Adsorption of Th and Pa onto particles and the effect of organic compounds in natural seawater  

作　　者：Xinxing ZHANG Weifeng YANG Yusheng QIU Minfang ZHENG 

机构地区：[1]College of Ocean and Earth Sciences,Xiamen University,Xiamen 361102,China [2]North China Sea Environmental Monitoring Center,State Oceanic Administration,Qingdao 266033,China [3]State Key Laboratory of Marine Environmental Science,Xiamen 361102,China

出　　处：《Journal of Oceanology and Limnology》2021年第6期2209-2219,共11页海洋湖沼学报（英文）

基　　金：Supported by the National Natural Science Foundation of China(Nos.42076030,41476061)and;National Key Basic Research Special Foundation Program of China(No.2015CB452902)。

摘　　要：^(231)Pa and ^(230)Th are two crucial isotopes in the ongoing GEOTRACES Project.However,the controversy on ^(231)Pa/^(230)Th proxy pertaining to archiving ocean circulation or recording paleoproductivity,is still unresolved,partly owing to the unclear understanding of fractionation between ^(231)Pa and ^(230)Th during adsorption.In this study,controlled experiments were conducted to examine the adsorption of ^(234)Th and ^(233)Pa onto biogenic particles(SiO_(2) and CaCO_(3)),authigenic minerals(MnO_(2) and Fe_(2)O_(3)),and lithogenic minerals(kaolinite,attapulgite,montmorillonite,and aluminum oxyhydroxides),and the role of organic compounds in regulating the adsorption of ^(234)Th and ^(233)Pa in natural seawater was evaluated.The distribution coefficients(K d,presented as logK_(d))varied from 3.56 to 6.05 and from 3.27 to 5.82 for ^(234)Th and ^(233)Pa,respectively.Fe_(2)O_(3) is the strongest sorbent for both ^(234)Th and ^(233)Pa.Most of the particles showed comparable logK_(d) values for either ^(234)Th(~4.8)or ^(233)Pa(~3.9)in the presence of dextran,indicating that the adsorption of Th and Pa is likely controlled by organic coating on particle surfaces.The fractionation factors(F Th/Pa)of SiO_(2)(3±1)and CaCO_(3)(33±1)suggest in situ observed preferential scavenging of ^(230)Th to ^(231)Pa in the surface water of low-to mid-latitude regions and the nearly equal removal in the Antarctic Ocean where biogenic silica dominates the particle regime.The F Th/Pa values of the lithogenic and biogenic particles indicate that ^(230)Th is scavenged prior to ^(231)Pa in the particle-scarce ocean interior.The equal scavenging of ^(230)Th and ^(231)Pa at the ocean margins and the ridge crests is dominated by high particle fl uxes instead of particle composition control.These results imply that ^(230)Th/^(231)Pa can be used as different proxies in different oceanic settings.

关 键 词：THORIUM protactinium PALEOPRODUCTIVITY CIRCULATION particle dynamics 

分 类 号：P736.4[天文地球—海洋地质]