摘要
氧化还原敏感微量元素Re、Mo和U主要依靠扩散作用通过沉积物—水界面,在不同氧化还原条件下的沉积物中自生富集,Re在轻度还原的次氧化沉积环境中富集,Mo在还原性更强的硫化环境中富集,而U具有较宽的富集沉积深度区间。Re、Mo和U独特的地球化学行为使其可用于指示海洋环境的氧化还原状态,其在沉积物中的自生富集程度与沉积时所处的氧化还原条件具有良好的相关性:Re、Mo和U在氧化沉积环境(Re/Al<1.3×10^(-7),Mo/Al<0.4×10^(-4))和季节性缺氧区覆盖的沉积环境中富集程度较小,在常年性缺氧区覆盖的沉积环境(U/Al>5×10^(-4),Mo/Al>5×10^(-4))和硫化沉积环境(Mo/Al>5×10^(-4))中富集程度较大。除依据其地球化学行为特征和相对富集程度进行定性分析之外,还可以结合元素富集系数(TM_(EF)<1表示亏损,TM_(EF)>1表示富集,TM_(EF)>3表示明显富集,TM_(EF)>10表示强烈富集)、元素比值(Re/Mo≤0.3×10^(-3)指示氧化环境,Re/Mo≈10×10^(-3)~30×10^(-3)指示缺氧环境,Re/Mo≈0.7×10^(-3)~0.8×10^(-3)指示硫化环境)、元素共变体系(Mo_(EF)/U_(EF)≈0.1×现代海水值~0.3×现代海水值指示氧化—次氧化环境,Mo_(EF)/U_(EF)>1×现代海水值指示缺氧环境,Mo_(EF)/U_(EF)≈3×现代海水值~10×现代海水值指示硫化环境)以及同位素(氧化沉积环境中δ^(98/95)Mo≈-0.7‰,次氧化沉积环境中δ^(98/95)Mo≈-0.5‰~+1.3‰,缺氧沉积环境中δ^(98/95)Mo≈+1.6‰,硫化沉积环境中δ^(98/95)Mo≈+2.2‰~+2.5‰)等进行综合定量判别。值得关注的是,目前Re、Mo和U的氧化还原迁移转化机制尚未完善,现代海洋系统的数据较为有限,Re、Mo和U富集程度的区域分异性和高度可变性仍有待进一步研究。未来仍需要更多的现代海洋系统氧化还原敏感微量元素数据和应用实例,以更好地与古海洋体系相结合来完善氧化还原敏感微量元素指标的指示作用。
Redox Sensitive Trace Elements(RSE),such as Re,Mo,and U,are often autogenetically enriched in sediments because of their different solubilities and/or affinities for particulates under various redox states at the time of sediment deposition when diffusing through the sediment-water interface.The enrichment of Re is primarily in a suboxic depositional environment but that of Mo is in an euxinic environment.In contrast,U has a relatively large depositional depth range in sediments.The special geochemical behavior of the RSEs makes it possible to indicate the redox state,as the autogenetic enrichment degrees in sediments have a good correlation with the redox conditions of marine sedimentary environments.Lower enrichments were recorded from sediments deposited in oxic(Re/Al<1.3×10^(-7),Mo/Al<0.4×10^(-4))and beneath seasonal oxygen minimum zone environments,while higher enrichments were recorded from sediments deposited within the perennial oxygen minimum zone(U/Al>5×10^(-4),Mo/Al>5×10^(-4))and euxinic(Mo/Al>5×10^(-4))environments.In addition to the relative enrichment degree,the paleoredox proxies of the enrichment coefficient(TM_(EF)<1 means depletion;TM_(EF)>1 means enrichment;TM_(EF)>3 means obvious enrichment;TM_(EF)>10 means significant enrichment),trace elements ratios(Re/Mo≤0.3×10^(-3)indicates an oxic environment;Re/Mo≈10×10^(-3)~30×10^(-3)indicates an anoxic environment;Re/Mo≈0.7×10^(-3)~0.8×10^(-3)indicates an euxinic environment),the trace elements covariant system(Mo_(EF)/U_(EF)≈0.1×modern seawater value~0.3×modern seawater value indicates an oxic-suboxic environment;Mo_(EF)/U_(EF)>1×modern seawater value indicates an anoxic environment;Mo_(EF)/U_(EF)≈3×modern seawater value~10×modern seawater value indicates an euxinic environment),and isotope values(δ^(98/95)Mo≈-0.7‰in an oxic environment;δ^(98/95)Mo≈-0.5‰~+1.3‰in a suboxic environment;δ^(98/95)Mo≈+1.6‰in an anoxic environment;δ^(98/95)Mo≈+2.2‰~+2.5‰in an euxinic environment)could also be utilized to com
作者
张晓潼
袁华茂
宋金明
段丽琴
ZHANG Xiaotong;YUAN Huamao;SONG Jinming;DUAN Liqin(CAS Key Laboratory of Marine Ecology and Environmental Sciences,Institute of Oceanology,Chinese Academy of Sciences,Qingdao 266071,China;University of Chinese Academy of Sciences,Beijing 100049,China;Marine Ecology and Environmental Science Laboratory,Pilot National Laboratory for Marine Science and Technology,Qingdao 266237,China;Center for Ocean Mega-Science,Chinese Academy of Sciences,Qingdao 266071,China)
出处
《地球科学进展》
CAS
CSCD
北大核心
2022年第4期358-369,共12页
Advances in Earth Science
基金
中国科学院战略先导性专项“近海环境健康评估技术与海域评估方案”(编号:XDA23050501)
国家自然科学基金面上项目“微生物对富营养化近海沉积物砷循环的调控机制解析:以长江口为例”(编号:41976037)资助.
