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

Eleven sediment cores were analysed from the continental margins of the eastern Arabian Sea (22 degreesN to similar to 10 degreesN) 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 <similar to>1-6%, 0.10-0.82% and similar to 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 degreesN) 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 Samthein et al. [Miner. Soc. Spec. Publ. 64 (1992) 411] show increasing trend between similar to 10 and similar to2 ka with a significant periodicity of 3000 a corresponding to that observed for monsoon-induced productivity. (C) 2001 Elsevier Science B.V. All rights reserved.