Ocean acidification, the term for the decline in pH of ocean water resulting from increases in atmospheric carbon dioxide concentrations, poses severe potential threats to marine environments, including the Southern Ocean, not least because of the rapid rate at which it is progressing compared with anything organisms have faced in the past. This is likely to make adaptation difficult. The unique characteristics of the Southern Ocean suggest that ocean acidification will have its greatest initial impacts there in the waters surrounding Antarctica if greenhouse gas emissions continue to occur at present rates.
Aragonite, a form of calcium carbonate essential to shell forming organisms such as the pteropods that are important to the Southern Ocean food chain, will be undersaturated, or present at low levels, throughout the Southern Ocean by 2100 under the IPCC IS92a “business as usual” emissions scenario. The Southern Ocean is already relatively undersaturated with respect to calcium carbonate (CaCO3). Even under the more conservative IPCC S650 scenario, which assumes that atmospheric CO2 will only reach 563 ppm by 2100, the aragonite saturation horizon1 is likely to have shrunk from its present depth of 730 to 60 m by 2100, with the entire Weddell Sea undersaturated with respect to aragonite. Under these conditions, some organisms are likely to have difficulty forming shells, with possibly serious impacts on the food web.
It is imperative that more research programs be undertaken to fill current knowledge gaps on Southern Ocean acidification and its impacts as soon as possible. Long-term studies of acidification for the entire lifecycle of important species are needed, including implications for non-calcifying organisms and impacts of ocean acidification on other biological processes besides calcification in invertebrates and vertebrates.
Ocean Acidification and the Southern Ocean, ASOC Papers for the XXXIV ATCM, Web site.
