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Influence of physical and biological processes on the seasonal cycle of biogenic flux in the Equatorial Indian Ocean P.J. Vidya1, S. Prasanna Kumar1*, Mangesh Gauns1, Arati Verenkar1, Daniela Unger2 , V.Ramaswamy1 1National Institute of Oceanography, Dona Paula, Goa-403 004, India. 2Centre for tropical Marine Ecology GmbH, Fahrenheitstrabße 6, D-28359 Bremen, Germany. Email: [email protected], [email protected] Abstract Seasonal cycle of biogenic fluxes obtained from sediment trap at two locations, 5°24’N, 86°46’E (SBBT) and 3°34’N, 77°46’E (EIOT), within the equatorial Indian Ocean (EIO) were examined to understand the factors that control them. The enhanced biogenic flux at SBBT during summer monsoon could be explained with the help of bottom-up control wherein the physical processes controlled chlorophyll biomass through nutrient supply. The mismatch between the lack of seasonality of biogenic flux at EIOT and seasonality in the chlorophyll biomass can be explained by top-down control. Study area Introduction The Equatorial Indian Ocean (EIO) behaves uniquely compared to the other equatorial regions of the world ocean primarily due to the seasonal reversal of the winds between winter (December-March) and summer (June-September) [Hastenrath and Greishar, 1989]. The intense air-sea interaction makes this region important in earth’s climate. Hence, the quantitative study of the biogenic flux help us to understand the carbon cycle and related changes in the climate. Methodology Results Static stability Data Source Biogenic flux PARAFLUX Mark Vl series Sediment trap Chlorophyll-a & PAR SeaWiFS SSHA Topex- Poseidon/Jason-1 Wind speed QuickSCAT Temp. & Sal. World Ocean Atlas 2005 Nitrate, chl-a PP, phyto. Cellno. & MesoZ SK -227 Cruise, Sagar Kanya in August 2006 Ekman pumping m/day Advection SBBT EIOT Conclusion Sediment trap data gives insight into the processes that link the primary production to the sinking organic carbon in which physical and biological processes are intimately coupled. Though SBBT and EIOT are within the same geographical entity, the processes that control the primary production in the euphotic zone and the biogenic flux to the deep ocean are very different. Diatoms Larger size Classical food chain Pico-autotrophs smaller size Microbial loop Acknowledgement Authors thank the Director, National Institute of Oceanography (NIO), Goa, and Council of Scientific and Industrial Research (CSIR), New Delhi for the facilities provided. First author thank INSA for providing the travel support. Indian National Science Academy Reference: Hastenrath, S., and Greischar, L (1989), The monsoonal heat budget of the hydrosphereatmosphere system in the Indian Ocean sector, J. Geophys Res., 98, 6869–6881.