Abstract

Circulation along the west coast of South America originates from the eastward-flowing South Pacific Current, which bifurcates around 40-45 degrees S. Its northern branch forms the Humboldt Current (HC), while the southern branch continues along the continental shelf as the Cape Horn Current (CHC). Despite significant scientific efforts to understand the HC, the CHC has received considerably less attention. This study investigates the spatial structure, seasonal variability, and forcing mechanisms of the CHC using a combination of reanalysis data (GLORYS12, ERA5) and in-situ observations. Our results reveal that the CHC's dynamics are governed by the superposition of two distinct physical mechanisms with different vertical structures: a surface-intensified response to direct wind forcing, and a vertically-coherent geostrophic flow driven by sea surface height gradients. This dual structure explains both the year-round persistence of the current, due to its deep geostrophic core, and its seasonal cycle. The current exhibits a modest but consistent intensification during austral summer and spring, with mean velocities increasing from similar to 16 cm s(-1) in autumn/winter to similar to 18 cm s(-1) in the warmer seasons, a variability primarily associated with the surface wind-driven component. Correlation analysis confirms that wind and sea surface height gradients are the dominant forcings, particularly in the CHC core region (51 degrees-56 degrees S). Furthermore, the underlying physical mechanism is consistent with a coastal downwelling process, where persistent alongshore winds ultimately maintain the large-scale pressure gradient. In comparison with the Alaska Current, the CHC shows similarities in its wind-driven dynamics but differs in its largely barotropic geostrophic structure, in contrast to the strong baroclinic influence of freshwater in the Gulf of Alaska. Our findings clarify the dual nature of the CHC, highlighting its role as a key pathway in the Patagonian shelf-break region, which in turn influences regional climate, marine ecosystems, and biogeochemical cycles. Future research should focus on the interaction of these components using high-resolution hydrodynamic models to better elucidate its variability.