The utility of chromium isotopes as a redox tracer

English Abstract:

Advances in mass spectrometry allowing for the routine and precise measurement of metal stable isotope distributions in natural materials have revolutionized geochemistry. In particular, transition metal isotope systems have provided unique insight into the chemical evolution of Earth’s ocean-atmosphere system on a range of timescales. However, the oceanic isotope mass balance of a given trace element and the fidelity of signal transmission into the sedimentary record are typically governed by a complex array of syn- and post-depositional processes. As a result, the ultimate utility of a metal isotope system is context-dependent and often quite different from that initially anticipated. This talk will focus on the chromium (Cr) isotope system as both a paleoceanographic proxy and a potential ‘paleobarometer’ for atmospheric pO₂ levels. Some recent applications of Cr isotopes to ancient sedimentary rocks and modern marine sediments will be discussed, along with data from a range of high- and low-temperature systems that help to constrain processes that do and do not induce significant stable Cr isotope fractionation near Earth’s surface. In addition, the primary gaps and current frontiers in our understanding of modern Cr isotope mass balance at Earth’s surface and how it has evolved with time will be highlighted.