The Flinders current and upwelling in submarine canyons

Abstract

The continental shelf off South Australia is incised by some of the largest known submarine canyons. Extensive observations of submarine canyons in other parts of the world have shown submarine canyons can result in locally persistent upwelling regions. Along the southern coastline, westward slope currents including anticyclonic eddies and the Flinders Current (FC) can result in favourable conditions for upwelling in the vicinity of these canyons. Little data is available to describe the FC and so we review three global ocean circulation models and their representation of the FC. Though there are considerable differences between the outputs of these three models, this analysis provides a range of potential scales for the structure and transport of the FC. The reasons for the differences between the output of the three models are extensive, but to a first approximation, climatological surface wind stress products are compared. Dynamical descriptions of the flow past submarine canyons are reviewed and in part extended, in particular the vertical scale of the induced motion is estimated as the Rossby height RH. A description of upwelling and downwelling flow incorporating vorticity stretching is also presented. An idealised model of the southern Australian continental shelf and the submarine canyons reveals the circulation is heavily modified by the presence of the canyons, inducing persistent upwelling of dense water onto the downstream shelf. In addition, one prominent feature of the induced circulation – a coastal jet – is found to be peculiar to flat inner shelf topographies. More realistic topography including a sloped inner shelf results in reduced shoreward transport within the canyon and hence reduced upwelling.