ENSO-Driven Variability of Oxygen Content and Distribution in the Tropical Pacific Journal of Climate

The dissolved oxygen (O2) content of the tropical Pacific exhibits substantial variability from interannual to decadal time scales, challenging the detection of ocean deoxygenation in this region. Using a global observational synthesis of O2 along with eddying and noneddying global ocean–sea ice simulations, we examine the interannual variability of O2 and its underlying drivers in the tropical Pacific. We find a tight relationship between El Niño–Southern Oscillation (ENSO) and the O2 content and distribution across observations and models, with elevated O2 in the eastern and central parts of the basin during El Niño and reduced O2 in this region during La Niña. The variability of the O2 content in this region is generally similar across models and observation-based products, though regional patterns differ. ENSO-driven variability of O2 is shown to be the net balance of large and compensating effects between vertical advection and biological consumption that dominate over opposing changes in vertical mixing and lateral advection, such that the O2 content increases during El Niño despite a major reduction in ventilation. This variability in O2 ventilation is primarily driven by ENSO modulation of shear-driven turbulent mixing and the eastward transport of O2 by the Equatorial Undercurrent (EUC). We also note that ENSO positively couples the tropical Pacific heat and O2 contents, which contrasts sharply with their tight negative relationship at mid- and high latitudes, likely due to a larger role for ocean dynamics and biological processes in modulating the O2 response to climate perturbations in the tropical Pacific. Grant no. NA23OAR4310587 Grant no. NA20OAR4320271 Grant no. NA22OAR4310599 Grant no. NA24OARX431C0018