Poster Session 4, Thursday, October  6, 11:00–12:40

Poster 84

Spatial and Temporal Distribution of Chlorophyll-a in Relation to Environmental Factors in the Bay of Bengal: A Remote Sensing Approach

This study determined the spatial, and temporal distributions of Chlorophyll-a (Chl-a) concerning environmental factors in the Bay of Bengal (BoB) during 2003-2020. Three regions of interest (A, B and C) was selected by considering 2.5° × 2.5° grid for each in the BoB. Chl-a data had retrieved from MODIS-Aqua and the environmental factors (SST, POC, NPP, SSHA, Wind, Wind Vector, Current) data had been retrieved from satellites, whereas the in-situ Chl-a and nutrients data were retrieved from WOD, and the river discharge data were collected from BWDB for this study. The study showed that Chl-a ranged from 1.34 ± 2.23 mg/m 3 to 0.12 ± 0.02 mg/m 3 whereas the coastal area comprised higher Chl-a irrespective of the month, season, and year. The post-monsoon period showed the highest concentrations (1.19 ± 2.12 mg/m 3 ) of Chl-a while the pre-monsoon period showed the lowest concentrations (0.66 ± 1.12 mg/m 3 ) of that in the coastal area. Moreover, during the northeast, and post-monsoon period Chl-a was observed as 0.16 ± 0.02 mg/m 3 , and 0.14 ± 0.01 mg/m 3 respectively, whereas during the pre-, and southwest monsoon period the concentrations were lowest (0.13 ± 0.03 mg/m 3 ) in the offshore area. Chl-a showed a rising, and falling trend during the study period for the study area; however, BoB showed a rising trend of Chl-a at a rate of 0.02 mg/m 3 per decade. Chl-a and SST showed a significantly (p<0.05) negative relation, and for each additional SST, Chl-a showed a declination of 0.035 mg/m 3 in the BoB. Chl-a showed a positive relationship with POC, NPP, and SSHA, River Discharge and Nutrients (silicate, nitrate, phosphate) in the BoB where wind speed showed no significant relationship with Chl-a in the study area; however, southwesterly and northeasterly wind showed an effect on Chl-a concentrations. Regression analysis showed that for each additional POC, NPP, SSHA, Nitrate, Silicate, Phosphate, River Discharge, Chl-a increased by 0.006 mg/m 3 , 0.001 mg/m 3 , 0.531 mg/m 3 , 0.140 µg/l, 0.078 µg/l, 1.448 µg/l, 0.00001 mg/m 3 respectively in the BoB. Moreover, Nitrate had a great influence (45.65%) on Chl-a (µg/l) than Phosphate (37.57%) and Silicate (16.78%) in the BoB. Arabian Sea (AS) water entered into the BoB during the southwest monsoon season through activating the West India Coastal Current (WICC). Furthermore, during the post-monsoon season in October, AS waters flowed into the BoB, then reversed in November during this study. Northern BoB is mostly comprised of warm-core eddy founds in the eastern, and western boundary mostly. Except for the pre-monsoon season (except March) the eddy was observed during all other seasons; thus, productivity was high during all those seasons. Satellite-derived Chl-a data showed a correlation coefficient r = 0.75 (n=58, R 2 = 0.56), and the RMSE = 2.54% with WOD derived Chl in the BoB. This research will aid in the knowledge of marine ecosystem health, PFZ identification, and the development of the blue economy in Bangladesh’s maritime area.

*Md. Shahin Hossain Shuva, University of Chittagong, [email protected], 0000-0002-6939-1367

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