Sedimentary responses to the East Asian monsoon and sea level variations recorded in the northern South China Sea over the past 36 kyr

Abstract

Sediment grain size is an important proxy to detect sedimentary process and record paleoenvironmental variations in continental slopes. Grain size measurements were performed for 298 samples of the 5.96-m-long core PC338 spanning the past 36 kyr recovered from the northern South China Sea (SCS). Results show that sea level and climatic influences on grain size distributions are crucial. A turbidite formed during the Last Glacial Maximum (LGM) is ascribed to the favorable topography close to the Red River estuary induced by the low sea level. Four end-member (EM) components for the normal sediment layers were unmixed using a lognormal parametric end member modeling (EMM). With the sea level decreasing, more EM4 (∼15–100 μm) and less EM1 (∼0–2 μm) supplied the SCS slope. Because EM2 (∼2–10 μm) consisted of fluvial suspension is dominated by the East Asian summer monsoon (EASM) precipitation, it has the potential to substitute for the EASM intensity. EM2 varied in-phase with many south China paleoclimate records and the 30°N July insolation over the past 36 kyr, and cooling climate events (including the LGM, Heinrich events H1 and H3, Younger Dryas, 8.2 ka and 10.3 ka) lowered the EM2 content. Our results further confirm the synchronous EASM evolution in the South China continent mainly forced by the Northern Hemisphere summer insolation.