Iron fertilization-induced deoxygenation of Eastern Equatorial Pacific intermediate waters during the Paleocene-Eocene Thermal Maximum

Thousands of gigatons (~2500-4500 Gt) of carbon were released into the ocean and atmosphere system over several thousand years during the Paleocene-Eocene Thermal Maximum (PETM, ca. 56 Ma), a transient period of global warming, is considered an important analog for future greenhouse conditions. It was accompanied by a significant carbon cycle perturbation, intensified weathering and hydrological cycling, and ocean deoxygenation. Although ocean deoxygenation across the PETM is reported widely, its mechanism in the open ocean remains uncertain. We here present magnetic and geochemical analyses of sediments from the Eastern Equatorial Pacific (EEP) Ocean. We find that iron fertilization during the PETM by eolian dust and volcanic eruptions fueled EEP ocean productivity. This process led to increased organic matter degradation and oxygen consumption in intermediate waters, leading to deoxygenation. Our findings suggest that iron fertilization could be an important driver of open ocean oxygen loss, as a side effect of global warming. Our observation is important in the emerging discussion of how global warming will reduce dissolved oxygen in the open ocean and, in turn, affect the marine fishery industry and future food security.