Nutrient variability drivers in shallow coastal waters of the Eastern Arabian Sea during winter monsoon with implications for coastal productivity

The Eastern Arabian Sea (EAS) exhibits complex nutrient variability driven by seasonal monsoon dynamics and hydrographic processes. This study investigates the spatial distribution of dissolved inorganic nutrients (DIN, DIP, and DSi), hydrographic conditions, and primary productivity in shallow coastal waters of this region during the winter monsoon of 2019. Our findings reveal regional contrasts, with the North-Eastern Arabian Sea (NEAS) experiencing cooler, nutrient-enriched waters due to convective mixing, supporting higher chlorophyll biomass, whereas the South-Eastern Arabian Sea (SEAS) remains warmer with limited nutrient flux. The coexistence of nutrient maxima and temperature minima in the surface coastal waters of north-eastern region further supports the efficient transport of cooler, nutrient-rich waters to the surface. Nutrient stoichiometry indicates nitrogen limitation in the SEAS and silicate-fuelled productivity in the NEAS. Chlorophyll-a (Chl-a) concentrations were significantly higher in the north-eastern region, reflecting enhanced surface productivity. Dissolved inorganic carbon (DIC) and partial pressure of CO₂ (pCO₂) analyses highlight the supersaturated state of CO₂ in this region, likely driven by convective overturning. Principal component analysis underscores the critical role of temperature, salinity, and mixing in shaping nutrient dynamics and carbon flux. These findings emphasize the need for sustained observation to predict the ecosystem's response to climatic variability and anthropogenic influences, making this study a valuable reference for understanding coastal productivity in monsoon-driven systems.