Simulating ice segregation and thaw consolidation in permafrost environments with the CryoGrid community model
Abstract. The ground ice content in cold environments influences the permafrost thermal regime and the thaw trajectories in a warming climate, especially for very ice-rich soils. Despite their importance, the amount and distribution of ground ice are often unknown due to lacking field observations. Hence, modelling the thawing of ice-rich permafrost soils and associated thermokarst is challenging as ground ice content has to be prescribed in the model set-up. In this study, we present a model scheme, which is capable of forming segregated ice during a model spin-up together with associated ground heave. It provides the option to add a constant sedimentation rate throughout the simulation. Besides ice segregation, it can represent thaw consolidation processes and ground subsidence under a warming climate. The computation is based on soil mechanical processes, soil hydrology by Richards equation and soil freezing characteristics. The code is implemented in the CryoGrid community model (version 1.0), a modular land surface model for simulations of the ground thermal regime.
The simulation of ice segregation and thaw consolidation with the new model scheme allows us to analyze the evolution of ground ice content in both space and time. To do so, we use climate data from two contrasting permafrost sites to run the simulations. Several influencing factors are identified, which control the formation and thaw of segregated ice. (i) Model results show that high temperature gradients in the soil as well as moist conditions support the formation of segregated ice. (ii) We find that ice segregation increases in fine-grained soils and that especially organic-rich sediments enhance the process. (iii) Applying external loads suppresses ice segregation and speeds up thaw consolidation. (iv) Sedimentation leads to a rise of the ground surface and the formation of an ice-enriched layer whose thickness increases with sedimentation time.
We conclude that the new model scheme is a step forward to improve the description of ground ice distributions in permafrost models and can contribute towards the understanding of ice segregation and thaw consolidation in permafrost environments under changing climatic conditions.
Juditha Aga et al.
Status: final response (author comments only)
RC1: 'Comment on egusphere-2023-41', Anonymous Referee #1, 28 Feb 2023
- AC1: 'Reply on RC1', Juditha Aga, 02 Jun 2023
RC2: 'Comment on egusphere-2023-41', Anonymous Referee #2, 31 Mar 2023
- AC2: 'Reply on RC2', Juditha Aga, 02 Jun 2023
Juditha Aga et al.
Model code and software
Parameter files and model code for simulations in "Simulating ice segregation and thaw consolidation in permafrost environments with the CryoGrid community model" https://zenodo.org/record/6884775
Juditha Aga et al.
Viewed (geographical distribution)
This paper describes a new model scheme, in a suit of the CryoGrid community model (version 1.0. Under review at GMD), to simulate the temporal evolution and the vertical distributions of ground ice content by calculating ice segregation (excess ice) when cold and thaw consolidation when warm, and associated ground heave and subsidence. The model incorporates soil mechanical processes, soil hydrology, and soil freeze/thaw physics. The authors conducted a series of proof-of-concept examinations of the new scheme with respect to climatic (i.e., thermal, and hydrological) conditions, soil types, external loadings, and sedimentation, which demonstrated reasonable performance of the model. It is not so simple to evaluate an additional module when the base model is still under review, however, the reviewer found that the manuscript is moderately well organized and written. Yet, some elaborations and clarifications regarding the points raised below will improve the manuscript before being published in the Cryosphere journal.
Further, for the sake of reader-friendly discussions on evolution and relative impacts of ground heave (subsidence) and ice segregation (thaw consolidation), it is suggested to plot segregation ice and surface height changes together (possibly overplotted in figures 7, 8, and 10?).
Also, the near-surface zones such as active layer is very small, leading it difficult to read and compare especially for the argument of thermal gradients (e.g., ll. 401-408, ll. 420-425). Elaborations will be very helpful.
Also, it is suspected that the vertical lines showing the end of the spinup periods may be off by 10 years or so if that for the S-runs ends in 1969 and that for the B-run ends in 1989.