BROAD-SCALE WATERSHED RESPONSES ASSOCIATED WITH GROUND ICE IN PERMAFROST

Changes in precipitation and temperature regimes are affecting water budgets globally. Climate warming in Arctic regions can result in additional inputs to the hydrologic cycle from ground ice melt as permafrost degrades. Knowledge of ground ice type and distribution is necessary to understand potential impacts on thermokarst processes and hydrological system responses to climate change. The Permafrost map of Canada is the primary source depicting ground ice for the entire country, but mapping is based on the extrapolation of limited field data to broad physiographic units (Heginbottom et al., 1995).

To address this knowledge gap, we present new models of three ground ice types (massive, wedge, segregated) for Canada, and link ice type and abundance to observed thermokarst and hydrologic processes in major northern watersheds. We use an expert-system approach to model ground ice evolution over the last 17 ka in a GIS, accounting for broad-scale environmental changes. Ground ice of medium-to-high abundance occurs within about 45% of the continuous permafrost zone in Canada. All ice types are abundant in the western Arctic Ocean seaboard watershed, where there is evidence that intensive hillslope thermokarst processes can enhance the export of water, sediment and solutes to ocean waters. Abundant segregated ice in low-relief Hudson Bay seaboard watersheds results in wetland and shallow thaw lake thermokarst development, though the influence on streamflow remains undefined. The Mackenzie and Nelson River watersheds include large areas without permafrost and a lower fraction of terrain underlain by ice-rich ground. In these major basins, the hydrological response may be primarily through permafrost degradation that enhances subsurface flow pathways and increases baseflow.

Reference: Heginbottom, J. A., Dubreuil, M.-A., & Harker, P. A. C. (1995). Permafrost - Canada. Plate 2.1, MCR4177, National Atlas Information Service and Geological Survey of Canada, Ottawa, ON, Canada.