Productivity fluctuations in the southeastern Arabian Sea during the last 140 ka

Abstract

Detailed analyses of multiple geochemical productivity proxies such as calcium carbonate, biogenic opal, biogenic Ba, organic carbon and total nitrogen have been carried out on a sediment core from the southeastern Arabian Sea to trace the palaeoproductivity fluctuations over the last 140 ka. High calcium carbonate, biogenic opal, biogenic Ba contents (wt%) and their mass accumulation rates (g/cm u2/ka) suggest higher productivity during major interglacials than in the glacials. Organic carbon content (less than 0.8 wt%) and mass accumulation rates (less than 0.02 g/cm u2/ka) were lower during isotope stages 1, 2, 3, 4, and 6 and is of marine origin. The organic carbon distribution patterns do not coincide with other productivity proxies nor show any trends with interglacial and glacial periods. Interestingly, during interstadials (5.1, 5.3 and 5.5) of oxygen isotope stage 5, the organic carbon is low (0.3 wt%) and of marine origin. In contrast, during stadials (5.2 and 5.4), the organic carbon is high (1.8 wt%) and of terrigenous origin. This observation reflects the fluvially derived organic matter during the stadials of isotope stage 5 in the southeastern Arabian Sea. The lower Al/Ti ratio (11-16) of the sediment compared to crustal abundance norms, neither shows any correlation with the interglacial/glacial periods or with other productivity proxies, thus suggesting that this ratio cannot be used as a palaeoproductivity proxy in the southeastern Arabian Sea.