Canyons influence on cross-shelf exchange – when dense water goes down, warm water comes up

A combination of laboratory experiments and numerical simulations investigated the dynamics controlling the cross-shelf exchange in a prograde sloping canyon induced by dense shelf water descending into the canyon. This study is motivated by the dispersal of dense water generated by polynyas on the Antarctic continental shelves. Both laboratory and numerical results suggest that canyons are hotspots of cross-shelf exchange. When the dense water descends a canyon, it induces an onshore return flow of offshore water into the canyon. The mechanism responsible for this return flow will be discussed together with the influence of the Burger number (Rossby radius of deformation/canyon width) and the dense water source location with respect to the canyon head. Understanding these dynamics in the Antarctica region is of global significance for two main reasons: 1. The offshore flowing dense water forms Antarctic Bottom Water and thus affects the global meridional circulation; 2. The onshore heat transport induced by the return flow drives glacial ice melt and therefore contributes to sea level rise.