Abstract
Abstract. In continuous permafrost lowlands, thawing of ice-rich deposits and melting of massive ground ice lead to abrupt landscape changes called thermokarst, which have widespread consequences on the thermal, hydrological, and biogeochemical state of the subsurface. However, macro-scale land surface models (LSMs) do not resolve such localized subgrid-scale processes and could hence miss key feedback mechanisms and complexities which affect permafrost degradation and the potential liberation of soil organic carbon in high latitudes. Here, we extend the CryoGrid 3 permafrost model with a multi-scale tiling scheme which represents the spatial heterogeneities of surface and subsurface conditions in ice-rich permafrost lowlands. We conducted numerical simulations using stylized model setups to assess how different representations of micro- and meso-scale heterogeneities affect landscape evolution pathways and the amount of permafrost degradation in response to climate warming. At the micro-scale, the terrain was assumed to be either homogeneous or composed of ice-wedge polygons, and at the meso-scale it was assumed to be either homogeneous or resembling a low-gradient slope. We found that by using different model setups and parameter sets, a multitude of landscape evolution pathways could be simulated which correspond well to observed thermokarst landscape dynamics across the Arctic. These pathways include the formation, growth, and gradual drainage of thaw lakes; the transition from low-centred to high-centred ice-wedge polygons; and the formation of landscape-wide drainage systems due to melting of ice wedges. Moreover, we identified several feedback mechanisms due to lateral transport processes which either stabilize or destabilize the thermokarst terrain. The amount of permafrost degradation in response to climate warming was found to depend primarily on the prevailing hydrological conditions, which in turn are crucially affected by whether or not micro- and/or meso-scale heterogeneities were considered in the model setup. Our results suggest that the multi-scale tiling scheme allows for simulating ice-rich permafrost landscape dynamics in a more realistic way than simplistic one-dimensional models and thus facilitates more robust assessments of permafrost degradation pathways in response to climate warming. Our modelling work improves the understanding of how micro- and meso-scale processes affect the evolution of ice-rich permafrost landscapes, and it informs macro-scale modellers focusing on high-latitude land surface processes about the necessities and possibilities for the inclusion of subgrid-scale processes such as thermokarst within their models.
Highlights
Thawing of permafrost in response to climatic change poses a threat to ecosystems, infrastructure, and indigenous communities in the Arctic (AMAP, 2017; Vincent et al, 2017; Schuur and Mack, 2018; Hjort et al, 2018)
We employed a multi-scale tiling approach in the CryoGrid 3 numerical permafrost model to assess the response of ice-rich permafrost lowlands to a warming climate
We explored the sensitivity of the simulated pathways of landscape evolution and permafrost degradation to different representations of micro- and mesoscale heterogeneities
Summary
Thawing of permafrost in response to climatic change poses a threat to ecosystems, infrastructure, and indigenous communities in the Arctic (AMAP, 2017; Vincent et al, 2017; Schuur and Mack, 2018; Hjort et al, 2018). The macro-scale models used to project the response of permafrost to climate warming employ a simplistic representation of permafrost thaw dynamics which only reflects gradual and spatially homogeneous topdown thawing of frozen ground. Such models lack representation of thaw processes in ice-rich permafrost deposits that cause localized and rapid landscape changes called thermokarst (Kokelj and Jorgenson, 2013; Olefeldt et al, 2016). Thermokarst processes can be considered a key factor of uncertainty in future projections of how the energy, water, and carbon balances of permafrost environments will respond to Arctic climate change (Turetsky et al, 2019)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
