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Reduced calcification of marine plankton in response to increased atmospheric CO2


The formation of calcareous skeletons by marine planktonic organisms and their subsequent sinking to depth generates a continuous rain of calcium carbonate to the deep ocean and underlying sediments1. This is important in regulating marine carbon cycling and ocean–atmosphere CO2 exchange2. The present rise in atmospheric CO2 levels3 causes significant changes in surface ocean pH and carbonate chemistry4. Such changes have been shown to slow down calcification in corals and coralline macroalgae5,6, but the majority of marine calcification occurs in planktonic organisms. Here we report reduced calcite production at increased CO2 concentrations in monospecific cultures of two dominant marine calcifying phytoplankton species, the coccolithophorids Emiliania huxleyi and Gephyrocapsa oceanica . This was accompanied by an increased proportion of malformed coccoliths and incomplete coccospheres. Diminished calcification led to a reduction in the ratio of calcite precipitation to organic matter production. Similar results were obtained in incubations of natural plankton assemblages from the north Pacific ocean when exposed to experimentally elevated CO2 levels. We suggest that the progressive increase in atmospheric CO2 concentrations may therefore slow down the production of calcium carbonate in the surface ocean. As the process of calcification releases CO2 to the atmosphere, the response observed here could potentially act as a negative feedback on atmospheric CO2 levels.

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Figure 1: Response of organic and inorganic carbon production to CO2 concentration in laboratory-cultured coccolithophorids.
Figure 2: Ratio of calcification to POC production (calcite/POC) of Emiliania huxleyi as a function of CO2 concentration, [CO2].
Figure 3: Scanning electron microscopy (SEM) photographs of coccolithophorids under different CO2 concentrations.
Figure 4: Effects of CO2 manipulations on POC production, calcification and the ratio of calcification to POC production (calcite/POC) in subarctic North Pacific phytoplankton assemblages.


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We thank A. Dauelsberg, B. Höhnisch, A. Terbrüggen, and K.-U. Richter for laboratory assistance, F. Hinz for REM analyses, D. Crawford, M. Lipsen, F. Whitney and C. Mayfield for invaluable help at sea and C. S. Wong for providing space on RV J.P. Tully. The E. huxleyi strain PML B92/11A was generously supplied by J. Green, Plymouth Marine Laboratory, and the G. oceanica strain PC 7/1 by the CODENET Algae collection in Caen. This work was supported by the Netherlands-Bremen Cooperation in Oceanography (NEBROC).

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Riebesell, U., Zondervan, I., Rost, B. et al. Reduced calcification of marine plankton in response to increased atmospheric CO2. Nature 407, 364–367 (2000).

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