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 --> 00:00:20.443 align:middle line:90% at ocw.mit.educational. 00:00:20.443 --> 00:00:22.360 align:middle line:84% SCOTT DONEY: There were some questions on-- we 00:00:22.360 --> 00:00:25.180 align:middle line:90% had finished up on Thursday. 00:00:25.180 --> 00:00:27.720 align:middle line:84% We were talking about Sverdrup's critical depth 00:00:27.720 --> 00:00:29.768 align:middle line:90% hypothesis and light. 00:00:29.768 --> 00:00:31.560 align:middle line:84% And I gather from the recitation that there 00:00:31.560 --> 00:00:32.740 align:middle line:90% were some questions on that. 00:00:32.740 --> 00:00:34.800 align:middle line:84% So I wanted to go through it a little bit more 00:00:34.800 --> 00:00:37.800 align:middle line:84% to give you guys a little bit more background on that to help 00:00:37.800 --> 00:00:41.040 align:middle line:90% you with the problem set. 00:00:41.040 --> 00:00:45.960 align:middle line:84% And so the assumptions we're going to make 00:00:45.960 --> 00:00:54.200 align:middle line:84% is that there's some mixed layer-- 00:00:54.200 --> 00:00:57.800 align:middle line:90% so this would be depth. 00:00:57.800 --> 00:01:06.180 align:middle line:84% There's some mixed layer that's being turbulently mixed. 00:01:06.180 --> 00:01:09.820 align:middle line:84% And then below that if this was temperature, 00:01:09.820 --> 00:01:13.340 align:middle line:90% it would drop off like that. 00:01:13.340 --> 00:01:15.480 align:middle line:84% And that within that mixed layer, 00:01:15.480 --> 00:01:19.620 align:middle line:84% you have a phytoplankton community and also 00:01:19.620 --> 00:01:22.860 align:middle line:90% some heterotrophic activity. 00:01:22.860 --> 00:01:26.180 align:middle line:84% And the question was, as the mixed layer 00:01:26.180 --> 00:01:29.620 align:middle line:84% starts to shoal and shallow in the spring, 00:01:29.620 --> 00:01:33.000 align:middle line:84% at what point can the phytoplankton really bloom? 00:01:33.000 --> 00:01:36.420 align:middle line:84% At what point does the light limitation that's 00:01:36.420 --> 00:01:40.340 align:middle line:84% been holding them back all winter get relieved 00:01:40.340 --> 00:01:42.900 align:middle line:84% and you start to see the classic spring bloom that's 00:01:42.900 --> 00:01:46.860 align:middle line:84% a very common occurrence, for example, in the North Atlantic. 00:01:46.860 --> 00:01:50.600 align:middle line:84% So there were a couple of simple equations. 00:01:50.600 --> 00:01:56.100 align:middle line:84% We were going to assume that primary production is going 00:01:56.100 --> 00:02:02.310 align:middle line:84% to be proportional to irradiance so that everywhere 00:02:02.310 --> 00:02:05.670 align:middle line:84% within this mixed layer there would be some phytoplankton. 00:02:05.670 --> 00:02:08.070 align:middle line:84% And at any instance in time they're 00:02:08.070 --> 00:02:11.990 align:middle line:84% going to be seeing an instantaneous light 00:02:11.990 --> 00:02:14.910 align:middle line:84% and that the photosynthesis rate at that depth 00:02:14.910 --> 00:02:18.590 align:middle line:84% would be some constant of proportionality, alpha, 00:02:18.590 --> 00:02:23.750 align:middle line:84% this initial slope, times an irradiance. 00:02:23.750 --> 00:02:27.010 align:middle line:84% Now, eventually, this would saturate and turn over. 00:02:27.010 --> 00:02:30.630 align:middle line:84% But we're going to assume we're on the linear part of the curve. 00:02:30.630 --> 00:02:32.910 align:middle line:84% The second assumption that we're going to make 00:02:32.910 --> 00:02:37.310 align:middle line:84% is that the irradiance at any depth 00:02:37.310 --> 00:02:41.270 align:middle line:84% is simply going to be a surface irradiance 00:02:41.270 --> 00:02:52.470 align:middle line:84% times an exponential function, where k is our attenuation 00:02:52.470 --> 00:02:53.790 align:middle line:90% coefficient. 00:02:53.790 --> 00:02:56.490 align:middle line:90% So k equals attenuation. 00:02:56.490 --> 00:02:59.610 align:middle line:90% 00:02:59.610 --> 00:03:02.450 align:middle line:84% Now, if you look at this equation, what 00:03:02.450 --> 00:03:06.370 align:middle line:84% units does k have to have if it's up in an exponential 00:03:06.370 --> 00:03:09.330 align:middle line:84% like that, where it's e equals minus kz? 00:03:09.330 --> 00:03:12.058 align:middle line:90% 00:03:12.058 --> 00:03:12.874 align:middle line:90% [INAUDIBLE] 00:03:12.874 --> 00:03:13.874 align:middle line:90% AUDIENCE: 1 over meters. 00:03:13.874 --> 00:03:15.874 align:middle line:84% SCOTT DONEY: Has to have one over meters, right? 00:03:15.874 --> 00:03:18.410 align:middle line:90% It has to have 1 over length. 00:03:18.410 --> 00:03:20.710 align:middle line:84% Because otherwise, there would be a dimension up here. 00:03:20.710 --> 00:03:23.610 align:middle line:84% And then you can't take the exponential of a dimension. 00:03:23.610 --> 00:03:27.110 align:middle line:84% So k is going to have units of 1 over meters. 00:03:27.110 --> 00:03:31.170 align:middle line:90% 00:03:31.170 --> 00:03:37.130 align:middle line:84% We're also going to assume that respiration at any depth 00:03:37.130 --> 00:03:42.410 align:middle line:90% is going to be a constant. 00:03:42.410 --> 00:03:44.850 align:middle line:84% And we'll just call it r0 because it's 00:03:44.850 --> 00:03:46.970 align:middle line:84% constant through the mixed layer. 00:03:46.970 --> 00:03:50.950 align:middle line:90% Is everybody with me so far? 00:03:50.950 --> 00:03:52.210 align:middle line:90% OK. 00:03:52.210 --> 00:03:58.360 align:middle line:84% So then we're going to say we want to find the depth, 00:03:58.360 --> 00:04:05.980 align:middle line:90% the critical depth where-- 00:04:05.980 --> 00:04:07.480 align:middle line:90% and we'll call this zcr-- 00:04:07.480 --> 00:04:10.540 align:middle line:90% 00:04:10.540 --> 00:04:18.899 align:middle line:84% where the integrated respiration just equals the integrated 00:04:18.899 --> 00:04:19.839 align:middle line:90% production. 00:04:19.839 --> 00:04:22.347 align:middle line:90% 00:04:22.347 --> 00:04:24.180 align:middle line:84% And that's going to be the depth where we're 00:04:24.180 --> 00:04:32.740 align:middle line:84% going to say when mixed layer is greater than critical depth, 00:04:32.740 --> 00:04:39.500 align:middle line:84% it's light limited, and you get no bloom. 00:04:39.500 --> 00:04:44.620 align:middle line:84% And when mixed layer is less than that depth, 00:04:44.620 --> 00:04:45.600 align:middle line:90% you get a bloom. 00:04:45.600 --> 00:04:54.520 align:middle line:90% 00:04:54.520 --> 00:04:59.360 align:middle line:84% So if you go ahead and do the math, 00:04:59.360 --> 00:05:06.840 align:middle line:84% the integral on the lefthand side is just r0 zcr. 00:05:06.840 --> 00:05:10.980 align:middle line:90% 00:05:10.980 --> 00:05:13.240 align:middle line:84% We're going to integrate from the surface 00:05:13.240 --> 00:05:17.360 align:middle line:90% down to this critical depth. 00:05:17.360 --> 00:05:21.260 align:middle line:84% And since r is constant, it just turns out to be that. 00:05:21.260 --> 00:05:25.120 align:middle line:90% 00:05:25.120 --> 00:05:30.940 align:middle line:84% The other side, we're going to integrate-- 00:05:30.940 --> 00:05:33.520 align:middle line:90% 00:05:33.520 --> 00:05:44.980 align:middle line:84% we'll plug in alpha i0 e to the minus kz dz. 00:05:44.980 --> 00:05:54.770 align:middle line:90% 00:05:54.770 --> 00:05:58.850 align:middle line:84% And if you work this out, you'll get a nonlinear equation 00:05:58.850 --> 00:06:06.930 align:middle line:84% where k [? zcr ?] 1 minus e minus k [? zcr ?] 00:06:06.930 --> 00:06:28.090 align:middle line:84% equals r0 over alpha i0 or r0 over p0, 00:06:28.090 --> 00:06:31.770 align:middle line:84% where we're just going to set p0 to find p0 is equal alpha i0. 00:06:31.770 --> 00:06:36.170 align:middle line:90% 00:06:36.170 --> 00:06:39.850 align:middle line:84% So if you know your surface irradiance and your respiration, 00:06:39.850 --> 00:06:45.730 align:middle line:84% you can go ahead and calculate the critical depth. 00:06:45.730 --> 00:06:47.570 align:middle line:84% AUDIENCE: One more question on that-- 00:06:47.570 --> 00:06:52.590 align:middle line:84% just to clarify, the k par that you give, 00:06:52.590 --> 00:06:54.567 align:middle line:84% you told me yesterday that surface chlorophyll 00:06:54.567 --> 00:06:55.650 align:middle line:90% is what you plug in there. 00:06:55.650 --> 00:06:57.040 align:middle line:84% You don't have to plug in different chlorophyll 00:06:57.040 --> 00:06:57.192 align:middle line:90% [INAUDIBLE] ? 00:06:57.192 --> 00:06:57.984 align:middle line:90% SCOTT DONEY: Right. 00:06:57.984 --> 00:07:04.270 align:middle line:84% The assumption is that the mixed layer is well mixed. 00:07:04.270 --> 00:07:08.290 align:middle line:84% And for most situations, that's a pretty good approximation. 00:07:08.290 --> 00:07:10.790 align:middle line:84% If you actually have a turbulent mixed layer, 00:07:10.790 --> 00:07:16.790 align:middle line:84% the phytoplankton concentration just can't fight it. 00:07:16.790 --> 00:07:19.430 align:middle line:90% It can't grow fast enough. 00:07:19.430 --> 00:07:23.270 align:middle line:84% The turnover time is fast enough it 00:07:23.270 --> 00:07:25.010 align:middle line:90% maintains a homogeneous layer. 00:07:25.010 --> 00:07:27.890 align:middle line:90% 00:07:27.890 --> 00:07:28.390 align:middle line:90% OK? 00:07:28.390 --> 00:07:35.790 align:middle line:90% 00:07:35.790 --> 00:07:37.790 align:middle line:90% OK. 00:07:37.790 --> 00:07:38.370 align:middle line:90% Oops. 00:07:38.370 --> 00:07:39.170 align:middle line:90% On we go. 00:07:39.170 --> 00:07:45.070 align:middle line:90% 00:07:45.070 --> 00:07:48.670 align:middle line:90% Does everybody have that? 00:07:48.670 --> 00:07:53.170 align:middle line:84% So what we were going to do today was-- we did light. 00:07:53.170 --> 00:07:55.610 align:middle line:90% Now we want to look at-- 00:07:55.610 --> 00:07:58.730 align:middle line:90% nutrients is the next one. 00:07:58.730 --> 00:08:05.450 align:middle line:84% And typically, the way nutrient limitation is formulated 00:08:05.450 --> 00:08:07.730 align:middle line:84% is in terms-- of you'll hear it sometimes 00:08:07.730 --> 00:08:14.050 align:middle line:84% called a Monod curve, Michaelis-Menten 00:08:14.050 --> 00:08:15.630 align:middle line:90% from enzyme kinetics. 00:08:15.630 --> 00:08:19.050 align:middle line:90% 00:08:19.050 --> 00:08:21.890 align:middle line:84% It's essentially just a curve that saturates 00:08:21.890 --> 00:08:23.890 align:middle line:90% as you get to high nutrients. 00:08:23.890 --> 00:08:30.930 align:middle line:84% So if you have some uptake of a nutrient plotted 00:08:30.930 --> 00:08:34.870 align:middle line:84% against the nutrient, it's going to look something like this. 00:08:34.870 --> 00:08:41.730 align:middle line:84% There's going to be a period where it's fairly linear. 00:08:41.730 --> 00:08:47.050 align:middle line:84% And then it's going to saturate to some maximum value. 00:08:47.050 --> 00:08:51.360 align:middle line:84% So when you don't have a lot of the nutrient, 00:08:51.360 --> 00:08:54.560 align:middle line:84% it's going to slow the uptake down and slow growth down. 00:08:54.560 --> 00:08:58.140 align:middle line:84% But if you have the nutrient in abundance, it'll just saturate, 00:08:58.140 --> 00:09:00.660 align:middle line:84% and they'll be happy and fine, and they won't 00:09:00.660 --> 00:09:03.980 align:middle line:90% care if you add more nutrient. 00:09:03.980 --> 00:09:10.740 align:middle line:84% The typical form of this is that uptake is parameterized 00:09:10.740 --> 00:09:13.020 align:middle line:90% as some maximum uptake. 00:09:13.020 --> 00:09:25.340 align:middle line:84% So that would be this v max times n over n plus kn, 00:09:25.340 --> 00:09:28.480 align:middle line:90% where kn is a half saturation. 00:09:28.480 --> 00:09:32.460 align:middle line:90% 00:09:32.460 --> 00:09:39.380 align:middle line:84% And if you think about it, if n is equal to kn, 00:09:39.380 --> 00:09:43.860 align:middle line:84% the denominator is going to have a value of 2/1. 00:09:43.860 --> 00:09:55.640 align:middle line:84% And so kn really is the value of n at which uptake is 1/2 v max. 00:09:55.640 --> 00:10:01.700 align:middle line:84% So this would be kn, and this would be one half v max. 00:10:01.700 --> 00:10:05.000 align:middle line:90% 00:10:05.000 --> 00:10:09.480 align:middle line:84% Now, there's lots of nutrients that we worry about. 00:10:09.480 --> 00:10:13.280 align:middle line:84% So, for example, the standard macronutrients 00:10:13.280 --> 00:10:23.640 align:middle line:84% are nitrogen, phosphorus, silicon for diatoms. 00:10:23.640 --> 00:10:25.640 align:middle line:84% But there's now tremendous interest 00:10:25.640 --> 00:10:34.280 align:middle line:84% in various trace metals, so iron, cobalt, zinc, perhaps 00:10:34.280 --> 00:10:40.880 align:middle line:84% some vitamins, a vitamin just being some organic compound 00:10:40.880 --> 00:10:43.320 align:middle line:84% that the particular species you're looking at 00:10:43.320 --> 00:10:44.540 align:middle line:90% can't manufacture. 00:10:44.540 --> 00:10:47.130 align:middle line:84% So it needs to either get it from heterotrophy, 00:10:47.130 --> 00:10:49.210 align:middle line:84% or it needs to get it from the environment 00:10:49.210 --> 00:10:54.710 align:middle line:84% by taking up some dissolved organic compound. 00:10:54.710 --> 00:10:58.210 align:middle line:90% 00:10:58.210 --> 00:11:01.350 align:middle line:84% You need to worry about things like weather. 00:11:01.350 --> 00:11:03.890 align:middle line:84% For example, for nitrogen, is it in the form 00:11:03.890 --> 00:11:09.170 align:middle line:90% of nitrate or ammonia? 00:11:09.170 --> 00:11:12.210 align:middle line:90% It could be in the form of urea. 00:11:12.210 --> 00:11:15.370 align:middle line:84% It could be in the form of some other dissolved organic nitrogen 00:11:15.370 --> 00:11:18.022 align:middle line:90% compound. 00:11:18.022 --> 00:11:19.730 align:middle line:84% And you're going to have different uptake 00:11:19.730 --> 00:11:22.650 align:middle line:84% curves and different behavior depending upon which 00:11:22.650 --> 00:11:24.970 align:middle line:90% nutrient you're talking about. 00:11:24.970 --> 00:11:27.850 align:middle line:90% And in fact, some-- 00:11:27.850 --> 00:11:32.810 align:middle line:84% and we'll talk about this either today or Thursday-- 00:11:32.810 --> 00:11:40.370 align:middle line:84% organisms don't use nitrate, a organic form that has-- 00:11:40.370 --> 00:11:44.150 align:middle line:84% the organic nitrogen usually looks a lot more like ammonia, 00:11:44.150 --> 00:11:46.630 align:middle line:90% in terms of its redox state. 00:11:46.630 --> 00:11:48.190 align:middle line:84% And there are organisms that are not 00:11:48.190 --> 00:11:52.230 align:middle line:90% capable of assimilating nitrate. 00:11:52.230 --> 00:11:55.770 align:middle line:84% And so you need to know not only which nutrients are there 00:11:55.770 --> 00:11:58.110 align:middle line:84% but whether the organisms you're interested in 00:11:58.110 --> 00:12:02.832 align:middle line:84% can actually use that particular form of that nutrient. 00:12:02.832 --> 00:12:04.790 align:middle line:84% So it's not just enough to know whether there's 00:12:04.790 --> 00:12:08.830 align:middle line:84% an inorganic nitrogen, but what form it's actually in. 00:12:08.830 --> 00:12:12.710 align:middle line:84% And, in fact, in some communities, there's inhibition. 00:12:12.710 --> 00:12:15.110 align:middle line:84% When you have ammonia, ammonia is much easier 00:12:15.110 --> 00:12:17.230 align:middle line:90% to use than nitrate. 00:12:17.230 --> 00:12:19.130 align:middle line:84% And if you add ammonia to the system, 00:12:19.130 --> 00:12:21.430 align:middle line:84% you'll actually reduce the nitrate uptake 00:12:21.430 --> 00:12:23.390 align:middle line:84% because the organisms will switch 00:12:23.390 --> 00:12:25.390 align:middle line:84% because they don't have to expend 00:12:25.390 --> 00:12:28.170 align:middle line:90% the energy of reducing nitrate. 00:12:28.170 --> 00:12:31.390 align:middle line:90% 00:12:31.390 --> 00:12:36.990 align:middle line:84% A lot of interest now in dissolved organic nutrients, so 00:12:36.990 --> 00:12:40.030 align:middle line:90% DON, also DOP. 00:12:40.030 --> 00:12:45.480 align:middle line:84% The problem is that those are very heterogeneous pools. 00:12:45.480 --> 00:12:48.520 align:middle line:84% And you have to be very careful that you 00:12:48.520 --> 00:12:54.000 align:middle line:84% understand what exactly is being taken up by the organisms. 00:12:54.000 --> 00:12:57.300 align:middle line:84% You can't just call it a generic DON or a DOP. 00:12:57.300 --> 00:13:01.040 align:middle line:84% You really have to start characterizing which compounds 00:13:01.040 --> 00:13:02.980 align:middle line:90% within that are being taken up. 00:13:02.980 --> 00:13:24.440 align:middle line:90% 00:13:24.440 --> 00:13:32.120 align:middle line:84% Typically, we don't think of DIC as being a limiting nutrient. 00:13:32.120 --> 00:13:37.240 align:middle line:84% But it can be for some organisms in some environments. 00:13:37.240 --> 00:13:42.860 align:middle line:84% And the reason why is that many organisms can only 00:13:42.860 --> 00:13:47.500 align:middle line:90% take up dissolved CO2 gas. 00:13:47.500 --> 00:13:54.180 align:middle line:84% Remember, most of H2CO3 star is actually CO2 gas. 00:13:54.180 --> 00:14:08.960 align:middle line:84% And the rubisco enzyme, which is the main enzyme for CO2 00:14:08.960 --> 00:14:11.020 align:middle line:84% incorporation into the organic matter as part 00:14:11.020 --> 00:14:16.500 align:middle line:84% of the photosynthetic pathway, uses CO2 gas. 00:14:16.500 --> 00:14:24.580 align:middle line:84% So if you were to look at a plot of CO2 gas-- 00:14:24.580 --> 00:14:26.880 align:middle line:84% this is now dissolved in the water. 00:14:26.880 --> 00:14:30.540 align:middle line:90% So gas dissolved in the water-- 00:14:30.540 --> 00:14:33.780 align:middle line:84% versus photosynthesis rate, we're 00:14:33.780 --> 00:14:38.780 align:middle line:84% currently somewhere around 10 micromoles per kilogram. 00:14:38.780 --> 00:14:43.360 align:middle line:84% That would be a surface saturation value. 00:14:43.360 --> 00:14:45.520 align:middle line:84% There are some phytoplankton that 00:14:45.520 --> 00:14:49.920 align:middle line:84% would have a curve that look like that, which would suggest 00:14:49.920 --> 00:14:52.680 align:middle line:84% that they are actually sensitive to the DIC 00:14:52.680 --> 00:14:55.180 align:middle line:84% concentration or, more importantly, 00:14:55.180 --> 00:14:56.980 align:middle line:90% the CO2 gas concentration. 00:14:56.980 --> 00:15:01.520 align:middle line:84% So you'd need to know DIC and alkalinity or DIC and pH 00:15:01.520 --> 00:15:04.760 align:middle line:84% to figure out what the actual partitioning is. 00:15:04.760 --> 00:15:10.800 align:middle line:84% So, for example, a E. hux, which is a coccolithophore, 00:15:10.800 --> 00:15:13.360 align:middle line:84% appears to have a shape like that. 00:15:13.360 --> 00:15:16.640 align:middle line:90% Other organisms-- and this is-- 00:15:16.640 --> 00:15:19.400 align:middle line:84% AUDIENCE: So this is if you're growing something in culture? 00:15:19.400 --> 00:15:21.040 align:middle line:84% SCOTT DONEY: Well, yeah, these curves 00:15:21.040 --> 00:15:22.370 align:middle line:90% are mostly grown from culture. 00:15:22.370 --> 00:15:22.912 align:middle line:90% AUDIENCE: OK. 00:15:22.912 --> 00:15:24.660 align:middle line:90% So you can really isolate-- 00:15:24.660 --> 00:15:25.880 align:middle line:90% SCOTT DONEY: Yes. 00:15:25.880 --> 00:15:29.560 align:middle line:84% Yeah, you would do these experiments in culture. 00:15:29.560 --> 00:15:31.960 align:middle line:84% But there are many phytoplankton that look more 00:15:31.960 --> 00:15:35.360 align:middle line:84% like that, where they saturate quite quickly 00:15:35.360 --> 00:15:39.450 align:middle line:90% at quite low values of CO2 gas. 00:15:39.450 --> 00:15:44.330 align:middle line:84% And the E. hux curve looks a lot more like the enzyme 00:15:44.330 --> 00:15:48.770 align:middle line:84% if you just isolate the enzyme and look at the enzyme activity. 00:15:48.770 --> 00:15:58.190 align:middle line:84% So if you're growing-- so this is some plankton and rubisco. 00:15:58.190 --> 00:16:01.010 align:middle line:90% 00:16:01.010 --> 00:16:03.890 align:middle line:84% So in order for these other phytoplankton 00:16:03.890 --> 00:16:07.650 align:middle line:84% to have this steep saturation curve, 00:16:07.650 --> 00:16:11.010 align:middle line:84% they have to have some mechanism for concentrating CO2 00:16:11.010 --> 00:16:12.890 align:middle line:90% at the enzyme site. 00:16:12.890 --> 00:16:16.650 align:middle line:84% And you'll see this very creative, innovative term 00:16:16.650 --> 00:16:29.010 align:middle line:84% called a CCM for a Carbon Concentrating Mechanism. 00:16:29.010 --> 00:16:31.510 align:middle line:84% And there are a variety of ways you could do this. 00:16:31.510 --> 00:16:36.370 align:middle line:84% For example, having carbonic anhydrase, which 00:16:36.370 --> 00:16:44.350 align:middle line:84% is the enzyme that catalyzes the conversion between CO2 gas 00:16:44.350 --> 00:16:52.230 align:middle line:84% and H2CO3, the carbonic acid, if you had carbonic anhydrase, 00:16:52.230 --> 00:16:55.950 align:middle line:84% as you started to reduce CO2 at the enzyme site, 00:16:55.950 --> 00:16:57.770 align:middle line:90% it would catalyze this equation. 00:16:57.770 --> 00:17:01.790 align:middle line:84% And you could actually draw more carbon out 00:17:01.790 --> 00:17:03.810 align:middle line:90% of the inorganic carbon system. 00:17:03.810 --> 00:17:06.869 align:middle line:90% 00:17:06.869 --> 00:17:10.890 align:middle line:84% Another way would be-- so this would be our carbonic anhydrase. 00:17:10.890 --> 00:17:14.869 align:middle line:90% 00:17:14.869 --> 00:17:19.950 align:middle line:84% You can also have active transport, actually, 00:17:19.950 --> 00:17:22.710 align:middle line:84% the cell is expending energy in order 00:17:22.710 --> 00:17:25.589 align:middle line:84% to increase the CO2 concentration 00:17:25.589 --> 00:17:28.390 align:middle line:90% at the enzyme site. 00:17:28.390 --> 00:17:30.870 align:middle line:84% So there's not actually a tremendous amount 00:17:30.870 --> 00:17:32.090 align:middle line:90% known about this right now. 00:17:32.090 --> 00:17:35.360 align:middle line:84% It's of some interest because if you 00:17:35.360 --> 00:17:37.440 align:middle line:84% were to look into the future, we're 00:17:37.440 --> 00:17:41.120 align:middle line:84% going to be somewhere out around-- we're currently 00:17:41.120 --> 00:17:41.943 align:middle line:90% about here. 00:17:41.943 --> 00:17:44.360 align:middle line:84% By the end of the century, we're going to be somewhere out 00:17:44.360 --> 00:17:45.800 align:middle line:90% here on this curve. 00:17:45.800 --> 00:17:49.360 align:middle line:84% If there is a big sensitivity to photosynthesis, 00:17:49.360 --> 00:17:50.640 align:middle line:90% that's a big deal. 00:17:50.640 --> 00:17:53.000 align:middle line:84% But if they're already saturated, 00:17:53.000 --> 00:17:54.420 align:middle line:90% they're already saturated. 00:17:54.420 --> 00:17:55.440 align:middle line:90% Who cares? 00:17:55.440 --> 00:17:57.180 align:middle line:84% So there is a lot of interest in this, 00:17:57.180 --> 00:18:00.360 align:middle line:84% and people are starting to try to look at in different systems 00:18:00.360 --> 00:18:03.100 align:middle line:84% to figure out what exactly is going on. 00:18:03.100 --> 00:18:09.520 align:middle line:90% 00:18:09.520 --> 00:18:13.120 align:middle line:84% The last thing on nutrients is, you will often 00:18:13.120 --> 00:18:19.800 align:middle line:84% hear of something called Liebig's law or Liebig's 00:18:19.800 --> 00:18:21.340 align:middle line:90% law of the minimum. 00:18:21.340 --> 00:18:26.480 align:middle line:90% 00:18:26.480 --> 00:18:29.220 align:middle line:84% And Liebig was actually an agricultural-- 00:18:29.220 --> 00:18:31.760 align:middle line:90% 00:18:31.760 --> 00:18:34.840 align:middle line:90% I guess agricultural chemist. 00:18:34.840 --> 00:18:36.700 align:middle line:84% I don't know exactly how to-- he was 00:18:36.700 --> 00:18:39.620 align:middle line:84% dealing with agricultural plants, with crops. 00:18:39.620 --> 00:18:43.900 align:middle line:84% And he was interested in the issue of-- let's say you have 00:18:43.900 --> 00:18:45.680 align:middle line:90% multiple limiting nutrients. 00:18:45.680 --> 00:18:51.060 align:middle line:90% 00:18:51.060 --> 00:18:53.180 align:middle line:90% What happens? 00:18:53.180 --> 00:18:55.660 align:middle line:84% Well, there's a couple of possibilities. 00:18:55.660 --> 00:19:05.860 align:middle line:84% One is, you can say there's some function f, that as you have 00:19:05.860 --> 00:19:12.260 align:middle line:84% this, say, a saturation curve for some nutrient x, 00:19:12.260 --> 00:19:16.260 align:middle line:84% it can take on a value of somewhere between 0 to 1. 00:19:16.260 --> 00:19:18.700 align:middle line:84% At 0, it would be completely limiting. 00:19:18.700 --> 00:19:21.300 align:middle line:84% At 1, it wouldn't be limiting at all. 00:19:21.300 --> 00:19:25.420 align:middle line:84% So your primary production would be-- 00:19:25.420 --> 00:19:32.020 align:middle line:84% say, it would be f of x times p max. 00:19:32.020 --> 00:19:35.480 align:middle line:84% That would be for a single nutrient. 00:19:35.480 --> 00:19:37.220 align:middle line:84% Now, if you have multiple nutrients, 00:19:37.220 --> 00:19:43.420 align:middle line:84% it could be that p would be f of x, f of y, 00:19:43.420 --> 00:19:49.240 align:middle line:90% f of z, dot, dot, dot, p max. 00:19:49.240 --> 00:19:55.180 align:middle line:84% So if x was limiting you by 50% and y was limiting you by 50% 00:19:55.180 --> 00:19:58.320 align:middle line:84% and z was limiting you by 50%, by the time you're 00:19:58.320 --> 00:20:03.320 align:middle line:84% done with that string, it would be 0.5 times 0.5 times 0.5. 00:20:03.320 --> 00:20:06.280 align:middle line:90% You'd have very low production. 00:20:06.280 --> 00:20:09.200 align:middle line:84% What Liebig argued was that it actually 00:20:09.200 --> 00:20:31.090 align:middle line:84% should be that there's a single limiting nutrient at any time. 00:20:31.090 --> 00:20:34.890 align:middle line:84% So you'd look at the limitation due to x, 00:20:34.890 --> 00:20:37.730 align:middle line:84% limitation due to the y, limitation due to z. 00:20:37.730 --> 00:20:40.330 align:middle line:84% You'd take the one that was the most limiting, 00:20:40.330 --> 00:20:42.490 align:middle line:90% and that would set the rate. 00:20:42.490 --> 00:20:47.770 align:middle line:84% So if you don't have enough phosphorus-- phosphorus is only 00:20:47.770 --> 00:20:50.130 align:middle line:84% there to get you like 20% growth rate, 00:20:50.130 --> 00:20:51.930 align:middle line:90% of your maximum growth rate. 00:20:51.930 --> 00:20:55.690 align:middle line:84% Doesn't matter that nitrogen might be at 30% or silica 00:20:55.690 --> 00:20:57.370 align:middle line:90% might be at 40%. 00:20:57.370 --> 00:21:02.930 align:middle line:84% It would be set by that single that single maximum. 00:21:02.930 --> 00:21:06.490 align:middle line:84% This has become-- it's now called the law. 00:21:06.490 --> 00:21:09.890 align:middle line:84% Well, it's an empirical observation. 00:21:09.890 --> 00:21:11.930 align:middle line:84% And it's a guess that organisms would 00:21:11.930 --> 00:21:15.850 align:middle line:84% adapt themselves so that everything else-- 00:21:15.850 --> 00:21:19.330 align:middle line:84% that they would concentrate and be limited only 00:21:19.330 --> 00:21:21.072 align:middle line:84% by the thing that was most limiting, 00:21:21.072 --> 00:21:23.530 align:middle line:84% and that if everything else was a little greater than that, 00:21:23.530 --> 00:21:28.170 align:middle line:84% they could survive and limp along. 00:21:28.170 --> 00:21:29.590 align:middle line:90% It doesn't always hold. 00:21:29.590 --> 00:21:34.670 align:middle line:84% Sometimes you'll have what's called co-limitation, 00:21:34.670 --> 00:21:40.630 align:middle line:84% particularly if-- for example, a classic co-limitation is, 00:21:40.630 --> 00:21:44.170 align:middle line:90% you need this reaction. 00:21:44.170 --> 00:21:47.310 align:middle line:84% Remember that we talked about the nitrogen reduction 00:21:47.310 --> 00:21:48.250 align:middle line:90% to ammonia. 00:21:48.250 --> 00:21:52.230 align:middle line:90% 00:21:52.230 --> 00:21:54.870 align:middle line:84% The reductase, the enzyme that does 00:21:54.870 --> 00:21:59.190 align:middle line:84% this reduction, the enzyme system, is iron rich. 00:21:59.190 --> 00:22:01.230 align:middle line:84% And so you might have a co-limitation 00:22:01.230 --> 00:22:08.430 align:middle line:84% where there's an iron limitation on this reductase. 00:22:08.430 --> 00:22:10.510 align:middle line:84% And so your rate might depend on both 00:22:10.510 --> 00:22:12.510 align:middle line:84% how much nitrate you have there-- because that's 00:22:12.510 --> 00:22:14.550 align:middle line:84% what you're using-- but also the iron 00:22:14.550 --> 00:22:16.870 align:middle line:84% because the iron's limiting how quickly you 00:22:16.870 --> 00:22:18.710 align:middle line:90% can use that nitrate. 00:22:18.710 --> 00:22:21.690 align:middle line:84% So there are nutrient-nutrient co-limitations. 00:22:21.690 --> 00:22:26.490 align:middle line:84% You'll also see nutrient-light co-limitations. 00:22:26.490 --> 00:22:31.480 align:middle line:90% 00:22:31.480 --> 00:22:36.300 align:middle line:84% The Liebig's law of the minimum is a good first approximation, 00:22:36.300 --> 00:22:39.900 align:middle line:84% probably better than the multiplicative approach. 00:22:39.900 --> 00:22:41.900 align:middle line:84% This would be the multiplicative. 00:22:41.900 --> 00:22:45.440 align:middle line:90% 00:22:45.440 --> 00:22:49.820 align:middle line:84% But it's not like the law of gravity. 00:22:49.820 --> 00:22:54.218 align:middle line:90% 00:22:54.218 --> 00:22:56.760 align:middle line:84% AUDIENCE: There's [? probably ?] problems with that too but-- 00:22:56.760 --> 00:22:58.520 align:middle line:84% SCOTT DONEY: Yeah, the fifth force. 00:22:58.520 --> 00:23:00.567 align:middle line:90% AUDIENCE: It used to work. 00:23:00.567 --> 00:23:01.900 align:middle line:90% SCOTT DONEY: The law of gravity? 00:23:01.900 --> 00:23:02.280 align:middle line:90% AUDIENCE: Yeah. 00:23:02.280 --> 00:23:03.030 align:middle line:90% SCOTT DONEY: Yeah. 00:23:03.030 --> 00:23:09.200 align:middle line:90% 00:23:09.200 --> 00:23:10.840 align:middle line:90% One never knows. 00:23:10.840 --> 00:23:13.798 align:middle line:90% Maybe Congress will repeal it. 00:23:13.798 --> 00:23:14.840 align:middle line:90% AUDIENCE: They might try. 00:23:14.840 --> 00:23:15.560 align:middle line:90% SCOTT DONEY: I don't know. 00:23:15.560 --> 00:23:16.820 align:middle line:90% There's an apocryphal story. 00:23:16.820 --> 00:23:17.900 align:middle line:84% I don't know if it's actually true. 00:23:17.900 --> 00:23:19.960 align:middle line:84% But I read somewhere that the state of Ohio 00:23:19.960 --> 00:23:22.095 align:middle line:84% once tried to mandate that the value of pi 00:23:22.095 --> 00:23:23.720 align:middle line:84% had to be 3 because they thought it was 00:23:23.720 --> 00:23:25.200 align:middle line:84% too inconvenient for the students 00:23:25.200 --> 00:23:27.320 align:middle line:84% that it was an irrational number. 00:23:27.320 --> 00:23:27.820 align:middle line:90% But-- 00:23:27.820 --> 00:23:29.163 align:middle line:90% AUDIENCE: [INAUDIBLE] Ohio. 00:23:29.163 --> 00:23:31.080 align:middle line:84% SCOTT DONEY: That might just be one of those-- 00:23:31.080 --> 00:23:32.720 align:middle line:90% it sounds too good to be true. 00:23:32.720 --> 00:23:33.420 align:middle line:90% So-- 00:23:33.420 --> 00:23:34.628 align:middle line:90% AUDIENCE: It does sound good. 00:23:34.628 --> 00:23:40.460 align:middle line:90% 00:23:40.460 --> 00:23:41.210 align:middle line:90% SCOTT DONEY: OK. 00:23:41.210 --> 00:23:44.940 align:middle line:84% The last limitation is temperature. 00:23:44.940 --> 00:23:48.700 align:middle line:84% And temperature is an awkward one because-- 00:23:48.700 --> 00:23:53.300 align:middle line:84% people talk about temperature limitation. 00:23:53.300 --> 00:23:57.700 align:middle line:84% And it depends on what sort of background you come from. 00:23:57.700 --> 00:24:03.740 align:middle line:84% If you're a card-carrying biologist, 00:24:03.740 --> 00:24:07.540 align:middle line:84% we're going to define a parameter called mu, where 00:24:07.540 --> 00:24:10.920 align:middle line:90% mu is the specific growth rate. 00:24:10.920 --> 00:24:15.940 align:middle line:90% 00:24:15.940 --> 00:24:25.770 align:middle line:84% And let's say you're some phytoplankton. 00:24:25.770 --> 00:24:27.770 align:middle line:84% Or you're a biologist measuring phytoplankton. 00:24:27.770 --> 00:24:31.510 align:middle line:84% You don't actually have to be phytoplankton to do this. 00:24:31.510 --> 00:24:33.470 align:middle line:84% Mu is going to be-- you're going to look 00:24:33.470 --> 00:24:38.270 align:middle line:84% at the growth rate of whatever organism you're looking at. 00:24:38.270 --> 00:24:42.710 align:middle line:84% And then you're going to divide it by the instantaneous biomass 00:24:42.710 --> 00:24:45.710 align:middle line:90% that you're keeping track of. 00:24:45.710 --> 00:24:49.470 align:middle line:84% So if you're keeping track of moles of carbon in the organism, 00:24:49.470 --> 00:24:51.910 align:middle line:84% it would be the rate of change of moles 00:24:51.910 --> 00:24:56.790 align:middle line:84% of carbon divided by the moles of carbon in the organism. 00:24:56.790 --> 00:24:59.950 align:middle line:84% And so if you look at this, the units for mu-- 00:24:59.950 --> 00:25:02.070 align:middle line:90% so this is equal mu-- 00:25:02.070 --> 00:25:06.750 align:middle line:84% have to have units of 1 over time. 00:25:06.750 --> 00:25:10.090 align:middle line:84% So they're often expressed for phytoplankton in days, 00:25:10.090 --> 00:25:15.350 align:middle line:84% so like 1 over days, because that's about the generation 00:25:15.350 --> 00:25:18.350 align:middle line:84% time for phytoplankton and bacteria, 00:25:18.350 --> 00:25:21.450 align:middle line:84% is something like half a day to a few days. 00:25:21.450 --> 00:25:24.810 align:middle line:90% 00:25:24.810 --> 00:25:29.010 align:middle line:84% So that's the common-- and it's much better than if you just 00:25:29.010 --> 00:25:29.790 align:middle line:90% did-- 00:25:29.790 --> 00:25:32.850 align:middle line:84% if you just reported things as dp dt, 00:25:32.850 --> 00:25:38.730 align:middle line:84% it would really depend on how rich your culture was, how much 00:25:38.730 --> 00:25:41.490 align:middle line:90% phytoplankton you had there. 00:25:41.490 --> 00:25:45.530 align:middle line:84% Unfortunately, this is a culture-based view. 00:25:45.530 --> 00:25:48.890 align:middle line:84% And the reason why is, in the field, we 00:25:48.890 --> 00:25:55.370 align:middle line:84% often don't know how much actual biomass there is. 00:25:55.370 --> 00:25:59.810 align:middle line:84% So we'll talk about these photosynthesis rates. 00:25:59.810 --> 00:26:03.075 align:middle line:84% And you might try to normalize it to something. 00:26:03.075 --> 00:26:04.450 align:middle line:84% But it's often hard to figure out 00:26:04.450 --> 00:26:08.290 align:middle line:84% exactly how many viable living phytoplankton are there 00:26:08.290 --> 00:26:09.370 align:middle line:90% in the field. 00:26:09.370 --> 00:26:15.050 align:middle line:84% And so for culture stuff, you'll often see it in the form of mu. 00:26:15.050 --> 00:26:22.430 align:middle line:84% For a lot of field work, you'll just see it as dp dt, 00:26:22.430 --> 00:26:29.030 align:middle line:84% or it'll express as just a photosynthesis rate. 00:26:29.030 --> 00:26:31.390 align:middle line:90% For the temperature. 00:26:31.390 --> 00:26:33.610 align:middle line:84% Often what you see for a lot of organisms, 00:26:33.610 --> 00:26:36.270 align:middle line:84% whether aquatic or terrestrial, is 00:26:36.270 --> 00:26:40.270 align:middle line:84% that if you plot mu as a function of temperature, 00:26:40.270 --> 00:26:43.770 align:middle line:84% you'll see some tail where they'll grow pretty low-- well, 00:26:43.770 --> 00:26:47.350 align:middle line:84% they'll grow, but not well, at low temperatures. 00:26:47.350 --> 00:26:54.710 align:middle line:84% There'll be some optimal temperature band. 00:26:54.710 --> 00:26:59.790 align:middle line:84% And then it's a very steep fall off if you go above the optimum. 00:26:59.790 --> 00:27:05.290 align:middle line:84% So it's asymmetric with respect to the optimal temperature. 00:27:05.290 --> 00:27:10.750 align:middle line:90% 00:27:10.750 --> 00:27:13.210 align:middle line:84% That's great if you're doing individual organisms. 00:27:13.210 --> 00:27:17.250 align:middle line:84% But often, people are interested in what happens to a community. 00:27:17.250 --> 00:27:19.230 align:middle line:84% And the community will actually shift 00:27:19.230 --> 00:27:21.840 align:middle line:84% as you move through the seasons, in part 00:27:21.840 --> 00:27:24.040 align:middle line:84% because as the temperature warms up, 00:27:24.040 --> 00:27:26.000 align:middle line:90% bugs that weren't doing well-- 00:27:26.000 --> 00:27:31.498 align:middle line:84% as the temperature shifts-- and let's say it gets warmer. 00:27:31.498 --> 00:27:33.040 align:middle line:84% Some of the bugs, you've now exceeded 00:27:33.040 --> 00:27:36.160 align:middle line:84% their optimal temperature, and they die off. 00:27:36.160 --> 00:27:40.800 align:middle line:84% Other bugs, you're just kind of entering their suboptimal lower 00:27:40.800 --> 00:27:41.900 align:middle line:90% temperature range. 00:27:41.900 --> 00:27:44.040 align:middle line:90% And so they'll start to grow. 00:27:44.040 --> 00:27:48.640 align:middle line:84% And so what you'll often see is a curve that looks more 00:27:48.640 --> 00:27:55.420 align:middle line:84% like this, which is, for a community, 00:27:55.420 --> 00:28:01.280 align:middle line:84% there's a whole collection of temperatures over which it 00:28:01.280 --> 00:28:09.540 align:middle line:84% will grow, where if you were to plot the upper envelope of that, 00:28:09.540 --> 00:28:11.760 align:middle line:84% that upper envelope tends to increase as you 00:28:11.760 --> 00:28:13.440 align:middle line:90% get to higher temperatures. 00:28:13.440 --> 00:28:16.340 align:middle line:84% So for any particular organism, that might not be true. 00:28:16.340 --> 00:28:18.680 align:middle line:84% But for the community, as you go to warmer 00:28:18.680 --> 00:28:21.460 align:middle line:84% and warmer temperatures, growth rates tend to go up. 00:28:21.460 --> 00:28:26.060 align:middle line:84% Enzyme reactions go faster is the basic argument, 00:28:26.060 --> 00:28:31.900 align:middle line:84% that your metabolism can run faster at higher temperatures. 00:28:31.900 --> 00:28:36.340 align:middle line:84% Note the presence of warmth of warm-blooded, endothermic 00:28:36.340 --> 00:28:40.900 align:middle line:84% animals, in part because their metabolism can run faster. 00:28:40.900 --> 00:28:47.260 align:middle line:84% In '72, Epley published an equation 00:28:47.260 --> 00:28:52.660 align:middle line:84% that he probably never figured people would use this much, 00:28:52.660 --> 00:28:54.420 align:middle line:90% but they do. 00:28:54.420 --> 00:28:58.380 align:middle line:84% If you publish a useful approximation, 00:28:58.380 --> 00:29:00.180 align:middle line:84% people seem to just flock to it-- 00:29:00.180 --> 00:29:04.140 align:middle line:84% where he said that the upper envelope could 00:29:04.140 --> 00:29:12.060 align:middle line:84% be approximated for phytoplankton as mu of t t, 00:29:12.060 --> 00:29:15.803 align:middle line:90% in degrees, c. 00:29:15.803 --> 00:29:17.220 align:middle line:84% AUDIENCE: That's empirical, right? 00:29:17.220 --> 00:29:18.803 align:middle line:84% SCOTT DONEY: This is purely empirical. 00:29:18.803 --> 00:29:26.430 align:middle line:90% 00:29:26.430 --> 00:29:29.070 align:middle line:84% And that gives you a pretty useful sense for, 00:29:29.070 --> 00:29:31.670 align:middle line:84% if you're in cold climates, photosynthesis 00:29:31.670 --> 00:29:32.490 align:middle line:90% is going to be low. 00:29:32.490 --> 00:29:35.110 align:middle line:84% If you're in warmer climates, it gives a doubling 00:29:35.110 --> 00:29:39.750 align:middle line:90% of about every 10 degrees. 00:29:39.750 --> 00:29:44.470 align:middle line:84% c is approximately a doubling, yeah, doubling, 00:29:44.470 --> 00:29:47.370 align:middle line:90% doubling of growth rate. 00:29:47.370 --> 00:29:54.430 align:middle line:90% 00:29:54.430 --> 00:29:59.710 align:middle line:84% So what does this all look like if we pull this all together? 00:29:59.710 --> 00:30:02.090 align:middle line:90% We talked about-- 00:30:02.090 --> 00:30:05.150 align:middle line:84% AUDIENCE: Question-- question from MIT. 00:30:05.150 --> 00:30:07.050 align:middle line:90% What's below 0.6? 00:30:07.050 --> 00:30:08.950 align:middle line:90% Sorry. 00:30:08.950 --> 00:30:10.125 align:middle line:90% SCOTT DONEY: Days. 00:30:10.125 --> 00:30:10.750 align:middle line:90% AUDIENCE: Days. 00:30:10.750 --> 00:30:13.447 align:middle line:90% Thank you. 00:30:13.447 --> 00:30:14.530 align:middle line:90% AUDIENCE: Sorry, Virginia. 00:30:14.530 --> 00:30:15.370 align:middle line:90% We can't see you. 00:30:15.370 --> 00:30:16.550 align:middle line:90% 00:30:16.550 --> 00:30:18.370 align:middle line:90% AUDIENCE: Don't worry. 00:30:18.370 --> 00:30:24.250 align:middle line:84% SCOTT DONEY: So at 0 degrees C, this goes to 0. 00:30:24.250 --> 00:30:30.530 align:middle line:84% The 1.066-- anything raised to the 0 power is 1. 00:30:30.530 --> 00:30:35.210 align:middle line:84% So it's 0.6 days at 0 degrees C. So it 00:30:35.210 --> 00:30:47.250 align:middle line:84% would be at 0 degrees C goes to 0.61 over day. 00:30:47.250 --> 00:30:49.290 align:middle line:90% That's for-- it would be mu. 00:30:49.290 --> 00:30:51.790 align:middle line:84% Don't use Kelvin, does awful things. 00:30:51.790 --> 00:30:56.130 align:middle line:90% 00:30:56.130 --> 00:30:57.630 align:middle line:90% So what does this look like? 00:30:57.630 --> 00:31:01.050 align:middle line:90% We talked a little bit about-- 00:31:01.050 --> 00:31:02.250 align:middle line:90% oh. 00:31:02.250 --> 00:31:04.410 align:middle line:84% Well, there's, what does this look like, 00:31:04.410 --> 00:31:06.390 align:middle line:90% in terms of seasonal cycles? 00:31:06.390 --> 00:31:10.850 align:middle line:90% 00:31:10.850 --> 00:31:12.650 align:middle line:84% And I think I showed this the other day. 00:31:12.650 --> 00:31:17.180 align:middle line:84% There's two end members if you were 00:31:17.180 --> 00:31:19.120 align:middle line:90% to look at the annual cycle. 00:31:19.120 --> 00:31:24.180 align:middle line:90% 00:31:24.180 --> 00:31:26.480 align:middle line:84% Often, for the Northern Hemisphere, 00:31:26.480 --> 00:31:31.260 align:middle line:84% the mixed layer depth will do something like that. 00:31:31.260 --> 00:31:38.080 align:middle line:84% So it gets deeper in the winter, shallower in the summer, 00:31:38.080 --> 00:31:41.500 align:middle line:90% deeper in the winter. 00:31:41.500 --> 00:31:49.140 align:middle line:84% And you see, in some regions, like the North Atlantic, 00:31:49.140 --> 00:31:55.340 align:middle line:84% you'll see a big bloom of phytoplankton 00:31:55.340 --> 00:31:58.800 align:middle line:90% in both the spring and the fall. 00:31:58.800 --> 00:32:02.860 align:middle line:84% So this would be your phytoplankton. 00:32:02.860 --> 00:32:07.540 align:middle line:84% The proxy for that might be chlorophyll. 00:32:07.540 --> 00:32:20.920 align:middle line:84% And the nutrients might look like that, 00:32:20.920 --> 00:32:23.760 align:middle line:90% where this is the nutrients. 00:32:23.760 --> 00:32:26.060 align:middle line:84% And so the idea is, during the winter, 00:32:26.060 --> 00:32:28.760 align:middle line:84% you have a lot of mixing, brings a lot of nutrients up. 00:32:28.760 --> 00:32:31.440 align:middle line:84% When the mixed layer shoals, you get 00:32:31.440 --> 00:32:34.620 align:middle line:84% a bloom because of the release of light limitation. 00:32:34.620 --> 00:32:36.480 align:middle line:84% You have lots of nutrients present. 00:32:36.480 --> 00:32:38.720 align:middle line:90% That draws the nutrients down. 00:32:38.720 --> 00:32:40.520 align:middle line:84% You have a period over the summer where you 00:32:40.520 --> 00:32:42.220 align:middle line:90% don't have a lot of nutrients. 00:32:42.220 --> 00:32:44.800 align:middle line:84% You have a lot of light but not a lot of nutrients. 00:32:44.800 --> 00:32:48.280 align:middle line:84% You have some background phytoplankton concentration. 00:32:48.280 --> 00:32:51.140 align:middle line:84% And then in the winter, when you mix down again, 00:32:51.140 --> 00:32:53.300 align:middle line:84% you kick up a little bit of nutrients. 00:32:53.300 --> 00:32:56.960 align:middle line:84% And that tends to drive a fall bloom. 00:32:56.960 --> 00:33:02.680 align:middle line:84% So this would be spring and fall. 00:33:02.680 --> 00:33:04.880 align:middle line:84% A lot of this is based off of measurements 00:33:04.880 --> 00:33:07.760 align:middle line:84% that were made by the Scandinavians 00:33:07.760 --> 00:33:09.620 align:middle line:84% in the early part of the last century. 00:33:09.620 --> 00:33:13.460 align:middle line:84% That was where a lot biological oceanography really 00:33:13.460 --> 00:33:15.540 align:middle line:90% got its start. 00:33:15.540 --> 00:33:19.140 align:middle line:84% So that was considered canonical or normal. 00:33:19.140 --> 00:33:28.500 align:middle line:84% There are other places that have a fairly different seasonality. 00:33:28.500 --> 00:33:34.740 align:middle line:84% And-- oh, in this plot, the primary production 00:33:34.740 --> 00:33:39.940 align:middle line:90% follows phytoplankton. 00:33:39.940 --> 00:33:44.300 align:middle line:84% So I won't draw it on there because I'll just confuse 00:33:44.300 --> 00:33:47.140 align:middle line:90% an already complicated drawing. 00:33:47.140 --> 00:33:49.880 align:middle line:84% But for example-- so this would be the North Atlantic. 00:33:49.880 --> 00:33:54.220 align:middle line:90% 00:33:54.220 --> 00:33:59.020 align:middle line:84% But if you go to parts of the North Pacific, 00:33:59.020 --> 00:34:01.700 align:middle line:84% you see a very different pattern. 00:34:01.700 --> 00:34:09.139 align:middle line:84% There, the nutrients never get drawn all the way down. 00:34:09.139 --> 00:34:14.710 align:middle line:84% So there is a seasonality to the nutrients, 00:34:14.710 --> 00:34:19.949 align:middle line:84% but they're never reduced all the way down to 0. 00:34:19.949 --> 00:34:31.409 align:middle line:84% You see chlorophyll that looks pretty flat through the year. 00:34:31.409 --> 00:34:34.030 align:middle line:90% 00:34:34.030 --> 00:34:42.250 align:middle line:84% But primary production shows a seasonality. 00:34:42.250 --> 00:34:45.350 align:middle line:90% 00:34:45.350 --> 00:34:50.949 align:middle line:84% So this would be primary production. 00:34:50.949 --> 00:34:58.350 align:middle line:84% And in here, something needs to be controlling the chlorophyll 00:34:58.350 --> 00:35:01.190 align:middle line:84% or the phytoplankton biomass such 00:35:01.190 --> 00:35:05.990 align:middle line:84% that even as the primary production increases sharply, 00:35:05.990 --> 00:35:08.790 align:middle line:90% the biomass doesn't build up. 00:35:08.790 --> 00:35:18.810 align:middle line:84% So this is a region where you're focused on growth. 00:35:18.810 --> 00:35:21.450 align:middle line:84% You have these big events where you 00:35:21.450 --> 00:35:24.710 align:middle line:84% supply enough nutrients and enough light, and off they grow. 00:35:24.710 --> 00:35:27.130 align:middle line:84% And you're mostly focused on the growth term. 00:35:27.130 --> 00:35:29.010 align:middle line:84% And it's only after the bloom that you 00:35:29.010 --> 00:35:32.170 align:middle line:90% worry about the loss terms. 00:35:32.170 --> 00:35:36.410 align:middle line:84% So this is-- you might call it unbalanced, 00:35:36.410 --> 00:35:42.370 align:middle line:84% where there's a decoupling between growth and loss. 00:35:42.370 --> 00:35:46.710 align:middle line:84% The North Pacific, the sort of opposite extreme-- 00:35:46.710 --> 00:35:49.650 align:middle line:84% and these are, of course, obviously caricatures 00:35:49.650 --> 00:35:51.770 align:middle line:90% of the real system-- 00:35:51.770 --> 00:35:56.010 align:middle line:84% is more like a steady state, where you have 00:35:56.010 --> 00:36:01.290 align:middle line:90% growth being balanced by loss. 00:36:01.290 --> 00:36:04.930 align:middle line:84% So the biomass isn't changing significantly, 00:36:04.930 --> 00:36:06.770 align:middle line:90% but the growth term is. 00:36:06.770 --> 00:36:11.400 align:middle line:84% And so there has to be a corresponding control on loss. 00:36:11.400 --> 00:36:17.757 align:middle line:90% 00:36:17.757 --> 00:36:19.340 align:middle line:84% AUDIENCE: One more time-- like, what's 00:36:19.340 --> 00:36:25.020 align:middle line:84% causing the peak in the phytoplankton there? 00:36:25.020 --> 00:36:25.720 align:middle line:90% SCOTT DONEY: OK. 00:36:25.720 --> 00:36:29.780 align:middle line:84% So let's say your biomass is constant all year. 00:36:29.780 --> 00:36:31.980 align:middle line:84% And your nutrients, they go down, 00:36:31.980 --> 00:36:33.560 align:middle line:90% but they're always saturating. 00:36:33.560 --> 00:36:35.980 align:middle line:84% You're always up on that saturating curve. 00:36:35.980 --> 00:36:38.500 align:middle line:84% What are a couple of things that could give you seasonality 00:36:38.500 --> 00:36:39.880 align:middle line:90% in primary production? 00:36:39.880 --> 00:36:43.820 align:middle line:90% 00:36:43.820 --> 00:36:46.360 align:middle line:84% We just went through things that control primary production. 00:36:46.360 --> 00:36:47.980 align:middle line:84% What could generate seasonality, where 00:36:47.980 --> 00:36:51.500 align:middle line:84% you get a peak in primary production in the summer? 00:36:51.500 --> 00:36:53.100 align:middle line:90% AUDIENCE: Light and duration. 00:36:53.100 --> 00:36:53.767 align:middle line:90% AUDIENCE: Light. 00:36:53.767 --> 00:36:56.500 align:middle line:84% SCOTT DONEY: Light and temperature. 00:36:56.500 --> 00:36:59.620 align:middle line:84% So if you had constant biomass and you 00:36:59.620 --> 00:37:03.020 align:middle line:84% didn't have seasonality and nutrient limitation, 00:37:03.020 --> 00:37:04.940 align:middle line:90% this is what you would expect. 00:37:04.940 --> 00:37:07.480 align:middle line:84% You'd expect primary production to go up in the summer 00:37:07.480 --> 00:37:09.040 align:middle line:90% because you have more light. 00:37:09.040 --> 00:37:11.080 align:middle line:84% And you'd expect primary production 00:37:11.080 --> 00:37:14.080 align:middle line:84% to be higher, photosynthesis rates to be higher 00:37:14.080 --> 00:37:16.180 align:middle line:84% because you have warmer temperatures. 00:37:16.180 --> 00:37:19.960 align:middle line:90% 00:37:19.960 --> 00:37:20.680 align:middle line:90% Does that make-- 00:37:20.680 --> 00:37:22.430 align:middle line:84% AUDIENCE: pp is primary production and not 00:37:22.430 --> 00:37:23.420 align:middle line:90% phytoplankton? 00:37:23.420 --> 00:37:29.440 align:middle line:84% SCOTT DONEY: Yeah, sorry, primary production. 00:37:29.440 --> 00:37:32.520 align:middle line:84% AUDIENCE: And so why does chlorophyll stay constant then? 00:37:32.520 --> 00:37:34.400 align:middle line:84% SCOTT DONEY: Chlorophyll stays constant 00:37:34.400 --> 00:37:41.720 align:middle line:84% because somebody has to be eating all the growth 00:37:41.720 --> 00:37:43.400 align:middle line:90% I call this-- 00:37:43.400 --> 00:37:45.560 align:middle line:84% and this tells you how much I like yard work. 00:37:45.560 --> 00:37:50.208 align:middle line:84% This is the suburban lawn hypothesis. 00:37:50.208 --> 00:37:52.500 align:middle line:84% That's not actually called the suburban lawn hypothesis 00:37:52.500 --> 00:37:54.100 align:middle line:90% any place outside of this class. 00:37:54.100 --> 00:37:55.960 align:middle line:84% But to me, this is a classic example 00:37:55.960 --> 00:38:00.420 align:middle line:84% of the suburban lawn, which is, during the summer, 00:38:00.420 --> 00:38:03.040 align:middle line:84% I have to mow the lawn, like, twice a week because the lawn is 00:38:03.040 --> 00:38:04.920 align:middle line:90% growing like crazy. 00:38:04.920 --> 00:38:08.450 align:middle line:84% But I maintain no change in biomass 00:38:08.450 --> 00:38:10.130 align:middle line:84% by going out there every couple of days 00:38:10.130 --> 00:38:13.290 align:middle line:90% and mowing it back down flat. 00:38:13.290 --> 00:38:21.170 align:middle line:84% So this is a system where you have balanced growth, which 00:38:21.170 --> 00:38:27.130 align:middle line:84% is the more canonical term but just isn't as evocative. 00:38:27.130 --> 00:38:29.850 align:middle line:84% So you have balanced growth, where the loss terms 00:38:29.850 --> 00:38:33.770 align:middle line:84% have to be balancing the growth terms fairly closely 00:38:33.770 --> 00:38:39.090 align:middle line:84% and maintaining no net change in the biomass. 00:38:39.090 --> 00:38:41.610 align:middle line:90% 00:38:41.610 --> 00:38:44.330 align:middle line:84% AUDIENCE: The primary production is just like total carbon 00:38:44.330 --> 00:38:45.222 align:middle line:90% fixed here? 00:38:45.222 --> 00:38:45.930 align:middle line:90% SCOTT DONEY: Yep. 00:38:45.930 --> 00:38:48.950 align:middle line:84% Primary production would be total-- 00:38:48.950 --> 00:38:50.490 align:middle line:90% well, yeah. 00:38:50.490 --> 00:38:53.290 align:middle line:84% Usually, it's that net primary production. 00:38:53.290 --> 00:38:55.510 align:middle line:84% We're going to talk about techniques in a minute. 00:38:55.510 --> 00:38:58.890 align:middle line:84% But it's the total amount of net carbon going 00:38:58.890 --> 00:39:04.190 align:middle line:84% into the autotrophs going into the photosynthesizers, 00:39:04.190 --> 00:39:05.490 align:middle line:90% the phytoplankton. 00:39:05.490 --> 00:39:08.830 align:middle line:90% 00:39:08.830 --> 00:39:11.430 align:middle line:84% AUDIENCE: So would you see a change in biomass 00:39:11.430 --> 00:39:16.310 align:middle line:90% and primary consumers then? 00:39:16.310 --> 00:39:19.830 align:middle line:84% SCOTT DONEY: The assumption-- and I call it an assumption 00:39:19.830 --> 00:39:23.590 align:middle line:84% because there's not nearly as much data on the zooplankton, 00:39:23.590 --> 00:39:26.210 align:middle line:84% typically, as there are on phytoplankton. 00:39:26.210 --> 00:39:29.390 align:middle line:84% The reason is, there's a very easy assay for phytoplankton, 00:39:29.390 --> 00:39:30.630 align:middle line:90% which is chlorophyll. 00:39:30.630 --> 00:39:32.130 align:middle line:90% It's not the best assay. 00:39:32.130 --> 00:39:36.830 align:middle line:84% But it's the drunk looking under the lamppost for his keys. 00:39:36.830 --> 00:39:38.950 align:middle line:84% We measure phytoplankton and chlorophyll 00:39:38.950 --> 00:39:42.150 align:middle line:84% because it's straightforward and easy. 00:39:42.150 --> 00:39:44.430 align:middle line:84% If you were to look at zooplankton, 00:39:44.430 --> 00:39:46.990 align:middle line:84% you would assume that your zooplankton biomass would 00:39:46.990 --> 00:39:51.270 align:middle line:84% probably more closely track primary production in the system 00:39:51.270 --> 00:39:55.070 align:middle line:84% because there's got to be a much bigger pool of zooplankton 00:39:55.070 --> 00:39:58.210 align:middle line:84% in order to keep up with the primary production. 00:39:58.210 --> 00:40:03.410 align:middle line:90% 00:40:03.410 --> 00:40:05.430 align:middle line:84% Does that make sense to you guys up there? 00:40:05.430 --> 00:40:08.010 align:middle line:90% 00:40:08.010 --> 00:40:10.250 align:middle line:90% Yes, no? 00:40:10.250 --> 00:40:11.130 align:middle line:90% AUDIENCE: Yes. 00:40:11.130 --> 00:40:13.850 align:middle line:90% SCOTT DONEY: OK. 00:40:13.850 --> 00:40:16.850 align:middle line:84% And we'll get back to, later in the course, 00:40:16.850 --> 00:40:20.370 align:middle line:84% why these two systems are different. 00:40:20.370 --> 00:40:23.930 align:middle line:84% But the main thought is that one of the things that's 00:40:23.930 --> 00:40:28.130 align:middle line:84% different about these is that you have probably more iron 00:40:28.130 --> 00:40:31.450 align:middle line:84% limitation in this balanced growth. 00:40:31.450 --> 00:40:33.290 align:middle line:84% And the iron limitation basically 00:40:33.290 --> 00:40:37.830 align:middle line:84% knocks all of the phytoplankton down a little bit 00:40:37.830 --> 00:40:42.810 align:middle line:84% so you can't grow as fast, so the zooplankton 00:40:42.810 --> 00:40:46.290 align:middle line:84% have an easier time of grazing you and keeping you in check. 00:40:46.290 --> 00:40:50.710 align:middle line:84% And the bigger phytoplankton that tend to bloom, 00:40:50.710 --> 00:40:53.810 align:middle line:84% the bloom-forming species that are harder for the zooplankton 00:40:53.810 --> 00:40:59.250 align:middle line:84% to keep track of, are really limited in this system 00:40:59.250 --> 00:41:01.980 align:middle line:84% and really can't grow nearly as fast. 00:41:01.980 --> 00:41:10.380 align:middle line:84% And so that iron limitation, the proximate cause for this control 00:41:10.380 --> 00:41:11.320 align:middle line:90% is grazing. 00:41:11.320 --> 00:41:15.300 align:middle line:84% But the distal, underlying cause is iron limitation 00:41:15.300 --> 00:41:17.380 align:middle line:84% on the phytoplankton that changes 00:41:17.380 --> 00:41:20.260 align:middle line:84% both the primary production rates and the community 00:41:20.260 --> 00:41:23.560 align:middle line:84% structure, so who's there, the taxonomy of who's growing. 00:41:23.560 --> 00:41:36.220 align:middle line:90% 00:41:36.220 --> 00:41:38.520 align:middle line:90% OK. 00:41:38.520 --> 00:41:41.040 align:middle line:84% We also might want to look at vertical structure. 00:41:41.040 --> 00:41:56.380 align:middle line:90% 00:41:56.380 --> 00:42:00.040 align:middle line:84% Remember, if we look in depth, we 00:42:00.040 --> 00:42:04.960 align:middle line:84% tend to have light dropping off as an exponential. 00:42:04.960 --> 00:42:06.140 align:middle line:90% So this would be light. 00:42:06.140 --> 00:42:09.520 align:middle line:90% 00:42:09.520 --> 00:42:14.080 align:middle line:90% Nutrients often look like this. 00:42:14.080 --> 00:42:16.320 align:middle line:84% So you have more nutrients at depth 00:42:16.320 --> 00:42:21.000 align:middle line:90% than you do at the surface. 00:42:21.000 --> 00:42:24.040 align:middle line:84% And you'll commonly see, particularly 00:42:24.040 --> 00:42:29.420 align:middle line:84% in the subtropical gyres, you'll see a-- 00:42:29.420 --> 00:42:35.600 align:middle line:90% 00:42:35.600 --> 00:42:38.360 align:middle line:84% it's hard to do without color, but color doesn't show up 00:42:38.360 --> 00:42:42.440 align:middle line:90% very well on the monitors. 00:42:42.440 --> 00:42:45.260 align:middle line:84% You'll see what's called a deep chlorophyll maximum. 00:42:45.260 --> 00:42:52.880 align:middle line:90% 00:42:52.880 --> 00:42:56.240 align:middle line:84% And the deep chlorophyll maximum can have two causes. 00:42:56.240 --> 00:43:00.430 align:middle line:84% It can be caused by actual cell abundance. 00:43:00.430 --> 00:43:03.210 align:middle line:90% 00:43:03.210 --> 00:43:06.810 align:middle line:84% So it could actually be a real maximum and biomass or cell 00:43:06.810 --> 00:43:08.330 align:middle line:90% abundance. 00:43:08.330 --> 00:43:12.130 align:middle line:84% And the argument there is, well, up at the surface, 00:43:12.130 --> 00:43:14.530 align:middle line:84% I don't have enough nutrients to grow, 00:43:14.530 --> 00:43:17.450 align:middle line:84% or the phytoplankton don't have enough nutrients to grow. 00:43:17.450 --> 00:43:21.090 align:middle line:84% There's plenty of light but just no nutrients. 00:43:21.090 --> 00:43:24.850 align:middle line:84% Deep in the water column, I have nutrients but no light. 00:43:24.850 --> 00:43:26.750 align:middle line:84% And the deep chlorophyll maximum, 00:43:26.750 --> 00:43:30.550 align:middle line:84% which is often somewhere about the euphotic depth-- 00:43:30.550 --> 00:43:33.490 align:middle line:90% 00:43:33.490 --> 00:43:37.810 align:middle line:84% so, commonly, around the 1% light level-- 00:43:37.810 --> 00:43:40.530 align:middle line:84% is kind of a happy medium, where I might have some 00:43:40.530 --> 00:43:43.350 align:middle line:90% nutrients there and some light. 00:43:43.350 --> 00:43:45.450 align:middle line:90% And I need both to grow. 00:43:45.450 --> 00:43:47.610 align:middle line:84% And so the deep chlorophyll maximum 00:43:47.610 --> 00:43:52.570 align:middle line:84% can be a cell abundance maximum because of, basically, living 00:43:52.570 --> 00:43:56.990 align:middle line:84% on the interface where you get both light and nutrients. 00:43:56.990 --> 00:44:02.790 align:middle line:84% It can also be an apparent maximum 00:44:02.790 --> 00:44:05.670 align:middle line:84% because cellular chlorophyll to carbon ratios 00:44:05.670 --> 00:44:11.690 align:middle line:84% vary through a process called photoacclimation. 00:44:11.690 --> 00:44:14.390 align:middle line:90% 00:44:14.390 --> 00:44:19.310 align:middle line:84% Photoacclimation is if you take an individual cell, 00:44:19.310 --> 00:44:23.190 align:middle line:84% and if they are light starved, if they don't have enough light, 00:44:23.190 --> 00:44:26.910 align:middle line:84% they will increase their chlorophyll faster 00:44:26.910 --> 00:44:35.630 align:middle line:84% than carbon or other components of their cell mechanism. 00:44:35.630 --> 00:44:41.790 align:middle line:84% Because if you're light limited, what you need is light. 00:44:41.790 --> 00:44:45.170 align:middle line:84% And so you devote-- think about it from an energy point of view. 00:44:45.170 --> 00:44:49.910 align:middle line:84% You're going to devote energy to manufacturing the chlorophyll 00:44:49.910 --> 00:44:52.710 align:middle line:90% in order to boost that up. 00:44:52.710 --> 00:44:57.000 align:middle line:84% It can also occur through photoadaptation. 00:44:57.000 --> 00:45:03.160 align:middle line:84% And these terms are get bandied about a little bit too loosely. 00:45:03.160 --> 00:45:05.720 align:middle line:84% Photoadaptation, I think of as, there 00:45:05.720 --> 00:45:10.280 align:middle line:84% are some species that are better adapted 00:45:10.280 --> 00:45:13.280 align:middle line:90% for low light environments. 00:45:13.280 --> 00:45:20.400 align:middle line:84% And they tend to grow in the deep chlorophyll maximum. 00:45:20.400 --> 00:45:23.920 align:middle line:84% And they have inherent to them higher 00:45:23.920 --> 00:45:26.120 align:middle line:84% chlorophyll-to-carbon ratios because they're 00:45:26.120 --> 00:45:28.440 align:middle line:90% adapted to low light. 00:45:28.440 --> 00:45:33.720 align:middle line:84% So photoacclimation is a physiological response 00:45:33.720 --> 00:45:36.440 align:middle line:84% to an individual cell or cell culture. 00:45:36.440 --> 00:45:38.600 align:middle line:84% Photoadaptation probably technically 00:45:38.600 --> 00:45:42.280 align:middle line:84% is best thought of as a cell succession, 00:45:42.280 --> 00:45:46.120 align:middle line:84% as a species succession, over longer time periods, where 00:45:46.120 --> 00:45:49.120 align:middle line:84% one species can replace another because it's better 00:45:49.120 --> 00:45:50.860 align:middle line:90% acclimated to that niche. 00:45:50.860 --> 00:45:53.680 align:middle line:90% 00:45:53.680 --> 00:45:56.740 align:middle line:84% AUDIENCE: Can any phytoplankton acclimate to-- 00:45:56.740 --> 00:46:00.740 align:middle line:84% SCOTT DONEY: Most phytoplankton can show some acclimation. 00:46:00.740 --> 00:46:04.880 align:middle line:84% But there's a real question about how plastic cells are. 00:46:04.880 --> 00:46:07.740 align:middle line:90% 00:46:07.740 --> 00:46:12.660 align:middle line:84% So in addition to selling this book, which unfortunately I 00:46:12.660 --> 00:46:17.840 align:middle line:84% don't get any money from, I did bring down-- 00:46:17.840 --> 00:46:24.660 align:middle line:90% 00:46:24.660 --> 00:46:31.140 align:middle line:84% and just focus on the middle graph or the middle line. 00:46:31.140 --> 00:46:33.980 align:middle line:90% Let's do one at a time then. 00:46:33.980 --> 00:46:34.760 align:middle line:90% How's that? 00:46:34.760 --> 00:46:38.100 align:middle line:90% 00:46:38.100 --> 00:46:38.755 align:middle line:90% Is that good? 00:46:38.755 --> 00:46:39.380 align:middle line:90% AUDIENCE: Good. 00:46:39.380 --> 00:46:39.880 align:middle line:90% Yeah. 00:46:39.880 --> 00:46:41.940 align:middle line:90% SCOTT DONEY: OK. 00:46:41.940 --> 00:46:47.660 align:middle line:84% This is panel is showing the summertime primary production 00:46:47.660 --> 00:46:50.020 align:middle line:90% estimated from space. 00:46:50.020 --> 00:46:55.960 align:middle line:84% And the way this is done is, you look at visible radiation. 00:46:55.960 --> 00:46:58.340 align:middle line:84% You look at the different colors of the radiation. 00:46:58.340 --> 00:47:02.680 align:middle line:84% Remember, chlorophyll absorbs in what? 00:47:02.680 --> 00:47:03.740 align:middle line:90% Chlorophyll is green. 00:47:03.740 --> 00:47:04.922 align:middle line:90% So what does it absorb? 00:47:04.922 --> 00:47:05.880 align:middle line:90% AUDIENCE: Blue and red. 00:47:05.880 --> 00:47:08.760 align:middle line:84% SCOTT DONEY: It absorbs blue and red, leaving green. 00:47:08.760 --> 00:47:11.900 align:middle line:84% If you look at the light that's backscattered out of the water, 00:47:11.900 --> 00:47:17.760 align:middle line:84% some fraction of the sunlight comes down, enters the ocean. 00:47:17.760 --> 00:47:20.160 align:middle line:84% Some of it gets absorbed by chlorophyll 00:47:20.160 --> 00:47:21.760 align:middle line:90% and by phytoplankton. 00:47:21.760 --> 00:47:26.060 align:middle line:84% But some of the remaining light actually gets backscattered out, 00:47:26.060 --> 00:47:28.400 align:middle line:84% leaves the ocean surface, and you can measure it 00:47:28.400 --> 00:47:30.080 align:middle line:90% from a satellite. 00:47:30.080 --> 00:47:32.120 align:middle line:84% And if you look at the strength of the light 00:47:32.120 --> 00:47:35.000 align:middle line:84% and the different wavelength bands in the visible, 00:47:35.000 --> 00:47:37.760 align:middle line:84% you can actually say, well, that water looks 00:47:37.760 --> 00:47:39.640 align:middle line:90% more green than it looks blue. 00:47:39.640 --> 00:47:42.000 align:middle line:84% Therefore, it has more chlorophyll in it. 00:47:42.000 --> 00:47:44.840 align:middle line:84% It's a little more complicated than that but not that much. 00:47:44.840 --> 00:47:46.560 align:middle line:90% And it's very empirical because. 00:47:46.560 --> 00:47:48.600 align:middle line:84% We don't have excellent models for this. 00:47:48.600 --> 00:47:53.130 align:middle line:84% Using that, you can come up with the amount of chlorophyll 00:47:53.130 --> 00:47:54.050 align:middle line:90% that's there. 00:47:54.050 --> 00:47:57.210 align:middle line:84% You can then make assumptions about light limitation 00:47:57.210 --> 00:47:59.630 align:middle line:90% and nutrients and temperature. 00:47:59.630 --> 00:48:02.810 align:middle line:84% And you can come up with an estimate of primary production. 00:48:02.810 --> 00:48:05.130 align:middle line:84% So this is a seasonal primary production. 00:48:05.130 --> 00:48:11.550 align:middle line:84% It's on a log scale, which I cut off for this purposes. 00:48:11.550 --> 00:48:14.330 align:middle line:84% But maybe we can scan this figure in 00:48:14.330 --> 00:48:17.290 align:middle line:90% and get it into the notes. 00:48:17.290 --> 00:48:23.930 align:middle line:84% So there's almost a factor of 100 range between the purples, 00:48:23.930 --> 00:48:26.970 align:middle line:84% which are very low productivity, and the reds which 00:48:26.970 --> 00:48:30.330 align:middle line:90% are very high productivity. 00:48:30.330 --> 00:48:41.370 align:middle line:84% And so what you see is that to first order, primary production 00:48:41.370 --> 00:48:45.250 align:middle line:90% maps to regions of upwelling. 00:48:45.250 --> 00:48:48.690 align:middle line:84% In regions where you're bringing nutrients up to the surface, 00:48:48.690 --> 00:48:51.230 align:middle line:84% you have a lot of phytoplankton, and you 00:48:51.230 --> 00:48:53.590 align:middle line:90% have a lot of photosynthesis. 00:48:53.590 --> 00:48:59.030 align:middle line:84% So you see maxima along the equator 00:48:59.030 --> 00:49:01.550 align:middle line:84% in both the Pacific and the Atlantic, 00:49:01.550 --> 00:49:06.790 align:middle line:84% maxima in the Arabian Sea because of monsoonal upwelling. 00:49:06.790 --> 00:49:09.790 align:middle line:90% This is the summer season. 00:49:09.790 --> 00:49:12.590 align:middle line:84% Along the Benguela and North African coasts 00:49:12.590 --> 00:49:16.030 align:middle line:84% due to coastal upwelling, along Peru because 00:49:16.030 --> 00:49:19.950 align:middle line:84% of coastal upwelling, and then in the high-latitude North 00:49:19.950 --> 00:49:22.430 align:middle line:84% Atlantic and North Pacific, associated 00:49:22.430 --> 00:49:25.990 align:middle line:84% with nutrients that have been brought up by subpolar upwelling 00:49:25.990 --> 00:49:28.630 align:middle line:84% and also deep convective mixing in the winter. 00:49:28.630 --> 00:49:31.230 align:middle line:84% So you have deep convective mixing during the winter brings 00:49:31.230 --> 00:49:33.310 align:middle line:90% nutrients up to the surface. 00:49:33.310 --> 00:49:35.350 align:middle line:84% In the summer, the water stratifies, 00:49:35.350 --> 00:49:38.230 align:middle line:90% and you get a big bloom. 00:49:38.230 --> 00:49:40.750 align:middle line:84% If I slide this over without knocking 00:49:40.750 --> 00:49:43.990 align:middle line:90% my water off the table-- 00:49:43.990 --> 00:49:47.270 align:middle line:90% this is the winter season. 00:49:47.270 --> 00:49:52.600 align:middle line:84% And what you see is, similarly, at high latitudes in the winter 00:49:52.600 --> 00:49:54.600 align:middle line:84% in the Northern Hemisphere, almost no production 00:49:54.600 --> 00:49:56.600 align:middle line:90% because it's very light limited. 00:49:56.600 --> 00:49:59.760 align:middle line:84% You still see the equatorial bands, the coastal bands. 00:49:59.760 --> 00:50:02.240 align:middle line:84% And now you see this band of higher productivity 00:50:02.240 --> 00:50:05.440 align:middle line:84% in the Southern Ocean, which is another region of fairly 00:50:05.440 --> 00:50:09.680 align:middle line:84% deep mixing where you bring nutrients up from below. 00:50:09.680 --> 00:50:12.360 align:middle line:84% What's intriguing in the Southern Ocean is 00:50:12.360 --> 00:50:16.800 align:middle line:84% that you do see possible hints, depending on which set of data 00:50:16.800 --> 00:50:21.960 align:middle line:84% you look at, that the productivity is higher downwind 00:50:21.960 --> 00:50:29.200 align:middle line:84% or downstream of land masses and some subsurface geological 00:50:29.200 --> 00:50:30.400 align:middle line:90% features. 00:50:30.400 --> 00:50:34.840 align:middle line:84% And some people are arguing that those patterns are actually 00:50:34.840 --> 00:50:36.800 align:middle line:90% controlled by iron. 00:50:36.800 --> 00:50:40.360 align:middle line:84% This is a region where there's documented iron limitation. 00:50:40.360 --> 00:50:43.020 align:middle line:84% Iron has a fairly high scavenging rate. 00:50:43.020 --> 00:50:45.320 align:middle line:84% So there's not a lot of iron in the surface layer. 00:50:45.320 --> 00:50:48.440 align:middle line:84% And so where you have atmospheric deposition of dust, 00:50:48.440 --> 00:50:52.900 align:middle line:84% so, for example, off of Patagonia or downstream 00:50:52.900 --> 00:50:56.220 align:middle line:84% of the plateau that New Zealand sits on 00:50:56.220 --> 00:50:58.660 align:middle line:84% because of iron coming off the sediments, 00:50:58.660 --> 00:51:01.620 align:middle line:84% you might have elevated productivity. 00:51:01.620 --> 00:51:05.140 align:middle line:84% But those are basically the general patterns or story 00:51:05.140 --> 00:51:09.340 align:middle line:84% of primary production, which is a seasonality associated 00:51:09.340 --> 00:51:11.700 align:middle line:84% with mixing and temperature and light 00:51:11.700 --> 00:51:15.100 align:middle line:84% and then also broad geographic distribution 00:51:15.100 --> 00:51:18.800 align:middle line:84% controlled by convective mixing and upwelling of nutrients. 00:51:18.800 --> 00:51:22.140 align:middle line:90% 00:51:22.140 --> 00:51:24.060 align:middle line:84% AUDIENCE: I think I have a second [INAUDIBLE]. 00:51:24.060 --> 00:51:26.660 align:middle line:90% SCOTT DONEY: Yeah. 00:51:26.660 --> 00:51:32.700 align:middle line:84% The best satellite out there is SeaWiFS. 00:51:32.700 --> 00:51:33.200 align:middle line:90% Oops. 00:51:33.200 --> 00:51:33.700 align:middle line:90% Whoo. 00:51:33.700 --> 00:51:39.060 align:middle line:90% 00:51:39.060 --> 00:51:42.220 align:middle line:84% And if you just google SeaWiFS, you'll 00:51:42.220 --> 00:51:45.280 align:middle line:84% get more images than you want to. 00:51:45.280 --> 00:51:54.890 align:middle line:90% 00:51:54.890 --> 00:51:55.390 align:middle line:90% Yeah. 00:51:55.390 --> 00:51:56.765 align:middle line:84% As long as the instructor doesn't 00:51:56.765 --> 00:51:58.330 align:middle line:90% develop Tourette's, we're OK. 00:51:58.330 --> 00:52:02.470 align:middle line:90% 00:52:02.470 --> 00:52:03.750 align:middle line:90% OK. 00:52:03.750 --> 00:52:07.550 align:middle line:84% So I've been talking about photosynthesis 00:52:07.550 --> 00:52:09.930 align:middle line:84% and not really telling you how we measure it. 00:52:09.930 --> 00:52:12.350 align:middle line:84% AUDIENCE: [INAUDIBLE] really confused too [INAUDIBLE]. 00:52:12.350 --> 00:52:13.870 align:middle line:90% SCOTT DONEY: Oh, I'm sorry. 00:52:13.870 --> 00:52:17.410 align:middle line:84% There was somebody walking by the window of the classroom, 00:52:17.410 --> 00:52:20.750 align:middle line:90% making random, irrational-- 00:52:20.750 --> 00:52:22.150 align:middle line:90% I think he was calling-- yeah. 00:52:22.150 --> 00:52:24.510 align:middle line:84% Kristen thinks he was calling his dog. 00:52:24.510 --> 00:52:25.550 align:middle line:90% But-- 00:52:25.550 --> 00:52:28.532 align:middle line:90% [LAUGHTER] 00:52:28.532 --> 00:52:30.030 align:middle line:90% 00:52:30.030 --> 00:52:31.015 align:middle line:90% Sorry. 00:52:31.015 --> 00:52:32.890 align:middle line:84% It's not that I forget you guys are up there, 00:52:32.890 --> 00:52:35.030 align:middle line:84% but sometimes the jokes just don't translate 00:52:35.030 --> 00:52:37.710 align:middle line:90% through the video link. 00:52:37.710 --> 00:52:39.530 align:middle line:84% So we've been talking about photosynthesis, 00:52:39.530 --> 00:52:41.990 align:middle line:84% but we haven't really talked photosynthesis 00:52:41.990 --> 00:52:43.550 align:middle line:90% in primary production. 00:52:43.550 --> 00:52:46.450 align:middle line:84% But we haven't talked about how we measure it. 00:52:46.450 --> 00:52:51.010 align:middle line:90% And this is not a methods class. 00:52:51.010 --> 00:52:54.650 align:middle line:84% But what we're going to find in the next couple of lectures 00:52:54.650 --> 00:52:59.450 align:middle line:84% is that we're going to start defining particular processes. 00:52:59.450 --> 00:53:02.850 align:middle line:84% And they're somewhat operationally defined. 00:53:02.850 --> 00:53:05.610 align:middle line:84% And so you really need to have some understanding of how 00:53:05.610 --> 00:53:08.130 align:middle line:84% they're measured so that you can understand 00:53:08.130 --> 00:53:09.610 align:middle line:90% how they're interconnected. 00:53:09.610 --> 00:53:12.850 align:middle line:84% Because there are classic things that sound 00:53:12.850 --> 00:53:15.370 align:middle line:84% like they should be giving you the same results that they're 00:53:15.370 --> 00:53:22.010 align:middle line:84% measuring, the same broad parts of the elephant. 00:53:22.010 --> 00:53:23.810 align:middle line:84% The picturesque is a group of blind people 00:53:23.810 --> 00:53:26.310 align:middle line:84% walking around an elephant, trying to figure out what it is. 00:53:26.310 --> 00:53:28.720 align:middle line:84% You think you're all measuring the tail, 00:53:28.720 --> 00:53:30.470 align:middle line:84% but you're measuring it in different ways. 00:53:30.470 --> 00:53:32.690 align:middle line:84% And then you get inconsistent results. 00:53:32.690 --> 00:53:34.690 align:middle line:84% And the reason is because the way 00:53:34.690 --> 00:53:36.410 align:middle line:84% you're measuring them is measuring 00:53:36.410 --> 00:53:39.890 align:middle line:84% is truly actually measuring different aspects of the system. 00:53:39.890 --> 00:53:42.170 align:middle line:84% And so we're going to go through some description 00:53:42.170 --> 00:53:48.670 align:middle line:84% of primary production to give you some broad ideas on that. 00:53:48.670 --> 00:53:52.950 align:middle line:90% There's a few main ways. 00:53:52.950 --> 00:53:58.047 align:middle line:84% One would be, if you remember, photosynthesis-- oops, 00:53:58.047 --> 00:53:59.130 align:middle line:90% writing it the wrong way-- 00:53:59.130 --> 00:54:08.350 align:middle line:84% CO2 plus water goes to carbohydrate plus oxygen. 00:54:08.350 --> 00:54:11.150 align:middle line:90% That was the basic equation. 00:54:11.150 --> 00:54:13.830 align:middle line:84% So there's a couple ways we could attack this. 00:54:13.830 --> 00:54:23.550 align:middle line:84% We could measure the formation of the carbohydrate. 00:54:23.550 --> 00:54:30.190 align:middle line:84% We could measure the loss of CO2. 00:54:30.190 --> 00:54:37.232 align:middle line:84% Or we could measure the production of oxygen. 00:54:37.232 --> 00:54:39.190 align:middle line:84% We're not going to deal with water because it's 00:54:39.190 --> 00:54:43.200 align:middle line:84% an aquatic system, and it would be way too hard to track 00:54:43.200 --> 00:54:45.880 align:middle line:90% the water loss. 00:54:45.880 --> 00:54:55.040 align:middle line:84% Or we could look at light absorption utilization. 00:54:55.040 --> 00:55:00.960 align:middle line:84% Because there actually is a light term in the forward 00:55:00.960 --> 00:55:02.380 align:middle line:90% in the forward reaction. 00:55:02.380 --> 00:55:05.120 align:middle line:90% 00:55:05.120 --> 00:55:12.640 align:middle line:84% The initial work was done by [? Gran ?] starting 00:55:12.640 --> 00:55:16.520 align:middle line:84% around the end of the First World War. 00:55:16.520 --> 00:55:23.960 align:middle line:84% And they were doing incubations of the change in oxygen 00:55:23.960 --> 00:55:28.300 align:middle line:84% over time in light and dark bottles. 00:55:28.300 --> 00:55:32.560 align:middle line:90% 00:55:32.560 --> 00:55:38.620 align:middle line:84% So these would be incubations that were done in a laboratory. 00:55:38.620 --> 00:55:42.400 align:middle line:90% 00:55:42.400 --> 00:55:45.260 align:middle line:84% You would inoculate a certain amount of phytoplankton. 00:55:45.260 --> 00:55:47.120 align:middle line:84% You would then close up the bottle. 00:55:47.120 --> 00:55:50.980 align:middle line:84% Well, you'd inoculate the phytoplankton, 00:55:50.980 --> 00:55:53.460 align:middle line:84% measure the amount of oxygen that's there at the beginning 00:55:53.460 --> 00:55:58.460 align:middle line:84% time, close the bottle up, either put them in the dark 00:55:58.460 --> 00:56:02.380 align:middle line:84% or put them in the light, and then measure 00:56:02.380 --> 00:56:08.420 align:middle line:84% how much is there a day later, for example. 00:56:08.420 --> 00:56:11.240 align:middle line:84% And the limitations on this, of course, 00:56:11.240 --> 00:56:13.940 align:middle line:84% are that you need to have a big enough signal so 00:56:13.940 --> 00:56:19.260 align:middle line:84% that you can actually measure a drawdown of oxygen. 00:56:19.260 --> 00:56:24.460 align:middle line:84% So this was pretty good for coastal systems, 00:56:24.460 --> 00:56:27.380 align:middle line:84% not so good for open ocean systems because you just didn't 00:56:27.380 --> 00:56:33.540 align:middle line:84% have a strong enough signal because there just wasn't enough 00:56:33.540 --> 00:56:36.660 align:middle line:90% phytoplankton there. 00:56:36.660 --> 00:56:44.230 align:middle line:84% Also, this was around the time of the introduction of 00:56:44.230 --> 00:56:48.110 align:middle line:84% or the use of the Winkler O2 titration. 00:56:48.110 --> 00:56:51.750 align:middle line:84% So there were fairly good, precise ways 00:56:51.750 --> 00:56:54.890 align:middle line:84% of measuring changes in oxygen with the Winkler titration. 00:56:54.890 --> 00:56:58.190 align:middle line:90% 00:56:58.190 --> 00:57:00.710 align:middle line:90% And let's see. 00:57:00.710 --> 00:57:13.390 align:middle line:84% Nielsen in 1952 introduced the C14 carbon fixation approach. 00:57:13.390 --> 00:57:28.790 align:middle line:84% So this is-- you take an add radiolabeled CO2 to your system. 00:57:28.790 --> 00:57:35.190 align:middle line:84% That gets formed into radiolabeled organic matter. 00:57:35.190 --> 00:57:43.090 align:middle line:84% And you measure how much radiolabel ends up 00:57:43.090 --> 00:57:50.850 align:middle line:90% on particulate organic carbon. 00:57:50.850 --> 00:57:55.850 align:middle line:84% So the idea here is, you spike something with radiolabeled C14 00:57:55.850 --> 00:57:57.370 align:middle line:90% inorganic. 00:57:57.370 --> 00:57:59.690 align:middle line:84% After some period of time, you grow them 00:57:59.690 --> 00:58:00.990 align:middle line:90% again in dark and light. 00:58:00.990 --> 00:58:04.250 align:middle line:84% So you can look at the dark as your control 00:58:04.250 --> 00:58:09.050 align:middle line:84% to see if there are any effects due to absorption or problems 00:58:09.050 --> 00:58:11.570 align:middle line:90% like that. 00:58:11.570 --> 00:58:14.690 align:middle line:84% And then you would then filter the sample 00:58:14.690 --> 00:58:17.490 align:middle line:84% and then put it in a scintillation counter 00:58:17.490 --> 00:58:21.182 align:middle line:84% and count how much radioactivity is on your particles. 00:58:21.182 --> 00:58:22.890 align:middle line:84% And you'd have to be very careful to make 00:58:22.890 --> 00:58:27.410 align:middle line:84% sure you got rid of all the seawater that's on your filter. 00:58:27.410 --> 00:58:30.210 align:middle line:84% So you might actually acidify your filter 00:58:30.210 --> 00:58:34.410 align:middle line:84% to drive off any radiolabel that ends up in your inorganic carbon 00:58:34.410 --> 00:58:34.950 align:middle line:90% pool. 00:58:34.950 --> 00:58:39.630 align:middle line:90% 00:58:39.630 --> 00:58:44.090 align:middle line:84% Other than the fact that-- well, there's two issues with this. 00:58:44.090 --> 00:58:48.630 align:middle line:84% One is, if you do this, you're going to be in a constant battle 00:58:48.630 --> 00:58:50.470 align:middle line:84% with people who want to measure radiocarbon 00:58:50.470 --> 00:58:53.190 align:middle line:90% in the natural environment. 00:58:53.190 --> 00:58:57.070 align:middle line:84% In fact, at WHOI, because we have a big accelerator that 00:58:57.070 --> 00:59:00.990 align:middle line:84% measures radiocarbon at natural abundance levels, 00:59:00.990 --> 00:59:04.750 align:middle line:84% there's sort of an informal ban for people 00:59:04.750 --> 00:59:06.390 align:middle line:84% from walking from one set of buildings 00:59:06.390 --> 00:59:07.848 align:middle line:84% to another set of buildings because 00:59:07.848 --> 00:59:09.790 align:middle line:90% of cross-contamination issues. 00:59:09.790 --> 00:59:12.370 align:middle line:90% It is actually a serious issue. 00:59:12.370 --> 00:59:15.953 align:middle line:84% But that's more that's more social than it is analytical. 00:59:15.953 --> 00:59:17.370 align:middle line:84% AUDIENCE: Like change their shoes? 00:59:17.370 --> 00:59:19.390 align:middle line:84% SCOTT DONEY: Yeah, changing your shoes or going home 00:59:19.390 --> 00:59:21.598 align:middle line:84% and not coming back until you've showered and changed 00:59:21.598 --> 00:59:22.250 align:middle line:90% your clothes. 00:59:22.250 --> 00:59:24.950 align:middle line:90% 00:59:24.950 --> 00:59:28.150 align:middle line:84% One problem is that this technique typically 00:59:28.150 --> 00:59:32.990 align:middle line:84% only measures particulate organic carbon. 00:59:32.990 --> 00:59:36.380 align:middle line:84% I want to go on to a next page for this. 00:59:36.380 --> 00:59:55.280 align:middle line:90% 00:59:55.280 --> 00:59:59.920 align:middle line:90% So you've got this 14 CO2. 00:59:59.920 --> 01:00:09.440 align:middle line:84% It gets taken up into 14C organic matter. 01:00:09.440 --> 01:00:14.520 align:middle line:84% Now, if you ran this reaction instantaneously-- 01:00:14.520 --> 01:00:17.400 align:middle line:84% so if you were able to spike the sample 01:00:17.400 --> 01:00:22.120 align:middle line:84% and measure it a millisecond later-- 01:00:22.120 --> 01:00:25.360 align:middle line:84% and, presumably, everything was well mixed-- 01:00:25.360 --> 01:00:27.680 align:middle line:84% the only reaction you'd be measuring 01:00:27.680 --> 01:00:30.440 align:middle line:90% would be this forward reaction. 01:00:30.440 --> 01:00:35.740 align:middle line:84% Because there would be so little production of organic matter 01:00:35.740 --> 01:00:38.740 align:middle line:90% that has this radiolabel. 01:00:38.740 --> 01:00:40.340 align:middle line:84% You use high enough values that you 01:00:40.340 --> 01:00:42.940 align:middle line:84% don't worry about the natural background, 01:00:42.940 --> 01:00:48.560 align:middle line:84% that you won't have any loss of this. 01:00:48.560 --> 01:00:53.260 align:middle line:84% And so that would be an instantaneous measure of. 01:00:53.260 --> 01:00:55.140 align:middle line:90% gross primary production. 01:00:55.140 --> 01:01:01.680 align:middle line:84% Remember, gross primary production was photosynthesis. 01:01:01.680 --> 01:01:07.340 align:middle line:90% 01:01:07.340 --> 01:01:10.860 align:middle line:84% Net primary production is photosynthesis 01:01:10.860 --> 01:01:21.980 align:middle line:90% minus autotroph respiration. 01:01:21.980 --> 01:01:26.820 align:middle line:90% 01:01:26.820 --> 01:01:29.780 align:middle line:84% The problem comes because of the finite duration 01:01:29.780 --> 01:01:36.030 align:middle line:90% of the incubation. 01:01:36.030 --> 01:01:38.070 align:middle line:84% You have to run it long enough so 01:01:38.070 --> 01:01:41.030 align:middle line:84% that you get a big enough signal to actually see. 01:01:41.030 --> 01:01:43.490 align:middle line:84% But if you start to run it for, let's say, 01:01:43.490 --> 01:01:47.790 align:middle line:84% 24 hours or 12 hours-- those are the two common ones, 01:01:47.790 --> 01:01:50.310 align:middle line:90% are 12 hour-- 01:01:50.310 --> 01:01:57.190 align:middle line:90% you'll hear it as dawn to dusk-- 01:01:57.190 --> 01:01:58.850 align:middle line:90% or 24 hours. 01:01:58.850 --> 01:02:01.470 align:middle line:90% 01:02:01.470 --> 01:02:07.190 align:middle line:84% Some of this radiolabeled organic carbon 01:02:07.190 --> 01:02:11.030 align:middle line:84% might have other fates than staying in particulate. 01:02:11.030 --> 01:02:17.510 align:middle line:84% It might start forming radiolabeled DOC. 01:02:17.510 --> 01:02:19.470 align:middle line:84% And typically you only are looking 01:02:19.470 --> 01:02:24.430 align:middle line:84% at the stuff that's filtered onto particles, not 01:02:24.430 --> 01:02:25.910 align:middle line:90% in the dissolve pool. 01:02:25.910 --> 01:02:27.610 align:middle line:84% So if you're doing this technique, 01:02:27.610 --> 01:02:32.210 align:middle line:84% the C14 primary production technique, 01:02:32.210 --> 01:02:35.970 align:middle line:84% if there's a substantial production of DOC, 01:02:35.970 --> 01:02:37.770 align:middle line:84% you'd actually be underestimating 01:02:37.770 --> 01:02:41.010 align:middle line:84% your total photosynthesis rate because you'd 01:02:41.010 --> 01:02:43.450 align:middle line:84% be missing the fraction that ended up 01:02:43.450 --> 01:02:46.890 align:middle line:90% in the dissolved organic pool. 01:02:46.890 --> 01:02:50.050 align:middle line:84% If you ran it for long enough, you'd 01:02:50.050 --> 01:03:01.850 align:middle line:84% actually start having the back reaction, 01:03:01.850 --> 01:03:06.410 align:middle line:84% where some of this organic matter would then be respired. 01:03:06.410 --> 01:03:11.130 align:middle line:84% And that can be a problem if you have a lot of photorespiration, 01:03:11.130 --> 01:03:13.570 align:middle line:84% where you're forming organic matter 01:03:13.570 --> 01:03:16.290 align:middle line:84% and then you're respiring it right away. 01:03:16.290 --> 01:03:19.930 align:middle line:84% It might not be that the whole cell has to become radiolabeled 01:03:19.930 --> 01:03:24.490 align:middle line:84% but that certain metabolic pathways get radiolabeled and so 01:03:24.490 --> 01:03:27.370 align:middle line:84% that you lose organic matter fairly quickly. 01:03:27.370 --> 01:03:29.980 align:middle line:90% Those are both complications. 01:03:29.980 --> 01:03:33.940 align:middle line:84% And the C14 technique generally, although it's 01:03:33.940 --> 01:03:44.540 align:middle line:84% the most widely used, is somewhere between GPP and NPP. 01:03:44.540 --> 01:03:46.960 align:middle line:90% It's not truly NPP. 01:03:46.960 --> 01:03:48.780 align:middle line:90% It's not truly GPP. 01:03:48.780 --> 01:03:51.900 align:middle line:84% But it's what's most commonly measured 01:03:51.900 --> 01:03:53.440 align:middle line:90% and what's compared against. 01:03:53.440 --> 01:03:59.060 align:middle line:90% 01:03:59.060 --> 01:04:07.420 align:middle line:84% When they first started doing this about contamination-- 01:04:07.420 --> 01:04:12.460 align:middle line:84% and this is especially true for open ocean plankton. 01:04:12.460 --> 01:04:17.500 align:middle line:84% Open ocean plankton are used to relatively low trace metals. 01:04:17.500 --> 01:04:20.440 align:middle line:84% And in a lot of the bottle incubations, 01:04:20.440 --> 01:04:21.900 align:middle line:84% you were getting contamination that 01:04:21.900 --> 01:04:26.580 align:middle line:84% led to underestimates in primary production because 01:04:26.580 --> 01:04:28.920 align:middle line:90% of trace metal poisoning. 01:04:28.920 --> 01:04:33.840 align:middle line:84% And so there's been a lot of effort, back in the 1970s, 01:04:33.840 --> 01:04:39.068 align:middle line:84% to develop trace metal clean techniques for your C14 work. 01:04:39.068 --> 01:04:41.360 align:middle line:84% And they think they've gotten around most of the bottle 01:04:41.360 --> 01:04:43.280 align:middle line:90% incubation effects. 01:04:43.280 --> 01:04:45.660 align:middle line:84% But a lot of the older data is suspect. 01:04:45.660 --> 01:04:56.600 align:middle line:90% 01:04:56.600 --> 01:04:57.980 align:middle line:90% Where did I get last year? 01:04:57.980 --> 01:05:07.360 align:middle line:90% 01:05:07.360 --> 01:05:07.880 align:middle line:90% OK. 01:05:07.880 --> 01:05:13.580 align:middle line:90% 01:05:13.580 --> 01:05:17.520 align:middle line:84% There are a couple of other techniques that are used. 01:05:17.520 --> 01:05:26.940 align:middle line:90% There is an O18 technique. 01:05:26.940 --> 01:05:30.540 align:middle line:84% And the idea there is-- remember, one of the ways 01:05:30.540 --> 01:05:32.760 align:middle line:84% would be to look at oxygen production. 01:05:32.760 --> 01:05:35.940 align:middle line:90% 01:05:35.940 --> 01:05:39.540 align:middle line:84% But oxygen production has some of the same issues. 01:05:39.540 --> 01:05:43.540 align:middle line:84% If you run an incubation and you're producing oxygen, 01:05:43.540 --> 01:05:48.260 align:middle line:84% anybody who's respiring, who has respiration, not just 01:05:48.260 --> 01:05:51.300 align:middle line:84% the phytoplankton, but also any heterotrophs, 01:05:51.300 --> 01:05:53.320 align:middle line:90% are going to be reducing oxygen. 01:05:53.320 --> 01:05:56.260 align:middle line:84% So you could have a lot of photosynthesis 01:05:56.260 --> 01:05:59.700 align:middle line:84% but very little growth in oxygen in your container 01:05:59.700 --> 01:06:03.140 align:middle line:84% because somebody else is respiring at the same time. 01:06:03.140 --> 01:06:10.180 align:middle line:84% But if you spike the water and do this in heavy water 01:06:10.180 --> 01:06:19.580 align:middle line:84% and then measure the O18-O16 ratio in the oxygen, 01:06:19.580 --> 01:06:24.190 align:middle line:84% you can really get at just the forward reaction. 01:06:24.190 --> 01:06:26.110 align:middle line:84% And the reason why it's the forward reaction 01:06:26.110 --> 01:06:30.710 align:middle line:84% is, so little of your water is being used up 01:06:30.710 --> 01:06:36.390 align:middle line:84% that there's really little effect. 01:06:36.390 --> 01:06:38.110 align:middle line:84% Very little of the water's used up. 01:06:38.110 --> 01:06:40.190 align:middle line:84% Very little of the oxygen is changed 01:06:40.190 --> 01:06:43.070 align:middle line:84% because you have a lot of oxygen, typically, 01:06:43.070 --> 01:06:46.190 align:middle line:90% in the container. 01:06:46.190 --> 01:06:48.670 align:middle line:84% And so you can't really affect or back 01:06:48.670 --> 01:06:53.830 align:middle line:84% affect the reaction of your 18 oxygen 01:06:53.830 --> 01:06:56.030 align:middle line:90% if you use a big enough spike. 01:06:56.030 --> 01:07:00.190 align:middle line:84% And so this O18 spiking incubation really 01:07:00.190 --> 01:07:03.190 align:middle line:84% is probably one of our best measures 01:07:03.190 --> 01:07:05.550 align:middle line:90% of gross primary production. 01:07:05.550 --> 01:07:08.370 align:middle line:90% It's not commonly done. 01:07:08.370 --> 01:07:10.590 align:middle line:90% It's done a handful of times. 01:07:10.590 --> 01:07:18.510 align:middle line:84% Probably for every 100 cruises with C14, somebody does O18. 01:07:18.510 --> 01:07:20.590 align:middle line:84% But it does give some idea where then you 01:07:20.590 --> 01:07:35.730 align:middle line:84% can go and look at the correction for GPP to C14 NPP. 01:07:35.730 --> 01:07:38.170 align:middle line:84% So you could make a correction for what 01:07:38.170 --> 01:07:40.170 align:middle line:84% the true gross primary production is 01:07:40.170 --> 01:07:44.292 align:middle line:84% relative to the C14 measurements that are being made. 01:07:44.292 --> 01:07:46.250 align:middle line:84% AUDIENCE: That's just because it's a lot harder 01:07:46.250 --> 01:07:47.850 align:middle line:90% to do that technique than the-- 01:07:47.850 --> 01:07:50.330 align:middle line:90% SCOTT DONEY: Yeah. 01:07:50.330 --> 01:07:53.330 align:middle line:84% The C14, you can do by scintillation counter. 01:07:53.330 --> 01:07:57.170 align:middle line:84% This, first off, you're dealing with gases. 01:07:57.170 --> 01:08:00.930 align:middle line:84% So before, you're just filtering water and putting particles 01:08:00.930 --> 01:08:02.650 align:middle line:90% onto filters. 01:08:02.650 --> 01:08:05.690 align:middle line:84% Here, you actually need to do it in a gas-tight system, where 01:08:05.690 --> 01:08:08.210 align:middle line:84% you can keep track of that you're not having gas 01:08:08.210 --> 01:08:10.970 align:middle line:90% exchange during the experiment. 01:08:10.970 --> 01:08:15.290 align:middle line:84% Then you need to run this on a gas-proportional mass 01:08:15.290 --> 01:08:16.890 align:middle line:90% spectrometer. 01:08:16.890 --> 01:08:19.990 align:middle line:84% They're not nearly as common as scintillation counters. 01:08:19.990 --> 01:08:22.300 align:middle line:90% It's just it's a lot more work. 01:08:22.300 --> 01:08:24.399 align:middle line:90% Also, and this is expensive. 01:08:24.399 --> 01:08:27.540 align:middle line:90% 01:08:27.540 --> 01:08:32.540 align:middle line:84% AUDIENCE: Just to make sure here, the reason this works 01:08:32.540 --> 01:08:34.700 align:middle line:84% is because the oxygen from the water 01:08:34.700 --> 01:08:40.620 align:middle line:84% goes into oxygen gas rather than the organic matter. 01:08:40.620 --> 01:08:43.800 align:middle line:90% SCOTT DONEY: Right. 01:08:43.800 --> 01:08:47.420 align:middle line:90% AUDIENCE: I Just wanted to-- 01:08:47.420 --> 01:08:49.952 align:middle line:84% it's something we were questioning during generals. 01:08:49.952 --> 01:08:50.660 align:middle line:90% SCOTT DONEY: Yes. 01:08:50.660 --> 01:08:56.180 align:middle line:84% In photosynthesis, one of the oxygens in O2 01:08:56.180 --> 01:08:58.220 align:middle line:90% is coming from water. 01:08:58.220 --> 01:09:06.620 align:middle line:84% Remember, CO2 plus water goes to CH2O plus O2. 01:09:06.620 --> 01:09:09.080 align:middle line:90% So it's that. 01:09:09.080 --> 01:09:15.180 align:middle line:90% 01:09:15.180 --> 01:09:23.240 align:middle line:84% There have been a lot of advances 01:09:23.240 --> 01:09:28.439 align:middle line:84% in making DIC measurements and also oxygen measurements. 01:09:28.439 --> 01:09:30.640 align:middle line:84% So people are starting to do a lot more 01:09:30.640 --> 01:09:38.680 align:middle line:84% computer-controlled titrations of the changes in DIC 01:09:38.680 --> 01:09:39.800 align:middle line:90% and oxygen. 01:09:39.800 --> 01:09:42.020 align:middle line:84% So unlike [? Gran's ?] original experiments, 01:09:42.020 --> 01:09:46.040 align:middle line:84% where there just wasn't enough signal for him to measure, 01:09:46.040 --> 01:09:54.440 align:middle line:84% people can start to look at diurnal changes in DIC 01:09:54.440 --> 01:10:01.460 align:middle line:84% and oxygen, both in incubations and in the field. 01:10:01.460 --> 01:10:05.120 align:middle line:90% 01:10:05.120 --> 01:10:07.880 align:middle line:84% And gas exchange really isn't fast enough 01:10:07.880 --> 01:10:11.960 align:middle line:84% to equilibrate the water on diurnal timescales. 01:10:11.960 --> 01:10:16.440 align:middle line:84% So the diurnal drawdown if you looked at the diurnal cycle 01:10:16.440 --> 01:10:21.650 align:middle line:84% in the water-- let's say DIC was high in the morning, 01:10:21.650 --> 01:10:25.250 align:middle line:90% low and then high and then low. 01:10:25.250 --> 01:10:31.513 align:middle line:84% That would give you a pretty good estimate for photosynthesis 01:10:31.513 --> 01:10:32.930 align:middle line:84% because you could back out and say 01:10:32.930 --> 01:10:36.210 align:middle line:90% what respiration was at night. 01:10:36.210 --> 01:10:38.930 align:middle line:84% And so people have been trying to do that from the field 01:10:38.930 --> 01:10:41.350 align:middle line:84% to get away from doing bottle incubations, 01:10:41.350 --> 01:10:46.090 align:middle line:84% where anytime you collect an organism from the water column, 01:10:46.090 --> 01:10:48.290 align:middle line:84% there's a chance that you're going to screw it up 01:10:48.290 --> 01:10:50.550 align:middle line:84% and you're going to perturb the system. 01:10:50.550 --> 01:10:54.010 align:middle line:90% 01:10:54.010 --> 01:10:55.770 align:middle line:84% And then finally, we're not going 01:10:55.770 --> 01:10:59.890 align:middle line:84% to go into a lot of the details for the bio-optics. 01:10:59.890 --> 01:11:09.270 align:middle line:84% But the basic idea for the bio-optics is as follows. 01:11:09.270 --> 01:11:20.430 align:middle line:90% 01:11:20.430 --> 01:11:24.950 align:middle line:90% You have photons coming in. 01:11:24.950 --> 01:11:28.430 align:middle line:90% So this would be a photon. 01:11:28.430 --> 01:11:31.490 align:middle line:84% There's lots of different pathways that photon can take. 01:11:31.490 --> 01:11:33.550 align:middle line:90% It can heat the water. 01:11:33.550 --> 01:11:40.190 align:middle line:84% It can be absorbed by detrital junk, that [INAUDIBLE] stuff. 01:11:40.190 --> 01:11:45.470 align:middle line:84% But some of them are actually going to hit a phytoplankton 01:11:45.470 --> 01:11:46.690 align:middle line:90% and be absorbed. 01:11:46.690 --> 01:11:49.750 align:middle line:90% 01:11:49.750 --> 01:11:56.670 align:middle line:84% And if you knew how much was absorbed 01:11:56.670 --> 01:12:00.830 align:middle line:84% and then what the fate of that absorbed light is-- 01:12:00.830 --> 01:12:03.190 align:middle line:90% so that can go several pathways. 01:12:03.190 --> 01:12:09.830 align:middle line:84% So the absorbed photon, it could go to heat. 01:12:09.830 --> 01:12:12.250 align:middle line:84% You could just start cooking your phytoplankton. 01:12:12.250 --> 01:12:15.070 align:middle line:90% 01:12:15.070 --> 01:12:18.150 align:middle line:90% Some of it could be fluoresced-- 01:12:18.150 --> 01:12:23.530 align:middle line:90% 01:12:23.530 --> 01:12:26.930 align:middle line:90% that's not spelled right. 01:12:26.930 --> 01:12:30.930 align:middle line:84% That's supposed to be fluorescence, basically 01:12:30.930 --> 01:12:32.590 align:middle line:84% readmitted at a different wavelength. 01:12:32.590 --> 01:12:36.190 align:middle line:84% Remember, chlorophyll absorbs in the blue, emits in the red. 01:12:36.190 --> 01:12:39.330 align:middle line:90% 01:12:39.330 --> 01:12:48.470 align:middle line:84% Or it could be going to chemical energy for photosynthesis. 01:12:48.470 --> 01:12:52.810 align:middle line:90% 01:12:52.810 --> 01:12:57.370 align:middle line:84% So if you were able to understand and compute 01:12:57.370 --> 01:12:59.650 align:middle line:84% how many of the photons are actually being absorbed 01:12:59.650 --> 01:13:05.010 align:middle line:84% by phytoplankton and then able to partition how much of those 01:13:05.010 --> 01:13:09.050 align:middle line:84% absorbed photons are going into these different pathways, 01:13:09.050 --> 01:13:13.210 align:middle line:84% you would be able to then say something 01:13:13.210 --> 01:13:17.180 align:middle line:84% about how much photosynthesis rates are, 01:13:17.180 --> 01:13:19.540 align:middle line:90% which is this right here. 01:13:19.540 --> 01:13:23.980 align:middle line:84% Now, one of the really clever techniques that's been invented 01:13:23.980 --> 01:13:30.420 align:middle line:84% is it's sometimes called pump and probe 01:13:30.420 --> 01:13:34.480 align:middle line:84% or variable fluorescence, variable fluorescence. 01:13:34.480 --> 01:13:41.620 align:middle line:90% 01:13:41.620 --> 01:13:43.860 align:middle line:90% Basically, it's the idea that-- 01:13:43.860 --> 01:13:48.800 align:middle line:84% let's say you have your chlorophyll antennas. 01:13:48.800 --> 01:13:55.500 align:middle line:90% 01:13:55.500 --> 01:14:00.140 align:middle line:84% At any one particular time, many of these antenna 01:14:00.140 --> 01:14:04.820 align:middle line:90% are open at the reaction sites. 01:14:04.820 --> 01:14:06.940 align:middle line:90% And so a photon comes in. 01:14:06.940 --> 01:14:10.500 align:middle line:84% And some of it's going to get dissipated by heat because it's 01:14:10.500 --> 01:14:12.160 align:middle line:90% just a dissipative system. 01:14:12.160 --> 01:14:15.040 align:middle line:84% Some of it's going to go to chemical energy. 01:14:15.040 --> 01:14:23.460 align:middle line:84% But if you added enough light to the phytoplankton, 01:14:23.460 --> 01:14:28.340 align:middle line:84% you would actually fill up all the reaction centers. 01:14:28.340 --> 01:14:31.840 align:middle line:90% 01:14:31.840 --> 01:14:35.120 align:middle line:84% So let's say you're measuring your phytoplankton. 01:14:35.120 --> 01:14:37.320 align:middle line:84% And then you start giving it enough light 01:14:37.320 --> 01:14:41.260 align:middle line:84% so that you very quickly, on short time scales, 01:14:41.260 --> 01:14:43.800 align:middle line:84% you fill up all the reaction centers 01:14:43.800 --> 01:14:46.740 align:middle line:84% so that none of the reaction centers are open. 01:14:46.740 --> 01:14:49.940 align:middle line:84% They all have just received a photon. 01:14:49.940 --> 01:14:51.798 align:middle line:84% They can't receive another photon. 01:14:51.798 --> 01:14:54.340 align:middle line:84% They can't accept another photon for a certain amount of time 01:14:54.340 --> 01:14:56.800 align:middle line:84% because it takes a certain amount of time for the reaction 01:14:56.800 --> 01:15:01.840 align:middle line:84% centers to process that photon and reset themselves. 01:15:01.840 --> 01:15:09.600 align:middle line:84% If you looked at the change in fluorescence 01:15:09.600 --> 01:15:14.850 align:middle line:84% before and after you've closed all the reaction antenna, 01:15:14.850 --> 01:15:17.410 align:middle line:84% that would give you an idea of how many antenna were actually 01:15:17.410 --> 01:15:19.450 align:middle line:84% open and ready to accept a photon. 01:15:19.450 --> 01:15:26.330 align:middle line:84% Because before you've done this-- let's say some of them 01:15:26.330 --> 01:15:32.570 align:middle line:84% are going to heat, and some of them are going to fluorescence, 01:15:32.570 --> 01:15:34.830 align:middle line:84% and some of them are going to photosynthesis. 01:15:34.830 --> 01:15:37.770 align:middle line:90% 01:15:37.770 --> 01:15:42.130 align:middle line:84% But after you fill the reaction centers, 01:15:42.130 --> 01:15:43.730 align:middle line:84% the argument is, well, the same amount 01:15:43.730 --> 01:15:46.050 align:middle line:90% is going to be going to heat. 01:15:46.050 --> 01:15:48.130 align:middle line:84% You're then going to have this huge amount going 01:15:48.130 --> 01:15:52.210 align:middle line:84% to fluorescence because there's no other pathway for them to go. 01:15:52.210 --> 01:15:55.190 align:middle line:84% And you'd have zero going to photosynthesis. 01:15:55.190 --> 01:16:00.370 align:middle line:90% 01:16:00.370 --> 01:16:02.130 align:middle line:84% And by that pathway, you can then 01:16:02.130 --> 01:16:05.530 align:middle line:84% back out what the photosynthesis rate would 01:16:05.530 --> 01:16:08.570 align:middle line:84% have been before because you now know how many reaction 01:16:08.570 --> 01:16:12.390 align:middle line:90% centers were absorbing light. 01:16:12.390 --> 01:16:14.430 align:middle line:90% So it's pretty clever. 01:16:14.430 --> 01:16:18.230 align:middle line:84% It's just being developed over the last 10 or 15 years. 01:16:18.230 --> 01:16:22.590 align:middle line:84% And it nicely complements the C14 work. 01:16:22.590 --> 01:16:25.250 align:middle line:84% Because instead of focusing on the organic products, 01:16:25.250 --> 01:16:30.110 align:middle line:90% you're now looking at the light. 01:16:30.110 --> 01:16:33.390 align:middle line:84% I just wanted to show this, if I can fit it 01:16:33.390 --> 01:16:37.270 align:middle line:90% on here, this last figure. 01:16:37.270 --> 01:16:38.510 align:middle line:90% Oops. 01:16:38.510 --> 01:16:40.410 align:middle line:84% And then we'll wrap it up for the day. 01:16:40.410 --> 01:16:43.030 align:middle line:90% 01:16:43.030 --> 01:16:47.870 align:middle line:84% This is a summary plot out of this book 01:16:47.870 --> 01:16:51.230 align:middle line:84% I was showing earlier for primary production 01:16:51.230 --> 01:17:00.150 align:middle line:84% from the seven US JGOFS process studies and time series sites. 01:17:00.150 --> 01:17:04.150 align:middle line:84% And so it's primary production-- or photosynthesis, if you like-- 01:17:04.150 --> 01:17:07.550 align:middle line:84% in millimoles carbon per meter squared per day. 01:17:07.550 --> 01:17:11.360 align:middle line:84% This is measured by C14 in all cases. 01:17:11.360 --> 01:17:13.200 align:middle line:84% These are different environments. 01:17:13.200 --> 01:17:17.440 align:middle line:84% And the values range from-- down about the triangles 01:17:17.440 --> 01:17:18.920 align:middle line:90% are the means. 01:17:18.920 --> 01:17:21.780 align:middle line:90% The circles are the maximums. 01:17:21.780 --> 01:17:25.440 align:middle line:90% 01:17:25.440 --> 01:17:28.560 align:middle line:84% And then there are standard statistical ranges. 01:17:28.560 --> 01:17:30.360 align:middle line:84% Typical primary production values 01:17:30.360 --> 01:17:35.360 align:middle line:84% are somewhere between, say, 20 and 30 millimoles carbon 01:17:35.360 --> 01:17:40.640 align:middle line:84% per meter squared per day, with peak values during, say, bloom 01:17:40.640 --> 01:17:45.480 align:middle line:90% seasons as high as 100 to 150. 01:17:45.480 --> 01:17:48.780 align:middle line:84% And so that gives you a scaling for what to expect. 01:17:48.780 --> 01:17:57.560 align:middle line:90% 01:17:57.560 --> 01:17:58.320 align:middle line:90% Great. 01:17:58.320 --> 01:18:00.440 align:middle line:84% So what we'll do is, we'll start talking 01:18:00.440 --> 01:18:05.240 align:middle line:84% about export production and new production and net community 01:18:05.240 --> 01:18:08.750 align:middle line:90% production on Thursday.