Holocene bulk and n-alkane organic geochemical proxies from cores MD05-2905 and GeoB16601-5 from the Northern South China Sea

The South China Sea (SCS), characterized by a large continental shelf, is located at the edge of the Asian monsoon domain. In this study, two marine sediment cores from the northern SCS (NSCS) continental slope were investigated to construct composite vegetation and precipitation isotopic composition records based on the δ13C and δD values of plant-wax n-alkanes throughout the Holocene (last 11,200 years; i.e. 11.2 ka). The composite δ13Cwax record indicates an overall predominance of C3 vegetation over the last 11.2 ka. Before 8 ka BP, higher δ13Cwax values are attributed to preferential wax input from grassland and wetland biomes on the exposed continental shelf. After the inundation of the shelf by eustatic sea level rise until ca. 8 ka BP grassland and wetland biomes suffered a major size reduction and arboreal vegetation became better represented in the δ13Cwax record. The composite temperature corrected δDwax-T record suggests that moisture source variability drove precipitation isotopic composition changes during the Holocene. Lower δDwax-T values before 8.3 ka BP are interpreted as a larger moisture contribution by Pacific Ocean tropical cyclones, whereas higher δDwax-T values after 8.5 ka BP are interpreted as a larger moisture contribution from the Indian Ocean summer monsoon. Higher incidence of tropical cyclones in the NSCS during the Early Holocene was related to a temporary westward shift of the Western Pacific Warm Pool and enhanced insolation over the Northern Hemisphere. Both external and internal forcing mechanisms regulated moisture source changes in East Asia during the Holocene.