Terrigenous sediment variations in the western South China Sea and their implications to East Asian monsoon evolution during the last glacial-interglacial cycle

Abstract

Major-element geochemistry from two Cores MD05-2899 and MD05-2901 off central Vietnam in the lower continental slope of the western South China Sea is investigated to reconstruct a history of terrigenous sediment variations and East Asian monsoon evolution during the last glacial-interglacial cycle. The results suggest that the Pearl River can play a more important role in contributing terrigenous sediments to the western South China Sea than the Red River in the north, while the Mekong River can transport more terrigenous sediments to the region than the Sunda shelf and the Indonesian islands in the south. The Pearl River provides terrigenous sediments with higher Al2O3, but lower K2O, MgO, and Fe2O3 (Total Fe) than the Mekong River. K2O/Al2O3, MgO/Al2O3, and Fe2O3/Al2O3 ratios are then used as proxies to trace terrigenous sediment variations in the western South China Sea. Higher K2O/Al2O3, MgO/Al2O3, and Fe2O3/Al2O3 ratios indicate strengthened terrigenous sediments input from the southern source and lower the ratios suggest increased terrigenous sediments received from the northern source. These ratios show a glacial-interglacial cycle over the past 130 ka, implying a close relationship with the East Asian monsoon evolution. Northward surface currents forced by strengthened summer monsoon during interglacial periods bring relatively higher amounts of terrigenous sediments from the southern source to the western South China Sea, while relatively higher amounts of terrigenous sediments from the northern source are transported to the western South China Sea by southward surface currents in strengthened winter monsoon during glacial periods. Our study indicates that the terrigenous sediment variations in the western South China Sea are significantly controlled by surface currents under the strong influence of the East Asian monsoon evolution during the last glacial-interglacial cycle.