The Role of the Southern Ocean on Global Ocean Circulation and Climate

The Southern Ocean (SO) is a unique and highly dynamic region with strong temperature and salinity gradients. A comparison between satellite-derived salinity and observations indicates strong differences along coastal boundaries, areas of low temperature, and regions of strong currents. Although differences throughout much of the SO are shown to be negligible, resolution and smoothing in the products create large biases in horizontal gradients and errors in estimating the water cycle. The three-dimensional movement of water within the SO plays an important role in the global Meridional Overturning Circulation (MOC), where the Southern Hemisphere westerlies drive both zonal and meridional transports and strong vertical movements of local water masses. Using the Estimating the Circulation and Climate of the Ocean (ECCO) estimates of ocean circulation, recent trends in the lower cell of the MOC (1992-2015) show increased overturning within the South Atlantic and decreased overturning within the Indian and Pacific basins, increasing the net SO heat transports and storage. The path of the Antarctic Circumpolar Current (ACC) is mainly dictated by bathymetry, but recent variability indicates a northward shift in the central South Pacific ACC fronts. The movement and location of the ACC is highly correlated to salinity and temperature shifts up to 100 m depth and moderately correlated to depths of 1000 m. The location of the ACC is weakly-to-moderately correlated with the Antarctic and Southern Oscillations. These large-scale teleconnections are further driving surface cooling in the central South Pacific and warming in the subtropics and mid-latitudes of the Southern Hemisphere. Satellite-derived sea surface temperatures (SSTs) are highly correlated with both the Antarctic and Southern Oscillations during 1982-2016, particularly during the austral summer months when the oscillations tend to be the strongest. Changes in the westerlies are correlated with sea level and heat content anomalies and anti-correlated to SST in the high latitudes. The magnitude of the westerlies has recently increased throughout the ACC region, driving the increase in mid-latitude and decrease in the central South Pacific SST, heat content, and sea level anomalies. These analyses conclude that atmospheric variability is significantly contributing to recent changes in circulation and surface properties