Recent changes in the upper oceanic water masses over the Indian Ocean using Argo data

Abhijit Shee; Sourav Sil; Avijit Gangopadhyay

doi:10.1038/s41598-023-47658-9

Recent changes in the upper oceanic water masses over the Indian Ocean using Argo data

Sci Rep. 2023 Nov 20;13(1):20252. doi: 10.1038/s41598-023-47658-9.

Authors

Abhijit Shee^{1

2}, Sourav Sil³, Avijit Gangopadhyay⁴

Affiliations

¹ Ocean Analysis and Modelling Laboratory, School of Earth, Ocean and Climate Sciences, Indian Institute of Technology Bhubaneswar, Bhubaneswar, Odisha, India.
² Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru, Karnataka, India.
³ Ocean Analysis and Modelling Laboratory, School of Earth, Ocean and Climate Sciences, Indian Institute of Technology Bhubaneswar, Bhubaneswar, Odisha, India. souravsil@iitbbs.ac.in.
⁴ School for Marine Science and Technology, University of Massachusetts at Dartmouth, Dartmouth, MA, USA.

Abstract

Utilizing Argo data from 2003 to 2019, we examine thermohaline changes in the Indian Ocean within the upper 700 m. Widespread warming is observed except in the Southern Indian Ocean. Increasing salinity is obtained over all regions except the Bay of Bengal and Southern Indian Ocean. Thermohaline trends in regional water masses at various depths are first decomposed into spice and heave components, and then linked to processes like pure heave, pure freshening and pure warming. Three consistent patterns across all seven regions are: (1) Below 300 m spice dominates heave; (2) The freshening process within the spice component is the primary driver below 300 m; (3) Spice primarily influences salinity changes along isobars. The warming of Arabian Sea's Subsurface Minima and the Indian Equatorial Water are primarily dictated by spice and heave, respectively. Freshening of the Bay of Bengal Water is linked to heave changes under pure freshening and pure heave processes. In the upper 250 m of the western equatorial, southern Indian Ocean, and Seychelles-Chagos Thermocline Ridge, salinity rises due to spice under pure freshening. The southern Indian Ocean's advected mode water shows freshening and cooling trends due to pure freshening.