| Trace metals play an important role in marine biogeochemical cycles and participate in various Marine biological,chemical and geological processes,which is of great significance for understanding marine environmental changes.In this paper,the grain size,organic carbon,trace metals(V,Cu,Co,Ni,Mo,U)and metal morphology of multi-core sediments collected from four stations in the Laptev Sea are analyzed,and the distribution characteristics and controlling factors of trace metals in the Laptev Sea sediments are discussed.By using the improved BCR continuous extraction method,the speciation of trace metals is extracted into four metal forms:isolated weak acid soluble state,reducible state,oxidation state and residue.We further focus on the identification of forcing factors involved in the forming of the metal during the sedimentary process in order to discover the enriching mechanism of trace metals in the Laptev Sea from the continental shelf to the deep basin.Moreover,the total amount of trace metals and it's speciation of surface and multi-core(SR03,SR09,SR11 and SR14)and gravity core(R09)sediments of Chukchi Sea are also analyzed in this study.The internal relationship between variations of the total amount and phase states of trace metals in the Chukchi Sea and water depth(Sea-level changes)is determined.Combined with previous research results,the response of some trace metals occurrence forms in Chukchi Sea continental shelf to sea-level changes during the past ten thousand years is illustrated.The main results are as follows:1.An enrichment trend was found for V,Mo,Cu.Co,and Ni from Laptev sea continental shelf to the deep basin cores.The accumulation of these metals in the sediment core are mainly controlled by the incoming runoff(Lena and Yana rivers)and the removal of Fe/Mn oxides.The major speciation of trace metals in the sediment cores was residue,and the highest proportion of the non-residue was reducible state.The reducible fraction for these metals which are influenced by Fe/Mn oxides and organic matter also shows significant increase from Laptev Sea shelf to basin cores.Then we summarized the transporting and enriching trace metals from the Laptev sea shelf to the basin as the "shelf-to-basin shuttling" mechanism,which controlled by Fe/Mn oxides and sediment resuspension.2.The bulk contents of trace metals in the SR section of the Chukchi Sea and their distribution patterns are closely related to the water depth.The water depths of SR03,SR09 and SR11 on the Chukchi shelf are similar and shallow,and the contents of extractable(weakly acid soluble,reducible and oxidizable)metals in the sediments are similar.V,Cu,Co and Ni are mainly in the reducible speciation,and all of them show an increase with water depth,indicating that the migration of these four elements is mainly in the reducible speciation,which is related to the removal of Fe/Mn oxides.The content of oxidizable Mo increases with water depth,but the percentage of oxidizable Mo in the total metal varies less,all around 40%,indicating that Mo in sediments is mainly controlled by organic matter and has high stability.The content of extractable U in the sediments of each station is similar,and the percentage change of each form in the total metal is small,indicating that the chemical form of U in the sediments is relatively stable and less affected by the change of water depth.3.Based on the characteristics of sea level change,the changes of trace metals(V,Cu,Co,Ni)in sediment core R09 over the past 10000 years are divided into three stages:(1)10000-8000 yr BP: the sea level rises rapidly,and the intensity of Pacific Ocean inflow water injected through the Bering Strait is low but gradually increasing.the trends of two elements,Co and Ni,show high consistency The changes of Co and Ni show a high consistency,and the contents of both weakly acid soluble and reducible speciations fluctuate significantly within a short period of time,which corresponds to the large-scale climate oscillation in the Arctic caused by the combined effect of the Pacific Ocean inflow and the North Atlantic Ocean inflow during this period.(2)8000-4000 yr BP: Sea level rose slowly and the intensity of Pacific inflow water increased significantly.Due to the lower sedimentation rate and sea ice transport conditions,the flux of particulate matter in the water column is small and the phase change of trace metal content is relatively small during this period.(3)During the period from 4000 yr BP to the present,the sea level height and the intensity of Pacific Ocean inflowing water remain stable,and the trace metal content of each fugitive form varies greatly due to the high deposition rate and complex hydrodynamic conditions. |
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