Trends in the deep southern ocean (1958-2010): implications for antarctic bottom water properties and volume export

Abstract

Regional formation of deep and bottom water masses around the Antarctic continentalshelf is one of the most important processes contributing to variability of the globalmeridional overturning circulation deep cell. Southern Ocean hydrographic data collectedduring the years 1958–2010 indicate that dense shelf waters cooled and freshened duringthat period. In the surrounding open ocean, Antarctic Bottom Water (AABW) warmed, withno evidence of salinity change. As a result of source-water property changes, AABWexported from the Southern Ocean to the deep world ocean became lighter over the periodanalyzed. The average rate of density change within the areas that experienced statisticallysignificant change was0.0019 kg m3yr1. For the last 20 years of the analysis, anegative AABW volume anomaly (relative to the half-century average, 1958–2010) wasindicated, possibly due to production of a lighter AABW variety or to changes in formationrates. Over the entire five decades, the upper isopycnal of the AABW layer deepened at arate of8.1 m yr1. Changes in fundamental hydrographic properties such as these canhave important implications for long-term global ocean circulation and climate.