Meso- and Submesoscale Circulation Origins for Subsurface Oxygen Intrusions Into the Oxygen Deficient Zone of the Eastern Tropical North Pacific

Abstract

Subsurface oxygen maxima (SOM) are recurrent but poorly understood features within the eastern tropical North Pacific oxygen deficient zone (ODZ). Here, we analyze a subsurface oxygen maximum (SOM) observed during the SR2114 cruise using in situ biogeochemical and physical measurements, satellite remote sensing, and Lagrangian particle tracking. The SOM was detected around the 26.4 isopycnal (∼150–200 m) and spatially associated with elevated oxygen concentrations within an otherwise hypoxic environment. Our results show that intense gap winds in the Gulfs of Tehuantepec and Papagayo generate strong upwelling, vertical mixing, and horizontal advection near the coast, potentially allowing subsurface layers to come into contact with surface waters and become oxygenated. The observed vertical penetration of wind-driven features below the Ekman layer also suggests the influence of eddy-wind interactions that reinforce vertical coherence and enhance the offshore transport of oxygen-rich waters. The offshoreward jets observed down to the SOM layer depth highlight the contribution of such coupled processes to ventilating the ODZ interior. Furthermore, float-based observations along isopycnals indicate progressive oxygen loss over time, likely due to local respiration, pointing to dynamic interplay between physical supply and biogeochemical consumption. Together, these findings underscore the pivotal role of coastal wind forcing and mesoscale dynamics in shaping the subsurface oxygen landscape of the eastern tropical North Pacific. The Lagrangian analysis also highlights distinct pathways for water parcels within the ODZ: south of 14°N, water masses are primarily influenced by equatorial currents, whereas in the northern region, water parcels predominantly originate from coastal sources with extended residency times.