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<p>The Bay of Bengal (BoB), a semi-enclosed basin in the northern Indian Ocean, exhibits complex upper-ocean dynamics driven by monsoonal winds, intense freshwater influx, and strong seasonal stratification. These processes critically modulate vertical mixing and surface productivity, yet comprehensive assessments that integrate their combined influence over recent decades remain limited. This study addresses that gap by analyzing the seasonal and interannual variability of mixed layer depth (MLD), surface chlorophyll-a (Chl-a), seawater density, salinity, wind speed, Ekman pumping, ocean currents, and precipitation using high-resolution satellite-derived datasets (CMEMS, ERA5) spanning 2014–2023. The results reveal pronounced seasonal shifts in MLD, deepening to ~ 24&#xa0;m during the summer and winter monsoons and shoaling to ~ 12&#xa0;m in spring. While wind-induced mixing dominates the central and southern BoB during peak monsoon winds (~ 4.5&#xa0;m/s), strong freshwater stratification in the northern BoB limits vertical exchange, even under high wind stress. Surface Chl-a concentrations remain persistently low offshore (averaging 0.27 ± 0.15&#xa0;mg/m<sup>3</sup>) with weak correlations to MLD and sea surface temperature (SST), whereas elevated coastal productivity is linked to wind stress curl, fluvial inputs, and mesoscale features such as eddies and Rossby waves. By integrating physical and biological parameters across space and time, this study offers new insights into the mechanisms controlling upper-ocean structure and productivity in the BoB. The findings provide a valuable baseline for regional climate assessments, biogeochemical modeling, and sustainable marine resource management in this ecologically sensitive basin.</p>

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Seasonal and Interannual Variability of Mixed-Layer Depth and Surface Chlorophyll-a in the Bay of Bengal: Insights into Physical-Biological Coupling

  • 期刊论文

  • 发表日期：

    2025年9月15日

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  • Siraj Uddin Md Babar Chowdhury,
  • Md Minarul Hoque,
  • Anik Karmakar,
  • Nur Uddin Md Khaled Chowdhury,
  • K. M. Azam Chowdhury,
  • Tabassum Hossain Tahsin,
  • Ashraful Moontahab

摘要

The Bay of Bengal (BoB), a semi-enclosed basin in the northern Indian Ocean, exhibits complex upper-ocean dynamics driven by monsoonal winds, intense freshwater influx, and strong seasonal stratification. These processes critically modulate vertical mixing and surface productivity, yet comprehensive assessments that integrate their combined influence over recent decades remain limited. This study addresses that gap by analyzing the seasonal and interannual variability of mixed layer depth (MLD), surface chlorophyll-a (Chl-a), seawater density, salinity, wind speed, Ekman pumping, ocean currents, and precipitation using high-resolution satellite-derived datasets (CMEMS, ERA5) spanning 2014–2023. The results reveal pronounced seasonal shifts in MLD, deepening to ~ 24 m during the summer and winter monsoons and shoaling to ~ 12 m in spring. While wind-induced mixing dominates the central and southern BoB during peak monsoon winds (~ 4.5 m/s), strong freshwater stratification in the northern BoB limits vertical exchange, even under high wind stress. Surface Chl-a concentrations remain persistently low offshore (averaging 0.27 ± 0.15 mg/m3) with weak correlations to MLD and sea surface temperature (SST), whereas elevated coastal productivity is linked to wind stress curl, fluvial inputs, and mesoscale features such as eddies and Rossby waves. By integrating physical and biological parameters across space and time, this study offers new insights into the mechanisms controlling upper-ocean structure and productivity in the BoB. The findings provide a valuable baseline for regional climate assessments, biogeochemical modeling, and sustainable marine resource management in this ecologically sensitive basin.