Influence of vertical and lateral heat transfer on permafrost thaw, peatland landscape transition, and groundwater flow

Abstract

Recent climate change has reduced the spatial extent and thickness of permafrost in many discontinuous permafrost regions. Rapid permafrost thaw is producing distinct landscape changes in the Taiga Plains of the Northwest Territories, Canada. As permafrost bodies underlying forested peat plateaus shrink, the landscape slowly transitions into unforested wetlands. The expansion of wetlands has enhanced the hydrologic connectivity of many watersheds via new surface and near-surface flow paths, and increased streamflow has been observed. Furthermore, the decrease in forested peat plateaus results in a net loss of boreal forest and associated ecosystems. This study investigates fundamental processes that contribute to permafrost thaw by comparing observed and simulated thaw development and landscape transition of a peat plateau-wetland complex in the Northwest Territories, Canada from 1970 to 2012. Measured climate data are first used to drive surface energy balance simulations for the wetland and peat plateau. Nearsurface soil temperatures simulated in the surface energy balance model are then applied as the upper boundary condition to a three-dimensional model of subsurface water flow and coupled energy transport with freeze-thaw. Simulation results demonstrate that lateral heat transfer, which is not considered in many permafrost models, can influence permafrost thaw rates. Furthermore, the simulations indicate that landscape evolution arising from permafrost thaw acts as a positive feedback mechanism that increases the energy absorbed at the land surface and produces additional permafrost thaw. The modeling results also demonstrate that flow rates in local groundwater flow systems may be enhanced by the degradation of isolated permafrost bodies. Key Points:Observed permafrost thaw rates are compared to results from a 3-D groundwater flow and heat transfer model Lateral heat flow can accelerate discontinuous permafrost thaw and land cover change in peatlands Degradation of discontinuous permafrost enhances local groundwater flow Supporting Information:Supporting Information S1

Direct and indirect climate change effects on carbon dioxide fluxes in a thawing boreal forest–wetland landscape

“…Permafrost-free wetlands ('wetlands') occur mainly as collapse-scar bogs dominated by bryophytes (Sphagnum balticum and S. magellanicum), ericaceous shrubs (Chamaedaphne calyculata, Andromeda polifolia, Vaccinium oxycoccos), pod grass (Scheuchzeria palustris), and a few isolated black spruce (Picea mariana) and tamarack (Larix laricina). Warm soils in the wetlands cause lateral thawing of near-surface permafrost underlying the forests and, thus, a rapid expansion of permafrost-free wetlands (Kurylyk et al, 2016). and bryophytes (Sphagnum fuscum and S. capillifolium), respectively (Garon-Labrecque et al, 2015).…”

Increasing Winter Baseflow in Response to Permafrost Thaw and Precipitation Regime Shifts in Northeastern China

“…In eastern Siberia, Brutsaert and Hiyama [24] related changes in baseflow to the rate of the active layer thickening resulting from permafrost thaw, and inferred that the active layer thickness was increasing at average rates of 0.3 to 1 cm·year −1 from 1950 to 2008 in areas with discontinuous permafrost. Although the physical tenability of enhanced groundwater flow rates and increased baseflow due to the thawing of continuous and discontinuous permafrost is supported by numerical modeling results (e.g., [25][26][27]), as well as baseflow recession analyses [28,29], more observational evidence in different regions is required to upscale these results to the pan-Arctic basin and to inform regional water management decisions. In particular, increased attention should be placed in watersheds within the discontinuous permafrost zone, as this region is hydrologically and ecologically sensitive to atmospheric warming [6] because the permafrost temperature is close to 0 • C.…”

Strong degradation of palsas and peat plateaus in northern Norway during the last 60 years

“…However, the water bodies become 12 A. F. Borge et al: Strong degradation of palsas and peat plateaus in northern Norway during the last 60 years overgrown and many of them eventually disappear, which is evident from both the aerial images and field observations. The proximity between the standing water and the ice-rich core of the peat plateaus and palsas most likely contributes to thermal undercutting and eventually block erosion at the margins (Kurylyk et al, 2016), but a variety of factors, such as the height of the palsa and the ground ice content, can be expected to play a role for this process.…”

“…There exist a variety of approaches for how such small-scale variability of different factors can be included in modelling (e.g. Fiddes et al, 2015;Kurylyk et al, 2016;Westermann et al, 2015;Zhang et al, 2012). As exemplified by Gisnås et al (2014) for mountain permafrost environments in Norway, redistribution of snow due to wind drift could be a governing factor for the ground thermal regime also in palsa mires, especially since palsas and peat plateaus are elevated landscape elements which feature lower snow depths than the surrounding mire area (Seppälä, 1982).…”