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Icebergs and Sea Ice
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ICEBERGS
An iceberg is a floating mass of fresh water ice extending more than 5 m above the sea surface.  It may originate from a glacier flowing directly to the sea, such as the tidewater glaciers of Greenland, or from an ice shelf, such as those found in Antarctica.

Most icebergs appear white. Their white appearance is because sunlight doesn’t penetrate iceberg ice very far due to the presence of numerous small air bubbles frozen in the ice.  These bubbles scatter sunlight of all wave lengths giving the characteristic white appearance. Icebergs can also appear to be blue or green
 

Ice Reconnaissance

Photo of an iceberg taken from an IIP Ice Reconnaissance Detachment.

Colorful Icebergs

Sometimes icebergs can be quite colorful. It is common to see blue streaks in icebergs and, less frequently, brown stripes. Icebergs that are partly or wholly green have also been seen. Blue stripes are formed when cracks in the ice fill with melt water and the water refreezes. The melt water is nearly bubble free, so it takes on the characteristic blue tint of frozen freshwater. There have been reports of icebergs that were entirely blue such as this description in the 1958 IIP Annual Report:


“An unusual and most interesting iceberg drift occurred during April when, on the 10th, an iceberg was reported south of Heath Point, AnticostiIsland.  A Canadian Department of Transport survey flight located this iceberg (or growler) on 14 April and again on 17 April.  Capt. Angus Brown, Chief Ice Observer, reported it to be of “hard blue ice” and of glacial origin.  This agrees with IIP observations that icebergs with a bluish cast are particularly hard and long lived. This extremely rare iceberg was thought to be a survivor from the many icebergs that were driven through the Strait of Belle Isle during strong NE winds the previous month.”

It is not clear if this blue iceberg is the remnant of a refrozen, melt-water-filled crack, or was the result of some other process.

Ice Reconnaissance Detachment

Photo of an iceberg taken from an IIP Ice Reconnaissance Detachment.

Because icebergs originate from land, it is not surprising that dirt and rocks can become embedded within the ice. This can occur in layers creating stripes of varying shades of brown. Much has been written about bottle-green icebergs that are sometimes seen in the Antarctic. Several mechanisms have been proposed, but the most likely explanation for the green color is the freezing of organic-rich seawater to the underwater part of the ice shelf from which the iceberg calved. The green ice is exposed after an iceberg breaks free of the shelf and rolls over.