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.).Leppäranta, M. 2011. The Drift of Sea Ice. Berlin: Springer-Verlag. Unlike

fast ice Fast ice (also called ''land-fast ice'', ''landfast ice'', and ''shore-fast ice'') is sea ice that is "fastened" to the coastline, to the sea floor along shoals or to grounded icebergs.Leppäranta, M. 2011. The Drift of Sea Ice. Berlin: Springer- ...

, 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. Wind and currents can pile up that ice to form

ridges A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a continuous elevated crest for an extended distance. The sides of the ridge slope away from the narrow top on either side. The line ...

up to tens of metres in thickness. These represent a challenge for

icebreaker An icebreaker is a special-purpose ship or boat designed to move and navigate through ice-covered waters, and provide safe waterways for other boats and ships. Although the term usually refers to ice-breaking ships, it may also refer to smaller ...

s and offshore structures operating in cold oceans and seas. Drift ice consists of

ice floe An ice floe () is a large pack of floating ice often defined as a flat piece at least 20 m across at its widest point, and up to more than 10 km across. Drift ice is a floating field of sea ice composed of several ice floes. They may cau ...

s, individual pieces of sea ice or more across. Floes are classified according to size: ''small'' – to ; ''medium'' – to ; ''big'' – to ; ''vast'' – to ; and ''giant'' – more than . Drift ice affects: * Security of navigation * Climatic impact (see

Polar ice packs Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's o ...

) * 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 Antarctic sea ice is the sea ice of the Southern Ocean. It extends from the far north in the winter and retreats to almost the coastline every summer, getting closer and closer to the coastline every year due to sea ice melting. Sea ice is frozen ...

. 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. Image: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 The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and ...

Image:IceNomenclature-2LightPack.jpg,

Ice floe An ice floe () is a large pack of floating ice often defined as a flat piece at least 20 m across at its widest point, and up to more than 10 km across. Drift ice is a floating field of sea ice composed of several ice floes. They may cau ...

s / pack ice Image:Wrangelisland.jpg,

Satellite image Satellite images (also Earth observation imagery, spaceborne photography, or simply satellite photo) are images of Earth collected by imaging satellites operated by governments and businesses around the world. Satellite imaging companies sell ima ...

of drift ice in the Arctic Ocean around

Wrangel Island Wrangel Island ( rus, О́стров Вра́нгеля, r=Ostrov Vrangelya, p=ˈostrəf ˈvrangʲɪlʲə; ckt, Умӄиԓир, translit=Umqiḷir) is an island of the Chukotka Autonomous Okrug, Russia. It is the 91st largest island in the w ...

Image:Icebreaker Aurora on drift ice at Sea of Okhost.jpg, Drift ice in the Sea of Okhotsk Image:Aboard Aurora Icebreaker at Sea of Okhost.jpg, Aboard the ''Aurora'' icebreaker in the Sea of Okhotsk Seasonal ice drift in the Sea of Okhotsk by the northern coast of Hokkaidō, Japan, has become a tourist attraction, 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.

References

External links

"Ice in the Sea"
: chapter from Nathaniel Bowditch's ''American Practical Navigator''
Cryosphere Today : Current Arctic sea ice conditions

Data source for sea ice picture

Marine Modeling and Analysis Branch

* ttp://www.arctic.noaa.gov/detect/animations/halfsize_20030928-20040510.avi 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 {{DEFAULTSORT:Drift Ice Sea ice Oceanography

See also

References

External links