Tracing the Nd isotope evolution of North Pacific Intermediate and Deep Waters through the last deglaciation from South China Sea sediments

摘要

The intermediate and deep waters of the Pacific Ocean play a crucial role for regulating global climate changes on the millennium timescale. However, due to poor preservation of carbonate sediments in the deep Pacific, little attention has been received to better understand deep ocean circulation and its relationship with abrupt climate events. Here we present the first authigenic Nd isotope (ε_(Nd)) record extracted from Fe-Mn oxyhydroxides of the South China Sea (SCS) sediments (SO17940-2,1727 m water depth) in order to investigate changes of intermediate and deep-water circulations in the Pacific Ocean since the Last Glacial Maximum (LGM). In general, the seawater ε_(Nd) record extracted from the SCS sediments paralleled the existing Nd isotopes of fish teeth/debris from the eastern North Pacific core during the last deglaciation, demonstrating that our authigenic ε_(Nd) can faithfully record the seawater ε_(Nd) evolution in the deep Pacific Ocean. At the onset of the deglacial period, our data exhibit a clear negative shift in ε_(Nd) towards a gradually increased component of Antarctica Intermediate Water (AAIW) and reached a maximal influx during the mid Hein-rich Stadial 1 (HS1, ～16 kyr BP). Between the HS1 and Younger Dryas, deep-water circulation gradually shifted back to the modern condition during the Bolling-Allerod warm interval. A pronounced negative ε_(Nd) excursion had occurred during the Pre-Boreal (PB), suggesting a rapid reorganization of deep-water ventilation in the Pacific Ocean and was predominated by AAIW. This is most likely due to poor ventilation in the western North Pacific associated with an intensified summer monsoon during the PB-early Holocene warm period. After the PB period, the seawater ε_(Nd) values were once again dominated by Pacific Deep Water at the study site.