Trends in the deep Southern Ocean (1958–2010): Implications for Antarctic Bottom Water properties and volume export

Regional formation of deep and bottom water masses around the Antarctic continental shelf is one of the most important processes contributing to variability of the global meridional overturning circulation deep cell. Southern Ocean hydrographic data collected during the years 1958–2010 indicate that dense shelf waters cooled and freshened during that period. In the surrounding open ocean, Antarctic Bottom Water (AABW) warmed, with no evidence of salinity change. As a result of source‐water property changes, AABW exported from the Southern Ocean to the deep world ocean became lighter over the period analyzed. The average rate of density change within the areas that experienced statistically significant change was −0.0019 kg m−3 yr−1. For the last 20 years of the analysis, a negative AABW volume anomaly (relative to the half‐century average, 1958–2010) was indicated, possibly due to production of a lighter AABW variety or to changes in formation rates. Over the entire five decades, the upper isopycnal of the AABW layer deepened at a rate of −8.1 m yr−1. Changes in fundamental hydrographic properties such as these can have important implications for long‐term global ocean circulation and climate.