Recent advances in ground-ice studies

Julian Murton
(Department of Geography, University of Sussex)

Abstract
Ground ice can be defined as ice within frozen or partly-frozen ground, irrespective of the form of occurrence or origin of the ice. This plenary provides a geological perspective on 21st Century advances in ground-ice studies in terms of (1) ice distribution, (2) formative processes, (3) environmental change, and (4) research priorities.

Knowledge of the distribution of ground ice has benefited from continued improvements in imaging methods. At the scale of centimeters, Computing Tomography (CT) scanning of permafrost sediment cores has revealed the detailed architecture of ice, soil, voids and geological structures in two- and three dimensions. At the scale of meters, geophysical techniques such as Ground Penetrating Radar (GPR), Electrical Resistivity Tomography (ERT), and Seismic Refraction Tomography reveal the location of massive ice and small ice lenses. At the scale of planets, NASA's Phoenix Lander identified in June 2008 ground ice within soil on Mars; the ice is thought to be frozen water rather than carbon dioxide.

Geological understanding of ground-ice processes has recently focussed on ice segregation within porous bedrock and on the interactions between permafrost and ice sheets. Physical modelling experiments simulating bidirectional freezing in an active layer above permafrost, and unidirectional freezing of seasonally frozen rock have successfully led to rock fracture and heave by ice segregation. The ice and fracture distribution resemble those in Arctic permafrost regions underlain by fine-grained and porous (frost-susceptible) bedrocks. Field studies in permafrost regions glaciated during the Pleistocene indicate substantial amounts of buried basal glacier ice and frozen glacitectonite. The latter often contains fragments of ground ice (ice clasts) ripped up beneath the margin of the Laurentide Ice Sheet, demonstrating the cold-based ice sheets can cause substantial erosion of pre-glacial permafrost.

Ground ice is also an important archive of environmental change and is sensitive to global warming. Developments in dating of ice, for example using cosmogenic radionuclides such as 36Cl, may allow direct dating of ground ice that is hundreds of thousands of years old. Rather younger ground ice within the Ice Complex (or Yedoma) of northern Siberia preserves an important record of environmental change during the last glacial period. Organic material preserved within this icy sediment also constitutes a major source of carbon which is being released to the atmosphere as the ground ice melts, particularly within thaw lakes.

Research priorities in ground-ice studies over the coming years include a need for:
(a) higher resolution imaging of ground ice in soil and rock, and discrimination of genetic ground-ice types;
(b) improved knowledge of the distribution and origin of Martian ground ice;
(c) field and modelling studies of ground-ice processes and effects in bedrock;
(d) elucidation of permafrost rheology beneath ice sheets and its implications to ice-sheet dynamics and modelling; and
(e) improved knowledge of the rates of ground-ice melt and carbon release to the atmosphere.

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