Genesis of Turbic Cryosols on north-facing slopes in a dissected, unglaciated landscape, west-central Yukon Territory

Abstract

The characteristics and landscape distribution of Histic Dystric Turbic Cryosols were examined on a steep (>30%) northerly slope in the unglaciated Klondike Plateau, near Dawson City, Yukon Territory. Based on texture, major element geochemistry, and clay mineralogy, the mineral parent materials were crudely stratified, with a silty material of likely aeolian origin overlying sandy gravelly colluvium. Discontinuous organic matter-enriched horizons occurred 50 cm or more below the active layer, and contained abundant partially decomposed plant detritus. Eight accelerator radiocarbon dates, ranging from 350 ± 40 to 3680 ± 40 ¹⁴C years BP, suggested that incorporation of organic materials within and below the active layer was geologically recent, and had likely occurred by a combination of cryoturbation and slope processes. The widespread and rapid initiation of mass movements on slopes containing permafrost that followed forest fires in 2004 on the Klondike Plateau may be an analogue for the processes that contributed to organic matter burial in these Cryosols. These soils may represent a significant reservoir of C, as similar sites occupy at least 15% of a representative portion of the Plateau. This reservoir may be vulnerable to mobilization if future climatic warming increases the frequency of forest fires and resulting slope instability.Key words: Tyrbic Cryosol, Yukon Territory, cryoturbation, soil organic carbon, mass movement