Field observations of syngenetic ice wedge polygons, outer Mackenzie Delta, western Arctic coast, Canada

Low-centered ice wedge polygons in the Big Lake Delta Plain of the outer Mackenzie Delta are unusual because their bounding ramparts appear to have a single ridge. Twenty-two ice wedges in the area were examined between 2006 and 2009 to describe their morphology and diagnose their growth processes. The ground above ice wedges had a subtle microtopography, with ridges of 0.12m relief and 4.0m total width, bisected by troughs only 0.05m wide and 0.09m deep. The troughs, initially obscured by vegetation growth and organic matter, were underlain by ice wedges with average widths that increased downward in the uppermost 1m of permafrost from 0.03 to 0.95m. Shoulders on the ice wedges indicated vertical growth stages. Temperatures near the top of permafrost were favorable to thermal-contraction cracking, and ice veins connected to the top of wedge ice were observed in the active layer at five sites. These observations indicate the ice wedges are syngenetic and active, although without dating control, we cannot unequivocally dismiss the possibility that the wedges are epigenetic features that were truncated by a recent thaw unconformity. Muted relief above the ice wedges, which is uncommon above epigenetic ice wedges, was largely due to aggradation of the surface. Secondary ice wedges have not developed within the polygons, suggesting that climate variability has not led to polygon network development in this area. Wedge ice occupied only about 1.5% of the uppermost 1m of permafrost, a much smaller volumetric proportion than in epigenetic settings.