How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

Atmospheric CO2 and the Glacial Southern Ocean
Elderfield, H. and Rickaby, R.E.M.  2000.  Oceanic Cd/P ratio and nutrient utilization in the glacial Southern Ocean.  Nature 405: 305-310.

What was done
Elderfield and Rickaby provide a new interpretation of Cd/Ca systematics in sea water that allows them to more accurately estimate surface water phosphate at glacial times and determine the implications for atmospheric CO2 concentrations.

What was learned
In the words of the authors, "results from the Last Glacial Maximum show similar phosphate utilization in the subantarctic to that of today, but much smaller utilization in the polar Southern Ocean," which implies, in the words of Delaney, that "Antarctic productivity was lower then than it is now, and that subantarctic productivity was unchanged."  Noting that sea-ice cover in the Southern Ocean during glacial periods may have been as much as double the surface sea-ice area of modern winter ice, Elderfield and Rickaby further suggest that "by restricting communication between the ocean and atmosphere, sea ice expansion also provides a mechanism for reduced CO2 release by the Southern Ocean and lower glacial atmospheric CO2."

What it means
Elderfield and Rickaby note that "during glacial periods, low atmospheric carbon dioxide concentration has been associated with increased oceanic carbon uptake, particularly in the southern oceans."  Although there is considerable evidence to support this view, it has always seemed at odds with the general observation that plant photosynthesis is typically less in environments of lower atmospheric CO2 concentration.  This new work thus helps to reconcile these two facts; phytoplanktonic productivity in the glacial Southern Ocean may well have been lower than it is now during the previous glacial period of low atmospheric CO2.

Delaney, P.  2000.  Nutrients in the glacial balance.  Nature 405: 288-291.

Reviewed 15 July 2000