Coupled uranium isotope and sea-level variations in the oceans

Globally, rivers supply uranium to the oceans with excess U-234 relative to secular equilibrium and U-234 taken-up by corals can be used for dating. In addition, the U-234 abundance in sea water, at the time the coral was growing, can be measured independently. The veracity of U-series ages used in determining past sea-level variations is dependent on selecting pristine corals free from diagenetic alteration. A quantitative test for alteration assumes invariant U-234 abundances in the oceans for at least the past half a million years and results from samples outside of a narrow range in modern ocean U-234 abundance are excluded from data sets. Here, we have used previously published data to show that U-234 in the oceans appears to be variable and directly related to changes in sea-level, not only over long glacial-interglacial timescales but also at very short, centennial timescales. Most of the previously discarded data can be used to provide valuable additional sea-level information. The process permits a unique insight into the interplay between sources and sinks of uranium in the oceans mediated by sea-level changes at rates far faster than previously thought possible. Similar, rapid sea-level, forcing of other trace element abundances in the oceans is likely. Crown copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.