Coupled uranium isotope and sea-level variations in the oceans

Abstract

Globally, rivers supply uranium to the oceans with excess 234U relative to secular equilibrium and 234U taken-up by corals can be used for dating. In addition, the 234U 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 234U 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 234U abundance are excluded from data sets. Here, we have used previously published data to show that 234U 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.