Multi proxy reconstruction (δ^98/95Mo, δ^238/235U) of global ocean oxygenation during the Early Eocene

Early Eocene climate is characterised by extreme and persistent warmth punctuated by abrupt global warming events (‘hyperthermals’), such as the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma ago), when global temperatures became even warmer. These hyperthermals were associated with perturbations to the global carbon cycle that would have had a profound effect on the distribution of O2 in the oceans. However, the timing and extent of any fluctuations in global ocean oxygenation during these events are still poorly constrained. In this study, we investigate how seawater oxygen levels responded to environmental changes in the early Eocene by determining the Mo and U stable isotope compositions of anoxic sediments from the Arctic Ocean obtained by the Integrated Ocean Drilling Program Expedition 302. It has previously been shown that these two isotope systems each respond to changes in seawater oxygen levels and that they may be used to reconstruct the extent of global marine anoxia in Earth’s past. Furthermore, since Mo and U have different residence times in the oceans and their isotope fractionations display different sensitivities to dissolved oxygen concentrations, the use of both proxies enables us to estimate past changes in seawater oxygenation with greater confidence. By combining the information provided by these two isotope systems, we are able to better constrain the onset and the severity of the episodes of seawater anoxia during the Eocene, thereby allowing us to better understand the Earth processes that control ocean oxygenation levels