In recent decades, the ocean has experienced substantial oxygen loss, affecting marine ecosystems and fisheries. However, the future response of ocean deoxygenation to global warming remains controversial. The history of ocean deoxygenation can offer important mechanistic insights into its future evolution. Of particular interest is the Paleocene-Eocene Thermal Maximum (PETM), where the magnitude of carbon emission is analogous to the RCP8.5 scenario. Recent studies suggest that the impact of global warming on ocean deoxygenation during the PETM is more complex than previously understood, highlighting the need for further investigation into the extent and spatial distribution of oxygen-deficient zones (ODZs). Here, we present coupled records of foraminifera-bound nitrogen isotopes, marine barite sulfur isotopes, and ocean productivity from the same cores in the South Atlantic. Integrated into isotope-enabled box models, these data suggest the development of “ammonium-type” ODZs and increasing N2 fixation during the PETM. Simulations of cGENIE support the expansion of ODZs from suboxia to anoxia in the subsurface Atlantic, which is a combined effect of global warming and enhanced productivity. Our findings highlight the potential spatial variability of ocean deoxygenation in a warming world - while the Pacific might experience different oxygenation conditions, parts of the Atlantic thermocline water likely became anoxic during the PETM.
 

deoxygenation,oxygen-deficient zones,nitrogen cycle,marine barite,Paleocene-Eocene Thermal Maximum