Abstract

Today's surface ocean is saturated with respect to calcium carbonate, but increasing atmospheric carbon dioxide concentrations are reducing ocean pH and carbonate ion concentrations, and thus the level of calcium carbonate saturation. Experimental evidence suggests that if these trends continue, key marine organisms—such as corals and some plankton—will have difficulty maintaining their external calcium carbonate skeletons. Here we use 13 models of the ocean–carbon cycle to assess calcium carbonate saturation under the IS92a 'business-as-usual' scenario for future emissions of anthropogenic carbon dioxide. In our projections, Southern Ocean surface waters will begin to become undersaturated with respect to aragonite, a metastable form of calcium carbonate, by the year 2050. By 2100, this undersaturation could extend throughout the entire Southern Ocean and into the subarctic Pacific Ocean. When live pteropods were exposed to our predicted level of undersaturation during a two-day shipboard experiment, their aragonite shells showed notable dissolution. Our findings indicate that conditions detrimental to high-latitude ecosystems could develop within decades, not centuries as suggested previously.

1. Laboratoire des Sciences du Climat et de l'Environnement, UMR CEA-CNRS, CEA Saclay, F-91191 Gif-sur-Yvette, France
2. Department of Biological Sciences, California State University San Marcos, San Marcos, California 92096-0001, USA
3. Laboratoire d'Océanographie et du Climat: Expérimentations et Approches Numériques (LOCEAN), Centre IRD de Bretagne, F-29280 Plouzané, France
4. Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543-1543, USA
5. National Oceanic and Atmospheric Administration (NOAA)/Pacific Marine Environmental Laboratory, Seattle, Washington 98115-6349, USA
6. NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey 08542, USA
7. Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, California 90095-4996, USA
8. Frontier Research Center for Global Change, Yokohama 236-0001, Japan
9. Climate and Environmental Physics, Physics Institute, University of Bern, CH-3012 Bern, Switzerland
10. Atmospheric and Oceanic Sciences (AOS) Program, Princeton University, Princeton, New Jersey 08544-0710, USA
11. National Center for Atmospheric Research, Boulder, Colorado 80307-3000, USA
12. Max Planck Institut für Meteorologie, D-20146 Hamburg, Germany
13. CSIRO Marine Research and Antarctic Climate and Ecosystems CRC, Hobart, Tasmania 7001, Australia
14. Astrophysics and Geophysics Institute, University of Liege, B-4000 Liege, Belgium
15. Department of Meteorology, Pennsylvania State University, University Park, Pennsylvania 16802-5013, USA
16. LOCEAN, Université Pierre et Marie Curie, F-75252 Paris, France
17. Alfred Wegener Institute for Polar and Marine Research, D-27515 Bremerhaven, Germany
18. National Oceanography Centre Southampton, Southampton SO14 3ZH, UK
19. †Present addresses: Laboratoire d'Etudes en Géophysique et Océanographie Spatiales, UMR 5566 CNES-CNRS-IRD-UPS, F-31401 Toulouse, France (P.M.); AOS Program, Princeton University, Princeton, New Jersey 08544-0710, USA (K.B.R.); The Met Office, Hadley Centre, FitzRoy Road, Exeter EX1 3PB, UK (I.J.T.)

Correspondence to: James C. Orr¹ Correspondence and requests for materials should be addressed to J.C.O. (Email: orr@cea.fr).

Received 15 June 2005; Accepted 29 July 2005

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