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Drift ice

(Redirected fromPack ice)

Drift ice,also calledbrash ice,issea icethat is not attached to the shoreline or any other fixed object (shoals, grounded icebergs, etc.).[1][2][3]Unlikefast ice,which is "fastened" to a fixed object, drift ice is carried along by winds andsea currents,hence its name. When drift ice is driven together into a large single mass (>70% coverage), it is calledpack ice.[1]Wind and currents can pile up that ice to formridgesup to dozens of metres in thickness. These represent a challenge foricebreakersand offshore structures operating in cold oceans and seas.

Drift ice,Greenland
Fast ice(left, along shoreline) versusdrift ice(right) in a hypothetical sea ice dynamics scenario

Drift ice consists ofice floes,individual pieces of sea ice 20 metres (66 ft) or more across. Floes are classified according to size: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); andgiant– more than 10 kilometres (6.2 mi).[4][5]

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 theArctic ice packand theAntarctic ice pack.The most important areas of pack ice are the polar ice packs formed fromseawaterin the Earth'spolar regions:the Arctic ice pack of theArctic Oceanand the Antarctic ice pack of theSouthern 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 andatmosphere,the behavior of polar ice packs has a significant impact on global changes inclimate.

Seasonal ice drift in theSea of Okhotskby the northern coast ofHokkaidō,Japan,has become a tourist attraction,[6]and is one of the100 Soundscapes of Japan.The Sea of Okhotsk is the southernmost area in theNorthern Hemispherewhere drift ice may be observed.[7]

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See also

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  • Drifting ice station– Research stations built on the ice of the high latitudes of the Arctic Ocean
  • Iceberg– Large piece of freshwater ice broken off a glacier or ice shelf and floating in open water
  • Ice shove– Ice pushed onshore due to water movements or wind
  • Lead (sea ice)– Fracture that opens up in an expanse of sea ice
  • Polynya– Area of unfrozen sea within an ice pack
  • Pressure ridge (ice)– Linear accumulation of ice blocks resulting from the convergence between floes
  • Seabed gouging by ice– Outcome of the interaction between drifting ice and the seabed
  • Sea ice– Outcome of seawater as it freezes
  • Shelf ice– Ice formed on a lake and washed up on the shore

References

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  1. ^abWMO Sea-Ice Nomenclature
  2. ^Weeks, Willy F. (2010).On Sea Ice.University of Alaska Press. p. 2.ISBN978-1-60223-101-6.
  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",The 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 ".Journal of Climate.12.Journals.ametsoc.org: 3347. 1999.doi:10.1175/1520-0442(1999)012<3347:DATCOA>2.0.CO;2.ISSN1520-0442.
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