Guest Post by Willis Eschenbach [See updated graph]
Inspired by some comments on another thread, I decided to see what I could find in the way of actual measurements of the amount of CO2 in the surface layer of the ocean. I found the following data on the Scripps Institute web site. What they did was drive around the ocean on four different cruises, measuring both the atmospheric CO2 levels and at the same time, the amount of CO2 in the surface seawater. Figure 1 shows those results:
Figure 1. All air-ocean simultaneous measurements from four Scripps cruises are shown as blue dots. The horizontal axis shows sea surface temperature. The vertical axis shows the difference between the CO2 in the overlying air, and the CO2 in the water. The red line is a lowess curve through the data. The paper describing the Scripps data and methods is here.
Now, I have to say that those results were a big surprise to me.
The first surprise was that I was under the impression that there was some kind of close relationship between the atmospheric CO2, and the CO2 in the surface seawater. I expected their values to be within maybe 5 ppmv of each other. But in fact, many parts of the ocean are 50 ppmv lower than the CO2 concentration of the overlying air, and many other parts of the ocean have 50 ppmv or more of CO2 than the CO2 in the air above.
The second surprise was the change in not only the size but even in the sign of the trendline connecting temperature and CO2 (red line in Figure 1). Compared to the CO2 level in the air, below about 17°C the seawater CO2 decreases with increasing temperature, at a rate of about -2 ppmv per °C.
Above about 17°C, however, the seawater CO2 content relative to the air increases fairly rapidly with temperature, at about +4 ppmv per °C.
To describe the situation in another way, when the water is cool, it contains less CO2 than the overlying air … but when the water is warm, it has more CO2 than the overlying air.
Say what? I gotta confess, I have little in the way of explanations or comprehension of the reason for that pattern … all suggestions welcome.
w.
[UPDATE] By popular request, here is the same data, but in absolute rather than relative units and without the lowess curve.
Figure 2. As in Figure 1, but showing the CO2 content of the surface seawater directly. Atmospheric CO2 varied very little during the time of the measurements.
My main question in all of this is, how does the CO2 content of the seawater get to be up to 100 ppmv above the CO2 content of the overlying air? It seems to me that the driver must be biology … but I was born yesterday.
Regards,
w.
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
”when the water is cool, it contains less CO2 than the overlying air … but when the water is warm, it has more CO2 than the overlying air.”
That’s because the pCO2 of the overlying air is nearly irrelevant to the pCO2 of the seawater when compared to temperature, salinity, and biological activity.
”The pH and the pCO2 are not simply functions of the amount of CO2 in the overlying air.”
http://wattsupwiththat.com/2011/10/25/the-reef-abides/
Nick Stokes says:
November 27, 2013 at 4:02 am
Thanks, Nick. My question is, why is it so high, up to 100 ppmv higher than the concentration in the overlying air?
w.
Old England says:
November 27, 2013 at 5:32 am
This and many questions are answered in the cited reference … in any case, it’s from the surface.
w.
My expectation, prior to seeing the plot, was that there would be a huge blob with no particular correlation (r² ~ 0.1). Well the blob is there on the right side, a shotgun blast. The data on the left side is sparse and probably has no relevance compared to its uncertainty. The interesting detail in the center is probably an artifact of the methodology, plus wind and currents. Drawing a curve or curves through this stuff is like drawing canals on Mars, and just as useful.
Good comments, rgb, Nick, John West and many others, including lemiere, who kicked off the comments. Wind permits the equilibrium to have been established where the sample was not taken. Also, the fact that one variable (CO² in air) didn’t vary (much) could mean that the ordinate variable was poorly selected and the study is irrelevant. I’m wondering if the error bars are wider than the distance from the center of the Blob to the y = 0 axis.
Seems like there is a lot of embedded structure, which implies something else is causing the correlation. You might try making the same plot for different air temperature bands to see if it simplifies.
Not sure if posters are being silly, or trying to come up with arguments that are supposed to make the data make sense in an AGW argument, but Macha and others have said things along the lines of:
“Warmer water can absorb and hold more CO2, than cold.” Or that “warm water holds more CO2 than cold water”.
Not true. It’s the opposite. Cold water absorbs and holds more dissolved gas than warm water does.
That’s why the ocean is a perfect CO2 sink. The AGWarmists argument is that because the ocean is warming, it will not be able to continue to absorb the CO2 humans are spewing into the atmosphere as well-because of the principle that warmer water outgasses C02..it does not absorb more.
BUT saltier water does not absorb as much as fresh water. And saltier water is denser, so it would sink below fresher water. Add in ocean currents, time it takes for C02 the gas to dissolve in water, upwellings, winds, pressures etc and I’d expect there to be a difference between the two systems.
http://blogs.ei.columbia.edu/2010/07/07/does-temperature-control-atmospheric-carbon-dioxide-concentrations/
Some might find this paper interesting and there are many more out there in the free world. It is very interesting that the results of the research seems to tilt toward the FUNDING SOURCE – Follow the money is now not just a political reality it has infected Science.
http://www.usc.edu/dept/chemistry/loker/ReversingGlobalWarming.pdf
I would be interested in knowing whether they took samples from calm water or rough water or heavy seas – which in part may well explain why CO2 was high or low depending on the actions of the ocean itself.
I’ve added an update to the head post as follows:
[UPDATE] By popular request, here is the same data, but in absolute rather than relative units and without the lowess curve.
Figure 2. As in Figure 1, but showing the CO2 content of the surface seawater directly. Atmospheric CO2 varied very little during the time of the measurements.
My main question in all of this is, how does the CO2 content of the seawater get to be up to 100 ppmv above the CO2 content of the overlying air? It seems to me that the driver must be biology … but I was born yesterday.
Regards,
w.
johnmarshall says:
November 27, 2013 at 3:02 am
“Dissolved CO2 remaining in the water is used bu planktonic and other plants to photosynthesize. These chemical reactions speed up with temperature rise.”
Also, things are complex in terms of the relative aqueous concentrations (K=equilibrium constant at a given temperature) of the linked species: H2CO3, CO2, (HCO3^-, H^+) (the “first” dissociation of H2CO3) and (H^+ CO3^-2) the second dissociation. [H2CO3]/[CO2] = K1; [H+] * [HCO3]/[H2CO3]= K2 and [H+]*[CO3^2-]/[HCO3] = K3.
Going from 0 to 30C, K1 is ~ halved; K2 is ~ doubled and K3 is ~ tripled. In all this, the activities described by johnmarshall are happening as well as the inorganic carbonate precipitation with Ca2+ and Mg2+ in the seawater.
Making full sense , on the face of it, of this remarkable unexpected relationship between CO2 in seawater with temps would require experimentation with and without Ca-Mg and plankton. Since CO2 is the crux of all the CAGW issues, these are experiments that should be done. It seems that all- important CO2 behavior is, like other people-heat effects, a hand waving exercise by the climate and sistren. Please don’t let Al and the Science Guy do the experiments!
Oops, I lost the brethren!
I should imagine the plot would be very different for La Nina years:
http://www.pmel.noaa.gov/pubs/outstand/feel1868/text.shtml
http://www.pmel.noaa.gov/co2/elnino.html
In the atmosphere there’s background concentration, which is more or less global. This may be different in the sea (surface).
I haven’t read all the newest posts, so forgive me if I’m saying something that was already said.
I think it’s the way that the graph has set up the data that is screwing with you Willis. (it does me too) Not the data itself. It doesn’t measure the actual C02 in the water OR the air, it measures the DIFFERENCE between the two and then charts them relative to ONLY on the temperature of the surface water the sample was taken from. The chart is also not a linear chart of the same water over time comparing it’s Co2 rise and fall to the temperature changes of that water, The ABSTRACT says:
“Carbon dioxide (C02) in the surface water and atmosphere of the Pacitic, Indian, and Atlantic
Oceans was measured by nondispersive infiared gas analyzer on three oceanographic expeditions from October 1957 and August 1963.”
They are measuring samples from 4 DIFFERENT oceans on 3 different expeditions, comparing the C02 in the samples to the C02 in the air at the time that sample was taken.
To clarify (more for myself than anything)
Let’s say that for all the samples, the atmospheric co2 was roughly the same for a well mixed atmospheric 330 ppm. The left axis shows that we have to subtract that level of Co2-330 from the Co2 measurement in each SS sample and record the difference.
We take a sample in SS water that is 5 degrees C, and let’s say that the Co2 IN THE WATER is 380 ppm-higher than the CO2 in the atmosphere by 50 ppm. We are constrained to subtract the atmospheric Co2 FROM the ocean Co2 so, 380-330 is a +50 on the chart.
Now we sample SS water that is 5 C somewhere else. We get a CO2 reading in that water of 320ppm. Same temperatures, but different CO2 levels. We have to subtract the SAME atmospheric Co2 from the Ocean Co2-320-330 is -10 on the chart.
Then we sample SS water that is 20C. It’s Co2 reading is 180. 180-330=-150
Another location of SS water is 20C, but it’s Co2 reading is 375. 375-330=+45
Obviously the CO2 in the oceans surface is NOT as well mixed as the CO2 in the air, and thus the concentrations of it vary widely across the planet, even in places where the ocean surfaces are the same temperature.
We’re used to viewing such charts as linear in time and looking at the differences between one date and another. This chart just isn’t set up that way and it messes with my head at least. If I’m up in the night, I apologize for suggesting that my inability to grasp the chart is shared by anyone else here.
Looking at the description of the data, it appears to me they are not measuring the CO2 levels of sea water directly, but the CO2 level of an air stream that has been equilibrated with the sea water. If you take an air stream and spray seawater into it and monitor its CO2 content, you would expect the CO2 level in the air stream to increase whenever the seawater is warmer than the annual average SST and decrease when below the annual average SST. All it seems to mean is that the surface waters seldom in equilibrium with the air except when the sea water is close to the annual mean temperature.
I suspect that if the data were presented in terms of a deviation from the annual average SST
at the point the sample was collected, much of the apparent randomness of the plot will disappear.
Indeed, biology! Coral reefs and algae are net contributors of CO2. They “eat” more organics than they store in building their CaCO3 framework. Although full cycle they present a CO2 sink, due to semi-permanent storage of CO2 as limestone, locally, in their prime habitat between 25-30C waters, they appear to contribute to the CO2 production.
rgbatduke says:
November 27, 2013 at 8:36 am
Thanks as always for your interesting comments. Here is the data, divided by cruise:
Regards,
w.
Willis
Interesting. The low CO2 appears similar to the downwelling regions of the temperate deserts about 25 – 35 latitude No and So.
Suggest comparing against surface solar insolation and Hadley cells upwelling/downwelling.
Here’s an animation that shows how much atmospheric CO2 levels VARY depending on latitude yearly and over time. https://www.youtube.com/watch?v=k7jvP7BqVi4&feature=player_embedded
Being that water responds more slowly than air does, it’s easy to see how at certain points in a year, in certain latitudes, the air CO2 would be at a low for the year while the ocean CO2 could be at a high and they could criss-cross each other.
1. From the wide variation at any given temperature, I’d say that there are other things going on. There is NOT one factor contributing. Like you said, Willis, you expected the delta to be about 5ppm. And here it shows deltas at any given temp to be ranges up to and over 150ppm – 30 times what you suspected (which did not sound unreasonable).
2. From the colored cruise graph, three of the cruises look like they will have essentially the same curve as the overall. Only the blue 1957 cruise seems to vary much from the overall.
So, I think the data is inadequate to come up with an adequate “final” answer. I think it is even inadequate to come up with a really good next level question.
For complicated problems, the first returns don’t give final answers – they only lead to the next level questions. First level questions are going to be blind groping to a goodly extent. At each level, with better questions (leading to better experiments) come better answers. In my experience that means the first level question is uninformed and mostly ignorant – mostly ignorant of what other factors are involved. As those other factors are brought in, the results begin to make more sense – leading to second level questions that are better and give better results.
It is premature to think that that one graph is going to lead to a good answer. At best it can lead to pointing in the right direction for the next level of observations/experiments.
There is a whole lot of misinformation going on in the comments here; sorry.
The way CO2 is being measured here (equilibration with air) measures the partial pressure in the water, and in effect, the forcing function for CO2 to enter or leave the water to the atmosphere. Assuming the air temperature in the equilibrator and the water temperature are the same, the temperature, the salinity etc, do not effect the pCO2 at all. The 13 ft draft of the ship might have some effect, but not much, since the ocean surface is usually pretty well mixed to that depth.
There are only three ways for the surface water to be out of equilibrium with the atmosphere, photosynthesis, which uses CO2 and reduces pCO2, respiration of some sort which raises it, and advection of deep water (commonly high in CO2 due to respiration) into the surface. The total amount of CO2 dissolved in the water in equilibrium with the air depends on the temp, salinity, and most importantly, alkalinity, which in the open ocean, is closely correlated to salinity.
Here’s my view of your data. In cold water, photosynthesis and respiration are slow (especially in the open ocean where plankton concentrations are relatively low), while mixing due to weather is not, so its not surprising that those sample are generally close to equilibrium. At moderate temperatures, photosynthesis usually exceeds respiration (otherwise the oceans run out of food), and pCO2 should commonly be below the atmosphere. At temperatures above 25 C photosynthesis is inhibited in most phytoplankton, and respiration (mostly bacterial) dominates, using up all the loose organic carbon, and converting it to CO2, and raising pCO2 above atmospheric.
I suspect the obvious data clusters and “lines” are related to large scale oceanographic features of the water the cruise tracks covered, and a little teasing would pick them out easily enough.
I’ve actually used an equilibrator like this one in the Chesapeake Bay; we’ve seen pCO2 values as low as 50 ppmv in a dense phytoplankton bloom, and as high as 12,000 or more (it saturated our sensor) in the water filtering out of a salt marsh, and strong diurnal cycles as plankton photosynthesize during the day, and respire at night.
Here is a link to an Excel spreadsheet that can be used to do lots of calculation on the CO2 system in seawater:
http://cdiac.ornl.gov/oceans/co2rprt.html
Willis, it would be interesting to see how, when and where the readings were taken. Different areas of the ocean outgas and absorb CO2 at different times. The data looks very different to the implications of the following plot:
http://www.rocketscientistsjournal.com/2007/06/_res/Takahashi.jpg
Fritz says:
November 27, 2013 at 1:00 pm
Many thanks for that, Fritz, very interesting. I’ll need to consider all of that and run some numbers, but at first look it seems right.
It also accords with my contention, which is that what goes on in the ocean at all levels is not ruled by chemistry.
Instead, it is ruled by life, and what life does and doesn’t do.
Regards,
w.
Willis, regarding your question “why is it so high, up to 100 ppmv higher than the concentration in the overlying air?” A back of the napkin approximation may help –
When in equilibrium, the amount of dissolved CO2 in water at 15 deg C is 32% higher* than in water at 25 deg C. Take water at in equilibrium at 15 deg C with atmospheric CO2 equal to 400ppm, put it in a closed container with a small amount of air, heat to 25 deg C., shake hard until equilibrium is achieved and the CO2 content of the air should rise to 528 ppm.
*Handbook of Physics and Chemistry, 84th edition
equibrium
Fritz, a further comment. I don’t find that photosynthesis in phytoplankton is inhibited above 25°C … instead, it seems to be species specific, and there are a number of species who grow fastest at 30°C or above. See the interesting study, Temperature And Phytoplankton Growth in the Sea for further information.
Here’s a map of chlorophyll concentration, a marker for phytoplankton:
As you can see, the equatorial Pacific has more phytoplankton than the temperate zones, and there is plenty of chlorophyll in the “Pacific Warm Pool” around PNG and Indonesia.
Best regards.
w.