Planktonic foraminiferal records of East Asia monsoon changes in the southern South China Sea during the last 40,000 years

Abstract

Planktonic foraminiferal assemblages and benthic foraminiferal oxygen isotopes were obtained in a gravity core NS07-25 (6°39.945′ N, 113°32.936′ E, water depth 2006 m) collected from the southern South China Sea (SCS) to investigate East Asia monsoon changes during the last 40,000 years. Four cold events identified from four peaks of the relative abundance of Neogloboqua d rina pachyderma (dex.) and Globigerina quinqueloba correlate well with those in the Hulu monsoon record within age uncertainty, and can be linked to Heinrich events in the Northern Atlantic high latitudes. We suggest that the relative abundance of N. pachyderma (dex.) and G. quinqueloba in the southern SCS can be used as a direct proxy for East Asia winter monsoon (EAWM) changes during glacial periods. In contrast to its low abundance in the northern SCS and Okinawa Trough, the relative abundance of Pulleniatina obliquiloculata shows high values during the last glacial in the southern SCS, caused likely by the combined impact of optimum winter sea-surface temperature (SST) and stronger mixing/enhanced upwelling at that time. A P. obliquiloculata minimum event (PME) found in the Okinawa Trough and the northern and southern SCS during the H1 period was possibly related to a large drop in winter SST due to the intensified EAWM. We propose that this PME can be also used as a reliable regional stratigraphic marker as the Holocene one. A 9-cm sandy silt layer deposit in core NS07-25 during the H1 period probably related to the enhanced current that was caused by the especially strengthened EAWM at that time. The last deglacial warming recorded in the relative abundance of warm and cold species of planktonic foraminifer reveals that changes between the EASM and EAWM were not in phase but alternating between a winter monsoon dominated northern hemisphere influence and a summer monsoon dominated influence of the tropical dynamics and/or southern hemisphere climate changes.