Assessment of Impacts of Permafrost Degradation on Polar Bear Habitat

Activity Rationale

Female polar bears and caribou of the northern Hudson Bay Lowlands rely on frozen raised bogs for denning sites and winter forage respectively. If the climate warming of the past century continues, bogs will thaw, subside, and turn into wet fens. This change in habitat may also increase the ease with which rainfall and snowmelt drain to Hudson Bay. Understanding the sensitivity of permafrost-bearing peatlands to climate change will allow adverse biological and physical effects of this change to be anticipated.

Activity leaders: Dr. Larry Dyke and Wendy Sladen

The Topic

The extent of main wetland types and locations of ground temperature installations in Wapusk National Park. Larger  image

The Hudson Bay Lowlands border Hudson Bay from Churchill, Manitoba to southern James Bay, Ontario, and comprise the most extensive region of thick peatland soils in Canada. Peatlands allow permafrost to extend south because of the yearly variation in peat thermal conductivity associated with raised bog. Raised bogs are characterized by a relief of about one metre, allowing summer drying that lowers the thermal conductivity of surface peat during the warm part of the year. Wetter conditions during freeze-back and snow removal by wind in the winter accentuate the removal of heat in the winter. Although these unique thermal characteristics allow a southerly extension of permafrost, these permafost occurrences are actually left over from cooler conditions one or more centuries ago. Any process that alters the thermal properties of raised bog will probably initiate or accelerate permafrost degradation.

Topographic gradients are characteristically low on peatlands (approximately 1 m/km toward Hudson Bay for the Hudson Bay Lowlands), highlighting the importance of peatland type in the control of drainage. Since bogs are associated with a watertable, flow is restricted by the permeability of the peat. Fens usually have standing water and therefore permit more rapid surface flow. The result is that bogs act to detain rainfall and snow melt whereas fens act to transport this input to stream drainage. Permafrost in raised bog increases water retention of the bog.  In addition to controlling drainage, raised bog margins serve as polar bear denning habitat and bog surfaces provide winter caribou forage, ecological components that are included in Wapusk National Park.

Thawing of bog permafrost in response to a continuation of the warming regime of the past century raises the potential for significant habitat and hydrological changes. This activity generates information on the distribution of permafrost in the northern Hudson Bay Lowlands and on the role that permafrost may play in determining the biological and physical sensitivity of the Hudson Bay Lowlands to climate change.

Results

Until now, ground temperature data for the north Hudson Bay Lowlands has only been available from the immediate vicinty of Churchill. During the last two years, a transect of installations for measuring ground temperature to a depth of about 10 metres has been established extending from the Hudson Bay coast in northern Wapusk National Park to a point about 50 km inland. Installations now exist in raised bog, fen, shallow ponds, and beach ridges. Preliminary data from these installations indicate that permafrost is not continuous but rather is very sensitive to water depth and snow cover. In particular, the edges of raised peat areas accumulate depths of snow considerably higher than average, and this wintertime insulation results in permafrost being absent. Should the warming trend of the last century or so continue, it is likely that one of the first terrain responses will be the further degradation of permafrost along the edges of raised peat areas. Ultimately this process could involve the entire collapse of raised bog and transformation of this wetland type into fen.

The diagrams to the left show monthly temperature profiles below the ground surface for the primary environments of the Hudson Bay Lowlands (April 2007-April 2008). Permafrost (ground temperatures at or below zero degrees Celsius) is most likely to be found beneath peat plateaus (Figure 2) because of the low thermal conductivity of dry surface peat in summer and removal of insulating snow by wind in winter. However, snow accumulation at the edge of peat plateaus (Figure 1) provides insulation and reduces winter cooling, in this case preventing the formation of permafrost since ground temperatures are above zero. Plateau edges will be the starting locations for further permafrost thaw in the event of climate warming. Therefore, the condition of peat plateau margins can be used to indicate the response of peatlands to climate warming. Collapsing of plateau margins and tiling of trees growing along margins would be evidence of thawing. Evidence for this process is present along the very southern fringe of permafrost across central Manitoba and northern Saskatchewan and Alberta.

Publications

Please note that subscriptions may be required for access to some articles. To request a copy of publications, or for any more information, please contact Dr. Larry Dyke

Check for more recent publications in GEOSCAN, the publications database of the Geological Survey of Canada and the Canada Centre for Remote Sensing.

Zhang, Y., Chen, W. and Riseborough, D., 2008. Disequilibrium response of permafrost thaw to climate warming in Canada over 1850–2100, Geophysical Research Letters, v. 35, L02502, 4 p.

Zhang, Y., Chen, W. and Riseborough, D., 2008. Transient projections of permafrost distribution in Canada during the 21st century under scenarios of climate change; Global and Planetary Change, v. 60, p. 443-456.

Faruque Hossain, M., Zhang, Y., Chen, W., Wang, J. and Pavlic, G. 2007. Soil organic carbon content in northern Canada: A database of field measurements and its analysis. Canadian Journal of Soil Science. 87: 259-268.

Dyke, L., 2007. Permafrost Field Program - Wapusk National Park - April, 2007; in-house report to Parks Canada.

Dyke, L., 2008. Permafrost in Wapusk National Park - Summary of State of Knowledge; in-house report for Wapusk Research and Monitoring Conference, Winnipeg.

Dyke, L. and Sladen, W. Permafrost and peatland evolution in Wapusk National Park; paper intended for Arctic, presently submitted for internal review.