Exploring Upper Layer Bio-Physical Processes in the Bay of Bengal using BGC-Argos

The biogeochemical (BGC) Argos are providing high-resolution vertical profiles of the upper ocean in the Bay of Bengal since 2012. This work demonstrates the effective applications of BGC-Argos in understanding the biophysical interactions in the Bay of Bengal with four different studies carried out by our group. First, a study (Das & Sil, 2024; DSR-II) using a single BGC-Argo (WMO ID: 2902161), which measured temperature, salinity, chlorophyll-a, and dissolved oxygen at a high-frequency (∼5 h) cycle down to 80 m depth, showed temperature and chlorophyll-a are strongly linked to solar insolation. The mean chlorophyll-a in the upper layer increased from 0600 h and peaked around 1800 h local time; however, surface chlorophyll-a increased only after 1100 h. The similarity between dissolved oxygen and the difference between the surface and mean chlorophyll-a further indicated photoacclimation variations on a diurnal scale. In a follow-up study (Gupta et al., 2024; RSMA), the comparison of Bio-Argos (WMO ID: 2902158, 2902160, 2902114, and 2902161) with the CMEMS data (which does not include any data assimilation) showed a statistically significant correlation coefficient of more than 0.60 in the Bay of Bengal. Bio-Argo measurement of the Chl-a concentration can inform the model about the phytoplankton biomass, which affects light attenuation and absorption lengths in the water column. A Bio-Argo (WMO ID: 2902217) was then utilized for a regional biophysical model validation, which analyzed the influence of different types of eddies on biological productivity (Shee et al., 2024, DAO). Bio-Argo (WMO ID: 2902093) was also very useful in revealing the subsurface extent of increased productivity after the passage of a cyclone in another study (Pramanik and Sil, 2021; JGR-Ocean). The Bio-Argo (WMO ID:2902156) showed the development of the Sri Lankan Dome and was used for validation of a bio-physical regional model used for its interannual variation (Pramanik et al., 2020; IJRS). The high-resolution, in-situ measurements provided by BGC-Argo floats are instrumental in capturing temporal and spatial variations, thereby supporting the development of more accurate oceanographic models and assessments.