Autonomous Float Data Reveal Decoupled Trends in Chlorophyll and Stratification in the Indian Ocean

Recent studies have shown that the Indian Ocean is warming significantly, but how this warming impacts primary production is largely unresolved due to a relative lack of depth-resolved biological observations. In this study, we have used Biogeochemical-Argo data from 2013 to 2022, comprising over 9,000 individual profiles, to examine regional patterns and trends in depth-integrated chlorophyll, depth-integrated net primary production and stratification in the northern and Equatorial Indian Ocean. Our analysis shows that water column stratification is increasing in the majority of the study area, with the highest rate of increase observed in the western Bay of Bengal. At the same time, we find that depth-integrated chlorophyll and depth-integrated net primary production show an increasing trend in most parts of the Bay of Bengal, the western Arabian Sea, and some parts of the Equatorial Indian Ocean. However, the eastern Arabian Sea, the northern Bay of Bengal, and other parts of the Equatorial Indian Ocean have experienced a decrease in depth-integrated chlorophyll and net primary production. The Indian Ocean Dipole and El Niño Southern Oscillation were found mostly to be weakly negatively correlated with the depth-integrated chlorophyll and depth-integrated net primary production in the northern Indian Ocean. Our results show that depth-integrated chlorophyll and depth-integrated net primary production are not strongly or consistently correlated with stratification within our study region, suggesting that the projected increases in stratification with ocean warming in this region may not drive concurrent reductions in primary production.