Carbon isotope evidence for changes in Antarctic Intermediate Water circulation and ocean ventilation in the southwest Pacific during the last deglaciation

Abstract

Deep‐sea sediment core FR1/97 GC‐12 is located 990 mbsl in the northern Tasman Sea, southwest Pacific, where Antarctic Intermediate Water (AAIW) presently impinges the continental slope of the southern Great Barrier Reef. Analysis of carbon (δ13C) and oxygen (δ18O) isotope ratios on a suite of planktonic and benthic foraminifera reveals rapid changes in surface and intermediate water circulation over the last 30 kyr. During the Last Glacial Maximum, there was a large δ13C offset (1.1‰) between the surface‐dwelling planktonic foraminifera and benthic species living within the AAIW. In contrast, during the last deglaciation (Termination 1), the δ13Cplanktonic‐benthic offset reduced to 0.4‰ prior to an intermediate offset (0.7‰) during the Holocene. We suggest that variations in the dominance and direction of AAIW circulation in the Tasman Sea, and increased oceanic ventilation, can account for the rapid change in the water column δ13Cplanktonic‐benthic offset during the glacial‐interglacial transition. Our results support the hypothesis that intermediate water plays an important role in propagating climatic changes from the polar regions to the tropics. In this case, climatic variations in the Southern Hemisphere may have led to the rapid ventilation of deep water and AAIW during Termination 1, which contributed to the postglacial rise in atmospheric CO2.