Ice drift

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Under ice drift refers to the movement of sea ice in one main direction. The moving ice is referred to as drift ice , in contrast to fixed ice , which is anchored on the coast or on the seabed. The speed of movement depends on the wind, the prevailing ocean current , the compactness of the ice and the temperature (season) of the ice region. Ice drift can be measured selectively with buoys or ice drift stations or over a large area with satellite.

Ice drift in the Arctic

Map of the Arctic (mid-1970s): schematically drawn Beaufort vortex (Beaufort Gyral Stream) and transpolar drift (Transpolar Drift Stream)

There are two main currents of ice drift in the Arctic. The transpolar drift leads from Siberia to Greenland. It transports large amounts of ice through the Fram Strait into the Greenland Current along the east coast of Greenland. The Beaufort vortex rotates clockwise as seen from above from the northern coasts of Greenland , Canada and Alaska in the region of the Beaufort Sea . The speed of the ice drift is around 1% to 2% of the wind speed. In the monthly averages for the period 1992–2009, it ranges from around a quarter of a kilometer per hour after the maximum sea ice extent has been reached in April to half a kilometer per hour after the peak of the melting period in October. In large parts of the Arctic, the speed of ice drift has increased since 1992, by around 20% overall. There has been a clear acceleration since 2000. The reasons for this are the ever thinner ice sheet and higher wind speeds in parts of the Arctic.

The Norwegian polar researcher Fridtjof Nansen was one of the first to conduct a detailed study of the ice drift in the northern polar region. The report on the unsuccessful Jeanette expedition (1879 to 1881) under George W. DeLong confirmed Nansen in his theory of drifting in the pack ice across the polar sea, which was established in 1882 . He developed the idea of ​​freezing himself in a pack-ice ship in the polar ice in order to drift over the North Pole to the North Atlantic . From 1893 to 1896 he proved his theory with the Fram expedition with the packable sailing ship Fram .

On his expedition, Nansen observed a deviation of the ice drift from the prevailing wind direction. She inspired Vagn Walfrid Ekman to develop the Ekman spiral , which explains the deviation through the effect of the Coriolis force .

Ice drift in Antarctica

Sea ice drift in Antarctica

In the Antarctic, the sea ice near the coast moves with the Antarctic coastal current in a westerly direction. In the Weddell Sea , it partly enters the Antarctic Circumpolar Current in the Weddell Vortex along the Antarctic Peninsula to the north . In the Ross Sea , too, parts of the ice are transported northward into the Circumpolar Current by the Rosswirl , which then drifts it mainly in an easterly direction. Drift speeds in Antarctica are higher than in the Arctic. Measurements with buoys between 1985 and 1997 have shown mean drift speeds of 0.83 km / h in the Antarctic Coastal Current and 0.61 km / h in the Circumpolar Current. Observed top speeds ranged up to 3.25 km / h.

Several Antarctic expeditions failed in the ice drift of the Weddell Sea. In March 1912 Wilhelm Filchner's ship Deutschland was trapped in the pack ice and drifted north for nine months; they were not released until December in South Georgia . Another case is the endurance expedition from 1914 to 1917 under Ernest Shackleton . His expedition ship Endurance was trapped by the ice near Prinzregent-Luitpold-Land . The expedition members drifted as far as the vicinity of Elephant Island on the northern tip of the Antarctic Peninsula, where they were able to escape to the island.

literature

Individual evidence

  1. ^ A b W. J. Emery, CW Fowler and JA Maslanik: Satellite-derived maps of Arctic and Antarctic sea ice motion: 1988 to 1994 . In: Geophysical Research Letters . 1997, doi : 10.1029 / 97GL00755 .
  2. ↑ G. Spreen, R. Kwok and D. Menemenlis: Trends in Arctic sea ice drift and role of wind forcing: 1992-2009 . In: Geophysical Research Letters . tape 38 , 2011, doi : 10.1029 / 2011GL048970 .
  3. ↑ see also en: Jeannette Expedition
  4. ↑ Ice Drift and Deformation. Scientific Committee on Antarctic Research (SCAR), Expert Group on Antarctic Sea Ice Research (ASPeCt), 2011, accessed April 27, 2012 .

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