Lee effects of localized upwelling in a shelf-break canyon

Using a process-oriented modeling approach, this work explores the interaction between flow disturbances created by an isolated shelf-break canyon with coastal flows modulated by an irregular coastline such as a headland. Findings show that, on their own, both the canyon and the headland produce individual stationary barotropic topographic Rossby waves extending considerable distances >100 km) along the continental shelf. The canyon-induced wave is instrumental in the formation of stationary alternating zones of upwelling and downwelling along the shelf break. Waves created by a headland located downstream of the canyon tend to dramatically enhance the cross-shelf flow in favor of the formation of stationary coastal upwelling centers. In this case, process-individual zones of “squeezing vorticity” (negative ratio of relative vorticity to planetary vorticity) combine such as to trap previously upwelled water on the continental shelf. In contrast, headland-induced flow disturbances created upstream of the shelf-break canyon have only little impact on the cross-shelf flow. Moreover, sensitivity studies indicate that the efficiency of cross-shelf exchange critically depends on topographic parameters (in particular onshore variations of bottom slope) of the continental shelf.