Award: OCE-1624895

Quantifying the amount of oxygen in specific regions of the ocean is important as it is a required electron acceptor for animals. However, tracking the earliest changes in bottom water oxygen conditions has been elusive as the scientific community has lacked a reliable chemical (or biological) proxy to fingerprint such environments. Most of the geochemical signatures are highly efficient at recording well-oxygenated conditions or very reducing conditions which produce sulfide in the water column. Vanadium isotopes were investigated in this research to better constrain low but non-zero oxygen conditions in our modern ocean to investigate the utility of the proxy. Being able to fingerprint variable low oxygen conditions in the geological record is important as these could be related to various types of extinction events and the wide-spread burial of organic carbon (hydrocarbon reservoirs). This is especially important as recent studies suggest our modern ocean is losing oxygen which is likely related to warming oceans which likely occurred in the ancient record but we need better tools to investigate such changes. Thus, this research has provided the framework to investigate low marine oxygen conditions using vanadium isotopes in the ancient record to better understand the interconnection with biological and climatic perturbations. Our results have provided the first analysis of sediments with a range of oxygen conditions in the modern ocean and seawater values. This work suggests that there is a progressively larger isotope fractionation in more settings with more oxygen thus vanadium isotopes have the potential to track oxygen contents. A natural complement to this vanadium isotope study was to apply another unexplored redox proxy, thallium isotopes, to these sediments and test the proxy. The combination of multiple proxies to gather a more robust and complete redox picture of the ocean is required especially for the ancient record. Thallium isotopes had a strong framework as there has been a wide breath but we provided a new avenue of research. Our work has shown that deoxygenation of the oceans occurs at the onset of volcanism and warming which is prior to widespread carbon burial. Thus, the earliest signs of climatic disturbances could be warming induced deoxygenation. This work has highlighted the fact that vanadium and thallium isotopes can track local and global increases in non-sulfidic anoxia. Thus, we need to continue to probe the geological record with these new proxies to better understand the natural feedbacks associated with oceanic oxygenation and the severity of the biological record with such variability. Last Modified: 01/31/2019 Submitted by: Jeremy D Owens