Seasonal variability in biological carbon biomass standing stocks and production in the surface layers of the Bay of Bengal

Abstract

As a part of the Bay of Bengal Process Study, several biological characteristics were investigated during summer monsoon (SuM; July-August 2001), fall intermonsoon (FIM, September-August 2002), spring intermonsoon (SpIM; April-May 2003) and northeast monsoon (NEM, Dec 2005-January 2006). Chl <i style="">a</i> carbon during SuM, FIM, SpIM and NEM averaged 688, 767, 1212 and 1057 mg C m^{-2 in the western Bay (WB) and 518, 904, 789 and1023 mg C m-2 in the central Bay (CB). Primary productivity (PP) averaged 326, 281, 366 and 280 mg C m-2 d}-1^{in the WB and 144, 306, 241 and 375 mg C m-2}d^{-1 in the CB respectively. Shallow euphotic depths (~<55m) apparently are not conducive for (PP) in the 0-120 m column. Heterotrophic bacterial carbon biomass was sizable and averaged 282, 662, 95 and 288 mg C m-2 in the WB and was 677, 227, 104 and 333 mg C m-2 in the CB during SuM, FIM, SpIM and NEM respectively. They appear very crucial in governing the abundances of microheterotrophs in the southern and, open-ocean regions of the Bay. Microzooplankton were much poorer in abundance than those in the Arabian Sea except during SpIM. Their maximum carbon biomass (WB: 233; CB: 327 mg C m-2 in the top 120 m was observed during SpIM. In the upper 200 m, the mesozooplankton biomass did not show much variation between the season (WB: 222, 906, 2428 and 988 mg C m-2} and CB: 587, 1036, 821 and 808 mg C m^-2d^-1 respectively during SuM, FIM, SpIM and NEM). Incidentally it was mostly decoupled with chl <i>a</i> and PP. Cold-core eddies observed during most sampled seasons seem to bear an enhancing influence on the overall biological productivity processes.