Mean structure, long-term change and eddy motions in the Southern Ocean: A perspective from altimetry, Argo and state estimation
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
The low stratification of the Southern Ocean means that eddies detected by altimetry at the ocean surface extend through the top 2 km of the ocean. Sea surface height anomalies are more strongly correlated with sub-surface variability at depths between about 600 and 1400 dbars than they are with variability in the upper 200 dbars. Altimetric variability can thus be used to remove eddy-related anomalies from individual Argo profiles, resulting in a smoother estimate of mean temperature and salinity. This “eddy-free” mean field serves as a benchmark against which to assess decadal-scale changes in the Southern Ocean, and we use historic hydrographic data to evaluate temperature and salinity changes through the second half of the 20th century. We also evaluate the behavior of Southern Ocean eddies themselves: Although in most parts of the ocean closed oceanic eddies appear to result in thermally indirect heat transport, eddies that are carried eastward by the ACC tend to propagate in the opposite direction, resulting in thermally direct, cross-ACC heat transport. This thermally direct cell seems to be unique to the ACC. Evidence suggests that this cell is maintained by the effective eastward propagation of eddies relative to the mean flow at deep levels.