Ocean acidification and the Southern Ocean

Abstract Ocean acidification poses severe potential threats to marine ecosystems, including the Southern Ocean. The relative undersaturation of CaCO3 in the Southern Ocean suggests that ocean acidification will have its greatest initial impacts there if greenhouse gas emissions continue on their projected trajectory. Aragonite is a form of calcium carbonate essential to shell forming organisms such as the pteropods that form the base of much of the Southern Ocean food chain. Orr et al (2005) predicted that under the Intergovernmental Panel on Climate Change (IPCC) IS92a warming scenario , which assumes “business as usual” - emissions leading to 778 ppm of CO2 in the atmosphere by 2100 - aragonite will be undersaturated throughout the Southern Ocean. Even under the more conservative IPCC S650 scenario, which assumes that atmospheric CO2 will only reach 563 ppm by 2100, the aragonite saturation horizon is likely to have shrunk from 730 to 60 m by 2100, with the entire Weddell Sea undersaturated with respect to aragonite. Current greenhouse gas emission projections make it imperative that CCAMLR Members develop research programs to fill in the gaps of current research on Southern Ocean impacts as soon as possible. Longer-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 is relevant to consideration of the impacts of fishing on benthic organisms (including cold water corals) and the management of vulnerable marine ecosystems (VMEs). Acidification is likely to negatively affect recovery period and whether species can recover.