Simulating the thermal regime and ice mass balance in blocky terrain in mountain environments

• Main Author: Renette, Cas
• Format: Master Thesis
• Language: English
• Published: 2022
• Subjects: mountain permafrost; ground ice; thermal anomaly; CryoGrid; blocky material; permafrost model; Norway; glacier; Ice; Northern Norway; permafrost; Siberia
• Online Access: http://hdl.handle.net/10852/95119; http://urn.nb.no/URN:NBN:no-97646

Ground temperatures in coarse, blocky deposits such as in mountain blockfields and rock glaciers have long been observed to be lower in comparison with other (sub)surface material. One of the reasons for this negative temperature anomaly is the lower soil moisture content in blocky terrain, which decreases the duration of the zero curtain in autumn and can introduce a zero curtain in spring. Many permafrost modelling studies did not include varying water and ice contents. In this thesis, the CryoGrid community model is used to simulate the effect of drainage in blocky terrain on the ground thermal regime and ground ice at two Norwegian mountain permafrost sites and at three ancillary sites in the global permafrost extent. Three idealized stratigraphies are used to investigate thermal anomalies under different amounts of snowfall. The stratigraphies are labeled blocks only, blocks with sediment and sediment only and are either drained or undrained of water, resulting six ‘scenarios’. The model setup features a surface energy balance, heat conduction and advection, a bucket water scheme with a lateral drainage component and (an adaptation of) the CROCUS snow scheme. The results show markedly lower ground temperatures in the blocks only, drained scenario compared to all five other scenarios. A sensitivity analysis to snowfall results in a thermal anomaly is up to 1.5 °C at the sites in Norway for scenarios with relatively high snowfall amounts and up to 3.5 °C at a continental site in northern Siberia. The effect almost vanishes when no persistent ground ice is present. Stable permafrost conditions are simulated at the location of a rock glacier in northern Norway with a mean annual ground surface temperature (MAGST) of 2.0-2.5 °C in the blocks only, drained scenario. Other scenarios under the same climate forcing feature positive ground temperatures. At the location of a blockfield in southern Norway, it is shown that stable permafrost can be present in the blocks only, drained scenario even under an extremely ...