Northern Indian Ocean Salt Transport (NIOST): Estimation of Fresh and Salt Water Transports in the Indian Ocean using Remote Sensing, Hydrographic Observations and HYCOM Simulations

Abstract

Abstract : Ocean salinity is one of the most important variables in oceanic and climate studies. Together with temperature they regulate the density of ocean water and are used to determine the formation of water masses and circulation. Whereas temperature has been measured very extensively in the world s oceans by both in-situ and remote means, salinity observations are very limited and not uniformly distributed geographically; they are mainly confined to shipping lanes and the summer season. Consequently, basin wide oceanic processes, air-sea interaction and climate studies that require the incorporation of salinity data are quite a challenge. In the Indian Ocean where seasonal reversals of winds lead to reversal of ocean currents and transport processes, salinity shows very wide variability. It is therefore important to understand the dynamics of exchange of salt in this Ocean, especially when net fresh water flux is seasonally different in the various basins of the ocean. Such ocean-wide studies have been limiting in the past as a result of the lack of basin-wide salinity data. Though ocean salinity is one of the most important variables in the oceanic and climate studies, a gap in the Indian Ocean observing system to date has been the scarcity of surface salinity data. This study involves the use of high resolution (1/12 ) HYbrid Coordinate Ocean Model (HYCOM) numerical model and salinity derived from satellites (SMOS and Aquarius Salinity missions), hydrographic data, and Argo floats to understand the freshwater and salt transport dynamics in the Indian Ocean. This preliminary study, in 5 months, emphasizes that HYCOM sea surface salinity is a good proxy to compare the satellite-derived salinity. Additionally, the study on long-term salt transport (2003-2012) reveals seasonal reversal in the mean salt transport which is more pronounced in the northern Indian Ocean. On interannual scale, the Indian Ocean Dipole and El Ni o Southern Oscillation events also influence salt t