High Frequency Oscillations Of The Sedimentary Sequences From The Inner Shelf Of The East China Sea And Their Response To The Multiscale Climatic Oscillations In The Past200Years

The first scientific subject in the Integrated Ocean Drilling Program (IODP) Planningindicates that the past climatic change can be well recorded in the marine sediment, whichcan help us to understand the evolution of the earth system on temporal and spatial scalesand test the accuracy of the climatic models. The area of muddy sediment on the inner shelf of theEast China Sea (ECS) is regarded as an excellent place to explore high-resolution recordsand sedimentary responses to global climate changes due to its high sedimentation rate andgood preservation conditions. In particular, this area is under the influence of the East Asianmonsoon (EAM), resulting in significant seasonal differences in sediment flux from theChangjiang River, as well as changes in the intensity and direction of the nearshore currentsystem and marine biological productivity, which create the necessary conditions forannually deposited laminae. In this study, the interdisciplinary methods which includesedimentary method, geochemical method, and paleontology method will be introduced toreveal the high frequency oscillation and the sedimentary laminae in the marine sedimentsand construct the ultra-high resolution sedimentary records during the short-time sacle in thisstudy area. The relationship between high frequency oscillation in the depositional sequenceand short climate oscillations containing ENSO and PDO will be further studied. Theresearch results would be helpful to better evaluate the influence of anthropogenic acticity onthis area.First, we study the ultra-resolution sedimentary proxy: the grayvalue from thesedimentary gray image, using X-ray image processing technology and the continuouselement geochemical data from an X-ray fluorescence core scanner (X-ray core scanner).The study indicates that:1. The X-ray gray image includes comprehensive geologyinformation (e.g. sediment density, texture and structure), which is significantly negativecorrelated with water content of sediment core, therefore we get the emendation formula ofwater content in sediment core.2. The vertical changing tendency of the corrected gray valueis quite consistent with the results from the grain-size and the percentage of sand and silt;The district sedimentary environment is compartmentalized based on corrected gray value and the result is quite consistent with the experimental data from the grain-size compositionand grain size parameters. an elemental analysis quality was appraised by comparing theresults of two analysis methods, which are an X-ray fluorescence core scanner (X-ray corescanner) and an X-ray fluorescence spectrometer (XRF). The results show that:1. There ispositive correlation between the dry density and water content of of sediment cores, and theanalysis results of gray value from the sedimentary images and the intensities of theseelements measured by the X-ray core scanner affected by compaction.2. The elementsdetected by the X-ray core scanner can be divided into four classes. Elements in Class I showa high detecting quality, and the intensities of element measured by the X-ray core scannercan be taken as contents directly. The measuring intensities of elements in class II are greatsignificant, and that in class III are low significant. However，the measurement intensities ofelements in class IV are worthless and minor significant.Based on the radioactive age dating and sedimentary laminated dating, we constructethe precise dating with one or two years in the inner shelf of the East China Sea in the last200years. Then, time-series analyses of the data with spectral analysis and empirical modedecomposition (EMD) methods show that the oscillation modes in core18are composed ofmulti-timescale fluctuations on intra-annual, annual, inter-annual and decadal cycles, andwhich in the cores C0702, DH6-1and DH7-2are composed of multi-timescale fluctuationson quasi-2years, inter-annual and decadal cycles.A coupling analysis is accomplished to the relationship between the multi-scale highfrequency oscillation and the index of East Asian Winter monsoon, ENSO and PDO. Thestudy indicates that:1. The intra-annual and annual cycles in the core18correspond with thecyclical changes of sediment discharge in the Yangtze river, and the quasi-2years cycles inthe other cores is consistent well with the quasi-2years cycles of the EAM.2. The ENSO arethe main factors contributing to the inter-annual fluctuation with its effect on the intensity ofEAM.3. The decadal fluctuation is also one of the main oscillations in the sedimentarysequences, it matches the ‘regime shifts’ of the PDO, we conclude that the PDO phase shiftwill cause the EAM abnormal over mainland, and which can change the intensity of EastAsian Winter monsoon, therefore affect the decadal cyclical of sedimentary records.