Speciation and enrichment of trace metals in Laptev Sea shelf sediment

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 speciation of multi-core sediments collected from four stations in the Laptev Sea were analyzed, and the distribution characteristics and controlling factors of trace metals were discussed. By using our improved BCR continuous extraction method, the speciation of trace metals was extracted into four metal forms in the states of isolated weak acid soluble, reducible, oxidative, and residue. In addition, to understand the enriching mechanism of trace metals in the Laptev Sea from the continental shelf to the deep basin, the main factors involved in the formation of the metals during sedimentation were identified. Results show that the bulk contents of V, Cu, Co, Ni, Mo and U increased from Laptev Sea shelf to the adjacent slope, and the accumulation of trace metals in the sediment are controlled by the scavenging removal of iron and manganese oxides, and the input of terrigenous rivers. The phase state experiments show that the metallic elements exist mainly in residue state, while those in non-residue state, the reducible state dominated and its content increased from shelf to slope. Therefore, the mechanism of enrichment and transportation of trace metals from continental shelf to sea basin of the study region is mainly the “shelf-to-basin shuttling” controlled by Fe/Mn oxides, and affected by sediment re-suspension as well.