Dense water cascading off the continental shelf

Cascading is a specific type of buoyancy-driven current in which dense water formed by cooling, evaporation, or freezing in the surface layer over the continental shelf descends down the continental slope to a greater depth. We have identified, by world-wide trawling and analysis of raw databases, several distinct mechanisms of preconditioning for cascades. We have validated, where possible, existing theories and developed simple models, which allow estimation of the parameters for preconditioning, initiating, and down-slope fluxes as well as evolution of the temperature contrasts during cascading events. Compliance or noncompliance of observations with these simple and easy-to-use models has been related to the stage of cascade development and to local factors. Estimates of observed down-slope transport rates in case studies accord with theory, which is thereby substantially validated. Typical values of cascading transport rates were in the range 0.5–1.6 m2s−1. We hazard a very approximate global estimate of order 105 km3yr−1 or average 3 Sv based on our findings and previous studies.