Long Term Variations of Uranium Isotopes and Radiocarbon in the Surface Seawater Recorded in Corals

Abstract. U-series isotopes and radiocarbon are extensively used for dating and as tracers of various processes during the late Quaternary. Advanced, mass spectrometric U-Th and radiocarbon isotope ratio measurement techniques, as opposed to detection of decay products, routinely achieve high temporal precision with smaller sample sizes. Thermal ionization mass spectrometry (TIMS) in U-series dating, and accelerator mass spectrometry (AMS) in 14C dating, have enabled significant advances in each field. In this paper, we review the techniques of TIMS U-series dating and AMS methods for radiocarbon dating as applied to corals. Coupled measurements of U-isotopes and 14C in corals provide enhanced insights into past changes in climate. Radiocarbon measurements in Papua New Guinea corals from Huon Peninsula terraces of the last glacial period, dated by U-series, show large discrete 14C peaks which appear to be correlated with reorganizations of the North Atlantic thermohaline circulation and Heinrich events. Residence time of Uranium in the oceans with respect to riverine inflow is estimated to be about 300–600 thousand years, a time span accessible to U-series disequilibrium dating of corals which concentrate U from seawater in their skeletons. Measurements of the 234U/238U ratio in the glacial-age Huon Peninsula corals, when combined with previous data, indicate long term variations in 234U in seawater by up to about 7%. The variations appear to be linked to major glacial-interglacial climate transitions and to sea-level changes