Distribution, Morphology and Carbon Stock of Earth Hummocks in the Chuck Creek Trail Valley, Northern British Columbia, Canada

Abstract

Cryoturbation translocates surface organic-rich horizons deeper in the soils and as such is an important process for carbon sequestration in the active layer (e.g., Kaiser et al., 2007; Van Vliet-Lanoë, 2004). Hummocks, which are non-sorted patterned ground, are sub-meter to meter-scale circular to oval-shaped mounds found in fine-grained frost susceptible sediments. This project examines the distribution, morphology and internal structure of hummocks in the sub-alpine region of the Chuck Creek Trail Valley in the Tatshenshini-Alsek Provincial Park, northern British Columbia. Morphological, sedimentological and geochemical analysis showed that the inter-field differences in hummock morphology of the Chuck Creek Trail Valley were dictated by the silt content within the soil. Hummock fields were found to have an average SOCC for a 1 m pedon of 16.3 kg/m2, 38 % situated in the B-horizon. For this pedon, hummocks fields contained 0.05 Pg – 0.2 Pg according to the distribution probability model. Dating of bulk sediments exhibited a cluster of radiocarbon dates around 2000 cal BP for cryoturbated intrusions, implying subduction rates ranging between 0.03 mm/yr to 0.10 mm/yr and coinciding with a period of climatic cooling (Viau, 2008). In conclusion, the differential frost heave model (Van Vliet-Lanoë, 1991) is the only hypothesis for hummock formation consistent with field evidence in the Chuck Creek Trail Valley.