Geostrophic volume transport and eddies in the region of sub-tropical and sub-Antarctic waters south of Madagascar during austral summer (January–February) 2004

Geostrophic volume transport based on hydrographic data is estimated across two transects that are covered south of Madagascar in the region of the sub-tropical and sub-Antarctic waters as a part of the Indian Pilot Expedition to the Southern Ocean on board ORV Sagar Kanya during austral summer 2004. Strong density current shears are encountered in the study area suggesting high potential for the generation of mesoscale eddies. Volume transports with reversing directions are encountered especially in the depth range of 0–1000 m between Madagascar and around Sub-Tropical Convergence (STC) and they reach maximum values of 40 and 80 Sv (1 Sv = 106 m3 s−1) directed towards southeast and east across tracks 1 and 2 respectively. Such reversing flows, however, are not much seen in the sub-Antarctic and Antarctic waters. The sea surface height anomaly (SSHA) field in the southwestern Indian Ocean based on satellite altimetry during January–February 2004 further shows that relatively high meso-scale variability associated with the regions of larger volume transports promotes meandering of East Madagascar current (EMC) and combined Agulhas return current (ARC)/Antarctic circumpolar current (ACC) systems from where eddies are likely to shed out with a developmental tendency of clockwise (anti-clockwise) rotations on right (left) side of these current streams. A positive correlation between SSHA and mixed layer depth (MLD) is confined to the sub-tropical waters, suggesting the influence of eddies on the dynamics of MLD in the study area.