Ice shelves disintegrate mainly through the calving of ice islands. This occurs as the terminus of an ice shelf breaks off and becomes a free floating island of ice.

Although no complete explanations of the mechanisms which cause ice island calving have been accepted, the following is an overview of proposed plausible scenarios:

Scenario One

Persistent winds, tidal action and pressure from the surrounding ice pack may cause cracks to develop within the ice shelf: this producing an ice island. (Holdsworth 1971, Jeffries 1985)

Scenario Two

Vibrations due to wave action cause a resonance. This motion is generally called oscillation. Sometimes the oscillation is easy to see such as the motion of a swing on a playground or the vibration in a guitar string. In other cases the oscillation is impossible to see without measuring instruments. For example, electrons in an electrical circuit can oscillate but it happens on a molecular level.

Ultimately some of the energy in the oscillations has to be removed from the object or the size of the oscillations get so large that the object breaks. Taken from The Physics of Resonance that causes stresses in the ice shelf to the point where a fracture can occur. (Holdsworth & Glynn 1978)

Scenario Three

Strong tides associated with storm surges occur, creating a period of time of intense pressure against the ice shelf, which causes the shelf to crack. The prevailing winds then change, creating open water and areas where the newly calved ice island can flow into. (Sackinger 1987)

Ice Island Drift Mechanisms

There are two main influences on the drift patterns of ice islands once they have calved: Ocean Currents and Prevailing Winds.

Much of the bulk of an ice island is beneath the water's surface, therefore, ocean currents play a major role in ice island transport. Similarly, because ice islands also have large surface areas exposed to the atmosphere above water, prevailing winds will also play an important role in generating drift. In most cases, the prevailing wind patterns will complement ocean currents (as winds are an important aspect of creating ocean currents).Therefore the drift of ice islands usually results due to the complementary nature of ocean currents and winds.

The Beaufort Gyre

The Beaufort Gyre plays a significant role in determining the drift patterns of ice islands in the Arctic Ocean.

The Beaufort Gyre is a slowly rotating current of mostly fresh water originating from the Pacific Ocean which is funnelled through the Bering Strait into the Beaufort Sea area of the Arctic Ocean. The gyre is created bye the clockwise rotation of prevailing winds over the Arctic Ocean, which in turn causes a clockwise rotation of the waters under them.

The Beaufort Gyre makes one complete rotation approximately every four years. (Related link - Remote Beaufort Gyre expeditions reveal clues to climate change, Woods Hole Oceanographic Institution)

The clockwise rotation of the Beaufort Gyre causes the immediate south-westward drift of ice islands calved from Ellesmere Island's northwest coastline. The ice islands usually hug the coastline of the Queen Elizabeth Islands as they make their way toward the Mackenzie Delta. From here, the common drift pattern is for the islands to move northwest following the Alaskan coastline, then move northeast toward the North Pole, and finally back along the coast of Ellesmere Island.

Transpolar Drift

Transpolar drift is another current within the Arctic Ocean that plays an important role in determining the drift patterns of ice islands. This current carries water from the coast of Siberia across the North Pole and into the Atlantic Ocean, and continues down the coast of Greenland.

The transpolar drift current is mainly driven by the prevailing westerly winds of the Arctic which push the Arctic Ocean surface waters to the east. This eastward flow of water is an important mechanism for ejecting ice islands into the Atlantic Ocean.

Implications of Drift

Oil Exploration

With the prospect of increased oil exploration in the Beaufort Sea, there is a great need to understand the drift patterns of ice islands and whether or not these patterns will create problems for oil rigs in the region.

Only in exceptional cases do ice islands not follow a direct south-western drift pattern toward the Beaufort Sea. Therefore, it is highly probable that any new ice islands that calve from the Ellesmere Island ice shelves will pose a threat to oil platforms in the Beaufort Sea.

Impacts on Shipping

There are no great complications arising from ice islands in terms of threats to Arctic shipping. Arctic waters are un-navigable for most of the year and, with good reporting and surveillance, ships should be able to avoid ice islands.

Implications to shipping arise when ice islands do not follow a direct south-western drift pattern towards the Beaufort Sea. In the summer of 1965 the Ward Hunt ice shelf calved several ice islands. One of these islands, Ward Hunt 5, drifted northeast after break-off and was flushed through the Nares strait. Ice islands that follow this route would likely be swept by the Labrador Current down the east coast. This could disrupt shipping in the east coast shipping lanes.