ABSTRACT: Sea ice, sea-level rise, and shore-zone stability in Aulavik National Park, M'clure Strait Coast of Banks Island, Western Canadian Arctic Archipelago.

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Abstract

The north coast of Banks Island is generally beset by multi-year sea ice, although some open water usually develops in summer close to shore. Inexceptional years, the ice is light enough to allow limited navigation, as in 1850 when HMS Investigator reached Mercy Bay. Although the polar pack along thewestern margin of the archipelago sometimes withdraws to the north end of Banks Island, heavy ice pressure in this part of the Arctic Ocean forces multiyear ice into M'Clure Strait. Nevertheless, the coastal geomorphology attests to episodes of wave reworking that have generated coastal scarps, narrow beaches, and low spits at several sites along the north coast of Banks Island. In Castel Bay and Mercy Bay, two large embayments where more open water occurs, small forelands have developed at several locations. These comprise prograded sequences of seaward-facing gravel beach ridges, with crest elevations rising successively seaward, truncated on the flank by atransgressive gravel beach ridge migrating landward into the low area behind. This morphology demonstrates rising relative sea level accompanied byintermittent wave action over the past few thousand years. Submerged supratidal peat deposits at the mouth of Mercy Bay and flooded-valley estuaries(Castel Bay being the largest) support this interpretation, which is consistent with geophysical models of postglacial isostatic adjustment in the region.Baseline coastal surveys were conducted at four sites in July 2003. These were the first georeferenced coastal surveys on northern Banks Island and the first in Aulavik National Park. The surveys were conducted using real-time kinematic GPS with base stations referenced to permanent GPS survey monuments. Three sites were in the Mercy Bay area within the park and a fourth was further west near Ballast Brook. The sites in Mercy Bay included asmall foreland, as described above, and two sites on the outer coast, one on each side of Mercy Bay. These sites were resurveyed in July 2006. Despite thefresh appearance of gravel in the transgressive storm ridge at the foreland site in Mercy Bay, the repeat surveys showed no significant reworking and nofurther landward migration between 2003 and 2006. Similarly, small spits at the mouth of Mercy Bay, north of Investigator Point on the west and at Back Point on the east, showed negligible change in the beaches, all attributable to limited ice ride-up. Minor retreat of low cliffs developed in soft sediments suggested minor wave action at the shore in some places. These results indicate very little coastal change over the past three years. On the other hand, it is clear that substantial reworking of the coast has occurred with limited open-water fetch in some years. It is evident that ongoing slow retreat of the coast is occurring and, with rising relative sea levels, can be expected tocontinue in future. If the ice in M'Clure Strait diminishes, with more frequent occurrences of open water, dramatic acceleration of coastal erosion is possible in this region.

Bibliography of Canadian Geomorphology