Sediment Provenance Discrimination And Paleoenvironment Records In The Mud Area Of East China Seas Since The Holocene

The East China Seas (ECSs), consisted of the Bohai Sea, Yellow Sea and East China Sea, is one of the largest continental marginal seas in the world. Two large rivers (Huanghe and Changjiang) annually delivered more than 1.5 billion tons of sediments to the ECSs. These huge amounts of sediments are the primary terrigenous sediment sources of these epicontinental seas, and hence have immense impacts on the sedimentary, aquatic and ecological systems, as well as the geochemical cycles in these epicontinental seas. Therefore discriminating the provenances of the sediments is critical not only for understanding the temporal and spatial dispersal pattern of the sediments from the Changjiang and Huanghe, but also for deciphering and reconstructing paleoenvironmental changes archived in the sediment deposits. In recent years, great advances in discriminating the Changjiang and Huanghe sediments have been reached; however, there is also considerable uncertainty to distinguish them in the mixed areas. In addition, the mud depositional areas of ECSs archived abundant paleoenvironment information, which reflected both of the changes in the continent and ocean. Multi-proxies (bulk sediment and Quartz grain size, Magnetic properties, pollen, geochemical data, Alkenone-derived sea surface temperature) have been used to study the paleoclimate history archived in these mud deposits. However, there is little consensus about the long-term and high resolution records of the East Asia Winter Monsoon and the Yellow Sea Warm Current.A total of 23 samples collected from the Huanghe (12) and Changjiang (11) Estuary are separated into seven particle-size fractions (<2μm,2-4μm,4-8μm, 8-16μm,16-32μm,32-63μm,63-125μm). These sub-samples are analyzed by X-ray diffraction (XRD) to characterize its mineral assembles. The results show that the mineral assembles of the Huanghe and Changjiang sub-samples are much different with each other. Particularly, the carbonate minerals (calcite and dolomite) in the <16μm particle-size fractions exhibit significant discrepancy between the Huanghe and Changjiang samples, the calcite is the dominant carbonate minerals in the Huanghe sub-samples in<16μm fractions whereas the dolomite became more enrichment in the Changjiang sub-samples (<16μm). This discrepancy (Calcite/Dolomite ratio) is the result of the different chemical weathering intensity and sediment source within these two river basins. Therefore, it can be used as a reliable and simple proxy to distinguish the Huanghe and Changjiang sediments.The discrepancy of Calcite/Dolomite ratio in<16μm particle-size fractions is applied to identify the sediment provenance of 150 samples collected from the mud depositional area of ECSs. Results show that this proxy can easily distinguish the Huanghe and Changjiang sediment provenance in the mud area of ECSs, especially in the areas where the Huanghe and Changjiang sediments mixed. The Huanghe sediments can be found in almost all of the mud depositional areas whereas the Changjiang sediments are mostly constrained in the inner shelf and the Southwestern Cheju Island Mud (SWCIM).This proxy is also used to identify the Huanghe and Changjiang sediment provenance in the core-B3 (located in the SWCIM) during the Holocene. Results show that the Changjiang sediments have an effect on the SWCIM until 6.0 ka B.P., which consistent with the transition of the Changjiang Delta from the accumulation to progradation in 6.0 ka B.P.. Moreover, the contribution of the Huanghe sediments to the SWCIM only existed in two periods (6.8-4.1 and 0.8-0 ka B.P.), which likely revealed the history shift of the lower Huanghe in the Subei Plain. The evolvement history of sediment provenance in this area largely depend on the formation of marine current system, as well as the changes in the Huanghe and Changjiang sediment supplies, which related to the delta evolution and channel shifting.Three cores (ZY-1, ZY-2 and ZY-3) are retrieved from the central Yellow Sea mud (CYSM). AMS 14C dating, Grain-size and XRF-geochemical data for these cores are used to reconstruct the history of the East Asian Winter Monsoon (EAWM) since the mid-Holocene. Results show that these data provide a continuous history of the EAWM over the past 7200 years, and the EAWM can be divided into three periods:strong and highly fluctuation during 7.2～4.2 ka B.P.; moderate and relatively stable during 4.2～1.8 ka B.P. and weakened during 1.8-0 ka B.P.. The evolution history of EAWM broadly follows the orbital-derived winter insolation with a similar long-term step-decreased trend as the East Asian Summer Monsoon (EASM); however, an anti-relationship existed between them in centennial-scale, mostly likely caused by solar activity.Alkenone-derived sea surface temperature (UK37-SST) at Core-ZY2 varied largely over the past 6200 years, the UK37-SST of Core-ZY2 is relative low with three abrupt cooler events (5.0～5.4,3.8～4.0 and 3.0z 2.4 ka B.P.) during 6.2-2.0 ka B.P.; since 2.0 ka B.P., the UK37-SST of Core-ZY2 increased largely and relatively stable. The millennial-scale cooler events in Core-ZY2 are consistent with the Kuroshio current decreased events and the North Atlantic ice-drift events (Bond events). This implies the climate change in the low-latitude continental marginal seas is synchronized with the high-latitude areas, likely derived by the same driving force (e.g. solar irradiance).The sea surface temperature differences between several cores are used to reflect the intensity of the Yellow Sea Warm Current (YSWC). Results show that the intensity of YSWC in 6.2-2.0 ka B.P. is weaker than the later period (2.0～0 ka B.P.), with ten centennial-scale YSWC weaker events. The long-term trend and centennial-scale weaker events of the YSWC are consistent with the changes in UK37-SST of the Core MD05-2908 (located at Southern Okinawa Trough) and Mg/Ca-SST of the Core MD 81 (located at Western Pacific Warm-Pool). This suggests that the intensity of KC-self is the dominant factor controlling the variation of YSWC. The reconstructed intensity of TWC and KE is consistent with the previous studies.