Drift ice
Drift ice, also called brash ice, is sea ice that is not attached to the shoreline or any other fixed object (shoals, grounded icebergs, etc.).<ref name="WMO"/><ref name="Weeks">Template:Cite book</ref><ref name="Lepparanta">Leppäranta, M. 2011. The Drift of Sea Ice. Berlin: Springer-Verlag.</ref> Unlike fast ice, which is "fastened" to a fixed object, 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.<ref name="WMO">WMO Sea-Ice Nomenclature</ref> Wind and currents can pile up that ice to form ridges up to dozens of metres in thickness. These represent a challenge for icebreakers and offshore structures operating in cold oceans and seas.
Drift ice consists of ice floes, individual pieces of sea ice Template:Convert or more across. Floes are classified according to size: small – Template:Convert to Template:Convert; medium – Template:Convert to Template:Convert; big – Template:Convert to Template:Convert; vast – Template:Convert to Template:Convert; and giant – more than Template:Convert.<ref name=NSIDC>NSIDC All About Sea Ice</ref><ref name="ECGlossary">Environment Canada Ice Glossary</ref>
Drift ice affects:
- Security of navigation
- Climatic impact (see Polar ice packs)
- Geological impact
- Biosphere influence (see Ecology of sea ice)
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.
Seasonal ice drift in the Sea of Okhotsk by the northern coast of Hokkaidō, Japan, has become a tourist attraction,<ref>"A Port's Ice Is Thinning, and So Is Its Tourist Trade", The New York Times, March 14, 2006.</ref> 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.<ref>Template:Cite journal</ref>
GalleryEdit
- Kontio towing.jpg
The icebreaker Kontio, which in this picture became stuck in drift ice while towing a cargo ship in pack ice in the northern Baltic Sea
- IceNomenclature-2LightPack.jpg
Ice floes / pack ice
- Wrangelisland.jpg
Satellite image of drift ice in the Arctic Ocean around Wrangel Island
- Icebreaker Aurora on drift ice at Sea of Okhost.jpg
Drift ice in the Sea of Okhotsk
- Aboard Aurora Icebreaker at Sea of Okhost.jpg
Aboard the Aurora icebreaker in the Sea of Okhotsk
See alsoEdit
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ReferencesEdit
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External linksEdit
- "Ice in the Sea" : chapter from Nathaniel Bowditch's American Practical Navigator
- Cryosphere Today : Current Arctic sea ice conditions Template:Webarchive
- Data source for sea ice picture
- Marine Modeling and Analysis Branch Template:Webarchive
- Everything you ever wanted to know about sea ice but were afraid to ask
- Animation of the movement of sea ice, September 2003 through May 2004
- Atlas of Antarctic Sea Ice Drift
- The Papers of Paul Gordienko on Ice and Ice Drifts at Dartmouth College Library