Arguments
Seawater Equilibria
Posted on 10 January 2011 by hfranzen
The audience for whom this piece is intended consists of people who know some chemistry and are uncertain about how to consider the often made claim by deniers that the oceans contain so much dissolved carbon that human production is inconsequential. What the article points out is that the elementary chemical concepts of chemical equilibrium and charge balance put restraints on the ability of the ocean to release carbon dioxide to the air. Because of these restraints the oceans locally can release only a small part of the total dissolved carbon dioxide and, more importantly, when averaged over a year the amount released equals the amount dissolved, i.e. there is not net addition of carbon dioxide to the atmosphere from the oceans so long as the temperature averaged over a year remains constant from year to year.
This topic deals with the acid-base chemistry of the species important in the solubility of
. These are: (g), (aq), 
, 
, 
, 
, 
, 
and 
. The amount of each of the dissolved substances is described by its molality, 
which is the number of moles dissolved in a kilogram (kg) of water. In order to consider the chemistry it is necessary to propose a model system. A model for the average ocean is: A 3.5% sodium chloride solution in water at T=288K in equilibrium with 387 ppm 
in air 
at a pH of 8.00 and in addition 0.416 millimoles of dissolved boric acid per kg of water. The molalities of the seven solute species are fixed by seven independent equations . 
is known from the Keeling curve so 
is fixed by the Henry’s law constant for
The molality of hydrogen ion is fixed by the measured pH, and the observed quantity of dissolved boric acid yields
.
Thus there are three restraints placed on the solute molalities at 288K by the known properties of average seawater. There are four more relations (restraints) relating the molalities namely the equilibrium constants for the four independent net reactions among the solute species. These were obtained as functions of T using tabulated thermodynamic data. Algebra then yields the molalities of the remaining solute species at 288K, specifically the equilibrium molalities of 
, , and
, as well as the other species, are determined for the average ocean. The total carbon dioxide molallity
is thus fixed in the equilibrium average ocean (its value is 1.65 millimolal). Bicarbonate is 91.5% of this total molality. An essential requirement for the evolution of carbon dioxide from the equilibrium ocean into the atmosphere is a perturbing influence. The one property of the solution that can be altered so as to affect the total molality is the temperature of the system.
E.g. consider the effect of changing the temperature at constant partial pressure of . The pH will change with T so the pH=8.00 restraint is lost. On the other hand, by charge balance
is constant ( 
are not included in the sum because they are present at such low concentration that they can be neglected). Thus even when T differs from 288K there are as many restraints as there are molalities. Tabulated thermodynamic data were used to calculate the equilibrium constants (including the Henry’s Law constant) at each of eight temperatures between 276 and 304K and the molalities for all species were found algebraically at the eight temperatures. In particular the three molalities in 
were found at each T . The eight values for 
were fit to a straight line as a function of T with the result:
.
This means that the 
locally in the ocean decreases by only 13.5 micromoles per kg for each degree that T increases. The opposite is also true: the increases by 13.5 micromoles locally for each degree of decrease. Since 288K is the average T, when there is an increase in one place there is a decrease in another and thus the net exchange of between the ocean and the atmosphere is zero if there is no other source of carbon dioxide such as human combustion of fossil fuels. Considering this human production leads to the conclusion that there is necessarily a net increase in dissolved carbon dioxide (see Henry's Law above) and the calculations yield in this case a decreasing average pH in the oceans. Perhaps someone more knowledgeable than I could add a comment about the effect of increasing acidity on coral reefs, plankton, fish, etc.
In conclusion :
1: Thermodynamics and charge balance place serious restraints on the ability of dissolved carbon dioxide to pass into the gas phase as a result of local temperature changes. The significance of these restraints should be considered by the deniers when they assert that the amount of carbon dioxide dissolved in the oceans is so large that exchanges between the ocean and the atmosphere dwarf human production.
2. The nature of the average temperature and the thermodynamics of the reactions means that there is, on the average, no net exchange of carbon dioxide between the oceans and the atmosphere i.e. the notion that somehow carbon dioxide is belched into the atmosphere by the oceans ignores the basic fact that whatever carbon dioxide is released in one part is compensated by an equal quantity dissolved in another.
The 'CO2 rise isn't human caused' arguments is one of the stupidest I can think of once you look at the data. Sure, to someone who's new to the whole deal and hasn't seen the figures it might make sense, but consistent 'skeptics' should know better.
CDIAC
Chemware: You can download CO2SYS from the CDIAC web site as an Excel file to perform the calculations you may wish to play with. It is well documented so that educators can use it for classroom exercises.
Others have used full ocean models to calculate the change in atmospheric CO2 concentration in response to the changes in whole-ocean average temperature. I don't remember the source or I would cite it, but the sensitivity is about 7 or 8 ppm increase in atmospheric CO2 per degree of warming of the ENTIRE ocean (mainly the deep ocean). Since the deep ocean has warmed hardly at all, and the surface ocean has warmed only a fraction of a degree, the contribution to rising atmospheric CO2 by warming of the ocean over the past century is negligible.
One other comment: The calculations described by hfranzen are for a lifeless ocean. The net effect of organisms in the ocean is to transfer carbon from the atmosphere and the surface ocean down into the deep sea, commonly known as the "biological pump". The net effect is that the dissolved carbon concentration in the deep ocean is about 10% greater than it would be in a lifeless ocean, while the concentration of CO2 in the atmosphere is much lower than it would be if the ocean were lifeless. Calculations done in the early 1980's indicate that atmospheric CO2 could be as high as 450 ppm in a lifeless ocean. These calculations are summarized more recently in the textbook "Ocean Biogeochemical Cycles" by Jorge Sarmiento and Niki Gruber.
Despite massive human impact on fisheries, as yet there is no evidence that humans have measurably perturbed the biological pump, but perturbation remains a possibility that could lead to either a positive or a negative feedback for atmospheric CO2.
For example, the idea to lower atmospheric CO2 by adding iron to the ocean around Antarctica is based on stimulating the biological pump to transfer more carbon into the deep sea.
C02 has been higher on this planet prior to humans being here. Oceans supply most of our oxygen supplies as well. C02 lags temperature changes. C02 has very different effects in an open system than in a closed one like in a lab experiment where controlled conditions do not necessarily mimick real world, natural behavior.
Thermodynamics also limits how much temperature changes can be possible due to rising greenhouse gases. Large amounts of C02 and CH4 can be added to the system with no net temperature change.
As hfranzen correctly mentions: the oceans are full of life and complex biological cycles and buffering capacity. Water with a high heat capacity covering around 75% of the earth's surface with incredible depths can trap heat indefinitley as it goes from the warmer body to the cooler body due to temperature differences. This is basic thermodynamics: heat travels to the cooler body.Even process like convection and advection are not going to grab all of the heat and trap it in a manner that raises temperature, which is just the statistical averaging of kinetic motion of molecules. It is still impossible to actually average global temperature though the GCM's and techniques are getting better.
Effectively dealt with here.
"C02 lags temperature changes."
And dealt with here.
I would challenge anyone who believes that the observable atmospheric CO2 increase is coming from the oceans to show some data supporting that assertion. See the relevant thread.
Thus this piece is simply a response to the deniers. many of whom still maintain that the oceans are respnsible for the increases in atmospheric carbon dioxide. What is demonstrated here is that a very simple model of the ocean, but one that catches the essence of the surface ocean inorganic chemistry because it includes all of the restraints, clearly shows that the average ocean does not give off carbon dioxide.
The major point is that deniers (and many others) discuss the ocean-atmosphere interaction as though the carbon dioxide were simply free to pass back and forth without restraint. Most discussions of the topic fail to discuss the charge balance restraint.
A striking point to me is that sitting in my office and working with established thermodynamic data (which are available worldwide in numerous texts and compilations) I can demonstrate using only the ,easured pH and the partial presssure of carbon dioxide hat some 90+% of the dissoved carbon dioxide is present as bicarbonate nad thus that the majority of what is in the ocean is of terrestrial origin.
The only point that need be made about averages (and this is also the answer to the deniers who confuse weather and climate) is the if one averages over an earth-year they get an average temperature which means that if the local temperature increases at one place and/or time it will necessarily decrease in another.
http://books.google.com/books...
It seems in your calculations you neglect temperature and regional effects on C02 release and absorption in bodies of water.
Look, Dr Franzen is describing the arc of a falling object as a parabola, and you are interjecting air resistance as a function of altitude, temperature, and humidity. Besides, it's more accurately an arc-segment of an ellipse.
Yeah, we know there is more to it than what Dr Franzen describes above, but as he stated, it's a starting point. Unless you really feel that a student should be taught drag coefficients for various shaped bodies and how drag varies with atmospheric composition and approximately with the square of the velocity at the same time that they are taught about projectile paths using the mechanics of gravitational constants (which aren't constant, btw), your points are extraneous. You can get a working estimate of what a throw rock will do using a parabolic curve and 9.8 m/s^2, and you can get a working estimate of CO2 exchange between air and sea with the above.
I'm sure I don't want to know, but from where does your friend with the ocean heat theory think that the energy to heat the ocean is coming from? Or, what has changed in the last 1-2 hundred years that should give the ocean so much extra energy? I mean, the oceans are warming, but not by 12 K. You could also say that they are loosing heat less rapidly just as well, it depends on how you want to look at it, but the physical science is the same.
I'm having trouble grasping how someone who should have a good working knowledge of heat content and conservation of energy could be thinking that the oceans are heating spontaneously.
I read several pages of your reference at #12 and it appears to support Dr. Franzens position. It describes the ocean as complicated on the page you cited, but on page 62 it estimates ocean uptake of CO2 as 2 Gt per year. It certainly does not say that AGW violates the first and second law of thermodynamics, as you claim. You need to find a reference that actually supports your position, not one that contradicts what you are asserting.
If you cannot find a reference that supports your position perhaps you should reconsider.
How does one then explain the end of the ice ages?
I thought the end of an ice age was triggered by a change in the earth's orbit around the sun and then the warmed ocean started outgassing CO2. And this in turn would have led to increasing temperatures, and so on.
I'm not able to calculate how much the ocean would have warmed by a change in the earth's orbit. But after reading your post, it seems to me that the ocean would not have warmed sufficiently for there to be significant CO2 outgassing.
Something seems to be missing here? Or perhaps it's just me who is missing something?
by Frank J. Millero
Chem. Rev., 2007, 107 (2), pp 308–341
DOI: 10.1021/cr0503557
http://pubs.acs.org/doi/abs/10.1021/cr0503557
provides in depth discussion.
see:
http://imars.usf.edu/~carib/Public/Millero_2006_2007/Millero_review_Article.pdf
if you have no access to paid version
1. every fraction of a second billions of billions of CO2 molecules leave ocean
2. every fraction of a second billions of billions of CO2 molecules enter ocean
3. with such huge numbers chance is not important, only averages count
4. if CO2 was the same as nitrogen or oxygen, situation would be simple, the only force keeping the CO2 in ocean would be week intermolecular forces (van der Waals) - the higher temperature the faster are molecules moving they do not spent enough time together and so it is not so advantageous from energy point of view to stay in liquid
5. CO2 dissolves in water to carbonic acid which is very weak but still acid and so neutralization comes to picture and it quickly starts to be rather tricky as also these reactions depend on temperature
6. but as long as you do not find a reaction which would be accelerated with increasing temperature (and faster than decreased solubility of gases with temperature) and which would transform CO2 to something insoluble which would drop to the ocean bottom you have to be aware of the possibility that with increasing temperature ocean as carbon sink will be less efficient
7. but of course the major driving force for carbon removal is biological pump (http://en.wikipedia.org/wiki/Biological_pump); actually one of reasons behind ice ages is that in time of ice ages was less water in atmosphere -> more dust -> biological pump more efficient as oceans far away from lands were fertilized -> 190ppm of CO2 in atmosphere -> less warm -> less moisture - more dust ...
8. and that is the main problem with science, I wanted a short break from programming and so started a replay after 10 minutes of writing I have not mentioned a lot of arguments which would be useful to mention , wrote from top of head and did not think about arguments much so the replay may contain a few factual mistakes
but at least you may see another chemist view ;)
"the observed quantity of dissolved of boric acid yields" needs to be fixed, too. It is hard enough to follow the chemistry without such grammatical errors and/or omissions of substantives.
Don't take this as a criticism, but people relying on your reasoning had better also read up on the isotopic signal as well, because it doesn't matter if you dodge the jab if he follows with a crushing uppercutwelling.
It´s difficult to say "skeptics don't say this". They claim anything that would suggest emissions don't have to be cut.
That includes "skeptics" implying the chemistry above does not take place, like Monckton here on page 47: "this minuscule and chemichally-irrelevant perturbation".
So yes, I'd say that Franzen's post does address skeptical claims.
Your discussion about bicarbonate and carbonate (I ignore carbonic acid - to my mind it is more aptly described as hydrated CO2 - the only disticntion between dissolved CO2 and carbinic acid is that in the later case there must be identifiable species with one water moleclule attached to the CO2 as oposed to a cage of water molecules with some leaving and some entering the cage over time.)At any rate, the species are all included in the thermodynamic treatment and the temperature deoendence is also. That's how I was able to arrive at a total carbon dioxide solubility as a function of tamperature, which is the main result of what I presented.
Good one! However, look at the monthly records of atmospheric CO2 concentration at various monitoring sites around the world. Within a band of latitudes, there is no measurable difference between island stations and mid-continent stations. There are significant differences according to latitude. If CO2 is primarily sourced from the oceans, the former requires immediate mixing throughout the atmosphere; the latter says its not mixing. That's a TKO by contradiction. Land sourcing of CO2 does not face this problem.
See the flux maps and flux time series displays here for some comparative rates, organized by geographic setting. Also look at CO2 weather while you're on that ESRL site; you can literally see the seasonal cycles of atmospheric CO2.
Oceans are complicated, as you well know. There are some comments and maps of locallized ocean sourcing in the deep southern hemisphere vs. sinking elsewhere on the ocean acidification threads here and here.
You can find the errors by using your browser's search (find) function. "Restaraint" is in the third sentence of the first paragraph.
The "of dissolved of boric acid" phrase comes in "The molality of hydrogen ion is fixed by the measured pH, and the observed quantity of dissolved of boric acid yields" just before your second embedded equation.
As a side note, you could also make it a little more readable by using HTML instead of images for things like CO3-2(aq). You just need to use the sub and sup tags around subscripts and superscripts.
I've noticed that some people are confused by your statements about the small amount of CO2 released with one degree change in the temperature of the water. I was also a little perplexed by that, since the absorption/release of CO2 from the ocean is the major feedback factor in the transition into/out of glacial periods.
It might help if you were simply a little more direct in explaining that you are referring in your post to daily or seasonal changes in temperature of regions of the ocean, not long term changes in temperature of the oceans as a whole, and that it is the net exchange over the entire ocean on which you are focusing — so it is not so much "how much" that is important as "this offsets that".
You might also alter the phrasing of this statement:
The use of the word "only" implies that CO2 release from the ocean is inconsequential with change in temperature, when that is clearly not the case in the transitions between glacial and interglacial periods, as evidenced by the ice cores.
Thinking it through just a little more, I suppose a major difference between the current environment and the glacial/interglacial transitions is the fact that in the current environment, the partial pressure of CO2 in the atmosphere is very high, as opposed to the normal glacial/interglacial transition, where it is much lower. This must also affect things greatly.
In fact, I am only just now realizing that there are other complications due to a partial pressure of CO2 being now historically inconsistent with other factors... for example, the fact that this imbalance between atmosphere/ocean is currently causing oceans to absorb CO2, but eventually, as temperatures stabilize relative to the new CO2 levels, that process will inevitably slow, halt, and possibly reverse, allowing much of the CO2 which has been absorbed to date instead make it into the atmosphere, raising CO2 levels even higher.
So the ocean has been acting as a CO2 speed bump that will eventually be overwhelmed.
If we succeed in decreasing our production of CO2 so its parial pressure would drop all things being equal we will find that all things aren't equal and, even at constant average temperature (which seems unlikely on the time scale of decades) the amount by which the atmospheric ppm is decreased will be slowed by evolution of CO2 from the ocean as the partial pressure drops. That is, if from the described system you remove some of the partial pressure of CO2 (decrease the ppm) the equilibria in the ocean will shift to increase that partial pressure above what it would have been without the evolution from the ocean.
This in turn means that the bicarbonte entered the oceans from the land (and/or the ocean bottom) and I would guess that entering has been going on for millenia. The equilibria I describe are based upon the current pH and thus also the bicarbonate and carbonate molalities (which are fixed by the pH and the partial pressure) and probably do not provide an accurate description of the ocean's inorganic chemistry thousands of years ago.
Certainly both are frightening, the idea that temperature increases might accelerate if the oceans begin to release instead of absorb CO2, and that even if we get things under control, CO2 levels may continue to rise, or at least will stay elevated for quite a very long while.
The analogy that I like is that CO2 is like the thermostat on your house. It's like we've dialed it way up, then broken it so we can't turn it back down. Sure, it's not that hot yet. But it's going to keep getting hotter, and when it's finally bad enough to bother enough people, it's too late. We can't go back and dial down the thermostat, because we "broke it."
The other analogy I like, for people who keep saying "this isn't so bad" (yet), is the old story about the guy who jumped off of the top of the Empire State Building. Every time he passed an open window, he was heard to say "so far, so good!"
I am not certain as to the correct answer to 3, but Indermuhle et al cite Bacastrow to the effect that:
"A change of SST by 1 8C causes a change
in the surface ocean's CO2 partial pressure by 4.2% which
translates into an atmospheric change of similar magnitude"
I believe, but am not certain, that this translates out as a 12 ppm increase in CO2 concentration for each 1 degree C increase in SST. Interestingly, using data from Law Dome, it is apparent that the CO2 concentration in the atmosphere varied by no more than 14 ppm between the peak of the MWP and the mimimum of the LIA. On the estimate above, this is a temperature fluctuation of no more than 1.2 degrees C. For comparison, the temperature variation between the minimum of the LIA and 2000 is about 1.6 degrees C (based on Moberg et al) or 1.2 (based on the average of a number of reconstructions.
Of course, many sceptics are committed to the views that the MWP was warmer than current temperatures and that the modern rise in CO2 is due the warming of the oceans, an example of massive cognitive dissonance.
http://www.ncdc.noaa.gov/paleo/taylor/taylor.html
http://medias.obs-mip.fr/paleo/taylor/indermuehle99nat.pdf
This all brought that to mind, and I've been trying to find it, without any luck.
I'd like to contrast that with your link, and look at it again with a new (if fractional) understanding of ocean chemistry.
Yeah, I kinda remember the article. Was it this one: http://www.realclimate.org/index.php/archives/2010/12/losing-time-not-buying-time/?
If so, it was based on this NAS Report/book: http://books.nap.edu/openbook.php?record_id=12877&page=R1
A PDF of the Executive Summary should be available here.
Lemme know if I'm misremembering.
These flattening of emissions are all predicated on us actually doing something now. Due to the long tail, the longer we wait, the more likely the ocean-sequestered CO2 (long thought removed from the playing field) will make its triumphant re-entry into the game.
Hence the article I alerted you to earlier (and the headline discussed best-case scenarios...).
The Yooper
How on earth do you take that conclusion out of this analysis?
From #43: "Increased average temperature will drive some of the dissolved CO2 out of the ocean"
From #46: "this translates out as a 12 ppm increase in CO2 concentration for each 1 degree C increase in SST."