Monitoring spatial and temporal variation of ocean productivity in the Bay of Bengal using remote sensing

Abstract

Ocean productivity plays an important role in the global carbon cycle, climate change and food supply. An alarming issue about the ocean productivity is that it is decreasing gradually in most world biomes where the decreasing rate in certain oceans, such as in the Bay of Bengal is higher as compared to other oceans. Although historically the Bay of Bengal is less productive as compared to the other oceans, there are large number of population living along the coastal areas depend on food supply from this bay. Therefore, productivity of the Bay of Bengal is very crucial and this study investigates the trend of ocean productivity by monitoring the long term variation of Chlorophyll-a concentration, and its relationships with sea surface temperature, precipitation and ocean current. Several steps of processing were adopted, which includes i) estimate the spatial and temporal variation of all parameters, ii) examine the variation of all parameters along the five selected transects from coastal to offshore area, iii) perform change detection of all parameters, and iv) investigate relationships between Chlorophyll-a and all other parameters. Results indicated several aspects, such as i) ocean productivity in the Bay of Bengal varies spatially and seasonally, ii) during northeast monsoon, Chlorophyll-a concentration in the western part of the bay is remarkably high but low in other parts particularly in the middle part of the bay, iii) during southwest monsoon, the observed Chlorophyll-a concentration is high in the south-western and north-western part of the bay, whereas the middle part of the bay maintains low productive, iv) anomaly of Chlorophyll-a concentration is high (1 to 2.5 mg/m³) in coastal area and very low (less than 0.5 mg/m3) in the offshore area, v) low Chlorophyll-a area (0-0.10 mg/m³) fluctuates highly from year to year, while very less fluctuation observed in high Chlorophyll-a concentrated area (1-6.5 mg/m³), vi) sea surface temperature and precipitation are normally higher during southwest monsoon as compared to northeast monsoon, and vii) strong ocean current was observed in western part of bay during both seasons. As conclusion, this study highlights the potential of remote sensing technique in monitoring ocean productivity, and identified that the productivity of the Bay of Bengal is changing with no constant rate of change from year to year. The rate of change depends on several factors including temperature, precipitation, ocean current, and location.