Transport and mixing of dissolved oxygen in the Bay of Bengal during the summer monsoon
Anoop A. Nayak*, P. N. Vinayachandran, Jenson V. George
Centre for Atmospheric and Oceanic Sciences, IISc, Bengaluru
A1 Boys Hostel, A mess, Indian Institute of Science Bengaluru, Karnataka, India Pincode: 560012 Mobile: 9632138420 E-mail: firstname.lastname@example.org
Bay of Bengal (BoB) hosts an oxygen minimum zone (OMZ) to its north. OMZ in BoB is unique from other OMZs globally because of steady concentration levels of dissolved oxygen within. The atmospheric interactions modulate near-surface concentrations of dissolved oxygen (DO), but below the surface, large-scale circulation and vertical mixing modulate the distribution and concentrations of DO. OMZs are regions in the ocean interior where the consumption of DO is more significant than its supply. Steady concentration of DO within BoB OMZ creates interest in understanding the supply of oxygen. This study uses DO and microstructure profiles in the southern BoB (BoBBLE in July 2016) to estimate turbulent and salt fingering fluxes for dissolved oxygen. Profiles from ARGO floats in BoB show signatures of high salinity core observed in the BoBBLE as far as 19 $^\circ$N. As observed in the southern BoB, high salinity water recorded by the ARGO floats is also rich in oxygen. During the summer monsoon, summer monsoon current (SMC) advects high salinity Arabian Sea water rich in DO, to the south of BoB, and circulations within the basin help in northward movement of the high salinity, high DO water. A high salinity core indicates salt fingering, which effectively mixes salt and dissolved oxygen downwards than turbulent processes. Vertical mixing due to salt fingering and turbulent processes recharge the DO concentration in the thermocline. These processes are essential since strong stratification in northern BoB prevents atmospheric interactions with the subsurface.