Unravelling the controls on the molybdenum isotope ratios of river waters

Horan, K. and Hilton, R. G. and McCoy-West, A. J. and Selby, D. and Tipper, E. T. and Hawley, S. and Burton, K.W. (2020) Unravelling the controls on the molybdenum isotope ratios of river waters. Geochemical Perspectives Letters, 13. pp. 1-6. ISSN 2410-3403 DOI https://doi.org/10.7185/geochemlet.2005

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Abstract

The molybdenum (Mo) isotope ratios (δ98/95Mo) of river waters control the δ98/95Mo values of seawater and impact on the use of Mo isotope ratios as a proxy of past redox conditions. The δ98/95Mo values of river waters vary by more than 2 ‰, yet the relative roles of lithology versus fractionation during weathering remain contested. Here, we combine measurements from river waters (δ98/95Modiss), river bed materials (δ98/95MoBM) and soils from locations with contrasting lithology. The δ98/95Mo values of river bed materials (δ98/95MoBM), set by rock type, vary by ~1 ‰ between rivers in New Zealand, the Mackenzie Basin, and Iceland. However, the difference between dissolved and solid phase Mo isotopes (Δ98/95Modiss-BM) varies from +0.3 ‰ to +1.0 ‰. We estimate Mo removal from solution using the mobile trace element rhenium and find that it correlates with Δ98/95Modiss-BM across the sample set. The adsorption of Mo to Fe-Mn-(oxyhydr)oxides can explain the observed fractionation. Together, the amount of Mo released through dissolution and taken up by (oxyhydr)oxide formation on land may cause changes in the δ98/95Mo values of rivers, driving long term changes in the Mo isotope ratios of seawater.

Item Type:	Article
Uncontrolled Keywords:	2019AREP; IA76
Subjects:	01 - Climate Change and Earth-Ocean Atmosphere Systems 07 - Sedimentary Geology
Divisions:	01 - Climate Change and Earth-Ocean Atmosphere Systems 07 - Gold Open Access 11 - Sedimentary Geology
Journal or Publication Title:	Geochemical Perspectives Letters
Volume:	13
Page Range:	pp. 1-6
Identification Number:	https://doi.org/10.7185/geochemlet.2005
Depositing User:	Sarah Humbert
Date Deposited:	15 Apr 2020 00:05
Last Modified:	15 Apr 2020 00:05
URI:	http://eprints.esc.cam.ac.uk/id/eprint/4680

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