Low-frequency transport variability in the Southern Ocean: the importance of regional variations
Event: 2015 Ocean Surface Topography Science Team Meeting
Session: Science III: Large scale and global change ocean processes: the ocean's role in climate
Presentation type: Type Oral
We use satellite altimetry, temperature/salinity from Argo, ocean bottom pressure from GRACE and the ECCO2 state estimate, and satellite vector winds to quantify and understand zonal geostrophic transport variability in the Southern Ocean. Altimetry and Argo data are used to estimate the transport variability above 2000 dbar, while GRACE and ECCO2 are used to measure the full-depth transport associated with the bottom current (i.e., the barotropic component). We find that for interannual periods, the transport variations are dominated by the Southern Annular Mode (SAM) variability, but that there are significant differences in the two estimates. The barotropic component is more highly correlated with SAM, suggesting either issues in the altimetry/Argo estimate or significant baroclinic differences. More importantly, we observe a significant difference in decadal trends between the Southern Indian Ocean and South Pacific, with different signs. This is found in both the GRACE and ECCO2 estimates, and is shown to be related to regional wind differences – the winds in the Atlantic/Indian Ocean sectors have been decreasing over the last decade while they have been increasing west of the Drake Passage, although zonally averaged winds show little change. These results have important implications for studies trying to estimate changes of the Antarctic Circumpolar Current transport at the Drake Passage.