[Coral-List] CO2 and tropical waters.

John Ware jware at erols.com
Wed Feb 11 14:43:35 EST 2009

Dear List,

I agree with much of what Thomas Goreau has written (see below), but I 
do not agree about his implication that tropical surface waters can 
continue to be a source of CO2 as BOTH temperature and pCO2 increase.

Surely logic would lead one to conclude that, at the very least, CO2 
emissions from warm tropical surface waters must decrease at atmospheric 
partial pressure of CO2 increases.

To put the argument in concrete terms, suppose, just for the sake of 
discussion, that the warm surface waters were in equilibrium for 
atmospheric CO2 for CO2 at 275 ppmv, salinity 33 ppt, temperature 30 oC. 
My computer program indicates that dissolved inorganic carbon (DIC) is 
about 2.75 mM/L at a pH of 8.449.  (Your computer program will probably 
give different answers because we use different constants or slightly 
different computational methods.  However, what counts is not absolute 
values, but differences.)

Now, suppose nothing else happens but that pCO2 doubles to 550 ppmv. DIC 
increases by 23% to 3.37 mM/L and pH decreases by about 0.2 units to 8.27. 

Of course, global warming would increase water temperature and the 
solubility of  CO2 would decrease.  So, by how much would temperature 
have to increase to offset the increase in DIC due to increased pCO2? 
The answer is over 10 Co to approximately 40 oC!!  (In fact, my program, 
which could be wrong, indicates a temperature increase to 45 oC.)

And, of at least equal importance, the pH stays almost the same as the 
temperature increases, so the acidification due to increased pCO2 is NOT 
affected by the increase in temperature.

Now, a lot of assumptions go into this type of calculations, and I would 
appreciate my conclusions being confirmed or rejected if they are wrong. 
However, the confirmation or rejection should be based upon 
calculations, not hand waving arguments.


P.S. On slightly different, but related, topic.  The recent paper by 
Solomon et al (PNAS, 2009, 106:1704-1709) shows that, even if 
anthropogenic CO2 emissions were to magically go to zero instantly, the 
effects continue for at least 1000 yrs.


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