A coupled approach based on grain size and geochemical elements is used to trace the provenance of surface sediments and to confirm the distribution patterns of grain size and elements on the continental shelf off western Guangdong Province and northeastern Hainan Island. The mean grain size ranges from 0.05 φ to 7.28 φ with a mean value of 5.60 φ. The average concentra- tions of major elements descend in the order of SiO2 > Al2O3 > CaO > Fe2O3 > K2O > MgO > Na2O > TiO2 > P2O5 > MnO, while those of trace elements exhibit a descending order of Sr > Rb > Zn > V > Cr > Pb > Ni > Cu > As > Cd. On the basis of the distribution patterns of elements and results of statistical analysis, the study area is classified into three zones. Zone I locates on the continental shelf off western Guangdong Province, and the sediments are mainly from Pearl River, Taiwan Residents rivers, and small rivers nearby. Zone II locates in the eastern exit of Qiongzhou Strait and the coastal area off Leizhou Peninsula, and the sediments are mainly from the ero- sion products of Qiongzhou Strait and Hainan Island. Zone III locates off the eastern Hainan Island and the continental shelf deeper than 50 m isobaths, and the sediments are mainly from Hainan Island and coral reef. The influence from open water should also be considered. Results indicate that the grain size is the main controlling factor for major and trace element contents and that anthropo- genic impact and biological activity also play an important role in the distribution of these elements.
GE QianXUE Z. GeorgeYE LimingXU DongYAO ZhigangCHU Fengyou
The history of the East Asian monsoon(EAM)since Last Glacial Maximum is reconstructed based on records in a sediment core retrieved from the northern South China Sea.The provenance of organic carbon and the EAM’s evolution are investigated using combined organic carbon,grain size,and AMS 14 C dating analysis.Responding to the strong winter monsoon,the marine organic matter was dominated in the sediments,andδ13 C of organic matter was high during the last glacial period.During the Holocene,the primary productivity decreased and the dilution effect of riverine inorganic clastics strengthened.Accordingly,the total organic carbon contents andδ13 C values decreased,and terrestrial organic matter content increased in the core sediments.The 4μm grain size fraction,as the environmental sensitive grain size component,is determined to reconstruct the paleoclimatic records.During the last glacial period,the contents of 4μm grain size component were mainly controlled by the sea level changes.Upon the Holocene,the influence of the sea level changes weakened and the roles of current system and provenance strengthened.The correlation between the EAM and solar insolation forcing is also discussed in this paper.
The relationship between the East Asian winter monsoon(EAWM) and East Asian summer monsoon(EASM) during the Holocene is complicated and remains controversial.In this study,analysis of grain size and benthic foraminiferal oxygen isotope,as well as accelerator mass spectrometry ^(14)C dating was performed on a sediment core retrieved from the newly revealed muddy deposit on the northern South China Sea continental shelf.The history of the EAWM and EASM were reconstructed for the last 8200 a BP.Further analysis in conjunction with previously published paleo-climate proxies revealed that the relationship between the EAWM and EASM during the Holocene is more complex than a simple and strict anti-phase one-both negative and positive correlations were identified.The EAWM and EASM are negatively correlated around 7500,4800,4200,3200,and 300 a BP(cooling periods),while positively correlated around 7100,3700,and 2100 a BP(warm periods).In particular,both the EAWM and EASM intensified during the three positive correlation periods.However,we also found that the relationship between these two sub-monsoons is anti-phase during the final phase of particularly hot periods like Holocene Optimum and Medieval warm period.The possible impact from variations of solar irradiance on the relationship between the EAWM and EASM was also discussed.
GE QianXUE ZuoYAO ZhigangZANG ZhengchenCHU Fengyou
