Oxygen isotope measurements of marine sulfate.

Turchyn, A. V. and Schrag, D. P. (2003) Oxygen isotope measurements of marine sulfate. ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 229 (Part 1). 055-GEOC.

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Sulfate plays an important role in the modern ocean, serving as the primary oxidant for much of the organic matter and nearly all the methane produced in ocean sediments, yet the biogeochemical cycle of marine sulfate is assumed to be relatively stable with a long residence time of over 10 million years. Nearly all investigations into the long term dynamics of the marine sulfate cycle have focused on the sulfur isotopes of reduced sulfate deposits, primarily pyrite, and most have concluded that marine sulfate concentrations were low in the Archean, increased in the Proterozoic to modern values, and have remained more or less unchanged through much of the Phanerozoic. Because of the widely varying oxygen isotopic composition of the various sources and sinks of sulfate to the ocean, we suggest that temporal variations in the oxygen isotopes of marine sulfate may provide a closer look at the dynamics of the biogeochemical sulfate cycle. We present a continuous record of oxygen isotopes in marine sulfate measured in marine barite over the last 10 million years. Large shifts in the oxygen isotopic composition of marine sulfate, including a decrease of 6 per mil over the past 2.5 million years, indicate that the marine sulfate cycle is far more dynamic than previously thought. We use these measurements with a numerical model to explore changes in marine sulfate over the past 10 million years. Although many parameters in the sulfate budget are not well constrained, we identify several scenarios which can explain the observed pattern of oxygen isotopic variations. We suggest that changes in the sulfate cycle are linked closely to changes in sulfate reduction and sulfide reoxidation on continental shelves, which were affected by the periodic glaciations of the Plio-Pleistocene.

Item Type: Article
Uncontrolled Keywords: NIL AREP; 2003
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Volume: 229
Page Range: 055-GEOC
Depositing User: Sarah Humbert
Date Deposited: 24 Mar 2009 14:35
Last Modified: 23 Jul 2013 09:54
URI: http://eprints.esc.cam.ac.uk/id/eprint/879

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