Abstract
Abstract. Permafrost presence is determined by a complex interaction of climatic, topographic, and ecological conditions operating over long time scales. In particular, vegetation and organic layer characteristics may act to protect permafrost in regions with a mean annual air temperature (MAAT) above 0 °C. In this study, we document the presence of residual permafrost plateaus in the western Kenai Peninsula lowlands of south-central Alaska, a region with a MAAT of 1.5 ± 1 °C (1981–2010). Continuous ground temperature measurements between 16 September 2012 and 15 September 2015, using calibrated thermistor strings, documented the presence of warm permafrost (−0.04 to −0.08 °C). Field measurements (probing) on several plateau features during the fall of 2015 showed that the depth to the permafrost table averaged 1.48 m but at some locations was as shallow as 0.53 m. Late winter surveys (augering, coring, and GPR) in 2016 showed that the average seasonally frozen ground thickness was 0.45 m, overlying a talik above the permafrost table. Measured permafrost thickness ranged from 0.33 to > 6.90 m. Manual interpretation of historic aerial photography acquired in 1950 indicates that residual permafrost plateaus covered 920 ha as mapped across portions of four wetland complexes encompassing 4810 ha. However, between 1950 and ca. 2010, permafrost plateau extent decreased by 60.0 %, with lateral feature degradation accounting for 85.0 % of the reduction in area. Permafrost loss on the Kenai Peninsula is likely associated with a warming climate, wildfires that remove the protective forest and organic layer cover, groundwater flow at depth, and lateral heat transfer from wetland surface waters in the summer. Better understanding the resilience and vulnerability of ecosystem-protected permafrost is critical for mapping and predicting future permafrost extent and degradation across all permafrost regions that are currently warming. Further work should focus on reconstructing permafrost history in south-central Alaska as well as additional contemporary observations of these ecosystem-protected permafrost sites south of the regions with relatively stable permafrost.
Highlights
Permafrost is a major component of the cryosphere in the Northern Hemisphere covering ∼ 24 % of the terrestrial landscape (Brown et al, 1998)
Permafrost may persist in regions with a mean annual air temperature (MAAT) above 0 ◦C, and it may degrade in regions with a MAAT below −10 ◦C (Jorgenson et al, 2010)
This study aims to document and incorporate the loss of ecosystem-protected permafrost into the overall understanding of landscape dynamics in the western Kenai Peninsula lowlands
Summary
Permafrost is a major component of the cryosphere in the Northern Hemisphere covering ∼ 24 % of the terrestrial landscape (Brown et al, 1998). Four zones describe the lateral extent of permafrost regions: continuous (90–100 %), discontinuous (50–90 %), sporadic discontinuous (10–50 %), and isolated discontinuous (< 10 %). In reality complex interactions between climatic, topographic, hydrologic, and ecologic conditions operating over long time scales regulate permafrost presence and stability (Shur and Jorgenson, 2007). Due to these interactions, permafrost may persist in regions with a mean annual air temperature (MAAT) above 0 ◦C, and it may degrade in regions with a MAAT below −10 ◦C (Jorgenson et al, 2010). The extent and dynamics of permafrost and permafrost-related landscape features remain poorly mapped and modelled at sufficiently fine resolution needed for predicting the impact of climate change on specific local landscapes, which is necessary for many decision makers
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