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Large sea ice production affects the climate?

04.06.08

Last winter there was a substantial amount of sea ice in Storfjorden on Svalbard, resulting in a cold and saline current that flowed out of the fjord. This event can have impact on the global sea currents and on the Arctic climate.

Text: Frank Nilsen, UNIS Associate professor in ocenaography and Tor Gammelsrød, BIAC

The phenomenon was discovered by UNIS students in early May. The International Polar Year (IPY) project BIAC will investigate if this formation of dense water can affect the global sea currents.

Photo: Kjersti Lundmark Daae
UNIS students tackle blocks of sea ice on their cruise with R/V Lance on the west side of Svalbard in May. (Photo: Kjersti Lundmark Daae).

Important process
On a UNIS student cruise in early May with R/V Lance a substantial, cold and saline bottom current south of Storfjorden was discovered (figure 1).



Figure 1: Distribution of ice around Svalbard April 9. 2008. (MODIS data, NASA). The ice pack in Storfjorden was so dense that it was impossible for R/V Lance to penetrate. Note the dark areas down-wind from Barentsøya and Edgeøya. These are polynyas where ice freezing is particularly effective. The line SE from Sørkapp (Sørkapp Section) indicates where the cold dense plume was observed from R/V Lance. The origin of this bottom plume is Storfjorden and may be tracked all the way to the Arctic Ocean. Also indicated is the prolongation of a branch of the Gulf Stream, which here is called the West Spitsbergen Current. Ill: Frank Nilsen/UNIS

This cold and saline water (figure 2) is generated when sea water cools off and freezes. The formation of sea ice increases the salinity of the water column because salt is expelled from the ice.

The freezing of the sea is therefore a very important process in the production of dense bottom water, which is a driving force in the global sea circulation, and thus is of importance for the climate.


Figure 2: Profiles of temperature, salinity and density obtained 120km south of the sill of Storfjorden. The cold, saline and dense current is revealed in the lower 40 meters. Ill: BIAC.

Enormous sea ice formation
The winter of 2008 has been very favorable for the formation of sea ice in Storfjorden. Cold winds from the north and east have been the dominating weather pattern this winter. The shifting winds and tidal currents have constantly produced polynyas in the sea ice where ice freezes very quickly.

If one could gather all the sea ice produced in Storfjorden through one winter, there would be a 15 meter thick ice cover. Storfjorden can in other words be called a real “ice factory”.

Unknown destiny
The dense water from Storfjorden flows first southward, but is affected by the Earth’s rotation and turns right. It then follows the continental shelf slope northwards on the west side of Svalbard before it ends up in the Arctic. It’s destiny in the polar basin is so far unknown (figure 1).

It is too early to estimate the importance of this bottom current from Storfjorden has on a global scale. The IPY project BIAC (Bipolar Atlantic Thermohaline Circulation) has five current meter moorings in Storfjorden and data from these can hopefully give some answers.

Due to the large amount of sea ice R/V Lance did not manage to enter the Storfjorden to pick up these moorings. We are now hoping that the sea ice keeps the trawlers out of the fjord until the Coast guard ship KV Svalbard can enter Storfjorden in June to collect the current meter moorings.

BIAC also has five moorings in the Russian sector between Franz Josef Land and Novaya Zemlja, which will be picked up by a Russian expedition in the fall. It will be exciting to the results from these moorings after a winter with large sea ice formation in the Barents Sea.

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