Study the effect of tropical cyclones on dissolved oxygen in the north Indian Ocean using Argo and satellite data

The study investigates the role of tropical cyclones (TCs) in dissolved oxygen (DO) distributions and Oxygen Minimum Zone (OMZ) variability in the northern Indian Ocean (IO) for 2019-2022. The analyses revealed under the influence TCs the thickness of OMZ varied between ∼610-753 m and ∼ 922-1179 m at different locations in Bay of Bengal (BoB) and Arabian Sea (AS) respectively. The OMZ thickness during TC Sitrang was >740 m unlike during TCs Fani and Yaas which occurred in post monsoon season. Strong near-surface wind stress on right side of TC track causes thickening of OMZ after the cyclone. OMZ thickness decreases at the BGC-Argo located on left side of the cyclone track. The observed vertical profiles also suggest three different surface and subsurface DO variability during TCs. The TC-induced upwelling during Sitrang decreased DO up to ∼80 m by bringing cold, high saline and low-oxygen waters from deep subsurface layers to shallow layers. While at Argo 2902271, DO first decreased up to 48 m then increased in the subsurface layer between 49 and 89 m and between 99 and 176 m due to the vertical mixing induced by TC Vayu.Such response occurred during TCs Kyarr (Argo 2902270, 2902275), and Maha (Argo 2902271, 2902272, 2902275) that mixed the surface DO rich water with the subsurface layers. Lastly, the third type is characterized by layered thermal and DO profile due to combined effect of TC induced upwelling and vertical mixing observed during TCs Fani (Argo 2902264), Yaas (Argo 2902758), Tauktae (Argo 2902273), Vayu (Argo 2902276), Kyarr (2902277), and Maha (2902270).