Drift ice
Pack ice or 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 meters in height. These represent a challenge for icebreakers and offshore structures operating in cold oceans and seas.
Pack ice consists of floes, individual pieces of sea ice 20 meters (66 ft) or more across. Floes are classified according to size: small – 20 meters (66 ft) to 100 meters (330 ft); medium – 100 meters (330 ft) to 500 meters (1,600 ft); big – 500 meters (1,600 ft) to 2,000 meters (6,600 ft); vast – 2 kilometers (1.2 mi) to 10 kilometers (6.2 mi); and giant – more than 10 kilometers (6.2 mi).
Drift ice affects:
- Security of navigation
- Climatic impact
- Geological impact
- Biosphere influence
Pack 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 most important ice packs are the Arctic ice pack and the Antarctic ice pack. Polar packs significantly change their size during seasonal times 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.
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