北极拉普捷夫海沉积物痕量金属赋存形态及富集机制

Speciation and enrichment of trace metals in Laptev Sea shelf sediment

痕量金属在海洋生物地球化学循环中发挥着重要作用,参与各种海洋生物、化学和地质过程,对于认识海洋环境变迁具有重要意义。本文针对北极拉普捷夫海陆架–陆坡断面的4个沉积物短柱,开展了痕量金属元素(Mo、U、V、Cu、Co、Ni)总量及其赋存形态研究,同时结合沉积物粒度、有机碳含量等相关参数,探讨了拉普捷夫海沉积物中痕量金属的分布特征及其主控因素。采用改进的BCR连续提取法对金属元素进行了化学形态分析,分离出弱酸溶态、可还原态、可氧化态和残渣态4种金属相态,结合研究区物质供应、河流输入、洋流状况等特点,尝试建立了痕量金属在沉积物中的富集埋藏机制。结果表明,研究区痕量金属总量表现出陆坡区高于陆架区的特点,元素相关性分析显示痕量金属在沉积物中的积累主要受铁锰氧化物的清除作用和陆源河流输入的影响。痕量金属形态提取结果表明,金属元素主要以残渣态存在,可提取态中可还原态占比最高且其含量由陆架向陆坡增加。痕量金属由陆架向海盆的迁移、富集概括为受铁锰氧化物控制的“shelf-to-basin shuttling”机制,同时受到沉积物再悬浮作用影响。

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.