Diss. (sammanfattning) Uppsala : Univ., 2003. / Härtill 5 uppsatser.

This research focused on measuring permafrost patch size and related variables between Fort St. John, BC and Whitehorse, YT. Methods used included electrical resistivity tomography, climate monitoring, active layer measurement, analysis of historical aerial photos, and on-site near-vertical aerial imaging. Where permafrost is present along the transect, mean annual air temperature (2010-2014) varied from -3.3 ºC to -0.9 ºC, mean annual ground surface temperature from 0.7 ºC to 2.4 ºC and mean annual ground temperature from -0.3 ºC to 0.2 ºC (at TTOP). Permafrost patches are in the order of 10 – 50 000 m2 in area and there is a strong positive log-log relationship between patch area and maximum permafrost thickness. A conceptual model of permafrost patch size evolution under a warming climate is proposed. It is concluded that permafrost patch size depends on site-specific characteristics, the time since permafrost began to degrade and the local climate conditions.

Between 2009 and 2013, 16 ice-bearing permafrost cores were collected from 10 polygons along the floor of University Valley (McMurdo Dry Valleys of Antarctica) and were subsequently analysed in order to assess the geochemical properties of the valley’s icy soils and ground ice. Elemental analysis showed that icy soils located in the seasonally non-cryotic zone (NCZ) of the valley contained (on average) twice as much organic carbon (1.19 mg/g) as the ice cemented permafrost soils sampled in its perennially cryotic zone (PCZ). It also showed that nitrogen accumulation in the icy soils was a result of atmospheric fallout and chemical weathering of mineral soils. Isotopic analysis showed that the organic matter contained in the valley’s icy soils are mostly derived from the deposition and burial of cryptoendolithic communities living in the adjacent sandstone valley walls. Dissolved organic carbon (DOC) concentration measures indicated that soils containing the highest amounts of DOC were enriched in 13CDOC relatively to soils with low DOC concentrations. This indicated that microbial activity in soils was the highest during past super interglacial periods. A soil habitability index calculation from Stoker et al. (2010) was used to establish that soils located in the NCZ were more habitable than soils sampled in the PCZ and also presumably more habitable than soils at many Mars landing sites.

Thesis advisor: Jeremy D. Shakun / The Arctic is one of the fastest warming regions on the planet. Currently, much of the Arctic is covered by permafrost, which contains approximately 1,700 gigatons of organic carbon. Permafrost thaw could release a substantial amount of this carbon as greenhouse gases into the atmosphere through microbial decomposition, potentially dramatically amplifying anthropogenic warming. However, the risk of permafrost thaw is uncertain, with models exhibiting a wide range of possibilities. Assessing the stability of permafrost during past interglacial periods enables evaluation of the sensitivity of permafrost to warming. Cave mineral deposits (speleothems) in areas currently covered with permafrost can act as a proxy for past permafrost thaw, as liquid water is one criterion for speleothem growth and thus speleothem deposition implies thawed ground conditions. Previous uranium-thorium (U-Th) dating of speleothems (n=73) from a wide range of latitudes and permafrost zones across the southern Canadian Rockies, Northwest Territories, and northern Yukon indicate that most of these formations exceed the U-Th dating limit of 500 ka. In this study, I apply uranium-lead (U-Pb) geochronology to several of these speleothems to extend the record of speleothem growth further back in time. Results include a U-Pb age of 412.8 ± 1.3 ka that replicates a previous U-Th age of 415.0 ± 11.5 ka, demonstrating the reliability of the U-Pb methodology. Additionally, U-Pb ages on six other speleothems are determined to be 876 ± 9 ka, 1501 ± 31 ka, 1570 ± 66 ka, 2046 ± 106 ka, 7636 ± 184 ka, and 7697 ± 185 ka. Further application of this technique could result in long records of past permafrost thaw and Arctic terrestrial climate extending back millions of years. / Thesis (MS) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

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Thesis (M.Sc.). / Title from title page of PDF (viewed 2008/01/30). Written for the Dept. of Geography. Includes bibliographical references.

Retrogressive thaw slumps are one of the most dynamic geomorphic features in ice-rich permafrost environments. These features impact aquatic environments by releasing previously frozen organic and inorganic sediments into nearby waterbodies. The objective of this study is to quantify the effect of thaw slumps growth on the hydro-geochemical regime of streams in the Richardson Mountains–Peel Plateau region, northwestern Canada (Fig. 1), within a geospatial hydrological framework (sub-basin, watershed and sub-watershed units). The sub-basin level is determined as the most effective to represent the geochemical properties because of the higher number of sample points within each unit. Based on correlation values, the average surface area of slumps has the most impact on stream geochemistry (as opposed to the number of slumps). Larger single slumps (>5ha) contribute more to changes in geochemistry than clusters of smaller slumps. These slumps can alter the geochemistry of the water to such levels as to exceed limits for freshwater aquatic life.

The objectives of this thesis were: (1) to quantify seasonal groundwater contribution to total stream discharge and (2) further our understanding of sub-arctic carbon sources and pathways within a sub-arctic discontinuous permafrost river catchment. Twenty-two samples were taken from the North Klondike River, 14 samples from 5 of its tributaries, and 46 rain and snowmelt samples from the Dawson City Airport, Yukon, Canada,. During the winter months, groundwater is responsible for greater than 95% of total river discharge. Spring freshet and summer flow bring snowmelt and precipitation, contributing anywhere from 30% to greater than 60% of total river discharge. Groundwater is characterised by high concentrations of geogenic solutes from weathering during recharge, dissolved inorganic carbon, and carbon-14 activities of 0.61 pMC. Tritium activities indicate a fast moving system, with groundwater ages measuring less than 10 years. The most significant discharge of organic carbon from the system is during spring freshet (434,192 kg carbon). Primary productivity within the system is estimated to be 10.2 grams of carbon per metre squared, with approximately 96% of carbon being sequestered or emitted as carbon dioxide.

This study seeks to better understand the relationship between permafrost, elevation and vegetation cover, and to test the hypothesis that changes in mountain permafrost distribution and characteristics occur at vegetation type boundaries, as they do in latitudinal permafrost. Twelve electrical resistivity tomography (ERT) surveys were completed at vegetation transitions on selected slopes near Whitehorse and Dawson, Yukon, in July 2015. Wenner arrays with 2 m spacing between electrodes were used to complete the 80-280 m long surveys. Organic layer thickness and vegetative species composition were recorded in a transect for each survey. Ground-truthing via frost probing, pit digging, and ground temperature data from past and present weather stations aided in the analysis of ERT profiles. Several different resistivity patterns are present along the profiles. These patterns indicate some presence of permafrost along most of the slopes sampled. Exceptions include south-facing slopes free of permafrost and a few slopes with inconclusive resistivity interpretations due to complex resistivity patterns and ground-truthing difficulties. Overall, the results indicate that changes in permafrost distribution and characteristics do not consistently occur at vegetation type boundaries. At the scale examined, treeline is not as important a demarcation point for changes in permafrost as initially thought. Changes in organic mat, surficial geology, and snow cover (via micro-topography) appear to be as important as vegetation variation. These local controls play a significant role on permafrost distribution across both altitudinal and latitudinal forest-tundra ecotones. However, the propensity of alpine environments for cold air drainage and surface lapse rate inversions can create differences between the permafrost trends across altitudinal and latitudinal ecotones.

This study focuses on a mid-sized watershed of upper Ogilvie River (~4,500 km2 at the western extent of the 77,000 km2 Peel River basin) located at the northern extent of the discontinuous permafrost in central Yukon. Annual hydrograph is analyzed by characterizing the river flow components using geochemical tracers (anions, cations, and dissolved organic and inorganic carbon), stable isotopes (δ2H, δ18O, and δ13C) and radioactive isotopes (14C and 3H). The 2014 and 2015 flows are characterized by high weathering solute concentrations (Ca2+, Mg2+, SO42-, and DIC) in the winter that spike just prior to freshet, diluted to the lowest concentrations at the peak of freshet, and slowly recover throughout the summer and fall responding to overall flow fluctuations. Biogenic solutes (K+ and DOC) are lowest in the winter time and spike at the start of freshet. Two groundwater components, shallow and deep, were identified with corresponding tritium-based residence times of less than a year and three years, respectively. The local meteoric water line, developed based on the local precipitation samples δ2H=6.77·δ18O-24.54 (R2=0.98), was used to determine the recharge mix of the groundwaters: 65% rain and 35% snowmelt. The recharge waters interact greatly with soil (open system weathering) and carbonate bedrock (closed system weathering) as evident via the δ13C and F14C signatures of the active layer waters, shallow groundwater and deep groundwater. Radiocarbon of DIC proved to be an important tool to differentiate the weathering conditions by demonstrating F14C carbonate dilution resulting in groundwater F14C as low as 0.57. Based on the δ18O based hydrograph separation, deep groundwater comprised almost half of the annual discharge. The groundwater discharge reached its maximum flow of 129 m3/s during freshet when it contributed 44% to the flow. The potential groundwater recharge pathways include thermal contraction cracks in permafrost and bedrock fractures. The recharge is thought to occur over vegetated areas. In the summer, likely only large precipitation events result in recharge. In comparison to discharge, the annual DIC exports from the study catchment (5.6 gC/m2/yr) were disproportionally high in the winter time and the DOC exports (2.1 gC/m2/yr) varied proportionally with discharge.