Variability of surface circulation and biological productivity of Southern Indian Ocean in remote sensing perspective

Abstract

The Indian Ocean has a unique geographic location that is not connected to the North Pole (blocked by the Asian Land mass at around 26°N) but it has a wide opening to the Antarctic Ocean. Therefore, the oceanic and atmospheric circulation of the Indian Ocean is significantly controlled by the processes occurring in the Southern Ocean region. In this study, a comprehensive analysis was carried out to derive information of the spatial and temporal variability of surface circulation, and biological productivity of the Southern Indian Ocean using the available remote sensing observations. The monthly multi-mission merged satellite altimeter data with a resolution of 1/3 x 1/3 degrees in latitude and longitude from Archiving, Validation and Interpretation of Satellite Oceanographic Data, Collective Localisation Satellites; France (AVISO) for the period of 1993-2010 were used to estimate the surface currents in this study. The biological productivity was analysed using the Chlorophyll-a (Chl-a) data from Sea Viewing Wide Field-of-View Sensor (SeaWiFS) from September 1997 until December 2010. The maps of seasonal circulation patterns and the Chl-a distribution were prepared and analysed. The Empirical Orthogonal Function analysis was carried out to identify the spatial and temporal modes of Chl-a variability of Southern Indian Ocean. Available in-situ oceanographic observations of currents were used to validate the accuracy of the estimated velocity field. The surface velocity field in the Southern Indian Ocean shows active circulations comprising of Agulhas Current, Agulhas Return Current and Antarctic Circumpolar Current. The seasonal Chl-a maps show high Chl-a concentration prevails in the coastal region of Africa, central region and south of Australia. At south of Africa, influence of coastal current is more significant than the climatic indices. Meanwhile, in the central region, large topographic barriers near Kerguelen Island play an important role in modulating the Chl-a concentration. In south of Australia, high Chl-a concentration along the west coast is related to Leuuwin Current eddies and land run-off. In this study, no significant relationship was found between the climate modes of El Nino Southern Oscillation (ENSO)/Indian Ocean Dipole (IOD) and Southern Annular Mode (SAM). The propagation of Antarctic Circumpolar Wave (ACW) also influences the mesoscale dynamics as well as the Chl-a distribution.