Stratified Ocean Chlorophyll-a and Nutrient Availability in the Eastern Tropical Indian Ocean during La Nina 2022-2023

This study investigated ocean productivity in the Eastern Tropical Indian Ocean (ETIO), a region defined by high biodiversity and complex interactions between physical and biogeochemical processes. This study reveals vertical patterns essential to ocean productivity by examining the dynamics of nutrients (nitrate, phosphate, and silicate) and chlorophyll-a concentrations. Nutrient data were obtained from the Copernicus Marine Service (CMEMS) with spatial resolution of 0.25° × 0.25°, concentrating on the 0–500m depth range for nitrate, phosphate, silicate, and chlorophyll-a concentrations from January 2022 to December 2023. Additional in-situ data were acquired from the World Ocean Database (WOD-18) utilizing quality-controlled CTD and OSD datasets, encompassing analogous nutrients in regions 3010, 3110, and 3111. According to observations, nutrient profiles show a clear nutricline at around 100 meters, where concentrations swiftly rise maximum in the subsurface. Productivity hotspots with increased phytoplankton growth are highlighted by the impact of monsoon-driven upwelling along Java's southern coast. El Niño-Southern Oscillation (ENSO)-driven seasonal changes significantly impact surface productivity, as shown by nutrient fluxes and chlorophyll-a dynamics. This study highlights how physical and chemical mechanisms shape productivity and provides crucial information for understanding how climatic variability affects marine ecosystems in the ETIO.