High‐Resolution Observations Unveil (Sub)Mesoscale Heat Fluxes Shaping Upper‐Ocean Heat Content

Abstract Upper‐ocean heat content (UOHC) modulates air–sea exchange in tropical regions; however, its variability at (sub)mesoscale remains insufficiently resolved. Here we combine Surface Water and Ocean Topography (SWOT) observations with high‐resolution glider sections in the northeastern tropical Pacific, where mesoscale eddies and sharp frontal structures associated with currents up to 1 m were sampled. The gliders reveal strong spatial variability of UOHC along the transects, with localized anomalies reaching 20 kJ , superimposed on a mesoscale background state. Mesoscale eddies and fronts define the background thermal structure, within which submesoscale frontal dynamics drive localized and intermittent vertical heat redistribution. In these structures, a complex interplay of ageostrophic circulations, Ekman‐related processes, and enhanced mixing generates vertical heat fluxes reaching O (–) W , comparable to air–sea heat fluxes. These results provide observation‐based constraints on submesoscale vertical heat redistribution and its quantification, which remain poorly represented in ocean models.