Anatomy and Dynamics of the Patagonia Shelf-Break Front

Abstract

The Patagonia shelf-break front presents sharp offshore changes in sur- face temperature, salinity, chlorophyll, and horizontal velocity. In summer, the cross-shore temperature and salinity changes are not uniform, suggesting the exis- tence of multiple fronts. In winter, the offshore changes are fairly uniform, display- ing a single thermohaline front located just offshore from the shelf-break. Cross-front temperature and salinity present significant seasonal variations associated with intense vertical stratification over the shelf during summer. The thermocline pro- vides a density interval for cross-front isopycnal exchange, which may fertilize the outer shelf waters. The salinity front extends from the surface to the bottom and is observed year-round. Frontal displacements occur throughout the water column. The high surface chlorophyll along the front suggests a sustained nutrient flux to the shelf-break upper layer. Numerical experiments indicate intense frontal upwelling mediated by the interaction of the Malvinas Current with the bottom topography and suggest that upwelling in upstream portions of the shelf-break, advected north- ward along the shelf edge, may further modulate the nutrient fluxes required to sustain frontal productivity. A southward displacement of the northernmost exten- sion of the front observed during the past decades may have biological and biogeo- chemical impacts.