Variability and budgets of Dissolved Inorganic Carbon and Alkalinity over the north Indian Ocean using a high-resolution model

This study employs a high-resolution MITgcm-DIC model at 5 km spatial resolution with climatological forcing to investigate the biogeochemical dynamics of surface dissolved inorganic carbon (DIC) and alkalinity (ALK) over the northern Indian Ocean. The physico-chemical parameters of the model are validated against available observational data to ensure its accuracy. The DIC biogeochemical module is integrated within the model framework, considering multiple DIC sources and sinks, including air-sea CO₂ exchange, biological production, and carbonate mineral dissolution. To analyse the influences of various processes within our domain, we focussed on the surface DIC and ALK budgets. This investigation helps us understand the intricate interplay of drivers impacting the budgets. The DIC and ALK budgets are found to be significantly influenced by the counterbalancing effects of advective and diffusive terms. We also assessed the role of biological activity and observed that productivity causes a continuous uptake of CO₂, which leads to a reduction in surface DIC. Since freshwater intrusion is an important factor governing the surface dynamics of waters in north Indian Ocean, we examined the impact of freshwater dilution on surface DIC and ALK concentrations. The surface ALK budget is predominantly governed by freshwater flux. The dilution of ALK and DIC is attributed to the influence of both precipitation and river runoff. Regions where evaporation exceeds precipitation and river runoff exhibit an increase in the concentration of these variables. The findings shed light on the regional variations along the north Indian Ocean, providing valuable insights into the dominance and interactions of these mechanisms. This study is valuable for enhancing our understanding of regional carbon cycling dynamics in our domain with implications for global carbon cycle models and climate-related predictions. The findings are relevant not only for the scientific community but also for policymakers and stakeholders concerned with oceanic and environmental health.