DEGLACIAL SHOALING OF THE EASTERN EQUATORIAL PACIFIC OXYGEN MINIMUM ZONE

The presence and extent of low-oxygen waters plays a key role in global climate and marine nutrient cycles, with observations suggesting that the Oxygen Minimum Zone (OMZ) is highly responsive to global climatic and oceanographic change. However, it has been difficult to disentangle changes in the extent and intensity of the OMZ in the past given proxy and sample limitations. Here we use a new OMZ tracer (the OMZ-dwelling Globorotaloides hexagonus) during the last deglaciation, to investigate changes in the extensive Eastern Equatorial Pacific OMZ, due to the region’s role as a net source of carbon to the atmosphere over this interval. More specifically, we use the stable isotopes (δ¹⁸O and δ¹³C) from the shells of OMZ-dwelling G. hexagonus to reassess the positioning of the mid-water OMZ relative to both shallow-dwelling planktic and deep benthic foraminiferal records. Oxygen isotope records show a rapid shoaling of OMZ habitat during Heinrich Stadial 1 which persisted through the deglaciation. Meanwhile, δ¹³C similarities between the shells of G. hexagonus and benthic foraminifera suggest a shared source water through the deglaciation and into the Holocene. Together, this supports the deglacial presence of a single massive low oxygen carbon reservoir in the Eastern Equatorial Pacific, a deglacial expansion of the Eastern Equatorial Pacific OMZ, a restructuring of mid-water oxygen and carbon from the glacial to the Holocene, and a new role for deep-dwelling planktic foraminifera in interpreting paleoclimate records.