Geochemistry of sediments in contact with oxygen minimum zone of the eastern Arabian Sea: Proxy for palaeo-studies

Abstract

The Arabian Sea encompasses oxygen minimum zone with denitrifying conditions. For the present study, sediments were collected across three transects off Goa transect (GT), Mangalore transect (MT) and Kochi transect (KT) in contact with water column dissolved oxygen (DO) range of 1.4-118.0 �M. Sediments were investigated for texture, clay mineralogy, total organic carbon (Corg), total nitrogen, CaCO3, ?15N, ?13C, metal content to infer their distribution with changing DO and their use as possible palaeo-proxies. The Corg (0.9-8.6%) is largely marine and ?15N from GT and MT preserves signatures of higher water column denitrification. Al normalised ratios of Cu, Ni, Zn, V and Mo are GT > MT > KT. Nickel could be a productivity proxy for DO <80 �M; Cr, U could be a redox proxy for DO <20 �M; Co and Mn could be a better proxy for DO <80 �M; U/Mo vs. DO could separate sediments with DO less than and >80 �M. We observed that eastern Arabian Sea dataset does not always fall within the defined proxies of the other anoxic basins. The metal concentrations in modern day sediments from the eastern Arabian Sea may be used as a proxy to infer the ancient sediment redox conditions. Highlights: Organic carbon distribution in anoxic sediments. Provenance of sediments. Nitrogen isotopes and geochemistry as palaeo-proxy for anoxic basins.