Holocene Vegetation And Climate Changes And Provenance Input Based On Geochemical Records From The Mud Shelf Sediments Of The East China Sea

Continuous and relative stable mud sedimental depositions in the continental shelves of the East China Sea(ECS)provide archives for better understandanding of the climatic and environmental changes in the Holocene.However,few studies focused on climatic and environmental reconstructions by the use of mud sediments,in this particular,to disentangle the complex interactions of the East Asian Summer Monsoons(EASM),ocean currents,terrestrial material inputs,and vegetation changes from the drainage areas of the Yangtze River into the ECS.In this study,analysis of inorganic geochemical elements and organic records,including n-alkanes contents and compound-specific carbon isotopic compositions,from core MD06-3039 and MD06-3040 in Min-zhe mud area are presented to discuss the source material input,vegetation and climatic changes in the source area since the mid-to late Holocene.Based on our analysis,the input of organic matter associated with debris of terrestrial higher plants into the studied site have been increased since the 4400 cal.a BP,and then decreased during a stage of 3200-1300 cal.a BP,reflecting most likely the decreased summer precipitation in this region.In addition,the n-alkanes distributions indicate that the input of organic matter is dominantly from Yangtze River basin.Furthermore,the indices of the n-alkanes suggest that the drainage area vegetation patterns have experienced three-stage fluctuation,with more herbaceous plants during the early and late stages and more woody plants during the middle stage of 3200-1300 cal.a BP.During short-term functions,the increases of herbaceous vegetation coincident with the Sui-Tang warm period and the increases of the woody vegetation with the early Ming-Qing cold period are well-expressed in our records.Temperature change appears to be one of the most important effects in the controlling the change of grass/woody plants as inferred from our record.Our studies also suggest that herbaceous plants have increased since the 1300 cal.a BP though the climatic has been continuously cooler,implying anthropogenic changes in the land use patterns have been responsible for.Through the XRF element scanning analysis of core MD06-3039,the geochemical distribution characteristics of the sediments in the Min-Zhe mud area and the history of paleoclimate change in the source area since the 4400a in the ECS are obtained.The geochemical characteristics of the sediments indicate that the sediments in mud area along Min-Zhe have typical land-based features.Al,Si,K,Zr,Rb,Sr,are significant different from the elements which affected by marine endogenous such as Ca.In this area,Rb/Sr and Zr/Rb present similar pattern with the changes in loess sections,and the increase of Zr/Rb reflects the strengthening of the winter monsoon,and the decreasing of the Rb/Sr indicates the weakening of the summer monsoon.Ba/(Zr+Rb)indicates the difference of marine productivity before and after 1300 cal.a BP,and the enhanced marine productivity after 1300 cal.a BP is consistent with the results of organic geochemical indicators.The carbon isotope of n-alkanes from MD06-3040 core reveals that C3 plants have been dominant since 8500 cal.a BP in the middle and lower reaches of the Yangtze River.Combined with the result analysis of nC31/nC27,a slight increase in C4 herbs in the period of 8500-7000 cal.a BP is observed and C3 plants increased significantly,but the ratio of grass to woody did not change significantly during period of 7000-4400 cal.a BP.During the period of 4400-3200 cal.a BP,herbs of C4 increased.During the period of 3200-1300 cal.a BP,especially during the period of 2200-2600 cal.a BP,C3 increased.During 1300-0 cal.a BP,C4 increased.Effective moisture may be the control factor on the changes of C3/C4 plants abundance in this area.The carbon isotope of n-alkanes indicate that ESAM has been weakened since 5000 a,though showing short-time strengthening around 6400 cal.a BP,4800 cal.a BP,2600 cal.a BP,200 cal.a BP.The record of compound-specific carbon isotopes from MD06-3040 reveals that the regional vegetation and climate change has 2 ka cycle.The correspondence between the ?13Calkane and the North Atlantic IRD events showed the important interaction of the high latitude climate process with the East Asian monsoon system.