Authigenic uranium in foraminiferal coatings: A proxy for ocean redox chemistry

Boiteau, Rene and Greaves, Mervyn and Elderfield, Henry (2012) Authigenic uranium in foraminiferal coatings: A proxy for ocean redox chemistry. Paleoceanography, 27 (3). PA3227. DOI

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The rate of uranium accumulation in oceanic sediments from seawater is controlled by bottom water oxygen concentrations and organic carbon fluxes—two parameters that are linked to deep ocean storage of CO2. To investigate glacial-interglacial changes in what is known as authigenic U, we have developed a rapid method for its determination as a simple addition to a procedure for foraminiferal trace element analysis. Foraminiferal calcite acts as a low U substrate (U/Ca < 15 nmol/mol) upon which authigenic U accumulates in reducing sediments. We measured a downcore record of foraminiferal U/Ca from ODP Site 1090 in the South Atlantic and found that U/Ca ratios increase by 70–320 nmol/mol during glacial intervals. There is a significant correlation between U/Ca records of benthic and planktonic foraminiferal species and between U/Ca and bulk sediment authigenic U. These results indicate that elevated U/Ca ratios are attributable to the accumulation of authigenic U coatings in sediments. Foraminiferal Mn/Ca ratios were lower during the glacial intervals, suggesting that the observed U accumulation on the shells is not directly linked to U incorporation into secondary manganese phases. Thus, foraminiferal U/Ca ratios may provide useful information on past changes in sediment redox conditions.

Item Type: Article
Uncontrolled Keywords: 2012AREP; IA64;
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title: Paleoceanography
Volume: 27
Page Range: PA3227
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 05 Oct 2012 16:19
Last Modified: 23 Jul 2013 10:04

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