BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-10-7493-2013 Influence of physical and biological processes on the seasonal cycle of biogenic flux in the equatorial Indian Ocean Vidya P. J. 1 Prasanna Kumar S. 1 Gauns M. 1 Verenkar A. 1 Unger D. 2 Ramaswamy V. 1 National Institute of Oceanography, Dona Paula, Goa-403 004, India Leibniz Centre for Tropical Marine Ecology GmbH, Fahrenheitstraße 6, 28359 Bremen, Germany 21 11 2013 10 11 7493 7507 Copyright: © 2013 P. J. Vidya et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/10/7493/2013/bg-10-7493-2013.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/10/7493/2013/bg-10-7493-2013.pdf

Seasonal cycle of biogenic fluxes obtained from sediment trap at two locations 5°24' N, 86°46' E (southern Bay of Bengal trap; SBBT) and 3°34' N, 77°46' E (equatorial Indian Ocean trap; EIOT) within the equatorial Indian Ocean (EIO) were examined to understand the factors that control them. The sediment trap data at SBBT was collected for ten years from November 1987 while that at EIOT was for a one year period from January 1996. The characteristic of biogenic flux at SBBT was the strong seasonality with peak flux in August, while lack of seasonality characterised the flux at EIOT. The high chlorophyll biomass at the SBBT during the summer monsoon was supported by a combination of processes such as wind-mixing and advection, both of which supplied new nitrogen to the upper ocean. In contrast, the elevated chlorophyll at EIOT during summer monsoon was supported only by wind mixing. High cell counts of phytoplankton (> 5 μm) at SBBT dominated by diatoms suggest the operation of classical food web and high carbon export. On the contrary, dominance of pico-phytoplankton and one-and-a-half time higher magnitude of micro-zooplankton biomass along with 2-fold lesser meso-zooplankton at EIOT indicated the importance of microbial loop. The substantial decrease in the carbon export at EIOT indicated faster remineralization of photosynthetically produced organic matter.

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