Stephen Wolfe - Academia.edu (original) (raw)

Papers by Stephen Wolfe

Research paper thumbnail of Oriented-lake development in the context of late Quaternary landscape evolution, McKinley Bay Coastal Plain, western Arctic Canada

Quaternary Science Reviews

Research paper thumbnail of Subedi et al. (tc-2020-33) Comments

Research paper thumbnail of Ecohydrological dynamics of a degrading subarctic peatland: Implications for Arsenic mobility

<p&amp... more <p>A peatland from subarctic Canada (Handle Lake 62°29’26.44”N, 114°23’18.23”W) is a degrading permafrost peatland chosen for detailed study due to a legacy of regional arsenic (As) contamination as a result of almost 8 decades of gold mining. The fate of permafrost peatlands and their element stores is unknown due to complex feedbacks between peat accumulation, hydrology, and vegetation that affect redox state and element mobility. We combine palynology with study of plant macrofossils, testate amoebae, organic matter composition, and bulk geochemistry preserved in a ca. 4180-4972 cal year old peat monolith retrieved from the Handle Lake peatland to reconstruct the ecohydrological dynamics to assess future trajectories of permafrost peat, and contaminant storage or release, in response to current and future warming. Sphagnum riparium macrofossils are rare in modern peat habitats and sub-fossils are rare in paleoecological records. Plant macrofossils of this taxon occur in an 11-cm thick layer together with Sphagnum angustifolium between 43 cm (ca.  3390-3239 cal BP) and 25 cm depth (ca. 2755-2378 cal BP) in the monolith. The S. riparium sub-fossils are present with the hydrophilous testate amoebae species Archerella flavum, Hyalosphenia papilio and Difflugia globulosa that are used to quantitatively reconstruct a water table depth of 0-4 cm below the peat surface. Sub-fossils of S. riparium disappear at ca. 2755-2378 cal BP, likely due to an autogenic trophic shift and succession towards more acidophilic conditions favourable to species such as Sphagnum fuscum and Sphagnum russowii. We interpret the occurrence of S. riparium as an indicator of wet and minerotrophic conditions linked to peatland development form rich fen to oligotrophic bog.  Because S. riparium is a key pioneer species of disturbed peatlands that have experienced permafrost degradation it will likely be favoured in northern regions experiencing rapid climate warming. In the palynological record the proportion of Sphagnum-type A spores increases (up to 80%) between ca.  3390-3239 cal BP and ca. 2755-2378 cal BP concurrent with a decline in other Sphagnum-type spores. A peak in micro- and macroscopic charcoal occurs between ca. 3557-3286 cal BP and ca. 3275-2771 cal BP, concurrent with a decline in Picea pollen and an increase in Alnus pollen. Regionally, between ca. 3500 and ca. 2500 cal BP Neoglacial climate prevailed with post-Neoglacial warming at ca. 2500 cal BP. It is therefore possible that regional fire occurrence stimulated permafrost degradation at ca. 3500 cal BP. Background As in the active layer monotlith is ~20-30 ppm. The upper 10 cm of the peat are impacted by aerial deposition of As from ore processing and concentrations range up to ~360 ppm. An increase in the concentration of As in the monolith from ~15-20 ppm at the base of the monolith to ~30-40 ppm during this interval may reflect water table depth dynamics that affected the mobility and fate of this redox sensitive element and/or downward mobility from layers impacted by contamination from mineral processing. Degradation of this permafrost within the Handle Lake peatland will release the currently stored As and other contaminants to the regional environment.</p>

Research paper thumbnail of A landsystems approach to understanding the evolution of ice-cored topography and distribution of retrogressive thaw slumps, western Canadian Arctic

<p&amp... more <p>The landscape of the Tuktoyaktuk Coastlands, western Canadian Arctic is dominated by glacial and geocryological processes that have modified, imprinted and sculpted the surface, depositing surficial materials upon underlying bedrock. Climate warming continues in this region at a rate that is twice the global average, and retrogressive thaw slump (RTS) activity is increasing. Recently, RTS distribution was associated with glacial limits reached by the Laurentide Ice Sheet and corresponding morainal deposits, but RTS are common in other local terrain units. In this glacial-marginal region, permafrost existed pre-glacially, and non-glacial geomorphic processes occurred throughout the Late Quaternary. Superimposed on these conditions are the effects of thermokarst during the Holocene climatic optimum, followed by a period of cooling. Collectively, these processes and associated forms and deposits have contributed variously to preservation, development, or degradation of permafrost and ground ice. The multifaceted Late Quaternary history in this region has impeded understanding of the distributions of ice-cored topography and RTS. For example, rather than glaciogenic ice, the long reigning regional model for ice-cored topography is according to post-glacial development of intrasedimental segregation-intrusion ice. Toward better understanding the evolution of the whole landscape and the distribution of climate-sensitive terrain, we use a landsystems approach as a means to understand how the ice-cored topography developed where RTS form, through analysing the cryostratigraphy. To this end, we identify 6 RTS representing a suite of ice-cored topographic settings, including: (i) preserved basal glacial ice facies within clayey diamict that has been thrusted and folded by glacial push representing morainal deposits of the Sitidgi Stade; (ii) ice contact outwash sediments associated with the Sitidgi Stade, overlying a thermo-erosional contact with underlying basal glacial icy diamict of the Toker Point Stade; (iii) deformed basal glacial ice, eroded down by meltwater-deposited outwash sands some time between the Toker Point and Sitidgi Stades (could be ca. 12.9 kyr BP); (iv) massive, undeformed segregation-intrusion basal ice, likely formed subglacially by freezing of intrasedimental water in pre-existing Pleistocene sands into the base of the glacier, overlain by glacial diamicton;  (v) deformed basal ice facies of intermediate Toker Point – Sitidgi Stades, with an upper layer that may be supra-glacial melt-out till into which segregated ice formed; and (vi) segregation ice that formed as permafrost aggraded into glaciolacustrine clays deposited in proglacial or glacially dammed basins, that was subsequently eroded down by glaciofluvial outwash (Sitidgi Stade). To summarize, the distribution of RTS reflects primarily the distribution of icy basal glacial diamict preserved in moraines, but also basal ice and icy basal diamict that are preserved beneath glaciofluvial deposits, segregation ice in glaciolacustrine deposits, and massive segregation-intrusion ice in Pleistocene sands beneath a till plain.</p>

Research paper thumbnail of Composition and origin of a lithalsa related to lake-level recession and Holocene terrestrial emergence, Northwest Territories, Canada

Earth Surface Processes and Landforms

Research paper thumbnail of Recent warming impacts in the Mackenzie Delta, Northwest Territories, and northern Yukon Territory coastal areas

Ice wedges on northern Richards Island, Northwest Territories, and along the Yukon Territory coas... more Ice wedges on northern Richards Island, Northwest Territories, and along the Yukon Territory coastlands, have responded to increased thaw depths. Observations made in 1999 are compared to those last made in these areas in 1975 and 1984, respectively. Climate data indicate that air temperatures in these areas have been warmer than average since 1978 and that warming in 1998 was an extreme event. Increased thaw in response to this warming has caused a decrease in the number of secondary and tertiary ice wedges, and is attributed to thaw truncation. Depths to the tops of ice wedges on Richards Island have increased, whereas depths have decreased on the Yukon Territory coastlands due to thaw consolidation. Thaw-tube observations indicate that 1998 thaw depths were the greatest since 1991 across the northern Mackenzie Delta region, with increases of as much as 21 cm. 1 Résumé : Les fentes de glace dans le nord de l'île Richards (Territoires du Nord-Ouest) et le long des terrains côtiers du Territoire du Yukon, ont réagi à l'accroissement de la profondeur de dégel. On compare les observations faites en 1999 avec celles faites dans les mêmes régions en 1975 et en 1984, respectivement. Les données climatiques indiquent que depuis 1978, la température de l'air dans ces régions a été plus élevée que la moyenne et qu'en 1998, le réchauffement a été un événement extrême. Suite à ce réchauffement, un dégel plus profond a causé une diminution du nombre de fentes de glace secondaires et tertiaires et est attribuable à la troncature par le dégel. La profondeur jusqu'au sommet des fentes de glace a augmenté dans l'île Richards alors qu'elle a diminué le long des terrains côtiers du Territoire du Yukon en raison de la consolidation due au dégel. Les observations dans les tubes de dégel ont indiqué qu'en 1998, la profondeur de pénétration du dégel a été la plus grande depuis 1991 dans le nord du delta du Mackenzie, avec des augmentations allant jusqu'à 21 cm.

Research paper thumbnail of Geological and meteorological controls on icing (aufeis) dynamics (1985 to 2014) in subarctic Canada

Journal of Geophysical Research: Earth Surface

Icings are widespread yet poorly understood winter hydrological phenomena that develop over the w... more Icings are widespread yet poorly understood winter hydrological phenomena that develop over the winter by freezing successive overflows of groundwater to the surface. Groundwater hydrology in arctic regions is constrained by geological setting and permafrost extent, and overflows are possibly driven by cold winters, winter warming intervals, high antecedent autumn rainfall, and low early winter snowfall. Consequently, icings are spatially recurrent but not necessarily annually nor to the same extent. We test the significance of identified meteorological forcing variables against a long-term data set of icing dynamics and distribution we developed for the Great Slave region around Yellowknife, Northwest Territories. Climate is regionally consistent, but variable geology and permafrost create hydrological conditions representative of much of the subarctic. We mapped 5500 icings in the study area (21,887 km 2) with a semiautomated approach utilizing late spring Landsat archival images (1985 to 2014). Individual icing size, ranging 3 orders of magnitude (1.8 × 10 À3 km 2 to 4.1 km 2), is related to return frequency. Infrequent ice (25% return frequency) accounts for 94% of the total icing area (86 km 2). Winter warming intervals (≥5°C; typically over 1-3 days) and autumn rainfall (September and October) explain 28% of icing density interannual variation overall. Interannual icing variation and significant meteorological forcing variables differ among ecoregions where varied geological settings and permafrost conditions influence the hydrological regime. Future icings may develop less frequently due to decreasing winter warming intervals, but increasing autumn rainfall may increase icing density where Canadian Shield leads to strong threshold-mediated runoff generation processes. This paper assesses how identified local and regional factors affect long-term icing dynamics in the subarctic. We hypothesize that icing area varies over time according to meteorological forcing variables, with spatial variation due to hydrological setting moderated by geological conditions. We test this hypothesis by examining the influence of autumn rainfall, early winter snowfall and air temperature, total winter snowfall, and frequency of sporadic winter air warming events on interannual variation of annual icing area, in a study area (Figure 1) with a uniform regional climate [

Research paper thumbnail of Geological and geophysical investigations of ground ice in glaciofluvial deposits, Slave Province, District of Mackenzie, Northwest Territories

Research paper thumbnail of Sand dunes of the northern Great Plains of Canada and the United States

Mostly ~lable dune fields are widespread over the subhumid to semiarid northern Greal Plains. Alt... more Mostly ~lable dune fields are widespread over the subhumid to semiarid northern Greal Plains. Although winds in the region are strong, most dunes are presently inacti ve hecause or rclati vely high ratios of precipitation to potential evapotranspiration, which has the dual effect or increasing dune moisture con tenl and maintaining a vegetation cover. Dune fields are relatively ~malL as most are derived from finite sup plies of glaciotluvial or glaciolacuslline sediments from the last deglaciation. Many dunes. however. are nOI relict featmes from the last deglaciation. The last epi ~odcs or eolian activity were during the lale Holocene, although there is as yet little evidence for regional synchroneity of sand movement. The strong winds and negati ve moiSlure regime have combined to produce an eolian system that is highly sensitive to small shifts in climate. The potential for reactivation ofnorrhern Great Plains sand dunes is great. whether due to natural climatic variations or human-induced greenhouse warming. Resume: De nombreux champs de dune" dont la plupart sont stable" par,cmenl lcs grandes plaines ~eptentrionales subhumides asemi-arides. Malgre la force des vents dam la region, la plupan des dunes sonl ac luellement inacti ve s en rai ~on d1I rapport relativement e leve des precipilations aI' evapotran sp irati on potenrielle, ce qui a pour double dIet d'accroltre Ie contenu cn humidik des dunes et de maintenir une couverture vegeta1e. Les champs de dunes sont rc1ativcment petits. car la plupalt proviennent d'un approvisimlllemenl fini de sediments fluvioglaciaires ou glaciolacustres de la dernicre deglaciation. Toutcfois, de nombreuses dunes ne sont pas des vestiges de la derniel'e deglaciation. Les demiers episodes d'acli vile eolienne ant en effet eu lieu au COllI'S de I'Holocelle superieur, bien qll'on ne dispose pas jusqu' it present d' indices de synchronisme regional des depJacements du sable. L' action combinee des forts vents el Liu regime d'humidite negative ant engendre un systemc colien qui <':st tres sensible ade legeres modifica tions du chma!. II exiSle un fort potentiel de reactivation des dunes de sable des grandes plaines septentrionalc~,que ce SOil en raison de variatiolls climatiques nature lles ou d' un rcchaulTemenr par dIet de selTe d'01igine anthropique.

Research paper thumbnail of 11.19 Cold-Climate Aeolian Environments

Research paper thumbnail of El Ni�o Stills Winter Winds Across The Southern Canadian Prairies

Research paper thumbnail of Impacts of Future Climate Change on the Southern Canadian Prairies: A Paleoenvironmental Perspective

Research paper thumbnail of Recent stabilization of active sand dunes on the Canadian prairies and relation to recent climate variations

Geomorphology, May 15, 2005

... In this regard, the area of active sand at Brandon North has decreased by 91% in 60 years (19... more ... In this regard, the area of active sand at Brandon North has decreased by 91% in 60 years (1928–1988). Overall, the temporal measurements at the Brandon dune occurrences are in line with those previously reported by Wolfe et al. (2000). ...

Research paper thumbnail of Glacial History, Paleogeography and Paleoenvironments in Glaciated North America. Géographie physique et Quaternaire :, vol. 58, no. 2-3, 2004

Geographie Physique Et Quaternaire, 2004

Research paper thumbnail of Age and paleoenvironmental significance of Late Wisconsinan dune fields in the Mount Watt and Fontas River map areas, northern Alberta and British Columbia

Seven optical ages from two dune fields in northern Alberta and British Columbia record Late Wisc... more Seven optical ages from two dune fields in northern Alberta and British Columbia record Late Wisconsinan dune activity between about 13.9 and 10.3 ka. Sand dunes in the Fontas River area of British Columbia (NTS 94-I) formed between 13.9 and 11.7 ka. Initial winds blew from the northwest, funnelled between the Laurentide and Cordilleran ice sheets. These were replaced by winds from the west, likely associated with the Pacific air mass. Dunes in the High Level area of Alberta (Mount Watt, NTS 84 K) first formed at about 13.4 ka under transporting winds from the northeast and southeast, probably originating katabatically from the Laurentide Ice Sheet. Subsequent winds between about 11.7 and 11.0 ka were from the southeast, originating from glacial anticyclonic winds generated by a stationary high-pressure centre over the Laurentide Ice Sheet. These dunes were further modified by winds from the east. The High Level dunes stabilized at about 10.3 ka with the onset of boreal forest vegetation cover and reduced wind strength. Résumé : Deux champs de dunes dans le nord de l'Alberta et de la Colombie-Britannique ont fait l'objet de sept datations par stimulation optique qui ont révélé une activité dunaire au Wisconsinien supérieur, il y a entre environ 13,9 et 10,3 ka. Des dunes de sable dans la région de la rivière Fontas (SNRC 94-I), en Colombie-Britannique, se sont formées il y a entre 13,9 et 11,7 ka. Les vents qui les ont accumulées ont soufflé d'abord du nord-ouest, canalisés entre les inlandsis laurentidien et de la Cordillère. Par la suite, des vents soufflant de l'ouest, vraisemblablement associés à la masse d'air du Pacifique, ont remplacé ces vents du nord-ouest. Les dunes de la région de High Level, en Alberta (mont Watt, SNRC 84 K), se sont formées il y a environ 13,4 ka sous l'effet de vents d'origine katabatique probablement engendrés sur l'Inlandsis laurentidien, qui soufflaient du nord-est et du sud-est. Par la suite, il y a entre environ 11,7 et 11,0 ka, des vents anticycloniques glaciaires, engendrés par un centre de haute pression stationnaire sur l'Inlandsis laurentidien, ont soufflé du sud-est. Ces dunes ont été davantage remaniées par des vents soufflant de l'est. Les dunes de la région de High Level se sont stabilisées il y a environ 10,3 ka à l'apparition de la couverture végétale de la forêt boréale alors que la force des vents à diminué.

Research paper thumbnail of Aspects of geomorphology and thermoluminescence dating of cold-climate Eolian sandsJ.W.A. Dijkmans. Geografisch Instituut, Rijksuniversiteit Utrecht, 250 pp. 1990. Price: Dfl. 36.50. ISBN 90-6809-120-4

Research paper thumbnail of The influence of vegetation and soil characteristics on active-layer thickness of permafrost soils in boreal forest

Global change biology, Sep 8, 2016

Carbon release from thawing permafrost soils could significantly exacerbate global warming as the... more Carbon release from thawing permafrost soils could significantly exacerbate global warming as the active-layer deepens, exposing more carbon to decay. Plant community and soil properties provide a major control on this by influencing the maximum depth of thaw each summer (active-layer thickness; ALT), but a quantitative understanding of the relative importance of plant and soil characteristics, and their interactions in determine ALTs, is currently lacking. To address this, we undertook an extensive survey of multiple vegetation and edaphic characteristics and ALTs across multiple plots in four field sites within boreal forest in the discontinuous permafrost zone (NWT, Canada). Our sites included mature black spruce, burned black spruce and paper birch, allowing us to determine vegetation and edaphic drivers that emerge as the most important and broadly applicable across these key vegetation and disturbance gradients, as well as providing insight into site-specific differences. Acro...

Research paper thumbnail of V.P. Tchakerian, Editor, Desert aeolian processes, Chapman and Hall, London (1995) ISBN 0-412-04241-X, p. 326

Research paper thumbnail of Spatiotemporal impacts of wildfire and climate warming on permafrost across a subarctic region, Canada

Journal of Geophysical Research: Earth Surface, 2015

Field observations show significant impacts of wildfires on active layer thickness and ground tem... more Field observations show significant impacts of wildfires on active layer thickness and ground temperatures. However, the importance of fires to permafrost conditions at regional scales remains unclear, especially with climate warming. This study evaluated the regional impacts of fire on permafrost with climate change from 1942 to 2100 using a process-based model in a large subarctic region in the Northwest Territories, Canada. Climate warming is shown to be the dominant factor for permafrost reduction. The warming trend of climate reduces permafrost extent in this region from 67% at present to 2% by 2100. For burned areas, fire increases the reduction of permafrost extent by up to 9% on average, with up to 16% for forest, 10% for tundra and bogs, and 4% for fens. Fire accelerates permafrost disappearance by 5 years on average. The effects of fire on active layer thickness and permafrost extent are much larger in forest areas than in tundra, bogs, and fens. Since active layer is thicker after a fire and cannot recover in most of the areas, the fire effects on active layer are widespread. On average, fires thickens active layer by about 0.5 m. The fire effects on active layer increased significantly after 1990 due to climate warming.

Research paper thumbnail of The INQUA Dunes Atlas chronologic database

Quaternary International, 2015

Research paper thumbnail of Oriented-lake development in the context of late Quaternary landscape evolution, McKinley Bay Coastal Plain, western Arctic Canada

Quaternary Science Reviews

Research paper thumbnail of Subedi et al. (tc-2020-33) Comments

Research paper thumbnail of Ecohydrological dynamics of a degrading subarctic peatland: Implications for Arsenic mobility

&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp;amp;amp;amp... more &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;A peatland from subarctic Canada (Handle Lake 62&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#176;29&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#8217;26.44&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#8221;N, 114&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#176;23&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#8217;18.23&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#8221;W) is a degrading permafrost peatland chosen for detailed study due to a legacy of regional arsenic (As) contamination as a result of almost 8 decades of gold mining. The fate of permafrost peatlands and their element stores is unknown due to complex feedbacks between peat accumulation, hydrology, and vegetation that affect redox state and element mobility. We combine palynology with study of plant macrofossils, testate amoebae, organic matter composition, and bulk geochemistry preserved in a ca. 4180-4972 cal year old peat monolith retrieved from the Handle Lake peatland to reconstruct the ecohydrological dynamics to assess future trajectories of permafrost peat, and contaminant storage or release, in response to current and future warming. Sphagnum riparium macrofossils are rare in modern peat habitats and sub-fossils are rare in paleoecological records. Plant macrofossils of this taxon occur in an 11-cm thick layer together with Sphagnum angustifolium between 43 cm (ca.&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#160; 3390-3239 cal BP) and 25 cm depth (ca. 2755-2378 cal BP) in the monolith. The S. riparium sub-fossils are present with the hydrophilous testate amoebae species Archerella flavum, Hyalosphenia papilio and Difflugia globulosa that are used to quantitatively reconstruct a water table depth of 0-4 cm below the peat surface. Sub-fossils of S. riparium disappear at ca. 2755-2378 cal BP, likely due to an autogenic trophic shift and succession towards more acidophilic conditions favourable to species such as Sphagnum fuscum and Sphagnum russowii. We interpret the occurrence of S. riparium as an indicator of wet and minerotrophic conditions linked to peatland development form rich fen to oligotrophic bog.&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#160; Because S. riparium is a key pioneer species of disturbed peatlands that have experienced permafrost degradation it will likely be favoured in northern regions experiencing rapid climate warming. In the palynological record the proportion of Sphagnum-type A spores increases (up to 80%) between ca.&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#160; 3390-3239 cal BP and ca. 2755-2378 cal BP concurrent with a decline in other Sphagnum-type spores. A peak in micro- and macroscopic charcoal occurs between ca. 3557-3286 cal BP and ca. 3275-2771 cal BP, concurrent with a decline in Picea pollen and an increase in Alnus pollen. Regionally, between ca. 3500 and ca. 2500 cal BP Neoglacial climate prevailed with post-Neoglacial warming at ca. 2500 cal BP. It is therefore possible that regional fire occurrence stimulated permafrost degradation at ca. 3500 cal BP. Background As in the active layer monotlith is ~20-30 ppm. The upper 10 cm of the peat are impacted by aerial deposition of As from ore processing and concentrations range up to ~360 ppm. An increase in the concentration of As in the monolith from ~15-20 ppm at the base of the monolith to ~30-40 ppm during this interval may reflect water table depth dynamics that affected the mobility and fate of this redox sensitive element and/or downward mobility from layers impacted by contamination from mineral processing. Degradation of this permafrost within the Handle Lake peatland will release the currently stored As and other contaminants to the regional environment.&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;/p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;

Research paper thumbnail of A landsystems approach to understanding the evolution of ice-cored topography and distribution of retrogressive thaw slumps, western Canadian Arctic

&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp;amp;amp;amp;amp;amp... more &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;The landscape of the Tuktoyaktuk Coastlands, western Canadian Arctic is dominated by glacial and geocryological processes that have modified, imprinted and sculpted the surface, depositing surficial materials upon underlying bedrock. Climate warming continues in this region at a rate that is twice the global average, and retrogressive thaw slump (RTS) activity is increasing. Recently, RTS distribution was associated with glacial limits reached by the Laurentide Ice Sheet and corresponding morainal deposits, but RTS are common in other local terrain units. In this glacial-marginal region, permafrost existed pre-glacially, and non-glacial geomorphic processes occurred throughout the Late Quaternary. Superimposed on these conditions are the effects of thermokarst during the Holocene climatic optimum, followed by a period of cooling. Collectively, these processes and associated forms and deposits have contributed variously to preservation, development, or degradation of permafrost and ground ice. The multifaceted Late Quaternary history in this region has impeded understanding of the distributions of ice-cored topography and RTS. For example, rather than glaciogenic ice, the long reigning regional model for ice-cored topography is according to post-glacial development of intrasedimental segregation-intrusion ice. Toward better understanding the evolution of the whole landscape and the distribution of climate-sensitive terrain, we use a landsystems approach as a means to understand how the ice-cored topography developed where RTS form, through analysing the cryostratigraphy. To this end, we identify 6 RTS representing a suite of ice-cored topographic settings, including: (i) preserved basal glacial ice facies within clayey diamict that has been thrusted and folded by glacial push representing morainal deposits of the Sitidgi Stade; (ii) ice contact outwash sediments associated with the Sitidgi Stade, overlying a thermo-erosional contact with underlying basal glacial icy diamict of the Toker Point Stade; (iii) deformed basal glacial ice, eroded down by meltwater-deposited outwash sands some time between the Toker Point and Sitidgi Stades (could be ca. 12.9 kyr BP); (iv) massive, undeformed segregation-intrusion basal ice, likely formed subglacially by freezing of intrasedimental water in pre-existing Pleistocene sands into the base of the glacier, overlain by glacial diamicton; &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#160;(v) deformed basal ice facies of intermediate Toker Point &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#8211; Sitidgi Stades, with an upper layer that may be supra-glacial melt-out till into which segregated ice formed; and (vi) segregation ice that formed as permafrost aggraded into glaciolacustrine clays deposited in proglacial or glacially dammed basins, that was subsequently eroded down by glaciofluvial outwash (Sitidgi Stade). To summarize, the distribution of RTS reflects primarily the distribution of icy basal glacial diamict preserved in moraines, but also basal ice and icy basal diamict that are preserved beneath glaciofluvial deposits, segregation ice in glaciolacustrine deposits, and massive segregation-intrusion ice in Pleistocene sands beneath a till plain.&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;/p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;

Research paper thumbnail of Composition and origin of a lithalsa related to lake-level recession and Holocene terrestrial emergence, Northwest Territories, Canada

Earth Surface Processes and Landforms

Research paper thumbnail of Recent warming impacts in the Mackenzie Delta, Northwest Territories, and northern Yukon Territory coastal areas

Ice wedges on northern Richards Island, Northwest Territories, and along the Yukon Territory coas... more Ice wedges on northern Richards Island, Northwest Territories, and along the Yukon Territory coastlands, have responded to increased thaw depths. Observations made in 1999 are compared to those last made in these areas in 1975 and 1984, respectively. Climate data indicate that air temperatures in these areas have been warmer than average since 1978 and that warming in 1998 was an extreme event. Increased thaw in response to this warming has caused a decrease in the number of secondary and tertiary ice wedges, and is attributed to thaw truncation. Depths to the tops of ice wedges on Richards Island have increased, whereas depths have decreased on the Yukon Territory coastlands due to thaw consolidation. Thaw-tube observations indicate that 1998 thaw depths were the greatest since 1991 across the northern Mackenzie Delta region, with increases of as much as 21 cm. 1 Résumé : Les fentes de glace dans le nord de l'île Richards (Territoires du Nord-Ouest) et le long des terrains côtiers du Territoire du Yukon, ont réagi à l'accroissement de la profondeur de dégel. On compare les observations faites en 1999 avec celles faites dans les mêmes régions en 1975 et en 1984, respectivement. Les données climatiques indiquent que depuis 1978, la température de l'air dans ces régions a été plus élevée que la moyenne et qu'en 1998, le réchauffement a été un événement extrême. Suite à ce réchauffement, un dégel plus profond a causé une diminution du nombre de fentes de glace secondaires et tertiaires et est attribuable à la troncature par le dégel. La profondeur jusqu'au sommet des fentes de glace a augmenté dans l'île Richards alors qu'elle a diminué le long des terrains côtiers du Territoire du Yukon en raison de la consolidation due au dégel. Les observations dans les tubes de dégel ont indiqué qu'en 1998, la profondeur de pénétration du dégel a été la plus grande depuis 1991 dans le nord du delta du Mackenzie, avec des augmentations allant jusqu'à 21 cm.

Research paper thumbnail of Geological and meteorological controls on icing (aufeis) dynamics (1985 to 2014) in subarctic Canada

Journal of Geophysical Research: Earth Surface

Icings are widespread yet poorly understood winter hydrological phenomena that develop over the w... more Icings are widespread yet poorly understood winter hydrological phenomena that develop over the winter by freezing successive overflows of groundwater to the surface. Groundwater hydrology in arctic regions is constrained by geological setting and permafrost extent, and overflows are possibly driven by cold winters, winter warming intervals, high antecedent autumn rainfall, and low early winter snowfall. Consequently, icings are spatially recurrent but not necessarily annually nor to the same extent. We test the significance of identified meteorological forcing variables against a long-term data set of icing dynamics and distribution we developed for the Great Slave region around Yellowknife, Northwest Territories. Climate is regionally consistent, but variable geology and permafrost create hydrological conditions representative of much of the subarctic. We mapped 5500 icings in the study area (21,887 km 2) with a semiautomated approach utilizing late spring Landsat archival images (1985 to 2014). Individual icing size, ranging 3 orders of magnitude (1.8 × 10 À3 km 2 to 4.1 km 2), is related to return frequency. Infrequent ice (25% return frequency) accounts for 94% of the total icing area (86 km 2). Winter warming intervals (≥5°C; typically over 1-3 days) and autumn rainfall (September and October) explain 28% of icing density interannual variation overall. Interannual icing variation and significant meteorological forcing variables differ among ecoregions where varied geological settings and permafrost conditions influence the hydrological regime. Future icings may develop less frequently due to decreasing winter warming intervals, but increasing autumn rainfall may increase icing density where Canadian Shield leads to strong threshold-mediated runoff generation processes. This paper assesses how identified local and regional factors affect long-term icing dynamics in the subarctic. We hypothesize that icing area varies over time according to meteorological forcing variables, with spatial variation due to hydrological setting moderated by geological conditions. We test this hypothesis by examining the influence of autumn rainfall, early winter snowfall and air temperature, total winter snowfall, and frequency of sporadic winter air warming events on interannual variation of annual icing area, in a study area (Figure 1) with a uniform regional climate [

Research paper thumbnail of Geological and geophysical investigations of ground ice in glaciofluvial deposits, Slave Province, District of Mackenzie, Northwest Territories

Research paper thumbnail of Sand dunes of the northern Great Plains of Canada and the United States

Mostly ~lable dune fields are widespread over the subhumid to semiarid northern Greal Plains. Alt... more Mostly ~lable dune fields are widespread over the subhumid to semiarid northern Greal Plains. Although winds in the region are strong, most dunes are presently inacti ve hecause or rclati vely high ratios of precipitation to potential evapotranspiration, which has the dual effect or increasing dune moisture con tenl and maintaining a vegetation cover. Dune fields are relatively ~malL as most are derived from finite sup plies of glaciotluvial or glaciolacuslline sediments from the last deglaciation. Many dunes. however. are nOI relict featmes from the last deglaciation. The last epi ~odcs or eolian activity were during the lale Holocene, although there is as yet little evidence for regional synchroneity of sand movement. The strong winds and negati ve moiSlure regime have combined to produce an eolian system that is highly sensitive to small shifts in climate. The potential for reactivation ofnorrhern Great Plains sand dunes is great. whether due to natural climatic variations or human-induced greenhouse warming. Resume: De nombreux champs de dune" dont la plupart sont stable" par,cmenl lcs grandes plaines ~eptentrionales subhumides asemi-arides. Malgre la force des vents dam la region, la plupan des dunes sonl ac luellement inacti ve s en rai ~on d1I rapport relativement e leve des precipilations aI' evapotran sp irati on potenrielle, ce qui a pour double dIet d'accroltre Ie contenu cn humidik des dunes et de maintenir une couverture vegeta1e. Les champs de dunes sont rc1ativcment petits. car la plupalt proviennent d'un approvisimlllemenl fini de sediments fluvioglaciaires ou glaciolacustres de la dernicre deglaciation. Toutcfois, de nombreuses dunes ne sont pas des vestiges de la derniel'e deglaciation. Les demiers episodes d'acli vile eolienne ant en effet eu lieu au COllI'S de I'Holocelle superieur, bien qll'on ne dispose pas jusqu' it present d' indices de synchronisme regional des depJacements du sable. L' action combinee des forts vents el Liu regime d'humidite negative ant engendre un systemc colien qui <':st tres sensible ade legeres modifica tions du chma!. II exiSle un fort potentiel de reactivation des dunes de sable des grandes plaines septentrionalc~,que ce SOil en raison de variatiolls climatiques nature lles ou d' un rcchaulTemenr par dIet de selTe d'01igine anthropique.

Research paper thumbnail of 11.19 Cold-Climate Aeolian Environments

Research paper thumbnail of El Ni�o Stills Winter Winds Across The Southern Canadian Prairies

Research paper thumbnail of Impacts of Future Climate Change on the Southern Canadian Prairies: A Paleoenvironmental Perspective

Research paper thumbnail of Recent stabilization of active sand dunes on the Canadian prairies and relation to recent climate variations

Geomorphology, May 15, 2005

... In this regard, the area of active sand at Brandon North has decreased by 91% in 60 years (19... more ... In this regard, the area of active sand at Brandon North has decreased by 91% in 60 years (1928–1988). Overall, the temporal measurements at the Brandon dune occurrences are in line with those previously reported by Wolfe et al. (2000). ...

Research paper thumbnail of Glacial History, Paleogeography and Paleoenvironments in Glaciated North America. Géographie physique et Quaternaire :, vol. 58, no. 2-3, 2004

Geographie Physique Et Quaternaire, 2004

Research paper thumbnail of Age and paleoenvironmental significance of Late Wisconsinan dune fields in the Mount Watt and Fontas River map areas, northern Alberta and British Columbia

Seven optical ages from two dune fields in northern Alberta and British Columbia record Late Wisc... more Seven optical ages from two dune fields in northern Alberta and British Columbia record Late Wisconsinan dune activity between about 13.9 and 10.3 ka. Sand dunes in the Fontas River area of British Columbia (NTS 94-I) formed between 13.9 and 11.7 ka. Initial winds blew from the northwest, funnelled between the Laurentide and Cordilleran ice sheets. These were replaced by winds from the west, likely associated with the Pacific air mass. Dunes in the High Level area of Alberta (Mount Watt, NTS 84 K) first formed at about 13.4 ka under transporting winds from the northeast and southeast, probably originating katabatically from the Laurentide Ice Sheet. Subsequent winds between about 11.7 and 11.0 ka were from the southeast, originating from glacial anticyclonic winds generated by a stationary high-pressure centre over the Laurentide Ice Sheet. These dunes were further modified by winds from the east. The High Level dunes stabilized at about 10.3 ka with the onset of boreal forest vegetation cover and reduced wind strength. Résumé : Deux champs de dunes dans le nord de l'Alberta et de la Colombie-Britannique ont fait l'objet de sept datations par stimulation optique qui ont révélé une activité dunaire au Wisconsinien supérieur, il y a entre environ 13,9 et 10,3 ka. Des dunes de sable dans la région de la rivière Fontas (SNRC 94-I), en Colombie-Britannique, se sont formées il y a entre 13,9 et 11,7 ka. Les vents qui les ont accumulées ont soufflé d'abord du nord-ouest, canalisés entre les inlandsis laurentidien et de la Cordillère. Par la suite, des vents soufflant de l'ouest, vraisemblablement associés à la masse d'air du Pacifique, ont remplacé ces vents du nord-ouest. Les dunes de la région de High Level, en Alberta (mont Watt, SNRC 84 K), se sont formées il y a environ 13,4 ka sous l'effet de vents d'origine katabatique probablement engendrés sur l'Inlandsis laurentidien, qui soufflaient du nord-est et du sud-est. Par la suite, il y a entre environ 11,7 et 11,0 ka, des vents anticycloniques glaciaires, engendrés par un centre de haute pression stationnaire sur l'Inlandsis laurentidien, ont soufflé du sud-est. Ces dunes ont été davantage remaniées par des vents soufflant de l'est. Les dunes de la région de High Level se sont stabilisées il y a environ 10,3 ka à l'apparition de la couverture végétale de la forêt boréale alors que la force des vents à diminué.

Research paper thumbnail of Aspects of geomorphology and thermoluminescence dating of cold-climate Eolian sandsJ.W.A. Dijkmans. Geografisch Instituut, Rijksuniversiteit Utrecht, 250 pp. 1990. Price: Dfl. 36.50. ISBN 90-6809-120-4

Research paper thumbnail of The influence of vegetation and soil characteristics on active-layer thickness of permafrost soils in boreal forest

Global change biology, Sep 8, 2016

Carbon release from thawing permafrost soils could significantly exacerbate global warming as the... more Carbon release from thawing permafrost soils could significantly exacerbate global warming as the active-layer deepens, exposing more carbon to decay. Plant community and soil properties provide a major control on this by influencing the maximum depth of thaw each summer (active-layer thickness; ALT), but a quantitative understanding of the relative importance of plant and soil characteristics, and their interactions in determine ALTs, is currently lacking. To address this, we undertook an extensive survey of multiple vegetation and edaphic characteristics and ALTs across multiple plots in four field sites within boreal forest in the discontinuous permafrost zone (NWT, Canada). Our sites included mature black spruce, burned black spruce and paper birch, allowing us to determine vegetation and edaphic drivers that emerge as the most important and broadly applicable across these key vegetation and disturbance gradients, as well as providing insight into site-specific differences. Acro...

Research paper thumbnail of V.P. Tchakerian, Editor, Desert aeolian processes, Chapman and Hall, London (1995) ISBN 0-412-04241-X, p. 326

Research paper thumbnail of Spatiotemporal impacts of wildfire and climate warming on permafrost across a subarctic region, Canada

Journal of Geophysical Research: Earth Surface, 2015

Field observations show significant impacts of wildfires on active layer thickness and ground tem... more Field observations show significant impacts of wildfires on active layer thickness and ground temperatures. However, the importance of fires to permafrost conditions at regional scales remains unclear, especially with climate warming. This study evaluated the regional impacts of fire on permafrost with climate change from 1942 to 2100 using a process-based model in a large subarctic region in the Northwest Territories, Canada. Climate warming is shown to be the dominant factor for permafrost reduction. The warming trend of climate reduces permafrost extent in this region from 67% at present to 2% by 2100. For burned areas, fire increases the reduction of permafrost extent by up to 9% on average, with up to 16% for forest, 10% for tundra and bogs, and 4% for fens. Fire accelerates permafrost disappearance by 5 years on average. The effects of fire on active layer thickness and permafrost extent are much larger in forest areas than in tundra, bogs, and fens. Since active layer is thicker after a fire and cannot recover in most of the areas, the fire effects on active layer are widespread. On average, fires thickens active layer by about 0.5 m. The fire effects on active layer increased significantly after 1990 due to climate warming.

Research paper thumbnail of The INQUA Dunes Atlas chronologic database

Quaternary International, 2015