Geographic extent and drivers of Pliocene Oxygen Minimum Zones

Tuesday, 15 December 2020: 11:42
Catherine V Davis, Yale, Earth and Planetary Sciences, New Haven, CT, United States, Elizabeth C Sibert, Harvard University, Earth and Planetary Sciences & Harvard Society of Fellows, Cambridge, MA, United States, Peter Jacobs, George Mason University, Environmental Science and Policy, Fairfax, VA, United States, Natalie Burls, George Mason University, Atmospheric, Oceanic and Earth Sciences, Fairfax, VA, United States, Andy Ridgwell, University of California Riverside, Department of Earth and Planetary Sciences, Riverside, CA, United States and Pincelli M Hull, Yale University, Department of Earth and Planetary Sciences, New Haven, CT, United States
The extent and distribution of regions of especially low oxygen below the ocean’s surface, known as oxygen minimum zones (OMZs), are critical components of the global biogeochemical cycle and may act as a vertical barrier for many marine organisms. Growing evidence that modern OMZs are expanding and intensifying in response to climate change makes developing long-term records of OMZs, and establishing the drivers of their distributions, increasingly important for understanding our future oceans. However, the extent of pelagic OMZs in the geologic past has rarely been investigated due to a lack of proxies to track them. Here we use the presence of the OMZ-affiliated planktic foraminifer, Globorotaloides hexagonus, in deep-sea sediments as a proxy for pelagic Pliocene OMZs. We target the Pliocene as inclusive of the most recent period in geological history with stable atmospheric CO2 concentrations analogous to modern levels (~ 400-450 ppm), and for having both globally distributed species counts of planktic foraminifera via the PRISM database and extensive model predictions of oceanographic conditions. We find that the distribution of G. hexagonus and model outputs are in broad agreement as to the arrangement of Pliocene OMZs, including distinct OMZs in the Indian, Eastern Atlantic, Southeast Pacific, and Eastern Equatorial Pacific similar to modern. However, we find more restricted low-oxygen waters in the Northeast Pacific, and more pervasive OMZs in the Western Atlantic and Caribbean. We further explore the drivers of differing modern and Pliocene OMZ distributions using both high and low resolution earth system models.