冲绳海槽中南部柱状沉积物氧化还原敏感元素赋存机理与环境指示意义

Occurrence mechanism of redox sensitive elements in columnar sediments in South Central Okinawa Trough and their environmental implications

沉积物中氧化还原敏感元素(Redox Sensitive Element,RSE)含量变化是上覆水体氧化还原环境良好的替代指标。本文通过冲绳海槽中南部两个柱状沉积物(深度:30 cm)粒度、总有机碳、总氮及其同位素含量和氧化还原敏感元素含量等指标,探究复杂环境背景下冲绳海槽柱状沉积物中RSE的赋存机理与环境指示意义。研究发现,柱状沉积物中除了Cr亏损,其他RSE均显示有不同程度的富集。“粒控效应”对冲绳海槽柱状沉积物的RSE含量影响较小;分析可知,海水表层生产力是影响沉积物氧化还原环境的主要因素,通过Mn(氢)氧化物的吸附或解吸附作用实现RSE的富集与亏损。δCe、V/Cr、Ni/Co和V/(V+Ni)等指标指示沉积物整体处于氧化−弱氧化环境。沉积物中Mn元素通过还原作用以Mn^(2+)形式向上扩散,在25~30 cm处被含氧间隙水氧化富集形成锰峰,指示柱状沉积物0~25 cm处为氧化环境,25~30 cm处为弱氧化环境。

Changes in the content of redox sensitive elements(RSE)in sediments are good surrogate indicators for the redox environment of the overlying water.The RSE in the columnar sediments under complex environmental backgrounds through the grain size,total organic carbon and total nitrogen and its isotopes contents,and redox sensitive elements contents of the two columnar sediments(30 cm)in South Central Okinawa Trough are explored in this paper.And to explore the occurrence mechanism and environmental indication significance.The study found that in addition to the depletion of Cr in the columnar sediments,other RSEs showed different degrees of enrichment.The“grain size effect”has little effect on the RSE content of columnar sediments in the Okinawa Trough;analysis and judgment show that seawater surface productivity is the main factor affecting the redox environment of sediments,and RSE is achieved through the adsorption or desorption of Mn(hydrogen)oxides enrichment and loss.Indicators such asδCe,V/(V+Ni),Ni/Co and V/Cr indicate that the sediment is in an oxic-dysoxic water environment.The Mn element in the sediment diffuses upward in the form of Mn^(2+)through reduction,and is oxidized and enriched by oxygen-containing interstitial water at 25−30 cm to form a manganese peak.The 0−25 cm columnar sediment is in an oxic water column,and 25−30 cm is in a dysoxic water column.