On the descent of dense water on a complex canyon system in the southern Adriatic basin

Using the results of a numerical model for the description of bottom-arrested currents and statisticalanalyses, we elucidate different characteristics of the dynamics of a southward propagating vein of NorthAdriatic Dense Water (NAdDW) observed to evolve within a complex canyon system of the southernAdriatic basin. The vein, monitored from March 2004 to March 2005 by three distinct mooring lines,exhibits a complex, highly time-dependent dynamics characterized by large velocity and densityfluctuations. In particular, lag correlation analyses performed on the observed velocity and temperaturedata show that a temporal lag ranging between 7 and 10 h governs the NAdDW signal propagation alongthe different canyons, its magnitude inversely depending on vein downslope velocities and densityanomalies. The performed model simulations reveal that, weakly depending on its initial layer thickness,exact position, and density contrast with the upper ocean, a coherent flow of dense water locatedupstream of the canyon system on the Italian shelf will always bifurcate at the entrance of that system;while its shallower part will disintegrate into several branches, its deeper part will continue to flowmorecoherently, injecting part of the bottom water downward. Regions dominated by supercritical flowregimes are simulated, which contributes to explain part of the observed flow variability. Simulated lagtimes between signals propagating in the canyons are consistent with observations. They are found todepend crucially on initial, upstream vein location, layer thickness, and density contrast with the upperocean.Wefinally use this information, retrieved by ournumerical simulations on the basis of the availableobservations, to infer, in a kind of inverse problem solving, possible shape, location, and density contrastpossessed by the observed vein of NAdDW on the Italian continental shelf, prior to its sinking toward theBari canyon system.