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Science 6 August 2004:
Vol. 305. no. 5685, pp. 851 - 854
DOI: 10.1126/science.1099673
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Reports

Climatic Control of Riverine and Seawater Uranium-Isotope Ratios

Laura F. Robinson,*{dagger} Gideon M. Henderson, Lisa Hall,{ddagger} Iain Matthews

The large variation in the ratio of uranium-234 to uranium-238 (234U/238U) in rivers is not well understood, but may provide information about past weathering and rainfall and is important because it controls seawater (234U/238U). Here, we demonstrate the importance of physical weathering and rainfall for (234U/238U), using rivers from South Island, New Zealand. These data allow interpretation of an existing speleothem (234U/238U) record and suggest that New Zealand glacier advance 13,000 years ago was influenced by increased rainfall rather than by Younger Dryas–like cooling. A model of seawater (234U/238U) during glacial cycles indicates that rejection of corals based on modern (234U/238U) ± <0.01 is not merited and may reject the highest quality ages.

Department of Earth Sciences, University of Oxford, Parks Road, Oxford, OX1 3PR, UK.



{dagger} Present address: California Institute of Technology, MS 100-23, 1200 East California Boulevard, Pasadena, CA 91125, USA.

{ddagger} Present address: RMS Inc., 7015 Gateway Boulevard, Newark, CA 94560, USA.

* To whom correspondence should be addressed. E-mail: laurar{at}gps.caltech.edu

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