Observational evidence of the southward transport of water masses in the Indian sector of the Southern Ocean

The southward transport of water masses in the Indian sector of the Southern Ocean (SO) is compared using the hydrographic data collected during the austral summer of 2010 and 2011. It has been found that subtropical surface water (STSW) underwent maximum southward displacement during the study period. The southward extent of STSW was at 45°S during 2011, but was restricted to 42°S during 2010. During 2011, three eddies were identified along the cruise track, whereas during 2010 eddies were absent. Satellite sea-level anomaly showed that these eddies were associated with the highly unstable Agulhas Return Current (ARC). The present study shows that STSW is transported along the peripheries of these eddies during 2011. There are indications of transport of mode water as well, but this is not resolved in the present study. Analysis of eddy kinetic energy shows a positive linear decadal trend; also, peak eddy lagged the southern annular mode by a year. This indicates that though the eddies may act locally, they are linked to the large-scale variability in the southern hemisphere.