Long-Term Permafrost Degradation and Thermokarst Subsidence in the Mackenzie Delta Area Indicated by Thaw Tube Measurements

O'Neill, H B; Smith, Sharon L.; Duchesne, C

doi:10.1061/9780784482599.074

Cited by 27 publications

(35 citation statements)

References 12 publications

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“…After 9 years, thaw penetration was 49% greater than ALT in soil warming plots and 19% greater than ALT in control plots. This is similar to the findings of two studies that did not experimentally warm soils, with thaw penetration being~20% to >50% greater than ALT (O'Neill et al, 2019;Streletskiy et al, 2017). Additionally, we showed that this increased rate of permafrost thaw corresponded to a doubling of the rate of C thaw.…”

Section: 1029/2019jg005528supporting

confidence: 90%

“…Subsidence is rarely quantified when monitoring permafrost thaw, and this is problematic because long‐term measurements of ALT have been shown to underestimate the rate of permafrost thaw (O'Neill et al, 2019; Shiklomanov et al, 2013; Streletskiy et al, 2017). The typical method of monitoring ALT is to insert a metal probe into the ground until it hits permafrost and measure the distance from the soil surface to the bottom of the probe (Hinkel & Nelson, 2003).…”

Section: Introductionmentioning

confidence: 99%

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Carbon Thaw Rate Doubles When Accounting for Subsidence in a Permafrost Warming Experiment

et al. 2020

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Permafrost thaw is typically measured with active layer thickness, or the maximum seasonal thaw measured from the ground surface. However, previous work has shown that this measurement alone fails to account for ground subsidence and therefore underestimates permafrost thaw. To determine the impact of subsidence on observed permafrost thaw and thawed soil carbon stocks, we quantified subsidence using high‐accuracy GPS and identified its environmental drivers in a permafrost warming experiment near the southern limit of permafrost in Alaska. With permafrost temperatures near 0°C, 10.8 cm of subsidence was observed in control plots over 9 years. Experimental air and soil warming increased subsidence by five times and created inundated microsites. Across treatments, ice and soil loss drove 85–91% and 9–15% of subsidence, respectively. Accounting for subsidence, permafrost thawed between 19% (control) and 49% (warming) deeper than active layer thickness indicated, and the amount of newly thawed carbon within the active layer was between 37% (control) and 113% (warming) greater. As additional carbon thaws as the active layer deepens, carbon fluxes to the atmosphere and lateral transport of carbon in groundwater could increase. The magnitude of this impact is uncertain at the landscape scale, though, due to limited subsidence measurements. Therefore, to determine the full extent of permafrost thaw across the circumpolar region and its feedback on the carbon cycle, it is necessary to quantify subsidence more broadly across the circumpolar region.

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Section: 1029/2019jg005528supporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Carbon Thaw Rate Doubles When Accounting for Subsidence in a Permafrost Warming Experiment

et al. 2020

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“…It is thought to be the largest single source of sediments in the Arctic (Rachold et al, 2000). Although future climate projections in the area contain substantial variability, a study of 18 future projections to 2,039 showed continued temperature and precipitation increases and many are already being exceeded (Bonsal and Kochtubajda, 2009), with significant trends in deeper thaw penetration also noted from 1991-2016 (O'Neill et al, 2019). Recent concerns have centered on the potentially under-estimated (O'Rourke, 2017) and accelerating rates of coastal erosion in the area (Lantuit et al, 2012;Irrgang et al, 2018), and particularly the vulnerability of communities (Alvarez et al, 2020), infrastructure (Warren et al, 2005), ecosystems (Waugh et al, 2018) and significant archaeological sites across the Inuvialuit area (O'Rourke, 2017).…”

Section: Field Sitementioning

confidence: 99%

Effective Monitoring of Permafrost Coast Erosion: Wide-scale Storm Impacts on Outer Islands in the Mackenzie Delta Area

et al. 2020

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Permafrost coasts are extensive in scale and complex in nature, resulting in particular challenges for understanding how they respond to both long-term shifts in climate and short-term extreme weather events. Taking examples from the Canadian Beaufort Sea coastline characterized by extensive areas of massive ground ice within slump and block failure complexes, we conduct a quantitative analysis of the practical performance of helicopter-based photogrammetry. The results demonstrate that large scale (>1 km 2) surface models can be achieved at comparable accuracy to standard unmanned aerial vehicle surveys, but 36 times faster. Large scale models have greater potential for progressive alignment and contrast issues and so breaking down image sequences into coherent chunks has been found the most effective technique for accurate landscape reconstructions. The approach has subsequently been applied in a responsive acquisition immediately before and after a large storm event and during conditions (wind gusts >50 km h −1) that would have prohibited unmanned aerial vehicle data acquisition. Trading lower resolution surface models for large scale coverage and more effective responsive monitoring, the helicopter-based data have been applied to assess storm driven-change across the exposed outer islands of the Mackenzie Delta area for the first time. These data show that the main storm impacts were concentrated on exposed North orientated permafrost cliff sections (particularly low cliffs, >20 m in height) where cliff recession was 43% of annual rates and in places up to 29% of the annual site-wide erosion volume was recorded in this single event. In contrast, the thaw-slump complexes remained relatively unaffected, debris flow fans were generally more resistant to storm erosion than the icerich cliffs, perhaps due to the relatively low amounts of precipitation that occurred. Therefore, the variability of permafrost coast erosion rates is controlled by interactions between both the forcing conditions and local response mechanisms. Helicopter-based photogrammetric surveys have the potential to effectively analyze these controls with greater spatial and temporal consistency across more representative scales and resolutions than has previously been achieved, improving the capacity to adequately constrain and ultimately project future Arctic coast sensitivity.

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“…The formation and melt of excess ice, the volume of ice in the ground exceeding the total pore volume under natural unfrozen conditions, is an expression of the redistribution of mass and energy and often a major determinant of surface heave and subsidence in response to freezing and thawing of soil. Excess ice forms through a number of processes (Outcalt, 1971;Rempel et al, 2004), and when it melts, the soil consolidates (Nixon et al, 1971). These phenomena are superimposed on the volume changes without redistribution of mass, which are due to thermal expansion of soil materials and the density contrast of water and ice.…”

Section: Introductionmentioning

confidence: 99%

Ground subsidence and heave over permafrost: hourly time series reveal interannual, seasonal and shorter-term movement caused by freezing, thawing and water movement

Gruber

2020

The Cryosphere

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Abstract. Heave and subsidence of the ground surface can offer insight into processes of heat and mass transfer in freezing and thawing soils. Additionally, subsidence is an important metric for monitoring and understanding the transformation of permafrost landscapes under climate change. Corresponding ground observations, however, are sparse and episodic. A simple tilt-arm apparatus with logging inclinometer has been developed to measure heave and subsidence of the ground surface with hourly resolution and millimeter accuracy. This contribution reports data from the first two winters and the first full summer, measured at three sites with contrasting organic and frost-susceptible soils in warm permafrost. The patterns of surface movement differ significantly between sites and from a prediction based on the Stefan equation and observed ground temperature. The data are rich in features of heave and subsidence that are several days to several weeks long and that may help elucidate processes in the ground. For example, late-winter heave followed by thawing and subsidence, as reported in earlier literature and hypothesized to be caused by infiltration and refreezing of water into permeable frozen ground, has been detected. An early-winter peak in heave, followed by brief subsidence, is discernible in a previous publication but so far has not been interpreted. An effect of precipitation on changes in surface elevation can be inferred with confidence. These results highlight the potential of ground-based observation of subsidence and heave as an enabler of progress in process understanding, modeling and interpretation of remotely sensed data.

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Long-Term Permafrost Degradation and Thermokarst Subsidence in the Mackenzie Delta Area Indicated by Thaw Tube Measurements

Cited by 27 publications

References 12 publications

Carbon Thaw Rate Doubles When Accounting for Subsidence in a Permafrost Warming Experiment

Carbon Thaw Rate Doubles When Accounting for Subsidence in a Permafrost Warming Experiment

Effective Monitoring of Permafrost Coast Erosion: Wide-scale Storm Impacts on Outer Islands in the Mackenzie Delta Area

Ground subsidence and heave over permafrost: hourly time series reveal interannual, seasonal and shorter-term movement caused by freezing, thawing and water movement

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