Uranium Isotope Fractionation in Non-sulfidic Anoxic Settings and the Global Uranium Isotope Mass Balance - INSU - Institut national des sciences de l'Univers Access content directly
Journal Articles Global Biogeochemical Cycles Year : 2020

Uranium Isotope Fractionation in Non-sulfidic Anoxic Settings and the Global Uranium Isotope Mass Balance

Devon B. Cole
  • Function : Author
Noah J. Planavsky
  • Function : Author
Martha Longley
  • Function : Author
Philipp Böning
  • Function : Author
Daniel Wilkes
  • Function : Author
Xiangli Wang
  • Function : Author
Elizabeth D. Swanner
  • Function : Author
Chad Wittkop
  • Function : Author
David K. Loydell
  • Function : Author
Andrew C. Knudsen
  • Function : Author
Erik A. Sperling
  • Function : Author

Abstract

Uranium isotopes (238U/235U) have been used widely over the last decade as a global proxy for marine redox conditions. The largest isotopic fractionations in the system occur during U reduction, removal, and burial. Applying this basic framework, global U isotope mass balance models have been used to predict the extent of ocean floor anoxia during key intervals throughout Earth's history. However, there are currently minimal constraints on the isotopic fractionation that occurs during reduction and burial in anoxic and iron-rich (ferruginous) aquatic systems, despite the consensus that ferruginous conditions are thought to have been widespread through the majority of our planet's history. Here we provide the first exploration of δ238U values in natural ferruginous settings. We measured δ238U in sediments from two modern ferruginous lakes (Brownie Lake and Lake Pavin), the water column of Brownie Lake, and sedimentary rocks from the Silurian-Devonian boundary that were deposited under ferruginous conditions. Additionally, we provide new δ238U data from core top sediments from anoxic but nonsulfidic settings in the Peru Margin oxygen minimum zone. We find that δ238U values from sediments deposited in all of these localities are highly variable but on average are indistinguishable from adjacent oxic sediments. This forces a reevaluation of the global U isotope mass balance and how U isotope values are used to reconstruct the evolution of the marine redox landscape.
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insu-03584747 , version 1 (24-06-2022)

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Devon B. Cole, Noah J. Planavsky, Martha Longley, Philipp Böning, Daniel Wilkes, et al.. Uranium Isotope Fractionation in Non-sulfidic Anoxic Settings and the Global Uranium Isotope Mass Balance. Global Biogeochemical Cycles, 2020, 34, p. 201-226. ⟨10.1029/2020GB006649⟩. ⟨insu-03584747⟩
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