Physically Driven Uncertainty in Future Indian Ocean Chlorophyll: Roles of Stratification, Winds, and Bias Correction

Uncertainty in Earth System Model (ESM) projections of Indian Ocean biogeochemistry is often attributed primarily to differences in biogeochemical process representations. Here, we demonstrate that large present-day physical biases and divergent future physical climates also play a substantial role. Using a bias-corrected ocean-only model forced by air–sea flux anomalies from multiple CMIP6 models, we show that correcting present-day physical biases strongly amplifies projected summer surface chlorophyll (SChl) changes and substantially improves inter-model consistency.

Across key Indian Ocean upwelling regions, increased upper-ocean stratification driven by heat-flux anomalies consistently reduces SChl, highlighting the role of ocean warming in shaping future biogeochemical change. In contrast, wind-driven changes dominate the SChl response in several regions, particularly off southern India and off Sumatra, emphasizing strong regional differences in physical controls. These results underscore the central importance of monsoonal wind variability and its future evolution for Indian Ocean biogeochemistry, with implications for ecosystem functioning and the predictability of regional climate impacts.