Drift ice, also called brash ice, is

sea ice 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 oce ...

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, 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 up to tens 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 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) * Geological impact * Biosphere influence (see

Ecology of sea ice 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 oce ...

) 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 The Arctic ice pack is the sea ice cover of the Arctic Ocean and its vicinity. The Arctic ice pack undergoes a regular seasonal cycle in which ice melts in spring and summer, reaches a minimum around mid-September, then increases during fall a ...

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 region The polar regions, also called the frigid geographical zone, zones or polar zones, of Earth are the regions of the planet that surround its geographical poles (the North Pole, North and South Poles), lying within the polar circles. These high l ...

s: 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 An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

, 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 Image:IceNomenclature-2LightPack.jpg, Ice floes / pack ice Image:Wrangelisland.jpg, Satellite image of drift ice in the Arctic Ocean around Wrangel Island Image:Icebreaker Aurora on drift ice at Sea of Okhost.jpg, Drift ice in the

Sea of Okhotsk The Sea of Okhotsk ( rus, Охо́тское мо́ре, Ohótskoye móre ; ja, オホーツク海, Ohōtsuku-kai) is a marginal sea of the western Pacific Ocean. It is located between Russia's Kamchatka Peninsula on the east, the Kuril Islands ...

Image:Aboard Aurora Icebreaker at Sea of Okhost.jpg, Aboard the ''Aurora'' icebreaker in the Sea of Okhotsk Seasonal ice drift in the

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