EVIDENCE FOR INCREASED OCEAN OXYGENATION DURING THE RECOVERY OF THE PALEOCENE–EOCENE THERMAL MAXIMUM

The rate and magnitude of the release of carbon that characterizes the Paleocene-Eocene Thermal Maximum (PETM; ~55.9 Ma) and the most recent climate perturbation make it the best analogue to study to better constrain modern climate scenarios. The mechanism(s) triggering the PETM remain debated but include a bolide impact and/or release of greenhouse gases via volcanoes, wildfires, or other marine and terrestrial carbon reservoirs, which all produce isotopically light sources of carbon. The sharp ~3‰ negative carbon isotope excursion defines the PETM and suggests a major perturbation to the global carbon cycle through the release of isotopically light carbon to the ocean-atmosphere system. In addition to warming, other environmental perturbations during this event include ocean acidification, permafrost loss, and a small increase in global euxinia (anoxic and sulfidic water column). There is limited evidence, however, for widespread deoxygenation or organic carbon burial, which contrasts the PETM with Mesozoic oceanic anoxic events. This research aims to better constrain the global spatiotemporal redox structure across the PETM global oceans using both novel and traditional geochemical tools.

We analyzed samples from IODP Expedition 302, Site M0004-A using a suite of novel geochemical proxies such as trace metal concentrations, iron speciation, and thallium isotopes to constrain the local and global redox conditions before, during, and after the PETM. Thallium isotopes – a novel proxy that responds to the global burial of manganese oxides across short-term redox events and thus tracks earliest changes in marine oxygenation – suggest that reducing conditions prevailed before and during the carbon isotope excursion, followed by more oxic conditions during the recovery of the event, or that the basin was restricted before the event and became more connected to the oxic open ocean. Potential restriction may impact conclusions of previous geochemical work on the same samples. If this is a global signal, then it suggests the ocean can rapidly reoxygenate in the wake of a climate perturbation, which has important implications for modern deoxygenation. To corroborate these data, additional sections will be analyzed to constrain the global vs. local signatures for thallium isotopes and other geochemical data.