On the Dynamics of Canyon–Flow Interactions

Jochen Kämpf

doi:10.3390/jmse6040129

Abstract

This paper explores the dynamical origin and physical characteristics of flow disturbances induced by ocean currents in interaction with shelf-incised submarine canyons. To this end, a process-oriented hydrodynamic model is applied in a series of case studies. The focus of studies is the canyon-upwelling process in which seawater is moved from the upper continental slope onto the shelf within a shelf-break canyon. Results reveal that the generation of canyon upwelling, to zero-order approximation, is a barotropic and friction-independent quasi-geostrophic process. Hence, the principle of conservation of potential vorticity for such flows is sufficient to explain the fundamental physical properties of the canyon-upwelling process. For instance, this principle explains the direction-dependence of the canyon-upwelling process. This principle also explains the formation of stationary topographic Rossby waves downstream from the canyon that can lead to far-field effects. Density effects, being of secondary influence to the canyon-upwelling process, result in the intensification of canyon-upwelling flows via the formation of narrow near-bottom density fronts and associated baroclinic geostrophic frontal flows. Findings of this work reveal that the apparently complex canyon-upwelling process is much more basic than previously thought.

Highlights

Submarine canyons are typical bathymetric features of continental margins of the oceans
Flow disturbances were created in interaction with the canyon and were carried downstream via topographic Rossby waves propagating into the same direction as the ambient flow
The method of process-oriented high-resolution hydrodynamic modeling was employed to study the interaction of coastal flow with a shelf-break canyon

Summary

Introduction

Submarine canyons are typical bathymetric features of continental margins of the oceans. TThhee idealliizzeedd suubbmmaarriinnee sshheellff--bbrreeaakk ccaannyyoonn hhaass a wwidth ooff WW ≈≈ 3300 kkmm and aa mmaaxxiimmum ddeeppth relaattiivvee ttoo tthhee aaammmbbiieenntt ssseeeaaflfflloooorr ooofff ∆ΔΔhhh === 111000000 mmm. UUssiinngg tthhee aabboovveecoconnfifigguurartaitoionn, ,twtwo oscesnceanriaorsioasreacreoncsoidnesirdeder.eTdh.e fTirhset sficresntasricoeneaxrpilooreexsprliogrhetsrbioguhnt-dbeodunfdloewd flionwthine tnhoernthoerrtnherhnemheismphiseprheer(eeq(ueqivuailveanltenttotolelfet-fbt-obuonudneddedflfloowwinin tthhee ssoouutthheerrnn hemisphere) being characterized by free continental shelf waves travelling into the same direction as the coastal flow. This scenario is referred to as “topographic steering scenario”. The second scenario explores right-bounded flow in the southern hemisphere (equivalent to left-bounded flow in the northern hemisphere) being characterized by free continental shelf waves travelling opposite to the ambient coastal flow This scenario is referred to as “canyon-upwelling scenario”. The total simulation time of all experiments is 25 days, over which no dramatic disturbances develop near the open boundaries

Topographic Steering Scenario

Impacts of Density Effects

Conclusions