Neodymium isotopes in authigenic phases, bottom waters and detrital sediments in the Gulf of Alaska and their implications for paleo-circulation reconstruction

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• 作者：Jianghui Du ; ^{dujia@oregonstate.edu" class="auth_mail" title="E-mail the corresponding author} ; Brian A. Haley ; Alan C. Mix
• 关键词：Authigenic phases ; Pore water ; Detrital sediments ; Neodymium isotope composition ; Early diagenesis ; Sediment-water interaction ; Gulf of Alaska ; North Pacific ; Paleo-circulation
• 刊名：Geochimica et Cosmochimica Acta
• 出版年：2016
• 出版时间：15 November 2016
• 年：2016
• 卷：193
• 期：Complete
• 页码：14-35
• 全文大小：2566 K

文摘

The isotopic composition of neodymium (ε_Nd) extracted from sedimentary Fe–Mn oxyhydroxide offers potential for reconstructing paleo-circulation, but its application depends on extraction methodology and the mechanisms that relate authigenic ε_Nd to bottom water. Here we test methods to extract authigenic ε_Nd from Gulf of Alaska (GOA) sediments and assess sources of leachate Nd, including potential contamination from trace dispersed volcanic ash. We show that one dominant phase is extracted via leaching of core-top sediments. Major and trace element geochemistry demonstrate that this phase is authigenic Fe–Mn oxyhydroxide. Contamination of leachate (authigenic) Nd from detrital sources is insignificant (<1%); our empirical results are consistent with established kinetic mineral dissolution rates and theory. Contamination of extracted ε_Nd from leaching of volcanic ash is below analytical uncertainty. However, the ε_Nd of core-top leachates in the GOA is consistently more radiogenic than bottom water. We infer that authigenic phases record pore water ε_Nd, and the relationships of ε_Nd among bottom waters, pore waters, authigenic phases and detrital sediments are primarily governed by the exposure time of bottom water to sea-floor sediments, rate of exchange across the sediment-water interface and the reactivity and composition of detrital sediments. We show that this conceptual model is applicable on the Pacific basin scale and provide a new framework to understand the role of authigenic phases in both modern and paleo-applications, including the use of authigenic ε_Nd as a paleo-circulation tracer.