Sedimentary records of East Asian Summer Monsoon evolution and source-sink variations in the northern continental slope of the South China Sea since 70 ka

Abstract

The orbital-scale evolution of the East Asian Summer Monsoon (EASM) and its response mechanism to low- and high-latitude driving processes remains unclear. The South China Sea (SCS), characterized by thick sedimentary sequences with high accumulation rates, preserves a detailed record of the EASM variability across different climatic periods during the Quaternary period. Here, Core SCSZ22–3 from the northern SCS was systematically analyzed using lithological examination, accelerator mass spectrometry (AMS) ¹⁴C dating, stable oxygen isotopes (δ¹⁸O), SrNd isotopic compositions, and grain size end-member modeling (EMM) to investigate provenance and sedimentary responses to EASM evolution over the past 70 ka. The results indicate that the Taiwan, the Pearl, and the Luzon rivers are the primary contributors to the deposition on the northern slope of the SCS. EM2 component (1.8–12.1 μm) can serve as a proxy indicator for the EASM, thereby providing insights into global millennial-scale climate changes. Spectral analysis and continuous wavelet transform of EM2 reveals distinct orbital periodicities of 31.1, 18.7, and 11.7 ka, and the semi-orbital periodicities of 5.9, 2.3, and 1.2 ka. The 18.7 ka periodicity suggests that precession is the dominant factor controlling the EASM in the SCS. Additionally, the 11.7 ka periodicity indicates that semi-precession exerts a significant influence on monsoon variations within low-latitude regions. Simultaneously, the periodicities of 5.9, 2.3, and 1.2 ka may be attributed to a combined effect resulting from variations of global ice sheets and insolation. The response of the monsoon indicator to these orbital periodicities implies that EASM changes are driven by both low- and high- latitude climatic processes. The findings will highlight the influence of low-latitude forcing on global climatic changes and its implications for late Quaternary evolution of the EASM.