Understanding biological carbon pump in the central Arabian Sea using phytoplankton biomarkers and diatom frustules from surface sediments.

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The Central Arabian Sea, a tropical ocean basin, is impacted by monsoon winds that lead to high biological productivity in surface waters and form an oxygen minimum zone (OMZ) at intermediate depth. The present study aimed to understand the pattern of biological carbon pump driven by different phytoplankton groups along the central Arabians Sea, an area strongly impacted by monsoon wind forcings. The surface sediment samples from 5 locations along the central Arabian Sea were collected from 21 ° N to 11 ° N (at 2 ° intervals) along 64 ° E. These sediments accumulate materials originating from surface waters and can be used to understand the surface processes including the contributions of various phytoplankton groups in sinking materials. Bulk sediment parameters (total organic carbon, inorganic carbon, total nitrogen) were analyzed along with plankton biomarkers (sterols and alkenone) and sea surface temperature (SST) proxy using alkenone. Additionally, the frustules of diatoms that are siliceous phytoplankton shells, were also measured from the same sediments. We noticed a north-south gradient in all parameters and the biological proxies showed more organic matter preservation from larger diatoms in the north. Whereas, lower organic matter contributed by smaller phytoplankton and zooplankton were found in the south. These trends were attributed to ocean-atmospheric processes and oxygen availability in the water column.

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