A significant aspect of ice break-up in the Beaufort Sea is the disappearance of landfast ice in the coastal zone, and the immediate impact of this event on the start of hunting, fishing, marine transportation, local weather patterns, and the botanical and zoological cycles both offshore and on the coastlands. Marine coastal erosion, local land failures and sedimentation begin at this time, and subsequently alter the configuration of the coastline. Such processes continue to be effective during the ensuing months of summer and early fall.

Ice.

Arctic ice pack.

Polar bear and ice floe, Lancaster Sound.

Ice Zonation

During the winter and early spring, ice in the Beaufort Sea has a characteristic zonation: landfast ice, active shear ice, transitional shear ice and the polar pack. Landfast ice is newly formed each year, and is about 2 m thick. It is attached to all coasts, and typically has a width of several kilometres; however, this width may vary up to 40 km from one year to the next.

The shear zone lies adjacent to the landfast ice, and is produced when the moving polar pack shears against the inshore ice that is held fast to the coastal seabed, and shore. A long arcuate lead opens at this time, forming an area of open water that may expand or contract, depending upon the prevailing winds. A transitional shear zone forms seaward of the first shear zone, and develops additional, but smaller arcs of open water that are parallel with the first major arc. This shear zone consists of large matching fractures in opposite slabs of ice, and a profusion of huge ice blocks and multi-year floes. It parallels the same arcuate pattern of the original shear zone, and extends into the polar pack directly.

Polar pack ice lies adjacent and seaward of the transitional shear zone, and comprises thick multi-year ice, frozen leads, rare ice-island fragments and numerous oblique fractures and open leads. Its surface is characterized by ridges and hummocks, and generally has an extremely rough aspect to it. This is in contrast to the smooth, almost featureless surface of landfast ice. The polar pack may be several metres thick, particularly in areas where floes have rafted onto each other.

Ice Movement

Movement of the ice is controlled by atmospheric systems and oceanographic circulation. Surface winds drive the ice canopy forward, and the clockwise motion of the Beaufort Gyre may enhance this movement of ice in the windward direction; however, a wind blowing in the reverse direction of the gyral flow may impede the advance of the ice and cause it to be retarded or reversed. Eventually the ice will resume its gyral circulation under the influence of the prevailing winds, and continue its course around the Arctic Ocean.

Authors: L.W. Sobczak and B.R. Pelletier
Geological Survey of Canada