How does rising atmospheric CO2 affect marine organisms?

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More Evidence that Algae Help to Regulate Earth's Climate
Kouvarakis, G. and Mihalopoulos, N.  2002.  Seasonal variation of dimethylsulfide in the gas phase and of methanesulfonate and non-sea-salt sulfate in the aerosols phase in the Eastern Mediterranean atmosphere.  Atmospheric Environment 36: 929-938.

Dimethylsulfide (DMS) is a climatically-important trace gas produced by certain types of marine phytoplankton that is believed to play a major role in keeping the temperature of the earth within bounds that are conducive to the continual existence of life.  In response to some impetus for warming (such as an increase in atmospheric greenhouse gases, for example), the climate-stabilizing mechanism begins with a warming-induced increase in the productivity of marine phytoplankton, which results in a greater production of oceanic DMS and its release to the atmosphere, where greater gas-to-particle conversions increase the air's population of cloud condensation nuclei and, ultimately, the albedos of marine stratus and altostratus clouds via a narrowing of the cloud droplet spectrum and a decrease in the mean radius of the cloud droplets, both of which phenomena tend to counteract the initial impetus for warming.

What was done
The authors investigated the seasonal variations of gaseous dimethylsulfide (DMS) and its oxidation products - non-sea-salt sulfate (nss-SO42-) and methanesulfonic acid (MSA) - at a remote coastal location in the Eastern Mediterranean Sea from May 1997 through October 1999.  In addition, they studied the diurnal variation of DMS during two intensive measurement campaigns in September 1997.

What was learned
In the seasonal investigation, DMS concentrations tracked sea surface temperature (SST) almost perfectly, going from a low of 0.87 nmol m-3 in the winter to a high of 3.74 nmol m-3 in the summer.  Such was also the case in the diurnal study: DMS concentrations were lowest just before sunrise, rose rapidly thereafter to about 1100, followed by a little dip and then a further rise to 2000, whereupon a decline set in that continued until just before sunrise.

MSA concentrations exhibited a similar seasonal variation to that displayed by DMS, ranging from a wintertime low of 0.04 nmol m-3 to a summertime high of 0.99 nmol m-3.  The same was also true of aerosol nss-SO42-, which varied from 0.6 to 123.9 nmol m-3 in going from winter to summer.

What it means
As the temperature of the ocean surface rises in response to increases in diurnal and seasonal forcing factors, concentrations of DMS and its oxidation products (MSA and nss-SO42-) rise dramatically, inducing a negative feedback that tends to counter the impetus for warming.  Hence, there is every reason to believe that the same negative feedback phenomenon operates in the case of long-term warming that could arise as a result of increasing greenhouse gas concentrations, and that it could substantially mute their combined climatic impact.

Reviewed 10 July 2002