SWEET Ontology Realm Cryosphere

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This zone usually occurs at higher elevations and generally overlaps the conversion of snow to glacial ice.

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The greater part of an iceberg's mass (4/5 to 8/9) is below sea level, which makes them dangerous to shipping in high and mid-latitude regions of the ocean. The top of an ice berg usually protrudes more than 5 m above water-level and typically extends from tens of meters to many tens of kilometres across. Icebergs may be described as tabular, dome-shaped, sloping, pinnacled, dry-docked, blocky, weathered or glacier bergs in addition to having a size qualifier. Icebergs are not sea ice, when they melt they add fresh water to the ocean. The unmodified term iceberg usually refers to the irregular masses of ice formed by the calving of glaciers along an orographically rough coast, whereas tabular icebergs and ice islands are calved from an ice shelf, while bergs formed from sea ice are called floebergs. In decreasing size, they are classified as: ice island (few thousand square meters to 500 km^2 in area); tabular iceberg; iceberg; bergy bit (less than 5 m above sea level, between 1 and 200 m^2 in area); and growler (less than 1 m above sea level, about 20 m^2 in area). Alaskan icebergs rarely exceed 500 feet in maximum dimension. Antarctic icebergs originate from the ice mass of the Antarctic continent that has accumulated over many thousands of years.

Land ice is any part of the Earth's seasonal or perennial ice cover that has formed over land as the result, principally, of the freezing of precipitation; opposed to sea ice formed by the freezing of seawater. Thus, an iceberg or tabular iceberg is land ice as well as its parent glacier, ice sheet, or ice shelf. The two major concentrations of land ice are the ice sheets of Greenland and Antarctica. Glaciers and ice caps are the other important forms; however, some members of the glaciology community hold that glaciers (i.e. rock glaciers) need not have any ice.

Generally, leads are wide enough (and deep enough) for navigation by surface vessels. The term is generally applied to linear features. If the open area is very large it may be called a polynya, although the application of these terms is under debate.

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In the United States, NOAA sea ice operations does not include superstructure icing as being sea ice. In sea ice operations however, sea ice is any form of ice found at sea which has originated from the freezing of sea water. It presents the main kind of floating ice encountered at sea. Except where it forms ridges, sea ice is up to a few metres thick, in which respect it differs from shelf ice. Sea ice may be discontinuous pieces (ice floes) moved on the ocean surface by wind and currents (pack ice), or a motionless sheet attached to the coast (land-fast ice). In brief, it forms first as lolly ice (frazil crystals), thickens into sludge, and coagulates into sheet ice, pancake ice, or into floes of various shapes and sizes. Thereafter, sea ice may develop into pack ice and/or become a form of pressure ice. Sea ice less than one year old is called first-year ice. Perennial ice is sea ice that survives at least one summer. It may be subdivided into second-year ice and multi-year ice, where multiyear ice has survived at least two summers.

Sea ice develops from young ice; thickness from 0.3 to 2 meters (1 to 6.6 feet). Sea ice be subdivided into thin first-year ice (white ice), medium first-year ice, and thick first-year ice. First-year ice is distinguished from older ice primarily by having a higher salinity. Undeformed first-year ice differs from older ice in that it is smoother and lacks refrozen melt ponds. Characteristically level where undisturbed by pressure, but where ridges occur, they distinguished by being larger, more angular, and more porous than multiyear ridges.

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Newly formed tabular icebergs have nearly vertical sides and flat tops. In the Antarctic, they may be tens of kilometers wide, up to 160 km (100 miles) long, and as much as 300 m (1000 ft) thick, with about 30 m (100 ft) exposed above the sea surface. In the Arctic, large icebergs of this type are called ice islands, but they are considerably smaller than the largest of the antarctic variety. Has synonyms tabular berg, table iceberg. Formerly called barrier iceberg.

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