Paleoclimatic evolution of the SW and NE South China Sea and its relationship with spectral reflectance data over various age scales
Abstract Spectral analysis of sediment from International Ocean Discovery Program (IODP) Site U1433 in the South China Sea can be used to constrain humidity and temperature through time by constructing hematite/goethite records spanning the last 10 million years. Records in the southwest and northern parts of this basin show long-term contrasting trends, despite the fact that geochemical evidence for alteration is similar in both parts of the basin, i.e. towards less alteration since 10 Ma. However, contrasting clay mineral assemblages in the northern and southwestern areas do suggest long-term changes in the relative climate of Indochina and southern China. We interpret this to reflect the northward migration of the ITCZ since the Miocene resulting in a progressive drying of Indochina and increasingly wet conditions in South China. Sediment believed to be supplied from the Mekong River (IODP Site U1433) shows increasing chemical weathering at a time of long-term drying of the climate. This probably reflects increasing chemical weathering driven by slower transport and despite reduced rates of chemical alteration in the context of a colder, drier climate since the Miocene. In general hematite/goethite data are consistent with pollen constraints from the same drill site that show colder conditions with increasing hematite/goethite since 3 Ma and with a transition to apparently wetter conditions since the mid-Pleistocene transition (MPT). This implies that most of the sediment in the southwestern basin is weathered and eroded during warmer, wetter interglacial phases, at least since the MPT.