Séminaire
This study examines the role of processes transporting tracers across the Polar Front (PF) in the depth interval between the surface and the sill of Drake Passage, which we refer to as the "PF core". A preindustrial control simulation of an eddying climate model coupled to a biogeochemical model (CM2.6-miniBLING) is used to investigate the transport of heat, carbon, oxygen and phosphate across the PF core, with a particular focus on mesoscale eddies. Over most of the Southern Ocean, we find that northward Ekman transport is the main driver of tracer transport across the PF core. The eddy transport is generally to the south but smaller in magnitude than the Ekman transport, only partially compensating Ekman transport within the Ekman layer, but dominating the total transport below the Ekman layer. At major topographic features, eddies dominate the total transport over the entire depth of the PF core, so that these regions are found to be gateways for the transport of tracers to the south. Cross-frontal tracer exchange is enhanced at topographic features, but sums to a small net transport due to a near-cancellation of southward and northward transports. Hence, these "hot spots" of tracer exchange only play a secondary role for the net transport of tracers across the PF core. We estimate the relative contributions of eddy tracer advection and diffusion, and find thateddy-advection is the leading-order component for all four tracers. Due to the combined action of its advection and diffusion components, eddy transport across the PF core is much more efficient for heat than for biogeochemical tracers.