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Delimiting the shelf

12/08/2005 The water depth in the Arctic Ocean determines the size of the Norwegian continental shelf. In September the Norwegian Petroleum Directorate (NPD) heads north in order to determine the outer limits of the shelf.

By signing the UN Law of the Sea Treaty, Norway has committed itself to chart and document the limits beyond 200 nautical miles from land. Geologists and geophysicists in the NPD have been working for nine years in order to determine the extent of the Norwegian continental shelf.

The Law of the Sea regulations on economic zones and the continental shelf have lead to Norway having jurisdiction over an area that is among the largest sea areas in the world under the jurisdiction of one country (six times larger than the mainland area).

Most of the Norwegian continental shelf has already been demarcated, but there are some areas still remaining, such as in The Barents Sea Loophole (Smutthullet) in the Barents Sea, in The Banana Hole of the Northeast Atlantic(Smutthavet) east of Jan Mayen and in The Nansen Basin in the Arctic Sea north of Svalbard.


According to the Law of the Sea Convention, the continental shelf can stretch beyond 200 nautical miles, depending on the geological conditions. For such areas the Convention allows a choice of different methods to determine the limits of the shelf:

One method involves setting the limit of the continental shelf at a distance of 60 nautical miles outside the foot of the continental slope. The other method is to determine the position of the limit with reference to the thickness of the rocks under the seabed outside the continental slope. The limit will then be set where the thickness of the sediments is at least one per cent of the distance in to the foot of the continental slope.

Data collected in connection with the icebreaker Oden's expedition to the Nansen basin in the Arctic Sea during the autumn of 2001 proved sedimentary layers in the deep sea north of Svalbard which are thick enough for the Norwegian continental shelf to be stretched further north than first thought.

The expedition, which took place in cooperation with the University of Bergen under the direction of the NPD, gathered approximately 1000 kilometres of reflection seismics, 50 sonar buoy measurements and around 1900 kilometres of echo sound measurements.

This data has great scientific value as well and has been the basis of several post-graduate theses in geology/geophysics at the universities of Bergen and Oslo. Research fellow Øyvind Engen at the Department of Geosciences, University of Oslo is currently about to defend his doctoral thesis "Evolution of High Arctic Ocean Basins and Continental Margins"  based on the same data. 

The icebreaker ODEN (Photo: Sjöfartsverket, Sweden)

The Swedish Oden, which during the winter breaks up the ice in the Finnish Bay, is going on another expedition under NPD's direction this autumn. Once again the ship is heading for the area north of Svalbard, this time to measure sea depths, says senior geologist Harald Brekke in the NPD.

"The expedition sets out at the end of September, and we shall be collecting sea depth data in the area north of Kvitøya on Svalbard. We have a rough idea of the depths in this area, but the Law of the Sea Commission demands exact measurements from the foot of the slope, i.e. where the continental shelf slope changes into a deep sea plain. This is the only data collection that remains before Norway can submit its limit proposal to the UN," Brekke says.

Norway's limit proposal for the continental shelf will be submitted next summer. The final decision is expected a couple of years later.

As it looks now, the northern limit for the Norwegian continental shelf will lie between 84o and 85o North.

Senior geologist Harald Brekke in the NPD is Norway's representative in the UN Commission on the Limits of the Continental Shelf. The Commission's mandate is to ensure that the limits of all the world's continental shelves are determined in accordance with the Law of the Sea Treaty.

The Law of the Sea Treaty has so far been signed by 140 countries. Norway signed the treaty in 1996, 12 years after it entered into force.

Contact person in the NPD:
Eldbjørg Vaage Melberg, tel. +47 51 87 61 00

Updated: 14/12/2009