The active layer: A conceptual review of monitoring, modelling techniques and changes in a warming climate

Abstract

This paper provides a review of research and techniques that focus on the seasonally thawed portion of the Earth above permafrost terrain known as the active layer. The paper examines various different conceptual active layer systems, identifying five active layer types: bedrock (Type I), rock glacier or debris covered (Type II), mineral soil (Type III), organic mat or soil (Type IV) and submerged (Type V) active layer systems. These systems can be independent or mixed (frequently) in a permafrost environment, but all respond differently to climatic change or disturbance based on the thermal properties of the material and ice/water content. The review also highlights various active layer monitoring techniques including: probing, the Circumpolar Active Layer Monitoring Program (CALM) and frost tubes. Active layer modelling techniques are also reviewed, including the Stefan and the Kudryavtsev equations. In addition, the study highlights the active layer in a changing climate, examining the sensitivities of this layer to changes in temperature, precipitation and surface changes. Although the active layer has been well studied, knowledge gaps still exist including conflicting definitions between the thermal definition (0°C) and the physical definition (frozen water), which can become significant in areas with pore water that contains high levels of dissolved solids.

Effects of changing permafrost and snow conditions on tundra wildlife: critical places and times

“…Seasonal variations in surface heating from solar irradiance and convective heat exchange with the atmosphere are conducted vertically through the soil with increased time lag as depth increases (Romanovsky and Osterkamp 1995). Horizontal heat exchange can also be important, particularly adjacent to streams, rivers, and surface water bodies (Bonnaventure and Lamoureux 2013). Additionally, physical disturbance of the landscape through thermo-erosional incision (Bowden et al 2008) and slope failures can result in abrupt increases in horizontal heat flux and perturbation of active layer dynamics.…”

Impacts of mean annual air temperature change on a regional permafrost probability model for the southern Yukon and northern British Columbia, Canada

“…The range of potential effects of climate change identified for this and other permafrost regions include warming of ground temperatures at the surface and at depth (IPCC, 2007;ACIA, 2005), increasing active layer thickness (Haeberli et al, 1993;Burn and Zhang, 2010;SWIPA, 2012;Bonnaventure and Lamoureux, 2013), basal thaw resulting in permafrost thinning (Harris et al, 2001;Woo et al, 2008), runoff changes (Woo et al, 2008), and the development of thermokarst features (Harris et al, 2001;Woo et al, 2008). Natural hazards associated with permafrost degradation (Kääb, 2008) may also develop as climate change will affect permafrost slopes, possibly generating or enhancing mass movements such as creeprelated processes, rockslides, rock falls, mudslides, and active layer detachment failures (Evans and Clague, 1994;Harris et al,2001;Lewkowicz and Harris, 2005;Dorren, 2003;Lipovsky et al, 2006;Haeberli et al, 2006;Kääb, 2008).…”

Water flow in the active layer along an arctic slope – An investigation based on a field campaign and model simulations

“…The layer is in direct contact with the atmosphere and provides the basis of vegetation growth and is therefore an important part of permafrostaffected arctic ecosystems (Bonnaventure and Lamoureux, 2013). As a result of infiltration, a thin saturated layer is commonly formed at the base of the active layer and on top of the mostly impermeable permafrost table.…”

“…Part of these impacts are directly linked to changes in the hydrological conditions (Bense et al, 2009) with profound changes in the permafrost hydrology, active soil moisture distribution and flow patterns 20 (Bring et al, 2016). The deepening of the active layer will change the flow and transport pattern and typically lead to longer travel paths and times (Frey and McClelland, 2009;Frampton and Destouni, 2015).…”

“…Ireson et al, 2012;Bring et al, 2016). The objective of the present study is to quantify water flow and transport mechanisms in the active 15 layer along an arctic hill slope with particular focus on the potential transport mode and time for nutrients released upstream.…”