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Antoni G. Lewkowicz - One of the best experts on this subject based on the ideXlab platform.
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Frontal advance of turf-banked solifluction lobes, Kluane Range, Yukon Territory, Canada
Geomorphology, 2005Co-Authors: Christophe Kinnard, Antoni G. LewkowiczAbstract:Humus horizons associated with thirteen solifluction lobes on a single slope were radiocarbon dated at fixed distances behind the risers, as well as ahead of the lobes. The dated horizons, together with stratigraphic observations of planar discontinuities inside the lobes and shallow burial of vegetation ahead of the lobes, all suggest rapid advance of lobe fronts. We infer that lobe advance at this site results from slow accumulation of soliflucted material behind a relatively rigid riser, progressive steepening of the riser and build-up of stress, and finally rupture of the front and its collapse onto the slope. Rebuilding of the lobe usually then takes place. The time for a full cycle of development is estimated to be in the order of a few hundred years. Long-term frontal movement appears inversely related to lobe size, and is mainly controlled by soil moisture and sediment characteristics. These findings call into question the usefulness of solifluction lobe advance rates for paleoclimate reconstructions, at least at this site.
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morphometry and environmental characteristics of turf banked solifluction lobes kluane range Yukon Territory canada
Permafrost and Periglacial Processes, 2002Co-Authors: Chris H Hugenholtz, Antoni G. LewkowiczAbstract:Measurements of turf-banked solifluction lobes at a site in the Kluane Range, Yukon Territory, are compared to observations made by L.W. Price of similar features located 50 km to the north in the Ruby Range. Both studies show that a threshold depth of snow is necessary for lobes to develop. The relative importance of solifluction on slopes with different orientations, however, is not congruent. The largest lobes at our site are present on northeast-facing slopes and the smallest on northwest-facing slopes. Lobe dimensions increase downslope in association with a greater organic mat thickness, a higher soil fines content, and a reduced late-summer thaw depth. Riser heights that are large relative to tread length-to-width ratios are correlated with a thin organic mat, a thick active layer and a high coarse particle content. The lobe plan-form, described by the ratio of tread length to tread width, is significantly correlated with only one biophysical variable. Mean and median length-to-width ratios are below unity for all aspects at our site and in several other studies, suggesting a common evolutionary form. A cycle of solifluction lobe development is proposed, in which a lobe enlarges to a maximum size that depends on micro-site environmental characteristics. Copyright © 2002 John Wiley & Sons, Ltd.
Chris H Hugenholtz - One of the best experts on this subject based on the ideXlab platform.
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morphometry and environmental characteristics of turf banked solifluction lobes kluane range Yukon Territory canada
Permafrost and Periglacial Processes, 2002Co-Authors: Chris H Hugenholtz, Antoni G. LewkowiczAbstract:Measurements of turf-banked solifluction lobes at a site in the Kluane Range, Yukon Territory, are compared to observations made by L.W. Price of similar features located 50 km to the north in the Ruby Range. Both studies show that a threshold depth of snow is necessary for lobes to develop. The relative importance of solifluction on slopes with different orientations, however, is not congruent. The largest lobes at our site are present on northeast-facing slopes and the smallest on northwest-facing slopes. Lobe dimensions increase downslope in association with a greater organic mat thickness, a higher soil fines content, and a reduced late-summer thaw depth. Riser heights that are large relative to tread length-to-width ratios are correlated with a thin organic mat, a thick active layer and a high coarse particle content. The lobe plan-form, described by the ratio of tread length to tread width, is significantly correlated with only one biophysical variable. Mean and median length-to-width ratios are below unity for all aspects at our site and in several other studies, suggesting a common evolutionary form. A cycle of solifluction lobe development is proposed, in which a lobe enlarges to a maximum size that depends on micro-site environmental characteristics. Copyright © 2002 John Wiley & Sons, Ltd.
Christophe Kinnard - One of the best experts on this subject based on the ideXlab platform.
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Frontal advance of turf-banked solifluction lobes, Kluane Range, Yukon Territory, Canada
Geomorphology, 2005Co-Authors: Christophe Kinnard, Antoni G. LewkowiczAbstract:Humus horizons associated with thirteen solifluction lobes on a single slope were radiocarbon dated at fixed distances behind the risers, as well as ahead of the lobes. The dated horizons, together with stratigraphic observations of planar discontinuities inside the lobes and shallow burial of vegetation ahead of the lobes, all suggest rapid advance of lobe fronts. We infer that lobe advance at this site results from slow accumulation of soliflucted material behind a relatively rigid riser, progressive steepening of the riser and build-up of stress, and finally rupture of the front and its collapse onto the slope. Rebuilding of the lobe usually then takes place. The time for a full cycle of development is estimated to be in the order of a few hundred years. Long-term frontal movement appears inversely related to lobe size, and is mainly controlled by soil moisture and sediment characteristics. These findings call into question the usefulness of solifluction lobe advance rates for paleoclimate reconstructions, at least at this site.
Wayne H Pollard - One of the best experts on this subject based on the ideXlab platform.
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late glacial and holocene sedimentation vegetation and climate history from easternmost beringia northern Yukon Territory canada
Quaternary Research, 2012Co-Authors: Michael Fritz, Hugues Lantuit, Ulrike Herzschuh, Sebastian Wetterich, Gregory P De Pascale, Wayne H Pollard, Lutz SchirrmeisterAbstract:Abstract Beringian climate and environmental history are poorly characterized at its easternmost edge. Lake sediments from the northern Yukon Territory have recorded sedimentation, vegetation, summer temperature and precipitation changes since ~ 16 cal ka BP. Herb-dominated tundra persisted until ~ 14.7 cal ka BP with mean July air temperatures ≤ 5°C colder and annual precipitation 50 to 120 mm lower than today. Temperatures rapidly increased during the Bolling/Allerod interstadial towards modern conditions, favoring establishment of Betula-Salix shrub tundra. Pollen-inferred temperature reconstructions recorded a pronounced Younger Dryas stadial in east Beringia with a temperature drop of ~ 1.5°C (~ 2.5 to 3.0°C below modern conditions) and low net precipitation (90 to 170 mm) but show little evidence of an early Holocene thermal maximum in the pollen record. Sustained low net precipitation and increased evaporation during early Holocene warming suggest a moisture-limited spread of vegetation and an obscured summer temperature maximum. Northern Yukon Holocene moisture availability increased in response to a retreating Laurentide Ice Sheet, postglacial sea level rise, and decreasing summer insolation that in turn led to establishment of Alnus-Betula shrub tundra from ~ 5 cal ka BP until present, and conversion of a continental climate into a coastal-maritime climate near the Beaufort Sea.
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fifty years of coastal erosion and retrogressive thaw slump activity on herschel island southern beaufort sea Yukon Territory canada
Geomorphology, 2008Co-Authors: Hugues Lantuit, Wayne H PollardAbstract:Abstract Patterns of coastal erosion in the Arctic differ dramatically from those coasts in more temperate environments. Thick sea ice and shore-fast ice limit wave-based erosional processes to a brief open water season, however despite this, permafrost coasts containing massive ice, ice wedges and ice-bonded sediments tend to experience high rates of erosion. These high rates of erosion reflect the combined thermal–mechanical processes of thawing permafrost, melting ground ice, and wave action. Climate change in the Arctic is expected to result in increased rates of coastal erosion due to warming permafrost, increasing active layer depths and thermokarst, rising sea levels, reduction in sea ice extent and duration, and increasing storm impacts. With the most ice-rich permafrost in the Canadian Arctic, the southern Beaufort Sea coast between the Tuktoyaktuk Peninsula and the Alaskan border is subject to high rates of erosion and retrogressive thaw slump activity. Under many climate change scenarios this area is also predicted to experience the greatest warming in the Canadian Arctic. This paper presents results of a remote sensing study on the long-term patterns of coastal erosion and retrogressive thaw slump activity for Herschel Island in the northern Yukon Territory. Using orthorectified airphotos from 1952 and 1970 and an Ikonos image from 2000 corrected with control points collected by kinematic differential global positioning system and processed using softcopy photogrammetric tools, mean coastal retreat rates of 0.61 m/yr and 0.45 m/yr were calculated for the periods 1952–1970 and 1970–2000, respectively. The highest coastal retreat rates are on north–west facing shorelines which correspond to the main direction of storm-related wave attack. During the period 1970–2000 coastal retreat rates for south to south–east facing shorelines displayed a distinct increase even though these are the most sheltered orientations. However, south to south–east facing shorelines correspond to the orientations where the highest densities of retrogressive thaw slumps are observed. Differences in rates of headwall retreat of retrogressive thaw slumps and coastal erosion results in the formation of larger thermokarst scars and the development of polycyclic thaw slumps on south to south–east exposures. The number and the total area of retrogressive thaw slumps increased by 125% and 160%, respectively, between 1952 and 2000. As well, the proportion of active retrogressive thaw slumps increased dramatically. Polycyclic retrogressive thaw slumps appear to develop in a periodic fashion, related to retrogressive thaw slump stage and maximum inland extent.
R. A. Bodaly - One of the best experts on this subject based on the ideXlab platform.
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evolution of lake whitefish coregonus clupeaformis in north america during the pleistocene evidence for a nahanni glacial refuge race in the northern cordillera region
Canadian Journal of Fisheries and Aquatic Sciences, 1992Co-Authors: C J Foote, C C Lindsey, J W Clayton, R. A. BodalyAbstract:Lake whitefish (Coregonus clupeaformis) could have survived through (at least) the Illinoisan and Wisconsinan Pleistocene glacial maxima in an area in the vicinity of the present Nahanni National Park in the Northwest Territories of Canada according to the geological evidence. This possibility was addressed by an analysis of the genetic makeup of 43 lake whitefish populations in the Northwest Territories, the Yukon Territory, British Columbia, and Alberta. Populations in the lower Liard, Tetcela, Fraser, and upper Peace River systems as well as the headwaters of the Athabasca River were distinguished from both the Bering glacial refuge race populations inhabiting the Yukon and upper Liard River basins in the Yukon Territory and the Mississippi–Missouri glacial refuge race populations inhabiting most of the Northwest Territories, Alberta, and areas further to the east by a specific combination of electrophoretic mobility alleles. This evidence supports the hypothesis of the survival and subsequent dispersa...
