Variability of Southern Ocean Transports

The Southern Ocean (SO) is capable of transporting vast amounts of salt, heat, and nutrients, which allows it to influence and regulate global climate. The variability of depth- and density-integrated volume transports in the SO is studied using the Estimating the Circulation and Climate of the Ocean (ECCO), version 4, release 3 (1992-2015), ocean state estimate. The estimate has a net eastward transport of 150.6 +/- 5.5, 162.6 +/- 7.4, and 148.2 +/- 5.4 Sv (1 Sv 10(6) m(3) s(-1)) between the Atlantic-Indian, Indian-Pacific, and Pacific-Atlantic basins, respectively. The time-mean meridional volume transport across 30 degrees S in the Atlantic is estimated to be -1.4 +/- 0.6 Sv, -14.4 +/- 3.5 Sv in the Indian basin, and 15.5 +/- 4.1 Sv in the Pacific, where negative values are southward. Trends in net volume transport between the basins are statistically insignificant. Within the water column, however, the middle and lower branches of the meridional overturning circulation have trends of -0.289 and 0.248 Sv decade(-1) in the Atlantic basin. The Indian and Pacific basins have decreasing trends in their lower overturning cells. These results indicate increased overturning circulation within the lower branch in the South Atlantic and decreased lower branch circulation within the Indian and Pacific basins and have implications on the thermohaline-driven circulation. Using ECCO, we estimate a southward potential temperature transport of -176.2 degrees +/- 197.2 degrees C Sv and salinity transport of -1.71 +/- 22.4 psu Sv into the SO and indicate potential temperature transport is increasing by -15.0 degrees +/- 13.2 degrees C Sv decade(-1).