Middle to late Miocene surface water history in the northern South China Sea (SCS): Relationship to the East Asian Monsoon (EAM) evolution and variability
Final Report Abstract
The monsoon system represents one of the basic elements of global atmospheric circulation and its evolution and variability play an essential role in our understanding of global climate. This project investigated the evolution and variability of the East Asian Monsoon (EAM) for the Middle to Late Miocene (-13 Ma to 6 Ma), a period of postulated profound shifts in EAM intensity. To this end, sediment samples of ODP Site 1146 located in the northern South China Sea (SCS) were analysed for planktonic foraminiferal Mg/Ca ratios and stable oxygen isotope in order to reconstruct the hydrographic history of the northern SCS surface waters. Located offshore the modern Peari River, or its predecessor, the location of Site 1146 is considered as providing a very sensitive record for changes in river run-off as a result of changes in continental humidity/aridity. Local seawater δ18O reconstructions reveal that the EASM development since the middle Miocene can be regarded as a period of alternating phases of stronger and weaker EASM intensity rather than a continuous decrease in EASM intensity since the middle Miocene as proposed by previous published proxy records. After ≈ 7.5 Ma, a prominent decrease in EASM intensity has occurred. It is suggested that an EASM weakening after ≈ 7.5 Ma was most likely the driving force for decreasing aridity in east and south Asia at 8-6 Ma, leading to widespread ecosystem changes in east and south Asia.
