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Argo Reveals the Scales and Provenance of Equatorial Island Upwelling Systems

Equatorial islands have distinct oceanographic signatures, including cool sea surface temperature and high productivity immediately to their west. It has long been hypothesized that topographic upwelling is responsible for such characteristics—upward deflection by the islands of the eastward‐flowing equatorial undercurrent (EUC). Using 22 years of in situ measurements by Argo, we provide the first direct observations of this process occurring with consistency at two prominent archipelagos in the equatorial Pacific. Argo measurements resolve a clear subsurface thermal fingerprint of vertical divergence at the depth of the EUC, confined to within 100 km of both the Gilbert (∼175°E) and Galápagos Islands (∼90°W). This signal at the Galápagos is well‐reproduced by a high‐resolution ocean reanalysis, enabling the estimation of vertical velocities balancing the zonal convergence of the EUC upon the islands. This sharpened view of the physics underpinning such important tropical ecosystems has implications for strategies to model and predict them.