The shifting mosaic of ice-wedge degradation and stabilization in response to infrastructure and climate change, Prudhoe Bay Oilfield, Alaska, USA

Mikhail Kanevskiy,Jana L Peirce,Georgiy Matyshak,Ronald Daanen,Helena Bergstedt,Benjamin M Jones,Martha K Raynolds,Amy L Breen,Anna Liljedahl,Marcel Buchhorn,Torre Jorgenson,Vladimir E Romanovsky,Emily Watson-Cook,D.A (Skip) Walker,Billy Connor,Yuri Shur

doi:10.1139/as-2021-0024

Abstract

We studied processes of ice-wedge degradation and stabilization at three sites adjacent to road infrastructure in the Prudhoe Bay Oilfield, Alaska, USA. We examined climatic, environmental, and subsurface conditions and evaluated vulnerability of ice wedges to thermokarst in undisturbed and road-affected areas. Vulnerability of ice wedges strongly depends on the structure and thickness of soil layers above ice wedges, including the active, transient, and intermediate layers. In comparison with the undisturbed area, sites adjacent to the roads had smaller average thicknesses of the protective intermediate layer (4 cm vs. 9 cm), and this layer was absent above almost 60% of ice wedges (vs. ∼45% in undisturbed areas). Despite the strong influence of infrastructure, ice-wedge degradation is a reversible process. Deepening of troughs during ice-wedge degradation leads to a substantial increase in mean annual ground temperatures but not in thaw depths. Thus, stabilization of ice wedges in the areas of cold continuous permafrost can occur despite accumulation of snow and water in the troughs. Although thermokarst is usually more severe in flooded areas, higher plant productivity, more litter, and mineral material (including road dust) accumulating in the troughs contribute to formation of the intermediate layer, which protects ice wedges from further melting.

Highlights

Areas affected by development: Colleen Site (CS) and Airport Site (AS)
We suggest to estimate vulnerability levels based on measurements of protective layers PL1, PL2, and PL3, which may be performed during two time periods: late July to mid-August and late August to mid356 September
We presumed that most of ice wedges in the study area were active, which was confirmed by occurrence of young ice wedges that had developed in recently formed TCI bodies (e.g., Fig. S6, profiles DI2 and SA2). 393 In many cases, massive-ice bodies were protected by a frozen intermediate layer (PL3) up to 84 cm 394 thick, with the average thickness 8.6 cm (n=83) (Tables 2, S1)

Summary

Introduction

Initial degradation is caused by extreme weather conditions (e.g., exceptionally warm and wet summers) or physical disturbance, which leads to increase in the active-layer thickness (ALT) and partial thawing of ice wedges with formation of shallow troughs. Water impoundment and additional snow accumulation in troughs leads to further thawing of ice wedges and deepening of troughs Interacting factors such as climate, topography, vegetation, surface and groundwater, and soil properties create positive and negative feedbacks to ice-wedge degradation (Jorgenson et al 2006, 2010, 2015, Shur and Jorgenson 2007, Kanevskiy et al 2017). The intermediate layer, which constitutes the lower part of the transition zone, forms due to a gradual decrease in the ALT, mostly as a result of accumulation of organic matter after termination or slow-down of sedimentation This long-term process transforms the initial transient layer and a part of the initial active layer into a perennially frozen state (Shur 1988, Shur et al 2011). The probability of such transformation is much higher in areas with warmer permafrost, like the Seward Peninsula in Alaska (Shur et al 2012)

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Discussion

Conclusion