Reduced calcification of marine plankton in response to increased atmospheric CO2

Reduced calcification of marine plankton in response to increased atmospheric CO2
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Journal Article
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Riebesell U, Zondervan I, Rost B, Tortell PD, Zeebe RE, Morel FMM

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co2, acidification, Plankton, carbonate chemistry, mesocosm, Espegrend, Bergen, 11 m3, Norway


The formation of calcareous skeletons by marine planktonicorganisms and their subsequent sinking to depth generates acontinuous rain of calcium carbonate to the deep ocean andunderlying sediments1. This is important in regulating marinecarbon cycling and ocean±atmosphere CO2 exchange2. The presentrise in atmospheric CO2 levels3 causes signi®cant changes insurface ocean pH and carbonate chemistry4. Such changes havebeen shown to slow down calci®cation in corals and corallinemacroalgae5,6, but the majority of marine calci®cation occurs inplanktonic organisms. Here we report reduced calcite productionat increased CO2 concentrations in monospeci®c cultures of twodominant marine calcifying phytoplankton species, the coccolithophoridsEmiliania huxleyi and Gephyrocapsa oceanica. Thiswas accompanied by an increased proportion of malformedcoccoliths and incomplete coccospheres. Diminished calci®cationled to a reduction in the ratio of calcite precipitation toorganic matter production. Similar results were obtained inincubations of natural plankton assemblages from the northPaci®c ocean when exposed to experimentally elevated CO2levels. We suggest that the progressive increase in atmosphericCO2 concentrations may therefore slow down the production ofcalcium carbonate in the surface ocean. As the process of calci®cationreleases CO2 to the atmosphere, the response observed herecould potentially act as a negative feedback on atmospheric CO2levels

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