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 --> 00:00:18.550 align:middle line:90% at ocw.mit.edu. 00:00:18.550 --> 00:00:21.840 align:middle line:90% 00:00:21.840 --> 00:00:24.320 align:middle line:84% SCOTT DONEY: So what I was planning on doing 00:00:24.320 --> 00:00:27.760 align:middle line:84% was starting off by having a discussion 00:00:27.760 --> 00:00:32.000 align:middle line:84% about the Sigman and Boyle paper, 00:00:32.000 --> 00:00:36.840 align:middle line:84% and then we can go into more general questions and review. 00:00:36.840 --> 00:00:39.460 align:middle line:84% And I brought my notebook with me. 00:00:39.460 --> 00:00:43.900 align:middle line:84% I didn't bring all of, for example, Meg's lectures, 00:00:43.900 --> 00:00:46.080 align:middle line:84% but, if there are other questions 00:00:46.080 --> 00:00:49.380 align:middle line:84% that I can't immediately answer off the top of my head, 00:00:49.380 --> 00:00:54.120 align:middle line:84% I can send some emails out later this afternoon. 00:00:54.120 --> 00:00:57.040 align:middle line:84% So let's just start off by having-- 00:00:57.040 --> 00:00:58.520 align:middle line:84% I mean, so what did you guys think 00:00:58.520 --> 00:01:00.780 align:middle line:90% of the Sigman and Boyle paper. 00:01:00.780 --> 00:01:05.140 align:middle line:84% I mean, I tried to choose a paper that was challenging, 00:01:05.140 --> 00:01:08.600 align:middle line:84% but hopefully, you've learned enough in the semester 00:01:08.600 --> 00:01:11.240 align:middle line:84% that you could at least understand 00:01:11.240 --> 00:01:12.460 align:middle line:90% what the arguments were. 00:01:12.460 --> 00:01:14.858 align:middle line:84% If not, there are parts where it's like, OK, well, 00:01:14.858 --> 00:01:16.400 align:middle line:84% I don't know the particular data sets 00:01:16.400 --> 00:01:18.660 align:middle line:84% they're talking about and some of the arguments, 00:01:18.660 --> 00:01:22.280 align:middle line:84% but what did you guys think of it? 00:01:22.280 --> 00:01:24.760 align:middle line:84% STUDENT: I thought it was a good paper for tying things 00:01:24.760 --> 00:01:29.080 align:middle line:84% together and just thinking through a lot of the concepts 00:01:29.080 --> 00:01:33.540 align:middle line:84% that we've been having that are conceptually not the simplest. 00:01:33.540 --> 00:01:36.148 align:middle line:90% 00:01:36.148 --> 00:01:37.940 align:middle line:84% SCOTT DONEY: What about you guys up at MIT? 00:01:37.940 --> 00:01:40.600 align:middle line:90% This has got to be-- 00:01:40.600 --> 00:01:42.120 align:middle line:90% you guys are part of the-- 00:01:42.120 --> 00:01:43.320 align:middle line:90% STUDENT: Actually-- 00:01:43.320 --> 00:01:44.360 align:middle line:84% SCOTT DONEY: Well, why don't we start then 00:01:44.360 --> 00:01:45.620 align:middle line:90% from the folks up at MIT? 00:01:45.620 --> 00:01:47.380 align:middle line:84% Because we can hear you guys quite well. 00:01:47.380 --> 00:01:50.600 align:middle line:90% 00:01:50.600 --> 00:01:53.260 align:middle line:84% I mean, did you guys understand the main themes? 00:01:53.260 --> 00:01:55.660 align:middle line:84% Was there part of the paper that didn't make sense? 00:01:55.660 --> 00:02:01.560 align:middle line:84% Should we walk through the arguments just in a review? 00:02:01.560 --> 00:02:03.080 align:middle line:90% What would help you guys? 00:02:03.080 --> 00:02:07.040 align:middle line:84% This is really to help you guys pull things together 00:02:07.040 --> 00:02:12.700 align:middle line:90% in your mind for the final. 00:02:12.700 --> 00:02:16.560 align:middle line:90% 00:02:16.560 --> 00:02:19.560 align:middle line:84% STUDENT: I mean, you guys-- a question-- 00:02:19.560 --> 00:02:22.240 align:middle line:90% the text. 00:02:22.240 --> 00:02:27.480 align:middle line:84% STUDENT: I had a question about why the carbon-13 to carbon-12 00:02:27.480 --> 00:02:31.040 align:middle line:90% system of the-- 00:02:31.040 --> 00:02:39.120 align:middle line:84% it says that the land plants have a lower carbon-13 carbon-12 00:02:39.120 --> 00:02:43.560 align:middle line:84% ratio, and it was using that as an explanation on why you 00:02:43.560 --> 00:02:46.040 align:middle line:90% could've gotten-- 00:02:46.040 --> 00:02:48.180 align:middle line:84% if there was less carbon stored in land, 00:02:48.180 --> 00:02:53.160 align:middle line:84% you would get a decrease in carbon-13/carbon-12 ratio 00:02:53.160 --> 00:02:57.000 align:middle line:90% of the ocean atmosphere system. 00:02:57.000 --> 00:02:58.360 align:middle line:90% I didn't understand-- 00:02:58.360 --> 00:03:00.500 align:middle line:90% SCOTT DONEY: OK, good question. 00:03:00.500 --> 00:03:05.670 align:middle line:90% So we'll go over the C13-- 00:03:05.670 --> 00:03:07.340 align:middle line:90% pen is dying on me. 00:03:07.340 --> 00:03:11.960 align:middle line:84% The semester must be over-- my pen is dying. 00:03:11.960 --> 00:03:19.000 align:middle line:84% So the C13 to C12 ratio, and it's usually 00:03:19.000 --> 00:03:24.480 align:middle line:90% defined in a del notation. 00:03:24.480 --> 00:03:28.120 align:middle line:84% And remember the del notation is simply the fact 00:03:28.120 --> 00:03:33.680 align:middle line:84% that we typically don't measure the absolute ratio of isotopes. 00:03:33.680 --> 00:03:37.760 align:middle line:84% We measure things, mass-for-mass spectrometers, almost always 00:03:37.760 --> 00:03:39.880 align:middle line:90% against some reference standard. 00:03:39.880 --> 00:03:43.240 align:middle line:84% And so you're going to be actually measuring 00:03:43.240 --> 00:03:56.600 align:middle line:84% the C13/C12 of your sample relative to some C13/C12 00:03:56.600 --> 00:03:59.620 align:middle line:90% of a reference. 00:03:59.620 --> 00:04:03.380 align:middle line:90% 00:04:03.380 --> 00:04:05.860 align:middle line:84% And then you're going to take this. 00:04:05.860 --> 00:04:08.060 align:middle line:90% This is going to vary about 1. 00:04:08.060 --> 00:04:12.440 align:middle line:84% If the sample and the reference had the same value, 00:04:12.440 --> 00:04:14.440 align:middle line:90% this ratio would be 1. 00:04:14.440 --> 00:04:17.399 align:middle line:84% And you're going to look at deviations from 1. 00:04:17.399 --> 00:04:20.480 align:middle line:84% And since the deviations are pretty small, 00:04:20.480 --> 00:04:24.000 align:middle line:84% you're going to multiply by 1,000. 00:04:24.000 --> 00:04:31.280 align:middle line:84% And it's often reported as per mille or the cute little percent 00:04:31.280 --> 00:04:34.840 align:middle line:90% sign with an extra extra zero. 00:04:34.840 --> 00:04:36.800 align:middle line:84% Now, there's a couple of things that 00:04:36.800 --> 00:04:41.560 align:middle line:90% can fractionate C13 from C12. 00:04:41.560 --> 00:04:46.080 align:middle line:84% And we went through a couple of-- 00:04:46.080 --> 00:04:50.380 align:middle line:84% there's equilibrium fractionation. 00:04:50.380 --> 00:04:53.480 align:middle line:90% 00:04:53.480 --> 00:04:56.720 align:middle line:84% And that's just that in a chemical system, 00:04:56.720 --> 00:05:01.520 align:middle line:84% let's say if you have a phase transition, 00:05:01.520 --> 00:05:04.160 align:middle line:84% if you have a phase transition, you'll 00:05:04.160 --> 00:05:06.800 align:middle line:84% often find that one phase will have 00:05:06.800 --> 00:05:09.000 align:middle line:84% a slightly different isotopic composition 00:05:09.000 --> 00:05:11.880 align:middle line:90% than the other phase. 00:05:11.880 --> 00:05:14.420 align:middle line:84% Another is kinetic fractionation. 00:05:14.420 --> 00:05:17.920 align:middle line:90% 00:05:17.920 --> 00:05:22.600 align:middle line:84% And so for example, in the case of C13 and C12, 00:05:22.600 --> 00:05:32.760 align:middle line:84% when you form organic matter inside a cell. 00:05:32.760 --> 00:05:35.480 align:middle line:90% So you have this little-- 00:05:35.480 --> 00:05:42.880 align:middle line:84% my nice little cell, you have to diffuse in CO2. 00:05:42.880 --> 00:05:53.640 align:middle line:84% And the C12 CO2 diffuses in faster than the C13 CO2 00:05:53.640 --> 00:05:58.640 align:middle line:90% because the C12 CO2 is lighter. 00:05:58.640 --> 00:06:04.600 align:middle line:84% And so what you see in both land plants and in marine plants 00:06:04.600 --> 00:06:13.040 align:middle line:84% is you see that you have the del C13 is less than 0. 00:06:13.040 --> 00:06:20.920 align:middle line:84% And the reference for C13 where the reference is a Peedee 00:06:20.920 --> 00:06:24.080 align:middle line:90% Belemnite calcium carbonate. 00:06:24.080 --> 00:06:25.460 align:middle line:90% Essentially, it's a fossil. 00:06:25.460 --> 00:06:28.520 align:middle line:90% 00:06:28.520 --> 00:06:31.100 align:middle line:84% So the reference is a calcium carbonate. 00:06:31.100 --> 00:06:34.860 align:middle line:84% It looks a lot like what you might 00:06:34.860 --> 00:06:38.440 align:middle line:84% expect the inorganic, dissolved inorganic carbon to look like. 00:06:38.440 --> 00:06:41.240 align:middle line:84% The organic matter is usually less than that. 00:06:41.240 --> 00:06:50.370 align:middle line:84% And the range is, for marine organic matter, 00:06:50.370 --> 00:06:58.370 align:middle line:84% it's something like minus 20 per mille somewhere around in there. 00:06:58.370 --> 00:07:01.590 align:middle line:84% And for terrestrial-- and we won't go into the details-- 00:07:01.590 --> 00:07:05.450 align:middle line:84% it depends upon on the carbon fixation pathway, 00:07:05.450 --> 00:07:09.610 align:middle line:84% so some ecosystems have very different-- 00:07:09.610 --> 00:07:13.930 align:middle line:84% have different C13 signature than others. 00:07:13.930 --> 00:07:18.770 align:middle line:84% You guys remember C3 and C4 plants from biochemistry? 00:07:18.770 --> 00:07:23.490 align:middle line:84% Anyway, detail that you don't really need to know here. 00:07:23.490 --> 00:07:26.010 align:middle line:90% Somewhere between-- what? 00:07:26.010 --> 00:07:27.450 align:middle line:90% STUDENT: Question at MIT. 00:07:27.450 --> 00:07:29.130 align:middle line:90% SCOTT DONEY: Sure. 00:07:29.130 --> 00:07:30.890 align:middle line:84% STUDENT: Is the diffusion rate as 00:07:30.890 --> 00:07:36.650 align:middle line:84% important as the enzymatic kinetic fractionation there? 00:07:36.650 --> 00:07:42.050 align:middle line:84% SCOTT DONEY: For RuBisCO, basically, RuBisCO 00:07:42.050 --> 00:07:48.490 align:middle line:84% uses everything that gets to it in photosynthesis. 00:07:48.490 --> 00:07:51.850 align:middle line:90% And so it really is-- 00:07:51.850 --> 00:07:54.990 align:middle line:84% it's not a enzymatic fractionation. 00:07:54.990 --> 00:07:57.270 align:middle line:84% It's a diffusional fractionation. 00:07:57.270 --> 00:08:00.970 align:middle line:90% 00:08:00.970 --> 00:08:03.470 align:middle line:84% There are systems that are enzymatic fractionation. 00:08:03.470 --> 00:08:04.970 align:middle line:84% And you would have to, if you wanted 00:08:04.970 --> 00:08:06.678 align:middle line:84% to go into this in detail, you would look 00:08:06.678 --> 00:08:08.030 align:middle line:90% at both of those components. 00:08:08.030 --> 00:08:10.330 align:middle line:90% But in this case, it's a-- 00:08:10.330 --> 00:08:12.530 align:middle line:84% excuse me, particularly on land plants, 00:08:12.530 --> 00:08:16.650 align:middle line:84% you have to diffuse through quite a barrier of dead air 00:08:16.650 --> 00:08:18.450 align:middle line:90% space in the leaf. 00:08:18.450 --> 00:08:25.330 align:middle line:84% And so basically, it's diffusion limited rather than enzymatic 00:08:25.330 --> 00:08:28.210 align:middle line:90% limited. 00:08:28.210 --> 00:08:30.850 align:middle line:84% Land plants are somewhere between, say minus 10 00:08:30.850 --> 00:08:35.210 align:middle line:90% and minus 30 per mille. 00:08:35.210 --> 00:08:37.049 align:middle line:84% And people do use the differences 00:08:37.049 --> 00:08:39.730 align:middle line:84% in the C13 of the organic matter to say something 00:08:39.730 --> 00:08:41.970 align:middle line:90% about marine and terrestrial. 00:08:41.970 --> 00:08:44.370 align:middle line:84% In the context of the Sigman and Boyle 00:08:44.370 --> 00:08:50.210 align:middle line:84% paper, what it's comparing to is the DIC 00:08:50.210 --> 00:09:00.130 align:middle line:84% of seawater, which is more like approximately 0. 00:09:00.130 --> 00:09:03.330 align:middle line:90% Yeah, more like about 0. 00:09:03.330 --> 00:09:07.250 align:middle line:84% And so organic matter of either form 00:09:07.250 --> 00:09:15.010 align:middle line:84% is isotopically depleted in C13 relative to the inorganic pool 00:09:15.010 --> 00:09:16.370 align:middle line:90% in seawater. 00:09:16.370 --> 00:09:28.810 align:middle line:84% So if you took a large slug of organic matter from land, 00:09:28.810 --> 00:09:36.930 align:middle line:84% so you took a bunch of trees, and you chop them down, 00:09:36.930 --> 00:09:41.170 align:middle line:84% and you stuck that carbon into the ocean as CO2-- 00:09:41.170 --> 00:09:42.810 align:middle line:84% now, presumably, these got ground up 00:09:42.810 --> 00:09:46.090 align:middle line:90% as the glacier was coming. 00:09:46.090 --> 00:09:48.830 align:middle line:84% Or reverse when the glacier retreated, 00:09:48.830 --> 00:09:50.250 align:middle line:84% you started to grow trees, and you 00:09:50.250 --> 00:09:53.010 align:middle line:84% suck CO2 out of the atmosphere, but eventually 00:09:53.010 --> 00:09:59.490 align:middle line:84% that CO2 came out of the ocean to replenish the atmosphere. 00:09:59.490 --> 00:10:03.770 align:middle line:84% If you added a bunch of terrestrial carbon to the ocean, 00:10:03.770 --> 00:10:08.050 align:middle line:84% you would change the del C13 of the ocean, 00:10:08.050 --> 00:10:11.330 align:middle line:84% and you would make it lighter because you're 00:10:11.330 --> 00:10:13.290 align:middle line:84% adding light organic carbon, and that 00:10:13.290 --> 00:10:17.710 align:middle line:84% would push down the C13 of the inorganic carbon in the ocean. 00:10:17.710 --> 00:10:20.770 align:middle line:84% So this would be in the DIC system. 00:10:20.770 --> 00:10:25.210 align:middle line:84% And the records we have for the C13 in the ocean 00:10:25.210 --> 00:10:27.770 align:middle line:84% come from calcium carbonate shells, 00:10:27.770 --> 00:10:30.890 align:middle line:84% and so it's recording that inorganic carbon 00:10:30.890 --> 00:10:34.050 align:middle line:90% concentration of seawater. 00:10:34.050 --> 00:10:36.430 align:middle line:84% So that was the argument that they were making. 00:10:36.430 --> 00:10:39.538 align:middle line:90% Does that make sense? 00:10:39.538 --> 00:10:41.830 align:middle line:84% STUDENT: It's not important that they were land plants. 00:10:41.830 --> 00:10:45.798 align:middle line:84% It's just important that plants are-- 00:10:45.798 --> 00:10:46.590 align:middle line:90% SCOTT DONEY: Right. 00:10:46.590 --> 00:10:48.603 align:middle line:84% STUDENT: Biomass is being put into the ocean. 00:10:48.603 --> 00:10:50.270 align:middle line:84% SCOTT DONEY: Yeah, it's more important-- 00:10:50.270 --> 00:10:53.050 align:middle line:84% and the reason why they focus on-- 00:10:53.050 --> 00:10:55.750 align:middle line:84% it is it's the organic matter going into the ocean. 00:10:55.750 --> 00:10:59.050 align:middle line:84% And the reason they focus on terrestrial organic matter 00:10:59.050 --> 00:11:02.170 align:middle line:84% versus ocean organic matter is, other 00:11:02.170 --> 00:11:05.610 align:middle line:84% than the dissolved organic pool, which we know so little about 00:11:05.610 --> 00:11:08.450 align:middle line:90% and have no-- 00:11:08.450 --> 00:11:12.050 align:middle line:84% this is the classic searching under the-- the drunks looking 00:11:12.050 --> 00:11:12.790 align:middle line:90% for their keys. 00:11:12.790 --> 00:11:13.582 align:middle line:90% Where do they look? 00:11:13.582 --> 00:11:16.050 align:middle line:84% They look under the lamppost, even if they drop their keys 00:11:16.050 --> 00:11:17.850 align:middle line:90% a couple hundred yards away. 00:11:17.850 --> 00:11:20.610 align:middle line:84% Well, you look because that's where you can see things. 00:11:20.610 --> 00:11:22.290 align:middle line:84% We have no information about what 00:11:22.290 --> 00:11:24.850 align:middle line:84% the dissolved organic carbon pool might've been 00:11:24.850 --> 00:11:26.530 align:middle line:90% in the glacial/interglacial. 00:11:26.530 --> 00:11:29.350 align:middle line:84% And so the assumption is, well, it was probably constant. 00:11:29.350 --> 00:11:31.610 align:middle line:84% It's got a fairly long residence time. 00:11:31.610 --> 00:11:35.410 align:middle line:84% And most of these analyzes ignore that. 00:11:35.410 --> 00:11:37.530 align:middle line:84% The particulate organic pool in the ocean 00:11:37.530 --> 00:11:40.370 align:middle line:84% is so small, only a few petagrams, 00:11:40.370 --> 00:11:43.430 align:middle line:84% that it wouldn't have a big impact. 00:11:43.430 --> 00:11:46.210 align:middle line:84% And so if you're looking for something 00:11:46.210 --> 00:11:50.970 align:middle line:84% to change a large organic carbon source that's mobile, 00:11:50.970 --> 00:11:53.010 align:middle line:84% usually you would look on land, and there's 00:11:53.010 --> 00:11:55.790 align:middle line:84% good reason to think there was less organic carbon on land. 00:11:55.790 --> 00:11:58.810 align:middle line:90% 00:11:58.810 --> 00:11:59.710 align:middle line:90% Good question. 00:11:59.710 --> 00:12:02.450 align:middle line:90% 00:12:02.450 --> 00:12:05.010 align:middle line:90% Other questions? 00:12:05.010 --> 00:12:07.170 align:middle line:90% Yeah, Caitlin. 00:12:07.170 --> 00:12:09.850 align:middle line:84% STUDENT: I have a question about something 00:12:09.850 --> 00:12:12.750 align:middle line:84% on in the last paragraph on page 860. 00:12:12.750 --> 00:12:16.170 align:middle line:84% They talked about the organic matter reservoir. 00:12:16.170 --> 00:12:18.250 align:middle line:84% The terrestrial organic matter reservoir 00:12:18.250 --> 00:12:22.530 align:middle line:90% is decreasing during ice ages. 00:12:22.530 --> 00:12:27.590 align:middle line:84% And they say that they talked about a 500, a potential 500 00:12:27.590 --> 00:12:28.733 align:middle line:90% teragram carbon-- 00:12:28.733 --> 00:12:29.650 align:middle line:90% SCOTT DONEY: Petagram. 00:12:29.650 --> 00:12:34.530 align:middle line:84% STUDENT: --addition, I guess, due to either-- 00:12:34.530 --> 00:12:38.650 align:middle line:84% this is my question, how are they adding that carbon back 00:12:38.650 --> 00:12:39.730 align:middle line:90% into-- 00:12:39.730 --> 00:12:42.490 align:middle line:84% or taking it out of the terrestrial reservoir? 00:12:42.490 --> 00:12:45.150 align:middle line:90% Is it decaying on land into CO2? 00:12:45.150 --> 00:12:50.010 align:middle line:84% Or is it being transported as organic matter into the ocean 00:12:50.010 --> 00:12:53.090 align:middle line:84% and then being remineralized in the deep ocean? 00:12:53.090 --> 00:12:57.730 align:middle line:84% Or is there some partitioning between those two things? 00:12:57.730 --> 00:12:59.930 align:middle line:84% SCOTT DONEY: For their arguments, 00:12:59.930 --> 00:13:01.730 align:middle line:90% because they're looking at-- 00:13:01.730 --> 00:13:08.070 align:middle line:84% the main focus of this particular article, of course, 00:13:08.070 --> 00:13:14.610 align:middle line:84% are these large amplitude, the large amplitude CO2 changes. 00:13:14.610 --> 00:13:17.690 align:middle line:84% And so they're trying to understand 00:13:17.690 --> 00:13:20.610 align:middle line:84% the difference between these interglacial periods 00:13:20.610 --> 00:13:25.210 align:middle line:84% with about 280 PPM and the glacial maximum that 00:13:25.210 --> 00:13:29.370 align:middle line:90% had 180 to 200. 00:13:29.370 --> 00:13:31.250 align:middle line:84% So they're looking at timescales. 00:13:31.250 --> 00:13:33.530 align:middle line:90% Remember, this is 100,000 years. 00:13:33.530 --> 00:13:36.090 align:middle line:90% STUDENT: So it doesn't matter? 00:13:36.090 --> 00:13:40.430 align:middle line:84% SCOTT DONEY: For their argument, it doesn't matter. 00:13:40.430 --> 00:13:43.690 align:middle line:90% One of the things we always-- 00:13:43.690 --> 00:13:51.210 align:middle line:84% one of the anthropomorphic distortions 00:13:51.210 --> 00:13:58.130 align:middle line:84% is we always think about going from a interglacial back 00:13:58.130 --> 00:14:01.465 align:middle line:84% to a glacial, but we forget that time actually-- really, 00:14:01.465 --> 00:14:02.590 align:middle line:90% the time ran the other way. 00:14:02.590 --> 00:14:04.007 align:middle line:84% So the best way to think about it, 00:14:04.007 --> 00:14:08.430 align:middle line:84% the really sharp change is you were at a glacial period, 00:14:08.430 --> 00:14:12.850 align:middle line:84% and that's actually the norm for the last 500,000 years was being 00:14:12.850 --> 00:14:16.090 align:middle line:84% in glacial period, not in the nice tropical weather we have 00:14:16.090 --> 00:14:17.090 align:middle line:90% now. 00:14:17.090 --> 00:14:19.330 align:middle line:84% And so the way I usually think about it 00:14:19.330 --> 00:14:22.570 align:middle line:84% is, as the ice sheets retreat, you 00:14:22.570 --> 00:14:25.610 align:middle line:90% expose all of this barren land. 00:14:25.610 --> 00:14:29.128 align:middle line:84% Trees start to grow-- well, first off, mosses and lichens 00:14:29.128 --> 00:14:29.670 align:middle line:90% and all that. 00:14:29.670 --> 00:14:31.810 align:middle line:84% But eventually, you get and you build forests, 00:14:31.810 --> 00:14:34.090 align:middle line:84% and then you build peatlands because that's 00:14:34.090 --> 00:14:35.630 align:middle line:84% where a lot of the carbon is stored, 00:14:35.630 --> 00:14:38.810 align:middle line:84% is either in wood or in peat and high-latitude peat. 00:14:38.810 --> 00:14:41.250 align:middle line:84% And you didn't have any of the boreal forests 00:14:41.250 --> 00:14:43.870 align:middle line:84% or any of the peatlands during the glacial period 00:14:43.870 --> 00:14:46.290 align:middle line:84% because that has all been scraped clean. 00:14:46.290 --> 00:14:51.530 align:middle line:84% And so that carbon had to come from the atmosphere. 00:14:51.530 --> 00:14:58.570 align:middle line:84% But the atmosphere on timescales of a few decades, 00:14:58.570 --> 00:15:00.730 align:middle line:84% you can't really draw down the atmosphere 00:15:00.730 --> 00:15:04.610 align:middle line:84% without the ocean starting to pump CO2 back into it. 00:15:04.610 --> 00:15:07.050 align:middle line:84% And so the way I usually think about it is the glaciers 00:15:07.050 --> 00:15:09.970 align:middle line:84% retreated, land plants started to grow, 00:15:09.970 --> 00:15:11.690 align:middle line:84% and that carbon had to be pulled out 00:15:11.690 --> 00:15:14.290 align:middle line:90% of the ocean via a gas phase. 00:15:14.290 --> 00:15:17.650 align:middle line:84% Now, what happens in the reverse when the glaciers advance, 00:15:17.650 --> 00:15:19.210 align:middle line:84% and you knock down all these forests, 00:15:19.210 --> 00:15:20.770 align:middle line:90% and you destroy the peat? 00:15:20.770 --> 00:15:23.290 align:middle line:84% And how that carbon gets released is a little bit more 00:15:23.290 --> 00:15:24.610 align:middle line:90% complicated. 00:15:24.610 --> 00:15:27.890 align:middle line:84% And I don't think anybody's-- it's not exactly clear. 00:15:27.890 --> 00:15:32.150 align:middle line:84% Is some of the carbon buried underneath the glacier? 00:15:32.150 --> 00:15:34.810 align:middle line:90% And what happens to that? 00:15:34.810 --> 00:15:38.150 align:middle line:84% But eventually, the argument is eventually it gets to the ocean. 00:15:38.150 --> 00:15:41.170 align:middle line:84% Whether it goes through a gas phase because of decay 00:15:41.170 --> 00:15:45.710 align:middle line:84% or whether it goes as a solid or dissolved phase via rivers 00:15:45.710 --> 00:15:49.410 align:middle line:84% I don't think is completely resolved. 00:15:49.410 --> 00:15:51.510 align:middle line:84% STUDENT: Do you think, as a follow up to that, 00:15:51.510 --> 00:15:54.610 align:middle line:84% we could think through what the difference would 00:15:54.610 --> 00:15:58.930 align:middle line:84% be if we were just releasing a ton of CO2 to the atmosphere 00:15:58.930 --> 00:16:01.130 align:middle line:84% directly from land versus dumping 00:16:01.130 --> 00:16:04.170 align:middle line:84% a whole bunch of organic matter into the ocean? 00:16:04.170 --> 00:16:05.350 align:middle line:90% SCOTT DONEY: OK. 00:16:05.350 --> 00:16:09.890 align:middle line:84% STUDENT: Actually, was that what you mean in terms 00:16:09.890 --> 00:16:11.570 align:middle line:90% of time scales, I guess? 00:16:11.570 --> 00:16:15.570 align:middle line:84% SCOTT DONEY: OK, so let's look at shorter term-- 00:16:15.570 --> 00:16:19.610 align:middle line:84% Caitlin's question is basically, let's look 00:16:19.610 --> 00:16:24.890 align:middle line:84% at shorter-term perturbations to the ocean inorganic carbon-- 00:16:24.890 --> 00:16:29.410 align:middle line:90% or the global carbon system. 00:16:29.410 --> 00:16:31.610 align:middle line:84% And there's a couple of important-- 00:16:31.610 --> 00:16:34.430 align:middle line:84% and I'm going to have to go back again. 00:16:34.430 --> 00:16:38.370 align:middle line:90% 00:16:38.370 --> 00:16:40.907 align:middle line:84% So there's a couple of important timescales. 00:16:40.907 --> 00:16:43.490 align:middle line:84% And these are important things that you guys should probably-- 00:16:43.490 --> 00:16:46.610 align:middle line:84% irrespective of the exam, it would be useful 00:16:46.610 --> 00:16:50.570 align:middle line:84% for you to have these floating around in your brain. 00:16:50.570 --> 00:16:52.930 align:middle line:84% And they talk about this a little bit 00:16:52.930 --> 00:16:56.890 align:middle line:84% in the paper, which is they divide 00:16:56.890 --> 00:17:16.410 align:middle line:84% the ocean up into a warm thermocline box, a deep box, 00:17:16.410 --> 00:17:18.609 align:middle line:90% that vents to the poles. 00:17:18.609 --> 00:17:21.810 align:middle line:84% So you have warm thermocline, and this is basically 00:17:21.810 --> 00:17:27.250 align:middle line:84% all that thermocline circulation and wind-driven circulation. 00:17:27.250 --> 00:17:30.290 align:middle line:84% And this has timescales of, well, 00:17:30.290 --> 00:17:32.810 align:middle line:84% we'll worry about timescales in a minute. 00:17:32.810 --> 00:17:36.510 align:middle line:84% And then you have then you have land. 00:17:36.510 --> 00:17:39.370 align:middle line:90% 00:17:39.370 --> 00:17:41.970 align:middle line:90% That was not my best tree. 00:17:41.970 --> 00:17:43.950 align:middle line:84% And then you have atmospheric CO2. 00:17:43.950 --> 00:17:47.450 align:middle line:90% 00:17:47.450 --> 00:17:51.530 align:middle line:90% The timescales of this are-- 00:17:51.530 --> 00:17:54.870 align:middle line:84% so we would want to know the gas exchange timescales. 00:17:54.870 --> 00:17:59.090 align:middle line:90% 00:17:59.090 --> 00:18:05.650 align:middle line:84% So if there's a perturbation in the surface air 00:18:05.650 --> 00:18:11.890 align:middle line:84% or the surface ocean on some timescale, 00:18:11.890 --> 00:18:16.370 align:middle line:84% gas exchange is going to try to drive the ocean and atmosphere 00:18:16.370 --> 00:18:18.410 align:middle line:90% back to equilibrium. 00:18:18.410 --> 00:18:20.890 align:middle line:90% And so we talked about that. 00:18:20.890 --> 00:18:26.250 align:middle line:84% If you remember, for oxygen gas exchange timescales 00:18:26.250 --> 00:18:35.330 align:middle line:84% were typically like a month and where we got the timescale 00:18:35.330 --> 00:18:40.010 align:middle line:84% by saying that the flux of gas was 00:18:40.010 --> 00:18:51.250 align:middle line:84% equal to some transfer velocity times a delta concentration. 00:18:51.250 --> 00:18:57.570 align:middle line:84% That was the core of the gas exchange argument. 00:18:57.570 --> 00:19:03.690 align:middle line:84% And so that if you looked at, say, 00:19:03.690 --> 00:19:07.770 align:middle line:84% that delta C at any particular time 00:19:07.770 --> 00:19:13.770 align:middle line:84% after you had a perturbation, it would be your delta C initial 00:19:13.770 --> 00:19:15.710 align:middle line:90% and then e to the minus-- 00:19:15.710 --> 00:19:20.650 align:middle line:90% 00:19:20.650 --> 00:19:33.180 align:middle line:84% let's see, it would be k over h t, 00:19:33.180 --> 00:19:36.540 align:middle line:84% where k is your transfer velocity 00:19:36.540 --> 00:19:39.260 align:middle line:90% and h is your mixed layer depth. 00:19:39.260 --> 00:19:47.120 align:middle line:90% So h is the mixed layer depth. 00:19:47.120 --> 00:19:51.100 align:middle line:90% 00:19:51.100 --> 00:19:56.380 align:middle line:84% So that would be k has units of, say, length per time. 00:19:56.380 --> 00:19:57.860 align:middle line:90% h is in length. 00:19:57.860 --> 00:20:01.073 align:middle line:84% So this would be 1 over time multiplied by time, 00:20:01.073 --> 00:20:02.740 align:middle line:84% and so it becomes unitless which is what 00:20:02.740 --> 00:20:04.240 align:middle line:90% you need for the exponential. 00:20:04.240 --> 00:20:06.940 align:middle line:90% 00:20:06.940 --> 00:20:10.800 align:middle line:84% For oxygen, it was about an order a month. 00:20:10.800 --> 00:20:14.440 align:middle line:84% It might be two weeks, it might be a month and a half. 00:20:14.440 --> 00:20:18.460 align:middle line:90% But that's a good approximation. 00:20:18.460 --> 00:20:24.620 align:middle line:84% For CO2, because of the fact that you 00:20:24.620 --> 00:20:30.920 align:middle line:84% have this large additional DIC reservoir-- 00:20:30.920 --> 00:20:35.060 align:middle line:90% 00:20:35.060 --> 00:20:37.560 align:middle line:84% remember, you had the large DIC reservoir 00:20:37.560 --> 00:20:39.780 align:middle line:84% so that any change in CO2, you also 00:20:39.780 --> 00:20:42.660 align:middle line:84% had to fill up that DIC reservoir 00:20:42.660 --> 00:20:44.900 align:middle line:90% and alter that DIC reservoir. 00:20:44.900 --> 00:20:50.100 align:middle line:84% Was more like, the gas exchange timescale was more like a year. 00:20:50.100 --> 00:20:58.660 align:middle line:84% And then for 14 CO2, it was more like something like 10 years, 00:20:58.660 --> 00:21:02.420 align:middle line:84% where the difference between C14 and CO2 was, 00:21:02.420 --> 00:21:07.160 align:middle line:84% in the case of the CO2, the DIC reservoir-- 00:21:07.160 --> 00:21:09.260 align:middle line:84% you still have to fill up the DIC reservoir, 00:21:09.260 --> 00:21:12.700 align:middle line:90% but you also can shift-- 00:21:12.700 --> 00:21:21.980 align:middle line:84% you have shift in pH and between H2CO3 star 00:21:21.980 --> 00:21:25.660 align:middle line:90% carbonate and bicarbonate-- 00:21:25.660 --> 00:21:27.640 align:middle line:84% or excuse me, bicarbonate and carbonate. 00:21:27.640 --> 00:21:30.220 align:middle line:90% 00:21:30.220 --> 00:21:34.460 align:middle line:84% So this actually went faster because, along the way, 00:21:34.460 --> 00:21:38.740 align:middle line:84% you altered-- you added a little bit of CO2 00:21:38.740 --> 00:21:41.780 align:middle line:84% and that made the system a little bit more acidic. 00:21:41.780 --> 00:21:44.620 align:middle line:84% And so you actually got more bang for your buck 00:21:44.620 --> 00:21:47.500 align:middle line:84% in terms of the change in H2CO3 star 00:21:47.500 --> 00:21:52.060 align:middle line:84% than what you would expect if the pH had stayed constant. 00:21:52.060 --> 00:21:54.660 align:middle line:84% If the CO2 system didn't buffer-- 00:21:54.660 --> 00:21:58.300 align:middle line:84% was not the primary controlling buffer on ocean pH, 00:21:58.300 --> 00:22:01.380 align:middle line:84% then it would look more like C14. 00:22:01.380 --> 00:22:03.180 align:middle line:90% But because it does change the-- 00:22:03.180 --> 00:22:09.140 align:middle line:84% it does control the pH, it has that nonlinear feedback in it. 00:22:09.140 --> 00:22:12.500 align:middle line:84% STUDENT: So the reason that C14 doesn't 00:22:12.500 --> 00:22:16.300 align:middle line:84% affect the pH is just because you're not adding 00:22:16.300 --> 00:22:17.440 align:middle line:90% that substantial component. 00:22:17.440 --> 00:22:20.580 align:middle line:84% SCOTT DONEY: Yeah, you're adding a trace amount of CO2, 00:22:20.580 --> 00:22:22.020 align:middle line:84% and you're looking at it in terms 00:22:22.020 --> 00:22:24.640 align:middle line:84% of the change of isotopic equilibrium. 00:22:24.640 --> 00:22:27.740 align:middle line:90% 00:22:27.740 --> 00:22:30.600 align:middle line:90% So that's the first timescale. 00:22:30.600 --> 00:22:36.420 align:middle line:84% If you perturb, if either you have a perturbation in the ocean 00:22:36.420 --> 00:22:40.740 align:middle line:84% or a perturbation in the atmosphere on the timescale 00:22:40.740 --> 00:22:44.940 align:middle line:84% of about a year, the surface mixed layer 00:22:44.940 --> 00:22:47.100 align:middle line:90% will try to approach that-- 00:22:47.100 --> 00:22:49.540 align:middle line:90% or try to reequilibrate. 00:22:49.540 --> 00:22:52.060 align:middle line:84% Now, that doesn't mean that the surface water PCO2 00:22:52.060 --> 00:22:54.800 align:middle line:84% scope will be at atmospheric equilibrium 00:22:54.800 --> 00:22:57.940 align:middle line:84% because there's all sorts of other factors. 00:22:57.940 --> 00:23:11.940 align:middle line:84% In addition to gas exchange, you have biology and circulation. 00:23:11.940 --> 00:23:15.900 align:middle line:84% So the biology, the important factors 00:23:15.900 --> 00:23:20.560 align:middle line:84% are the net community production. 00:23:20.560 --> 00:23:26.540 align:middle line:90% 00:23:26.540 --> 00:23:30.620 align:middle line:84% Remember, that's the conversion of CO2 00:23:30.620 --> 00:23:41.300 align:middle line:84% plus water into C organic plus O2. 00:23:41.300 --> 00:23:47.180 align:middle line:84% And when you have a net, either a net autotrophic system, which 00:23:47.180 --> 00:23:51.500 align:middle line:84% would drive it this way, or a net heterotrophic system, which 00:23:51.500 --> 00:23:54.900 align:middle line:84% would drive the system back the other way, 00:23:54.900 --> 00:24:00.140 align:middle line:84% you actually have a net removal of carbon. 00:24:00.140 --> 00:24:02.240 align:middle line:84% One of the things people sometimes confuse, 00:24:02.240 --> 00:24:05.180 align:middle line:84% and it gets confused in the literature a lot, is they-- 00:24:05.180 --> 00:24:09.140 align:middle line:84% and this is a really important thing 00:24:09.140 --> 00:24:12.180 align:middle line:84% to keep in mind-- is they confuse net community 00:24:12.180 --> 00:24:21.500 align:middle line:84% production, which is the net reaction of the conversion 00:24:21.500 --> 00:24:25.540 align:middle line:84% of inorganic carbon to organic carbon, 00:24:25.540 --> 00:24:28.900 align:middle line:84% they confuse that with primary production, which 00:24:28.900 --> 00:24:32.580 align:middle line:84% is primary production is just the uptake by CO2 00:24:32.580 --> 00:24:35.060 align:middle line:90% by the autotrophs. 00:24:35.060 --> 00:24:43.540 align:middle line:84% So there can be a huge loop where you have a big-- 00:24:43.540 --> 00:24:48.220 align:middle line:84% so this would be, say, primary production. 00:24:48.220 --> 00:24:51.300 align:middle line:84% You can have a lot of primary production going on. 00:24:51.300 --> 00:24:54.380 align:middle line:84% But as long as all that organic carbon is remineralized 00:24:54.380 --> 00:24:59.220 align:middle line:84% or respired back and there's no build up or export 00:24:59.220 --> 00:25:04.152 align:middle line:84% of organic matter, then there's no net community production. 00:25:04.152 --> 00:25:05.860 align:middle line:84% And it's only when you have net community 00:25:05.860 --> 00:25:18.860 align:middle line:84% production that you can drive DOC and particulate export. 00:25:18.860 --> 00:25:27.460 align:middle line:84% So this is probably one of the big differences between looking 00:25:27.460 --> 00:25:29.660 align:middle line:84% at the world as a biologist versus looking 00:25:29.660 --> 00:25:32.220 align:middle line:90% at the world as a geochemist. 00:25:32.220 --> 00:25:35.140 align:middle line:84% At some fundamental level, geochemists 00:25:35.140 --> 00:25:37.660 align:middle line:84% are really interested in net community production 00:25:37.660 --> 00:25:40.580 align:middle line:84% because it's that net transfer of organic matter 00:25:40.580 --> 00:25:43.160 align:middle line:84% that then does all the things in the deep ocean. 00:25:43.160 --> 00:25:45.860 align:middle line:84% It changes the DIC distributions, 00:25:45.860 --> 00:25:49.820 align:middle line:84% oxygen distributions, nutrients, anything 00:25:49.820 --> 00:25:53.220 align:middle line:84% you're interested like that, where they might not 00:25:53.220 --> 00:25:56.700 align:middle line:84% be as interested in the exact cycling of the rates 00:25:56.700 --> 00:25:57.960 align:middle line:90% of primary production. 00:25:57.960 --> 00:26:04.020 align:middle line:90% 00:26:04.020 --> 00:26:07.100 align:middle line:84% So where I was going with this is-- 00:26:07.100 --> 00:26:09.435 align:middle line:84% going back to Caitlin's question, going off it, 00:26:09.435 --> 00:26:11.060 align:middle line:84% but a little bit of a tangent, but this 00:26:11.060 --> 00:26:14.020 align:middle line:90% is kind of a good review-- 00:26:14.020 --> 00:26:19.240 align:middle line:84% the things that alter-- you've got gas exchange 00:26:19.240 --> 00:26:24.860 align:middle line:84% that's trying to reset surface water PCO2s back 00:26:24.860 --> 00:26:27.180 align:middle line:90% towards atmospheric equilibrium. 00:26:27.180 --> 00:26:29.740 align:middle line:84% You have biology, which, for the most part, 00:26:29.740 --> 00:26:32.120 align:middle line:90% is trying to draw down PCO2. 00:26:32.120 --> 00:26:35.620 align:middle line:84% It's trying to take up CO2 and form it into organic matter 00:26:35.620 --> 00:26:36.900 align:middle line:90% and export it. 00:26:36.900 --> 00:26:43.380 align:middle line:84% And then you have upwelling and mixing, 00:26:43.380 --> 00:26:50.120 align:middle line:84% which bring up high DIC and high-nutrient waters. 00:26:50.120 --> 00:26:52.940 align:middle line:90% 00:26:52.940 --> 00:26:56.140 align:middle line:84% And so the PCO2 at any spot is going 00:26:56.140 --> 00:27:01.980 align:middle line:84% to depend upon, excuse me, the balance between the circulation 00:27:01.980 --> 00:27:05.100 align:middle line:84% effects, which are working on these biologically 00:27:05.100 --> 00:27:12.140 align:middle line:84% driven gradients, and the local biological effect, biology. 00:27:12.140 --> 00:27:16.760 align:middle line:84% The timescales for this are comparable to gas exchange. 00:27:16.760 --> 00:27:20.820 align:middle line:84% And so that's why you see, for example, on a seasonal cycle, 00:27:20.820 --> 00:27:28.060 align:middle line:84% you see large changes in CO2 and DIC 00:27:28.060 --> 00:27:31.140 align:middle line:84% because the circulation, the biology, and the gas exchange 00:27:31.140 --> 00:27:33.985 align:middle line:84% are all kind of working on comparable timescales. 00:27:33.985 --> 00:27:35.860 align:middle line:84% If you remember the homework assignment where 00:27:35.860 --> 00:27:38.140 align:middle line:90% we looked at the Brooks et al. 00:27:38.140 --> 00:27:41.740 align:middle line:84% analysis for the Hawaii Ocean Time-series, 00:27:41.740 --> 00:27:44.380 align:middle line:84% where we were looking at the thermal effects on PCO2 00:27:44.380 --> 00:27:49.020 align:middle line:84% and the biological effects on DIC, that's that seasonal cycle. 00:27:49.020 --> 00:27:50.840 align:middle line:84% That's why you get a nice seasonal cycle 00:27:50.840 --> 00:27:55.620 align:middle line:84% because they're all kind of interacting on that timescale. 00:27:55.620 --> 00:28:03.860 align:middle line:84% On longer timescales, the warm thermocline 00:28:03.860 --> 00:28:07.300 align:middle line:84% really depends upon-- you've got a mix layer, which 00:28:07.300 --> 00:28:11.880 align:middle line:84% I can't really draw because I didn't do a big enough scale, 00:28:11.880 --> 00:28:13.660 align:middle line:84% so that would be your mixed layer. 00:28:13.660 --> 00:28:15.560 align:middle line:84% Then you have that warm thermocline. 00:28:15.560 --> 00:28:22.340 align:middle line:84% Remember, this is down to about, say, 1000 meters 00:28:22.340 --> 00:28:26.100 align:middle line:90% in the tropics and subtropics. 00:28:26.100 --> 00:28:31.100 align:middle line:84% And we looked at, for example, tritium and Freons and helium, 00:28:31.100 --> 00:28:33.060 align:middle line:84% and the time scales for ventilation 00:28:33.060 --> 00:28:36.060 align:middle line:84% for this box, the warm thermocline, 00:28:36.060 --> 00:28:44.660 align:middle line:84% are on, say, 10 to 50 years, a few-decades time. 00:28:44.660 --> 00:28:51.580 align:middle line:84% And so if you had a perturbation in the ocean or a perturbation 00:28:51.580 --> 00:28:59.260 align:middle line:84% in the atmosphere, you would start 00:28:59.260 --> 00:29:03.820 align:middle line:84% to see the response-- let's say you increased atmospheric CO2. 00:29:03.820 --> 00:29:07.620 align:middle line:84% The warm thermocline would start to fill up with CO2 00:29:07.620 --> 00:29:11.420 align:middle line:90% on the order of a few decades. 00:29:11.420 --> 00:29:14.660 align:middle line:84% And that's what we see now with the anthropogenic CO2 00:29:14.660 --> 00:29:17.060 align:middle line:84% is most of the anthropogenic CO2 is caught 00:29:17.060 --> 00:29:19.260 align:middle line:84% in the upper half-- most of it's in the upper half 00:29:19.260 --> 00:29:21.500 align:middle line:90% kilometer or so. 00:29:21.500 --> 00:29:24.540 align:middle line:84% And that's because the gas exchange 00:29:24.540 --> 00:29:26.340 align:middle line:90% rate is no longer limiting. 00:29:26.340 --> 00:29:31.700 align:middle line:84% The gas exchange rate is able to adjust fairly quickly 00:29:31.700 --> 00:29:35.940 align:middle line:84% on the order of a year, couple of years. 00:29:35.940 --> 00:29:37.700 align:middle line:84% And then the rate-limiting step is 00:29:37.700 --> 00:29:40.500 align:middle line:84% circulation of that water into the interior. 00:29:40.500 --> 00:29:45.100 align:middle line:84% And so in the warm thermocline, it's order of 10 to 50 years. 00:29:45.100 --> 00:29:54.440 align:middle line:84% In the deep box, excuse me, the deep box, remember, 00:29:54.440 --> 00:29:56.800 align:middle line:84% is ventilated by sinking in the polls, 00:29:56.800 --> 00:29:59.740 align:middle line:84% so sinking in the Southern Ocean of Antarctic bottom water 00:29:59.740 --> 00:30:02.380 align:middle line:84% and sinking of North Atlantic deep water. 00:30:02.380 --> 00:30:07.040 align:middle line:84% And the timescales are hundreds to thousands of years. 00:30:07.040 --> 00:30:11.260 align:middle line:90% 00:30:11.260 --> 00:30:13.760 align:middle line:84% Now, there are a couple of longer timescales, 00:30:13.760 --> 00:30:19.300 align:middle line:84% and I'm surprised no one has asked the really fun question 00:30:19.300 --> 00:30:21.380 align:middle line:84% in the Sigman and Boyle problem, which 00:30:21.380 --> 00:30:24.220 align:middle line:84% is, let's go through the whole calcium carbonate 00:30:24.220 --> 00:30:27.353 align:middle line:90% cycle in detail. 00:30:27.353 --> 00:30:29.520 align:middle line:84% STUDENT: Someone asked that yesterday, so feel free. 00:30:29.520 --> 00:30:30.940 align:middle line:90% [LAUGHING] 00:30:30.940 --> 00:30:32.780 align:middle line:90% 00:30:32.780 --> 00:30:37.180 align:middle line:84% SCOTT DONEY: So the basic argument-- 00:30:37.180 --> 00:30:39.860 align:middle line:84% OK, so the ocean circulation gives you 00:30:39.860 --> 00:30:44.940 align:middle line:84% timescales of the deep ocean is hundreds to thousands of years. 00:30:44.940 --> 00:30:50.780 align:middle line:84% You have an additional timescale, 00:30:50.780 --> 00:30:54.740 align:middle line:84% which is the calcium carbonate timescale, 00:30:54.740 --> 00:31:01.977 align:middle line:84% which is more like order of 5,000 years, 00:31:01.977 --> 00:31:02.810 align:middle line:90% something like that. 00:31:02.810 --> 00:31:07.150 align:middle line:84% It's 2,000 to 5,000, depends upon who does the calculations 00:31:07.150 --> 00:31:11.270 align:middle line:90% or the exact usage. 00:31:11.270 --> 00:31:13.630 align:middle line:84% And then, of course, longer time frame-- 00:31:13.630 --> 00:31:16.750 align:middle line:84% if you remember back to Deedee's lecture, what 00:31:16.750 --> 00:31:20.230 align:middle line:84% are the longer timescales for the carbon system? 00:31:20.230 --> 00:31:22.610 align:middle line:84% What controls the longer the longer timescales, 00:31:22.610 --> 00:31:23.742 align:middle line:90% order of a million years? 00:31:23.742 --> 00:31:24.950 align:middle line:90% STUDENT: Silicate weathering. 00:31:24.950 --> 00:31:30.330 align:middle line:84% SCOTT DONEY: Yeah, so you'd have silicate-CO2 interactions, 00:31:30.330 --> 00:31:37.530 align:middle line:84% weathering, volcanism on the order 10 to the 6 years. 00:31:37.530 --> 00:31:40.710 align:middle line:90% 00:31:40.710 --> 00:31:43.870 align:middle line:84% And so what they've done-- and this is classic-- 00:31:43.870 --> 00:31:48.990 align:middle line:84% is they've said, OK, we are interested in the timescales 00:31:48.990 --> 00:31:51.370 align:middle line:90% of something like-- 00:31:51.370 --> 00:31:58.950 align:middle line:84% they're interested on timescales of 5,000 to say 100,000 years. 00:31:58.950 --> 00:32:03.590 align:middle line:84% So they're going to ignore mixing within the ocean, 00:32:03.590 --> 00:32:05.030 align:middle line:84% so they're basically saying, well, 00:32:05.030 --> 00:32:06.390 align:middle line:90% the ocean is just well, mixed. 00:32:06.390 --> 00:32:08.230 align:middle line:84% We don't need to really worry about-- 00:32:08.230 --> 00:32:12.415 align:middle line:84% we may need to worry about redistribution of properties, 00:32:12.415 --> 00:32:14.790 align:middle line:84% but we don't need to worry about the kinetics of how long 00:32:14.790 --> 00:32:18.730 align:middle line:84% it takes for the ocean to mix or the thermocline to ventilate 00:32:18.730 --> 00:32:21.150 align:middle line:84% or the mix layer to come to equilibrium. 00:32:21.150 --> 00:32:23.790 align:middle line:84% So they're going to ignore all the short-term processes 00:32:23.790 --> 00:32:25.498 align:middle line:84% because they're going to say, well, those 00:32:25.498 --> 00:32:28.610 align:middle line:90% are all in quasi steady state. 00:32:28.610 --> 00:32:32.390 align:middle line:84% And they'll adjust to whatever new base state we have. 00:32:32.390 --> 00:32:37.390 align:middle line:84% And then they're going to ignore the really long time scale-- 00:32:37.390 --> 00:32:42.230 align:middle line:84% the real long time scale processes like silicate and CO2 00:32:42.230 --> 00:32:43.110 align:middle line:90% weathering. 00:32:43.110 --> 00:32:46.050 align:middle line:84% They'll say, well, over the timescale that we're interested, 00:32:46.050 --> 00:32:51.070 align:middle line:84% we're going to assume that those are constant and can't really 00:32:51.070 --> 00:32:52.750 align:middle line:90% affect our system. 00:32:52.750 --> 00:32:54.470 align:middle line:84% These are the same sort of arguments 00:32:54.470 --> 00:32:56.950 align:middle line:84% we made, if you remember, very back at the beginning 00:32:56.950 --> 00:33:00.030 align:middle line:84% of the semester when we were talking about, 00:33:00.030 --> 00:33:06.910 align:middle line:84% why is the sodium concentration in the ocean proportional 00:33:06.910 --> 00:33:08.190 align:middle line:90% to salinity? 00:33:08.190 --> 00:33:10.270 align:middle line:84% Well, it's because the timescales for sodium 00:33:10.270 --> 00:33:14.150 align:middle line:84% are so long that they're much longer than the ocean turnover 00:33:14.150 --> 00:33:15.830 align:middle line:90% time. 00:33:15.830 --> 00:33:19.207 align:middle line:84% So it all does kind of fit together eventually. 00:33:19.207 --> 00:33:21.290 align:middle line:84% STUDENT: Can I ask you a question on that, though? 00:33:21.290 --> 00:33:21.690 align:middle line:90% I mean-- 00:33:21.690 --> 00:33:22.440 align:middle line:90% SCOTT DONEY: Sure. 00:33:22.440 --> 00:33:25.190 align:middle line:84% STUDENT: How does moving glaciers and grinding up rock 00:33:25.190 --> 00:33:27.150 align:middle line:84% and really exposing maximum surface 00:33:27.150 --> 00:33:29.670 align:middle line:84% area of rock affecting the timescale 00:33:29.670 --> 00:33:31.250 align:middle line:84% of silicate weathering, for example? 00:33:31.250 --> 00:33:34.790 align:middle line:84% I mean, I would imagine that it can move it from 100,000 years 00:33:34.790 --> 00:33:37.410 align:middle line:84% to, maybe, you're noticing something on 10,000 years, 00:33:37.410 --> 00:33:38.770 align:middle line:90% which is really relevant. 00:33:38.770 --> 00:33:42.150 align:middle line:90% 00:33:42.150 --> 00:33:46.310 align:middle line:84% SCOTT DONEY: There's a very interesting hypothesis of why-- 00:33:46.310 --> 00:33:53.910 align:middle line:84% what I didn't show here, if we go back to this, whoops, 00:33:53.910 --> 00:33:58.250 align:middle line:90% this is the last 450,000 years. 00:33:58.250 --> 00:34:01.870 align:middle line:84% We now have ice cores going back to about 800,000 years. 00:34:01.870 --> 00:34:07.630 align:middle line:84% Beyond that, we have the paleo record and paleo reconstructions 00:34:07.630 --> 00:34:09.870 align:middle line:90% of atmospheric CO2. 00:34:09.870 --> 00:34:12.550 align:middle line:84% If you go back about four million years ago, 00:34:12.550 --> 00:34:14.469 align:middle line:84% the paleo record, which is based on things 00:34:14.469 --> 00:34:18.230 align:middle line:84% like C13 isotopic signatures, suggests 00:34:18.230 --> 00:34:22.030 align:middle line:84% that, in Earth's history, where we think, 00:34:22.030 --> 00:34:24.690 align:middle line:84% the planet was quite warm, there was a lot of CO2 in the air, 00:34:24.690 --> 00:34:28.790 align:middle line:84% you think giant big swamps and dinosaurs and all sorts 00:34:28.790 --> 00:34:34.270 align:middle line:84% of stuff, crocodiles living in Antarctica, 00:34:34.270 --> 00:34:39.950 align:middle line:84% one of the hypotheses for why CO2 is as low now as it is 00:34:39.950 --> 00:34:45.469 align:middle line:84% is that, when the Indian subcontinent slammed into Asia, 00:34:45.469 --> 00:34:48.070 align:middle line:84% it started to uplift the Himalayas. 00:34:48.070 --> 00:34:51.590 align:middle line:84% And when you uplift land, you actually 00:34:51.590 --> 00:34:55.190 align:middle line:84% dramatically increase weathering rates 00:34:55.190 --> 00:34:57.950 align:middle line:90% because, essentially, you have-- 00:34:57.950 --> 00:35:04.350 align:middle line:84% well, steep slopes erode much faster than shallow slopes. 00:35:04.350 --> 00:35:06.190 align:middle line:84% So you keep having uplift, and you're 00:35:06.190 --> 00:35:07.830 align:middle line:90% exposing more and more rock. 00:35:07.830 --> 00:35:11.390 align:middle line:84% And so one of the arguments is that the uplift of the Tibetan 00:35:11.390 --> 00:35:15.030 align:middle line:84% plateau has actually led to a long-term drawdown 00:35:15.030 --> 00:35:17.550 align:middle line:84% in atmospheric CO2 because you've 00:35:17.550 --> 00:35:18.890 align:middle line:90% enhanced the weathering rate. 00:35:18.890 --> 00:35:24.430 align:middle line:84% You've exposed more fresh rock because the CO2 is taken up 00:35:24.430 --> 00:35:27.550 align:middle line:84% in the chemical weathering reaction. 00:35:27.550 --> 00:35:34.070 align:middle line:84% For the glacial-interglacial cycles part of it-- 00:35:34.070 --> 00:35:36.430 align:middle line:84% one of the reasons why people don't look at that as much 00:35:36.430 --> 00:35:39.390 align:middle line:84% is that a lot of the glacier weathering 00:35:39.390 --> 00:35:41.470 align:middle line:90% is physical, not chemical. 00:35:41.470 --> 00:35:45.690 align:middle line:84% So it basically grinds stuff up, but it dumps it into the ocean, 00:35:45.690 --> 00:35:49.670 align:middle line:90% as in-- 00:35:49.670 --> 00:35:52.510 align:middle line:84% it's still in fairly large particles. 00:35:52.510 --> 00:35:54.470 align:middle line:84% And it's not clear that the chemical weathering 00:35:54.470 --> 00:35:57.150 align:middle line:90% rate has gone up dramatically. 00:35:57.150 --> 00:35:59.510 align:middle line:84% The other argument is that even if you-- 00:35:59.510 --> 00:36:02.630 align:middle line:84% let's say you had a million-year time scale, 00:36:02.630 --> 00:36:08.690 align:middle line:84% even if you doubled the rate of weathering over, say, 00:36:08.690 --> 00:36:12.170 align:middle line:84% a 30,000-year period, it still would be a fairly small 00:36:12.170 --> 00:36:14.670 align:middle line:84% perturbation because you'd be going from a million-year time 00:36:14.670 --> 00:36:17.050 align:middle line:84% scale to a 500,000-year timescale, 00:36:17.050 --> 00:36:23.110 align:middle line:84% but your cycles are going on faster than that. 00:36:23.110 --> 00:36:24.350 align:middle line:90% That's a good question. 00:36:24.350 --> 00:36:27.270 align:middle line:84% STUDENT: So is the timescale for physical weathering longer 00:36:27.270 --> 00:36:29.110 align:middle line:90% than chemical weathering? 00:36:29.110 --> 00:36:30.750 align:middle line:90% Or is that separable? 00:36:30.750 --> 00:36:34.070 align:middle line:84% SCOTT DONEY: Well, if it's physical weathering, if you just 00:36:34.070 --> 00:36:38.630 align:middle line:84% grind it up, you don't use up any CO2, 00:36:38.630 --> 00:36:40.510 align:middle line:84% it's only the chemical weathering process 00:36:40.510 --> 00:36:44.070 align:middle line:90% that's actually using CO2. 00:36:44.070 --> 00:36:48.530 align:middle line:90% It's, do I pour-- 00:36:48.530 --> 00:36:53.070 align:middle line:84% I can take a piece of chalk, and I can take it and put it 00:36:53.070 --> 00:36:56.070 align:middle line:84% into a mortar and pestle, and I can grind it up 00:36:56.070 --> 00:36:59.442 align:middle line:84% into a fine dust, and then I can throw it into the stream, 00:36:59.442 --> 00:37:00.650 align:middle line:90% and it can back to the ocean. 00:37:00.650 --> 00:37:02.290 align:middle line:90% That's physical weathering. 00:37:02.290 --> 00:37:04.910 align:middle line:90% I just grind up the rock. 00:37:04.910 --> 00:37:06.910 align:middle line:90% Or I can pour acid on it. 00:37:06.910 --> 00:37:10.630 align:middle line:84% I could pour carbonic acid on it and let 00:37:10.630 --> 00:37:12.630 align:middle line:90% it dissolve and eat away. 00:37:12.630 --> 00:37:15.770 align:middle line:84% The physical weathering doesn't affect the chemistry where the-- 00:37:15.770 --> 00:37:20.230 align:middle line:84% STUDENT: But just in terms of the rock removal rate, 00:37:20.230 --> 00:37:22.270 align:middle line:90% is there a difference? 00:37:22.270 --> 00:37:24.270 align:middle line:84% SCOTT DONEY: Well, I'm not sure I would pose it 00:37:24.270 --> 00:37:25.890 align:middle line:90% as a difference in time scale. 00:37:25.890 --> 00:37:30.950 align:middle line:84% There are different environments that have chemical-- 00:37:30.950 --> 00:37:34.030 align:middle line:84% weathering occurs more-- chemical weathering 00:37:34.030 --> 00:37:37.310 align:middle line:84% is really enhanced by high temp-- by temperature 00:37:37.310 --> 00:37:40.710 align:middle line:84% and humidity versus physical weathering 00:37:40.710 --> 00:37:44.950 align:middle line:84% is more common in colder environments. 00:37:44.950 --> 00:37:47.790 align:middle line:84% Think ice getting into cracks and splitting rocks open 00:37:47.790 --> 00:37:48.770 align:middle line:90% and things like that. 00:37:48.770 --> 00:37:53.020 align:middle line:90% 00:37:53.020 --> 00:37:56.218 align:middle line:84% Yeah, but I guess I hadn't thought about it in that way. 00:37:56.218 --> 00:37:58.010 align:middle line:84% Yeah, I'd have to ponder that a little bit. 00:37:58.010 --> 00:38:00.230 align:middle line:84% STUDENT: I think they could be equal, 00:38:00.230 --> 00:38:02.397 align:middle line:84% or one could be faster than the other or vice versa, 00:38:02.397 --> 00:38:04.897 align:middle line:84% just depending on where you are and what the conditions are. 00:38:04.897 --> 00:38:06.610 align:middle line:84% SCOTT DONEY: Yeah, and they do interact. 00:38:06.610 --> 00:38:09.270 align:middle line:84% I mean, physical weathering creates more surface area, which 00:38:09.270 --> 00:38:11.190 align:middle line:90% enhances chemical weathering. 00:38:11.190 --> 00:38:14.510 align:middle line:84% Chemical weathering can weaken rocks and enhance 00:38:14.510 --> 00:38:15.530 align:middle line:90% physical weathering. 00:38:15.530 --> 00:38:19.990 align:middle line:90% 00:38:19.990 --> 00:38:23.550 align:middle line:84% So do you guys want to do the calcium carbonate cycle? 00:38:23.550 --> 00:38:25.612 align:middle line:90% Yeah, cool. 00:38:25.612 --> 00:38:28.070 align:middle line:84% STUDENT: One other thing that I got a question on yesterday 00:38:28.070 --> 00:38:30.687 align:middle line:84% and wasn't happy with my answer was-- 00:38:30.687 --> 00:38:32.770 align:middle line:84% SCOTT DONEY: You weren't happy with the questions. 00:38:32.770 --> 00:38:34.170 align:middle line:84% STUDENT: I wasn't happy with the question 00:38:34.170 --> 00:38:35.990 align:middle line:84% because I couldn't answer it very well. 00:38:35.990 --> 00:38:38.515 align:middle line:84% Just the critical depth and the difference 00:38:38.515 --> 00:38:40.390 align:middle line:84% between that and the compensation depth, just 00:38:40.390 --> 00:38:43.910 align:middle line:90% to go back to the-- 00:38:43.910 --> 00:38:48.870 align:middle line:84% SCOTT DONEY: OK, so let's go back you 00:38:48.870 --> 00:38:54.090 align:middle line:90% have calcium carbonate solid. 00:38:54.090 --> 00:38:54.590 align:middle line:90% Oops. 00:38:54.590 --> 00:38:59.950 align:middle line:90% 00:38:59.950 --> 00:39:05.350 align:middle line:84% So with calcium carbonate solid, that goes into calcium 2 00:39:05.350 --> 00:39:10.110 align:middle line:90% plus plus carbonate 2 minus. 00:39:10.110 --> 00:39:17.070 align:middle line:84% And you have some solubility product for that reaction. 00:39:17.070 --> 00:39:21.870 align:middle line:84% And we'll call it an effective solubility product 00:39:21.870 --> 00:39:23.610 align:middle line:90% and not worry about activities. 00:39:23.610 --> 00:39:32.910 align:middle line:90% 00:39:32.910 --> 00:39:37.110 align:middle line:84% And the reason why there's no calcium carbonate solid is 00:39:37.110 --> 00:39:40.590 align:middle line:90% the activity of a solid is 1. 00:39:40.590 --> 00:39:49.350 align:middle line:84% And so the things you need to know about the calcium carbonate 00:39:49.350 --> 00:39:53.610 align:middle line:84% system, we're going to assume, for most intents and purposes, 00:39:53.610 --> 00:39:56.370 align:middle line:84% that calcium is approximately constant. 00:39:56.370 --> 00:39:58.950 align:middle line:84% It does deviate slightly in the upper ocean 00:39:58.950 --> 00:40:01.710 align:middle line:84% when you have a lot of calcium carbonate formation. 00:40:01.710 --> 00:40:04.010 align:middle line:84% And it changes with salinity, obviously, 00:40:04.010 --> 00:40:08.230 align:middle line:84% because it's one of the major salts. 00:40:08.230 --> 00:40:12.910 align:middle line:84% But we're going to primarily focus 00:40:12.910 --> 00:40:17.830 align:middle line:84% in terms of looking at the solubility of calcium carbonate 00:40:17.830 --> 00:40:23.350 align:middle line:84% on the carbonate ion concentration. 00:40:23.350 --> 00:40:32.490 align:middle line:84% Now, there's a couple things we want to look at. 00:40:32.490 --> 00:40:40.310 align:middle line:84% One is Ksp is a function of temperature and pressure. 00:40:40.310 --> 00:40:43.270 align:middle line:84% Does anybody remember which way-- 00:40:43.270 --> 00:40:46.670 align:middle line:84% does calcium carbonate become more soluble or less soluble 00:40:46.670 --> 00:40:48.670 align:middle line:90% as you go down the water column? 00:40:48.670 --> 00:40:49.907 align:middle line:90% STUDENT: More soluble. 00:40:49.907 --> 00:40:51.490 align:middle line:84% SCOTT DONEY: OK, becomes more soluble. 00:40:51.490 --> 00:40:55.510 align:middle line:90% 00:40:55.510 --> 00:40:59.110 align:middle line:84% Increasing pressure and decreasing temperature. 00:40:59.110 --> 00:41:02.550 align:middle line:84% They work in concert, so as you move down the water column, 00:41:02.550 --> 00:41:04.950 align:middle line:84% it gets colder, you get more pressure, 00:41:04.950 --> 00:41:06.810 align:middle line:84% calcium carbonate wants to dissolve. 00:41:06.810 --> 00:41:09.910 align:middle line:90% 00:41:09.910 --> 00:41:12.710 align:middle line:84% We need to know that there's different Ksp's 00:41:12.710 --> 00:41:15.850 align:middle line:90% for calcite and aragonite. 00:41:15.850 --> 00:41:19.110 align:middle line:90% 00:41:19.110 --> 00:41:23.870 align:middle line:84% And so calcite-- or aragonite is more soluble, 00:41:23.870 --> 00:41:26.470 align:middle line:90% is the more soluble form. 00:41:26.470 --> 00:41:27.830 align:middle line:90% And then there's all sorts of-- 00:41:27.830 --> 00:41:30.890 align:middle line:84% Bill went into there's high magnesium, calcium carbonate. 00:41:30.890 --> 00:41:34.190 align:middle line:84% We won't go to that level of detail. 00:41:34.190 --> 00:41:37.830 align:middle line:84% So by the time you get down to the deep ocean, where 00:41:37.830 --> 00:41:43.950 align:middle line:84% the calcium carbonate sediments are, it's almost all calcite. 00:41:43.950 --> 00:41:46.210 align:middle line:84% Aragonite is only getting deposited-- 00:41:46.210 --> 00:41:50.950 align:middle line:84% so this is the deep sea, the deep sea sets. 00:41:50.950 --> 00:41:54.670 align:middle line:84% Aragonite is only getting deposited on shelves. 00:41:54.670 --> 00:41:58.130 align:middle line:84% So for example, coral reefs are aragonitic. 00:41:58.130 --> 00:42:03.110 align:middle line:90% 00:42:03.110 --> 00:42:07.250 align:middle line:84% What about the distribution of carbonate ion? 00:42:07.250 --> 00:42:08.830 align:middle line:84% What do we know about carbonate ion 00:42:08.830 --> 00:42:11.050 align:middle line:84% and how it might vary in the ocean? 00:42:11.050 --> 00:42:13.670 align:middle line:90% 00:42:13.670 --> 00:42:16.290 align:middle line:84% Anybody at MIT want to take a crack at that one? 00:42:16.290 --> 00:42:20.510 align:middle line:90% 00:42:20.510 --> 00:42:22.670 align:middle line:84% STUDENT: This was another question for my citation. 00:42:22.670 --> 00:42:24.230 align:middle line:90% SCOTT DONEY: Oh, good. 00:42:24.230 --> 00:42:27.570 align:middle line:84% So, yeah, come on, somebody just take a guess. 00:42:27.570 --> 00:42:30.110 align:middle line:84% How is carbonate ion going to vary in the ocean? 00:42:30.110 --> 00:42:33.740 align:middle line:84% Or what drives carbonate ion to vary? 00:42:33.740 --> 00:42:35.225 align:middle line:90% STUDENT: pH. 00:42:35.225 --> 00:42:36.710 align:middle line:90% SCOTT DONEY: pH. 00:42:36.710 --> 00:42:38.630 align:middle line:90% Yay, OK. 00:42:38.630 --> 00:42:41.330 align:middle line:90% So what changes pH? 00:42:41.330 --> 00:42:44.195 align:middle line:90% 00:42:44.195 --> 00:42:46.450 align:middle line:90% We should've talked about this. 00:42:46.450 --> 00:42:48.950 align:middle line:84% STUDENT: You're talking about the difference between surface 00:42:48.950 --> 00:42:51.090 align:middle line:84% and deep in the Atlantic and the Pacific, right? 00:42:51.090 --> 00:42:52.310 align:middle line:84% We're not talking about differences 00:42:52.310 --> 00:42:54.830 align:middle line:84% in surface concentration because we talked about both things 00:42:54.830 --> 00:42:55.510 align:middle line:90% yesterday. 00:42:55.510 --> 00:42:57.010 align:middle line:84% SCOTT DONEY: Well, we could do both, 00:42:57.010 --> 00:43:02.990 align:middle line:84% but, yeah, surface to deep, Atlantic to Pacific. 00:43:02.990 --> 00:43:12.910 align:middle line:84% If I were to draw my box ocean, and I have 0 to 6,000, 00:43:12.910 --> 00:43:15.870 align:middle line:90% and I start in the Atlantic-- 00:43:15.870 --> 00:43:22.830 align:middle line:84% the Altanic, the Atlantic, and I go to the North Pacific, 00:43:22.830 --> 00:43:26.910 align:middle line:84% how is it going to change along that path? 00:43:26.910 --> 00:43:30.230 align:middle line:84% STUDENT: It's going to Increase from the Atlantic to Pacific. 00:43:30.230 --> 00:43:34.606 align:middle line:84% SCOTT DONEY: OK, so it's going to be-- 00:43:34.606 --> 00:43:37.860 align:middle line:84% pH is going to be high in the deep North Atlantic, 00:43:37.860 --> 00:43:44.420 align:middle line:84% and it's going to be low in the Pacific, North Pacific. 00:43:44.420 --> 00:43:45.600 align:middle line:90% And why? 00:43:45.600 --> 00:43:46.760 align:middle line:90% STUDENT: Organic matter. 00:43:46.760 --> 00:43:48.718 align:middle line:84% SCOTT DONEY: Yeah, organic matter, respiration, 00:43:48.718 --> 00:43:50.920 align:middle line:90% because of respiration. 00:43:50.920 --> 00:43:54.880 align:middle line:84% And similarly, it's going to be even higher in surface 00:43:54.880 --> 00:43:56.380 align:middle line:90% waters for the most part. 00:43:56.380 --> 00:43:59.680 align:middle line:90% 00:43:59.680 --> 00:44:02.900 align:middle line:84% So as you take surface water and you advect it down, 00:44:02.900 --> 00:44:07.160 align:middle line:84% you add organic matter, you drive the pH down. 00:44:07.160 --> 00:44:12.100 align:middle line:84% Now, what happens when you lower the pH of seawater? 00:44:12.100 --> 00:44:14.800 align:middle line:90% What happens to carbonate ion? 00:44:14.800 --> 00:44:15.760 align:middle line:90% STUDENT: Decreases. 00:44:15.760 --> 00:44:20.920 align:middle line:84% SCOTT DONEY: Right, so this would be the same path 00:44:20.920 --> 00:44:23.060 align:middle line:90% for carbonate ion. 00:44:23.060 --> 00:44:25.220 align:middle line:84% There are temperature overlays to all of this. 00:44:25.220 --> 00:44:27.400 align:middle line:84% So if you looked in surface waters, 00:44:27.400 --> 00:44:30.340 align:middle line:90% there are temperature overlays. 00:44:30.340 --> 00:44:32.480 align:middle line:84% But generally, if you think about-- 00:44:32.480 --> 00:44:36.800 align:middle line:84% if you were thinking about polar surface waters, where there's 00:44:36.800 --> 00:44:39.840 align:middle line:84% no temperature change as it goes down into depth, 00:44:39.840 --> 00:44:41.740 align:middle line:84% it's the organic matter respiration, 00:44:41.740 --> 00:44:49.720 align:middle line:84% so you'd see a higher carbonate ion concentration 00:44:49.720 --> 00:44:50.820 align:middle line:90% in surface waters. 00:44:50.820 --> 00:44:52.280 align:middle line:84% And then as you went down and added 00:44:52.280 --> 00:44:54.920 align:middle line:84% more and more organic matter, you'd drive the system. 00:44:54.920 --> 00:45:01.560 align:middle line:84% Even though, along this path, you're increasing DIC, 00:45:01.560 --> 00:45:05.100 align:middle line:84% you're actually decreasing carbonate ion. 00:45:05.100 --> 00:45:08.440 align:middle line:90% 00:45:08.440 --> 00:45:13.280 align:middle line:84% There's more carbon, but there's less of it in the carbonate ion 00:45:13.280 --> 00:45:13.860 align:middle line:90% form. 00:45:13.860 --> 00:45:16.840 align:middle line:90% 00:45:16.840 --> 00:45:18.000 align:middle line:90% Excuse me. 00:45:18.000 --> 00:45:18.500 align:middle line:90% OK-- 00:45:18.500 --> 00:45:19.625 align:middle line:90% STUDENT: I have a question. 00:45:19.625 --> 00:45:20.640 align:middle line:90% SCOTT DONEY: Sure. 00:45:20.640 --> 00:45:25.280 align:middle line:84% STUDENT: You have the North Atlantic surface waters being 00:45:25.280 --> 00:45:32.240 align:middle line:90% higher pH and the bottom water. 00:45:32.240 --> 00:45:34.220 align:middle line:84% So is that the water is sinking down, 00:45:34.220 --> 00:45:36.460 align:middle line:84% and is it remineralizing the whole time? 00:45:36.460 --> 00:45:40.600 align:middle line:84% And is that why there's a difference between surfaces? 00:45:40.600 --> 00:45:43.680 align:middle line:84% SCOTT DONEY: The change of surface waters to deep waters 00:45:43.680 --> 00:45:47.760 align:middle line:84% isn't going to be huge in the North Atlantic. 00:45:47.760 --> 00:45:49.400 align:middle line:84% But there is some remineralization 00:45:49.400 --> 00:45:50.760 align:middle line:90% in the North Atlantic. 00:45:50.760 --> 00:45:54.200 align:middle line:84% And just in general, the pH of surface waters 00:45:54.200 --> 00:45:57.480 align:middle line:84% typically is higher than the pH of bottom water, 00:45:57.480 --> 00:46:00.760 align:middle line:84% of bottom waters, just that there's that contrast 00:46:00.760 --> 00:46:03.580 align:middle line:90% between surface and deep. 00:46:03.580 --> 00:46:04.080 align:middle line:90% So-- 00:46:04.080 --> 00:46:06.220 align:middle line:84% STUDENT: A temperature effect or just-- 00:46:06.220 --> 00:46:07.240 align:middle line:90% SCOTT DONEY: No, it's-- 00:46:07.240 --> 00:46:10.280 align:middle line:84% STUDENT: --mineralization is occurring at the surface. 00:46:10.280 --> 00:46:12.040 align:middle line:84% SCOTT DONEY: Right at the location 00:46:12.040 --> 00:46:13.840 align:middle line:84% of sinking in the North Atlantic, 00:46:13.840 --> 00:46:16.400 align:middle line:84% everything's going to be fairly homogeneous. 00:46:16.400 --> 00:46:20.440 align:middle line:84% But if you were looking in the middle of the North 00:46:20.440 --> 00:46:22.480 align:middle line:84% Atlantic and the subtropical gyre 00:46:22.480 --> 00:46:26.280 align:middle line:84% and you were comparing it to the bottom water that was underlying 00:46:26.280 --> 00:46:29.080 align:middle line:84% it, you're going to have higher DIC concentrations 00:46:29.080 --> 00:46:31.360 align:middle line:84% in the bottom water than you are in the surface water 00:46:31.360 --> 00:46:34.920 align:middle line:84% because, in the surface water, you've been taking up CO2. 00:46:34.920 --> 00:46:37.620 align:middle line:84% Taking up CO2 to form organic matter, 00:46:37.620 --> 00:46:40.560 align:middle line:90% that's going to increase the pH. 00:46:40.560 --> 00:46:44.760 align:middle line:84% So there will be a surface-to-deep concentration 00:46:44.760 --> 00:46:45.960 align:middle line:90% gradient. 00:46:45.960 --> 00:46:47.440 align:middle line:90% And if you look-- 00:46:47.440 --> 00:46:49.240 align:middle line:84% I think we showed some of these-- 00:46:49.240 --> 00:46:52.120 align:middle line:84% Bill showed some of these plots in class-- 00:46:52.120 --> 00:47:01.200 align:middle line:84% if you look at the carbonate ion concentration with depth, 00:47:01.200 --> 00:47:07.320 align:middle line:84% it tends to do something like that. 00:47:07.320 --> 00:47:10.100 align:middle line:84% So this would be carbonate ion concentration. 00:47:10.100 --> 00:47:14.520 align:middle line:90% 00:47:14.520 --> 00:47:22.380 align:middle line:84% And your, eek, your Ksp's look like that. 00:47:22.380 --> 00:47:31.540 align:middle line:90% 00:47:31.540 --> 00:47:36.280 align:middle line:84% STUDENT: What your C-- what your carbon will be? 00:47:36.280 --> 00:47:42.080 align:middle line:84% SCOTT DONEY: Well, yeah, I mean, yeah, this would be the-- 00:47:42.080 --> 00:47:49.320 align:middle line:84% Well, yeah, this would be CO3 2 minus equilibrium. 00:47:49.320 --> 00:47:53.740 align:middle line:84% Is actually going up because it requires-- it's more soluble. 00:47:53.740 --> 00:47:56.480 align:middle line:84% So you need a higher bottom water 00:47:56.480 --> 00:48:01.640 align:middle line:84% concentration of carbonate ion to stay in saturation. 00:48:01.640 --> 00:48:06.240 align:middle line:90% Does that make sense? 00:48:06.240 --> 00:48:07.460 align:middle line:90% STUDENT: Another question. 00:48:07.460 --> 00:48:09.260 align:middle line:90% SCOTT DONEY: Sure. 00:48:09.260 --> 00:48:12.160 align:middle line:84% STUDENT: I know that temperature is important 00:48:12.160 --> 00:48:15.580 align:middle line:84% when you're talking about the solubility of CO2 00:48:15.580 --> 00:48:18.240 align:middle line:84% aqueous in the surface water, like the drawdown 00:48:18.240 --> 00:48:21.560 align:middle line:84% from the atmosphere, but in looking at general ocean 00:48:21.560 --> 00:48:24.020 align:middle line:84% patterns of the carbonate system, 00:48:24.020 --> 00:48:28.240 align:middle line:84% is that really the only area where temperature is really 00:48:28.240 --> 00:48:30.200 align:middle line:90% a key player? 00:48:30.200 --> 00:48:37.480 align:middle line:84% SCOTT DONEY: Well, I mean, once you get into the deep ocean, 00:48:37.480 --> 00:48:40.220 align:middle line:84% the temperature differences in the deep ocean, 00:48:40.220 --> 00:48:42.520 align:middle line:84% once you get below about 1,000 meters, 00:48:42.520 --> 00:48:44.880 align:middle line:84% you're really talking about fairly small temperature 00:48:44.880 --> 00:48:46.520 align:middle line:90% gradients. 00:48:46.520 --> 00:48:49.180 align:middle line:84% By the time you get to about 1,000 meters, 00:48:49.180 --> 00:48:52.040 align:middle line:84% your temperature's about 4 degrees Celsius, 00:48:52.040 --> 00:48:56.960 align:middle line:84% and bottom waters are between 0 and 2 degrees Celsius. 00:48:56.960 --> 00:49:01.200 align:middle line:84% So once you get below, say, about 1 kilometer, 00:49:01.200 --> 00:49:03.520 align:middle line:84% the temperature gradients are small enough 00:49:03.520 --> 00:49:06.680 align:middle line:84% that other things swamp them out. 00:49:06.680 --> 00:49:10.280 align:middle line:84% In the upper ocean, yeah, there are temperature gradients, 00:49:10.280 --> 00:49:12.800 align:middle line:84% and they are important in the details. 00:49:12.800 --> 00:49:15.000 align:middle line:84% If you were to do this for a living, 00:49:15.000 --> 00:49:17.160 align:middle line:84% you would need to look at temperature 00:49:17.160 --> 00:49:20.280 align:middle line:90% effects on speciation. 00:49:20.280 --> 00:49:22.160 align:middle line:84% In terms of the calcium carbonate 00:49:22.160 --> 00:49:26.040 align:middle line:84% cycle, the main arguments, the biggest one 00:49:26.040 --> 00:49:28.680 align:middle line:84% is the temperature and pressure effects 00:49:28.680 --> 00:49:33.120 align:middle line:84% on carbonate equilibrium, where you do see fairly big changes 00:49:33.120 --> 00:49:36.500 align:middle line:84% in the upper kilometer, and then once you get below a kilometer, 00:49:36.500 --> 00:49:40.120 align:middle line:90% the big changes are pressure. 00:49:40.120 --> 00:49:44.160 align:middle line:84% That make-- I'm dodging the issue because, yeah, 00:49:44.160 --> 00:49:47.740 align:middle line:84% if you wanted to get into the details, all the Ks, 00:49:47.740 --> 00:49:51.423 align:middle line:84% the Ksp's, K1, all of those temperature-- 00:49:51.423 --> 00:49:53.340 align:middle line:84% STUDENT: That's why it gets kind of confusing. 00:49:53.340 --> 00:49:55.680 align:middle line:84% But when we're looking at big-picture trends, 00:49:55.680 --> 00:49:58.360 align:middle line:84% obviously, for carbonate, the Ksp's temperature 00:49:58.360 --> 00:50:00.800 align:middle line:84% is really key and also, in surface waters, 00:50:00.800 --> 00:50:02.640 align:middle line:90% looking at drawdown of CO2. 00:50:02.640 --> 00:50:04.060 align:middle line:84% And for a lot of the other things, 00:50:04.060 --> 00:50:07.320 align:middle line:84% it seems like it's safe to say that temperature 00:50:07.320 --> 00:50:09.960 align:middle line:90% isn't the primary effect. 00:50:09.960 --> 00:50:13.520 align:middle line:84% SCOTT DONEY: For the most part, the Sigman and Boyle 00:50:13.520 --> 00:50:17.040 align:middle line:84% do go through the argument that if you dropped if you dropped 00:50:17.040 --> 00:50:21.320 align:middle line:84% the deep water temperature from, say, 4 degrees to 0 degrees, 00:50:21.320 --> 00:50:25.320 align:middle line:84% you would increase the solubility of CO2 00:50:25.320 --> 00:50:27.920 align:middle line:90% and you would take up some CO2. 00:50:27.920 --> 00:50:32.080 align:middle line:84% So if you had such big dramatic changes, 00:50:32.080 --> 00:50:34.960 align:middle line:84% the deep ocean's is a large reservoir. 00:50:34.960 --> 00:50:38.920 align:middle line:84% If you dropped it by 4 degrees, that would be a big change, 00:50:38.920 --> 00:50:41.640 align:middle line:84% and it would affect CO2 solubility. 00:50:41.640 --> 00:50:45.120 align:middle line:84% But if you were looking in the modern ocean 00:50:45.120 --> 00:50:47.360 align:middle line:84% and looking at the contrast between the deep North 00:50:47.360 --> 00:50:49.520 align:middle line:84% Atlantic and the deep North Pacific, 00:50:49.520 --> 00:50:53.120 align:middle line:84% the temperature change isn't nearly 00:50:53.120 --> 00:50:57.960 align:middle line:84% big enough to drive the kind of changes we see in carbonate ion. 00:50:57.960 --> 00:51:00.740 align:middle line:90% There it is the biological CO2. 00:51:00.740 --> 00:51:03.440 align:middle line:90% 00:51:03.440 --> 00:51:05.137 align:middle line:90% OK, so-- 00:51:05.137 --> 00:51:06.220 align:middle line:90% STUDENT: Another question. 00:51:06.220 --> 00:51:07.880 align:middle line:90% SCOTT DONEY: Oh, sure. 00:51:07.880 --> 00:51:13.280 align:middle line:84% STUDENT: Could you draw the DIC profile on there too. 00:51:13.280 --> 00:51:18.480 align:middle line:84% SCOTT DONEY: So DIC would be low in the surface water, 00:51:18.480 --> 00:51:20.060 align:middle line:90% and it would be high at depth. 00:51:20.060 --> 00:51:23.520 align:middle line:90% 00:51:23.520 --> 00:51:27.400 align:middle line:84% STUDENT: Why does carbonate have a minimum at about a kilometer? 00:51:27.400 --> 00:51:30.680 align:middle line:84% And then Bill Martin showed a plot 00:51:30.680 --> 00:51:33.960 align:middle line:84% that had a minimum in about a kilometer 00:51:33.960 --> 00:51:36.200 align:middle line:84% and then it popped back up again. 00:51:36.200 --> 00:51:38.560 align:middle line:84% SCOTT DONEY: OK, I thought you meant-- 00:51:38.560 --> 00:51:41.120 align:middle line:84% I was like, did I draw a minimum? 00:51:41.120 --> 00:51:45.880 align:middle line:84% Remember where the oxygen minimum is? 00:51:45.880 --> 00:51:49.920 align:middle line:84% The oxygen minimum is about 1,000 meters. 00:51:49.920 --> 00:51:52.980 align:middle line:84% And we've got to back up a minute, 00:51:52.980 --> 00:51:55.000 align:middle line:90% so I'll use some space up here. 00:51:55.000 --> 00:52:06.280 align:middle line:84% The subsurface, DIC, nutrients, oxygen are all 00:52:06.280 --> 00:52:13.400 align:middle line:84% controlled by a combination of organic matter, 00:52:13.400 --> 00:52:16.480 align:middle line:90% remineralization. 00:52:16.480 --> 00:52:20.900 align:middle line:84% And the organic matter remineralization rate. 00:52:20.900 --> 00:52:22.600 align:middle line:84% Remember, the organic matter, if we 00:52:22.600 --> 00:52:26.640 align:middle line:84% looked at the sinking particles from the sediment traps, 00:52:26.640 --> 00:52:29.320 align:middle line:84% tended to be really high at the surface 00:52:29.320 --> 00:52:33.680 align:middle line:84% and then drop off and be pretty flat in the deep water. 00:52:33.680 --> 00:52:36.260 align:middle line:84% So it's the remineralization rate. 00:52:36.260 --> 00:52:40.200 align:middle line:90% So this is the sinking flux. 00:52:40.200 --> 00:52:44.720 align:middle line:84% The remineralization rate is the derivative of that. 00:52:44.720 --> 00:52:48.840 align:middle line:84% So you still have some remineralization rate 00:52:48.840 --> 00:52:53.480 align:middle line:84% through the thermocline, so this is 1 kilometer, but Not 00:52:53.480 --> 00:52:55.680 align:middle line:84% a huge amount of remineralization 00:52:55.680 --> 00:52:56.580 align:middle line:90% in the deep water. 00:52:56.580 --> 00:52:57.997 align:middle line:84% In fact, there are some people who 00:52:57.997 --> 00:53:01.200 align:middle line:84% argue that, in the deep water, most of the remineralization 00:53:01.200 --> 00:53:03.760 align:middle line:84% is actually going on within the sediments 00:53:03.760 --> 00:53:05.880 align:middle line:90% or at the sediment surface. 00:53:05.880 --> 00:53:08.280 align:middle line:84% But in the shallow water column, a lot of it's 00:53:08.280 --> 00:53:12.100 align:middle line:90% going on above 1 kilometer. 00:53:12.100 --> 00:53:15.440 align:middle line:84% A lot of it's going on in the water column. 00:53:15.440 --> 00:53:19.660 align:middle line:84% So you tend to get in some basins an oxygen minimum, 00:53:19.660 --> 00:53:24.900 align:middle line:84% which would then be a nutrient maximum at somewhere about 1,000 00:53:24.900 --> 00:53:26.680 align:middle line:90% meters. 00:53:26.680 --> 00:53:30.560 align:middle line:84% Now, some of that is because that's 00:53:30.560 --> 00:53:35.360 align:middle line:84% a region where local ventilation is relatively slow 00:53:35.360 --> 00:53:39.400 align:middle line:84% and organic remineralization's relatively high. 00:53:39.400 --> 00:53:41.920 align:middle line:84% And some of that is an artifact of the fact 00:53:41.920 --> 00:53:44.000 align:middle line:84% that you're bringing in water masses. 00:53:44.000 --> 00:53:46.600 align:middle line:84% You have lateral advection that's 00:53:46.600 --> 00:53:48.280 align:middle line:84% bringing in water masses that have 00:53:48.280 --> 00:53:54.200 align:middle line:84% different starting properties, and so you could get a maximum 00:53:54.200 --> 00:53:56.040 align:middle line:84% like that if you just happen to be advecting 00:53:56.040 --> 00:53:58.200 align:middle line:84% in an intermediate water mass that has 00:53:58.200 --> 00:54:01.680 align:middle line:90% a different set of properties. 00:54:01.680 --> 00:54:04.820 align:middle line:90% But it is common to see those. 00:54:04.820 --> 00:54:08.000 align:middle line:84% And if you had an oxygen minimum because of organic matter 00:54:08.000 --> 00:54:12.480 align:middle line:84% respiration, you'd expect a carbonate ion-- 00:54:12.480 --> 00:54:13.320 align:middle line:90% excuse me. 00:54:13.320 --> 00:54:15.700 align:middle line:84% You'd expect a carbonate ion minimum 00:54:15.700 --> 00:54:19.520 align:middle line:84% because if you have a lot of organic matter respiration, 00:54:19.520 --> 00:54:24.280 align:middle line:84% you're going to change the pH, and you're 00:54:24.280 --> 00:54:26.300 align:middle line:84% going to change the amount of carbonate ion. 00:54:26.300 --> 00:54:29.200 align:middle line:90% 00:54:29.200 --> 00:54:36.200 align:middle line:84% So if I wanted to, in some places, it looks more like that. 00:54:36.200 --> 00:54:38.060 align:middle line:84% And that would give a corresponding-- 00:54:38.060 --> 00:54:40.960 align:middle line:90% 00:54:40.960 --> 00:54:41.740 align:middle line:90% like that. 00:54:41.740 --> 00:54:47.800 align:middle line:90% 00:54:47.800 --> 00:54:50.380 align:middle line:84% OK I'm going to go to the new page. 00:54:50.380 --> 00:54:58.640 align:middle line:90% 00:54:58.640 --> 00:55:00.480 align:middle line:84% The good news is I don't have to do modeling 00:55:00.480 --> 00:55:01.540 align:middle line:90% classes this afternoon. 00:55:01.540 --> 00:55:06.140 align:middle line:84% So if my voice dies at noon, I'm fine. 00:55:06.140 --> 00:55:11.680 align:middle line:90% 00:55:11.680 --> 00:55:21.560 align:middle line:84% So just to repeat what we had up there, 00:55:21.560 --> 00:55:25.920 align:middle line:84% so this was a vertical profile of carbonate ion 00:55:25.920 --> 00:55:30.560 align:middle line:84% and the saturation carbonate ion. 00:55:30.560 --> 00:55:38.680 align:middle line:84% Now, Bill, in his lecture, defined a bunch of terms. 00:55:38.680 --> 00:55:42.940 align:middle line:84% And these are just they're arbitrary terms, 00:55:42.940 --> 00:55:50.973 align:middle line:84% but it's useful to know because that helps you understand 00:55:50.973 --> 00:55:52.640 align:middle line:84% reading the literature and communicating 00:55:52.640 --> 00:55:56.560 align:middle line:84% with other people who've learned these arcane jargon terms. 00:55:56.560 --> 00:56:00.440 align:middle line:84% So what was it called when the bicarbonate ion concentration 00:56:00.440 --> 00:56:04.960 align:middle line:84% went from being saturated in the shallow water to being under 00:56:04.960 --> 00:56:08.450 align:middle line:90% undersaturated at some depth? 00:56:08.450 --> 00:56:09.850 align:middle line:84% STUDENT: I know that's saturation 00:56:09.850 --> 00:56:13.190 align:middle line:84% SCOTT DONEY: Yeah, so you have a saturation horizon. 00:56:13.190 --> 00:56:22.970 align:middle line:90% 00:56:22.970 --> 00:56:26.170 align:middle line:84% What was it called when-- so saturation horizon 00:56:26.170 --> 00:56:34.950 align:middle line:84% is based solely on bottom water, chemistry, and thermodynamics. 00:56:34.950 --> 00:56:43.610 align:middle line:90% 00:56:43.610 --> 00:56:50.250 align:middle line:84% And the argument is, well, above the saturation horizon, 00:56:50.250 --> 00:56:52.850 align:middle line:90% you should-- 00:56:52.850 --> 00:56:55.790 align:middle line:90% all the calcium carbonate-- 00:56:55.790 --> 00:56:57.610 align:middle line:84% the water's supersaturated with respect 00:56:57.610 --> 00:56:59.690 align:middle line:84% to calcium carbonate, all the calcium 00:56:59.690 --> 00:57:01.970 align:middle line:84% carbonate that hits the sea floor should 00:57:01.970 --> 00:57:04.510 align:middle line:90% be buried with no degradation. 00:57:04.510 --> 00:57:08.050 align:middle line:84% Now, there's a caveat which we'll get back to in a minute. 00:57:08.050 --> 00:57:11.050 align:middle line:84% Below that depth, you can start to have 00:57:11.050 --> 00:57:15.210 align:middle line:84% influence of remineralization because the water is 00:57:15.210 --> 00:57:17.370 align:middle line:90% undersaturated. 00:57:17.370 --> 00:57:19.790 align:middle line:84% So the next one is the lysocline. 00:57:19.790 --> 00:57:22.570 align:middle line:90% 00:57:22.570 --> 00:57:24.950 align:middle line:84% And that was just the depth where what? 00:57:24.950 --> 00:57:27.715 align:middle line:90% 00:57:27.715 --> 00:57:32.627 align:middle line:84% STUDENT: You have sharp change in the [INAUDIBLE] floor. 00:57:32.627 --> 00:57:34.210 align:middle line:84% SCOTT DONEY: Yeah, well, the lysocline 00:57:34.210 --> 00:57:35.690 align:middle line:84% is basically where you could start 00:57:35.690 --> 00:57:43.810 align:middle line:84% to see a decrease in the calcium carbonate 00:57:43.810 --> 00:57:46.290 align:middle line:90% percent in the sediments. 00:57:46.290 --> 00:57:49.130 align:middle line:84% Another way that people define the calcium-- 00:57:49.130 --> 00:57:52.690 align:middle line:84% or the lysocline is they actually look in the sediments 00:57:52.690 --> 00:57:56.890 align:middle line:84% to see if they-- the forams have very pretty 00:57:56.890 --> 00:57:59.570 align:middle line:84% little shapes and their little shells, 00:57:59.570 --> 00:58:03.690 align:middle line:84% and you can spend a lifetime defining species 00:58:03.690 --> 00:58:06.110 align:middle line:84% and genera by looking at-- or genus, 00:58:06.110 --> 00:58:08.530 align:middle line:84% by looking at different shell forms. 00:58:08.530 --> 00:58:11.730 align:middle line:84% Well, if your shells start to look all corroded, 00:58:11.730 --> 00:58:14.510 align:middle line:84% then you're probably below-- that's where the lysocline is. 00:58:14.510 --> 00:58:18.810 align:middle line:84% You can actually see whether the shells show any examples 00:58:18.810 --> 00:58:21.450 align:middle line:90% of pitting or degradation. 00:58:21.450 --> 00:58:24.730 align:middle line:84% And then, finally, there was the calcium carbonate compensation 00:58:24.730 --> 00:58:28.810 align:middle line:84% depth, which is where, basically, all the calcium 00:58:28.810 --> 00:58:29.910 align:middle line:90% carbonate is gone. 00:58:29.910 --> 00:58:31.850 align:middle line:90% It's all remineralized. 00:58:31.850 --> 00:58:37.710 align:middle line:84% So no more calcium carbonate in the sediments. 00:58:37.710 --> 00:58:40.410 align:middle line:90% 00:58:40.410 --> 00:58:45.930 align:middle line:84% And so the classic is if you go along 00:58:45.930 --> 00:58:51.050 align:middle line:84% and you look at a mid-ocean ridge 00:58:51.050 --> 00:58:57.410 align:middle line:84% is you'll get basically a snow line. 00:58:57.410 --> 00:59:00.170 align:middle line:84% Calcium carbonate sediments are white. 00:59:00.170 --> 00:59:02.170 align:middle line:84% You basically get calcium carbonate 00:59:02.170 --> 00:59:04.810 align:middle line:84% at the tops of the ridges, and then, as you go down, 00:59:04.810 --> 00:59:09.370 align:middle line:84% you get no calcium carbonate sediments. 00:59:09.370 --> 00:59:14.970 align:middle line:84% Now, one of the key arguments that Sigman and Boyle discuss 00:59:14.970 --> 00:59:28.290 align:middle line:84% is that we have records of lysocline variations with time. 00:59:28.290 --> 00:59:34.570 align:middle line:84% So this is the CCD, is way down here. 00:59:34.570 --> 00:59:42.210 align:middle line:90% The lysocline-- lyso-- aah. 00:59:42.210 --> 00:59:49.314 align:middle line:84% Lysocline, oh, I can't spell anything tonight. 00:59:49.314 --> 00:59:51.250 align:middle line:84% The lysocline's going to be shallower 00:59:51.250 --> 00:59:53.450 align:middle line:84% than the calcium carbonate, sedimentation-- 00:59:53.450 --> 00:59:57.530 align:middle line:84% or the CCD, that compensation depth. 00:59:57.530 --> 01:00:02.570 align:middle line:84% And so you could imagine that the lysocline might be 01:00:02.570 --> 01:00:04.550 align:middle line:90% very sensitive to bottom water. 01:00:04.550 --> 01:00:08.970 align:middle line:84% If bottom water got more acidic, you'd start to see-- 01:00:08.970 --> 01:00:11.530 align:middle line:84% if bottom water got more acidic, the lysocline 01:00:11.530 --> 01:00:14.410 align:middle line:84% might extend all the way up to the top of the ridge. 01:00:14.410 --> 01:00:16.270 align:middle line:84% And so if you took a set of cores, 01:00:16.270 --> 01:00:20.770 align:middle line:84% If I took cores like here, here, here, here, and here, 01:00:20.770 --> 01:00:25.570 align:middle line:84% and then I looked downcore, so I would have time, 01:00:25.570 --> 01:00:29.330 align:middle line:84% and I would also have depth by making these sediment cores. 01:00:29.330 --> 01:00:32.810 align:middle line:84% I could reconstruct over time how that lysocline depth 01:00:32.810 --> 01:00:34.810 align:middle line:90% has gone up and down. 01:00:34.810 --> 01:00:37.130 align:middle line:84% And that might be a sensitive indicator 01:00:37.130 --> 01:00:44.090 align:middle line:84% for my bottom water, my bottom water calcium carbonate-- 01:00:44.090 --> 01:00:47.450 align:middle line:84% or my bottom water calcium carbonate saturation state 01:00:47.450 --> 01:00:49.630 align:middle line:84% or the bicarbonate ion concentration. 01:00:49.630 --> 01:00:53.930 align:middle line:90% 01:00:53.930 --> 01:00:56.690 align:middle line:90% Caitlin. 01:00:56.690 --> 01:01:00.090 align:middle line:84% STUDENT: I mean, wouldn't kinetic effects also 01:01:00.090 --> 01:01:01.710 align:middle line:90% determine that to some degree? 01:01:01.710 --> 01:01:03.750 align:middle line:84% When you're looking down a sediment core, 01:01:03.750 --> 01:01:06.570 align:middle line:84% what if there were just a whole bunch of coccolithophores 01:01:06.570 --> 01:01:12.450 align:middle line:84% in that spot for some reason at one time, dumping calcium 01:01:12.450 --> 01:01:14.010 align:middle line:90% carbonate down. 01:01:14.010 --> 01:01:18.050 align:middle line:84% Would that be then remineralized in sediments? 01:01:18.050 --> 01:01:20.890 align:middle line:90% Or would it be preserved? 01:01:20.890 --> 01:01:23.270 align:middle line:90% SCOTT DONEY: Well, if you got-- 01:01:23.270 --> 01:01:28.550 align:middle line:90% 01:01:28.550 --> 01:01:31.970 align:middle line:84% and this is where it gets very complicated, and I didn't-- 01:01:31.970 --> 01:01:35.650 align:middle line:90% this paper's now six years old. 01:01:35.650 --> 01:01:38.730 align:middle line:84% And there's been a ongoing discussion 01:01:38.730 --> 01:01:40.450 align:middle line:90% of a lot of these issues. 01:01:40.450 --> 01:01:43.810 align:middle line:84% And there are people-- there was a very nice talk this summer 01:01:43.810 --> 01:01:49.210 align:middle line:84% by Bob Anderson, who argues that maybe we're misinterpreting 01:01:49.210 --> 01:01:51.690 align:middle line:90% the lysocline data. 01:01:51.690 --> 01:01:54.570 align:middle line:84% And it does have to do with the complications 01:01:54.570 --> 01:01:56.750 align:middle line:84% that I don't want to get into too much. 01:01:56.750 --> 01:02:02.630 align:middle line:84% But let's say you had a sediment that did have calcium carbonate. 01:02:02.630 --> 01:02:04.370 align:middle line:84% Now let's say the lysocline dropped 01:02:04.370 --> 01:02:08.090 align:middle line:84% and you deposited some calcium carbonate rain down 01:02:08.090 --> 01:02:09.530 align:middle line:90% and didn't get dissolved. 01:02:09.530 --> 01:02:12.050 align:middle line:84% What happens later on when that sediment is 01:02:12.050 --> 01:02:14.910 align:middle line:84% sitting at the bottom and water chemistry changes? 01:02:14.910 --> 01:02:16.810 align:middle line:90% Does it all go away? 01:02:16.810 --> 01:02:19.170 align:middle line:84% And that leads into a whole series 01:02:19.170 --> 01:02:23.290 align:middle line:84% of arguments that does get into the kinetics and pore water 01:02:23.290 --> 01:02:26.670 align:middle line:84% chemistry and diffusion rates and things like that. 01:02:26.670 --> 01:02:30.610 align:middle line:84% And that, basically, complicates the clean story 01:02:30.610 --> 01:02:33.340 align:middle line:90% that Sigman and Boyle argue. 01:02:33.340 --> 01:02:35.090 align:middle line:84% STUDENT: And I have a feeling you're going 01:02:35.090 --> 01:02:36.392 align:middle line:90% into metabolic dissolution. 01:02:36.392 --> 01:02:38.850 align:middle line:84% SCOTT DONEY: I was going to touch on metabolic dissolution. 01:02:38.850 --> 01:02:43.250 align:middle line:84% STUDENT: And how that affects where the saturation horizon 01:02:43.250 --> 01:02:46.450 align:middle line:84% falls with respect to the lysocline of the CCD. 01:02:46.450 --> 01:02:52.330 align:middle line:84% SCOTT DONEY: OK, typically, the saturation horizon 01:02:52.330 --> 01:02:55.230 align:middle line:84% is based on bottom water concentrations. 01:02:55.230 --> 01:02:58.530 align:middle line:90% 01:02:58.530 --> 01:03:00.410 align:middle line:84% We know that the sinking particles 01:03:00.410 --> 01:03:04.830 align:middle line:84% bring with it both calcium carbonate and organic matter. 01:03:04.830 --> 01:03:08.490 align:middle line:90% 01:03:08.490 --> 01:03:12.170 align:middle line:84% And organic matter, when it decays, is an acid. 01:03:12.170 --> 01:03:14.010 align:middle line:90% It forms carbonic acid. 01:03:14.010 --> 01:03:17.130 align:middle line:90% So if you were looking in-- 01:03:17.130 --> 01:03:19.890 align:middle line:90% let's say we had-- 01:03:19.890 --> 01:03:23.490 align:middle line:90% this is my sediments. 01:03:23.490 --> 01:03:29.970 align:middle line:84% So you have all these little organic matters decaying away. 01:03:29.970 --> 01:03:33.890 align:middle line:84% And when I decay organic matter in the sediments, 01:03:33.890 --> 01:03:38.130 align:middle line:84% I decrease the pH of the pore waters. 01:03:38.130 --> 01:03:40.090 align:middle line:84% And this is happening both in the sediments 01:03:40.090 --> 01:03:43.430 align:middle line:84% and then also right at the sediment water interface, 01:03:43.430 --> 01:03:47.210 align:middle line:84% right in that little fuzzy filmy boundary. 01:03:47.210 --> 01:03:50.330 align:middle line:84% And there were some very nice papers-- 01:03:50.330 --> 01:03:52.210 align:middle line:84% and Bill showed some of these results 01:03:52.210 --> 01:03:55.770 align:middle line:84% where people have gone in with the microelectrodes 01:03:55.770 --> 01:03:57.870 align:middle line:90% and looked at oxygen profiles. 01:03:57.870 --> 01:04:00.890 align:middle line:90% 01:04:00.890 --> 01:04:02.730 align:middle line:84% And from the oxygen profiles, you 01:04:02.730 --> 01:04:04.810 align:middle line:84% can actually see where the organic matter 01:04:04.810 --> 01:04:07.410 align:middle line:90% is being remineralized. 01:04:07.410 --> 01:04:11.250 align:middle line:84% And if there's enough organic matter being remineralized, 01:04:11.250 --> 01:04:15.370 align:middle line:84% it can lower the pH near enough to the surface 01:04:15.370 --> 01:04:17.650 align:middle line:90% that some of the-- 01:04:17.650 --> 01:04:23.450 align:middle line:84% even though the carbonate ion concentration in the bottom 01:04:23.450 --> 01:04:32.550 align:middle line:84% waters might be greater than the corresponding equilibrium-- 01:04:32.550 --> 01:04:35.610 align:middle line:84% so the bottom waters are saturated-- 01:04:35.610 --> 01:04:39.150 align:middle line:84% in the pore waters, in the shallow pore waters-- 01:04:39.150 --> 01:04:41.550 align:middle line:84% and it has to be shallow enough to the surface 01:04:41.550 --> 01:04:45.250 align:middle line:84% so that stuff can actually diffuse, make it back out. 01:04:45.250 --> 01:04:48.350 align:middle line:84% But in the shallow pore waters, it might be reverse. 01:04:48.350 --> 01:04:52.970 align:middle line:90% 01:04:52.970 --> 01:04:56.890 align:middle line:84% Pore water might be less than saturation 01:04:56.890 --> 01:04:59.970 align:middle line:90% because of organic matter decay. 01:04:59.970 --> 01:05:03.850 align:middle line:84% And what that can do is, even though the bottom waters are 01:05:03.850 --> 01:05:08.810 align:middle line:84% supersaturated, you are getting dissolution. 01:05:08.810 --> 01:05:10.510 align:middle line:90% And you would have a flux. 01:05:10.510 --> 01:05:19.330 align:middle line:84% You'd have a dissolution out of DIC 01:05:19.330 --> 01:05:23.450 align:middle line:84% because you'd have this dissolution of calcium 01:05:23.450 --> 01:05:25.770 align:middle line:90% carbonate in the water. 01:05:25.770 --> 01:05:28.090 align:middle line:84% And what would happen is that will-- 01:05:28.090 --> 01:05:32.970 align:middle line:84% the saturation horizon stays the same, 01:05:32.970 --> 01:05:42.910 align:middle line:84% but the lysocline can be shifted up above the saturation horizon. 01:05:42.910 --> 01:05:47.770 align:middle line:90% 01:05:47.770 --> 01:05:51.590 align:middle line:84% OK, I would like to-- we've only got about 15 minutes left. 01:05:51.590 --> 01:05:53.430 align:middle line:90% We've talked a lot about carbon. 01:05:53.430 --> 01:05:56.650 align:middle line:84% I realize the whole world revolves around carbon, 01:05:56.650 --> 01:06:00.330 align:middle line:84% but unfortunately, the class didn't. 01:06:00.330 --> 01:06:05.050 align:middle line:84% And so are there questions outside of-- 01:06:05.050 --> 01:06:08.570 align:middle line:84% this is a nice review for a lot of it, 01:06:08.570 --> 01:06:13.650 align:middle line:84% but it didn't touch on, for example, thorium isotopes or-- 01:06:13.650 --> 01:06:17.910 align:middle line:84% it did touch on nitrogen, the nitrogen cycle a little bit. 01:06:17.910 --> 01:06:26.050 align:middle line:84% But were other questions more broadly about the class 01:06:26.050 --> 01:06:29.090 align:middle line:84% that you have this burning desire to know? 01:06:29.090 --> 01:06:31.770 align:middle line:84% STUDENT: We're having another review on Friday. 01:06:31.770 --> 01:06:33.993 align:middle line:84% SCOTT DONEY: Well, that sounds fun. 01:06:33.993 --> 01:06:35.910 align:middle line:84% STUDENT: Oh, yeah, you don't have to be there. 01:06:35.910 --> 01:06:37.868 align:middle line:84% I'm just saying, we're going to have more time. 01:06:37.868 --> 01:06:39.770 align:middle line:90% You should come. 01:06:39.770 --> 01:06:40.870 align:middle line:90% We can keep you busy. 01:06:40.870 --> 01:06:46.690 align:middle line:90% 01:06:46.690 --> 01:06:49.930 align:middle line:84% STUDENT: So it's not clear to me when 01:06:49.930 --> 01:06:53.330 align:middle line:84% we're talking about the critical depth 01:06:53.330 --> 01:06:55.810 align:middle line:90% how the critical depth versus-- 01:06:55.810 --> 01:06:58.530 align:middle line:84% SCOTT DONEY: OK, critical, which critical depth? 01:06:58.530 --> 01:07:02.170 align:middle line:84% STUDENT: Well, versus mixed layer depths for blooms. 01:07:02.170 --> 01:07:03.590 align:middle line:90% SCOTT DONEY: OK, great. 01:07:03.590 --> 01:07:07.130 align:middle line:90% 01:07:07.130 --> 01:07:10.770 align:middle line:84% STUDENT: I'm having some trouble conceptualizing why you get 01:07:10.770 --> 01:07:12.190 align:middle line:90% a bloom and why you don't. 01:07:12.190 --> 01:07:17.130 align:middle line:90% 01:07:17.130 --> 01:07:22.330 align:middle line:84% SCOTT DONEY: OK, let's ignore depth for a minute 01:07:22.330 --> 01:07:24.970 align:middle line:90% and take out depth. 01:07:24.970 --> 01:07:30.913 align:middle line:84% Let's say you just had a beaker of phytoplankton, 01:07:30.913 --> 01:07:32.330 align:middle line:84% and you had them in your incubator 01:07:32.330 --> 01:07:35.650 align:middle line:84% and you were torturing them, and you started off 01:07:35.650 --> 01:07:39.690 align:middle line:90% by keeping them in the dark. 01:07:39.690 --> 01:07:43.700 align:middle line:84% At some point, as you decrease the light, 01:07:43.700 --> 01:07:54.380 align:middle line:84% the photosynthesis would be less than the basal respiration rate, 01:07:54.380 --> 01:08:01.820 align:middle line:84% and these guys would crash because they can't maintain-- 01:08:01.820 --> 01:08:05.420 align:middle line:90% they can't grow enough. 01:08:05.420 --> 01:08:09.740 align:middle line:84% Their joint program stipend isn't as big as their rent, 01:08:09.740 --> 01:08:11.560 align:middle line:84% and their bank account goes to 0. 01:08:11.560 --> 01:08:20.640 align:middle line:90% 01:08:20.640 --> 01:08:30.020 align:middle line:84% As you increase-- so let's say this is light 01:08:30.020 --> 01:08:34.060 align:middle line:90% and this is p or r. 01:08:34.060 --> 01:08:38.279 align:middle line:90% So let's say r was constant. 01:08:38.279 --> 01:08:44.740 align:middle line:90% 01:08:44.740 --> 01:08:47.660 align:middle line:84% There's a certain amount of respiration that had to go on, 01:08:47.660 --> 01:08:50.500 align:middle line:90% it was very simplistic. 01:08:50.500 --> 01:08:54.060 align:middle line:84% And it might be constant R is a function of, say, carbon 01:08:54.060 --> 01:08:56.939 align:middle line:90% biomass. 01:08:56.939 --> 01:09:02.260 align:middle line:84% So every day, they lost 10% of their body weight 01:09:02.260 --> 01:09:05.700 align:middle line:90% for respiration. 01:09:05.700 --> 01:09:12.720 align:middle line:84% If you plotted photosynthesis rate, it might look like that. 01:09:12.720 --> 01:09:17.500 align:middle line:84% We looked at those PI curves where this was some maximum rate 01:09:17.500 --> 01:09:19.680 align:middle line:90% and this is some initial slope. 01:09:19.680 --> 01:09:22.939 align:middle line:90% 01:09:22.939 --> 01:09:24.920 align:middle line:84% This is alpha of the initial slope. 01:09:24.920 --> 01:09:28.660 align:middle line:90% 01:09:28.660 --> 01:09:32.920 align:middle line:84% All the argument is is there's some critical light level-- 01:09:32.920 --> 01:09:35.939 align:middle line:90% 01:09:35.939 --> 01:09:45.540 align:middle line:84% call it i crit, where until light reaches that point, 01:09:45.540 --> 01:09:49.060 align:middle line:84% the respiration exceeds photosynthesis. 01:09:49.060 --> 01:09:53.580 align:middle line:84% So from this point over that way, so 01:09:53.580 --> 01:09:58.160 align:middle line:84% the growth curve would look like this. 01:09:58.160 --> 01:10:02.000 align:middle line:90% It would be-- this was 0. 01:10:02.000 --> 01:10:04.120 align:middle line:90% This was net growth. 01:10:04.120 --> 01:10:07.780 align:middle line:90% 01:10:07.780 --> 01:10:11.500 align:middle line:84% So it's negative, and it's positive. 01:10:11.500 --> 01:10:16.395 align:middle line:84% And so as the light starts to ramp up, when it's negative, 01:10:16.395 --> 01:10:17.520 align:middle line:90% the net growth is negative. 01:10:17.520 --> 01:10:18.800 align:middle line:90% The system crashes. 01:10:18.800 --> 01:10:22.140 align:middle line:90% 01:10:22.140 --> 01:10:27.420 align:middle line:84% The complication is that there are two things going on 01:10:27.420 --> 01:10:28.860 align:middle line:90% at the ocean surface. 01:10:28.860 --> 01:10:32.840 align:middle line:84% As you go through a seasonal cycle, light is increasing. 01:10:32.840 --> 01:10:36.740 align:middle line:84% So it's just like putting a bottle in an incubator, 01:10:36.740 --> 01:10:40.700 align:middle line:84% but you also have changes in mixed layer depth. 01:10:40.700 --> 01:10:42.680 align:middle line:84% And the reason why that's important-- 01:10:42.680 --> 01:10:46.100 align:middle line:90% 01:10:46.100 --> 01:10:51.400 align:middle line:84% so here's your sea surface is let's say you have-- 01:10:51.400 --> 01:10:58.100 align:middle line:90% 01:10:58.100 --> 01:11:05.140 align:middle line:84% this is your winter temperature profile. 01:11:05.140 --> 01:11:07.700 align:middle line:84% You have a very deep mixed layer depth. 01:11:07.700 --> 01:11:10.140 align:middle line:90% Say you're up off of Iceland. 01:11:10.140 --> 01:11:11.280 align:middle line:90% So this would be z. 01:11:11.280 --> 01:11:16.420 align:middle line:90% 01:11:16.420 --> 01:11:19.700 align:middle line:84% Even though the phytoplankton up at the surface 01:11:19.700 --> 01:11:21.880 align:middle line:84% are seeing relatively high light, 01:11:21.880 --> 01:11:23.900 align:middle line:90% they don't stay there very long. 01:11:23.900 --> 01:11:26.300 align:middle line:84% And so the argument is that you want 01:11:26.300 --> 01:11:34.480 align:middle line:84% to look at the mean light over the mixed layer. 01:11:34.480 --> 01:11:37.660 align:middle line:84% Or alternatively, you can just think of it 01:11:37.660 --> 01:11:40.940 align:middle line:84% as you're going to look at the integrated 01:11:40.940 --> 01:11:48.420 align:middle line:84% production or the integrated net production over the mixed layer. 01:11:48.420 --> 01:11:50.940 align:middle line:84% And it does depend a little bit on how 01:11:50.940 --> 01:11:52.820 align:middle line:90% the phytoplankton respond. 01:11:52.820 --> 01:11:57.340 align:middle line:84% The Sverdrup hypothesis is based on an integrated production. 01:11:57.340 --> 01:12:00.260 align:middle line:84% So you're going to compare the integrated production 01:12:00.260 --> 01:12:03.700 align:middle line:90% to the integrated respiration. 01:12:03.700 --> 01:12:05.580 align:middle line:84% But you're looking at the same basic thing 01:12:05.580 --> 01:12:12.155 align:middle line:84% that if the integrated production's less 01:12:12.155 --> 01:12:13.780 align:middle line:84% than the integrated respiration, you're 01:12:13.780 --> 01:12:15.860 align:middle line:84% going to be in this negative zone. 01:12:15.860 --> 01:12:18.020 align:middle line:84% And then if the integrated production is greater 01:12:18.020 --> 01:12:22.500 align:middle line:84% than the integrated respiration then you can have a bloom. 01:12:22.500 --> 01:12:25.900 align:middle line:84% And the reason why people think there are blooms in the North 01:12:25.900 --> 01:12:28.460 align:middle line:84% Atlantic, one of the original arguments 01:12:28.460 --> 01:12:30.880 align:middle line:84% is that there are lots of nutrients there. 01:12:30.880 --> 01:12:31.920 align:middle line:90% There's lots of iron. 01:12:31.920 --> 01:12:34.820 align:middle line:84% There's nothing else to limit them. 01:12:34.820 --> 01:12:37.520 align:middle line:84% As the mix-- and you have deep winter mix layers. 01:12:37.520 --> 01:12:40.020 align:middle line:84% So you drive the phytoplankton to very low levels 01:12:40.020 --> 01:12:44.700 align:middle line:84% during the winter, but you drive their predators 01:12:44.700 --> 01:12:48.500 align:middle line:84% to even lower levels because their food source basically 01:12:48.500 --> 01:12:49.720 align:middle line:90% sucks during the winter. 01:12:49.720 --> 01:12:52.660 align:middle line:90% There's very low phytoplankton. 01:12:52.660 --> 01:12:59.500 align:middle line:84% And so as the mixed layer shoals, as you start to march up 01:12:59.500 --> 01:13:05.300 align:middle line:84% and you get shallower and shallower and warmer and warmer, 01:13:05.300 --> 01:13:07.540 align:middle line:84% you have all the conditions ready for bloom. 01:13:07.540 --> 01:13:10.940 align:middle line:84% Temperatures are warmer, so growth rates are faster. 01:13:10.940 --> 01:13:13.940 align:middle line:84% You have more solar insolation because it's getting further 01:13:13.940 --> 01:13:17.140 align:middle line:84% into the spring, and the mixed layer is shallower, 01:13:17.140 --> 01:13:21.620 align:middle line:84% so the community is seeing a higher average light level 01:13:21.620 --> 01:13:23.480 align:middle line:90% than it was when mixing is deep. 01:13:23.480 --> 01:13:26.500 align:middle line:90% 01:13:26.500 --> 01:13:31.500 align:middle line:84% And their predators aren't are poised to eat them. 01:13:31.500 --> 01:13:33.940 align:middle line:84% In some place like the North Pacific, 01:13:33.940 --> 01:13:36.880 align:middle line:84% you don't get really deep mixed layers 01:13:36.880 --> 01:13:39.660 align:middle line:84% at least in the Eastern side of the North Pacific, 01:13:39.660 --> 01:13:42.060 align:middle line:84% and you have this iron limitation. 01:13:42.060 --> 01:13:44.440 align:middle line:84% So even when the phytoplankton get enough light, 01:13:44.440 --> 01:13:46.300 align:middle line:90% they can't grow that fast. 01:13:46.300 --> 01:13:49.320 align:middle line:84% And so they can't outpace their predators, 01:13:49.320 --> 01:13:51.760 align:middle line:84% so you don't get the big spring bloom. 01:13:51.760 --> 01:13:55.700 align:middle line:90% 01:13:55.700 --> 01:13:56.840 align:middle line:90% How about from MIT? 01:13:56.840 --> 01:13:59.640 align:middle line:84% Questions of a generic, general sense? 01:13:59.640 --> 01:14:07.060 align:middle line:90% 01:14:07.060 --> 01:14:09.820 align:middle line:90% Nope. 01:14:09.820 --> 01:14:11.555 align:middle line:90% OK. 01:14:11.555 --> 01:14:12.680 align:middle line:90% STUDENT: I have a question. 01:14:12.680 --> 01:14:13.430 align:middle line:90% SCOTT DONEY: Sure. 01:14:13.430 --> 01:14:15.580 align:middle line:90% 01:14:15.580 --> 01:14:19.220 align:middle line:84% STUDENT: I don't understand how the microbial loop is actually 01:14:19.220 --> 01:14:20.180 align:middle line:90% a loop. 01:14:20.180 --> 01:14:22.180 align:middle line:90% STUDENT: Oh, how sad. 01:14:22.180 --> 01:14:25.140 align:middle line:84% SCOTT DONEY: Did you guys just lose power? 01:14:25.140 --> 01:14:27.900 align:middle line:90% STUDENT: No, she was asking-- 01:14:27.900 --> 01:14:28.740 align:middle line:90% STUDENT: It's OK. 01:14:28.740 --> 01:14:30.846 align:middle line:90% Keep going. 01:14:30.846 --> 01:14:32.035 align:middle line:90% [LAUGHING] 01:14:32.035 --> 01:14:33.160 align:middle line:90% SCOTT DONEY: What happened? 01:14:33.160 --> 01:14:35.060 align:middle line:84% STUDENT: A little funny, I don't know. 01:14:35.060 --> 01:14:38.700 align:middle line:84% STUDENT: We were asking a question, but you didn't hear. 01:14:38.700 --> 01:14:40.560 align:middle line:84% Oh, well, the camera changed too. 01:14:40.560 --> 01:14:43.140 align:middle line:84% So you guys always suddenly got very dark, 01:14:43.140 --> 01:14:45.648 align:middle line:90% and your desk got very orange. 01:14:45.648 --> 01:14:47.440 align:middle line:84% SCOTT DONEY: Why don't we do your question. 01:14:47.440 --> 01:14:49.148 align:middle line:84% Then I'll do the microbial loop question. 01:14:49.148 --> 01:14:51.420 align:middle line:90% What was your question? 01:14:51.420 --> 01:14:54.700 align:middle line:84% STUDENT: Why would the partitioning-- 01:14:54.700 --> 01:14:58.460 align:middle line:84% it says that if DIC increases when alkalinity remains 01:14:58.460 --> 01:15:04.140 align:middle line:84% constant, you get more of your DIC pool 01:15:04.140 --> 01:15:07.900 align:middle line:84% as carbonic acid and aqueous co2. 01:15:07.900 --> 01:15:09.300 align:middle line:90% I don't understand. 01:15:09.300 --> 01:15:11.780 align:middle line:84% When Kristen was talking in recitation, 01:15:11.780 --> 01:15:16.400 align:middle line:84% she was saying that the increasing DIC would just 01:15:16.400 --> 01:15:19.560 align:middle line:84% elevate all the concentrations but not change the partitioning. 01:15:19.560 --> 01:15:22.740 align:middle line:90% 01:15:22.740 --> 01:15:24.640 align:middle line:84% STUDENT: Those two things are not-- 01:15:24.640 --> 01:15:27.140 align:middle line:84% they don't-- they're not the same because if you think about 01:15:27.140 --> 01:15:29.418 align:middle line:84% the [? Darren ?] plot, then you just go up higher. 01:15:29.418 --> 01:15:31.460 align:middle line:84% The total amount would increase, but you wouldn't 01:15:31.460 --> 01:15:33.000 align:middle line:90% be moving side to side on it. 01:15:33.000 --> 01:15:34.500 align:middle line:84% SCOTT DONEY: If you want more time-- 01:15:34.500 --> 01:15:36.542 align:middle line:84% we're having some problems with the transmission. 01:15:36.542 --> 01:15:40.260 align:middle line:84% STUDENT: So why would increasing DIC change your partitioning? 01:15:40.260 --> 01:15:43.480 align:middle line:84% Because that's what it's saying in the paper, but Kristen was-- 01:15:43.480 --> 01:15:45.380 align:middle line:84% we were talking about two different CO. 01:15:45.380 --> 01:15:46.340 align:middle line:90% SCOTT DONEY: OK. 01:15:46.340 --> 01:15:47.740 align:middle line:90% STUDENT: CO's constant-- 01:15:47.740 --> 01:15:50.300 align:middle line:84% SCOTT DONEY: Let me give you my answer because I wasn't there 01:15:50.300 --> 01:15:51.780 align:middle line:90% for Kristen's discussion. 01:15:51.780 --> 01:15:53.260 align:middle line:90% Not sure the context. 01:15:53.260 --> 01:15:58.960 align:middle line:90% When you increase DIC, OK. 01:15:58.960 --> 01:16:07.380 align:middle line:84% So when you increase DIC But alkalinity is constant, 01:16:07.380 --> 01:16:10.820 align:middle line:84% the way you do that is you're adding-- 01:16:10.820 --> 01:16:19.100 align:middle line:84% the only way to do that is to add CO2, gas, or carbonic acid. 01:16:19.100 --> 01:16:22.140 align:middle line:84% If you're increasing the DIC, but the alkalinity 01:16:22.140 --> 01:16:24.420 align:middle line:84% is constant because, remember alkalinity 01:16:24.420 --> 01:16:28.900 align:middle line:84% is defined as the sum of or the carbonate alkalinity 01:16:28.900 --> 01:16:33.100 align:middle line:84% is the sum of carbonate-- or bicarbonate ion 01:16:33.100 --> 01:16:38.660 align:middle line:90% plus 2 times carbonate ion. 01:16:38.660 --> 01:16:46.500 align:middle line:90% OK, so the trick is-- 01:16:46.500 --> 01:16:49.260 align:middle line:84% and this is the nonlinearity of the carbonate system that 01:16:49.260 --> 01:16:51.760 align:middle line:90% drives people over the Wall. 01:16:51.760 --> 01:16:57.700 align:middle line:90% 01:16:57.700 --> 01:17:07.980 align:middle line:84% If alkalinity is constant, I have 01:17:07.980 --> 01:17:11.660 align:middle line:90% to maintain this relationship. 01:17:11.660 --> 01:17:15.920 align:middle line:84% So there's a variety of different ways of looking at it. 01:17:15.920 --> 01:17:24.020 align:middle line:84% One is that I'm actually adding an acid. 01:17:24.020 --> 01:17:30.940 align:middle line:84% And that acid, carbonic acid, is going to decrease the pH. 01:17:30.940 --> 01:17:39.400 align:middle line:84% And so I'm going to tend to favor if I have H2CO3 star-- 01:17:39.400 --> 01:17:44.660 align:middle line:90% 01:17:44.660 --> 01:17:50.380 align:middle line:90% bicarbonate and carbonate. 01:17:50.380 --> 01:17:56.100 align:middle line:84% If I decrease the pH, I'm going to tend to push the, reaction-- 01:17:56.100 --> 01:17:57.120 align:middle line:90% a decreased pH. 01:17:57.120 --> 01:18:02.620 align:middle line:84% I'm going to tend to push the reaction in that direction. 01:18:02.620 --> 01:18:05.860 align:middle line:84% And if you remember, there were a set 01:18:05.860 --> 01:18:11.060 align:middle line:84% of equations that control the acid base 01:18:11.060 --> 01:18:15.820 align:middle line:84% equilibrium between these different species. 01:18:15.820 --> 01:18:19.660 align:middle line:84% All of those depended upon pH, and so there's 01:18:19.660 --> 01:18:24.300 align:middle line:84% no way for these the relative fractions of these 01:18:24.300 --> 01:18:27.800 align:middle line:84% to stay the same as you change the pH. 01:18:27.800 --> 01:18:32.460 align:middle line:90% 01:18:32.460 --> 01:18:37.460 align:middle line:84% And remember, Bill drew this nice little diagram 01:18:37.460 --> 01:18:44.860 align:middle line:90% or had drawn where you have-- 01:18:44.860 --> 01:18:48.020 align:middle line:84% as a function of pH, you have bicarbonates 01:18:48.020 --> 01:18:56.620 align:middle line:84% in the middle, carbonate and H2T03 star, 01:18:56.620 --> 01:19:00.260 align:middle line:84% basically, showing that is basically 01:19:00.260 --> 01:19:03.180 align:middle line:84% showing, in graphical form, this relationship that, 01:19:03.180 --> 01:19:07.120 align:middle line:84% as you increase the-- or, excuse me, as you increase protons, 01:19:07.120 --> 01:19:11.240 align:middle line:84% decrease the pH, the speciation tends to shift. 01:19:11.240 --> 01:19:13.820 align:middle line:90% 01:19:13.820 --> 01:19:16.540 align:middle line:84% And basically, the reason it comes down to 01:19:16.540 --> 01:19:22.380 align:middle line:84% is CO2 is the main buffer factor in seawater that's 01:19:22.380 --> 01:19:23.900 align:middle line:90% controlling the pH. 01:19:23.900 --> 01:19:26.420 align:middle line:84% If I were doing this in the laboratory, 01:19:26.420 --> 01:19:31.780 align:middle line:84% I could set up a system that had some other buffer 01:19:31.780 --> 01:19:35.260 align:middle line:84% factor controlling the pH, so imagine a situation where 01:19:35.260 --> 01:19:39.200 align:middle line:84% the pH remained constant, and as I added CO2, 01:19:39.200 --> 01:19:41.340 align:middle line:84% it would be equally split between 01:19:41.340 --> 01:19:43.140 align:middle line:90% these different fractions. 01:19:43.140 --> 01:19:47.480 align:middle line:84% But that's not the chemical setup of seawater. 01:19:47.480 --> 01:19:50.620 align:middle line:90% 01:19:50.620 --> 01:19:52.640 align:middle line:90% Is that-- 01:19:52.640 --> 01:19:56.640 align:middle line:84% STUDENT: Think of more than just that plot and raising DIC, 01:19:56.640 --> 01:20:01.260 align:middle line:84% you have to think about, how you can raise DIC and seawater 01:20:01.260 --> 01:20:04.460 align:middle line:90% without changing alkalinity. 01:20:04.460 --> 01:20:08.180 align:middle line:84% SCOTT DONEY: Well, the obvious way of increasing DIC 01:20:08.180 --> 01:20:09.040 align:middle line:90% without changing-- 01:20:09.040 --> 01:20:13.720 align:middle line:84% I mean, there's a couple ways to increase DIC. 01:20:13.720 --> 01:20:20.790 align:middle line:84% The two obvious ways are the z obvious end members. 01:20:20.790 --> 01:20:28.990 align:middle line:84% I can increase DIC by adding CO2 gas, 01:20:28.990 --> 01:20:33.010 align:middle line:84% and that will not change alkalinity. 01:20:33.010 --> 01:20:36.630 align:middle line:90% 01:20:36.630 --> 01:20:43.110 align:middle line:84% And in that case, like I said, pH goes down, PCO2 goes up, 01:20:43.110 --> 01:20:49.310 align:middle line:90% and carbonate ion goes down. 01:20:49.310 --> 01:20:52.150 align:middle line:84% Sometimes you'll see-- and I think it's actually a little 01:20:52.150 --> 01:20:53.470 align:middle line:90% misleading-- 01:20:53.470 --> 01:20:58.050 align:middle line:84% sometimes you'll see this written as this reaction. 01:20:58.050 --> 01:21:01.590 align:middle line:90% 01:21:01.590 --> 01:21:04.310 align:middle line:84% Sometimes you'll see this written as this reaction. 01:21:04.310 --> 01:21:10.750 align:middle line:84% And people say, oh, well, the CO2 uses up carbonate ions. 01:21:10.750 --> 01:21:12.290 align:middle line:84% I don't like this for two reasons. 01:21:12.290 --> 01:21:15.590 align:middle line:84% One, this is not actually a chemical reaction. 01:21:15.590 --> 01:21:20.230 align:middle line:84% The chemical reaction is the acid base disequilibrium. 01:21:20.230 --> 01:21:22.830 align:middle line:84% And two, it's not actually quantitative. 01:21:22.830 --> 01:21:29.030 align:middle line:84% If you add CO2, it doesn't all get taken up bicarbonate ion 01:21:29.030 --> 01:21:33.750 align:middle line:84% and you know that because that CO2 is actually-- 01:21:33.750 --> 01:21:40.150 align:middle line:84% that CO2 or H2CO3 star actually does increase. 01:21:40.150 --> 01:21:42.150 align:middle line:84% And so this implies that it's all used up, 01:21:42.150 --> 01:21:44.170 align:middle line:84% and it all ends up in bicarbonate, 01:21:44.170 --> 01:21:47.830 align:middle line:84% but you'll see this a lot in textbooks. 01:21:47.830 --> 01:21:50.110 align:middle line:84% The other way to increase-- or another end member 01:21:50.110 --> 01:22:00.490 align:middle line:84% for increasing DIC is by dissolving calcium carbonate. 01:22:00.490 --> 01:22:03.070 align:middle line:90% 01:22:03.070 --> 01:22:13.630 align:middle line:84% And so there you you're really adding carbonate ion. 01:22:13.630 --> 01:22:19.510 align:middle line:84% And when that happens, alkalinity actually 01:22:19.510 --> 01:22:31.970 align:middle line:84% goes up at 2 times DIC because, for each mole of carbonate ion, 01:22:31.970 --> 01:22:35.790 align:middle line:84% you're adding 2 equivalents of alkalinity. 01:22:35.790 --> 01:22:43.950 align:middle line:84% When you do that, then pH actually goes up, PCO2 goes down 01:22:43.950 --> 01:22:49.590 align:middle line:90% and carbonate ion goes up. 01:22:49.590 --> 01:22:52.850 align:middle line:84% And we just happen to have a nice-- 01:22:52.850 --> 01:22:58.550 align:middle line:90% 01:22:58.550 --> 01:23:01.870 align:middle line:84% the Sigman and Boyle paper has a nice plot 01:23:01.870 --> 01:23:05.570 align:middle line:84% of that where they plotted alkalinity and DIC. 01:23:05.570 --> 01:23:11.470 align:middle line:90% 01:23:11.470 --> 01:23:16.950 align:middle line:84% And then, overlaying that, they've contoured PCO2, 01:23:16.950 --> 01:23:19.630 align:middle line:90% and so you have low PCO2 up. 01:23:19.630 --> 01:23:28.590 align:middle line:84% When you have low DIC and high alkalinity, you have low PCO2. 01:23:28.590 --> 01:23:33.350 align:middle line:84% When you have high DIC and low alkalinity, you have high PCO2. 01:23:33.350 --> 01:23:35.110 align:middle line:90% And then they've put arrows-- 01:23:35.110 --> 01:23:40.470 align:middle line:84% for example, if you they've done the reverse rather than adding 01:23:40.470 --> 01:23:45.430 align:middle line:84% organic matter, if they take out organic matter, DIC goes down. 01:23:45.430 --> 01:23:48.350 align:middle line:84% There's a small change in alkalinity because 01:23:48.350 --> 01:23:50.670 align:middle line:90% of the effect of nitrate. 01:23:50.670 --> 01:23:53.510 align:middle line:84% There's a small alkalinity effect, but that's pretty-- 01:23:53.510 --> 01:23:55.670 align:middle line:90% that's second order. 01:23:55.670 --> 01:24:00.390 align:middle line:84% So when you take out organic matter, 01:24:00.390 --> 01:24:04.530 align:middle line:84% DIC drops, alkalinity remains approximately constant. 01:24:04.530 --> 01:24:06.590 align:middle line:90% And PCO2 goes down out. 01:24:06.590 --> 01:24:10.790 align:middle line:90% 01:24:10.790 --> 01:24:14.110 align:middle line:90% For example, when you-- 01:24:14.110 --> 01:24:15.790 align:middle line:90% oh, here. 01:24:15.790 --> 01:24:20.630 align:middle line:84% I can redo it so I can actually draw on it. 01:24:20.630 --> 01:24:22.410 align:middle line:90% I see alkalinity. 01:24:22.410 --> 01:24:25.750 align:middle line:90% 01:24:25.750 --> 01:24:28.210 align:middle line:84% So these are constant lines of PCO2. 01:24:28.210 --> 01:24:34.150 align:middle line:90% 01:24:34.150 --> 01:24:40.350 align:middle line:90% This is low and high PCO2. 01:24:40.350 --> 01:24:43.050 align:middle line:90% This is organic matter input. 01:24:43.050 --> 01:24:47.510 align:middle line:90% 01:24:47.510 --> 01:24:51.190 align:middle line:84% Just what we showed above, you add organic matter, 01:24:51.190 --> 01:24:57.370 align:middle line:84% PCO2 goes up, carbonic acid goes up, alkalinity stays flat. 01:24:57.370 --> 01:25:00.110 align:middle line:90% 01:25:00.110 --> 01:25:05.670 align:middle line:84% The perversity of the CO2 system is 01:25:05.670 --> 01:25:08.750 align:middle line:84% that if you dissolve calcium carbonate 01:25:08.750 --> 01:25:15.390 align:middle line:84% or add calcium carbonate, alkalinity goes up, DIC goes up, 01:25:15.390 --> 01:25:22.070 align:middle line:84% but the slope that 2 times DIC slope is higher, 01:25:22.070 --> 01:25:26.750 align:middle line:84% is a steeper slope than the lines of PCO2 slope. 01:25:26.750 --> 01:25:29.310 align:middle line:84% And so PCO2 actually goes down even 01:25:29.310 --> 01:25:30.570 align:middle line:90% though you're adding carbon. 01:25:30.570 --> 01:25:35.150 align:middle line:90% 01:25:35.150 --> 01:25:37.757 align:middle line:90% Does that help at all? 01:25:37.757 --> 01:25:39.590 align:middle line:84% I feel like I'm starting to get to the point 01:25:39.590 --> 01:25:41.990 align:middle line:84% where I'm arguing in circles a little bit. 01:25:41.990 --> 01:25:44.810 align:middle line:84% STUDENT: That's what happens in this system. 01:25:44.810 --> 01:25:47.330 align:middle line:84% SCOTT DONEY: If anybody wants, I have a little Matlab code. 01:25:47.330 --> 01:25:49.230 align:middle line:84% If you run Matlab, I can give you the code 01:25:49.230 --> 01:25:53.190 align:middle line:84% and you can play with this to your heart's delight. 01:25:53.190 --> 01:25:55.470 align:middle line:84% To convince yourself that this is-- 01:25:55.470 --> 01:25:56.990 align:middle line:84% oh, I didn't see a lot of takers. 01:25:56.990 --> 01:25:57.750 align:middle line:90% [LAUGHING] 01:25:57.750 --> 01:25:59.190 align:middle line:90% STUDENT: It'd be hilarious. 01:25:59.190 --> 01:26:01.190 align:middle line:84% SCOTT DONEY: It'd be hilarious, OK. 01:26:01.190 --> 01:26:02.550 align:middle line:90% It's noon. 01:26:02.550 --> 01:26:04.780 align:middle line:90% I'm going to wrap up.