Introduction to permafrost
Permafrost denotes ground (soil, rock, concrete, made ground etc.) whose temperature remains at or below 0ºC for at least two years. Permafrost has been identified as one of six cryospheric indicators of global climate change within the monitoring framework of the WMO Global Climate Observing System (GCOS). Near-surface permafrost temperatures are highly sensitive to climate change as they depend on both air temperatures and precipitation (snow depth, duration). Permafrost temperatures represent a systematic running mean that filters the high-frequency changes in the upper thermal boundary. Thus, analysis of permafrost thermal profiles and trends provides the potential for investigating climate change over decades to centuries in sensitive terrestrial regions where instrumental records are sparse.
The critical importance of permafrost to geomorphology, Quaternary science, and engineering concerns the growth and melt of underground ice in porous media. Growth of segregated ice fractures porous soil and bedrock, heaves the ground surface, and stores water and carbon within an ice-rich layer in the upper metres of permafrost. Melt of the ice initiates slope and foundation instability, and causes exchange of water and carbon with the hydrosphere and atmosphere. The interplay between the build-up and decay of the ice-rich layer operates on a number of timescales. Unusually hot summers (e.g. 2003 in Europe) may lead to rapid active-layer thickening and hence thaw settlement, landslides, debris flows and rock-slope failure, whereas longer-term climate warming at the end of Quaternary glacial or stadial periods and that which is predicted for the 21st century and beyond may cause major permafrost degradation and substrate instability.
The key issues we must address to understand and predict the thermal and ground-ice dynamics in permafrost concern: (1) monitoring permafrost thermal status and ground-ice accumulation and melt along a transect from cold Arctic/Antarctic permafrost to warm sub-Arctic/Antarctic and mountain permafrost, in response to changing surface conditions (e.g. rising air temperatures, increasing snow cover); (2) developing numerical models that couple heat and moisture transfer with ice accumulation and rock/concrete fracture mechanics, so we can predict the rates and consequences of ice growth and decay in near-surface permafrost; (3) monitoring and modeling (a) carbon mass balance within the ice-rich layer, and (b) changes in surface hydrology consequent on changes to the icy layer thermal and hydrological regime; and (4) producing hazard zonation maps that integrate substrate sensitivity and projected climate change in permafrost regions.
Permafrost research is undoubtedly timely. With recent climate warming predicted to continue during the next century, amplified in polar regions, the warming and thawing of ice-rich permafrost is likely to destabilize many soil and bedrock substrates.
Ibyuk pingo, NWT, Canada, in autumn and winter colours (photos: Julian Murton)
Permafrost research at Sussex
Permafrost research at Sussex is directed by Julian Murton. Julian's research focuses on permafrost as a driver and archive of environmental change. It has four themes:
Research opportunities
The main research projects that I am seeking to pursue over the next several years concern:
- Monitoring of ice segregation in permafrost bedrock,Svalbard
- Physical modelling of ice segregation and bedrock fracture in mountain permafrost
- Imaging of cryogenic structure development in soil and rock
- Late Quaternary history of the Arctic Coastal Plain of NWT andYukon,Canada
- Pleistocene periglacial environments in mid-latitudes
I’m happy to discuss these projects with potential collaborators, research students and anyone with a general interest in permafrost.
Julian Murton
June 2011