Nonlinear thermal and moisture response of ice-wedge polygons to permafrost disturbance increases heterogeneity of high Arctic wetland

Twelve years of continuous monitoring of diverse ground properties reveals the dynamics of three ice wedges and adjacent ground in a low-centered polygon area in Svalbard. The monitoring documented ground displacements, the timing of crack generation, ground thermal and moisture conditions from the surface to the top permafrost, and snow conditions. The focus is on seasonal ground deformation in and around ice-wedge troughs, interannual variability of ice-wedge activity and thermal thresholds for ice-wedge cracking. Seasonal ice-wedge activity is mainly associated with frost heave and thaw settlement, as well as thermal expansion and contraction.In mid-to late winter, temporary expansion and cracking of troughs by thermal contraction occurs during rapid cooling periods. Following intensive ground microcracking events, troughs show rapid expansion and in some cases major cracking in the frozen active layer. A common threshold for cracking is identified by a combination of ground surface cooling below −20°C and a thermal gradient steeper than −10°C m −1 in the upper meter of ground, indicating that cracking requires both a brittle frozen layer and rapid ground cooling. Our results highlight that in marginal thermal conditions for ice-wedge activity, the primary control on ice-wedge cracking is rapid winter cooling enhanced by minimum snow cover. (eg, 5-8 ). These rules, however, give only rough estimates, because they ignore ground surface conditions (snow and vegetation), and short cold events rather than seasonal conditions may control thermal contraction cracking. 9,10 To date, the widely accepted rule is that ice-wedge pseudomorphs indicate the past presence of (probably continuous) permafrost. 1 Improving the precision of paleoclimatic reconstruction using wedge structures requires more precise ----------------------------------------------------This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Section: The Studied Ice‐wedge Sitementioning

confidence: 99%

“…The ice-wedge research site is located on the outermost part of a large late Holocene alluvial fan 23,24 26 ). The polygons occur mainly as quadrangles, pentagons and hexagons with an average diameter of about 20 m and three-way junctions 27,28 (Figure 2).…”

Section: The Studied Ice-wedge Sitementioning

confidence: 99%

Ice‐wedge polygon dynamics in Svalbard: Lessons from a decade of automated multi‐sensor monitoring

Matsuoka

Christiansen²,

Watanabe

2018

“…The study area has been described previously as a geomorphologically high-energy environment because of its high elevation, pronounced relief, and moisture availability (Gill, 1976). The relief varies from relatively flat valley bottoms with rolling hills to plateaus and steep cliffs.…”

Section: Geomorphology and Surficial Materialsmentioning

confidence: 99%

Recent Increases in Permafrost Thaw Rates and Areal Loss of Palsas in the Western Northwest Territories, Canada

Mamet

Chun

Kershaw

et al. 2017

Decay of palsas can indicate permafrost status, particularly in regions where air temperatures have increased rapidly in recent decades. Using weather data, annual surveys of active‐layer thickness, and analyses of high‐resolution aerial imagery from the eastern Selwyn/western Mackenzie Mountains, NT, Canada, we show that permafrost temperatures have increased, active layers have deepened, and palsa areal extents have decreased considerably since the 1940s. High‐altitude palsas thawed quickly from the 1940s to the 1980s, although some low‐altitude palsas have recently decreased rapidly in areal extent due to peat‐block calving. The linear rate of increasing active‐layer thickness may not be congruent with the non‐linear rate of areal loss of palsas. The rapid and episodic collapse of palsas at some sites highlights the necessity to consider hydrology, vegetation cover, landscape position, and morphology in palsa dynamics in addition to a warming climate. Copyright © 2017 John Wiley & Sons, Ltd.

“…Geomorphological processes triggered by lake drainage or sea level rise may, however, affect topography and surface hydrology on a local to subregional level. This may cause polygon growth or degradation independently of the regional climate trend . The respective influence of climate and geomorphology on the evolution of different types of ice‐wedge polygons is not well understood because of large temporal and spatial discrepancies between climatic forcing and geomorphological response processes.…”

Section: Introductionmentioning

confidence: 99%

“…This may cause polygon growth or degradation independently of the regional climate trend. [10][11][12] The respective influence of climate and geomorphology on the evolution of different types of ice-wedge polygons is not well understood because of large temporal and spatial discrepancies between climatic forcing and geomorphological response processes. In this study we therefore investigated past landscape dynamics on millennial time-scales to discriminate climate-driven and geomorphology-driven changes on ice-wedge polygon development.…”

mentioning

confidence: 99%

Climatic, geomorphologic and hydrologic perturbations as drivers for mid‐ to late Holocene development of ice‐wedge polygons in the western Canadian Arctic

Wolter

Lantuit

Wetterich

et al. 2018

Ice‐wedge polygons are widespread periglacial features and influence landscape hydrology and carbon storage. The influence of climate and topography on polygon development is not entirely clear, however, giving high uncertainties to projections of permafrost development. We studied the mid‐ to late Holocene development of modern ice‐wedge polygon sites to explore drivers of change and reasons for long‐term stability. We analyzed organic carbon, total nitrogen, stable carbon isotopes, grain size composition and plant macrofossils in six cores from three polygons. We found that all sites developed from aquatic to wetland conditions. In the mid‐Holocene, shallow lakes and partly submerged ice‐wedge polygons existed at the studied sites. An erosional hiatus of ca 5000 years followed, and ice‐wedge polygons re‐initiated within the last millennium. Ice‐wedge melt and surface drying during the last century were linked to climatic warming. The influence of climate on ice‐wedge polygon development was outweighed by geomorphology during most of the late Holocene. Recent warming, however, caused ice‐wedge degradation at all sites. Our study showed that where waterlogged ground was maintained, low‐centered polygons persisted for millennia. Ice‐wedge melt and increased drainage through geomorphic disturbance, however, triggered conversion into high‐centered polygons and may lead to self‐enhancing degradation under continued warming.