Carbonate and Organic Carbon Variations of the Past 900,000 Years Recorded in Sediments From the Southeastern South China Sea (IMAGES core MD972142)

High resolution records of biogenic sediments from an IMAGES core MD972142 (12¢X41.133'N, 119¢X27.90'E, water depth 1,557m) provide information of paleoceanographic variations in the Southeastern South China Sea (SCS). We have generated 900-kyr long records of carbonate and organic carbon contents from this core. Constrained by planktic foraminifer (G. ruber) oxygen isotope stratigraphies, the records show in general high carbonate and low organic carbon concentrations in interglacial stages, and low carbonate and high organic carbon in glacial stages. This pattern indicates that the biogenic components maybe controlled by terrigenous inputs which are associated with sea level fluctuations in the past glacial-interglacial stages. Several peaks of low values of carbonate contents correspond to the tephra layers in core MD972142, indicating the dilution effects by volcanic ash. The organic carbon record contains several high content peaks which are associated with lower SSTs estimated by using planktic foraminifer transfer functions (especially in 340-360kya and in 430-440kya), implying possibly a winter monsoon-driven productivity changes. We also find that organic carbon events in these two intervals can be correlated to monsoon records from Arabian Sea areas. In addition, we used cross-spectral analyses to study the biogenic records and found that the carbonate record shows clearly Milankovitch orbital periods in 100-kyr and 23-kyr, but the organic carbon record shows complex spectra mixed with orbital-related and non-orbital periods. When examining the secular variations of the periodicities by filter, our results show a change in amplitudes of 41-kyr and 23-kyr cycles at ~500 kya, indicating probably that different mechanisms that amplified and/or damped the response of the carbonate systems of the two cycles operating in the SCS in the late Quaternary.