Potential mechanisms responsible for spatial variability in intensity and thickness of oxygen minimum zone in the Bay of Bengal

Abstract

Spatial variability in boundaries and thickness of oxygen minimum zone (OMZ) is derived based on measured dissolved oxygen data obtained from sensors on board biogeochemical (BGC) Argo floats between 2013 and 2019 in the Bay of Bengal (BoB). Upper and lower boundaries of the OMZ varied from 60 to 200 m and 100 to 800 m respectively with the thickness of 80 to 650 m in the BoB. Relatively thicker OMZ is noticed in the northern than southern BoB associated with stratification. The oxygen concentrations in the OMZ in the NW was low (<1.5 mu M) than NE BoB (2.5 mu M) indicating that thick and intense OMZ occurs in the NW region associating with stratification and high primary production. Significant decrease in particle-back scatter signal was observed towards offshore from shelf indicating organic matter from the shelf sediments may be supporting bacterial carbon demand in the OMZ. The particle back-scatter signal peaked in the OMZ region with higher signal in the north than southern BoB and it is consistent with the low oxygen concentration in the former indicating that organic matter from shelf sediments may be supporting carbon needs in the OMZ. In addition to this, the occurrence of eddies significantly control the intensity of the OMZ in the BoB through mixing at the upper boundary of OMZ. Therefore, this study suggests that spatial variations in intensity of OMZ in the BoB is governed by stratification, primary and export productions, organic matter decomposition and eddy-driven mixing.