The Norwegian & North Cape Currents (2024)


	The Norwegian current as represented by the Mariano GlobalSurface Velocity Analysis (MGSVA). The Norwegian current has an offshorebranch and a coastal component that hugs the coast of Norway. Ittransports relatively warm, saline waters into the Arctic Ocan andthis influences the amount of winter-time convection and water massformation.Click here for example plots ofseasonal averages.

The current system in the North Sea is dominated by three main branches ofinflowing Atlantic Water and the outflow of the Norwegian Current (Mork1981). The wedge-shaped Norwegian Current (also known as the NorwegianCoastal Current) flows northward along the west coast of Norway in theupper 50-100 m of the water column (Helland-Hansen and Nansen 1909, Ikedaet al. 1989). The Baltic Sea provides the bulk of brackish water to thecurrent, but the North Sea and the Norwegian rivers and fjords alsocontribute significant amounts of low-salinity water (Mork 1981, Haugan etal. 1991, Saetre 1999). In addition, a branch of the North AtlanticCurrent turns northward and provides a warm core (McCartney and Talley1982). The Norwegian Current has a western boundary formed by a southwardinflow of Atlantic Water from the North Atlantic Current (Haugan et al.1991, James 1991). At this boundary there is a well-defined front betweenthe cold, low-salinity Norwegian Current and the warmer, more salineAtlantic Water (Ikeda et al. 1989). The temperature difference betweenthese two water masses is especially evident during winter, when atemperature gradient of 0.5°C/km can be observed (Audunson et al.1981, Saetre 1999). On average, winter temperatures in the NorwegianCurrent range from 2° to 5°C, and the salinity is less than 34.8.The Atlantic Water, on the other hand, has temperatures exceeding 6°Cand salinity greater than 35 (Saetre and Ljoen 1972, Haugan et al. 1991).

Estimates for the velocities of the current vary widely. With currentmeters at 25 m depth, Haugan et al. (1991) measured large temporal andspatial variations in the current, ranging from 5 cm s

^-1 to 60 cm s^-1. To them, this suggested a characteristic speed of 30 cm s^-1. Danielssen et al. (1997) found that the velocities varied greatly with time. During the first part of their experiments, the current exhibited velocities ranging from 10-40 cms^-1. Then, after 5-6 June, they recordedvelocities up to 100 cm s^-1 as a clear barotropic current componentdeveloped. Moorings deployed during the Norwegian Continental ShelfExperiment (NORCSEX '88) detected current velocities of 7 cm s^-1 to 20 cm s^-1 with a mean northeastward direction (Haugan et al. 1991). The direction was almost parallel to the isobaths, indicating significant topographic steering (Haugan et al. 1991).

At the central Norwegian shelf, the bottom topography is complex andinvolves shallow banks separated by deep trenches. Topographic steeringplays a major role in shaping circulation patterns in the area (Saetre1999). For example, the topography causes the current to split at about63°30'N (Ljoen and Nakken 1969). The outer minor branch follows thecontinental shelf break, and the inner major branch resembles a coastaljet (Saetre 1999). The outer branch mixes with Atlantic Water andeventually loses its identity, making it difficult to detect north of65°N. The inner branch is the wedge-shaped portion, and it flows in anarrow 20-30 km wide zone (Saetre 1999). The topography also influencesdirection and stability. The Norwegian Current generally follows theNorwegian Trench, the deepest feature in the North Sea (Johannessen et al.1989). The depth of the trench, along with density differences betweenNorwegian Current water and the adjacent Atlantic Water, result in eddiesof scales that are much greater than in most sea shelf fronts (James 1991).

Mesoscale eddies and meanders in the Norwegian Current have been studiedusing remote sensing and in situ observations. Most observations indicatethat they have wavelengths of 50-100 km and northward velocities of 10-20cm s

^-1 (Johannessen and Mork 1979, Audunson et al.1981, Mork 1981, Ikeda et al. 1989). Using combined Acoustic CopplerCurrent Profiler, towed, undulating CTD, and satellite infrared data,Johannessen et al. (1989) found that the cyclonic eddies were highlyasymmetric, had significant barotropic components, and extended to thebottom. Based on these observations, they concluded that the combinedeffects of topographic steering, vortex stretching, and barotropicinstability explained the generation of eddies between 60°N and61°N. Meanders and eddies generated upstream by baroclinicinstabilities grow and also enter this region. The resulting interactionscomplicate the eddy field (Johannessen et al. 1989).

An important aspect of the Norwegian Current is its effect on the icecover in the Barents Sea. Compared with the cold and fresh Arctic water,the waters of the Norwegian Current are relatively warm and saline. Theexchange of heat between these two water masses is enhanced during yearswith a positive NAO (North Atlantic Oscillation) pattern (Dickson et al.1996, Venegas and Mysak 2000). Under these conditions, the transport ofheat by the Norwegian Current into the Arctic region is stronger thannormal. When the NAO is negative, Atlantic waters do not penetrate so farnorth, and ice is easily formed and maintained in the Barents Sea. Thismechanism, which is closely tied to atmospheric variations, operates onquasi-decadal time scales (Venegas and Mysak 2000). Another mechanism thatinfluences ice variability in the Barents Sea is the changes in theupper-ocean temperature of the Atlantic waters that the Norwegian Seacarries. These changes are probably related to the advection of seasurface temperature anomalies by the subpolar and/or subtropical gyres(Grotefendt et al. 1998, Venegas and Mysak 2000). Dependent mainly on theadvection time of the ocean gyres, this mechanism has a longer period ofoscillation than the first (Venegas and Mysak 2000).

References

Audunson, T., V. Dalen, H. Krogstad, H.N. Lie, and O. Stinbakke, 1981:Some observations of ocean fronts, waves and currents in the surfacealong the Norwegian coast from satellite images and drifting buoys. In: The Norwegian Coastal Current, Proceedings from Symposium. R. Saetre and M. Mork (Eds.), pp. 20-57, University of Bergen, Norway.

Danielssen, D.S., L. Edler, S. Fonselius, L. Henroth, M. Ostrowski, E.Svendsen, and L. Talpsepp, 1997: Oceanographic variability in the Skagerrak and Northern Kattegat, May-June, 1990. ICES Journal of Marine Science, 54, 753-773.

Dickson, R.R., J. Lazier, J. Menicke, P. Rhines, and J. Swift, 1996:Long-term coordinated changes in the convective activity of the NorthAtlantic. Progress in Oceanography, 38, Pergamon, 241-295.

Gortefendt, K., K. Logemann, D. Quadfasel, and S. Ronski, 1998: Is the Arctic Ocean warming ? Journal of Geophysical Research, 103, 27679-27687.

Haugan, P.M., G. Evensen, J.A. Johannessen, O.M. Johannessen, and L.H.Pettersson, 1991: Modeled and observed mesoscale circulation and wave current refraction during the 1988 Norwegian continental shelf experiment.Journal of Geophysical Research, 96, 10487-10506.