Deep cyclogenesis and poleward heat advection beneath a standing meander in the Subantarctic Front

Meandering of a baroclinic jet in the atmosphere or ocean produces deep cyclones and anticyclones through a process known as cyclogenesis, driven by squashing of upper and stretching of lower layers. Our high-resolution simulation of a strongly curved meander in the Subantarctic Front shows that horizontal divergence created by ageostrophic velocities due to flow curvature in the gradient wind balance causes this stretching and squashing and is a good proxy ( R 2 = 0.35 at ~ 200 m depth) for identifying vertical motion within the water column. Vertical motions drive along-isopycnal flow, producing temperature anomalies in the upper ocean, similar to those in observations. A progressive warming from the upstream side of the trough to the downstream side of the crest matches rotation of the horizontal velocity vector with depth and associated cross-stream heat advection. In the deep ocean (> 1500 m), we identify strong, coherent cyclones and anticyclones that are dynamically linked to the meander above and capable of transporting heat across the front. Around the cyclone, temperature anomalies depart from expectations based on cyclonic motion and the usual meridional increase in isopycnal temperature across the front. Localised around the cyclone, the meridional gradient changes sign, likely due to turbulent mixing and flow-topography interactions. Crucially, resolving these features requires a depth-dependent vorticity balance: vertical averaging would obscure the eddy-driven heat transport and underestimate the influence of deep currents on cross-frontal exchange. Our results underscore the importance of meanders and deep eddies for the Southern Ocean’s uptake and redistribution of heat and carbon.