Quantifying the Contribution of Ocean Mesoscale Eddies to Low Oxygen Extreme Events

Abstract

Ocean mesoscale eddies have been identified as drivers of localized extremely low dissolved oxygen concentration ([O2]) conditions in the subsurface. We employ a global physical-biogeochemical ocean model at eddy-permitting resolution to conduct a census of open-ocean eddies near Eastern Boundary Upwelling Systems adjacent to tropical Oxygen Minimum Zones (OMZs). We track cyclonic and anticyclonic eddies with a surface signature over the period 1992–2018 and isolate their subsurface oxygen characteristics. We identify strongly deoxygenating eddies and quantify their contribution to low [O2] extreme events. Our results show that model simulated low [O2] extreme event frequency is 2–7 times higher in eddies versus non-eddying locations, with regionally more than half of low [O2] extreme events outside of the permanent OMZs being associated with eddies. Our study highlights the need for further work to investigate the drivers, characteristics and potential ecosystem impacts of low [O2] extreme events.