Arabian Sea high salinity core supplies oxygen to Bay of Bengal oxygen minimum zone

TL;DR

This study reveals that a high salinity, oxygen-rich water core transported by monsoon currents sustains the Bay of Bengal's oxygen minimum zone, potentially preventing it from expanding under climate change.

Contribution

It identifies a novel process where high salinity cores supply oxygen to the OMZ, highlighting a key mechanism maintaining oxygen levels in the Bay of Bengal.

Findings

High salinity core (HSC) supplies oxygen to OMZ.

HSC advected by Summer Monsoon Current into BoB.

Vertical mixing recharges DO in thermocline.

Abstract

The oxygen minimum zone (OMZ) in the Bay of Bengal (BoB) is unique owing to its curious capability to maintain steady dissolved oxygen (DO) levels. In this study, we identify a process by which the oxygen levels in BoB are sustained above the tipping point, using DO and microstructure profiles in the southern BoB and Argo profiles over the entire basin. High salinity core (HSC) rich in DO is advected by the Summer Monsoon Current (SMC) into BoB. Vertical mixing driven by turbulent and salt-fingering processes recharge DO concentration in thermocline above OMZ. HSC identified in the Argo data, also rich in oxygen, can be traced up to 19$^\circ$ N, confirming that HSC is a source of DO and potentially prevents OMZ from moving to the denitrification regime. In changing climate conditions, this might be the only significant oxygen source for the BoB OMZ in the future.