The Equatorial Undercurrent and the Oxygen Minimum Zone in the Pacific
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Warming-driven expansion of the oxygen minimum zone (OMZ) in the equatorial Pacificwould bring very low oxygen waters closer to the ocean surface and possibly impact global carbon/nutrientcycles and local ecosystems. Global coarse Earth System Models(ESMs) show, however, disparate trendsthat poorly constrain these future changes in the upper OMZ. Using an ESM with a high-resolution ocean(1/10◦), we show that a realistic representation of the Equatorial Undercurrent (EUC) dynamics is crucialto represent the upper OMZ structure and its temporal variability. We demonstrate that coarser ESMscommonly misrepresent the EUC, leading to an unrealistic “tilt” of the OMZ (e.g., shallowing toward theeast) and an exaggerated sensitivity to EUC changes overwhelming other important processes likediffusion and biology. This shortcoming compromises the ability to reproduce the OMZ variability andcould explain the disparate trends in ESMs projections.