University of Otago Geology Seminar
A Southern Ocean uranium isotope record since the last glaciation (~ 32 ka to present): reliability of a paleo redox proxy with Marie Hennequin, ENS de Lyon, France
The rise and fall of oxygen in the oceans and atmosphere has been powerfully interconnected with the evolution of life, carbon-cycle perturbations and major climate re-organisations throughout Earth’s 4.6 billion year history. The uranium (U) isotope system is widely used as a tracer for reconstructing oxygen variations in the past oceans. Today, the oceans are largely oxygenated and U is highly soluble. However, during periods of ocean anoxia, U becomes insoluble and is removed to sediments, inducing U-isotope fractionation in seawater. Evidence suggests that carbonates directly record past seawater U-isotope signatures, and numerous studies have used carbonate U-isotope stratigraphies to quantify the evolution of past ocean oxygenation.
We have acquired a continuous U-isotope record spanning the last 32,000 years in Southern Ocean carbonates (coccolithophore) while the oceans were oxygenated and contained stably dissolved U with a homogenous U-isotope signature. Our new results demonstrate, for the first time, that sizeable U-isotope fractionation can occur in open-ocean carbonate without changes in ocean oxygenation, challenging current assumptions and paving the way for more accurate reconstructions of Earth’s ocean-atmosphere-climate system.
This talk will take place in person in the Benson Common Room (Gn9, Geology Building) AND will be available live on Zoom at the following link: https://bit.ly/otagogeology.
Contact: matt.druce@otago.ac.nz