Mechanisms of Discontinuous Permafrost Thaw in Peatlands

Abstract

Climate warming in discontinuous permafrost peatlands is causing permafrost loss and changes in ecosystem dynamics at an unprecedented rate. Though rates of permafrost loss and landscape change have been widely documented based on remote sensing and field measurements, the local mechanisms of permafrost degradation remain under‐studied. These mechanisms were explored using data collected over three decades of research in the Scotty Creek study basin in the southern Northwest Territories of Canada. The data, when compared to numerical modeling results, demonstrated that vertical heat conduction accounts for most vertical permafrost degradation, while advective heat transfer drives thaw in features which are subject to seasonal flows. It was found that heat advection was necessary to describe lateral thaw rates of up to 115 cm annually, which are an order of magnitude greater than vertical thaw rates, which average 10 cm annually. Thaw from below, driven either by the geothermal gradient or groundwater flow, may account for up to 10 cm of permafrost thaw annually. The hydrologic, thermodynamic and geophysical function of taliks in different parts of the landscape were considered in light of the data collected at the field site and surrounding area. This analysis is supported through the use of ERT data detailing the subsurface permafrost structure. This understanding of local thaw mechanisms and trajectory is an important first step in being able to predict distributed permafrost thaw in peatlands.

Conceptual Model of Permafrost Degradation in an Inuit Archaeological Context (Dog Island, Labrador): A Geophysical Approach

“…As shown in Figure 10, the permafrost at Oakes Bay 1 is currently affected by multipoint thermal degradation due to a combination of the following factors: unfrozen sediments deep in the subsurface, contact with the sea, the well-insulated interior of the semi-subterranean sod houses, and already existing thermokarst features. The site is affected by two heat-transfer mechanisms: conduction and advection [74]. The movement of water along the coastal cliff interacting with the sea and within thermokarst ravines primarily accelerates permafrost degradation through advection mechanisms.…”

“…The central depression of the semi-subterranean sod houses on the other hand contributes to permafrost degradation mainly through conduction mechanisms. Permafrost can also thaw from its base due to geothermal heat conducted from the Earth's core [74].…”

Phase-separation physics underlies new theory for the resilience of patchy ecosystems

“…For example, phosphorous-limited Siberian peatlands exhibit patterning ( Fig. 1 E ) which is linked to the vascular plants that draw down the water table through evapotranspiration during the growth season, preventing phosphorous to leave the ridges dominated by dwarf shrubs, beech, and pine trees ( 34 , 71 , 72 ). Hence, phase separation could provide a viable alternative explanation for pattern formation in peat lands.…”

A new Stefan equation to characterize the evolution of thermokarst lake and talik geometry

“…The daily potential solar irradiation on a sloping surface can be computed by the trigonometric function (e.g., Eq. B.11 in DeWalle and Rango, 2008). The total daily radiation is a function of latitude and bank slope angle, which depend on the permafrost degradation rate, the maturity of the talik, and ground ice distribution.…”