HYCOM-ECOSMO for the Indian Ocean: a simulation of oxygen minimum zone variability over the last two decades
摘要
The Arabian Sea oxygen minimum zone (OMZ) has the smallest horizontal area of all open ocean OMZs but is the world's third most intense OMZ with the largest vertical extent. This study used a regional physical-biogeochemical coupled model, HYbrid Coordinate Ocean Model- ECOSystem (HYCOM-ECOSMO), to investigate the variations in Arabian Sea OMZ and deoxygenation for the period 2000–2020. The model was evaluated against BGC-Argo data and World Ocean Atlas 2018 (WOA18) to check the consistency of eddy-permitting simulation. It accurately simulated dissolved oxygen (DO) profiles, with RMSE of 16.5 µmol kg−1 for WOA18 and 21 µmol kg−1 for BGC-Argo. Model efficiency was estimated at 0.81 with percentage bias of 31% indicating that model performs well with observations. Interannual and seasonal variabilities showed good agreement with BGC-Argo profiling floats, but with slight DO overestimation. Despite a slight decreasing trend in the model's OMZ DO, Argo data indicated a minor increase. Sensitivity experiments identified detritus remineralization and sinking rates as key factors influencing DO levels. Surface DO, temperature, and Brunt-Väisälä frequency showed spatial warming impacts. OMZ exhibited seasonal variation, with higher DO concentrations during the winter monsoon due to convective mixing. ENSO and Indian Ocean Dipole (IOD) phases minimally influence surface DO levels, with lagged impacts (1–10 months) on temperature, productivity, organic matter sinking, and microbial respiration. The system responds more promptly to IOD than to ENSO. These findings establish a baseline for future research on marine ecosystems, fishery and regional climate projections in the Arabian Sea.