Sedimentary Provenance And Climate Change Records In The Sediments Of Kuroshio Mainstream,East Of Taiwan Over The Past Millennium

It is vital importance to research the characteristics of climate change during the last millennium for precisely forecasting the future climate change.The environmental change of marginal sea of West Pacific,especially the source area of the Kuroshio Current is vital important to the East Asian climate change,thus is the key area of global climate change researches and global carbon cycle researches.A core sediment in the main stream of Kuroshio,east of Taiwan were adopted in this thesis.Based on the AMS14 C dates,by analyzing the grain size,combination of the clay minerals and their crystallography features,we revealed the sedimentary characteristics,controlling factors and the provenance of the sediments of Kuroshio mainstream,east of Taiwan.The biogeochemistry features of rare earth element(REE)and its controlling factors in the research area were clear by analyzing the combination and form of REE in the sediments.It made use of total organic carbon(TOC)and carbon stable isotope compositions in organic matter(?13C)of sediments to estimate the sea-derived carbon contents.And the change of marine primary productivity in the research area for the past millennium were discussed based on the above study for the first time.Meanwhile,by correlation with environmental information revealed by indictors of this research,and other proxy data researches,we discussed the response of sedimentary characteristics in Kuroshio mainstream,east of Taiwan to the climate change during the past millennium.The major understandings and results have been obtained as follows:1.The average sedimentary rate of the sediments in the Kuroshio mainstream during the past millennium was about 34.44 cm/ka,which was lower than the southern Okinawa Trough(about 60 cm/ka),and was more than the open ocean(0.6~0.9 cm/ka),showing the features of transition from the continental shelf to the deep seas.The main component in the sediments of the research area was silt(83.53%~88.12%),the minor component was clay(11.79%~16.74%),it contained little sand in the sediments.It showed that the sediments in the Kuroshio mainstream came from several provenances,about 26%~72% of the clay minerals of sediments on this study came from the Asian continental dust,about 11%~55% of clay minerals came from rivers of eastern Taiwan,and about 11%~26% of clay minerals came from the Luzon Arc.2.The REEs in the sediments in Kuroshio mainstream,east of Taiwan,were mainly controlled by terrigenous materials,and was less influenced by the chemical and biological effect during the process of migration of sediment.Meanwhile,the distribution features of HREE and LREE provided geochemical basis for the theory of three end members mixing.Besides,the REE features of the sediments in the research area during the past millennium were slightly influenced by grain-size effect,and was closely related to the provenance and sedimentation.The research of the combined forms of REE in the sediments of Kuroshio mainstream revealed the reaction procedure of REE geochemical cycle and reflected as well the influence factors of the distribution features of REE as well.The REE in the sediments of the research area existed mainly by residual fractions(84.38%)and reducible forms(10.80%).The contents in the oxidizable forms(2.51%)and acidsoluble forms(2.31%)were low.Besides,La Ce Pr and Nd had the features of terrigenous source,other REEs were more likely to be influenced by the oxidationdeoxidation status.Among the four combined forms,acid-soluble,reducible and oxidizable forms had the features of relative HREE enrichment and negative Ce anomalies,the residual fractions had the features of relative LREE enrichment and positive Ce anomalies.This probably because that acid-soluble,reducible and oxidizable forms were influenced by the calcite compensation depth,oxidationdeoxidation status and biological productivity,thus had the prior to absorb and complex HREE.Besides,residual fractions were prior to absorb LREE and thus had the feature of positive Ce anomaly,it determined the feature of positive Ce anomaly in the total REE in the sediments of the research area.3.The organic matter in the sediments of the Kuroshio mainstream was mainly marine autogenic and was minor terrigenous input.It made use of biogenic elements and their isotope compositions of the sediments to estimate the sea-derived carbon contents,which was effective to indicate the marine primary productivity in the Kuroshio mainstream during the past millennium.The marine primary productivity was increased stably during 1152 AD~1400 AD,and was decreased during 1600 AD~1750 AD,and decreased first and then increased since 1800 AD.The marine primary productivity was mainly related to the sea surface temperature and the nutrients from Asian continental dust.Besides,the organic matter in the sediments of the research area was influenced mainly by the diagenesis and the resuspension of the sediments in submarine of east of Taiwan.4.There were good correlations between our research on the sedimentary features and paleoproductivity in the Kuroshio mainstream,east of Taiwan and those reported records in Taiwan and its adjacent areas,based of which we recognized three climate change stages,which were the Medieval Warm Period(MWP),the Little Ice Age(LIA)and the Current Warm Period(CWP).1152 AD~1400 AD might correspond to the MWP,relative high marine primary productivity and the ratio of warm-water to cool-water foraminifera might reflect the high sea surface temperature,high ratio of the contents of illite and chlorite to the contents of smectite reflected relative strong East Asian Winter Monsoon(EAWM).1400 AD~1800 AD might correspond to the LIA.The lower ratio of warm-water to cool-water foraminifera,the lower marine primary productivity and the weaker EAWM reflected consistently the climate features of cool and humid.The sedimentary features showed fluctuated rapidly climate change features.Although there was common point during the CWP and MWP,with relative high temperature,there was differentiation during two periods in the intension of EAM and the precipitation.The reason caused the difference might lie in the different external forcing factors of climate change.Meanwhile,the sedimentary features during the past millennium were not only influenced by long-time scale climate change,but also some sudden events,submarine earthquake,typhoon and rainstorm for example.