Abstract
In permafrost areas, the active layer undergoes seasonal frost heave and thaw subsidence caused by ice formation and melting. The amplitude and timing of the ground displacement cycles depend on the climatic and ground conditions. Here we used Sentinel-1 Synthetic Aperture Radar Interferometry (InSAR) to document the seasonal displacement progression in three regions of Svalbard. We retrieved June–November 2017 time series and identified thaw subsidence maxima and their timing. InSAR measurements were compared with a composite index model based on ground surface temperature. Cyclic seasonal patterns are identified in all areas, but the timing of the displacement progression varies. The subsidence maxima occurred later on the warm western coast (Kapp Linné and Ny-Ålesund) compared to the colder interior (Adventdalen). The composite index model is generally able to explain the observed patterns. In Adventdalen, the model matches the InSAR time series at the location of the borehole. In Kapp Linné and Ny-Ålesund, larger deviations are found at the pixel-scale, but km or regional averaging improves the fit. The study highlights the potential for further development of regional InSAR products to represent the cyclic displacements in permafrost areas and infer the active layer thermal dynamics.
Highlights
Permafrost, defined as ground that remains at or below 0 ◦ C for at least two consecutive years, is an essential component of the terrestrial cryosphere that is sensitive to climate change [1]
Our objectives are to (1) to develop Sentinel-1 InSAR products documenting the spatial variability and timing of the seasonal thaw subsidence maxima in three regions of Svalbard characterized by different geomorphological and climatic conditions; (2) compare the displacement time series with a composite index based on temperature and evaluate how a simple model can explain the progression of subsidence and heave patterns in the study areas; (3) discuss the potential and limitations of using the timing of the maximal subsidence as a proxy for the end of the thawing season and suggest ideas for the development of alternative InSAR products in polar areas characterized by cyclic patterns
The observed patterns are described by analysing the results at the landscape scale, as well as within selected km2 areas around the three boreholes and over landforms experiencing a behaviour that deviates from the regional trend
Summary
Permafrost, defined as ground that remains at or below 0 ◦ C for at least two consecutive years, is an essential component of the terrestrial cryosphere that is sensitive to climate change [1]. Permafrost thermal state and AL thickness (ALT) are the two components of the Permafrost Essential Climate Variable (ECV). These variables are typically measured by in-situ techniques [7], but the scarce network of monitoring sites makes remote and large polar regions difficult to comprehensively document. This leads to large uncertainties in the estimate of the current permafrost state and future projections [8].
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