The flow across submarine canyons off the North-Norwegian coast

The steep continental slope off the Lofoten-Vesterålen islands in Northern-Norway is carved up by several submarine canyons (see the figure). A number of studies suggest that such canyons may enhance shelf-slope exchanges of water and suspended material. Physical, chemical and biological processes are all modified in the vicinity of submarine canyons. Most canyon studies have focused on so-called ‘upwelling coasts’. Here the currents are the opposite direction of topographic wave propagation (the waves travel with the coast to their right in the northern hemisphere).

So the flow, if strong enough, is able to arrest topographic waves that may then grow in amplitude to create large cross-slope excursions. The resulting exchanges of nutrients, also in the vertical, make canyon-carved upwelling coasts very biologically productive. The Norwegian coast, in contrast, is a so-called ’downwelling coast’ in which topographic waves are not arrested. Still, there are observations that at least some of the canyons off Lofoten-Vesterålen are very productive. So what is going on here?

In this project, we will use observations and/or numerical models to investigate the dynamics of the flow across the canyons along the slope off Lofoten-Vesterålen. Our hypothesis will be that some processes are able to reverse the flow here episodically, long enough to set up arrested topographic waves and large cross-slope exchanges (of e.g. nutrients).

The cause for such flow reversal may be either 1) episodic winds from the north or 2) transient mesoscale eddies (they are efficiently formed here because of strongly unstable hydrodynamic fronts in the region). Flow reversals may then make Lofoten-Vesterålen an 'upwelling coast' for a few days at a time, setting up strong cross-slope exchanges that are important for e.g. the regional ecosystem.    

A student who is primarily interested in observations and data analysis will focus on studying observations from the region, e.g. searching for correlations between flows in canyons (again see the figure) and anomalies in atmospheric winds and/or the upper-ocean eddy field (as seen by satellites).

A student who is more inclined towards numerical modelling will instead study canyon dynamics in either idealized or realistic models. If things run smoothly the student may even study the problem using both observations and models, using the observations to validate the model and then using the model to better interpret the observations.

The bottom bathymetry off the Lofoten-Vesterålen islands showing the many submarine canyons that carve in across the continental slope. Red and yellow stars indicate observational sites where currents and hydrography have been measured. Click here for a bigger picture (opens in a new window). 

 

Published Sep. 11, 2019 10:35 AM - Last modified Sep. 11, 2019 10:37 AM

Supervisor(s)

Scope (credits)

60