| Summary: | Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 437 (2005): 681-686, doi:10.1038/nature04095. The surface ocean is everywhere saturated with respect to calcium carbonate (CaCO3). Yet increasing atmospheric CO2 reduces ocean pH and carbonate ion concentrations [CO32−] and thus the level of saturation. Reduced saturation states are expected to affect marine calcifiers even though it has been estimated that all surface waters will remain saturated for centuries. Here we show, however, that some surface waters will become undersaturated within decades. When atmospheric CO2 reaches 550 ppmv, in year 2050 under the IS92a business-as-usual scenario, Southern Ocean surface waters begin to become undersaturated with respect to aragonite, a metastable form of CaCO3. By 2100 as atmospheric CO2 reaches 788 ppmv, undersaturation extends throughout the entire Southern Ocean (< 60°S) and into the subarctic Pacific. These changes will threaten high-latitude aragonite secreting organisms including cold-water corals, which provide essential fish habitat, and shelled pteropods, an abundant food source for marine predators. All but the climate simulations were made as part of the OCMIP project, which was launched in 1995 by the Global Analysis, Interpretation, and Modeling (GAIM) Task Force of the International Geosphere-Biosphere Program (IGBP) with funding from NASA. OCMIP-2 was supported by the EU GOSAC project and the U.S. JGOFS SMP funded through NASA. The interannual simulation was supported by the EU NOCES project, which is part of OCMIP-3.
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