Circulation and shelf-ocean interaction off North Norway

The narrow continental shelf off Troms has a complex topography with deep trenches separating shallow banks. The front between Atlantic Water (AW) and Norwegian Coastal Water (NCW) is found near the shelf break and the currents in the area are topographically steered by the shelf slope. We have investigated the combined effects of topography, seasonal stratification, wind and tides on circulation and shelf-ocean interaction using field measurements and numerical simulations of hydrography and currents. Comparisons between simulation results and field measurements show that the model behaves realistically in terms of the distribution of NCW and general circulation. Effects of wind, tides and topography on the currents are shown to be strongly dependent on the stratification, which shows large seasonal variations in the area. Topographical effects on surface circulation are weakened when stratification increases. During stratified conditions winds have a strong impact on surface circulation and shelf-ocean exchange, and the wind direction is crucial for drift paths and residence times for particles (e.g. plankton) in the shelf area. When stratification is weak, tidal effects combined with topographic steering dominate the circulation.