{"refrec":{"BRefID":341129,"RR":"<b>He, Z.; Clarkson, M.O.; Andersen, M.B.; Archer, C.; Sweere, T.C.; Kraal, P.; Guthauser, A.; Huang, F.; Vance, D.</b> (2021). Temporally and spatially dynamic redox conditions on an upwelling margin: The impact on coupled sedimentary Mo and U isotope systematics, and implications for the Mo-U paleoredox proxy. <i>Geochim. Cosmochim. Acta 309</i>: 251-271. <a href=\"https://dx.doi.org/10.1016/j.gca.2021.06.024\" target=\"_blank\">https://dx.doi.org/10.1016/j.gca.2021.06.024</a>","BEntID":337764,"PublicFlag":1,"CheckedFlag":0,"wosflag":1,"vabbflag":1,"RefStringPartII":". <i>Geochim. Cosmochim. Acta 309</i>: 251-271. <a href=\"https://dx.doi.org/10.1016/j.gca.2021.06.024\" target=\"_blank\">https://dx.doi.org/10.1016/j.gca.2021.06.024</a>","DocTypID":8,"DocType":"Journal article","MarineFlag":0,"FreshFlag":0,"BrackishFlag":0,"TerrestrialFlag":0,"Authorstring":"He, Z.; Clarkson, M.O.; Andersen, M.B.; Archer, C.; Sweere, T.C.; Kraal, P.; Guthauser, A.; Huang, F.; Vance, D.","OrigTitleTranslFlag":0,"Authorstringtrunc":"He, Z. <i>et al.</i>","Englishabstract":"The abundances and isotope compositions of molybdenum (Mo) and uranium (U)    in ancient sediments are promising tracers of the redox state of the past    ocean, whose basis lies in the environmentally dependent Mo and U isotope    signatures in modern oceanic settings. Despite their dominance in oceanic    budgets, the controls on the Mo-U systematics of upwelling margin sediments    remain to be fully understood. Here we present a comprehensive    sediment-porewater Mo and U isotope study in the Benguela upwelling system    off Namibia, including the first dataset incorporating coupled Mo-U    abundance and isotope analysis of both solid authigenic phases and    porewaters.</p><p>    The investigated stations represent shelf-to-slope settings, which lie on    the upper edge, within and below the oxygen minimum zone (OMZ) of the South    Atlantic. The sediments across all stations share similar characteristics:    both Mo and U show increasing authigenic enrichment with depth, coupled to    an overall decrease in δ<sup>98</sup>Mo<sub>auth</sub> (from ~2.0‰ to 1.3‰    and from ~2.0‰ to 0.3‰) and increase in δ<sup>238</sup>U<sub>auth</sub>    (from −0.18‰ to 0.05‰ and from −0.34‰ to −0.21‰). Nevertheless, the extents    of Mo and U enrichment and associated isotopic fractionations display    spatial variability across the OMZ, reflecting variations in local    sedimentary redox conditions. Porewater Mo and U concentration patterns are    more complex, exhibiting peaks in Mo and U abundance well in excess of    seawater (up to 8 times seawater for Mo) associated with correlated shifts    in isotope composition. As a result, porewaters exhibit a wide range in    isotope compositions, between 0.90‰ and 2.79‰ for δ<sup>98</sup>Mo and    between −1.74‰ and 0.26‰ for δ<sup>238</sup>U.</p><p>    Porewater gradients at the time of sampling are inconsistent with diffusion    downwards across the sediment–seawater interface as a means of enrichment    of the sediment-porewater system. Though these sampled conditions may    represent only a snapshot, so that periodically more reducing conditions    could lead to concentration gradients that do permit downward diffusion,    the data are also readily explained by addition of Mo and U to the    sediment-porewater system in particulate form, also under more reducing    conditions than at the time of sampling. For example, sequestration of Mo    and U to particulate matter as a result of the presence of intermittent    sulfide, either in bottom water or in porewater right at the sediment–water    interface, explains much of the geochemical and isotope data.</p><p>    The data thus suggest that the early diagenetic enrichment of Mo and U in    sediments of upwelling margins is strongly governed by temporal redox    fluctuations. Early diagenesis under these dynamic redox conditions on the    Namibian upwelling margin are strongly reflected in Mo-U co-variation    patterns, as well as anti-correlations between authigenic δ<sup>98</sup>Mo    and δ<sup>238</sup>U in sediments. Overall, our new data demonstrate that    early diagenetic processes on open-marine continental margins reproduce    patterns previously observed for coupled Mo-U isotope systematics in    restricted and semi-restricted basins, but via a different set of processes    and with important implications for the use of such a coupled approach in    the study of ancient marine anoxia.","AbstractOtherLang":null,"BibLvlCode":"AS","StandardTitle":"Temporally and spatially dynamic redox conditions on an upwelling margin: The impact on coupled sedimentary Mo and U isotope systematics, and implications for the Mo-U paleoredox proxy","OrigTitleLangCode":"en","OrigTitleLangCodeExtended":"eng","OrigTitleLangID":15,"DateLastModified":{"date":"2026-04-26 01:32:04.828276","timezone_type":1,"timezone":"+02:00"},"UserAccessRight":null,"UserAccID":null,"AuthorKeywords":"Mo isotopes; U isotopes; Porewater; Continental margin sediments; OMZ","OtherDescriptors":null,"Notes":null,"AnaPub":2021,"MonPub":null,"DateUpdate":"2021-08-05","DateCreate":"2021-08-05","SecASFANote":null,"ConfID":null,"PeerRev":1,"VlizCoreFlag":1,"WoScode":"WOS:000682950000015","VABBcode":null,"OpenAcc":1,"DOI":"10.1016/j.gca.2021.06.024"},"refs":null,"anarec":{"AnaID":341129,"PubliDate":2021,"Pagination":"251-271","XtraPublOfAnaID":null,"ISBN":null,"Volume":"309","Issue":null,"BRefMon":null,"BRefMonRR":null,"BRefXtra":null,"BRefXtraRR":null,"SerBRefID":42901,"SerRR":"Geochimica et Cosmochimica Acta. 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