Several observations the last couple of years have indicated that the Atlantic Ocean deep-sea currents have been remarkable weakened, possibly as a consequence of global warming. What has concerned scientists the most, is the reports of the current beeing halved southwards with cold water from the Norwegian Sea, which will result in the Gulfstream warm current towards the Norwegian coast to be weakened equivalently. However, in a recent issue of Nature, with scientist from Denmark, the Faroe Islands, Germany and Norway, confirms that the deep cold sea currents are stable. These scientists have studied the sea currents strength over the submarine ridge between Greenland and Scotland. By combining measurements of sea currents strength with results from mathematic models, it has been possible for the team of scientists to prove that the sea current has held a constant strength the last 50 years.
Models back to 1948
Since the middle of the 1990s the scientist have measured the intensity of the sea currents between Greenland and Scotland. The last couple of years the Bjerknes Centre have had a main role in the development and improvement of instruments for measurement placed in the seabed, due to the Bjerknes Centre’s role as coordinator of a major Norwegian project. In addition the scientist have tried to recreate the sea currents in the area back to 1948 using models. According to the article, there where agreement between recreated sea currents in the models and in the directly measurements, which strengthen the confidence of the results.
Thermohaline circulation
The deep-sea cold currents, which are transported out of the Norwegian Sea and the warm currents in return northward, makes all together part of the Atlantic Ocean thermohaline circulation (THC). The Gulf Stream, which leads warm tropic water into the Norwegian Sea, is part of this grand scale circulation, which is driven by temperature and salt differences. Nevertheless, it has been observed that there are substantial changes in temperature and salt proportion in the Norwegian Sea, which should mean weaker pressure in the outgoing currents from the cold deep-water masses. But because of the changes in the wind system in this area, an increase in the sea level has compensated for this pressure difference. This could result in even warmer climate in Scandinavia than before estimated with global warming.
Consequences with warmer climate
An overheated ocean will mean that it will be warmer up north, but it will also have a consequence for the fish resources along the Norwegian coastline. Scientist will study these effects and the warm water transportation in the ocean towards the Arctic. The team of scientist emphasizes the importance of continuing to monitor the sea currents and keep developing the models to be able to forecast and warn about the risk for sudden changes. Also in this issue the Bjerknes Centre will have an important part as a coordinator in a new EU-project.
Article in Nature: Steffen M. Olsen, Bogi Hansen, Detlef Quadfasel og Svein Østerhus (2008): Observed and modelled stability of overflow across the Greenland–Scotland ridge. Nature 455, 519-522