Near‐shore talik development beneath shallow water in expanding thermokarst lakes, Old Crow Flats, Yukon

Abstract

It is generally assumed that permafrost is preserved beneath shallow lakes and ponds in the Western North American Arctic where water depth is less than about two thirds of the late‐winter lake ice thickness. Here we present field observations of talik development beneath water as shallow as 0.2 m despite a lake ice thickness of 1.5 m, in Old Crow Flats (OCF), YT. Conditions leading to the initiation and development of taliks beneath shallow water were investigated with field measurements of shore erosion rates, bathymetry, ice thickness, snow accumulation, and lake bottom temperature near the shores of two expanding lakes in OCF. The sensitivity of talik development to variations in lake bottom thermal regime was then investigated numerically. Where ice reached the lake bottom, talik development was controlled by the ratio of freezing degree days to thawing degree days at the lake bottom (FDDlb/TDDlb). In some cases, spatial variations in on‐ice snow depth had a minimal effect on annual mean lake bottom temperature (Tlb) but caused sufficient variations in FDDlb/TDDlb to influence talik development. Where Tlb was close to but greater than 0°C simulations indicated that the thermal offset allowed permafrost aggradation to occur under certain conditions, resulting in irregular near‐shore talik geometries. The results highlight the sensitivity of permafrost to small changes in lake bottom thermal conditions where the water column freezes through in early winter and indicate the occurrence of permafrost degradation beneath very shallow water in the near‐shore zone of Arctic ponds and lakes.

Seasonal Subsurface Thaw Dynamics of an Aufeis Feature Inferred From Geophysical Methods

“…This observation is consistent with the relatively abrupt AP boundary in the northern part of the study area in the late-summer GPR (Figure 6a). This rapid thinning out of a talik at its margins is in general agreement with other findings (e.g., Roy-Leveillee & Burn, 2017).…”

Development of perennial thaw zones in boreal hillslopes enhances potential mobilization of permafrost carbon

“…In response to surface warming, depth of thaw eventually exceeds depth of seasonal frost, and a perennial thaw zone (PTZ), or supra-permafrost talik, develops. Though vertical talik development beneath surface-water bodies is well established through theory and observations (Plug and West 2009, Minsley et al 2012, Wellman et al 2013, Parsekian et al 2013, Roy-Leveillee and Burn 2017 and has been linked to enhanced stream discharge from sub-permafrost flow , Jafarov et al 2018, lateral taliks in terrestrial landscapes and their potential role as conduits for groundwater and solute transport are less studied. Early work focused on characterizing large lateral taliks associated with aufeis (icings) formation (Boikov et al 1984).…”

Taliks, cryopegs, and permafrost dynamics related to channel migration, Colville River Delta, Alaska

“…Some direct observations on the geometry and properties of taliks and cryopegs are available in the literature, with most of them focused at shallow depths and/or obtained from limited data, implying that conclusions may have been partially based on assumptions rather than mainly on field measurements. Thorough field assessments that include drilling, soil sampling, laboratory testing, and measuring ground temperatures and groundwater levels at depths greater than tens of meters are typically challenging and expensive.…”

“…Thorough field assessments that include drilling, soil sampling, laboratory testing, and measuring ground temperatures and groundwater levels at depths greater than tens of meters are typically challenging and expensive. More accessible methods to estimate talik occurrence, configuration, properties and/or temporal changes include measuring bottom water temperatures in lakes and channels for subsequent analytical calculations, numerical modeling, and geophysical surveying . These methods typically do not provide much information on cryopegs, although the use of ground‐penetrating radar combined with direct current resistivity surveys may help to differentiate brine from freshwater…”