Role of internal tide mixing in keeping the deep Andaman Sea warmer than the Bay of Bengal

Abstract

Vertical profiles of temperature obtained from various hydrographic datasets show that deep waters (below 1,200 m) in the Andaman Sea are warmer (about 2 °C) than that of the Bay of Bengal. As a result, the biochemical properties in the deep waters also exhibit significant differences between these two basins. Higher temperature in the deep waters of Andaman Sea compared to the BoB had been widely attributed to the enclosed nature of the Andaman Sea. In this study, we show that strong tidal energy dissipation in the Andaman Sea also plays an important role in maintaining the higher temperatures in the deep waters. Dissipation rates inferred from the hydrographic data and internal tide energy budget suggests that the rate of vertical mixing in the Andaman Sea is about two-orders of magnitude larger than that in the Bay of Bengal. This elevated internal tide induced vertical mixing results in the efficient transfer of heat into the deeper layers, which keeps the deep Andaman Sea warm. Numerical experiments conducted using a high-resolution setup of Regional Ocean Modelling System (ROMS) further confirm the effect of tidal mixing in the Andaman Sea.