Deep Cyclogenesis and Poleward Heat Advection beneath a Standing Meander in the Subantarctic Front

Abstract 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 the 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. Localized 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. Significance Statement Strong westerly winds that blow over the Southern Ocean cause a northerly transport of surface waters, which is compensated by upwelling of deep waters, forming deep density-driven fronts. These fronts combined make up the Antarctic Circumpolar Current, which, because it circles the globe without continental barriers, separates warmer northern from colder southern waters. When the current encounters underwater topography, meanders develop and a link with circular vortices near the seafloor is observed. Using a high-resolution model, we show that a strongly curved meander generates vertical motion that forms deep horizontal vortices carrying heat across the front. Recognizing these processes is crucial for improving how climate models represent the ocean’s uptake and redistribution of heat and carbon.