:43:33.950 --> 00:43:35.670 align:middle line:90% in the sediments. 00:43:35.670 --> 00:43:39.570 align:middle line:84% And you often see that it is greater than Redfield. 00:43:39.570 --> 00:43:41.530 align:middle line:84% And so when that tells us is that there's 00:43:41.530 --> 00:43:45.090 align:middle line:84% a preferential release of phosphorus 00:43:45.090 --> 00:43:48.370 align:middle line:84% over carbon to the bottom water before this final burial 00:43:48.370 --> 00:43:49.390 align:middle line:90% actually occurs. 00:43:49.390 --> 00:43:52.960 align:middle line:90% 00:43:52.960 --> 00:43:57.288 align:middle line:84% But just like many studies, there's 00:43:57.288 --> 00:43:59.830 align:middle line:84% other studies, later studies, not necessarily better studies, 00:43:59.830 --> 00:44:06.170 align:middle line:84% but later studies that contradict these results. 00:44:06.170 --> 00:44:14.370 align:middle line:84% And this later study suggested, this study is from 1999, 00:44:14.370 --> 00:44:19.850 align:middle line:84% suggested that 1990, excuse me, systematic changes 00:44:19.850 --> 00:44:24.110 align:middle line:84% in this ratio, the C-to-P ratio, of the buried organic matter 00:44:24.110 --> 00:44:26.490 align:middle line:84% and thus the preservation or the organic matter, 00:44:26.490 --> 00:44:29.850 align:middle line:84% actually varied with the sedimentation rate. 00:44:29.850 --> 00:44:32.050 align:middle line:84% And so that gives us a clue as to how 00:44:32.050 --> 00:44:36.370 align:middle line:84% this is going to vary over the different regions of the ocean 00:44:36.370 --> 00:44:37.760 align:middle line:90% floor. 00:44:37.760 --> 00:44:40.940 align:middle line:84% And so this is a plot from their paper, 00:44:40.940 --> 00:44:44.740 align:middle line:84% which is sedimentation rate centimeters per year. 00:44:44.740 --> 00:44:48.360 align:middle line:84% This is a log scale as a function 00:44:48.360 --> 00:44:51.080 align:middle line:84% of the asymptotic organic C-to-P. 00:44:51.080 --> 00:44:53.360 align:middle line:84% And what that means is if you look at pore water 00:44:53.360 --> 00:44:58.120 align:middle line:84% concentrations they often have an exponential asymptotic type 00:44:58.120 --> 00:44:58.620 align:middle line:90% shape. 00:44:58.620 --> 00:45:01.440 align:middle line:84% And they took that value as the C-to-P 00:45:01.440 --> 00:45:04.040 align:middle line:84% to represent the sediment column. 00:45:04.040 --> 00:45:11.600 align:middle line:84% But what they found is that the C-to-P ratio of organic matter 00:45:11.600 --> 00:45:16.120 align:middle line:84% was actually close to Redfield, with Redfield being 106, 00:45:16.120 --> 00:45:16.780 align:middle line:90% and low. 00:45:16.780 --> 00:45:20.120 align:middle line:84% They classified everything less than 200 as low. 00:45:20.120 --> 00:45:21.720 align:middle line:84% So it was actually close to Redfield 00:45:21.720 --> 00:45:28.000 align:middle line:84% and low at really high sedimentation rates, which 00:45:28.000 --> 00:45:30.280 align:middle line:84% is greater than 1 centimeter per year, 00:45:30.280 --> 00:45:34.560 align:middle line:84% or at the really low sedimentation rates, so less 00:45:34.560 --> 00:45:37.260 align:middle line:90% than .002 centimeters per year. 00:45:37.260 --> 00:45:41.900 align:middle line:84% But it's in this intermediate range of sedimentation rates 00:45:41.900 --> 00:45:46.900 align:middle line:84% that we get these very high C-to-P ratios. 00:45:46.900 --> 00:45:49.460 align:middle line:84% And so what they took this to mean 00:45:49.460 --> 00:45:53.220 align:middle line:84% is that under oxic respiration conditions, 00:45:53.220 --> 00:45:57.340 align:middle line:84% they assume that the phosphorus is remineralized preferentially 00:45:57.340 --> 00:45:59.540 align:middle line:90% to the carbon. 00:45:59.540 --> 00:46:03.180 align:middle line:84% And so their interpretation was that at very high sedimentation 00:46:03.180 --> 00:46:08.783 align:middle line:84% rates, so in a coastal upwelling region or a delta type region, 00:46:08.783 --> 00:46:10.700 align:middle line:84% there's actually really excellent preservation 00:46:10.700 --> 00:46:15.860 align:middle line:84% of organic material when it hits the sea floor. 00:46:15.860 --> 00:46:19.240 align:middle line:84% And that's because there's such a large flux of organic matter, 00:46:19.240 --> 00:46:21.880 align:middle line:84% and you have a fairly small depth that you're talking about. 00:46:21.880 --> 00:46:25.020 align:middle line:84% So your actual time available for remineralization 00:46:25.020 --> 00:46:26.140 align:middle line:90% is much less. 00:46:26.140 --> 00:46:28.540 align:middle line:84% And so in that case, you'd expect the C-to-P ratio 00:46:28.540 --> 00:46:31.420 align:middle line:90% to be close to Redfield. 00:46:31.420 --> 00:46:34.810 align:middle line:84% And in contrast to that, in these very low sedimentation 00:46:34.810 --> 00:46:38.490 align:middle line:84% rates, so these are the really deep sea, 5,000, 00:46:38.490 --> 00:46:42.210 align:middle line:84% 6,000 meter pelagic-type environments that by the time 00:46:42.210 --> 00:46:45.570 align:middle line:84% that organic material hits the sea floor, 00:46:45.570 --> 00:46:49.130 align:middle line:84% that remineralization is complete. 00:46:49.130 --> 00:46:51.930 align:middle line:84% I mean, everything that can be remineralized is and what's left 00:46:51.930 --> 00:46:55.110 align:middle line:84% is just the refractory organic material. 00:46:55.110 --> 00:46:58.450 align:middle line:84% So again, you'd expect that to have that near Redfield ratio 00:46:58.450 --> 00:47:03.770 align:middle line:84% because it's going to reflect the initial values. 00:47:03.770 --> 00:47:06.690 align:middle line:84% And what they interpreted the mid-range sedimentation 00:47:06.690 --> 00:47:09.570 align:middle line:84% rates is that these are what they 00:47:09.570 --> 00:47:13.210 align:middle line:84% consider corresponding to the real continental margins 00:47:13.210 --> 00:47:14.530 align:middle line:90% type areas. 00:47:14.530 --> 00:47:18.090 align:middle line:84% And they this reflects the preferential regeneration 00:47:18.090 --> 00:47:19.708 align:middle line:90% of phosphate. 00:47:19.708 --> 00:47:21.250 align:middle line:84% So what you're going to see is you're 00:47:21.250 --> 00:47:26.050 align:middle line:84% going to see detrital compounds that are enriched in phosphate 00:47:26.050 --> 00:47:27.530 align:middle line:90% relative to carbon. 00:47:27.530 --> 00:47:34.800 align:middle line:84% Or what you're going to see are the remains 00:47:34.800 --> 00:47:38.360 align:middle line:84% of bacteria within the sediments that 00:47:38.360 --> 00:47:44.945 align:middle line:84% have a high C to P because they reflect what they're consuming. 00:47:44.945 --> 00:47:46.320 align:middle line:84% And so what this would do is this 00:47:46.320 --> 00:47:49.520 align:middle line:84% would actually decrease the importance of margin sediments 00:47:49.520 --> 00:47:51.460 align:middle line:90% as a sink for phosphate. 00:47:51.460 --> 00:47:54.160 align:middle line:84% And if we saw in the last slide that a lot of our estimates 00:47:54.160 --> 00:47:58.800 align:middle line:84% of burial have been of creeping up because people are starting 00:47:58.800 --> 00:48:02.480 align:middle line:84% to think that a lot more phosphate, I just said sulfate, 00:48:02.480 --> 00:48:06.720 align:middle line:84% but a lot more phosphate was buried on these shelf slope 00:48:06.720 --> 00:48:07.600 align:middle line:90% areas. 00:48:07.600 --> 00:48:09.400 align:middle line:84% And this type of phenomenon would actually 00:48:09.400 --> 00:48:13.600 align:middle line:84% start to actually decrease the importance of the margin areas. 00:48:13.600 --> 00:48:16.400 align:middle line:84% AUDIENCE: I haven't seen the [INAUDIBLE]. 00:48:16.400 --> 00:48:20.000 align:middle line:84% You said it's they're basing on this asymptotic-- 00:48:20.000 --> 00:48:21.200 align:middle line:90% DIERDRE TOOLE: Yeah. 00:48:21.200 --> 00:48:25.640 align:middle line:84% AUDIENCE: What about authigenic precipitation of particulate 00:48:25.640 --> 00:48:27.088 align:middle line:90% phosphate in those sediments? 00:48:27.088 --> 00:48:28.880 align:middle line:84% DIERDRE TOOLE: I'm going to talk about that 00:48:28.880 --> 00:48:31.200 align:middle line:84% in one minute in the next couple slides. 00:48:31.200 --> 00:48:34.682 align:middle line:90% But this is just in terms of-- 00:48:34.682 --> 00:48:36.640 align:middle line:84% AUDIENCE: But that would counter that argument. 00:48:36.640 --> 00:48:39.060 align:middle line:84% You could get very high dissolved carbon 00:48:39.060 --> 00:48:41.740 align:middle line:84% to phosphorus in the pore waters because phosphorus 00:48:41.740 --> 00:48:43.180 align:middle line:90% has been stripped out. 00:48:43.180 --> 00:48:46.060 align:middle line:84% DIERDRE TOOLE: Yeah in like apatites. 00:48:46.060 --> 00:48:49.267 align:middle line:84% AUDIENCE: Kathleen Ruttenberg would argue that counters that. 00:48:49.267 --> 00:48:50.100 align:middle line:90% DIERDRE TOOLE: Yeah. 00:48:50.100 --> 00:48:50.600 align:middle line:90% Yeah. 00:48:50.600 --> 00:48:53.300 align:middle line:84% No, that thing, again, one of the main points that I really 00:48:53.300 --> 00:48:55.020 align:middle line:84% do want to make is that there are 00:48:55.020 --> 00:48:57.642 align:middle line:84% a lot of different processes occurring simultaneously, 00:48:57.642 --> 00:48:59.100 align:middle line:84% and there are different people that 00:48:59.100 --> 00:49:01.660 align:middle line:84% have different opinions in terms of which 00:49:01.660 --> 00:49:03.980 align:middle line:90% is the dominant process. 00:49:03.980 --> 00:49:07.220 align:middle line:84% And this is just trying to understand 00:49:07.220 --> 00:49:12.360 align:middle line:84% the C-to-P though of the buried organic matter, this plot. 00:49:12.360 --> 00:49:17.700 align:middle line:84% They're not trying to tease it apart the total amount of carbon 00:49:17.700 --> 00:49:20.060 align:middle line:84% or phosphate, which we'll talk about 00:49:20.060 --> 00:49:23.000 align:middle line:84% in a second is the formation of those phosphate minerals. 00:49:23.000 --> 00:49:24.660 align:middle line:84% Again, they're specifically trying 00:49:24.660 --> 00:49:28.650 align:middle line:84% to just tease apart the ratios in the organic material 00:49:28.650 --> 00:49:30.110 align:middle line:84% and biological processing of that, 00:49:30.110 --> 00:49:32.010 align:middle line:84% and how that changes our interpretation 00:49:32.010 --> 00:49:37.090 align:middle line:84% of the importance of the slope as a loss mechanism. 00:49:37.090 --> 00:49:41.850 align:middle line:90% And so perfect segue, Scott. 00:49:41.850 --> 00:49:44.130 align:middle line:84% But what we do have to understand 00:49:44.130 --> 00:49:46.490 align:middle line:84% before we can take all these things to heart 00:49:46.490 --> 00:49:50.050 align:middle line:84% is the actual chemical nature of the buried phosphate 00:49:50.050 --> 00:49:51.970 align:middle line:84% in sediments, how much of it is going 00:49:51.970 --> 00:49:54.450 align:middle line:84% to be in the organic form versus how 00:49:54.450 --> 00:49:59.090 align:middle line:84% much is going to be tied up into secondary authigenic phases. 00:49:59.090 --> 00:50:02.450 align:middle line:84% And so basically at your bottom water, sediment pore water 00:50:02.450 --> 00:50:06.690 align:middle line:84% interface, there's going to be a great deal of organic matter 00:50:06.690 --> 00:50:08.650 align:middle line:90% decomposition. 00:50:08.650 --> 00:50:12.570 align:middle line:84% And what happens from this is this organic matter 00:50:12.570 --> 00:50:17.990 align:middle line:84% decomposition releases different forms of phosphate. 00:50:17.990 --> 00:50:20.290 align:middle line:84% In this case, I have hydrogen phosphate. 00:50:20.290 --> 00:50:24.330 align:middle line:84% And most of this is actually able to diffuse back 00:50:24.330 --> 00:50:27.280 align:middle line:90% out to the bottom water above. 00:50:27.280 --> 00:50:33.560 align:middle line:84% But some of it does precipitate with some of the iron 00:50:33.560 --> 00:50:35.360 align:middle line:84% and aluminum oxides in the sediment 00:50:35.360 --> 00:50:39.040 align:middle line:84% itself to become a phosphate mineral, essentially being 00:50:39.040 --> 00:50:44.560 align:middle line:84% trapped, and no longer available to be considered 00:50:44.560 --> 00:50:46.400 align:middle line:90% part of the organic pool. 00:50:46.400 --> 00:50:48.960 align:middle line:84% And so the fates of this released phosphorus 00:50:48.960 --> 00:50:52.100 align:middle line:84% from this organic matter decomposition in pore waters, 00:50:52.100 --> 00:50:56.120 align:middle line:84% it's ultimately going to dictate the C-to-P of the organic matter 00:50:56.120 --> 00:50:58.320 align:middle line:90% in the marine sediments. 00:50:58.320 --> 00:51:00.040 align:middle line:84% So we know that the phosphorus can 00:51:00.040 --> 00:51:03.560 align:middle line:84% be buried as the refractory organic phosphorus, 00:51:03.560 --> 00:51:07.040 align:middle line:84% but it can also be buried as these carbonate fluorapatite 00:51:07.040 --> 00:51:09.880 align:middle line:84% formed in sediments, so the sediment minerals, 00:51:09.880 --> 00:51:11.880 align:middle line:84% or it can be buried as absorption 00:51:11.880 --> 00:51:15.600 align:middle line:84% of dissolved phosphorus to iron oxides or aluminum 00:51:15.600 --> 00:51:17.868 align:middle line:90% oxides in hydrothermal plumes. 00:51:17.868 --> 00:51:20.160 align:middle line:84% And I'll get to in a second, but low temperature basalt 00:51:20.160 --> 00:51:22.100 align:middle line:84% interactions with the hydrothermal vents. 00:51:22.100 --> 00:51:25.980 align:middle line:90% 00:51:25.980 --> 00:51:28.620 align:middle line:84% Just kind of as an aside to think about, because there 00:51:28.620 --> 00:51:31.200 align:middle line:90% are oxic basins, anoxic basins. 00:51:31.200 --> 00:51:32.700 align:middle line:90% It depends on where you are. 00:51:32.700 --> 00:51:35.500 align:middle line:84% The extent of phosphate burial, it also 00:51:35.500 --> 00:51:38.940 align:middle line:84% seems to depend on the presence of oxygen in the bottom waters. 00:51:38.940 --> 00:51:40.900 align:middle line:84% So it's going to depend on the structure 00:51:40.900 --> 00:51:47.500 align:middle line:84% within your pore waters of your oxygen anoxic boundary. 00:51:47.500 --> 00:51:50.380 align:middle line:84% So in the presence of oxygen, the preservation 00:51:50.380 --> 00:51:52.940 align:middle line:84% of organic carbon decreases because there's 00:51:52.940 --> 00:51:55.460 align:middle line:84% more opportunities for remineralization, 00:51:55.460 --> 00:51:59.180 align:middle line:84% while that phosphate actually increases. 00:51:59.180 --> 00:52:02.020 align:middle line:84% And the reason for that is that due to the presence of this iron 00:52:02.020 --> 00:52:05.360 align:middle line:84% oxide layer near the sediment water interface, 00:52:05.360 --> 00:52:08.340 align:middle line:84% you're actually going to trap the phosphate release 00:52:08.340 --> 00:52:10.900 align:middle line:84% from the organic matter decomposition. 00:52:10.900 --> 00:52:15.940 align:middle line:84% So if you don't have this layer, this oxide layer, 00:52:15.940 --> 00:52:20.780 align:middle line:84% because you have low oxygen, the preservation of P 00:52:20.780 --> 00:52:22.500 align:middle line:90% is going to change. 00:52:22.500 --> 00:52:26.430 align:middle line:84% And so if no little or no oxygen is present, 00:52:26.430 --> 00:52:29.050 align:middle line:84% you're going to have more organic carbon preserved, 00:52:29.050 --> 00:52:31.050 align:middle line:84% but you're going to have more phosphate released 00:52:31.050 --> 00:52:33.970 align:middle line:84% from the aromatic, but the phosphate released 00:52:33.970 --> 00:52:35.850 align:middle line:84% from this organic matter decomposition 00:52:35.850 --> 00:52:38.130 align:middle line:84% by the bacteria in those pore waters, 00:52:38.130 --> 00:52:41.090 align:middle line:84% it's more likely to diffuse to the overlying water layer 00:52:41.090 --> 00:52:46.370 align:middle line:84% rather than getting trapped or adsorbed onto those oxides. 00:52:46.370 --> 00:52:51.490 align:middle line:84% And that'll give you a C-to-P that's greater than Redfield. 00:52:51.490 --> 00:53:00.210 align:middle line:84% So going back to, this is what Scott was starting to allude to, 00:53:00.210 --> 00:53:04.410 align:middle line:84% is we need to understand the formation 00:53:04.410 --> 00:53:10.170 align:middle line:84% of these phosphate minerals to understand ultimately 00:53:10.170 --> 00:53:12.970 align:middle line:84% how the phosphate released from organic matter 00:53:12.970 --> 00:53:15.750 align:middle line:84% decomposition, its ultimate fate, 00:53:15.750 --> 00:53:22.230 align:middle line:84% and the carbon-to-phosphate ratios 00:53:22.230 --> 00:53:24.750 align:middle line:84% that we use for all these flux calculations. 00:53:24.750 --> 00:53:30.030 align:middle line:84% And so basically I'll try to go through this. 00:53:30.030 --> 00:53:34.630 align:middle line:90% Is we have an iron oxide layer. 00:53:34.630 --> 00:53:37.910 align:middle line:84% And again, phosphate can adsorb onto this. 00:53:37.910 --> 00:53:41.070 align:middle line:84% And this is going to be subjected 00:53:41.070 --> 00:53:45.150 align:middle line:90% to burial within the sediments. 00:53:45.150 --> 00:53:49.830 align:middle line:84% And as these iron oxides are buried and reduced, 00:53:49.830 --> 00:53:52.470 align:middle line:84% once you get below the oxide layer and the anoxic layer 00:53:52.470 --> 00:53:55.790 align:middle line:84% of sediments as they're reduced, the adsorbed phosphate 00:53:55.790 --> 00:53:59.870 align:middle line:84% is going to be released to the pore water. 00:53:59.870 --> 00:54:04.210 align:middle line:84% And so you're going to have phosphate in the pore water. 00:54:04.210 --> 00:54:06.470 align:middle line:84% And you're actually going to have iron too. 00:54:06.470 --> 00:54:09.630 align:middle line:84% And once this phosphate is released in the pore waters, 00:54:09.630 --> 00:54:11.230 align:middle line:90% it can do one of two things. 00:54:11.230 --> 00:54:13.950 align:middle line:84% It can either slowly diffuse upward 00:54:13.950 --> 00:54:16.430 align:middle line:84% to get back out into the water column, 00:54:16.430 --> 00:54:21.020 align:middle line:84% or it's going to get trapped in these carbonate fluorapatites, 00:54:21.020 --> 00:54:25.740 align:middle line:84% in which case it's buried, it's deposited, it's there. 00:54:25.740 --> 00:54:27.700 align:middle line:84% And we also see simultaneously that 00:54:27.700 --> 00:54:29.720 align:middle line:84% as the organic phosphate materials, 00:54:29.720 --> 00:54:32.220 align:middle line:84% any refractory organic phosphate materials, if you're 00:54:32.220 --> 00:54:34.620 align:middle line:84% in the pelagic area or any organic materials, really 00:54:34.620 --> 00:54:38.300 align:middle line:84% it hits the sediment layer, a coastal slope, that those 00:54:38.300 --> 00:54:41.340 align:middle line:84% are also going to be subjected to burial and decomposition 00:54:41.340 --> 00:54:47.140 align:middle line:84% processes which will release phosphate again. 00:54:47.140 --> 00:54:50.500 align:middle line:84% And so that phosphate is subjected to the same processes. 00:54:50.500 --> 00:54:56.180 align:middle line:84% So either it can be diffused out or you can 00:54:56.180 --> 00:54:58.100 align:middle line:90% make these phosphate minerals. 00:54:58.100 --> 00:55:02.540 align:middle line:84% But essentially, it's pretty well-documented 00:55:02.540 --> 00:55:06.180 align:middle line:84% now that in sediments underlying upwelling and most margin 00:55:06.180 --> 00:55:09.260 align:middle line:84% regions that these fluorapatites, the CFAs, 00:55:09.260 --> 00:55:12.060 align:middle line:90% are very often observed. 00:55:12.060 --> 00:55:15.340 align:middle line:84% And so what they think is that these CFAs 00:55:15.340 --> 00:55:17.610 align:middle line:84% tend to precipitate from pore waters 00:55:17.610 --> 00:55:19.250 align:middle line:84% where the phosphate concentrations 00:55:19.250 --> 00:55:22.010 align:middle line:84% near the sediment water interface are high. 00:55:22.010 --> 00:55:25.290 align:middle line:84% And so what you have is you have a consistent recycling 00:55:25.290 --> 00:55:26.250 align:middle line:90% of this iron. 00:55:26.250 --> 00:55:29.050 align:middle line:90% Iron forms iron oxides. 00:55:29.050 --> 00:55:32.010 align:middle line:84% It's buried down in the sediment where it's reduced. 00:55:32.010 --> 00:55:35.370 align:middle line:84% And then it diffuses up to form the oxides again. 00:55:35.370 --> 00:55:39.330 align:middle line:84% And every time it goes through this recycling loop, 00:55:39.330 --> 00:55:43.610 align:middle line:84% it can actually scavenge phosphate, either the phosphate 00:55:43.610 --> 00:55:46.490 align:middle line:84% within the pore water column that's diffusing up 00:55:46.490 --> 00:55:49.810 align:middle line:84% or phosphate from the water column itself. 00:55:49.810 --> 00:55:53.345 align:middle line:84% And so what it does is as it scavenges more and more 00:55:53.345 --> 00:55:55.470 align:middle line:84% phosphate as it goes through these recycling loops, 00:55:55.470 --> 00:55:59.090 align:middle line:84% you're actually having phosphate building up at each cycle. 00:55:59.090 --> 00:56:06.330 align:middle line:84% And so when you end up with this loss of phosphate, 00:56:06.330 --> 00:56:09.610 align:middle line:84% this phosphate is replaced by phosphate being pulled out 00:56:09.610 --> 00:56:16.190 align:middle line:84% of the water column where the iron in this recycling 00:56:16.190 --> 00:56:19.610 align:middle line:84% is actually replaced by iron containing detrital materials. 00:56:19.610 --> 00:56:22.410 align:middle line:84% So when the iron is precipitated out to things such as pyrite, 00:56:22.410 --> 00:56:24.690 align:middle line:84% you can get iron from some of the detrital materials. 00:56:24.690 --> 00:56:28.390 align:middle line:90% 00:56:28.390 --> 00:56:34.870 align:middle line:84% So this CFA precipitation, it's been pretty widely documented, 00:56:34.870 --> 00:56:37.870 align:middle line:84% and it's moved beyond just being observed 00:56:37.870 --> 00:56:40.773 align:middle line:84% in the continental shelves, slope type areas. 00:56:40.773 --> 00:56:42.190 align:middle line:84% I mean, it's actually they've been 00:56:42.190 --> 00:56:46.750 align:middle line:84% observed pretty ubiquitously in the deep sea water. 00:56:46.750 --> 00:56:50.470 align:middle line:84% And so the way they've done this is 00:56:50.470 --> 00:56:53.470 align:middle line:84% they use a leaching procedure that's actually 00:56:53.470 --> 00:56:56.470 align:middle line:84% able to differentiate between the different forms of phosphate 00:56:56.470 --> 00:56:58.270 align:middle line:90% and sediments. 00:56:58.270 --> 00:56:59.870 align:middle line:84% And so what I have shown a plot here 00:56:59.870 --> 00:57:02.990 align:middle line:84% is its depth in centimeters of the sediment, 00:57:02.990 --> 00:57:06.270 align:middle line:84% and then weight percentage of phosphate. 00:57:06.270 --> 00:57:10.390 align:middle line:84% And you can see that the organic phosphate, which 00:57:10.390 --> 00:57:12.670 align:middle line:84% is represented by the open symbols 00:57:12.670 --> 00:57:17.060 align:middle line:84% and the authigenic phosphate, which is primarily 00:57:17.060 --> 00:57:20.140 align:middle line:90% these carbonate apatites. 00:57:20.140 --> 00:57:23.580 align:middle line:84% They tend to have an inverse relationship. 00:57:23.580 --> 00:57:27.260 align:middle line:84% So basically as the P organic, the organic phosphate 00:57:27.260 --> 00:57:28.860 align:middle line:90% decreases with depth. 00:57:28.860 --> 00:57:32.220 align:middle line:84% So as more and more of that is being remineralized with depth 00:57:32.220 --> 00:57:36.060 align:middle line:84% that the CFA concentration actually is increasing. 00:57:36.060 --> 00:57:37.940 align:middle line:84% So that means that most of the phosphate 00:57:37.940 --> 00:57:42.220 align:middle line:84% from these organic materials that 00:57:42.220 --> 00:57:44.540 align:middle line:84% are buried within the sediments are 00:57:44.540 --> 00:57:46.980 align:middle line:84% being recycled through the sediments 00:57:46.980 --> 00:57:50.540 align:middle line:84% and ultimately ending up being precipitated as these CFAs. 00:57:50.540 --> 00:57:56.260 align:middle line:84% And so this has been termed the phosphorus sink switch. 00:57:56.260 --> 00:58:02.260 align:middle line:84% They were also able to document the precipitation of phosphate 00:58:02.260 --> 00:58:04.820 align:middle line:84% released from the organic matter. 00:58:04.820 --> 00:58:09.300 align:middle line:84% It was also confirmed during a couple pore water modeling 00:58:09.300 --> 00:58:10.620 align:middle line:90% studies. 00:58:10.620 --> 00:58:13.300 align:middle line:84% And I know this figure speaker is small, 00:58:13.300 --> 00:58:16.520 align:middle line:84% but what we have again is depth in terms 00:58:16.520 --> 00:58:19.240 align:middle line:90% of centimeters from 0 to 300. 00:58:19.240 --> 00:58:23.240 align:middle line:84% And then we have the open circles or observations 00:58:23.240 --> 00:58:26.880 align:middle line:84% where the line is a model fit, the best model fit, 00:58:26.880 --> 00:58:30.020 align:middle line:84% and the first plot is ammonia in micromoles, 00:58:30.020 --> 00:58:36.100 align:middle line:84% and the second plot is hydrogen phosphate in micromoles. 00:58:36.100 --> 00:58:42.320 align:middle line:84% And what they were able to do is based on a stoichiometric ratio, 00:58:42.320 --> 00:58:44.360 align:middle line:84% it's a stoichiometric model for oxidation 00:58:44.360 --> 00:58:45.940 align:middle line:84% of sedimentary organic materials. 00:58:45.940 --> 00:58:48.840 align:middle line:84% You know that for x amount of moles of ammonia 00:58:48.840 --> 00:58:51.760 align:middle line:84% there's going to be x amount of moles change in phosphate. 00:58:51.760 --> 00:58:56.640 align:middle line:84% They were able to estimate what the expected pore water 00:58:56.640 --> 00:59:00.160 align:middle line:90% profile of phosphate would be. 00:59:00.160 --> 00:59:04.520 align:middle line:84% And the estimates is this black solid line 00:59:04.520 --> 00:59:17.470 align:middle line:84% where the open symbols are the actual organic observed, 00:59:17.470 --> 00:59:20.000 align:middle line:84% actual observations of observed phosphate. 00:59:20.000 --> 00:59:21.750 align:middle line:84% And what you can see is that the estimates 00:59:21.750 --> 00:59:23.510 align:middle line:84% of what should be there organically 00:59:23.510 --> 00:59:25.910 align:middle line:84% are far in excess of what actually 00:59:25.910 --> 00:59:28.910 align:middle line:90% are in the organic form. 00:59:28.910 --> 00:59:30.950 align:middle line:84% And so what that suggests is that there actually 00:59:30.950 --> 00:59:34.030 align:middle line:84% is this large precipitation of the authigenic phosphate 00:59:34.030 --> 00:59:35.007 align:middle line:90% materials. 00:59:35.007 --> 00:59:36.590 align:middle line:84% That's what's making up the difference 00:59:36.590 --> 00:59:40.430 align:middle line:84% between the expectation of how much dissolved phosphate should 00:59:40.430 --> 00:59:44.750 align:middle line:84% be there versus how much phosphate is actually there. 00:59:44.750 --> 00:59:48.750 align:middle line:84% And CFAs are now seen as the main form of phosphate present 00:59:48.750 --> 00:59:50.050 align:middle line:90% in deep sea sediments. 00:59:50.050 --> 00:59:52.350 align:middle line:84% That's a pretty wide held belief. 00:59:52.350 --> 00:59:57.190 align:middle line:84% So if we're going to look just at organic phosphate burial 00:59:57.190 --> 00:59:59.990 align:middle line:84% and remineralization, that's going to significantly 00:59:59.990 --> 01:00:02.872 align:middle line:84% underestimate the total reactive phosphate that's actually buried 01:00:02.872 --> 01:00:04.830 align:middle line:84% in these sediments, because there's a lot of it 01:00:04.830 --> 01:00:07.250 align:middle line:84% precipitated in these lithogenic materials. 01:00:07.250 --> 01:00:10.140 align:middle line:90% 01:00:10.140 --> 01:00:13.000 align:middle line:84% And so just of as an aside to something that you should know 01:00:13.000 --> 01:00:17.580 align:middle line:84% is that there also is phosphate removal at hydrothermal vents, 01:00:17.580 --> 01:00:19.460 align:middle line:90% hydrothermal processes. 01:00:19.460 --> 01:00:21.880 align:middle line:84% And it's the same type of reaction. 01:00:21.880 --> 01:00:24.300 align:middle line:84% But there's that scavenging of phosphate from the seawater 01:00:24.300 --> 01:00:25.980 align:middle line:90% by iron oxides. 01:00:25.980 --> 01:00:28.100 align:middle line:84% And these are just iron oxides found in the plumes 01:00:28.100 --> 01:00:31.740 align:middle line:90% of hydrothermal vents. 01:00:31.740 --> 01:00:35.700 align:middle line:84% Again, using element ratios, if you want to look at the iron 01:00:35.700 --> 01:00:38.020 align:middle line:84% fluxes at these hydrothermal vents, 01:00:38.020 --> 01:00:42.460 align:middle line:84% times a mean phosphate-to-iron ratio in the plume particles, 01:00:42.460 --> 01:00:46.220 align:middle line:84% you get a relatively small scavenging of phosphate out 01:00:46.220 --> 01:00:48.820 align:middle line:84% of the water column relative to the inventory of phosphate 01:00:48.820 --> 01:00:51.940 align:middle line:84% in the overlying waters, and it's on the order of 0.8 times 01:00:51.940 --> 01:00:56.060 align:middle line:90% 10 to the 10th moles per year. 01:00:56.060 --> 01:00:59.260 align:middle line:84% At these same locations, you also have phosphate being 01:00:59.260 --> 01:01:02.240 align:middle line:84% removed via, again, the formation of these same, 01:01:02.240 --> 01:01:07.920 align:middle line:84% the authigenic apatite minerals and absorption on secondary iron 01:01:07.920 --> 01:01:11.000 align:middle line:84% oxides, and this is primarily during low-temperature 01:01:11.000 --> 01:01:13.320 align:middle line:84% interactions between basalt and seawater, 01:01:13.320 --> 01:01:16.800 align:middle line:84% and it's a larger removal process in the order of 3 times 01:01:16.800 --> 01:01:19.480 align:middle line:84% 10 to the 10th moles per year, but that's still significantly 01:01:19.480 --> 01:01:22.220 align:middle line:84% smaller than the other removal processes. 01:01:22.220 --> 01:01:27.080 align:middle line:90% 01:01:27.080 --> 01:01:30.760 align:middle line:84% Ultimately, we want to understand the residence 01:01:30.760 --> 01:01:33.240 align:middle line:84% time and the turnover time of phosphorus 01:01:33.240 --> 01:01:37.760 align:middle line:84% in seawater because of its role as a limiting nutrient. 01:01:37.760 --> 01:01:43.160 align:middle line:84% And this recognition of the widespread distribution 01:01:43.160 --> 01:01:45.640 align:middle line:84% of these lithogenic phosphate materials 01:01:45.640 --> 01:01:50.440 align:middle line:84% has led to significant revision of our phosphate residence times 01:01:50.440 --> 01:01:53.800 align:middle line:84% in the ocean and downward revisions. 01:01:53.800 --> 01:01:59.080 align:middle line:84% And from the literature, the previous estimates of phosphate 01:01:59.080 --> 01:02:02.560 align:middle line:84% burial in 10 to the 10th moles per year was on the order 01:02:02.560 --> 01:02:04.240 align:middle line:90% of 3.8. 01:02:04.240 --> 01:02:07.950 align:middle line:84% But once we start taking into account the importance 01:02:07.950 --> 01:02:12.310 align:middle line:84% of the continental margin regions and the burial of these 01:02:12.310 --> 01:02:20.470 align:middle line:84% apatites, the modified estimates range from 8 to 18.5 times 10 01:02:20.470 --> 01:02:21.910 align:middle line:90% to the 10th moles per year. 01:02:21.910 --> 01:02:24.350 align:middle line:84% And these estimates are 2 to 5 times 01:02:24.350 --> 01:02:26.710 align:middle line:90% higher than previous estimates. 01:02:26.710 --> 01:02:29.970 align:middle line:84% So if we increase our burial rate significantly, 01:02:29.970 --> 01:02:33.750 align:middle line:84% it's going to give us a reduction in the mean residence 01:02:33.750 --> 01:02:35.470 align:middle line:90% time in the ocean. 01:02:35.470 --> 01:02:37.958 align:middle line:84% So for example, again going back to the same figure, 01:02:37.958 --> 01:02:39.750 align:middle line:84% if we want to look at our inventory divided 01:02:39.750 --> 01:02:45.810 align:middle line:84% by our turnover time using the original estimates, 01:02:45.810 --> 01:02:51.750 align:middle line:84% the residence time was on the order of 74,000 or 75,000 01:02:51.750 --> 01:02:55.030 align:middle line:90% to 80,000 years. 01:02:55.030 --> 01:02:57.350 align:middle line:84% But using these revised estimates, 01:02:57.350 --> 01:03:02.190 align:middle line:84% the turnover times are actually on the order of 15,000 to 30,000 01:03:02.190 --> 01:03:04.890 align:middle line:84% years for new burial flux estimates. 01:03:04.890 --> 01:03:07.930 align:middle line:84% And this reduction in time scale is telling us 01:03:07.930 --> 01:03:09.770 align:middle line:84% that the phosphorus might actually 01:03:09.770 --> 01:03:14.490 align:middle line:84% be able to vary on timescales relevant to interglacial 01:03:14.490 --> 01:03:16.210 align:middle line:90% glacial cycling. 01:03:16.210 --> 01:03:19.010 align:middle line:90% So that's important to consider. 01:03:19.010 --> 01:03:23.650 align:middle line:84% So again, if phosphate is the ultimate limiting nutrient 01:03:23.650 --> 01:03:28.090 align:middle line:84% on these longer-term scales, changes in the oceanic inventory 01:03:28.090 --> 01:03:31.010 align:middle line:84% are going to make a really big difference in terms 01:03:31.010 --> 01:03:34.770 align:middle line:84% of changing the intensity of the biological pump 01:03:34.770 --> 01:03:38.370 align:middle line:84% and potentially concentrations of CO2 and oxygen 01:03:38.370 --> 01:03:39.430 align:middle line:90% in the atmosphere. 01:03:39.430 --> 01:03:42.130 align:middle line:90% 01:03:42.130 --> 01:03:47.050 align:middle line:84% There has been some observations for reduce 01:03:47.050 --> 01:03:49.770 align:middle line:84% carbonate fluorapatite burial at upwelling margins 01:03:49.770 --> 01:03:51.930 align:middle line:90% during glacial periods. 01:03:51.930 --> 01:03:57.170 align:middle line:84% But again, this sink, this margin production of the CFAs, 01:03:57.170 --> 01:04:01.200 align:middle line:84% only accounts for about 10% of the total P being 01:04:01.200 --> 01:04:02.680 align:middle line:90% removed from the ocean. 01:04:02.680 --> 01:04:05.120 align:middle line:84% So if all other phosphorus sinks remain 01:04:05.120 --> 01:04:08.860 align:middle line:84% the same, the phosphate phosphorus inventories, 01:04:08.860 --> 01:04:10.880 align:middle line:90% it would change very little. 01:04:10.880 --> 01:04:12.880 align:middle line:84% Again, we don't have very good constraints 01:04:12.880 --> 01:04:14.500 align:middle line:90% on this at this point. 01:04:14.500 --> 01:04:17.520 align:middle line:90% 01:04:17.520 --> 01:04:22.240 align:middle line:84% Just as a last thought, how phosphate interacts 01:04:22.240 --> 01:04:23.920 align:middle line:84% with the carbon, the oxygen, some 01:04:23.920 --> 01:04:26.120 align:middle line:84% of the other biogeochemical cycles, 01:04:26.120 --> 01:04:31.320 align:middle line:84% this is a proposed climate feedback. 01:04:31.320 --> 01:04:37.363 align:middle line:84% And it is based on the crux that phosphate burial 01:04:37.363 --> 01:04:39.280 align:middle line:84% is more efficient when sediments are deposited 01:04:39.280 --> 01:04:41.160 align:middle line:90% under oxic conditions. 01:04:41.160 --> 01:04:44.320 align:middle line:84% And that's because of that scavenging by the Iron oxide 01:04:44.320 --> 01:04:45.680 align:middle line:90% minerals. 01:04:45.680 --> 01:04:48.080 align:middle line:84% And what I'm going to present here 01:04:48.080 --> 01:04:50.240 align:middle line:84% is just a potential negative feedback mechanism 01:04:50.240 --> 01:04:54.080 align:middle line:84% to control oxygen in the atmosphere over the Phanerozoic. 01:04:54.080 --> 01:04:57.840 align:middle line:84% And so this is getting back to your million-year timescales. 01:04:57.840 --> 01:05:00.790 align:middle line:84% And so what happens is if an atmospheric oxygen 01:05:00.790 --> 01:05:05.350 align:middle line:84% concentrations decrease and this bottom water oxygen 01:05:05.350 --> 01:05:07.910 align:middle line:84% concentrations will decrease, we'll 01:05:07.910 --> 01:05:12.270 align:middle line:84% actually have a decrease in the burial of phosphate 01:05:12.270 --> 01:05:16.550 align:middle line:84% in either form, organic or inorganic. 01:05:16.550 --> 01:05:18.590 align:middle line:84% And that seawater phosphate inventory 01:05:18.590 --> 01:05:20.430 align:middle line:84% is thus going to increase because it 01:05:20.430 --> 01:05:23.550 align:middle line:90% has nowhere else to go. 01:05:23.550 --> 01:05:25.927 align:middle line:90% Export production will increase. 01:05:25.927 --> 01:05:27.510 align:middle line:84% Basically, what that's saying is if we 01:05:27.510 --> 01:05:29.930 align:middle line:84% have more phosphate in the water, 01:05:29.930 --> 01:05:32.490 align:middle line:84% we're going to have more biological primary productivity. 01:05:32.490 --> 01:05:35.470 align:middle line:84% So our export production, our production and export 01:05:35.470 --> 01:05:38.430 align:middle line:84% production, are going to be able to increase. 01:05:38.430 --> 01:05:39.793 align:middle line:90% Hmm? 01:05:39.793 --> 01:05:41.210 align:middle line:84% AUDIENCE: Nothing, you'll find it. 01:05:41.210 --> 01:05:43.950 align:middle line:90% 01:05:43.950 --> 01:05:45.790 align:middle line:90% DIERDRE TOOLE: What did I-- 01:05:45.790 --> 01:05:47.852 align:middle line:84% AUDIENCE: The arrow for the atmospheric oxygen. 01:05:47.852 --> 01:05:48.810 align:middle line:90% DIERDRE TOOLE: Oh yeah. 01:05:48.810 --> 01:05:50.227 align:middle line:84% It's supposed to go the other way. 01:05:50.227 --> 01:05:52.030 align:middle line:90% Sorry. 01:05:52.030 --> 01:05:55.870 align:middle line:84% OK, so we have an increased production and export production 01:05:55.870 --> 01:05:57.650 align:middle line:84% because this increased productivity. 01:05:57.650 --> 01:06:00.810 align:middle line:84% We're going to have an increase in organic carbon burial, which 01:06:00.810 --> 01:06:04.090 align:middle line:84% is ultimately going to serve to come back around and increase 01:06:04.090 --> 01:06:06.610 align:middle line:84% the atmospheric oxygen concentration. 01:06:06.610 --> 01:06:10.050 align:middle line:84% So this is a stabilizing feedback loop in a way 01:06:10.050 --> 01:06:13.450 align:middle line:84% that the phosphate biogeochemical cycles 01:06:13.450 --> 01:06:16.090 align:middle line:90% can play into the climate. 01:06:16.090 --> 01:06:20.050 align:middle line:90% And that's all I have for today. 01:06:20.050 --> 01:06:26.290 align:middle line:84% And for August, you can come around here if you want. 01:06:26.290 --> 01:06:30.650 align:middle line:84% If this is actually just a fusion going on, and I think 01:06:30.650 --> 01:06:36.310 align:middle line:84% this is another case of where it's just the data. 01:06:36.310 --> 01:06:38.350 align:middle line:90% It looks a little bit funny. 01:06:38.350 --> 01:06:40.450 align:middle line:90% But no, it's not just effusion. 01:06:40.450 --> 01:06:44.610 align:middle line:84% You do have-- it looks like the boundary 01:06:44.610 --> 01:06:47.010 align:middle line:90% line isn't quite in there. 01:06:47.010 --> 01:06:55.710 align:middle line:84% But the reason that it goes down is because it's consumed. 01:06:55.710 --> 01:06:59.100 align:middle line:84% So even if there was some of diffusion going on, 01:06:59.100 --> 01:07:02.080 align:middle line:84% like the oxygen wasn't being used right at the surface, which 01:07:02.080 --> 01:07:03.600 align:middle line:90% is hard to imagine. 01:07:03.600 --> 01:07:07.560 align:middle line:84% Yeah something would have to be reducing it 01:07:07.560 --> 01:07:10.760 align:middle line:90% or because it's going away. 01:07:10.760 --> 01:07:16.000 align:middle line:90% So it is a very steep curve. 01:07:16.000 --> 01:07:18.280 align:middle line:84% AUDIENCE: Just since he was talking, 01:07:18.280 --> 01:07:20.080 align:middle line:84% so I understood just that you would 01:07:20.080 --> 01:07:23.760 align:middle line:84% see the consumption is lumped in along on the straight line. 01:07:23.760 --> 01:07:25.160 align:middle line:90% Or is that not a fair-- 01:07:25.160 --> 01:07:26.220 align:middle line:90% DIERDRE TOOLE: It's true. 01:07:26.220 --> 01:07:27.760 align:middle line:84% But in this case, the straight line 01:07:27.760 --> 01:07:31.640 align:middle line:84% is you would say straight line is like this or something. 01:07:31.640 --> 01:07:32.860 align:middle line:90% It is a curve. 01:07:32.860 --> 01:07:35.575 align:middle line:84% It's just a really sharp exponential curve. 01:07:35.575 --> 01:07:36.200 align:middle line:90% AUDIENCE: Yeah. 01:07:36.200 --> 01:07:40.000 align:middle line:90% 01:07:40.000 --> 01:07:42.560 align:middle line:90% DIERDRE TOOLE: OK. 01:07:42.560 --> 01:07:44.060 align:middle line:90% I have a ton of questions. 01:07:44.060 --> 01:07:50.560 align:middle line:84% I got a big email from Caron, Andrea, and Abigail 01:07:50.560 --> 01:07:52.500 align:middle line:90% that basically said, ah! 01:07:52.500 --> 01:07:56.700 align:middle line:90% 01:07:56.700 --> 01:08:01.940 align:middle line:84% So I don't know how far everyone has got on question 3. 01:08:01.940 --> 01:08:04.500 align:middle line:84% But the key thing to question 3, part B 01:08:04.500 --> 01:08:08.260 align:middle line:84% is that it's not asking you to diagram 01:08:08.260 --> 01:08:13.460 align:middle line:84% things with depth numbers, or rates, or anything like that. 01:08:13.460 --> 01:08:19.779 align:middle line:84% It's asking you to draw idealized cartoons basically. 01:08:19.779 --> 01:08:26.460 align:middle line:84% So one of the questions was how can we interpret the calcium 01:08:26.460 --> 01:08:30.200 align:middle line:90% carbonate thing here as depth? 01:08:30.200 --> 01:08:31.700 align:middle line:90% And you can't. 01:08:31.700 --> 01:08:33.800 align:middle line:84% Well, you can't get an actual depth off of it. 01:08:33.800 --> 01:08:35.880 align:middle line:90% That's not going to happen. 01:08:35.880 --> 01:08:38.500 align:middle line:84% I mean, you could find out what the exact depths are 01:08:38.500 --> 01:08:42.020 align:middle line:84% if you go to some literature or you look at an atlas. 01:08:42.020 --> 01:08:45.460 align:middle line:84% That's not what we're asking you to do. 01:08:45.460 --> 01:08:48.100 align:middle line:84% What we're asking you to do is I went 01:08:48.100 --> 01:08:50.340 align:middle line:84% through the question a little bit, 01:08:50.340 --> 01:08:52.890 align:middle line:84% but I don't want to give you my little answers I came up 01:08:52.890 --> 01:08:55.910 align:middle line:84% with because, one, I didn't think about them for very long, 01:08:55.910 --> 01:08:57.810 align:middle line:84% so I'm not sure how correct they are. 01:08:57.810 --> 01:09:01.250 align:middle line:90% And two, that's not fair. 01:09:01.250 --> 01:09:08.370 align:middle line:84% But what I want you to do is this is about it. 01:09:08.370 --> 01:09:11.330 align:middle line:84% Like you're drawing a little mid-ocean ridge 01:09:11.330 --> 01:09:15.270 align:middle line:84% and you're drawing the saturation horizon, 01:09:15.270 --> 01:09:18.130 align:middle line:90% the lysocline, the CCD. 01:09:18.130 --> 01:09:22.010 align:middle line:84% Draw where you think they are based on all the information 01:09:22.010 --> 01:09:22.870 align:middle line:90% you have. 01:09:22.870 --> 01:09:24.970 align:middle line:84% You don't have to go to outside sources. 01:09:24.970 --> 01:09:28.930 align:middle line:84% Based on what you have in these three or four plots, 01:09:28.930 --> 01:09:32.050 align:middle line:84% draw where about you think they would be. 01:09:32.050 --> 01:09:35.010 align:middle line:90% Does that make sense? 01:09:35.010 --> 01:09:43.890 align:middle line:84% So we know as an example, we know from the drawing here, 01:09:43.890 --> 01:09:49.069 align:middle line:84% we're looking at a cross section right here for the Atlantic. 01:09:49.069 --> 01:09:50.979 align:middle line:84% This is about the 30 degree point. 01:09:50.979 --> 01:09:52.779 align:middle line:84% The mid-ocean ridge is right here. 01:09:52.779 --> 01:09:54.220 align:middle line:90% Note, the high carbonate. 01:09:54.220 --> 01:09:56.900 align:middle line:84% Why on Earth would there be high carbonate on mid-ocean ridge, 01:09:56.900 --> 01:09:58.280 align:middle line:90% you may ask? 01:09:58.280 --> 01:09:59.700 align:middle line:90% Hope the answer. 01:09:59.700 --> 01:10:00.700 align:middle line:90% That's important. 01:10:00.700 --> 01:10:04.360 align:middle line:90% 01:10:04.360 --> 01:10:06.640 align:middle line:84% So you're asked to just draw what 01:10:06.640 --> 01:10:07.980 align:middle line:90% this little profile would be. 01:10:07.980 --> 01:10:15.840 align:middle line:84% So if you had depth, and you had distance across the Atlantic, 01:10:15.840 --> 01:10:19.120 align:middle line:84% the bottom would look something like this, right? 01:10:19.120 --> 01:10:21.620 align:middle line:84% And then you can see, OK, this is about 50. 01:10:21.620 --> 01:10:23.420 align:middle line:90% And then here's the 25 line. 01:10:23.420 --> 01:10:25.760 align:middle line:90% And then here's the 5 line. 01:10:25.760 --> 01:10:29.120 align:middle line:84% So from that, you can start to say, 01:10:29.120 --> 01:10:31.720 align:middle line:84% remember that plot that Bill put up 01:10:31.720 --> 01:10:41.640 align:middle line:84% that looked like this where he had the calcium carbonate? 01:10:41.640 --> 01:10:44.180 align:middle line:90% No 2 on that, solid. 01:10:44.180 --> 01:10:46.840 align:middle line:90% 01:10:46.840 --> 01:10:50.260 align:middle line:84% I think this was percent of seafloor sediments. 01:10:50.260 --> 01:10:52.080 align:middle line:84% And there are all these little plots. 01:10:52.080 --> 01:10:53.800 align:middle line:90% It was some percentage here. 01:10:53.800 --> 01:10:58.780 align:middle line:84% And then it went like this all the way down to 0. 01:10:58.780 --> 01:11:01.420 align:middle line:84% And we said that this would be the lysocline 01:11:01.420 --> 01:11:04.420 align:middle line:90% and this would be the CCD. 01:11:04.420 --> 01:11:07.180 align:middle line:84% These were all different core tops. 01:11:07.180 --> 01:11:08.700 align:middle line:90% Remember that? 01:11:08.700 --> 01:11:13.200 align:middle line:84% That's more or less the same information you're getting here. 01:11:13.200 --> 01:11:20.660 align:middle line:84% It's the percent carbonate in the sediments on the seafloor. 01:11:20.660 --> 01:11:23.940 align:middle line:84% So using that, you should be able to figure out 01:11:23.940 --> 01:11:27.160 align:middle line:84% approximately your lysocline and your CCD, right? 01:11:27.160 --> 01:11:30.580 align:middle line:90% 01:11:30.580 --> 01:11:35.180 align:middle line:84% I think that was probably the most confusing thing 01:11:35.180 --> 01:11:37.980 align:middle line:90% to figure out. 01:11:37.980 --> 01:11:42.140 align:middle line:84% The vertical profiles of the rain and the burial, 01:11:42.140 --> 01:11:45.360 align:middle line:84% again, we're plotting depth here, 01:11:45.360 --> 01:11:50.650 align:middle line:84% but instead of plotting like an actual vertical profile, 01:11:50.650 --> 01:11:57.770 align:middle line:84% you're going to be using, knowing the saturation horizon, 01:11:57.770 --> 01:12:03.850 align:middle line:84% and knowing about the depth of the CCD. 01:12:03.850 --> 01:12:06.530 align:middle line:84% You can say, OK, well, you're going 01:12:06.530 --> 01:12:12.050 align:middle line:84% to be plotting a flux of what you think at this 30 01:12:12.050 --> 01:12:15.390 align:middle line:84% degrees North for the North Pacific, North Atlantic, 01:12:15.390 --> 01:12:19.930 align:middle line:84% or 30 degrees South for the South, Southern Ocean. 01:12:19.930 --> 01:12:22.530 align:middle line:84% So you're plotting basically a flux, either a burial rate 01:12:22.530 --> 01:12:26.450 align:middle line:90% or a rain rate versus depth. 01:12:26.450 --> 01:12:31.070 align:middle line:90% And this isn't a single depth. 01:12:31.070 --> 01:12:33.430 align:middle line:90% This isn't a single CCD cast. 01:12:33.430 --> 01:12:37.770 align:middle line:90% 01:12:37.770 --> 01:12:40.930 align:middle line:84% So these are all places, if you put out sediment traps 01:12:40.930 --> 01:12:45.630 align:middle line:84% at the bottom of the basin, all over the basin, 01:12:45.630 --> 01:12:47.770 align:middle line:84% along this 30-degree horizon line. 01:12:47.770 --> 01:12:53.800 align:middle line:84% So you would have, as we talked about just before, the Atlantic 01:12:53.800 --> 01:12:55.550 align:middle line:84% one's going to have the mid-Atlantic ridge 01:12:55.550 --> 01:12:56.133 align:middle line:90% in the middle. 01:12:56.133 --> 01:13:01.290 align:middle line:84% So you're going to have a trap here, here, here, here, here, 01:13:01.290 --> 01:13:03.830 align:middle line:90% here, here, here. 01:13:03.830 --> 01:13:07.590 align:middle line:84% You're going to be covering all these different depths. 01:13:07.590 --> 01:13:11.310 align:middle line:84% And those different depths are this z-axis. 01:13:11.310 --> 01:13:16.470 align:middle line:84% So it's not like you're on the ship, 01:13:16.470 --> 01:13:19.870 align:middle line:84% and you throw your cast overboard and collect it 01:13:19.870 --> 01:13:21.290 align:middle line:90% from one different depth. 01:13:21.290 --> 01:13:23.910 align:middle line:84% You're not doing the burial rate like that, 01:13:23.910 --> 01:13:25.370 align:middle line:90% or the burial rates like this. 01:13:25.370 --> 01:13:26.953 align:middle line:84% You're getting burial rate information 01:13:26.953 --> 01:13:29.310 align:middle line:90% from all of these traps. 01:13:29.310 --> 01:13:31.670 align:middle line:90% Does that make sense? 01:13:31.670 --> 01:13:33.957 align:middle line:90% Does that help? 01:13:33.957 --> 01:13:34.790 align:middle line:90% AUDIENCE: Thank you. 01:13:34.790 --> 01:13:39.310 align:middle line:84% DIERDRE TOOLE: OK, and the same burial rate, rain rate, 01:13:39.310 --> 01:13:42.610 align:middle line:84% same basic idea, two different things, 01:13:42.610 --> 01:13:44.540 align:middle line:90% but same basic principle. 01:13:44.540 --> 01:13:46.980 align:middle line:84% AUDIENCE: Are we supposed to do all three of them? 01:13:46.980 --> 01:13:49.380 align:middle line:84% AUDIENCE: Rain rate, isn't the rain rate from the mixed 01:13:49.380 --> 01:13:50.693 align:middle line:90% layer at the surface? 01:13:50.693 --> 01:13:52.860 align:middle line:84% DIERDRE TOOLE: So the rain rate, yeah, the rain rate 01:13:52.860 --> 01:13:55.240 align:middle line:84% is what's falling into these traps. 01:13:55.240 --> 01:13:56.900 align:middle line:84% The burial rate is what's actually 01:13:56.900 --> 01:13:58.280 align:middle line:90% going to be getting buried. 01:13:58.280 --> 01:14:01.460 align:middle line:90% 01:14:01.460 --> 01:14:03.860 align:middle line:90% Yes, no? 01:14:03.860 --> 01:14:06.940 align:middle line:84% AUDIENCE: So how do you get values for z 01:14:06.940 --> 01:14:09.940 align:middle line:90% that is greater than-- 01:14:09.940 --> 01:14:12.000 align:middle line:90% so there's some minimum depth. 01:14:12.000 --> 01:14:14.240 align:middle line:84% I mean do you bring this all the way to the shore, 01:14:14.240 --> 01:14:17.000 align:middle line:84% so you get values of z that are really small? 01:14:17.000 --> 01:14:19.660 align:middle line:90% 01:14:19.660 --> 01:14:21.400 align:middle line:90% What about z equals 100 meters? 01:14:21.400 --> 01:14:23.365 align:middle line:90% 01:14:23.365 --> 01:14:24.740 align:middle line:84% DIERDRE TOOLE: We're not actually 01:14:24.740 --> 01:14:26.360 align:middle line:90% looking for specific values. 01:14:26.360 --> 01:14:29.620 align:middle line:84% Again, we're looking for a little cartoon. 01:14:29.620 --> 01:14:32.580 align:middle line:84% So rather than getting exact values 01:14:32.580 --> 01:14:35.580 align:middle line:84% for a burial rate, which I'm not even sure 01:14:35.580 --> 01:14:39.540 align:middle line:84% you can get off of this data, what 01:14:39.540 --> 01:14:42.090 align:middle line:84% you could do is you could say, OK, well I 01:14:42.090 --> 01:14:47.090 align:middle line:90% have three different diagrams. 01:14:47.090 --> 01:14:51.870 align:middle line:84% And if we have the same z1, z2, and z3 going across, 01:14:51.870 --> 01:14:57.770 align:middle line:84% so we have z1 is here, z2 is here, z3 is here. 01:14:57.770 --> 01:15:04.890 align:middle line:84% So how would the flux change differently 01:15:04.890 --> 01:15:08.130 align:middle line:84% in the Atlantic, versus the Pacific, 01:15:08.130 --> 01:15:09.830 align:middle line:90% versus the Southern ocean? 01:15:09.830 --> 01:15:13.090 align:middle line:84% So it would be relative to the different basins rather than 01:15:13.090 --> 01:15:15.450 align:middle line:90% an absolute value. 01:15:15.450 --> 01:15:18.330 align:middle line:84% So you would say, oh, it's higher here 01:15:18.330 --> 01:15:19.750 align:middle line:90% and then it's lower here. 01:15:19.750 --> 01:15:22.490 align:middle line:84% But this one's more like there and there. 01:15:22.490 --> 01:15:25.970 align:middle line:84% Do you understand what I'm saying? 01:15:25.970 --> 01:15:27.170 align:middle line:90% I don't think you do. 01:15:27.170 --> 01:15:29.330 align:middle line:90% Yes, Andrea is not-- 01:15:29.330 --> 01:15:30.530 align:middle line:90% really big so. 01:15:30.530 --> 01:15:34.810 align:middle line:90% 01:15:34.810 --> 01:15:36.810 align:middle line:84% AUDIENCE: Can I ask a question about the license 01:15:36.810 --> 01:15:41.010 align:middle line:84% line versus the calcite saturation horizon? 01:15:41.010 --> 01:15:43.532 align:middle line:90% DIERDRE TOOLE: Yeah. 01:15:43.532 --> 01:15:44.990 align:middle line:84% AUDIENCE: From my understanding, it 01:15:44.990 --> 01:15:46.490 align:middle line:84% seems like a lot of the time they're 01:15:46.490 --> 01:15:49.530 align:middle line:84% going to be at the same place, but I'm not sure that's right. 01:15:49.530 --> 01:15:53.150 align:middle line:90% 01:15:53.150 --> 01:15:57.830 align:middle line:84% DIERDRE TOOLE: Yeah I mean, this is a weird thing. 01:15:57.830 --> 01:16:01.530 align:middle line:84% The calcite saturation horizon is very well defined. 01:16:01.530 --> 01:16:05.850 align:middle line:84% We have a KSP value, we have an ion activity product. 01:16:05.850 --> 01:16:08.510 align:middle line:84% We can know where the calcite saturation horizon is. 01:16:08.510 --> 01:16:13.030 align:middle line:84% The lysocline is more looking at a plot of points and going, 01:16:13.030 --> 01:16:14.730 align:middle line:90% oh, it's about there. 01:16:14.730 --> 01:16:17.270 align:middle line:90% 01:16:17.270 --> 01:16:19.990 align:middle line:84% I actually have issues with the lysocline 01:16:19.990 --> 01:16:24.190 align:middle line:84% because I don't think it's really all that useful. 01:16:24.190 --> 01:16:26.910 align:middle line:84% But you're right, they'll probably be somewhere 01:16:26.910 --> 01:16:29.110 align:middle line:90% in the same vicinity. 01:16:29.110 --> 01:16:34.370 align:middle line:84% But remember, metabolic dissolution could affect that. 01:16:34.370 --> 01:16:36.390 align:middle line:84% If there's a lot of metabolic dissolution going 01:16:36.390 --> 01:16:40.060 align:middle line:84% on over the calcite saturation horizon in those sediments, 01:16:40.060 --> 01:16:44.260 align:middle line:84% the lysocline might creep up above the saturation horizon. 01:16:44.260 --> 01:16:47.060 align:middle line:84% However, again, if there's not a lot 01:16:47.060 --> 01:16:49.500 align:middle line:84% of metabolic dissolution going on, 01:16:49.500 --> 01:16:53.460 align:middle line:90% maybe it's a little bit below. 01:16:53.460 --> 01:16:56.020 align:middle line:84% I'll check this, but I'm pretty much certain 01:16:56.020 --> 01:17:00.560 align:middle line:84% that there's not a consistent difference between the two. 01:17:00.560 --> 01:17:05.780 align:middle line:84% They could theoretically be switched either way. 01:17:05.780 --> 01:17:07.520 align:middle line:84% But there are two very different things, 01:17:07.520 --> 01:17:10.403 align:middle line:84% and they're measured very differently. 01:17:10.403 --> 01:17:11.820 align:middle line:84% AUDIENCE: That's one of the things 01:17:11.820 --> 01:17:14.820 align:middle line:84% I'm confused about is because my interpretation 01:17:14.820 --> 01:17:16.820 align:middle line:84% of their definitions is that they're 01:17:16.820 --> 01:17:20.860 align:middle line:84% very similar because the calcite saturation horizon is where 01:17:20.860 --> 01:17:23.908 align:middle line:90% the saturation state is 1. 01:17:23.908 --> 01:17:24.700 align:middle line:90% DIERDRE TOOLE: Yep. 01:17:24.700 --> 01:17:27.740 align:middle line:84% AUDIENCE: So that means that it is saturated, 01:17:27.740 --> 01:17:29.878 align:middle line:84% and below that point, it seems to me 01:17:29.878 --> 01:17:31.420 align:middle line:84% that below that point is where you're 01:17:31.420 --> 01:17:34.220 align:middle line:84% going to start seeing evidence that it's not 01:17:34.220 --> 01:17:35.988 align:middle line:84% completely saturated, which would 01:17:35.988 --> 01:17:37.280 align:middle line:90% mean that that's the lysocline. 01:17:37.280 --> 01:17:39.480 align:middle line:84% DIERDRE TOOLE: Right, but remember 01:17:39.480 --> 01:17:43.440 align:middle line:84% to see a change in the percent calcium carbonate, 01:17:43.440 --> 01:17:45.320 align:middle line:84% you've got to get a lot of dissolution 01:17:45.320 --> 01:17:47.480 align:middle line:84% because calcium carbonate makes up so much 01:17:47.480 --> 01:17:49.600 align:middle line:90% of so many of these sediments. 01:17:49.600 --> 01:17:53.320 align:middle line:84% I mean, it's over 50% in a significant portion 01:17:53.320 --> 01:17:55.340 align:middle line:84% of the Atlantic and even the Pacific, 01:17:55.340 --> 01:18:00.960 align:middle line:84% which we think of as rather calcium carbonate poor. 01:18:00.960 --> 01:18:03.960 align:middle line:84% I mean, there's still areas that have huge amounts of calcium 01:18:03.960 --> 01:18:05.000 align:middle line:90% carbonate. 01:18:05.000 --> 01:18:09.540 align:middle line:84% So in order to see a drop of even 10%, 01:18:09.540 --> 01:18:13.640 align:middle line:84% remember you need over 50% of the calcium carbonate 01:18:13.640 --> 01:18:14.880 align:middle line:90% to decline. 01:18:14.880 --> 01:18:18.480 align:middle line:84% That's why the lysocline could be below the saturation horizon 01:18:18.480 --> 01:18:21.620 align:middle line:90% or above it. 01:18:21.620 --> 01:18:23.120 align:middle line:84% So I'll check on that because it may 01:18:23.120 --> 01:18:25.680 align:middle line:84% be that although theoretically it could be either place, 01:18:25.680 --> 01:18:27.380 align:middle line:84% it's consistently one or the other. 01:18:27.380 --> 01:18:28.540 align:middle line:90% And I can't remember. 01:18:28.540 --> 01:18:32.220 align:middle line:84% It's an issue I have with I just don't like the lysocline. 01:18:32.220 --> 01:18:34.390 align:middle line:84% I think that's why I don't remember it well. 01:18:34.390 --> 01:18:35.450 align:middle line:90% But I'll check on that. 01:18:35.450 --> 01:18:37.750 align:middle line:84% But theoretically it could be either. 01:18:37.750 --> 01:18:45.070 align:middle line:84% And as for doing part B, decide what you think is correct. 01:18:45.070 --> 01:18:50.030 align:middle line:84% Back it up with some evidence and cool. 01:18:50.030 --> 01:18:53.430 align:middle line:84% AUDIENCE: Are we supposed to back up part B with evidence? 01:18:53.430 --> 01:18:55.230 align:middle line:84% DIERDRE TOOLE: No, but if you're saying I 01:18:55.230 --> 01:19:01.110 align:middle line:84% think this is where the lysocline is, 01:19:01.110 --> 01:19:04.030 align:middle line:84% I guess it might help me to make a note. 01:19:04.030 --> 01:19:07.670 align:middle line:84% I probably won't be too harsh on grading the lysocline, given 01:19:07.670 --> 01:19:09.790 align:middle line:90% my feelings. 01:19:09.790 --> 01:19:14.150 align:middle line:90% 01:19:14.150 --> 01:19:16.210 align:middle line:84% I think we'll get into this next week, 01:19:16.210 --> 01:19:21.510 align:middle line:84% but there's a lot of trying to interpret paleo data saying, 01:19:21.510 --> 01:19:24.050 align:middle line:84% oh, the lysocline changed from here to here. 01:19:24.050 --> 01:19:27.410 align:middle line:84% And it's like, OK, maybe it changed, but what if it did? 01:19:27.410 --> 01:19:28.690 align:middle line:90% What does that even mean? 01:19:28.690 --> 01:19:31.370 align:middle line:90% I mean, it's kind of a-- 01:19:31.370 --> 01:19:34.660 align:middle line:84% I guess to me, it's a little bit of a hand-wavy definition 01:19:34.660 --> 01:19:38.820 align:middle line:90% of what the lysocline is. 01:19:38.820 --> 01:19:41.460 align:middle line:84% Just remember, saturation horizon 01:19:41.460 --> 01:19:43.380 align:middle line:84% determined from water column measurements, 01:19:43.380 --> 01:19:48.260 align:middle line:84% lysocline determined from sediment measurements. 01:19:48.260 --> 01:19:50.140 align:middle line:90% Are there other questions? 01:19:50.140 --> 01:19:52.180 align:middle line:84% AUDIENCE: I've got one with the question 01:19:52.180 --> 01:19:55.460 align:middle line:90% I had about the unit stuff. 01:19:55.460 --> 01:19:58.740 align:middle line:84% DIERDRE TOOLE: I did, yep, I printed this one out too. 01:19:58.740 --> 01:20:02.980 align:middle line:84% OK, so I've been looking at this and the question is, 01:20:02.980 --> 01:20:05.620 align:middle line:84% I'll write it a little bit bigger so people can see it. 01:20:05.620 --> 01:20:13.800 align:middle line:84% Is the fact that we are given on the problem set that, ooh, wow, 01:20:13.800 --> 01:20:23.140 align:middle line:84% that's tiny d sed equals dc water times porosity squared. 01:20:23.140 --> 01:20:30.560 align:middle line:84% So the units of diffusion in seawater are-- 01:20:30.560 --> 01:20:31.880 align:middle line:90% this is hard to do-- 01:20:31.880 --> 01:20:33.620 align:middle line:90% centimeters squared per year. 01:20:33.620 --> 01:20:37.640 align:middle line:84% That's centimeters squared of seawater per year. 01:20:37.640 --> 01:20:41.880 align:middle line:84% So in sediment, we still want it to be in water. 01:20:41.880 --> 01:20:45.420 align:middle line:84% But it's still going through water. 01:20:45.420 --> 01:20:47.440 align:middle line:84% But it's going to be in bulk sediment. 01:20:47.440 --> 01:20:52.920 align:middle line:84% So we want it to be in centimeters squared of bulk. 01:20:52.920 --> 01:20:56.040 align:middle line:90% So let's see here. 01:20:56.040 --> 01:21:01.640 align:middle line:84% d sed would be in centimeters squared 01:21:01.640 --> 01:21:05.300 align:middle line:90% of bulk sediment per year. 01:21:05.300 --> 01:21:07.120 align:middle line:90% Right? 01:21:07.120 --> 01:21:11.380 align:middle line:84% Now this equation doesn't give that to us. 01:21:11.380 --> 01:21:13.020 align:middle line:90% The units don't work. 01:21:13.020 --> 01:21:17.040 align:middle line:84% You have this in centimeters squared of seawater per year, 01:21:17.040 --> 01:21:21.040 align:middle line:84% and porosity is in centimeters cubed of pore water 01:21:21.040 --> 01:21:23.180 align:middle line:84% over centimeters cubed of bulk sediment. 01:21:23.180 --> 01:21:25.600 align:middle line:84% So what you end up in, is some crazy units 01:21:25.600 --> 01:21:29.790 align:middle line:84% of centimeter squared of seawater per year times 01:21:29.790 --> 01:21:33.610 align:middle line:84% centimeters to the sixth of pore water, 01:21:33.610 --> 01:21:38.470 align:middle line:84% over centimeters to the sixth of bulk sediment. 01:21:38.470 --> 01:21:39.870 align:middle line:90% The units don't work. 01:21:39.870 --> 01:21:43.710 align:middle line:84% And the reason for this is that this relationship we use 01:21:43.710 --> 01:21:45.210 align:middle line:90% because we can't get better. 01:21:45.210 --> 01:21:48.048 align:middle line:90% It's what we can do. 01:21:48.048 --> 01:21:49.590 align:middle line:84% We can do a little bit better, but it 01:21:49.590 --> 01:21:53.190 align:middle line:90% takes a lot more calculations. 01:21:53.190 --> 01:21:55.050 align:middle line:90% And I think people do it. 01:21:55.050 --> 01:21:58.310 align:middle line:84% But there was no reason to make you guys go through tortuosity 01:21:58.310 --> 01:22:01.190 align:middle line:90% and all these other things. 01:22:01.190 --> 01:22:04.430 align:middle line:84% This is a relationship that pretty much works. 01:22:04.430 --> 01:22:07.050 align:middle line:90% But of empirical. 01:22:07.050 --> 01:22:10.870 align:middle line:84% It's not a theoretical relationship. 01:22:10.870 --> 01:22:14.190 align:middle line:84% So it's just one of those things where you plug and chug, 01:22:14.190 --> 01:22:16.670 align:middle line:84% and it spits it out in the right units. 01:22:16.670 --> 01:22:20.230 align:middle line:84% And the reason I know this works, your porosity 01:22:20.230 --> 01:22:23.790 align:middle line:84% to be less than 1, because remember, you're multiplying it. 01:22:23.790 --> 01:22:26.350 align:middle line:90% 01:22:26.350 --> 01:22:29.850 align:middle line:84% You have less water there because of the particles. 01:22:29.850 --> 01:22:32.770 align:middle line:84% And also with depth, your porosity 01:22:32.770 --> 01:22:35.970 align:middle line:84% is going to decrease as your particles are packed together 01:22:35.970 --> 01:22:38.610 align:middle line:84% and the pore water is squeezed out. 01:22:38.610 --> 01:22:41.410 align:middle line:84% So I guess I'm going to end up giving you 01:22:41.410 --> 01:22:43.030 align:middle line:90% a little bit of the answer here. 01:22:43.030 --> 01:22:52.470 align:middle line:84% But your porosity is going to change to something like this. 01:22:52.470 --> 01:22:55.130 align:middle line:90% 01:22:55.130 --> 01:22:58.910 align:middle line:84% So as you can see at the top it goes from about 0.84. 01:22:58.910 --> 01:23:01.650 align:middle line:84% And then it just decreases with depth, 01:23:01.650 --> 01:23:05.350 align:middle line:84% and starts to come to pretty consistent value. 01:23:05.350 --> 01:23:07.110 align:middle line:84% And that's pretty common with compaction. 01:23:07.110 --> 01:23:09.810 align:middle line:84% It only occurs in the top few centimeters. 01:23:09.810 --> 01:23:12.330 align:middle line:90% And then it evens out. 01:23:12.330 --> 01:23:14.750 align:middle line:84% And these numbers are less than 1. 01:23:14.750 --> 01:23:16.010 align:middle line:90% They look right. 01:23:16.010 --> 01:23:17.710 align:middle line:84% This is what we see in sediments. 01:23:17.710 --> 01:23:21.530 align:middle line:84% So the equation that you get even though the units are 01:23:21.530 --> 01:23:24.830 align:middle line:90% total crap, it is right. 01:23:24.830 --> 01:23:26.140 align:middle line:90% And that's what we do. 01:23:26.140 --> 01:23:30.120 align:middle line:90% It's just it's not theoretical. 01:23:30.120 --> 01:23:33.920 align:middle line:84% AUDIENCE: I think when I was looking at it, 01:23:33.920 --> 01:23:36.540 align:middle line:84% I assumed that it was an empirical relationship, 01:23:36.540 --> 01:23:39.800 align:middle line:84% though I wasn't squaring my units. 01:23:39.800 --> 01:23:47.500 align:middle line:84% But so I assumed, when I was thinking about it, 01:23:47.500 --> 01:23:51.240 align:middle line:84% I was like, well, if I flip the porosity upside down, 01:23:51.240 --> 01:23:55.320 align:middle line:84% and I don't end up squaring the units, then the units work out. 01:23:55.320 --> 01:23:56.320 align:middle line:90% But I shouldn't do that? 01:23:56.320 --> 01:23:57.780 align:middle line:90% DIERDRE TOOLE: Right. 01:23:57.780 --> 01:23:58.780 align:middle line:90% AUDIENCE: Don't do that. 01:23:58.780 --> 01:24:00.113 align:middle line:90% DIERDRE TOOLE: That's not right. 01:24:00.113 --> 01:24:03.840 align:middle line:90% So you want the porosity to be-- 01:24:03.840 --> 01:24:07.960 align:middle line:84% you want a number less than 1, because you want your diffusion 01:24:07.960 --> 01:24:12.460 align:middle line:84% in bulk sediment to be less than your diffusion in water. 01:24:12.460 --> 01:24:14.560 align:middle line:90% Think about this. 01:24:14.560 --> 01:24:18.700 align:middle line:84% Not only does it like to go from point A to point B in water, 01:24:18.700 --> 01:24:20.920 align:middle line:90% it can just go straight. 01:24:20.920 --> 01:24:23.990 align:middle line:84% But in sediment, it's got to go all 01:24:23.990 --> 01:24:26.030 align:middle line:84% around the little sediment grains. 01:24:26.030 --> 01:24:28.390 align:middle line:84% AUDIENCE: Yeah, I think that we were 01:24:28.390 --> 01:24:30.650 align:middle line:84% happy with their actual number for porosity. 01:24:30.650 --> 01:24:34.190 align:middle line:84% It was the converting it into the diffusivity. 01:24:34.190 --> 01:24:35.610 align:middle line:90% DIERDRE TOOLE: No, you're right. 01:24:35.610 --> 01:24:38.378 align:middle line:84% The units totally don't work at all. 01:24:38.378 --> 01:24:40.670 align:middle line:84% AUDIENCE: Wait, I'm still confused about units, though. 01:24:40.670 --> 01:24:41.828 align:middle line:90% DIERDRE TOOLE: OK. 01:24:41.828 --> 01:24:42.370 align:middle line:90% AUDIENCE: OK. 01:24:42.370 --> 01:24:47.050 align:middle line:84% Can we look at the flux equation and just go through the units. 01:24:47.050 --> 01:24:50.470 align:middle line:84% Because when I do that, I still end up with wacky units. 01:24:50.470 --> 01:24:52.670 align:middle line:90% DIERDRE TOOLE: OK, yeah. 01:24:52.670 --> 01:24:54.390 align:middle line:90% So the flux-- 01:24:54.390 --> 01:24:55.710 align:middle line:90% Yep what? 01:24:55.710 --> 01:24:57.630 align:middle line:84% AUDIENCE: Sorry, the C is going to be 01:24:57.630 --> 01:25:03.868 align:middle line:84% in centimeters cubed water per centimeter cubed [INAUDIBLE]. 01:25:03.868 --> 01:25:05.410 align:middle line:84% DIERDRE TOOLE: I've got to move this. 01:25:05.410 --> 01:25:10.990 align:middle line:90% 01:25:10.990 --> 01:25:12.070 align:middle line:90% This can be any d. 01:25:12.070 --> 01:25:13.570 align:middle line:90% Just we're using d sed. 01:25:13.570 --> 01:25:14.670 align:middle line:90% So I'm using it. 01:25:14.670 --> 01:25:16.130 align:middle line:90% So sorry. 01:25:16.130 --> 01:25:17.590 align:middle line:90% What were you saying? 01:25:17.590 --> 01:25:22.200 align:middle line:84% AUDIENCE: B is going to be in centimeters cubed water 01:25:22.200 --> 01:25:24.490 align:middle line:90% to centimeter cubed [INAUDIBLE]. 01:25:24.490 --> 01:25:26.850 align:middle line:90% DIERDRE TOOLE: Yep. 01:25:26.850 --> 01:25:28.450 align:middle line:84% AUDIENCE: The d sediment is going 01:25:28.450 --> 01:25:31.130 align:middle line:84% to be in centimeter squared, bulk sediment per year 01:25:31.130 --> 01:25:32.898 align:middle line:90% is what we just said. 01:25:32.898 --> 01:25:33.690 align:middle line:90% DIERDRE TOOLE: Yep. 01:25:33.690 --> 01:25:40.570 align:middle line:90% 01:25:40.570 --> 01:25:42.530 align:middle line:90% Yep. 01:25:42.530 --> 01:25:44.530 align:middle line:84% AUDIENCE: And then the concentration 01:25:44.530 --> 01:25:47.290 align:middle line:84% is going to be in micromole per centimeter bulk 01:25:47.290 --> 01:25:50.530 align:middle line:84% sediment per year or the concentration dc. 01:25:50.530 --> 01:25:56.610 align:middle line:90% 01:25:56.610 --> 01:25:58.008 align:middle line:90% DIERDRE TOOLE: Yep. 01:25:58.008 --> 01:25:59.550 align:middle line:84% AUDIENCE: Why is it centimeter cubed? 01:25:59.550 --> 01:26:02.570 align:middle line:90% 01:26:02.570 --> 01:26:04.633 align:middle line:90% Isn't it just change in depth? 01:26:04.633 --> 01:26:06.050 align:middle line:84% DIERDRE TOOLE: Well, remember, you 01:26:06.050 --> 01:26:12.670 align:middle line:84% want to end up in micromoles per centimeters squared per year. 01:26:12.670 --> 01:26:15.998 align:middle line:90% 01:26:15.998 --> 01:26:16.790 align:middle line:90% AUDIENCE: That's c. 01:26:16.790 --> 01:26:17.832 align:middle line:90% DIERDRE TOOLE: Oh, sorry. 01:26:17.832 --> 01:26:20.440 align:middle line:90% 01:26:20.440 --> 01:26:21.100 align:middle line:90% Hold on. 01:26:21.100 --> 01:26:31.640 align:middle line:90% 01:26:31.640 --> 01:26:33.540 align:middle line:90% Yeah, I remember what this is. 01:26:33.540 --> 01:26:42.520 align:middle line:90% 01:26:42.520 --> 01:26:49.840 align:middle line:84% What you have to remember here is 01:26:49.840 --> 01:26:52.220 align:middle line:90% this is all getting very ugly. 01:26:52.220 --> 01:26:55.520 align:middle line:84% So we're just going to start over here. 01:26:55.520 --> 01:26:58.480 align:middle line:84% Your delta c is the key thing here. 01:26:58.480 --> 01:27:02.040 align:middle line:84% What are the units on your delta c exactly? 01:27:02.040 --> 01:27:03.600 align:middle line:90% AUDIENCE: Moles per liter. 01:27:03.600 --> 01:27:04.360 align:middle line:90% DIERDRE TOOLE: OK. 01:27:04.360 --> 01:27:07.400 align:middle line:90% Moles per liter. 01:27:07.400 --> 01:27:09.480 align:middle line:84% And it's actually delta c over delta 01:27:09.480 --> 01:27:15.240 align:middle line:84% z, because we're looking at the change in and c over a depth. 01:27:15.240 --> 01:27:16.860 align:middle line:90% So what's the z unit? 01:27:16.860 --> 01:27:20.110 align:middle line:90% 01:27:20.110 --> 01:27:23.030 align:middle line:90% AUDIENCE: Bulk sediment. 01:27:23.030 --> 01:27:25.670 align:middle line:90% DIERDRE TOOLE: Yep centimeters. 01:27:25.670 --> 01:27:27.650 align:middle line:90% AUDIENCE: Bulk sediment, right? 01:27:27.650 --> 01:27:30.550 align:middle line:84% DIERDRE TOOLE: Right, but let's go with centimeters 01:27:30.550 --> 01:27:31.670 align:middle line:90% for the moment. 01:27:31.670 --> 01:27:33.570 align:middle line:84% But you're right, yes, bulk sentiment. 01:27:33.570 --> 01:27:39.590 align:middle line:84% So what we end up with is if you convert liters to centimeters 01:27:39.590 --> 01:27:45.830 align:middle line:84% cubed, this whole thing becomes moles per centimeters 01:27:45.830 --> 01:27:46.968 align:middle line:90% to the fourth. 01:27:46.968 --> 01:27:47.510 align:middle line:90% AUDIENCE: OK. 01:27:47.510 --> 01:27:49.550 align:middle line:90% Here's my issue with that. 01:27:49.550 --> 01:27:52.653 align:middle line:84% Is when we're talking about phi and when 01:27:52.653 --> 01:27:54.070 align:middle line:84% we're talking about d sediment, we 01:27:54.070 --> 01:27:55.550 align:middle line:84% care about whether the centimeters 01:27:55.550 --> 01:27:59.390 align:middle line:84% is in water or sediment or bulk sediment. 01:27:59.390 --> 01:28:02.017 align:middle line:84% How can we arbitrarily decide that, well, that's 01:28:02.017 --> 01:28:03.850 align:middle line:84% in bulk sediment, but we don't care anymore. 01:28:03.850 --> 01:28:06.030 align:middle line:84% We're going to say that it's the same as water 01:28:06.030 --> 01:28:08.827 align:middle line:84% because if you convert liters to centimeter cubed. 01:28:08.827 --> 01:28:10.410 align:middle line:84% It's going to centimeters cubed water. 01:28:10.410 --> 01:28:11.868 align:middle line:84% DIERDRE TOOLE: Right, you basically 01:28:11.868 --> 01:28:16.970 align:middle line:84% have moles per centimeter cubed water 01:28:16.970 --> 01:28:20.190 align:middle line:90% and then centimeters sediment. 01:28:20.190 --> 01:28:21.190 align:middle line:90% Right? 01:28:21.190 --> 01:28:22.210 align:middle line:90% AUDIENCE: Bulk sediment. 01:28:22.210 --> 01:28:23.270 align:middle line:90% It's not even sediment. 01:28:23.270 --> 01:28:24.110 align:middle line:90% It's bulk sediment. 01:28:24.110 --> 01:28:26.430 align:middle line:84% DIERDRE TOOLE: Yes, I just if I write everything down, 01:28:26.430 --> 01:28:27.710 align:middle line:90% it gets really, really ugly. 01:28:27.710 --> 01:28:31.610 align:middle line:84% So I just use sediment as bulk sediment. 01:28:31.610 --> 01:28:34.850 align:middle line:90% That's kind of my notation. 01:28:34.850 --> 01:28:44.590 align:middle line:84% So what we then have is just making sure that yes, 01:28:44.590 --> 01:28:46.210 align:middle line:90% this does work as it should. 01:28:46.210 --> 01:28:48.850 align:middle line:90% I've gone through it before. 01:28:48.850 --> 01:28:54.250 align:middle line:84% Our d sed is in centimeters squared 01:28:54.250 --> 01:28:59.730 align:middle line:90% per year of bulk sediment. 01:28:59.730 --> 01:29:07.290 align:middle line:84% And then our phi is centimeters cubed water centimeters 01:29:07.290 --> 01:29:10.130 align:middle line:90% cubed sediment. 01:29:10.130 --> 01:29:21.800 align:middle line:84% So phi times d, we get centimeters cubed water 01:29:21.800 --> 01:29:29.640 align:middle line:90% over centimeters sed per year. 01:29:29.640 --> 01:29:31.430 align:middle line:90% Right? 01:29:31.430 --> 01:29:34.560 align:middle line:84% And if we multiply that times delta 01:29:34.560 --> 01:29:42.240 align:middle line:84% c, which we have right here, we get the centimeters of water 01:29:42.240 --> 01:29:47.400 align:middle line:84% cancel out, and we get moles per centimeter 01:29:47.400 --> 01:29:49.740 align:middle line:90% squared of sediment per year. 01:29:49.740 --> 01:29:54.560 align:middle line:90% 01:29:54.560 --> 01:29:56.920 align:middle line:84% AUDIENCE: And so this again gets to my-- 01:29:56.920 --> 01:29:59.240 align:middle line:90% I'm sorry I'm really confused. 01:29:59.240 --> 01:30:01.542 align:middle line:84% Isn't the bulk like the centimeters 01:30:01.542 --> 01:30:03.000 align:middle line:84% bulk sediment going to be different 01:30:03.000 --> 01:30:05.920 align:middle line:90% than centimeters sediment? 01:30:05.920 --> 01:30:07.440 align:middle line:90% DIERDRE TOOLE: Yes. 01:30:07.440 --> 01:30:09.360 align:middle line:90% I'm just using sediment. 01:30:09.360 --> 01:30:11.660 align:middle line:90% I'm using sed for bulk sediment. 01:30:11.660 --> 01:30:13.440 align:middle line:84% It's bulk sediment everywhere here. 01:30:13.440 --> 01:30:18.300 align:middle line:90% 01:30:18.300 --> 01:30:18.800 align:middle line:90% OK. 01:30:18.800 --> 01:30:20.008 align:middle line:90% I think this is your problem. 01:30:20.008 --> 01:30:24.580 align:middle line:84% The porosity is water per bulk sediment. 01:30:24.580 --> 01:30:25.680 align:middle line:90% It's less than 1. 01:30:25.680 --> 01:30:28.620 align:middle line:84% You have so much water in this volume. 01:30:28.620 --> 01:30:32.620 align:middle line:84% If you took a liter of mud and you evaporated out the water 01:30:32.620 --> 01:30:34.820 align:middle line:84% and you found out how much water was in it, 01:30:34.820 --> 01:30:37.920 align:middle line:84% it would be the water over the total mud. 01:30:37.920 --> 01:30:40.617 align:middle line:84% So the mud would include that water. 01:30:40.617 --> 01:30:42.200 align:middle line:84% AUDIENCE: I had that definition wrong. 01:30:42.200 --> 01:30:42.820 align:middle line:90% You're right. 01:30:42.820 --> 01:30:43.400 align:middle line:90% Thank you. 01:30:43.400 --> 01:30:43.740 align:middle line:90% DIERDRE TOOLE: OK. 01:30:43.740 --> 01:30:44.520 align:middle line:90% There we go. 01:30:44.520 --> 01:30:48.740 align:middle line:84% I was like, I don't understand why she's not getting this. 01:30:48.740 --> 01:30:49.620 align:middle line:90% That's why. 01:30:49.620 --> 01:30:50.900 align:middle line:90% That's why. 01:30:50.900 --> 01:30:54.318 align:middle line:90% That would make it confusing. 01:30:54.318 --> 01:30:54.860 align:middle line:90% AUDIENCE: OK. 01:30:54.860 --> 01:30:56.057 align:middle line:90% Thank you. 01:30:56.057 --> 01:30:58.140 align:middle line:84% DIERDRE TOOLE: I did, and I emailed you back right 01:30:58.140 --> 01:30:59.420 align:middle line:90% before I came over here. 01:30:59.420 --> 01:31:02.060 align:middle line:84% I don't remember what it asked, but I could answer it for you 01:31:02.060 --> 01:31:03.040 align:middle line:90% right now, too. 01:31:03.040 --> 01:31:05.860 align:middle line:84% AUDIENCE: I was wondering about the last part of question 01:31:05.860 --> 01:31:07.460 align:middle line:84% 1, where we're supposed to calculate 01:31:07.460 --> 01:31:11.010 align:middle line:84% the n2 fluxes and the [INAUDIBLE]. 01:31:11.010 --> 01:31:12.258 align:middle line:90% DIERDRE TOOLE: Yes. 01:31:12.258 --> 01:31:16.170 align:middle line:84% Yes, and you wanted to know if we calculate it 01:31:16.170 --> 01:31:16.883 align:middle line:90% at the interface? 01:31:16.883 --> 01:31:19.050 align:middle line:84% AUDIENCE: Yeah are we just doing it that interfaces? 01:31:19.050 --> 01:31:21.090 align:middle line:84% DIERDRE TOOLE: So and that's a good question 01:31:21.090 --> 01:31:24.450 align:middle line:84% because you get your numbers from the interface, 01:31:24.450 --> 01:31:27.390 align:middle line:84% because that's where the flux actually occurs. 01:31:27.390 --> 01:31:29.170 align:middle line:90% You're crossing that boundary. 01:31:29.170 --> 01:31:34.330 align:middle line:84% But the flux integrates over the entire layer 01:31:34.330 --> 01:31:37.490 align:middle line:90% because it's production. 01:31:37.490 --> 01:31:44.090 align:middle line:84% If you have once again our friend the nitrate curve. 01:31:44.090 --> 01:31:48.010 align:middle line:84% And this is the anoxic-oxic boundary. 01:31:48.010 --> 01:31:53.370 align:middle line:84% The production of nitrate from organic matter 01:31:53.370 --> 01:31:57.090 align:middle line:90% happens all over this region. 01:31:57.090 --> 01:32:00.230 align:middle line:84% And it fluxes out here and out here. 01:32:00.230 --> 01:32:01.730 align:middle line:90% Right? 01:32:01.730 --> 01:32:04.770 align:middle line:90% 01:32:04.770 --> 01:32:07.650 align:middle line:84% So the flux here, and the flux here 01:32:07.650 --> 01:32:11.160 align:middle line:84% together have to equal that production. 01:32:11.160 --> 01:32:15.120 align:middle line:84% So these fluxes are integrated over this entire layer. 01:32:15.120 --> 01:32:17.400 align:middle line:84% But you do calculate it from the numbers 01:32:17.400 --> 01:32:20.680 align:middle line:90% you get at the interface. 01:32:20.680 --> 01:32:23.240 align:middle line:84% AUDIENCE: So, OK because I calculated it 01:32:23.240 --> 01:32:26.640 align:middle line:84% from [INAUDIBLE] far enough, so you can't see it. 01:32:26.640 --> 01:32:29.667 align:middle line:84% But like from here to here originally. 01:32:29.667 --> 01:32:32.000 align:middle line:84% DIERDRE TOOLE: So you used a point here and a point here 01:32:32.000 --> 01:32:34.720 align:middle line:90% to calculate a slope? 01:32:34.720 --> 01:32:37.183 align:middle line:84% AUDIENCE: It doesn't seem like a great idea 01:32:37.183 --> 01:32:38.600 align:middle line:84% to pick the point right next to it 01:32:38.600 --> 01:32:41.480 align:middle line:84% because then you're really compounding any measurement 01:32:41.480 --> 01:32:42.087 align:middle line:90% errors. 01:32:42.087 --> 01:32:42.920 align:middle line:90% DIERDRE TOOLE: Well. 01:32:42.920 --> 01:32:43.740 align:middle line:90% Yeah, that's true. 01:32:43.740 --> 01:32:44.420 align:middle line:90% You can do that. 01:32:44.420 --> 01:32:48.200 align:middle line:84% I did actually choose the two points closest to the interface, 01:32:48.200 --> 01:32:50.340 align:middle line:84% just because that's the steepest point. 01:32:50.340 --> 01:32:51.600 align:middle line:90% I was doing it fast. 01:32:51.600 --> 01:32:57.240 align:middle line:84% Also, it makes it really easy to just calculate the slope. 01:32:57.240 --> 01:32:59.260 align:middle line:84% If you just do the points next to each other, 01:32:59.260 --> 01:33:00.800 align:middle line:84% then you just calculate the slopes 01:33:00.800 --> 01:33:05.440 align:middle line:84% all the way down like you just compare. 01:33:05.440 --> 01:33:07.127 align:middle line:90% Does that make sense? 01:33:07.127 --> 01:33:09.460 align:middle line:84% AUDIENCE: Well, I did that to get the inflection points. 01:33:09.460 --> 01:33:10.335 align:middle line:90% DIERDRE TOOLE: Right. 01:33:10.335 --> 01:33:14.620 align:middle line:84% But I'm just saying if you do these points next to each other, 01:33:14.620 --> 01:33:16.620 align:middle line:90% it's easier to do in Excel. 01:33:16.620 --> 01:33:19.080 align:middle line:90% It's not easier to actually do. 01:33:19.080 --> 01:33:21.420 align:middle line:90% It's easier to drag. 01:33:21.420 --> 01:33:22.800 align:middle line:90% AUDIENCE: So should I redo that? 01:33:22.800 --> 01:33:24.092 align:middle line:90% DIERDRE TOOLE: No, that's fine. 01:33:24.092 --> 01:33:24.940 align:middle line:90% That's fine. 01:33:24.940 --> 01:33:27.160 align:middle line:84% Actually, that may be the way they actually-- 01:33:27.160 --> 01:33:29.500 align:middle line:84% I don't remember exactly how they choose their points. 01:33:29.500 --> 01:33:30.083 align:middle line:90% AUDIENCE: Why? 01:33:30.083 --> 01:33:31.980 align:middle line:84% Because they don't give you an answer key? 01:33:31.980 --> 01:33:34.540 align:middle line:84% DIERDRE TOOLE: No, no, no, I mean, 01:33:34.540 --> 01:33:37.583 align:middle line:84% if they were to go out and make these measurements in sediments. 01:33:37.583 --> 01:33:39.500 align:middle line:84% AUDIENCE: [INAUDIBLE] makes up these questions 01:33:39.500 --> 01:33:41.330 align:middle line:90% and doesn't tell you. 01:33:41.330 --> 01:33:45.260 align:middle line:84% DIERDRE TOOLE: No, sometimes I'm as lost as you guys are. 01:33:45.260 --> 01:33:46.895 align:middle line:90% AUDIENCE: Sorry. 01:33:46.895 --> 01:33:48.520 align:middle line:84% DIERDRE TOOLE: That is absolutely true. 01:33:48.520 --> 01:33:52.220 align:middle line:84% I don't get answer keys, only the old ones from our TAs. 01:33:52.220 --> 01:33:53.705 align:middle line:90% AUDIENCE: That's very strange. 01:33:53.705 --> 01:33:55.080 align:middle line:84% DIERDRE TOOLE: One second, Caron, 01:33:55.080 --> 01:33:56.500 align:middle line:90% I'll get to your question. 01:33:56.500 --> 01:33:57.875 align:middle line:84% AUDIENCE: Oh, I have another one. 01:33:57.875 --> 01:33:58.760 align:middle line:90% But she can go ahead. 01:33:58.760 --> 01:34:01.010 align:middle line:84% DIERDRE TOOLE: No, why don't you finish your question? 01:34:01.010 --> 01:34:02.660 align:middle line:84% AUDIENCE: OK, well there's another. 01:34:02.660 --> 01:34:10.850 align:middle line:84% So then if you assume it was on the number 2.3A, 01:34:10.850 --> 01:34:13.570 align:middle line:84% so it was assuming the oxygen consumption rates. 01:34:13.570 --> 01:34:17.290 align:middle line:84% So then if you assume that that's not a diffusion curve 01:34:17.290 --> 01:34:19.610 align:middle line:84% and it's a consumption curve, just you 01:34:19.610 --> 01:34:21.360 align:middle line:84% use the flux to get the consumption rates? 01:34:21.360 --> 01:34:22.152 align:middle line:90% DIERDRE TOOLE: Yes. 01:34:22.152 --> 01:34:22.730 align:middle line:90% AUDIENCE: OK. 01:34:22.730 --> 01:34:24.150 align:middle line:84% DIERDRE TOOLE: Yep, the same thing as we did. 01:34:24.150 --> 01:34:25.850 align:middle line:84% I actually was confused why we're 01:34:25.850 --> 01:34:26.970 align:middle line:84% doing the same thing twice, but we're 01:34:26.970 --> 01:34:28.150 align:middle line:90% doing the same thing twice. 01:34:28.150 --> 01:34:31.330 align:middle line:84% AUDIENCE: So I got a higher consumption rate 01:34:31.330 --> 01:34:34.730 align:middle line:84% on the August and the March doing that. 01:34:34.730 --> 01:34:38.090 align:middle line:84% Except from the profiles we looked at in class, 01:34:38.090 --> 01:34:41.930 align:middle line:84% I thought the August one looked like a lower production type 01:34:41.930 --> 01:34:42.930 align:middle line:90% profile. 01:34:42.930 --> 01:34:44.210 align:middle line:90% DIERDRE TOOLE: Because? 01:34:44.210 --> 01:34:46.810 align:middle line:90% AUDIENCE: I don't remember. 01:34:46.810 --> 01:34:48.430 align:middle line:90% But that doesn't sound wrong. 01:34:48.430 --> 01:34:50.638 align:middle line:84% DIERDRE TOOLE: No, I mean, if you think about it just 01:34:50.638 --> 01:34:52.910 align:middle line:84% in terms of the biology, at a higher temperature, 01:34:52.910 --> 01:34:55.785 align:middle line:84% there'll be more active even in the water column 01:34:55.785 --> 01:34:56.910 align:middle line:90% as well as in the sediment. 01:34:56.910 --> 01:34:58.830 align:middle line:84% So there's going to be more organic matter. 01:34:58.830 --> 01:35:01.790 align:middle line:84% And then if you look at these curves, the oxygen curves, 01:35:01.790 --> 01:35:04.430 align:middle line:84% this one goes away really fast, which 01:35:04.430 --> 01:35:08.210 align:middle line:84% means that this is a really, really steep flux. 01:35:08.210 --> 01:35:11.322 align:middle line:84% So even though it doesn't look like there's a lot, 01:35:11.322 --> 01:35:13.030 align:middle line:84% the fact that oxygen is going away really 01:35:13.030 --> 01:35:14.710 align:middle line:84% fast means that the organic matter 01:35:14.710 --> 01:35:17.870 align:middle line:90% is going away really fast. 01:35:17.870 --> 01:35:20.310 align:middle line:90% Caron? 01:35:20.310 --> 01:35:23.990 align:middle line:84% AUDIENCE: This is kind of along a similar line-- 01:35:23.990 --> 01:35:25.250 align:middle line:90% or actually, I don't know. 01:35:25.250 --> 01:35:31.670 align:middle line:84% This is for 2.4B, where we're calculating the rate of removal 01:35:31.670 --> 01:35:35.670 align:middle line:84% of uranium from the core columns. 01:35:35.670 --> 01:35:42.070 align:middle line:84% And the way I did it is I looked at like the nitrate curve 01:35:42.070 --> 01:35:43.150 align:middle line:90% essentially. 01:35:43.150 --> 01:35:47.750 align:middle line:84% And I said, OK, well if we've got-- 01:35:47.750 --> 01:35:52.030 align:middle line:84% I don't have my problems with me. 01:35:52.030 --> 01:35:55.435 align:middle line:84% Yeah, so if you look at it like the nitrate curves, 01:35:55.435 --> 01:35:57.810 align:middle line:84% then you've got the flux at the sediment water interface. 01:35:57.810 --> 01:36:02.460 align:middle line:84% And then the flux at the point where around 6 centimeters 01:36:02.460 --> 01:36:04.420 align:middle line:90% where the inflection point is. 01:36:04.420 --> 01:36:07.140 align:middle line:84% And I calculated the flux at those two points 01:36:07.140 --> 01:36:10.100 align:middle line:84% and added them, like we had been doing for the nitrate in order 01:36:10.100 --> 01:36:11.600 align:middle line:90% to calculate the consumption. 01:36:11.600 --> 01:36:15.002 align:middle line:90% 01:36:15.002 --> 01:36:17.460 align:middle line:84% DIERDRE TOOLE: Yeah, I mean, the uranium profiles certainly 01:36:17.460 --> 01:36:19.380 align:middle line:90% go back up. 01:36:19.380 --> 01:36:24.200 align:middle line:84% And I can't remember why right now that they do that. 01:36:24.200 --> 01:36:27.780 align:middle line:90% 01:36:27.780 --> 01:36:31.880 align:middle line:84% But let me just read this really fast. 01:36:31.880 --> 01:36:46.060 align:middle line:90% 01:36:46.060 --> 01:36:52.280 align:middle line:84% It's not as if uranium here is all of a sudden soluble. 01:36:52.280 --> 01:36:54.120 align:middle line:90% It's not like this turns oxic. 01:36:54.120 --> 01:36:56.680 align:middle line:84% I don't remember why it goes back up. 01:36:56.680 --> 01:37:00.050 align:middle line:84% I will find out, but I don't remember why it is. 01:37:00.050 --> 01:37:04.430 align:middle line:84% But you can just use this consumption curve. 01:37:04.430 --> 01:37:07.490 align:middle line:90% 01:37:07.490 --> 01:37:08.885 align:middle line:90% OK? 01:37:08.885 --> 01:37:11.010 align:middle line:84% AUDIENCE: OK, so you're just saying ignore the fact 01:37:11.010 --> 01:37:11.692 align:middle line:90% that it goes up? 01:37:11.692 --> 01:37:12.650 align:middle line:90% DIERDRE TOOLE: For now. 01:37:12.650 --> 01:37:15.130 align:middle line:84% AUDIENCE: And just flux at the surface. 01:37:15.130 --> 01:37:16.530 align:middle line:90% DIERDRE TOOLE: For now, yes. 01:37:16.530 --> 01:37:20.370 align:middle line:84% Because I cannot remember why it goes back up and therefore I 01:37:20.370 --> 01:37:23.010 align:middle line:84% can't remember if you should include that or not. 01:37:23.010 --> 01:37:25.050 align:middle line:84% And so I'm just going to say right now 01:37:25.050 --> 01:37:27.570 align:middle line:90% it goes from oxic to anoxic. 01:37:27.570 --> 01:37:29.250 align:middle line:90% That's a consumption term. 01:37:29.250 --> 01:37:36.270 align:middle line:84% What's going on down here, sediments are kind of funky. 01:37:36.270 --> 01:37:41.690 align:middle line:90% 01:37:41.690 --> 01:37:44.210 align:middle line:84% It could be in the past that this was oxic. 01:37:44.210 --> 01:37:48.970 align:middle line:84% It could be that there's some of advective force coming 01:37:48.970 --> 01:37:53.210 align:middle line:84% through these that's advecting oxic seawater down here. 01:37:53.210 --> 01:37:55.070 align:middle line:90% So I don't know what this is. 01:37:55.070 --> 01:37:57.410 align:middle line:84% I can't remember if this happens everywhere 01:37:57.410 --> 01:38:00.350 align:middle line:84% or perhaps this is just something that's 01:38:00.350 --> 01:38:02.230 align:middle line:90% going on in this location. 01:38:02.230 --> 01:38:05.890 align:middle line:84% So for now, just go with this as the consumption term, 01:38:05.890 --> 01:38:07.130 align:middle line:90% because that's what we know. 01:38:07.130 --> 01:38:09.630 align:middle line:84% We know it's being consumed there. 01:38:09.630 --> 01:38:12.150 align:middle line:84% I'll find out what's going on in the lower 01:38:12.150 --> 01:38:14.670 align:middle line:90% portions of that graph. 01:38:14.670 --> 01:38:18.830 align:middle line:84% AUDIENCE: I realize that it's just being consumed there. 01:38:18.830 --> 01:38:20.310 align:middle line:84% DIERDRE TOOLE: Well, it could be, 01:38:20.310 --> 01:38:24.230 align:middle line:84% I mean if there is an advective force, an advective flow 01:38:24.230 --> 01:38:28.030 align:middle line:84% of oxic seawater here for some reason, 01:38:28.030 --> 01:38:30.770 align:middle line:84% then perhaps it is being redissolved. 01:38:30.770 --> 01:38:32.850 align:middle line:84% But I don't know that that's what's going on. 01:38:32.850 --> 01:38:36.370 align:middle line:84% It could be just, I mean, if these are ancient, 01:38:36.370 --> 01:38:42.590 align:middle line:84% if this is pelagic, then this is burial. 01:38:42.590 --> 01:38:43.650 align:middle line:90% This is old. 01:38:43.650 --> 01:38:45.510 align:middle line:90% This is real old. 01:38:45.510 --> 01:38:49.670 align:middle line:84% If this is coastal, then this is rather current. 01:38:49.670 --> 01:38:52.210 align:middle line:84% And it could still be effectively active. 01:38:52.210 --> 01:38:55.310 align:middle line:84% So I just I don't know enough right now in order 01:38:55.310 --> 01:39:00.580 align:middle line:90% to answer what's going on deep. 01:39:00.580 --> 01:39:03.500 align:middle line:84% Right, just don't worry about it for right now. 01:39:03.500 --> 01:39:06.500 align:middle line:84% I'm going to be grading based on this. 01:39:06.500 --> 01:39:09.780 align:middle line:90% How's that? 01:39:09.780 --> 01:39:11.500 align:middle line:84% I understand your frustration and I 01:39:11.500 --> 01:39:13.080 align:middle line:90% will try and figure it out. 01:39:13.080 --> 01:39:19.100 align:middle line:84% But to do this problem set, just worry about this curve here. 01:39:19.100 --> 01:39:23.780 align:middle line:84% Well, I can't believe that we didn't cover uranium. 01:39:23.780 --> 01:39:27.803 align:middle line:84% I was going to ask you about it, but that's just me. 01:39:27.803 --> 01:39:30.220 align:middle line:84% AUDIENCE: Because there was one thing, use your knowledge. 01:39:30.220 --> 01:39:31.335 align:middle line:90% DIERDRE TOOLE: Of uranium? 01:39:31.335 --> 01:39:31.960 align:middle line:90% AUDIENCE: Yeah. 01:39:31.960 --> 01:39:35.190 align:middle line:90% 01:39:35.190 --> 01:39:36.980 align:middle line:84% DIERDRE TOOLE: I'm pretty sure that this 01:39:36.980 --> 01:39:42.660 align:middle line:84% came from some old sediments problems that's 01:39:42.660 --> 01:39:45.080 align:middle line:84% from the sediments class where we do cover uranium. 01:39:45.080 --> 01:39:48.235 align:middle line:84% AUDIENCE: So can I ask another units question on number two? 01:39:48.235 --> 01:39:49.860 align:middle line:84% DIERDRE TOOLE: You can, but I have to-- 01:39:49.860 --> 01:39:51.760 align:middle line:84% AUDIENCE: I can ask you the units question. 01:39:51.760 --> 01:39:55.320 align:middle line:84% So am I missing a factor of 1,000 somewhere? 01:39:55.320 --> 01:39:56.560 align:middle line:90% AUDIENCE: Where? 01:39:56.560 --> 01:39:59.280 align:middle line:84% AUDIENCE: Did you switch from micromoles to moles? 01:39:59.280 --> 01:40:00.120 align:middle line:90% AUDIENCE: Where? 01:40:00.120 --> 01:40:02.240 align:middle line:90% In the number? 01:40:02.240 --> 01:40:06.000 align:middle line:84% I don't what is that, 2, or the one with the porosity 01:40:06.000 --> 01:40:07.272 align:middle line:90% and all that. 01:40:07.272 --> 01:40:09.480 align:middle line:84% AUDIENCE: Well in all of those, what I ended up doing 01:40:09.480 --> 01:40:13.880 align:middle line:84% is I ended up calculating phi, and then converting phi 01:40:13.880 --> 01:40:16.680 align:middle line:84% into liters per centimeter cubed. 01:40:16.680 --> 01:40:17.680 align:middle line:90% AUDIENCE: You're psycho. 01:40:17.680 --> 01:40:19.792 align:middle line:90% All right. 01:40:19.792 --> 01:40:22.000 align:middle line:84% AUDIENCE: So that's where I got my factor of 1,000 is 01:40:22.000 --> 01:40:24.815 align:middle line:90% because that conversion. 01:40:24.815 --> 01:40:25.440 align:middle line:90% AUDIENCE: Yeah. 01:40:25.440 --> 01:40:26.640 align:middle line:84% AUDIENCE: But I know Louis did it 01:40:26.640 --> 01:40:28.015 align:middle line:84% the other way, where he converted 01:40:28.015 --> 01:40:31.280 align:middle line:84% his other thing into centimeters cubed 01:40:31.280 --> 01:40:32.735 align:middle line:90% instead of liters or something. 01:40:32.735 --> 01:40:34.860 align:middle line:84% AUDIENCE: So you did end up with a factor of 1,000. 01:40:34.860 --> 01:40:39.440 align:middle line:84% So your final answer is in micromoles, not moles? 01:40:39.440 --> 01:40:42.560 align:middle line:90% No, that doesn't make sense. 01:40:42.560 --> 01:40:43.760 align:middle line:90% What's that? 01:40:43.760 --> 01:40:44.640 align:middle line:90% AUDIENCE: For flux? 01:40:44.640 --> 01:40:46.080 align:middle line:90% AUDIENCE: Yeah. 01:40:46.080 --> 01:40:48.880 align:middle line:84% AUDIENCE: Yeah, my final answer is in micromoles. 01:40:48.880 --> 01:40:50.720 align:middle line:90% AUDIENCE: Instead of millimoles? 01:40:50.720 --> 01:40:51.440 align:middle line:90% AUDIENCE: Yeah. 01:40:51.440 --> 01:40:53.230 align:middle line:90% AUDIENCE: All right.