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Drift ice is ice that floats on the surface of the water in cold regions, as opposed to fast ice, which is attached ("fastened") to a shore. Usually drift ice is carried along by winds and sea currents, hence its name, "drift ice".
When the drift ice is driven together into a large single mass, it is called pack ice. Wind and currents can pile up ice to form ridges three to four metres high, creating obstacles difficult for powerful icebreakers to penetrate. Typically areas of pack ice are identified by high percentage of surface coverage by ice: e.g., 80-100%.
An ice floe is a large piece of drift ice that might range from tens of metres (yards) to several kilometres in diameter. Wider chunks of ice are called ice fields.
In many areas such as the Baltic, drift ice is traditionally a seasonal event, appearing in winter and vanishing in warmer seasons.
Seasonal ice drift in the Sea of Okhotsk by the northern coast of Hokkaidō, Japan has become a tourist attraction of this area with harsh climate, 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.
Drift ice affects:
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.
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