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Major elements were studied for reconstruction of sediment provenance and paleoenvironment over the last 24 kaBP with the samples collected from Core PC-1 in the northern Okinawa Trough.In addition to major elements,grain size of 402 samples and planktonic foraminifer δ18O of 344 samples have been analyzed that leads to an average resolution at centennial scale.The study offers a new high resolution material for reconstructing the history and main control factors of the sediment input in the northern Okinawa Trough over the last 24 ka.In according to the variation in major element compositions,the core could be divided into three distinct depositional units,separated by two volcanic layers at 7.3 and 12.7 cal kaBP respectively.Both provenance discriminating plot and R-mode factor analysis indicate that vertical changes in major elements are mainly contributed by the nearby terrestrial materials,whereas the contribution from hydrothermal activity,marine biologic deposition,and volcanism are minor.In particular,the contribution of nearby terrestrial materials show an obvious change trend and can be well correlated with the sea level fluctuation and the evolution of the Tsushima Warm Current.It seems that paleoclimate renders no significant impact on the change in terrigenous sediment provenance.

Synthetic analyses on typical element ratio and source discrimination function were carried out for a sediment core with high sedimentary rate collected along the Tsushima Warm Current(TWC) main stream on the southwestern slope of Japan Sea,in order to trace the sediment provenance change of the study area in the Holocene.Data suggest that the Nakdong River of Korea and Changjiang of China are the main source of the studied sediments.Affected by the TWC strength evolution and sea level rise,their contributions changed with time.There are five stages.In the early Holocene(9.6-6.5 kaBP),especially during the two Melt Water Pulse(MWP) stages including MWP-1C(9.4-8.7 kaBP) and MWP-1D(7.8-7.4 kaBP),the contribution of these rivers was high.Their contribution became lower during 6.5-3.0 kaBP and 2.0-0.7 kaBP,corresponding to the temporally weakening of TWC in the northern East China Sea and southwestern Japan Sea.In 3.0-2.0 kaBP and 0.7-0 kaBP,TWC was strengthened and more fluvial materials from the Nakdong River and Changjiang River were deposited in the study area.

Gravity core EC2005, located in the mud wedge off the Zhejiang-Fujian coast in the inner shelf of the East China Sea (ECS), was analyzed for its lithology, grain size, rare earth elements (REE) and AMS(14)C dating. Results revealed high-resolution paleoenvironmental evolution and multiple switches of sediment provenances in the inner shelf of ECS. The lithology, grain size and REE concentrations of sediments varied significantly down the core. Mean grain size ranged from 8 to 121 mu m, and the values of Sigma REE were 152.8-227.9 mu g/g. The chondrite- and shale-normalized REE patterns indicated their similarity to the terrigenous sediments in the study area. Between 17.3-12.3 ka BP the sediments in the inner shelf of ECS were mainly originated from local drainage basins. The source then gradually switched to the Yangtze River between 12.3 and 9.8 ka BP. Since about 10-9.8 ka BP, the sediments in the study area were dominantly derived from the Yangtze River. The continuous rising of sea level and formation of coastal current along the inner shelf played a key role in the switches of sediment provenances.

Based upon analyses of grain-size, rare earth element (REE) compositions, elemental occurrence phases of REE, and U-series isotopic dating, the sediment characteristics and material sources of the study area were examined for the recently formed deep-sea clays in the eastern Philippine Sea. The analytical results are summarized as follows. (1) Low accumulation rate, poor sorting and roundness, and high contents of grains coarser than fine silt indicate relatively low sediment input, with localized material source without long distance transport. (2) The REE Contents are relatively high. Shale-normalized patterns of REE indicate weak enrichment in heavy REE (HREE), Ce-passive anomaly, and Eu-positive anomaly. (3) Elemental occurrence phases of REE between the sediments with and without crust are similar. REE mainly concentrate in residual phase and then in ferromanganese oxide phase. The light REE (LREE) enrichment, Ce-positive anomaly, and Eu-positive anomaly occur in residual phase. Ferromanganese oxide phase shows the characteristics of relatively high HREE content and Ce-passive anomaly. (4) There are differences in each above mentioned aspect between the sediments with and without ferromanganese crust. (5) Synthesizing the above characteristics and source discriminant analysis, the study sediments are deduced to mainly result from the alteration of local and nearby volcanic materials. Continental materials transported by wind and/or river (ocean) flows also have minor contributions.

Concentrations and carbon isotopic (14C, 13C) compositions of black carbon (BC) were measured for three sediment cores collected from the Changjiang River estuary and the shelf of the East China Sea. BC concentrations ranged from 0.02 to 0.14 mg/g (dry weight), and accounted for 5% to 26% of the sedimentary total organic carbon (TOC) pool. Among the three sediment cores collected at each site, sediment from the Changjiang River estuary had relatively high BC contents compared with the sediments from the East China Sea shelf, suggesting that the Changjiang River discharge played an important role in the delivery of BC to the coastal region. Radiocarbon measurements indicate that the ages of BC are in the range of 6910 to 12250 years old B.P. (before present), that is in general, 3700 to 9000 years older than the 14C ages of TOC in the sediments. These variable radiocarbon ages suggest that the BC preserved in the sediments was derived from the products of both biomass fire and fossil fuel combustion, as well as from ancient rock weathering. Based on an isotopic mass balance model, we calculated that fossil fuel combustion contributed most (60%–80%) of the BC preserved in these sediments and varied with depth and locations. The deposition and burial of this “slow-cycling” BC in the sediments of the East China Sea shelf represent a significant pool of carbon sink and could greatly influence carbon cycling in the region.

Manganese abnormity has been observed in the Holocene sediments of the mud area of Bohai Sea. On the basis of grain size, chemical composition, heavy mineral content and accelerator mass spectrometry (AMS) C-14 dating of foraminifer, relationships between manganese abnormity and sedimentation rates, material source, hydrodynamic conditions are probed. Manganese abnormity occurred during the Middle Holocene when sea level and sedimentation rates were higher than those at present. Sedimentary hiatus was not observed when material sources and hydrodynamic conditions were quite similar. Compared with the former period, the latter period showed a decrease in reduction environment and an inclination toward oxidation environment with high manganese content, whereas provenance and hydrodynamic conditions showed only a slight change. From the above observations, it can be concluded that correlation among manganese abnormity, material source, and hydrodynamic conditions is not obvious. Redox environment seems to be the key factor for manganese enrichment, which is mainly related to marine authigenic process.

Eolian dust is an important material source of marine sediment and heavy metals influencing marine environment and primary productivity. Although the eastern China Seas and their adjacent regions are downwind of East Asian dust sources and have potentially high atmospheric input, study on the eolian dus in these regions is limited. This study on the compositions of eolian dust indicated that dust concentration and particle sizes varied with seasons and meteorologic conditions, that mineral and chemical compositions have significant regional variation, and that high Fe content is one of the characteristics of eolian dust which was found to be a mixture of natural loess and/or soil and anthropogenic matter that contained fairly high S and heavy metals.

Clay mineral assemblages, crystallinity, chemistry, and micromorphology of clay particles in sediments from ODP Site 1146 in the northern South China Sea (SCS) were analyzed, and used to trace sediment sources and obtain proxy records of the past changes in the East Asian monsoon climate since the Miocene, based on a multi-approach, including X-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive X-ray spectrometry (SEM-EDS). Clay minerals consist mainly of illite and smectite, with associated chlorite and kaolinite. The illite at ODP Site 1146 has very well-to-well crystallinity, and smectite has moderate-to-poor crystallinity. In SEM the smectite particles at ODP Site 1146 often appear cauliflower-like, a typical micromorphology of volcanic smecites. The smectite at ODP Site 1146 is relatively rich in Si element, but poor in Fe, very similar to the smectite from the West Philippine Sea. In contrast, the chemical composition of illite at ODP Site 1146 has no obvious differences from those of the Loess plateau, Yellow River, Yangtze River, and Pearl River. A further study on sediment source indicates that smectite originates mainly from Luzon, kaolinite from the Pearl River, and illite and chlorite from the Pearl River, Taiwan and/or the Yangtze River. The clay mineral assemblages at ODP Site 1146 were not only controlled by continental eathering regimes surrounding the SCS, but also by the changing strength of the transport processes. The ratios of (illite+chlorite)/smectite at ODP Site 1146 were adopted as proxies for the East Asian monsoon evolution. Relatively higher ratios reflect strongly intensified winter monsoon relative to summer monsoon, in contrast, lower ratios indicate a strengthened summer monsoon relative to winter monsoon. The consistent variation of this clay proxy from those of Loess plateau, eolian deposition in the North Pacific, planktonic, benthic foraminifera, and black carbon in the SCS since 20 Ma shows that three profound shifts of the East Asian winter monsoon intensity, and aridity in the Asian inland and the intensity of winter monsoon relative to summer monsoon, occurred at about 15 Ma, 8 Ma, and the younger at about 3 Ma. The phased uplift of the Himalaya-Tibetan plateau may have played a significant role in strengthening the Asian monsoon at 15 Ma, 8 Ma, and 3 Ma.