Meso- to submesoscale surface thermohaline variability in Indian Ocean

The horizontal thermohaline structure at the sea surface is investigated in the Indian Ocean at length scales from five to hundreds of kilometers, i.e. at submeso- to meso-scales. The near-surface temperature and salinity data from thermosalinograph (TSG) gathered from merchant and research vessels across different regions over the Indian Ocean are used to compute the horizontal temperature, salinity and density fluctuations, as well as the density ratio. Several regimes are identified depending on the region. In Arabian Gulf and Bay of Bengal, salinity strongly dominate the mesoscale density fluctuations, while temperature variations have much small amplitude and scale features than salinity. In the eastern tropical Indian Ocean, due to strong input of fresh water from the Indonesian Throughflow and high precipitation rates, the salinity gradient also dominates the density variability, while in the western tropical Indian, temperature and salinity both have constructive effects on density gradient. Strongly compensated fronts are observed at the southern Subtropical Front where tens of degrees are compensated by strong salinity variations. Such different regimes will be discussed in term of impact on horizontal turbulence and vertical mixing in the Indian Ocean.