Glacial-interglacial contrast in deep-water δ13C of the Arabian Sea

Abstract

Carbon and oxygen isotopic ratios of foraminiferal test are exclusively used for tracing the past changes in ocean circulation, air-sea exchange, global carbon cycle and temperature variations of water masses. Here we present the carbon and oxygen isotopic ratios of benthic foraminifera from sediment core AAS-9/21 retrieved from a water depth of 1800 m from the southeastern Arabian Sea, for the last ~58 ka. The Cibicidoides wuellerstorfi δ13C ranged between ~0.28‰ and -0.3‰, whereas ?18O ranged between ~2.2‰ and 3.7‰ for the study period. The lowest δ13C values of -0.3‰ were observed during the last glacial maximum (LGM) which indicate the presence of nutrient-enriched and less-ventilated water mass. The bottom waters were ~2°C cooler during this time compared to the Holocene, as suggested by a δ18O shift of 0.5‰ . The shift in δ13C from negative values during the LGM to positive during the Holocene, indicates the presence of a nutrient-depleted and ventilated water mass, which could have resulted from the resumption of North Atlantic Deep Water (NADW) flow. A large contrast in δ13C between depths of ~1800 and ~4000 m suggests better water mass ventilation during the marine isotope stage (MIS) 3 and 1.