Interannual changes in seasonal ground freezing and near‐surface heat flow beneath bottom‐fast ice in the near‐shore zone, Mackenzie Delta, NWT, Canada

Abstract

AbstractInterannual changes in seasonal ground freezing and near‐surface heat flow beneath zones of bottom‐fast ice (BFI) were examined over the winters of 2005–06 and 2006–07 within the near‐shore zone of the Mackenzie Delta, Canada. Winter variability in ground thermal conditions was determined at three monitoring sites. Ground‐penetrating radar surveys were conducted in late winter to determine spatial variability in landfast ice conditions and the extent of ice‐bonded sediments. Shallow water sites (<0.5 m‐water depth) were characterised by early onset of BFI, freezeback of the active layer and mean winter sediment bed temperatures ranging between −3°C and −10°C. In contrast, deep water sites (>1 m of water) experienced prolonged periods of floating ice, which limited the duration of ice contact with the sediment bed and the depth of seasonal frost, and resulted in warmer winter ground temperatures (between −0.5°C and −2.6°C). Under similar water depths, interannual changes in ice growth altered the timing of BFI and winter heat loss from the ground. When comparing conditions over the two winters, 2005–06 was characterised by a decrease in ice thickness that limited the extent of BFI and seasonal cooling of the ground. These changes in ice conditions had a greater effect on the thermal conditions at sites where water depths were close to the maximum ice thickness. The short ice contact times at these sites are important to the thermal state of permafrost, as only minimal heat exchange contributing to permafrost cooling occurs prior to freezeback of the active layer. Copyright © 2010 John Wiley & Sons, Ltd.