HYDROCLIMATIC AND LANDSCAPE CONTROLS OVER MUDBOIL FORMATION IN THE CANADIAN HIGH ARCTIC
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This study aimed to gain an understanding of changing active layer dynamics in the High Arctic, specifically in terms of understanding the spatial distribution of mudboils to identify climatic and landscape controls, and active layer processes driving their formation. Systematic mapping of mudboils and sediment and water sampling was undertaken at the Cape Bounty Arctic Watershed Observatory (CBAWO), Melville Island, Nunavut in 2012 and 2013. Based on borehole stratigraphic profiles taken at CBAWO, three primary soil units were determined: mudboils at surface; overburden (soil) material; and a grey, fine-grained layer at approximately 80cm depth. These soil classes were used for comparison to gain an understanding of the properties and origins of the mudboil materials. Results indicate that these features only occur late in the melt season during exceptionally warm years (2007, 2011, and 2012) and in some cases closely follow major rainfall events. High-resolution satellite imagery was analyzed to determine landscape controls over mudboil formation. Notably, mudboils were significantly associated with bare soil and polar semi-desert vegetation settings, corresponding to increased active layer depth and rate of thaw when compared to more vegetated areas. Further, localized occurrence of mudboils appears to be related to differential soil moisture retention and spatially heterogeneous soil water pressurization due to thaw into the ice-rich transient layer in warm years. We hypothesize that the locally drier locations develop soil ped structures that contribute to diapir development and mud ejection when seasonal melt and hydraulic conditions pressurize soil water. Geotechnical and geochemical analysis of soil samples indicates that mudboils at surface do not significantly differ in terms of composition and physical properties from the undisturbed overburden material. This is consistent with a fine-grained slurry likely being generated in situ from a parent bed and subsequently ejected to surface. This research provides insights into the processes and landscape controls over mudboil formation to aid in understanding localized soil water response to deep summer thaw, with implications for surface water quality and predictions and potential mitigation of permafrost-related degradation and disturbance.