Drift ice

Last updated on 22 October 2017

Drift ice is any sea ice other than fast ice, the latter being attached ("fastened") to the shoreline or other fixed objects (shoals, grounded icebergs, etc.).[1][2][3] Drift ice is carried along by winds and sea currents, hence its name. When drift ice is driven together into a large single mass (>70% coverage), it is called pack ice.[1] Wind and currents can pile up that ice to form ridges up to several metres in height. These represent a challenge for icebreakers and offshore structures operating in cold oceans and seas.

Drift ice consists of floes, individual pieces of sea ice 20 metres (66 ft) or more across. There are names for various floe sizes: small – 20 metres (66 ft) to 100 metres (330 ft); medium – 100 metres (330 ft) to 500 metres (1,600 ft); big – 500 metres (1,600 ft) to 2,000 metres (6,600 ft); vast – 2 kilometres (1.2 mi) to 10 kilometres (6.2 mi); and giant – more than 10 kilometres (6.2 mi).[4][5]

Seasonal ice drift in the Sea of Okhotsk by the northern coast of Hokkaidō, Japan has become a tourist attraction of this area with harsh climate,[6] and is one of the 100 Soundscapes of Japan. The Sea of Okhotsk is the southernmost area in the Northern hemisphere where drift ice may be observed.[7]

Drift ice affects:

Drift ice can exert tremendous forces when rammed against structures, and can shear off rudders and propellers from ships and strong structures anchored to the shore, such as piers. These structures must be retractable or removable to avoid damage. Similarly, ships can get stuck between drift ice floes.

The two major ice packs are the Arctic ice pack and the Antarctic ice pack. The most important areas of pack ice are the polar ice packs formed from seawater in the Earth's polar regions: the Arctic ice pack of the Arctic Ocean and the Antarctic ice pack of the Southern Ocean. Polar packs significantly change their size during seasonal changes of the year. Because of vast amounts of water added to or removed from the oceans and atmosphere, the behavior of polar ice packs has a significant impact on global changes in climate.

Kontio towing.jpg
Icebreaker Kontio assisting merchant vessel in pack ice in the northern Baltic sea. In this photo the Kontio has become stuck in drift ice while towing a cargo ship.
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Ice floes / pack ice
Wrangelisland.jpg
Satellite image of drift ice in the Arctic Ocean around Wrangel Island
Greenland East Coast 7.jpg
Drift ice, Greenland
Sea ice Drawing General features.svg
Fast ice (left, along shoreline) versus drift ice (right) in a hypothetical sea ice dynamics scenario.

See also

References

  1. ^ a b WMO Sea-Ice Nomenclature
  2. ^ Weeks, Willy F. (2010). On Sea Ice. University of Alaska Press. p. 2. ISBN 978-1-60223-101-6.
  3. ^ Leppäranta, M. 2011. The Drift of Sea Ice. Berlin: Springer-Verlag.
  4. ^ NSIDC All About Sea Ice
  5. ^ Environment Canada Ice Glossary
  6. ^ "A Port's Ice Is Thinning, and So Is Its Tourist Trade", New York Times, March 14, 2006.
  7. ^ Honda, Meiji, Koji Yamazaki, Hisashi Nakamura, Kensuke Takeuchi, 1999: Dynamic and Thermodynamic Characteristics of Atmospheric Response to Anomalous Sea-Ice Extent in the Sea of Okhotsk. J. Climate, 12, 3347–3358.

External links

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