Observations of tracer ventilation in the Cape Basin, Agulhas Current Retroflection

Abstract. The Cape Basin is a highly dynamic region, strongly influenced by the Agulhas Retroflection and its associated ring shedding. The region is characterized by high eddy kinetic energy, amplified mixing and water mass transformation. While model studies have shown that meso- to submesoscale features enhance water mass formation and tracer stirring, there have been limited observations made at the required spatiotemporal scales to capture such stirring and mixing processes. This study integrates high-resolution glider observations with satellite data to indicate the presence of shear-driven instabilities occurring at submesoscale fronts that enhance vertical diapycnal transport, leading to low apparent oxygen utilization and high levels of particulate organic carbon in the deeper ocean. These tracers are then distributed within the ocean interior via mesoscale advection and stirring along isopycnals, providing observational evidence for the role of the meso- to submesoscale strain field in surface to ocean interior water mass transformation and their broader implications on ocean circulation.