Half a century of discontinuous permafrost persistence and degradation in western Canada

Holloway, Jean; Lewkowicz, Antoni G.

doi:10.1002/ppp.2017

Cited by 30 publications

(16 citation statements)

References 52 publications

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“…January is the coldest month (−22.8°C), July is the warmest (16.1°C), and mean annual precipitation is 391 mm. The study area is a heterogeneous landscape with a mix of upland forests and peatlands, with permafrost found predominantly in peatlands (Holloway & Lewkowicz, 2019) . These peatland complexes are in turn comprised of permafrost‐affected peat plateaus interspersed with nonpermafrost thermokarst bogs, fens, and ponds.…”

Section: Methodsmentioning

confidence: 99%

Long‐term Impacts of Permafrost Thaw on Carbon Storage in Peatlands: Deep Losses Offset by Surficial Accumulation

et al. 2020

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Peatlands in northern permafrost regions store a significant proportion of global soil carbon. Recent warming is accelerating peatland permafrost thaw and thermokarst collapse, exposing previously frozen peat to microbial decomposition and potential mineralization into greenhouse gases. Here, we show from a site in the sporadic‐discontinuous permafrost zone of western Canada that thermokarst collapse leads to neither large losses nor gains following thaw, as deep carbon losses are offset by surficial accumulation. We collected peat cores along two thaw chronosequences, from peat plateau, through young (~30 years since thaw), intermediate (~70 years), and mature (~200 years) thermokarst bog locations. Macrofossil and 14C analysis showed synchronicity of peatland development until recent thaw, with wetland initiation ~8,500 cal yr BP followed by succession through peatland stages prior to permafrost aggradation ~1,800 cal yr BP. Analysis and modeling of soil carbon stocks indicated 8.7 ± 12.4 kg C m−2 of carbon accumulated prior to thaw was lost in ~200 years post‐thaw. Despite these losses, there was no observed increase in peat humification as assessed by Fourier transform infrared and C:N ratios. Rapid peat accumulation post‐thaw (9.8 ± 1.6 kg C m−2 over 200 years) offset deeper losses. Our approach constrains the net carbon balance to be between uptake of 27.3 g C m−2 yr−1 and loss of 106.6 g C m−2 yr−1 over 200 years post‐thaw. While our approach cannot determine whether thermokarst bogs in the sporadic‐discontinuous permafrost zone act as long‐term carbon sinks or sources post‐thaw, our study better constrains post‐thaw C losses and gains.

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Section: Methodsmentioning

confidence: 99%

Long‐term Impacts of Permafrost Thaw on Carbon Storage in Peatlands: Deep Losses Offset by Surficial Accumulation

et al. 2020

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“…The NCSCD is also a polygon database developed by the Bolin Centre for Climate Research through synthesizing data from numerous regional and national soil maps alongside field data collected across Canada, USA, Russia, and the European Union. The NCSCD includes data on the fractional coverage of different soil types and stored soil organic carbon (Hugelius et al, 2013a, b). In the present study, the layer containing information on the fractional coverage of soil types was used.…”

Section: Geomatics Methodsmentioning

confidence: 99%

Long-term climate-influenced land cover change in discontinuous permafrost peatland complexes

Carpino

Haynes

Connon

et al. 2021

Hydrol. Earth Syst. Sci.

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Abstract. The discontinuous permafrost zone is undergoing rapid transformation as a result of unprecedented permafrost thaw brought on by circumpolar climate warming. Rapid warming over recent decades has significantly decreased the area underlain by permafrost in peatland complexes. It has catalysed extensive landscape transitions in the Taiga Plains of northwestern Canada, transforming forest-dominated landscapes to those that are wetland dominated. However, the advanced stages of this landscape transition, and the hydrological and thermal mechanisms and feedbacks governing these environments, are unclear. This study explores the current trajectory of land cover change across a 300 000 km2 region of northwestern Canada's discontinuous permafrost zone by presenting a north–south space-for-time substitution that capitalizes on the region's 600 km latitudinal span. We combine extensive geomatics data across the Taiga Plains with ground-based hydrometeorological measurements collected in the Scotty Creek basin, Northwest Territories, Canada, which is located in the medial latitudes of the Taiga Plains and is undergoing rapid landscape change. These data are used to inform a new conceptual framework of landscape evolution that accounts for the observed patterns of permafrost thaw-induced land cover change and provides a basis for predicting future changes. Permafrost thaw-induced changes in hydrology promote partial drainage and drying of collapse scar wetlands, leading to areas of afforestation forming treed wetlands without underlying permafrost. Across the north–south latitudinal gradient spanning the Taiga Plains, relatively undisturbed forested plateau–wetland complexes dominate the region's higher latitudes, forest–wetland patchwork are most prevalent at the medial latitudes, and forested peatlands are increasingly present across lower latitudes. This trend reflects the progression of wetland transition occurring locally in the plateau–wetland complexes of the Scotty Creek basin and informs our understanding of the anticipated trajectory of change in the discontinuous permafrost zone.

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“…Tomograms were generated using a customized R v3.4 script, and areas below the depth of investigation from RES2DINV (per Loke and others 2003) were excluded. For validation, we used instantaneous ground temperature profiles collected with Onset Hobo UX120-006M Analog Data Loggers (accuracy ± 0.15°C) connected to two to four vertically arranged thermistors separated by 20 cm and mounted on a wooden dowel (for example, Way and Lewkowicz 2015;Holloway and Lewkowicz 2020). The observed thermal gradient in the lower 20 cm was used to extrapolate temperatures to 0°C in order to approximate the thaw depth.…”

Section: Permafrost Investigationmentioning

confidence: 99%

Plant–Environment Interactions in the Low Arctic Torngat Mountains of Labrador

et al. 2020

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The eastern Canadian Subarctic and Arctic are experiencing significant environmental change with widespread implications for the people, plants, and animals living there. In this study, we integrate 10 years of research at the Nakvak Brook watershed in Torngat Mountains National Park of Canada, northern Labrador, to assess the sensitivity of ecological and geomorphological systems to regional climate warming. A time series of the Normalized Difference Vegetation Index indicates that the area has undergone a significant greening trend over the past four decades. Analyses of shrub cross sections suggest that greening has been caused by a combination of rapid establishment and growth that began in the late 1990’s and coincided with warmer growing season temperatures. Recent (2010–2015) vegetation change has been subtle and heavily moderated by soil moisture status. Plant canopy height is greater in wet areas and has an insulating effect on ground surface temperatures during the winter, a consequence of snow trapping by shrub canopies. Observations of subsurface conditions indicate that the study site is best characterized as having discontinuous near-surface permafrost. The importance of subsurface conditions for above-ground vegetation depends on the geomorphological context, with plants in wet areas underlain by fine materials being the most likely to be growth-limited by permafrost, thus being potential hot-spots for future change. With the expectation of sustained climate change, loss of adjacent sea ice, and proximity to the forest-tundra ecotone, it is likely that the Torngat Mountains will continue to be an area of rapid environmental change in the coming decades.

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Half a century of discontinuous permafrost persistence and degradation in western Canada

Cited by 30 publications

References 52 publications

Long‐term Impacts of Permafrost Thaw on Carbon Storage in Peatlands: Deep Losses Offset by Surficial Accumulation

Long‐term Impacts of Permafrost Thaw on Carbon Storage in Peatlands: Deep Losses Offset by Surficial Accumulation

Long-term climate-influenced land cover change in discontinuous permafrost peatland complexes

Plant–Environment Interactions in the Low Arctic Torngat Mountains of Labrador

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