Mixed layer variability and chlorophyll a biomass in the Bay of Bengal

[摘要] The mixed layer is the most variable and dynamically active part of themarine environment that couples the underlying ocean to the atmosphere andplays an important role in determining the oceanic primary productivity. Weexamined the basin-scale processes controlling the seasonal variability ofmixed layer depth in the Bay of Bengal and its association with chlorophyllusing a suite of in situ as well as remote sensing data. A coupling betweenmixed layer depth and chlorophyll was seen during spring intermonsoon andsummer monsoon, but for different reasons. In spring intermonsoon thetemperature-dominated stratification and associated shallow mixed layer makesthe upper waters of the Bay of Bengal nutrient depleted and oligotrophic. Insummer, although the salinity-dominated stratification in the northern Bay ofBengal shallows the mixed layer, the nutrient input from adjoining riversenhance the surface chlorophyll. This enhancement is confined only to thesurface layer and with increase in depth, the chlorophyll biomass decreasesrapidly due to reduction in sunlight by suspended sediment. In the south,advection of high salinity waters from the Arabian Sea and westwardpropagating Rossby waves from the eastern Bay of Bengal led to the formationof deep mixed layer. In contrast, in the Indo–Sri Lanka region, the shallowmixed layer and nutrient enrichment driven by upwelling and Ekman pumpingresulted in chlorophyll enhancement. The mismatch between the nitrate andchlorophyll indicated the inadequacy of present data to fully unravel itscoupling to mixed layer processes.

[学科分类] 地球化学与岩石