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.
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CO2 roduced by biomass …rain…evaporation…
Can it be a agw survey? Cold water absorbes CO2 and warm water let it go by out gassing. It looks to me that someone wants to let look to work the other way to help agw.
Are we assuming equilibrium? The air temperature is constantly changing, I would presume the water temperature also, though less so. CO2 levels may also be changing. Would be nice to have a ‘dynamic’ record from a single location, showing response to temperature or CO2 change.
oh sorry and wind…some co2 arrived from elsewhere land for instance…so you can see a dynamical process…and some saturation too…quite complicated indeed for sure you can’t see it like an equilibrium…
well and the water at the surface exchange a bit withe the water underneath…
you should try to figure out how co2 concentration vary in the atmospheric surface layer how it varies in the ocean surface layer… temperature paly a role..
another point…temperature of what? air of temperature?
it they are fifferent it is weird to assume that there should be some kind of equilibrium.
You missed most of the reaction. Sea water is an ionic solution and dissolved CO2 continues reacting to form bicarbonate ions, which increase the pH so maintaining the pH balance, and this bicarbonate ion is used by animals to form shell and skeletal frameworks. Without this further reaction corals would not grow. So the takeup of CO2 depends on planktonic life, the more active this life the more bicarbonate is used then the faster the CO2>bicarb reaction continues. Dissolved CO2 remaining in the water is used bu planktonic and other plants to photosynthesize. These chemical reactions speed up with temperature rise.
A lot of photosynthesis goes on in the ocean. Could the dip from 5 to 25 degrees reflect favorable conditions for photosynthetic growth?
It would seem like the correlation between higher CO2 and higher temperatures would be only verified for seawaters above 25c? Alternatively, another way to look at it, is that the radiative equations only work when the angle formed by the sun and the surface close to perpendicular: Global warmist assume a flat earth as a greenhouse, they may underestimate the fact that without direct sunshine there is no greenhouse effect going and temperatures and sinking rapidly.
Relative difference is not the same as absolute. Warmer water can absorb and hold more CO2, than cold. The rate of change I more a question of kinetics.
The vast majority of their dots are for sea surface temperatures greater than 20ºC.
Perhaps the cruises in oceans where this was the case were more popular with the psyentists than those trawling around oceans with temperatures below 10ºC?
Or maybe the latter group just kept warm and cosy below decks?
“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.”
When water is cool CO2 flows from air to water – net absorption.
When water is warm CO2 flows from water to air – net release.
” 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.”
Looks like there are mechanisms in play that make the application of Henry’s Law rather hit and miss.
Most likely the CO2 exchange rate varies as many other factors such as internal ocean movements and winds in the air interfere with the exchange process.
Purely from eye-balling the data, the Lowess curve line at SST 0. Without this cluster a normal linear regression would seem to fit well (don’t have time to do it right now) crossing the OSco2-Aco2 axis at about SST = 18 and with d(OSco2-Aco2)/dSST =1 approx.
Sorry – the first sentence of my post above should be: Purely from eye-balling the data, the Lowess curve line at SST less than 5 seems to rest essentially on the small data cluster at around SST = 2, OSco2-Aco2 greater than 0. Without this cluster …
The vast majority of CO2 in the oceans is in the form of bicarbonate. Only a tiny fraction is in the form of the dissolved gas, which is what this paper is measuring. The inorganic exchange between dissolved gas (as in soda water) and bicarbonate is governed mostly by the reaction:
CO2 + H2O —> HCO3- + H+
You can see the H+ lowers the pH. There is a huge organic component to this process as well. We escaped the fate of Venus in large part due to the formation of calcium carbonate by marine organisms, that pulled nearly all of the original CO2 out of the atmosphere to create limestone, the abundance of which is evident to anyone who has looked at rocks around the world.
The most straightforward observation I can make regarding the scatterplot is that the data looks rather inhomogeneous – clusters here and there and gaps between them. To me, this would indicate that other factors are at play here beyond CO2 and temperature.
Just possible that at close to zero (0 to 5 C) CO2 in air and water are in equilibrium – not much happening. As the water warms, the amount of CO2 in water decreases, as one would expect. Further, as temperatures approach 10 to 15 C plant life does well and it reduces CO2. However, past 17C, it is better for animal life, and this eats the plants and exhales CO2, so increasing the amount of CO2 in the sea water.
BTW – we “exhale” via our lungs – does a fish “exhale” via its gills – if not, what is the correct term for “a fish getting rid of CO2?”
In areas with lower temps the sea water might be down-welling thereby taking the CO₂ below depths where the measurements were being taken.
My only response is – What? You would draw a TREND line? Through THAT? REALLY?
It almost looks as though the CO2 rising from deeper down is encountering a choke at the surface slowing down release. Perhaps the surface tension is doing it. But it seems to result in a CO2 rich zone close to the underwater surface with only a slow release to the atmosphere.
Interesting finding W
In summary: You can’t cough it up unless you have more of it.
Unfrozen Caveman said:
“We escaped the fate of Venus in large part due to the formation of calcium carbonate by marine organisms, that pulled nearly all of the original CO2 out of the atmosphere to create limestone”.
Circular reasoning. If the runaway greenhouse effect were valid, with all that original CO2 in the UnfrozenCavemanMD said:
“We escaped the fate of Venus in large part due to the formation of calcium carbonate by marine organisms, that pulled nearly all of the original CO2 out of the atmosphere to create limestone”.
Circular reasoning. If the ‘runaway greenhouse’ effect were true, with the original atmosphere largely of CO2, temperatures would be on average above boiling point of water, there would be no oceans – no liquid water in which marine organizms could exist, and which could turn the CO2 into limestone. These marine organisms would most likely have been very happy with an ocean temperature perhaps 8 to 10 degrees C above present – which would probably be the likely figure if the atmosphere were 60 – 90% CO2.
Thanks a lot for this article Willis, it made me think and I love it when new data or ideas make me think.
I had to reconsider everything I know, even regarding outgassing, as it is at odds with the outgassing of CO2 from the ocean that supposedly happens when temperature increases. Is it really true?
Well, of course it is. What perhaps may be not so true, is that this outgassing affects the atmospheric concentration of CO2. There will be more CO2, yes, but I’m guessing that the oceans will NOT ONLY release CO2. There must be other gasses disolved as well. So it outgasses CO2, and maybe O2, N2, Argon… as well. So concentration of CO2 in the atmosphere MAY NOT change as a result of the outgassing.
But wait! We have paleoclimatic records showing more atmospheric CO2 when warmer! Isn’t that proof of CO2 release by the oceans? Well, it may perhaps be proof of more CO2 PRODUCTION in the ocean, increasing the ammount of CO2 that is dissolved in the water just because of biological productivity (more O2 consummers than CO2 consummers), making the concentration greater than there is in the atmosphere as your calculation here has showm… and then by outgassing, transfering some of this difference in CO2 concentration to the atmosphere.
That’s the only explanation I can think of right now. But it brings interesting conclussions if it happens to be true, doesn’t it? To begin with, all the story about ocean acidification crumbles. Ocean acidifies, yes, but not necessarily because of our emissions, but because of its own biological processes as a result of the warming… And part of the accumulated CO2 in the atmosphere would have been released by the oceans, not us.
Willis,
I don’t think the water measurement reflects concentration of CO2, and I’m sure it isn’t ppmv of water. It’s described in your link as pCO2, which would be the partial pressure of CO2 in equilibrium with the seawater.
In that case, there’s no particular expectation about variation with temperature. With no flux, it would be zero at any temperature. What it does reflect is which way CO2 is moving.
On that basis it should indeed be higher in warm water, because that is thought to be a region of degassing. So pCO2 must be higher below the surface. CO2 moves down a gradient of pCO2.
In fact, though, it would be very seasonally dependent. All sea water loses CO2 toward summer, and takes it back before winter. So timing of the readings would be important.
As has been pointed out many times, the more the CO2, the less the additional effect of ‘greenhouse warming’. The additional temperatures would be due to the increased internal heat of the earth escaping to the surface, and increased heat as a result of a turbulent atmosphere. Those good with figures can calculate the surface air pressure if all the CO2 in the rocks in the form of chalk, limestone and marble were free in gaseous form, and what the surface air temperature would be if the atmosphere were turbulent, and the temperature on the surface were due to compression of downward moving air. And of course, in those early days, there would be plenty of vulcanism adding heat at ground level.
Remember that much of the CO2 was removed from the atmoshere not so long ago – the chalk was laid down in the Cretaceous. Before that what was the amount of CO2 in the atmosphere, and what was the surface temperature?
I apologize for the previous post – the start of my comment disappeared, so I wrote it in again, and then found that the end had been disappeared. So I chpped it and found that the end was still on my clipboard, and put it here.
Five years of measurements, fifty years ago, with the instruments available then. I am impressed.
So, according to that plot when I pop the top on my barley pop I will get more CO2 as it warms up and it shouldn’t go flat faster standing at warmer temperatures? I’m not sure what they were measuring but the concentration of CO2 (all forms) is inversely proportional to temperature. CO2 chemistry in water is a bit more complicated so if they were just measuring dissolved CO2 they might have gotten strange results. You need to know pH and total carbonate also. http://www.soest.hawaii.edu/oceanography/faculty/zeebe_files/Publications/ZeebeWolfEnclp07.pdf