Nutrients and chlorophyll-a in the northern Bay of Bengal: the need for focused research on Bangladesh’s shelf.

Author: Most Israt Jahan Mili, Md. Ashifur Rahman Shaheen, Md Masud-Ul-Alam, Md. Shafiq Reza, Kayes Mohammad, Ashraful Moontahab
DOI: doi.org/10.70279/bmj-v8-1030
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Nutrients and chlorophyll-a (chl-a) are critical to understanding marine ecosystem, yet in situ data on Bangladesh’s continental shelf remained sparse compared to offshore Bay of Bengal (BoB). This study addresses this gap by measuring chl-a and nutrients, including nitrate (NO₃⁻-N), nitrite (NO₂⁻-N), phosphate (PO₄³⁻), ammonia (NH₃-N) and silica (SiO₂) across the eastern continental shelf of Bangladesh. These observations were compared with data from the Copernicus Marine Environment Monitoring Service (CMEMS) and relevant literature. Shelf in situ data varied as nutrients (mg l^-1): nitrate: 1.8-5.3; nitrite: 0.002-0.008, phosphate: 0.02-0.12, ammonia: 0.42-5.2, silica: 0.5-3.0 and chl-a: 0.426 – 10.119 mg m^-3. Trend observed in the order: nitrate > ammonia
> silica > phosphate > nitrite. Nitrite and phosphate, characterized by relatively low concentrations, can act as limiting nutrients in this region. Weak correlations were observed between chl-a and most nutrients, with a moderate negative correlationbetween chl-a and silica (r = - 0.46) and a moderate positive correlation between nitrate and ammonia (r = 0.334). The concentrations of all in situ measured parameters weresignificantly higher than CMEMS-derived  estimates, specifically adjacent to the coast. This underscores the need for a comprehensive, multi-seasonal investigation of the northern BoB’s continental shelf particularly focusing on measuring the riverine flux of these measured parameters into the BoB. These datasets are crucial for validating
remote sensing observations and improving estimates in this understudied region.