Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms

James C. Orr, Laurent Bopp, Patrick Monfray¹, and Keith B. Rodgers^2,3, Laboratoire des Sciences du Climat et de l'Environnement, UMR CEA-CNRS, CEA Saclay, F-91191 Gif-sur-Yvette, France.
¹Now at Laboratoire d'Etudes en Geophysique et Oceanographie Spatiales, UMR 5566 CNES-CNRS-IRD-UPS, F-31401 Toulouse, France
²Also at LOCEAN, Universite Pierre et Marie Curie, F-75252 Paris, France.
³Now at AOS Program, Princeton University, Princeton, New Jersey 08544-0710, USA

Victoria J. Fabry, Department of Biological Sciences, California State University San Marcos, San Marcos, California 92096-0001, USA.

Olivier Aumont, Laboratoire d'Oceanographie et du Climat: Experimentations et Approches Numeriques (LOCEAN), Centre IRD de Bretagne, F-29280 Plouzane, France.

Scott C. Doney, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543-1543, USA.

Richard A. Feely and Christopher L. Sabine, National Oceanic and Atmospheric Administration (NOAA)/Pacific Marine Environmental Laboratory, Seattle, Washington 98115-6349, USA.

Anand Gnanadesikan, NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey 08542, USA.

Nicolas Gruber, Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, California 90095-4996, USA.

Akio Ishida and Yasuhiro Yamanaka, Frontier Research Cen ter for Global Change, Yokohama 236-0001, Japan.

Fortunat Joos and Gian-Kasper Plattner⁴, Climate and Environmental Physics, Physics Institute, University of Bern, CH-3012 Bern, Switzerland.
⁴Also at Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, California 90095-4996, USA.

Robert M. Key, Jorge L. Sarmiento, and Richard D. Slater, Atmospheric and Oceanic Sciences (AOS) Program, Princeton University, Princeton, New Jersey 08544-0710, USA.

Keith Lindsay, National Center for Atmospheric Research, Boulder, Colorado 80307-3000, USA.

Ernst Maier-Reimer, Max Planck Institut für Meteorologie, D-20146 Hamburg, Germany.

Richard Matear, CSIRO Marine Research and Antarctic Climate and Ecosystems CRC, Hobart, Tasmania 7001, Australia.

Anne Mouchet, Astrophysics and Geophysics Institute, University of Liege, B-4000 Liege, Belgium.

Raymond G. Najjar. Department of Meteorology, Pennsylvania State University, University Park, Pennsylvania 16802-5013, USA.

Reiner Schlitzer and Marie-France Weirig, Alfred Wegener Institute for Polar and Marine Research, D-27515 Bremerhaven, Germany.

Ian J. Totterdell⁵ and Andrew Yool, National Oceanography Centre Southampton, Southampton SO14 3ZH, UK.
⁵Now at The Met Office, Hadley Centre, FitzRoy Road, Exeter EX1 3PB, UK

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.