Letter abstract
Nature Geoscience 1, 597 - 600 (2008)
Published online: 31 August 2008 | doi:10.1038/ngeo282
Subject Categories: Biogeochemistry | Palaeoclimate and palaeoceanography
The isotopic signature of the global riverine molybdenum flux and anoxia in the ancient oceans
C. Archer & D. Vance
Despite its important biological and biogeochemical consequences1, 2, 3, the identification of extensive oceanic anoxia in the geological record is controversial. In particular, global anoxia is difficult to distinguish from spatially restricted anoxia in the deep ocean, or in tectonically isolated basins such as the modern Black Sea. The marine isotope geochemistry of molybdenum (Mo) can help quantify the past oxygenation state of the ocean4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, because to first approximation under oxic conditions lighter isotopes of Mo are preferentially removed to sediments, whereas in euxinic conditions quantitative removal leads to no fractionation. However, the isotopic composition of the Mo input from rivers, the main contributor of Mo to the oceans, is poorly constrained and had been assumed to be isotopically comparable to the narrow range found in a small dataset of continental rocks4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14. Here we present an isotopic analysis of Mo in a set of rivers that together account for 22% of the global riverine water discharge. We find a broad range of variability in the Mo isotopic composition of these rivers, with almost all samples enriched in the heavy isotopes compared with continental rocks. Our data remove key uncertainties associated with the marine Mo isotope budget14 and strongly suggest near-total anoxia in the mid-Proterozoic ocean8 as well as during Mesozoic ocean anoxic events13.
- Bristol Isotope Group, Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol BS8 1RJ, UK
Correspondence to: C. Archer e-mail: c.archer@bristol.ac.uk
MORE ARTICLES LIKE THIS
These links to content published by NPG are automatically generated.
NEWS AND VIEWS
Ruling in the improbableNature News and Views (17 Jun 1993)
Acid rain at the K/T boundaryNature News and Views (29 Aug 1991)
See all 9 matches for News And ViewsRESEARCH
Tracing the stepwise oxygenation of the Proterozoic oceanNature Letters to Editor (27 Mar 2008)
Biomarker evidence for green and purple sulphur bacteria in a stratified Palaeoproterozoic seaNature Letters to Editor (06 Oct 2005)
See all 62 matches for Research
