Paleoceanographic Insights on Recent Oxygen Minimum Zone Expansion: Lessons for Modern Oceanography Moffi%, S. E.*, R. Moffi%, W. Sauthoff, C. V. Davis, K. Hewe%, T. M. Hill *Correspondence to Sarah E. Moffi4, email: semoffi4@ucdavis.edu Oxygen Minimum Zones (OMZ) are major barriers to oxygen-­‐respiring ocean life. Modern OMZs are distributed globally Economically-­‐important fish and crabs don’t like OMZs, and specialized worms, snails and bacteria live in them. Thick modern OMZ in Here we invesSgate sediment records to NE Pacific understand how OMZs change during abrupt climate warming, such as the recent deglaciaSon 10,000-­‐17,000 years ago. What we found: Our analyses show that vast expanses of the upper ocean deoxygenate during global-­‐scale warming, resulSng in the verScal compression of oxygenated ocean ecosystems. Modern oceanographers can anScipate that modern Eastern Boundary Current OMZ have the capacity to expand to states that have never been instrumentally observed. The Last Glacial Maximum 18,000 years ago Mid-­‐way through deglacia<on/warming 14,000 years ago No OMZs in a glacial ocean! California margin is cold, oxygenated and sea level is -­‐120 meters lower than modern levels Major OMZ expansion mid-­‐
way through deglaciaSon, OMZ evidence from 330-­‐ 1,500 meters below sea level (mbsl) Gray shoreline illustrates the “paleoshoreline” and sea level rise through the deglaciaJon. Red (severe hypoxia) Orange (intermediate hypoxia) The Holocene 4,000 years ago A]er climate warming, OMZs retracted to a state that is similar to the modern OMZ What we did: Thirty six ocean sediment cores from the Eastern Pacific conSnental margin were used to reconstruct the Sming, depth and intensity of OMZs change during the deglaciaSon. We chose high-­‐resoluSon sediment archives with oxygenaSon proxies (geochemical, sedimentary, microfossil) and considered the impact of sea level rise. 14,000 years ago 13,000 years ago Subarc@c Pacific OMZ from 600-­‐2,900 mbsl 14,000 years ago Mexico Margin OMZ from 330-­‐830 mbsl Oxygen Disturbance in the Modern Ocean VerJcal expansion of OMZs in the water column Geological OMZ expansion dwarfs modern scales of marine ecosystem perturbaSon and highlights the scale of future management and conservaSon challenges. Humboldt Current and Equatorial Pacific OMZ from 110-­‐3,100 mbsl EXPANSION OF OMZS MEAN: Compression of surface ocean oxygenated ecosystems: major loss of habitat for fisheries, biodiversity. Expansion of OMZ ecosystems, invasion of low-­‐oxygen tolerant species, such as the Humboldt Squid in the California Current. © MBARI 2003 WHY IS THIS IMPORTANT? •  Major losses of dissolved oxygen have been detected in the modern ocean, indicaJng climate-­‐driven changes in ocean oxygen are already underway. •  Previous events of abrupt climate warming provide informaJve examples of how rapidly and extensively the global ocean can lose dissolved oxygen.