How does rising atmospheric CO2 affect marine organisms?

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Adding to Our Knowledge of the Global-Ocean Biophysical Thermostat
Simo, R. and Pedros-Alio, C.  1999.  Role of vertical mixing in controlling the oceanic production of dimethyl sulphide.  Nature 402: 396-399.

What was done
The authors used satellite imagery and in situ experiments to study the production of dimethyl sulphide (DMS) by enzymatic cleavage of dimethylsulphoniopropionate (DMSP) in the North Atlantic Ocean about 400 km south of Iceland between 6 June and 9 July 1998.  They then compared their findings with those of others from various parts of the world and different seasons of the year to derive a conceptual overview of just what mediates DMS production in the world's oceans, with a view towards developing a better understanding of the role of marine phytoplankton in moderating global climate change.

What was learned
It was discovered that the depth of the surface mixing-layer has a substantial influence on DMS yield in the short term, via a number of photo-induced (and thereby mixing-depth mediated) influences on several complex physiological phenomena, as do longer-term seasonal variations in vertical mixing, via their influence on seasonal planktonic succession scenarios and food-web structure.  The authors thus conclude that "climate-controlled mixing controls DMS production over vast regions of the ocean."

What it means
The authors' findings are of great significance, for they help to establish the role of biology in moderating the effects of climate change precipitated by variations in other climate forcing factors.  As a specific example, literally hundreds of scientific studies have discussed how an initial impetus for warming could (1) stimulate primary production in marine phytoplankton, which could (2) result in the production of more copious quantities of DMSP, which could (3) lead to the evolution of greater amounts of DMS in the surface waters of the world's oceans, which could (4) diffuse into the atmosphere, where the DMS could (5) be oxidized, which could (6) lead to the creation of acidic aerosols, which could (7) function as cloud condensation nuclei, which could (8) create more and brighter clouds, which could (9) reflect more incoming solar radiation back to space, which could (10) cool the planet and thereby counter the initial impetus for warming.  The unique contribution of this paper is that, in addition, it shows how warming-induced changes in mixing-layer depth promote this same chain of events via a number of phenomena not previously elucidated.  Hence, there is greater reason than ever to believe that intricately-related biological-physical processes tend to maintain earth's surface temperature regime within limits conducive to life's continued existence on the face of the planet; and the chief implication of this world-view is that rising levels of atmospheric CO2 should not lead to deleterious global warming.

Reviewed 15 January 2000