Changing Permafrost Landscapes

Long-term measurements of permafrost degradation and ground surface subsidence in the Mackenzie Delta area from a network of thaw tubes

Tuesday, November 19, 2019 - 3:40pm to 4:00pm Theatre Three


H.B. O'Neill (Presenting)
Natural Resources Canada
S.L. Smith
Natural Resources Canada
C. Duchesne
Natural Resources Canada

Significant climate warming in the Mackenzie Delta area in the past few decades has resulted in increases in permafrost temperatures and thaw depths. In ice-rich permafrost, these increases result in differential ground surface subsidence that may damage infrastructure and alter ecosystems. The Geological Survey of Canada maintains a network of thaw tubes to monitor long-term changes in active layer conditions in the Mackenzie Valley and Delta. We analyzed annual measurements (1991-2016) from a subset of 17 thaw tubes in the Mackenzie Delta region to investigate changes in thaw penetration (TP), ground surface (GS) elevation relative to a stable benchmark, and active-layer thickness (ALT). Over the whole study period, TP increased significantly at 10 of the sites, at a median rate of 0.5 cm a-1 (min: 0.2, max: 1.5 cm a-1), indicating progressive degradation of upper permafrost. Significant ground surface subsidence occurred at 10 sites, at a median rate of 0.4 cm a-1 (min: 0.2, max: 0.8 cm a-1), indicating melt of ground ice. These results highlight long-term permafrost degradation and subsidence of ice-rich terrain in the western Arctic. The measurements show that between ~5 to 38 cm of permafrost have thawed over 25 years at the sites, and ~5 to 20 cm of excess ground ice have melted. In contrast with TP, ALT increased significantly at only 5 sites, decreased at 4 sites, and was unchanged at 8 sites. In ice-rich ground, measured increases in TP can be more than double increases in ALT. For example, ALT increased by only 19 cm between 1994 and 2016 at a site near Inuvik, but TP increased by about 40 cm and was accompanied by 20 cm of surface subsidence. At sites with ice-poor permafrost, negligible settlement occurs, and increases in TP and ALT are similar. The observations further highlight that the degradation of ice-rich permafrost cannot be detected by traditional probing for active-layer thickness. The results have implications for forecasting changes to permafrost in Earth system models due to climate change. Simulations that do not account for ground surface subsidence may not adequately represent heat flow through the active layer/permafrost system and hydrological implications caused by thaw of ice-rich ground.