| The Arctic Ocean plays an important role in the late Cenozoic evolution of the Earth's environmental s ystem, includin g modern climatic changes. The Chukchi Sea, together with its northern borderland, is the key area to understand modern and past oceanographic changes of the Arctic Ocean. 60 surface sediment samples and Core M03 were selected and analyzed major and minor elements, stable carbon and nitrogen isotopes, and other sedimentologic parameters, with the objectives for understanding sediment sources, spatial and temporal changes of sedimentary environments in the area.Based on numerous studies of surface sediments, several conclusions are summarized as follows: (1) Controlled by hydrodynamics and ice, surface sediments in the study area are relatively coarse and have bad sorting and low structure maturity. (2) Sediments also have relatively low chemical maturity and remain clear fingerprints of their sources. K-rich illite. Mg-, Ca-, Na-, Zn-rich smectite, Mn- and Fe-rich chlorite produce a clear coupling relationship between clay minerals and chemical compositions of clay fraction. Major elements Al, K, Mg, Fe, Ti and minor elements Li, V, Sc, La, Z,n, Y, Cu, Ni are enriched in fine-grained sediments, the former are main components to form clay minerals and the latter are generally related to adsorption and integration of fine-grained materials. (3) The dispersals of terrigenous components in the study area are controlled mainly by marine circulation. Kaolinite-, illite-, K- and Al-rich sediments in the northeast and the north of the study area are derived mainly from Canadian Mackenzie River due to the transport of i:he clockwise Beaufort Gyre. Sediments in the nearshore of Northwest Alaska enrich chlorite, and have variable kaolinite and high SiO2 contents, indicating a large fraction of sediments from the Northwest Alaskan coasts and riven;. Sediments off Wrangel Island in the west of the study area enrich chlorite, Na, Sr and Zr, indicating an elevated influences from Siberian continent and shelves. The Pacific waters entering from the Bering Strait entrain a large amount of the Yukon River materials; its northward dispersal possibly cause sediments in the central part of the Chukchi Sea to enrich smectite and elements Na, Mg, Ca, Zn, Sr etc. (4) REEs are relatively rich in fine-grainedsediments and deplete in coarse-grained sediments, and exhibit flat shale- normalized REEpattern in the Chukchi Sea, indicating surface sediments are composed dominantly ofterrigenous components with weak chemical weathering from Alaska and Siberia. (5)Transitional metals Mn, Co, Ni, Cu coexist and their enrichments denote oxidizingenvironments. The distributions of authigenic Mn and Ni indicate the northern deep seahas an oxidizing seabed environment while the Chukchi Sea has a reducing sedimentaryenvironment. (6) Biogenic SiO2 contents, organic 513C and 515N values in surfacesediments reflect surface water productivity and supply of terrigenous organic materials,which are controlled by marine circulation and seawater nutrient structure. After enteringthe study area, the Pacific waters disperse northward cross the Chukchi shelf as threebranches with different nutrients, and cause differentiations in nutrient and surface waterproductivity in the study area. Due to the influence of the nutrient-rich waters, themidwest of the study area have high surface water productivity, and weak signals ofterrigenous organic 513C and 515N; The nearshore of Northwest Alaska has the lessnutrient-rich seawater, and so has decreasing surface water productivity and enhancedsignals of terrigenous organic 6I3C and 615N. The Chukchi Plateau and the Canadian Basinin the northeast and the north of the study area have relatively long duration of ice coverand the least nutrient-rich seawater, so they have the lowest surface water productivity andthe highest terrigenous organic component, the latter is derived mainly from CanadianMackenzie River due to the transport of the clockwise Beaufort Gyre. For th...
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