Sediment sources and East Asian monsoon intensity over the last 450 ky. Mineralogical and geochemical investigations on South China Sea sediments

Abstract

A coupled approach based on clay mineral assemblages and isotopic data (Sr and Nd) of sediment from Ocean Drilling Program (ODP) Site 1145 has been used to trace the sources of sediment feeding the northern part of the South China Sea, and to investigate the evolution of East Asian monsoon intensity over the last 450 ky. Clay mineral assemblages are dominated by illite and smectite, with lesser abundance of chlorite and kaolinite. 87Sr / 86Sr and ɛ Nd(0) isotopic data, combined with the smectite / (illite + chlorite) ratio, indicate that the Pearl River is the main contributor for detrital material to the northern margin of the SCS, with variable continental input of volcanic material derived from the erosion of the Luzon Arc. These inputs follow the low-latitude solar insolation with a 23 ky periodicity, as recorded by a periodic change of the clay mineralogy. For the first time, this study presents a SCS deep-sea sediment high-resolution record of climatic changes in the last 450 ky, showing that smectite / (illite + chlorite) variations are mainly related to changes in the East Asian summer monsoon intensity. Because the mineralogical record is independent of other external forcing phenomena such as global glacial/interglacial oscillations, the smectite / (illite + chlorite) ratio has been used here as a proxy to reconstruct past changes of the South-East Asian summer monsoon intensity.