Sediment Geochemistry And Environmental Implication Since The Last Glacial Peroid In The Scotia Sea,Antarctica

Based on the comprehensive analysis of the major elements,trace elements and rare earth elements of the DC-11 core in the southeastern area of the Scotia Sea,We discussed the geochemical characteristics,provenances of sediments and the transport history by iceberg-current-atmosphere since 34 ka BP.The results showed that:The analyses for the vertical variation and their relationships with each other of major elements indicated that South American eolian dust and terrigenous detritus from Antarctic continent had a leading role in shaping the geochemical characteristics of DC-11 core sediments.However,biogenic silicon（BSi O₂）has obvious dilution effect on terrigenous detritus.The temporal variation of TFe₂O₃,K₂O,Mg O,Mn O,P₂O₅and Ti O₂is similar to that of Al₂O₃,indicating a decrease in terrigenous detritus supply from the Glacial period to the Holocene,however Na₂O was inversely correlated with Al₂O₃,indicating more contribution from volcanic material.The analyses for the temporal variation of K₂O/Ti O₂,Al₂O₃/Ti O₂,Fe₂O₃/Mg O,ICV,CIA,K₂O/Na₂O indicated that they were mainly dominated by the supply of terrigenous detritus from South America and East Antarctica during the Glacial period,conversely,but the supply of terrigenous detritus carried by the southern branch of Antarctic Circumpolar Current（ACC）decreased,showing the characteristic of multivariate mixing.During the Deglaciation,the supply of eolian dust from South America and terrigenous detritus from East Antarctica showed a downward trend.On the contrary,the supply from terrigenous detritus carried by ACC increased.During the Antarctic Cold Reversal period（ACR,14.1-12.9 ka BP）,the terrigenous detritus supply from East Antarctica sharply increased but South American eolian dust supply was still few.During the Holocene,the geochemical characteristics were mainly dominated by the mixing of the sediments from Antarctic continent because of the few supply of South American eolian dust.The La-Th-Sc and Th-Sc-Zr/10 triangle diagrams indicated that the provenances of DC-11 can be divided into two types:Type I.South Shetland Islands sediments with oceanic island arc characteristics;Type II.the sediments of the South American loess and the East Antarctic glacier sediments with continental island arc and continental margin characteristics.The temporal variation of DC-11 core sediments generally show the provenance types decreased from Glacial period to Holocene:the less contribution of felsic material supply,the more contribution of mafic material supply,as well as the transition from Type I to Type II.Rare earth elements（REE）and their relationships with biogenic silica（BSi O₂）,magnetic susceptibility,Al₂O₃and Fe₂O₃in Core DC-11 were analyzed and showed tha temporal variation of REE is similar to that of Al₂O₃,indicating they mainly occurs in terrigenous detritus and BSi O₂has obvious dilution effect on it.Sediments with high REE concentration,flat shale-normalized pattern,weak positive Eu anomaly,and high La _N/Yb _Nratio during the last glacial period indicated they are transferred from the Weddell Sea and eroded from the bordering lands with relatively old crust.The increases in magnetic susceptibility,ΔAl₂O₃,TFe₂O₃/Eu ratio indicated the input of South America dust increased during glacial period.In early Deglaciation,increasing Eu positive anomaly and lower La _N/Yb _Nratio indicated the southern branch of Antarctic Circumpolar Current（ACC）strengthened and more sediment contributions from the South Shetland Islands and Antarctic Peninsula due to the southward shifts of oceanic fronts,while decreasing magnetic susceptibility,ΔAl₂O₃,TFe₂O₃/Eu ratios showed rapid decrease in dust supply from South America.During the ACR period,sediments from the South Shetland Islands and Antarctic Peninsula decreased sharply due to cold condition and weakened ACC branch,the weakest Eu positive anomaly and highest La _N/Yb _Nratio indicated that the sediments from the Weddell Sea dominated in the core again,and the peak of ice raft debris indicated ice rafting is vital or dominant agent.In the late Deglaciation the return of ACC branch to the South Shetland Islands and Antarctic Peninsula contributed more to the sediments in Core DC-11;In Holocene,the ACC branch in the area between the South Shetland Islands and Antarctic Peninsula was generally enhanced,and its contribution to core sediments was increased to roughly equivalent to the amount of sediments from the Weddell Sea.