High-resolution Sedimentary Record In The Typical Mud Areas Of East China Sea And Its Response To Climate And Environmental Changes

Mud areas in the continental Shelf were formed in the are Postglacial period withhigh sea level with huge input of terrigenous clastic materials and Pollutants fromlarge rivers and anthropogenic emission, and with a high sedimentation rate. Mudareas are considered as good targets to develope researches on global paleo-climatereconstruction and land-sea interactions in the margins. The sedimentation process inthe continental shelf of the East China Sea (ECS) was controlled by the hugeterrigenous input from the west and the robust boundary current from the east in theWest Pacific Ocean, making the mud areas ideal locations to record the influence andimpact of both of the directions. At the same time, the sedimentary record in differentregions tended to respond to climate chang and environmental variation in theirspecial ways, due to the diversity in distance to the Changjiang River estuary, marinehydrodynamic factors and water depth. So, mud areas in the inner and distal shelf ofthe ECS was employed in this research to undertake the high-resolution andmulti-parameter study of sedimentary record in interannual to decadal scales, for thepurpose of revealing and understanding the regional response to natural processes andhuman activities and thus to favor the scientific research in regional response toglobal change.In this research, high-resolution records of grain size, clay mineral composition,element geochemistry, and biogenic silica (BSi) were reconstructed in the cores ofC0702, C0803(in the inner shelf) and CFJ103(southwest to Cheju Island), andabout one hundred surface sediments. combing with accurate dating to illustrate thesedimentation process and sedimentary response to environmental evolution in the latest200years or500years. At the same time, a comprehensive study of BSi insurface sediments and cores was developed to analyze the spatial and temporaldistribution of biogenic silica, with the help of power spectrum analysis (REDFIT)and Empirical Mode Decomposition)(EMD), so as to deepen understanding of theuse of BSi in the ECS.The results suggested that:(1) sediments in the inner shelf of ECS are mainlyfrom the transportation of particles of the Changjiang River, the sedimentation ratevaried in different regions with a marked reduction in the adjacent ares of theChangjiang River mouth, according to the Profiles of210Pb and137Cs. While, in themud area southwest to Cheju, sediments are largely derived from the aboundedYellow rivers and Yellow Sea,and the sedimentation rate is lower but consistent.(2)The reconstruction of sedimentary record of grain size, clay mineral and elementalcomposition, biogenic silica and biogenic barium in high resolution, revealed thesedimentary characteristic with different stages and stable trend, together withperiodic cycles etc. Events caused by storm surges and floods changed the characterof grain size and elements prone to affected by grain size, and heavy metals such asPb and Zn tended to concentrate significantly in the latest50years, due to theanthropogenic emission.(3) Clay mineral distribution reported significant changesnear1950with lower illite content and higher kaolinite and chlorite, which wasaccounted to the strength variation of coastal current and the impact of decreasingsediment flux from Changjiang River.(4) The record sequence of sensitive grain sizeand clay mineral composition showed general phased change.in the mud areas ofinner shelf and distal shelf. In the inner shelf, the East Asian monsoon and theZhejiang-Fujian coastal current dominate the environmental evolution, while, coldeddy and upwelling in southwest of Cheju Island. When East Asian winter Monsoonstrengthened, coarse populations also increased, with their content and mean size uptogether, on the other hand, upwelling was strengthened, with more nutrients supplyto support high primary productivity.(5) The distribution of BSi in different sizefractions of the surface sediment suggested significant grain-size effect, and the BSicontent peaked in the fraction finer than16μm, which was mainly account to the diatom structure with the majoring contribution of micro-diatoms and pico-diatomsand the hydrodynamic condition.(6)BSi flux in the mud sediments was estimated inthe continental shelf of ECS and Yellow Sea, with high values in the ChangjiangRiver mouth and mud areas in the inner shelf, next in the mud areas in the SouthYellow Sea, the results suggested the BSi burial corresponded to the spatialdistribution of phytoplankton productivity and was controlled by accumulation rate.(7) The analysis of BSi records by the tool of REDFIT and EMD revealed its periodicchanges of11a,22a and~50-60a, which were mainly influenced by intensity variationof East Asian monsoon, sunspot activity, ENSO and Pacific Decadal Oscillation (PDO)etc., while ratio changes of nutrients input which was caused by human activities,decreased the contribution of diatoms in the phytoplankton ecosystem, and thus madethe BSi content in the sediment changed with a reducing trend in the latest30years.