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

摘要

Eleven sediment cores were analysed from the continental margins of the eastern Arabian Sea (22 deg N to approx 10 deg N) for organic carbon (C_(org)), nitrogen (N) and CaCO_3 contents. Similar variations are observed in both lateral and the vertical (<1.6 m) distribution of the concentrations of C_(org). N and CaCO_3 ranging from approx 1-6 percent, 0.10-0.82 percent and approx 10-81 percent, 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 CaCO_3 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 CaCO_3 (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 percent. BE values greater than 100 percent in the northern (>15 deg 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 CaCO_3 distribution is indicative of post-depositional effects due to sulphate reduction associated processes. This can lead to dissolution of CaCO_3 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 approx 10 and approx 2 ka with a significant periodicity of 3000 a corresponding to that observed for monsoon-induced productivity.