Norwegian Current

The Norwegian Current (also known as the Norwegian Coastal Current) is a water current that flows north-easterly along the Atlantic coast of Norway at depths of between 50 and 100 meters. It contrasts with the North Atlantic Current because it is colder and has less salt in it, having most of its tributary water coming from the brackish Baltic Sea as well as the Norwegian fjords and rivers. It is, however, considerably warmer and saltier than the Arctic Sea. Winter temperatures in the Norwegian current are typically between 2 and 5 °C whereas the temperature of the Atlantic water exceeds 6 °C.

The Norwegian coastal current is a north-easterly flowing current that proceeds from north of Scotland around the coast of Norway into the Barents Sea. It is both wind-driven ,“piling up” of water along the Norwegian coast by southwesterly winds creates elevation and thus pressure differences, and also driven by its salinity distribution which in turns creates density gradients .^[1]

Sources

It is composed primarily of outflow from the Baltic Sea (50% of freshwater input), flowing through the Skagerrak strait into the North Sea (10% freshwater input) circulation, joining with a fraction of the Gulf Stream.^[1] The North Sea forms the third largest input of brackish-fresh water preceded by the inputs of fjords and rivers of Norway (40% of freshwater input).^[1][2] The Skagerrak area receives about 2100 m³/s of freshwater inflow, 75% of which is Baltic outflow, 15% is North Sea outflow and 10% is runoff from Norway and Sweden^[1] It is sometimes considered to be a continuation of the Baltic Current^[2] and is a major source of freshwater for the Barents Sea and Arctic Sea. It is formed by the branch of Atlantic current that flows into the North Sea and circulates through the North Sea basin along the Norwegian Trench picking up fresh and brackish water. It is a surface current and flows along the top 50–100 m of the sea surface.^[3][4][5]

Properties

Salinity

The Norwegian coastal current is a warm wedge-shaped current that has varying salinity and temperature characteristics, and thus densities. The volume of freshwater inputs is greatest in the summer months and smaller during the winter months, contributing to the variability in salinity. On average, it has a salinity of about 34.5 psu (ppt); however, the coastal waters have a slightly lower salinity (32-31 psu) and the current’s boundary waters have a slightly higher salinity of 35 ppt.^[2]

Temperature

The average winter temperature of the Norwegian Current is about 3.5 °C^[3][6] and ranges from 2 to 5 °C, while in summer the temperature of the current is warmer as the tributary sources (Baltic sea, Norwegian fjords, rivers) are warmer.

Velocity

Although there is much variability in the current’s velocities, ranging from as little as 20 cm/s to 100 cm/s at its maximum^[1] it is characterized by a velocity of 30 cm/s.^[7]

Effects on climate

The Norwegian Coastal Current is cooler and fresher than the Atlantic water flowing into the North Sea via the Gulf Stream; however, it is warmer and saltier in comparison to the Arctic Sea, into which the current eventually flows. The current generally follows the Norwegian Trench and channels warmer water around the Norwegian coast. The exchange of energy between the atmosphere and ocean surface, generally leading to a release of heat from the ocean surface to the atmosphere, has a moderating effect on the climate of Norway, making it wetter and warmer than it would be without the current. Additionally, the current, bringing warmer water into the Barents Sea, decreases the amount of ice that can form there.^[3]

Fisheries effects

The current brings warmer, nutrient rich water along the coast of Norway, and with it rich fisheries of cod, herring, and capelin. Wind driven upwelling along the strait of Skagerrak brings abundant nutrients to the surface which are then carried along the coastline. Norway has one of the biggest fishing industries in the world, harvesting an average of 3 million tonnes of fish each year. The Norwegian Coast is also an enormously important spawning ground for many of the commercial fish.^[1]

Coastal water masses

The current is dominated by two main water masses, the Norwegian Coastal Water and the Atlantic Water. Atlantic water has a higher salinity of about 35 ppt, comparatively, Coastal Water has a lower salinity of below 35 ppt. The current is stratified by temperature and salinity differences.

Climate change

The 1990s were an exceptional decade for interannual climate variations. The temperatures each year have been on average warmer, producing wet, warm winters and hot summers in Norway. This has led to increased precipitation extremes, and changes in fish stocks. Increased atmospheric temperatures due to global climate change cause strong south westerly winds to pile water up along the Norwegian coast. The pressure difference creates storm surges that have increased coastal flooding in recent years.^[1] Temperatures have also been climbing in the deepest layers of Norwegian coastal waters. Increasing temperatures cause a decrease in sea ice, supplying the Norwegian Sea with greater amounts of freshwater and lowering the salinities overall. This decrease in salinity could cause changes in the sinking of cooling Atlantic Waters and may inhibit the formation of bottom water, thus reducing Atlantic inflow to the Nordic Seas.^[1] If Atlantic inflow is decreased, the climate will be cooler in the Norwegian region.

See also

• Ocean current
• Norwegian trench

References

1. ^ ^{a b c d e f g h} Saetre, Roald, ed. 2007. The Norwegian Coastal Current—Oceanography and Climate. Tapir Academic Press; Trondheim. ISBN 8251921848
2. ^ ^{a b c} Mork, M. (1981). "Circulation Phenomena and Frontal Dynamics of the Norwegian Coastal Current". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 302 (1472): 635. doi:10.1098/rsta.1981.0188. 
3. ^ ^{a b c} Gyory, Joanna , Arthur J. Mariano, Edward H. Ryan. 2001–2008. "The Norwegian & North Cape Currents." Ocean Surface Currents. (Accessed 2009)
4. ^ Helland-Hansen, B., and F. Nansen, 1909: The Norwegian Report on Norwegian Fishery and Marine-Investigations, 2, 1–359.
5. ^ Ikeda, M.; Johannessen, J.A.; Lygre, K.; Sandven, S. (1989). "A Process Study of Mesoscale Meanders and Eddies in the Norwegian Coastal Current". Journal of Physical Oceanography 19: 20. doi:10.1175/1520-0485(1989)019<0020:APSOMM>2.0.CO;2. ISSN 1520-0485. 
6. ^ Saetre, R., and R. Ljoen, 1972: The Norwegian Coastal Current. Proceedings of the First International Conference on Port and Ocean Engineering, vol.1, pp.514–535.
7. ^ Haugan, Peter M.; Evensen, Geir; Johannessen, Johnny A.; Johannessen, Ola M.; Pettersson, Lasse H. (1991). "Modeled and Observed Mesoscale Circulation and Wave-Current Refraction During the 1988 Norwegian Continental Shelf Experiment". Journal of Geophysical Research 96: 10487. Bibcode 1991JGR....9610487H. doi:10.1029/91JC00299. 

External links

• Norwegian current

Coordinates: 67°N 3°E / 67°N 3°E / 67; 3