Abrupt change of sediment records in the southern South China Sea during the last glacial period and its environment significance

Abstract

Chemical compositions of sediments at core NS07-25 (6°39.945′N, 113°32.936′E; water depth 2006 m) are analyzed to discuss abrupt change of sediment records in the southern South China Sea (SCS) during the last glacial period and its environmental implications. Major and trace elements experienced three significant changes, which occurred at 31.9, 26.1 and 18.5 ka BP respectively. At 31.9 ka BP when sea-surface temperature remained relatively low, terrigenous sediment flux increased but biogenic activities weakened greatly. At 26.1 ka BP, both terrigenous sediment flux and biogenic fractions number were steady. However, some elemental ratios changed noticeably at that time. Before 26.1 ka BP, core sediments with low Nb/Ta but high Zr/Hf ratios were mainly derived from the paleo-Mekong and/or Molengraaff Rivers exposed on the Sunda Shelf at that time. After 26.1 ka BP, sediments with high Nb/Ta but low Zr/Hf ratios probably relate to strengthened impact of deep water current. Since 18.5 ka BP, sea level ascended rapidly from ∼110 m below the present, terrigenous sediment flux decreased and biogenic activities strengthened continuously, probably related with the East Asian monsoon evolution.