East China Sea δ18O Record Detects Millennial-Scale Changes in the East Asian Summer Monsoon

Abstract:

The East Asian Summer Monsoon (EASM) brings heavy summer rainfall to some of Asia’s most densely-populated areas, impacting agricultural production and water resources. Sediment cores were recovered from International Ocean Drilling Program Site U1429 in the East China Sea (31° 37.04’ N, 128° 59.50’ E, 732 mbsl). This location receives runoff from the Yangtze River, which serves as a major drainage system for monsoon-induced precipitation. Hence, the δ¹⁸O record of planktonic foraminifera at Site U1429 reflects changes in regional, monsoon-driven salinity. The top 100 meters of core at Site U1429 were sampled at a preliminary resolution of 15 cm and processed to isolate the planktonic foraminifer Globigerinoides ruber for δ¹⁸O mass spectrometry analyses. Abrupt, millennial-scale regional climate variability in the EASM and its linkage to orbital forcings have been reconstructed using stratigraphic analysis of δ¹⁸O. The sub-orbital scale structure of the δ¹⁸O record over the past 400 kyr matches the structures of both the composite speleothem δ¹⁸O from eastern China (Sanbao and Hulu caves) and the planktonic δ¹⁸O record from northern South China Sea Site 1146. The similarities between these δ¹⁸O records indicate a strong regional response to monsoon forcing. Removal of the temperature component of the δ¹⁸O signal by using Mg/Ca (G. ruber) paleothermometry will provide a record of changes in the δ¹⁸O composition of seawater in response to Yangtze River runoff.