An atmosphere–ocean coupled model for simulating physical and biogeochemical state of north Indian Ocean: Customisation and validation

An atmosphere-ocean biogeochemistry coupled model is configured, customised and validated to decipher the role of atmospheric and oceanic processes in the north Indian Ocean (NIO, 3–30° N, 40–100° E), Arabian Sea (AS, 4–25° N, 50–75° E) and Bay of Bengal (BoB, 4–25° N, 76–100° E). The validation of model results with measurements shows that Sea Surface Temperature is better simulated by the coupled model than the standalone ocean model, with an average bias of ±0.2 °C in NIO. The simulated Sea Surface Salinity has a smaller bias with respect to reanalysis in AS (0.2 psu), but slightly higher in BoB (0.5 psu). The vertical distribution of temperature and salinity is also better represented in the coupled model. The atmospheric forcing, such as Long Wave Radiation, wind stress, and net surface heat and salt fluxes are better simulated by the coupled model with comparable variability and seasonality to the reanalysis data. The winter and summer Chlorophyll-a (Chl-a) blooms in AS are also well reproduced by the coupled model. The model also well simulates NO₃ within top 100 m in AS and BoB. The nitrate budget analysis indicates that vertical advection and entrainment play big roles in governing the overall budget in upwelling regions of NIO. Nitrate uptake by phytoplankton is the dominant biological process, except in the northern AS, where denitrification is dominant. New production contributes to Net Primary Productivity (NPP) in most upwelling regions in AS except in the northern AS, where regenerated production is higher than the new production. In BoB, the regenerated production dominates except in East Coast of India during monsoon season. Therefore, our study provides new insights on the capability of the coupled ocean-atmosphere models in simulating the physical and biogeochemical processes, and air-sea interactions in NIO.