Rapid Decline in Global Marine Oxygen During Carbon Excursion of the Paleocene-Eocene Thermal Maximum (PETM)

The geologically instantaneous release of massive quantities of isotopically light carbon during the most recent abrupt climate perturbation, the Paleocene-Eocene Thermal Maximum (PETM; ~55.9 Ma), makes it the best and most recent analog to better understand future climate scenarios. There is a negative carbon isotope shift that suggests a major perturbation to the global carbon cycle due to an abrupt release of isotopically light carbon from various sources of methane. The large addition of carbon to the ocean-atmosphere system likely caused a cascade of events that started extreme warming and had additional impacts such as ocean acidification, permafrost loss, and a small increase in global euxinia (anoxia with sulfide in the water column). There is, however, limited evidence for widespread deoxygenation leading to enhanced burial of organic carbon, which contrasts the PETM to other periods of oceanic anoxic events (OAEs). 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 the Arctic (IODP Expedition 302, Site M0004-A) and the North American Atlantic Coastal Plain (Cambridge-Dorchester Airport) using geochemical proxies including trace metal concentrations, iron speciation, and thallium isotopes to constrain the local and global redox conditions throughout the PETM. Trace metal and iron speciation proxies tracking local conditions suggest that the Arctic experienced persistent euxinia while the Atlantic Coastal Plain maintained an anoxic water column during the PETM. Thallium isotopes a new global proxy that responds to the global burial of manganese oxides for short-term events and thus tracks the earliest marine (de)oxygen perturbation record a rapid loss of global oxygen that appears to recover before the carbon isotope record returns to pre-event values. This suggests that marine anoxic seafloor area expanded during the initial phase of the PETM. An expansion of deoxygenation from the PETM provides a template for warming events and thus has important implications for modern and future anthropogenic warming scenarios.