Concentrations and burial fluxes of organic and inorganic carbon on the eastern margins of the Arabian Sea

Abstract

Eleven sediment cores were analysed from the continental margins of the eastern Arabian Sea (22°N to ~10°N) for organic carbon (C_org), nitrogen (N) and CaCO₃ contents. Similar variations are observed in both lateral and the vertical ( < 1.6 m) distribution of the concentrations of C_org, N and CaCO₃ ranging from ~1-6%, 0.10-0.82% and ~10-81%, respectively. The C/N ratios, varying from 6-15 averaging 9.3, indicate that C_org is mostly of marine origin. The burial fluxes (BF) of C_org and CaCO₃ are in the range of 0.8-21 and 39-194 g m⁻² a⁻¹, respectively. The upper limits of burial efficiency (BE) for CaCO₃ (compared to its rain rate of 25 g m⁻² a⁻¹ in sediment trap at a depth of 2500 m from a nearby region) ranges from 39 to 780%. BE values greater than 100% in the northern ( > 15°N) could be most likely due to redeposition of material from shelf and slope regions as well as influx of detrital carbonates from coastal areas. The inverse correlation observed in C_org and CaCO₃ distribution is indicative of post-depositional effects due to sulphate reduction associated processes. This can lead to dissolution of CaCO₃ and a better preservation of C_org due to faster deposition rate and higher detrital (clay) content. The BF and paleoproductivity calculated using the transfer function of Sarnthein et al. [Miner. Soc. Spec. Publ. 64 (1992) 411] show increasing trend between ~10 and ~2 ka with a significant periodicity of 3000 a corresponding to that observed for monsoon-induced productivity.