Influence of basin-scale and mesoscale physical processes onbiological productivity in the Bay of Bengal during the summer monsoon

Author(s): Muraleedharan KR, Jasmine P, Achuthankutty CT, Revichandran C, Dineshkumar PK, et al


Physical forcing plays a major role in determining biological processes in the ocean across the full spectrum of spatial and temporal scales. Variability of biological production in the Bay of Bengal (BoB) based on basin-scale and mesoscale physical processes is presented using hydrographic data collected during the peak summer monsoon in July–August, 2003. Three different and spatially varying physical processes were identified in the upper 300 m: (I) anticyclonic warm gyre offshore in the southern Bay; (II) a cyclonic eddy in the northern Bay; and (III) an upwelling region adjacent to the southern coast. In the warm gyre (>28.8 °C), the low salinity (33.5) surface waters contained low concentrations of nutrients. These warm surface waters extended below the euphotic zone, which resulted in an oligotrophic environment with low surface chlorophyll a (0.12 mg m−3), low surface primary production (2.55 mg C m−3 day−1) and low zooplankton biovolume (0.14 ml m−3). In the cyclonic eddy, the elevated isopycnals raised the nutricline upto the surface (NO3–N > 8.2 μM, PO4–P > 0.8 μM, SiO4–Si > 3.5 μM). Despite the system being highly eutrophic, response in the biological activity was low. In the upwelling zone, although the nutrient concentrations were lower compared to the cyclonic eddy, the surface phytoplankton biomass and production were high (Chl a – 0.25 mg m−3, PP – 9.23 mg C m−3 day−1), and mesozooplankton biovolume (1.12 ml m−3) was rich. Normally in oligotrophic, open ocean ecosystems, primary production is based on ‘regenerated’ nutrients, but during episodic events like eddies the ‘production’ switches over to ‘new production’. The switching over from ‘regenerated production’ to ‘new production’ in the open ocean (cyclonic eddy) and establishment of a new phytoplankton community will take longer than in the coastal system (upwelling). Despite the functioning of a cyclonic eddy and upwelling being divergent (transporting of nutrients from deeper waters to surface), the utilization of nutrients leading to enhanced biological production and its transfer to upper trophic levels in the upwelling region imply that the energy transfer from primary production to secondary production (mesozooplankton) is more efficient than in the cyclonic eddy of the open ocean. The results suggest that basin-scale and mesoscale processes influence the abundance and spatial heterogeneity of plankton populations across a wide spatial scale in the BoB. The multifaceted effects of these physical processes on primary productivity thus play a prominent role in structuring of zooplankton communities and could consecutively affect the recruitment of pelagic fisheries.

Similar Articles

Wind-driven coastal upwelling along the western boundary of the Bay of Bengal during the southwest monsoon

Author(s): Shetye SR, Shenoi SSC, Gouveia AD, Michael GS, Sundar D, et al.

The Western Boundary Current of the seasonal subtropical gyre in Bay of Bengal

Author(s): Shetye SR, AD Gouveia, SSC Shenoi, DSundar, GSMichael, et al.

Hydrography and circulation in the western Bay of Bengal during the northeast monsoon

Author(s): Shetye SR, Gouveia AD, Shankar D, Shenoi SSC, Vinayachandran PN, et al.

Observation of the western boundary current of the Bay of Bengal Deep-Sea Res 44:135-145

Author(s): Sanilkumar KV, Kuruvilla TV, Jogendranath D, and Rao RR

Eddy-mediated biological productivity in the Bay of Bengal during fall and spring intermonsoons Deep Sea Research II 54: 1619-1640

Author(s): Prasanna Kumar S, Nuncio M, Ramaiah N, Sardesai S, Narvekar, Jayu, Fernandes, Veronica, & Paul, Jane T

Are eddies nature’s trigger to enhance biological productivity in the Bay of Bengal? Geophys Res Lett 31

Author(s): Prasanna Kumar S, Nuncio M, Narvekar J, Kumar A, Sardesai S, et al.

Seasonal cycle of physicalforcing and biological response in the Bay of BengalIndian J Mar Sci 39: 388-405

Author(s): Prasanna Kumar S, Nuncio M, Narvekar J, Ramaiah N, Sardessai S, et al

ICES zooplankton methodology manual

Author(s): Harris RP, Wiebe PH, Lenz JH, Skjoldal R & Huntley M

Detection of Bay of Bengaleddies from Topex and in situ observations

Author(s): Gopalan AKS, GopalaKrishna VV, Ali MM, Sharma R

Forcing mechanisms of the Bay of Bengal circulation Current SciIndia 71: 753-763

Author(s): Vinayachandran PN, Shetye SR, Sengupta D, Gadgil S

Development of a subsurface chlorophyll maximum at the entrance to the Gulf of Finland, Baltic Sea

Author(s): Kononen KJ, S Hallfors, M Kokkonen, H Kuosa, J Laanemets, J Pavelson

Analysis of Marine Ecosystems

Author(s): Owen RW

Vertical flux of respiratory carbon by oceanic diel migrant biota Deep-Sea Res 37: 685–694

Author(s): Longhurst AR, Bedo A, Harrison WG, Head EJH, Sameoto DD

Zooplankton vertical migration and the active transport of dissolved organic and inorganic carbon in the Sargasso

Author(s): Steinberg DK, Carlson CA, Bates NR, Goldthwait SA, Madin LP, et al.