Short-term offshore extension of Brahmaputra-Ganges and Irrawaddy freshwater plumes to the central northern Bay of Bengal based on in situ and satellite observations

Abstract. The mixed layer is the most variable and dynamically active part of the marine environment that couples the underlying ocean to the atmosphere and plays an important role in determining the oceanic primary productivity. We examined the basin-scale processes controlling the seasonal variability of mixed layer depth in the Bay of Bengal and its association with chlorophyll using a suite of in situ as well as remote sensing data. A coupling between mixed layer depth and chlorophyll was seen during spring intermonsoon and summer monsoon, but for different reasons. In spring intermonsoon the temperature-dominated stratification and associated shallow mixed layer makes the upper waters of the Bay of Bengal nutrient depleted and oligotrophic. In summer, although the salinity-dominated stratification in the northern Bay of Bengal shallows the mixed layer, the nutrient input from adjoining rivers enhance the surface chlorophyll. This enhancement is confined only to the surface layer and with increase in depth, the chlorophyll biomass decreases rapidly due to reduction in sunlight by suspended sediment. In the south, advection of high salinity waters from the Arabian Sea and westward propagating Rossby waves from the eastern Bay of Bengal led to the formation of deep mixed layer. In contrast, in the Indo–Sri Lanka region, the shallow mixed layer and nutrient enrichment driven by upwelling and Ekman pumping resulted in chlorophyll enhancement. The mismatch between the nitrate and chlorophyll indicated the inadequacy of present data to fully unravel its coupling to mixed layer processes.

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Seasonal and annual variability in chlorophyll-a in the shelf region of the Northern Bay of Bengal using MODIS-Aqua data

Oceanological and Hydrobiological Studies ◽

10.1515/ohs-2020-0035 ◽

2020 ◽

Vol 49 (4) ◽

pp. 398-407

Author(s):

Muhammad Abdur Rouf ◽

Al-Hasan Antu ◽

Imran Noor

Keyword(s):

Satellite Data ◽

Bay Of Bengal ◽

River Discharge ◽

Monsoon Season ◽

Northeast Monsoon ◽

Discharge Data ◽

Annual Variability ◽

Northern Bay Of Bengal ◽

Shelf Region

AbstractChlorophyll-a (Chl-a) concentration is an important issue in ocean ecosystem management and research. This study investigates seasonal and annual variability in Chl-a and its relationship with sea surface temperature (SST) and river discharge in the shelf region of the Northern Bay of Bengal (BoB), as well as validates satellite data against in-situ data. Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua satellite data on Chl-a concentration and SST from 2002–2018 were used in this study. River discharge data were obtained from the Bangladesh Water Development Board (BWDB). The annual Chl-a concentration ranged from 2.08 to 2.94 mg m−3, with an average of 2.43 ± 0.24 mg m−3. The Chl-a concentration was found higher (2.21 ± 0.56 mg m−3) during the northeast monsoon (October–February) and lower (1.81 ± 1.14 mg m−3) during the pre-monsoon season (March–May). The study revealed a declining trend in Chl-a concentration from 2002 to 2018, and the rate of change was −0.0183 mg m−3 year−1. Chl-a concentration showed a weak inverse relationship with SST, both annually and seasonally, especially in the pre-monsoon season. River discharge masked the effect of SST on Chl-a variability during the southwest and northeast monsoon. A reasonable correlation (r = 0.78) was found between the MODIS-Aqua data and in-situ Chl-a observations.

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An exclusive in-situ dataset on physicochemical parameters in the gappy northern Bay of Bengal

Data in Brief ◽

10.1016/j.dib.2020.106024 ◽

2020 ◽

Vol 31 ◽

pp. 106024 ◽

Cited By ~ 1

Author(s):

Md Masud-Ul-Alam ◽

Ashif Imam Khan ◽

Saif Khan Sunny ◽

Atiqur Rahman ◽

Muhammad Shahinur Rahman ◽

...

Keyword(s):

Bay Of Bengal ◽

Physicochemical Parameters ◽

Northern Bay Of Bengal

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Evolution of freshwater plumes and salinity fronts in the northern Bay of Bengal

Journal of Geophysical Research Atmospheres ◽

10.1029/2005jc003308 ◽

2007 ◽

Vol 112 (C8) ◽

Cited By ~ 8

Author(s):

Lingjuan Wu ◽

Fan Wang ◽

Dongliang Yuan ◽

Maochang Cui

Keyword(s):

Bay Of Bengal ◽

Freshwater Plumes ◽

Northern Bay Of Bengal

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In-situ datasets of important physical and bio-chemical parameters in the continental shelf of the northern Bay of Bengal

Data in Brief ◽

10.1016/j.dib.2021.106947 ◽

2021 ◽

pp. 106947

Author(s):

Most Israt Jahan Mili ◽

Md Kawser Ahmed ◽

Md Masud-Ul-Alam ◽

Md Hasnain ◽

Md. Ashif Imam Khan ◽

...

Keyword(s):

Continental Shelf ◽

Bay Of Bengal ◽

Chemical Parameters ◽

Northern Bay Of Bengal

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Low CO2 evasion rate from the mangrove-surrounding waters of the Sundarbans

Biogeochemistry ◽

10.1007/s10533-021-00769-9 ◽

2021 ◽

Author(s):

Anirban Akhand ◽

Abhra Chanda ◽

Kenta Watanabe ◽

Sourav Das ◽

Tatsuki Tokoro ◽

...

Keyword(s):

Bay Of Bengal ◽

Dissolved Inorganic Carbon ◽

Monsoon Season ◽

Buffering Capacity ◽

Marine Water ◽

High Temporal Resolution ◽

Post Monsoon Season ◽

Biogeochemical Parameters ◽

Northern Bay Of Bengal ◽

The Sundarbans

AbstractGlobally, water bodies adjacent to mangroves are considered significant sources of atmospheric CO2. We directly measured the partial pressure of CO2 in water [pCO2(water)] and related biogeochemical parameters with high temporal resolution, covering both diel and tidal cycles, in the mangrove-surrounding waters around the northern Bay of Bengal during the post-monsoon season. Mean pCO2(water) was marginally oversaturated in two creeks (470 ± 162 µatm, mean ± SD) and undersaturated in the adjoining estuarine stations (387 ± 58 µatm) compared to atmospheric pCO2, and was considerably lower than the global average. We further estimated the pCO2(water) and buffering capacity of all possible sources of the mangrove-surrounding waters and concluded that their character as a CO2 sink or weak source is due to the predominance of marine water from the Bay of Bengal with low pCO2 and high buffering capacity. Marine water with high buffering capacity suppresses the effect of pCO2 increase within the mangrove system and lowers the CO2 evasion even in creek stations. The δ13C of dissolved inorganic carbon (DIC) in the mangrove-surrounding waters indicated that the DIC sources were a mixture of mangrove plants, pore-water, and groundwater, in addition to marine water. Finally, we showed that the CO2 evasion rate from the estuaries of the Sundarbans is much lower than the recently estimated world average. Our results demonstrate that mangrove areas having such low emissions should be considered when up-scaling the global mangrove carbon budget from regional observations.

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