The Southern Ocean in the Earth System

Abstract

Southern Ocean processes influence climate and biogeochemical cycles on global scales. The Southern Ocean connects the ocean basins and links the shallow and deep limbs of the overturning circulation, a globalscale system of ocean currents that determines how much heat and carbon the ocean can store. The upwelling of deep waters releases carbon and returns nutrients that support biological productivity in the surface ocean; the compensating sinking of surface waters into the ocean interior sequesters carbon and heat and renews oxygen levels. The capacity of the ocean to moderate the pace of climate change is therefore controlled strongly by the circulation of the Southern Ocean. The future of the Antarctic ice sheet, and hence sea level rise, is increasingly understood to be determined by the rate at which the relatively warm ocean can melt floating glacial ice around the margin of Antarctica. Given the significance of the Southern Ocean to the Earth system, any change in the region would have impacts that extend well beyond the high southern latitudes. Recent studies suggest change is underway: the Southern Ocean is warming and freshening throughout most of the ocean depth; major currents are shifting to the south, causing regional changes in sea level and the distribution of organisms and supplying additional heat to melt ice around the rim of Antarctica; and the future of the Southern Ocean carbon sink is a topic of vigorous debate. Many of these discoveries are the result of the concerted multidisciplinary effort during the International Polar Year, which has provided an unprecedented view of the status of the Southern Ocean, a baseline for assessing change, and a demonstration of the feasibility, value, and timeliness of a Southern Ocean Observing System. The sustained observations of the Southern Ocean provided by such an observing system are essential to provide the knowledge needed to inform policy decisions and wise stewardship of the region. THE ROLE OF THE SOUTHERN OCEAN IN THE EARTH SYSTEM For many years, studies of the Southern Ocean were somewhat neglected by the Antarctic science community. The “real” Antarctic science took place on the continent itself; the rough ocean crossing was the uncomfortable prelude and postscript to a season of excitement in the last great wilderness on Earth. However, growing recognition of the global influence of Southern Ocean processes has heightened interest in oceanographic studies of the region. The Southern Ocean in the Earth System