Year-round characterization of upwelling along the Uruguayan coast using a high-resolution regional ocean model

Abstract. Upwelling along the Uruguayan coast has largely been interpreted as a summertime process, primarily based on surface temperature signals. Here, we investigate coastal upwelling year-round using a high-resolution regional ocean model (Coastal and Regional Ocean Community, CROCO), with the aim of reassessing how upwelling manifests across seasons under contrasting thermohaline conditions. The seasonal covariability between daily winds and sea surface salinity anomalies was analyzed through a Maximum Covariance Analysis, revealing upwelling signatures during spring, autumn, and summer, marked by positive sea surface salinity anomalies (SSSa) along the Uruguayan coast. Summer upwelling events were characterized by positive SSSa and negative sea surface temperature anomalies (SSTa), indicating that both are reliable upwelling proxies during this season. In contrast, during spring and autumn, SSSa resulted in a better proxy. In this regard, upwellings were clearly marked by increases in SSSa, but the SSTa pattern in the coast was variable due to distinct vertical temperature stratification patterns. Based on the thermal properties of the upwelled waters, three upwelling regimes can be identified: cold-water upwellings associated with warm-season stratified conditions, transitional upwellings occurring under weak or absent thermal stratification, and warm-water upwellings linked to cold-season conditions, characterized by inverse thermal stratification. Overall, our results highlight that upwelling events along the Uruguayan coast cannot be described by a single thermal signature, but rather by seasonally dependent thermohaline regimes.