Abstract

Flows of dense water down the continental slope – cascades – are initiated in Arctic shelf regions by surface cooling or sea ice formation. In the Arctic Ocean there is growing understanding of the influence of cascading on the formation and maintenance of the halocline and on the global overturning circulation. The process is also believed to be influential in the off-shelf transport of carbon and other suspended or dissolved matter. Cascades thus present a potentially important link between shelf waters and the deep ocean, but their role in the Arctic Ocean remains largely unquantified.

Shelf-ocean exchange is inhibited by a combination of steep slopes and geostrophy, so there is considerable interest in processes that break the geostrophic constraint to facilitate cross-slope flow. The theoretical background and a 1 ½ layer ‘reduced physics’ model for these near-bottom gravity currents is reviewed, a classification of cascades and their life-cycle phases is introduced and some observations from the Storfjorden cascade in Svalbard are presented.

Results from recent modelling experiments in POLCOMS and NEMO show that a hydrostatic ocean circulation model is capable of representing the correct boundary layer physics to successfully model cascading. The models are first validated against laboratory experiments and then set up to simulate conditions that were not created in the laboratory to study the properties and behaviour of density-stratified cascades.