Major role of the equatorial current system in setting oxygen levels in the eastern tropical Atlantic Ocean: A high- resolution model study

Understanding the causes of the observed expansion of tropical ocean's oxygen minimum zones (OMZs) is hampered by large biases in the representation of oxygen distribution in climate models, pointing to incorrectly represented mechanisms. Here we assess the oxygen budget in a global biogeochemical circulation model, focusing on the Atlantic Ocean. While a coarse (0.5 degrees) configuration displays the common bias of too large and too intense OMZs, the oxygen concentration in an eddying (0.1 degrees) configuration is higher and closer to observations. This improvement is traced to a stronger oxygen supply by a more realistic representation of the equatorial and off-equatorial undercurrents, outweighing the concurrent increase in oxygen consumption associated with the stronger nutrient supply. The sensitivity of the eastern tropical Atlantic oxygen budget to the equatorial current intensity suggests that temporal changes in the eastward oxygen transport from the well-oxygenated western boundary region might partly explain variations in the OMZs. Key Points Large improvement in oxygen field representation in an eddy resolving model Major sensitivity of OMZs extension to the equatorial current system strength Asymmetric response of oxygen supply and consumption to circulation intensity