Letters to Nature

Nature 407, 364-367 (21 September 2000) | doi:10.1038/35030078; Received 2 August 1999; Accepted 18 July 2000

Reduced calcification of marine plankton in response to increased atmospheric CO2

Ulf Riebesell1, Ingrid Zondervan1, Björn Rost1, Philippe D. Tortell2, Richard E. Zeebe1,3 & François M. M. Morel2

  1. Alfred Wegener Institute for Polar and Marine Research, P.O. Box 120161, D-27515 Bremerhaven, Germany
  2. Department of Geosciences & Department of Ecology and Evolutionary Biology, Princeton University, Princeton , New Jersey 08544, USA
  3. Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964 , USA

Correspondence to: Ulf Riebesell1 Correspondence and requests for materials should be addressed to U. R. (e-mail: Email: uriebesell@awi-bremerhaven.de).

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.