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

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Abstract The dissolved oxygen (O 2 ) 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 O 2 along with eddying and noneddying global ocean–sea ice simulations, we examine the interannual variability of O 2 and its underlying drivers in the tropical Pacific. We find a tight relationship between El Niño–Southern Oscillation (ENSO) and the O 2 content and distribution across observations and models, with elevated O 2 in the eastern and central parts of the basin during El Niño and reduced O 2 in this region during La Niña. The variability of the O 2 content in this region is generally similar across models and observation-based products, though regional patterns differ. ENSO-driven variability of O 2 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 O 2 content increases during El Niño despite a major reduction in ventilation. This variability in O 2 ventilation is primarily driven by ENSO modulation of shear-driven turbulent mixing and the eastward transport of O 2 by the Equatorial Undercurrent (EUC). We also note that ENSO positively couples the tropical Pacific heat and O 2 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 O 2 response to climate perturbations in the tropical Pacific.

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