Geochemical Characteristics Of Sediments In The East Siberian Sea Since The Middle Pleistocene And Their Responses To Paleoenvironmental Changes

The Arctic region is very sensitive to global climate change and is a key area for studying the paleoenvironmental and paleoclimatic changes.With the global climate warming,arctic sea ice is melting more rapidly.The East Siberian Sea is one of the important marginal seas in the Arctic,and its sedimentary environment has changed greatly since the Middle Pleistocene.In particular,changes in sea ice and ocean currents control the distribution and sedimentary characteristics of sediments in the East Siberian Sea.Therefore,research on the sediment provenance in the East Siberian shelf and slope will help to improve the understanding of the Arctic sedimentary environment and climate change.Based on the analysis of major&trace?rare earth elements and Sr-Nd isotopes in sediments of cores LV77-36-1 and LV77-27-3,the purpose of this paper is to decipher the changes in geochemical characteristics of silicate phase,to discusses the provenances and the transport mechanism in the East Siberian Sea during the Middle Pleistocene,and finally,to reveal the response of provenance evolution to paleoenvironmental changes since Middle Holocene.The Middle Holocene records in core LV77-36-1 shows that the elements in the clasts changed little and fluctuate only at 6.7 cal.ka and 2.5 cal.ka;then the ⁸⁷Sr/⁸⁶Sr ratio increased gradually from 8.3 cal.ka,indicating the radioactivity increased,while the?_Ndisotope showed a decreasing trend.The results show that since the Middle Holocene,the sediments in core LV77-36 are mainly derived from the suspended materials from the Lena,Indigirka,Yana and Mackenzie rivers,and the sediments of Laptev and Kara Seas,as well as coastal erosive materials from the Siberian platform and New Siberian Islands.According to the Comparison with other paleoclimate parameters,it was found that the changes of sea ice and ocean currents have important effects on the dispersion and deposition of source materials on the East Siberian shelf.In the late Holocene,due to the increase of sea ice in the Chukchi sea?the weakening of the Siberian coastal current and the strengthening of the Beaufort circulation,the material contribution of the North American end member increased slightly compared with the Middle Holocene.According to the vertical changes of element contents and Sr-Nd isotopes in the clasts of core LV77-27-3,it was found that the contents of major and trace elements?rare earth elements and Sr-Nd isotopes fluctuate to different degrees in the MIS 7-5period,which shows that the changes of MIS 7 and MIS 5 are small.However,there was a large fluctuation in MIS 6.Based on the evidence of principal component analysis?(La/Sm)_NASC-(La/Yb)_NASCand ⁸⁷Sr/⁸⁶Sr-?_Ndratio diagram,the sediments in core LV77-27-3 was dominated by the material contribution of the Siberian end element since the Middle Pleistocene.The provenances include river inputs(Ob,Yenisei,Khatanga,Lena,Yana,Indigirka)?coastal erosion(Siberian platform and Canadian Arctic Islands)and Marine sediments(Laptev Sea,Kara Sea,and western Chukchi Sea).During MIS7-5,the East Siberian Sea sediments were mainly supplied by Siberian end-elements,while a small amount of North American end-elements were imported in late MIS7 and MIS 6.The sediments of the East Siberian Sea,the material of the Siberian terminal element is mainly transported to the study area by the Transpolar Drift,while the material of the North American terminal element is mainly carried to the continental slope by the Beaufort Gyre.