Biogenic magnetite reveals marine deoxygenation during the Paleocene-Eocene Thermal Maximum

Magnetotactic bacteria produces biogenic magnetite in marine environments with low oxygen (O₂) concentrations. These conditions are typical of past global warming events, which has led to generation of biogenic magnetite records that have been interpreted as proxies for O₂ variability. However, biogenic magnetite is still poorly studied and there are no records of this mineral in land-based sections. Here, we present a new biogenic magnetite record for the Palaeocene-Eocene Thermal Maximum interval of the land-based Contessa Road section (Gubbio, Italy). We quantified biogenic magnetite in the marine sedimentary rocks of Contessa Road with new geochemical, rock magnetic and electron microscopy data, which indicate that biogenic magnetite contents increase during the PETM body phase and reduce in coincidence with the PETM recovery. These patterns are similar to those of the stable carbon/oxygen isotopes, and reveal warming-induced deoxygenation in the Contessa Road setting in the PETM peak phase, and gradual marine reoxygenation during the PETM interval of carbon uptake. Our results are compared to a new model that confirms strong coupling between the carbon and oxygen cycles during the PETM.