Numerical study of the circulation in a steep canyon off the Catalan coast(western Mediterranean)

We use a limited-area fine-resolution primitive equation model to carry out a case study of the circulation in the steep and narrow Blanes Canyon, loc ated off the Catalan coast (western Mediterranean). This area is characteri zed by a permanent along-slope density-driven current and strong northerly and easterly wind bursts in autumn. In a first step the slope current is al lowed to adjust to the bottom topography, leading to a stationary circulati on pattern which presents large vertical variations related to the canyon g eometry. In the surface layer the strong stratification allows the current to flow straight over the canyon rim, ignoring bottom topography. In the in termediate layer the canyon is wide, and waters are isolated in a geostroph ic anticyclonic eddy maintained by friction at the edge of the slope curren t. In the deep layer the canyon is narrow, and a topographic upwelling lift s bottom waters toward the canyon head. In a second step the circulation is forced by easterly (along-shore with the coast on its right) and northerly (seaward) 1-day wind bursts which induce significant vertical and cross-sh ore motions steered by the bottom slope. This ageostrophic circulation is s ubstantially amplified in the canyon where the flow pattern presents large- amplitude oscillations characterized by a downwelling (upwelling) during th e easterly (northerly) wind burst followed by a rebound upwelling (downwell ing) as the wind relaxes. The upwelling induced by the northerly wind burst is capable of renewing waters trapped in the canyon eddy. Our results appe ar to be in fairly good agreement with in situ physical and biogeochemical data collected in Blanes Canyon and comparable canyons of the world ocean. The three-dimensional features obtained in this study can explain some of t he observed patterns of larvae distribution and exchanges between the coast al zone and the open sea.