Climate Science

Choose Calcifiers with Care

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Science  03 Aug 2007:
Vol. 317, Issue 5838, pp. 572
DOI: 10.1126/science.317.5838.572a

In contrast to near-term estimates, prediction of atmospheric CO2 content several centuries from now is severely hampered by the multitude of poorly understood feedback mechanisms. The most important of these is probably the interaction between atmospheric CO2 and marine calcification. In a nutshell, the amount of CO2 absorbed by the ocean depends on the quantity depleted through calcium carbonate incorporation into the skeletons of calcifying organisms such as foraminifera and coccolithophorids. This bioactivity is a function of the alkalinity and the pH of the ocean, which in turn depend largely on the partial pressure of atmospheric CO2, as well as the type of calcifying organism (E. huxleyi and O. universa are shown). Although the carbonate chemistry of the ocean is well known, the response of different species to changes in pH and alkalinity is incompletely understood, and large differences exist between the species that have been studied. Ridgwell et al. have performed model calculations for a range of calcifying behaviors. They find that the strength of CO2 calcification feedback is dominated by the assumption of which species of calcifier contributes most to carbonate production, and that ocean CO2 sequestration could reduce the atmospheric fossil fuel CO2 burden by 4 to 13% in the year 3000. This long-term view is needed to help understand the full impact of current energy use. — HJS

Biogeosciences 4, 481 (2007).

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