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

Abstract

[1] 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 0.12 m relief and 4.0 m total width, bisected by troughs only 0.05 m wide and 0.09 m 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 1 m of permafrost from 0.03 to 0.95 m. "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 1 m of permafrost, a much smaller volumetric proportion than in epigenetic settings.

Microtopographic control on the ground thermal regime in ice wedge polygons

“…Recently, a 30 number of investigations have used electronic temperature sensors to more tightly constrain thermal conditions at the time of cracking at field sites across the Arctic (e.g., Mackay, 1993;Allard and Kasper, 1998;Christiansen, 2005 Kokelj et al, 2007). Although heterogeneity exists between sites, it has been generalized that ice wedge cracking is most favorable when ground temperature drops below -13°C, and the rate of cooling exceeds 0.1°C d -1 for two days or more (Morse and Burn, 2013).…”

“…Following each simulation, winter temperatures were extracted from 2014-2015 from the uppermost cell at the center of the SE (right) ice wedge, and compared to the criteria identified by Morse and Burn (2013) The ensemble of topographies for our analysis (Fig 4) were created by altering the original mesh used to represent 5 field site topography. When either trough depth or rim height was increased, the elevation of every rim or trough node was directly reassigned.…”

An Estimate of Ice Wedge Volume for a High Arctic Polar Desert Environment, Fosheim Peninsula, Ellesmere Island

“…Field intensive studies to characterize IW terrain and estimate ground ice content have recently been carried out in the Mackenzie Delta by Morse and Burn (2013) and on the Beaufort Sea coast in Alaska by Kanesvskiy et al (2013).…”

“…Pollard and French, 1980;Bode et al, 2008;Morse and Burn, 2013;Jorgenson et al, 2015). When lacking subsurface data, IW morphology is often approximated to be an inverted isosceles triangle and mean cross-sectional area of IWs is estimated with the use of width to depth ratios based on observations from exposed wedges.…”

“…When lacking subsurface data, IW morphology is often approximated to be an inverted isosceles triangle and mean cross-sectional area of IWs is estimated with the use of width to depth ratios based on observations from exposed wedges. This works well for epigenetic and anti-syngenetic IWs but would underestimate syngenetic ice volume due to their chevron pattern (Morse and Burn, 2013). Many other assumptions are often made which 25 lead to over/under-estimation of wedge ice.…”