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Title: Mononuclear to Polynuclear U IV Structural Units: Effects of Reaction Conditions on U‐Furoate Phase Formation
Award ID(s):
1904616 1607905
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Chemistry – A European Journal
Page Range / eLocation ID:
5872 to 5886
Medium: X
Sponsoring Org:
National Science Foundation
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    Speleothem initial uranium isotope ratios ((234U/238U)i) can be influenced by processes along the seepage water flow‐path including alpha‐recoil into porewater during238U decay and hostrock weathering, the balance of which can reflect the infiltration rate. Thus, speleothem (234U/238U)imay provide information about past changes in rainfall amounts. However, the utility of (234U/238U)ias a paleo‐infiltration proxy has only been explored in a limited set of rainfall regimes. We present a speleothem (234U/238U)irecord from Mawmluh Cave in northeast India, an area influenced by the Indian Summer Monsoon, covering 1964–2012 CE. Speleothem (234U/238U)iwas relatively constant from 1964 to 1984 but then linearly increased by 0.05 over ∼15 years, a trend that does not correspond with observed rainfall changes. To evaluate potential drivers of (234U/238U)ivariability, we model the evolution of water (234U/238U) in a simple karst system using an advection‐reaction model parameterized by Mawmluh Cave variables. Although varying infiltration influences modeled water (234U/238U), the larger, sustained change observed in the speleothem record can only be modeled by varying the U concentration and (234U/238U) of the weathering hostrock. This suggests that larger shifts in speleothem (234U/238U)imay result from flow path changes, bringing waters in contact with hostrock of variable U characteristics. Consideration of published Mawmluh Cave records suggests that these mechanisms may also explain variability in stalagmite (234U/238U)ion precessional timescales. Further examination of speleothems (234U/238U)ifrom climates characterized by high rainfall and extensive weathering is warranted to better constrain the controls on (234U/238U)iin these dynamic environments.

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