1,721,012 research outputs found
Morphologie et hydrogéochimie des coins de glace en dégradation, Monts Ogilvie, Yukon, Canada
No full textDepuis près de 30 ans, une dégradation des coins de glace est observée à un site d’étude situé dans les monts Ogilvie, au Yukon. Cette thèse examine la morphologie et le volume de glace des sols polygonaux, ainsi que les conditions hydrologiques et géochimiques de deux sites de la vallée de la rivière Blackstone présentant différents degrés d'évolution (stables et dégradés). Les résultats suggèrent que la dégradation a débuté dans les années 1990 et a été influencée par la construction de la route du Dempster, qui a favorisé l’accumulation d’eau en surface en amont de celle-ci. Cette dégradation a ensuite causé la formation d'un étang thermokarstique et son élargissement progressif, passant de 3500 m² à 9500 m² entre 2007 et 2023. Un drainage et un remplissage rapides de l’étang ont également été observés durant les étés 2022 et 2023. Bien que la cause exacte de ces fluctuations demeure incertaine, cette étude suggère que le phénomène peut être associé à la couche active et au type de sédiment du site. Les résultats indiquent que les coins de glace datent de l’Holocène et que, de façon générale, les impacts de leur dégradation sur la géochimie (COD/CID et ions) sont significativement moins importants que ceux de d’autres types de dégradation du pergélisol, comme les glissements dus au dégel. Cependant, l’impact de la fonte des coins de glace sur la distribution de l’eau et l’écoulement de surface n’est pas à négliger, puisqu’elle peut modifier l’écosystème naturel et poser un risque pour les infrastructures
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Ground Ice Content and Geochemistry of Active Layer and Permafrost in Northwestern Arctic Canada
No full textThis study aimed to contribute to baseline knowledge of permafrost geochemistry within the uppermost 3-4 m of permafrost at 8 sites on the Peel Plateau and east of the Mackenzie Delta, NWT (67-68oN). The following variables were measured: gravimetric water content (GWC), pore water conductivity (PWC), leachate conductivity (LC), dissolved ions by ICP-AES (i.e. Ca, SO4, Mg, Fe, K, Na, Mn, Cl), organic carbon content (calculated by linear regression from organic matter content), as well as inorganic carbon content (obtained from loss on ignition analysis). PWC was positively correlated to GWC and values were generally at least 5 times less than LC values, likely underestimating total dissolved solutes using the former method. LC increased with depth to reach maximum values below the paleo thaw unconformity (>10 mS/cm). Carbon content typically remained low throughout the cores with the exception of samples associated to the shallow-rooted vegetation cover at the ground surface. Results showed that the active layer, relict active layer and the permafrost below the thaw unconformity can be divided into three statistically significant layers. PCA results indicated some spatial patterns with increasing LC values at greater depth, suggesting that layer geochemical profiles reflect varying degrees of soil chemical weathering processes since the early Holocene
Distribution, Morphology and Carbon Stock of Earth Hummocks in the Chuck Creek Trail Valley, Northern British Columbia, Canada
No full textCryoturbation translocates surface organic-rich horizons deeper in the soils and as such is an important process for carbon sequestration in the active layer (e.g., Kaiser et al., 2007; Van Vliet-Lanoë, 2004). Hummocks, which are non-sorted patterned ground, are sub-meter to meter-scale circular to oval-shaped mounds found in fine-grained frost susceptible sediments. This project examines the distribution, morphology and internal structure of hummocks in the sub-alpine region of the Chuck Creek Trail Valley in the Tatshenshini-Alsek Provincial Park, northern British Columbia. Morphological, sedimentological and geochemical analysis showed that the inter-field differences in hummock morphology of the Chuck Creek Trail Valley were dictated by the silt content within the soil. Hummock fields were found to have an average SOCC for a 1 m pedon of 16.3 kg/m2, 38 % situated in the B-horizon. For this pedon, hummocks fields contained 0.05 Pg – 0.2 Pg according to the distribution probability model. Dating of bulk sediments exhibited a cluster of radiocarbon dates around 2000 cal BP for cryoturbated intrusions, implying subduction rates ranging between 0.03 mm/yr to 0.10 mm/yr and coinciding with a period of climatic cooling (Viau, 2008). In conclusion, the differential frost heave model (Van Vliet-Lanoë, 1991) is the only hypothesis for hummock formation consistent with field evidence in the Chuck Creek Trail Valley
Carbon-14 as a Tracer of Soil Movement in Earth Hummocks: A Case Study From Northwestern Arctic Canada
No full textInvoluted soil horizons and buried organic matter in the active layer and near-surface permafrost provide evidence that soil movement or cryoturbation is occurring within the active layer in hummocky terrain. Cryoturbation in the active layer of permafrost-affected soils could have significant implications in sequestering carbon, including trace metals and contaminants that are absorbed onto organic matter. Though several hummock development theories exist, there has thus far been limited evidence to support them; similarly, few studies have been able to establish hummock age. This study aimed to contribute radiocarbon-dated ages of buried organics in both the active layer and permafrost, as well as provide evidence for the convective cell/equilibrium model and the collapse model. Trenches were dug along a transect at two well-developed hummock sites in the Mackenzie Delta near Inuvik, NWT. Active layer and permafrost samples were analyzed for distribution of gravimetric water content (GWC), organic matter, inorganic carbon, and carbon-14 (C14). Results determined material ranged in age from the modern period (1959-1987AD) to 2300 yr BP with a generally normal distribution. Buried organics within the active layer ranged from 557-670 yr BP and 1023-1240 yr BP, with average displacement rates of 0.43 mm/yr and 0.16 mm/yr, respectively. These results suggest the convective cell/equilibrium and hummock collapse models can function simultaneously
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
A Geospatial Approach to Display the Hydrological Impacts of Permafrost Disturbances on the Geochemistry of Streams, Lower Peel River and Western Mackenzie Basin, Northwestern Canada
No full textRetrogressive 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
Experimental Study of the Growth and Stable Water Isotopes of Ice Formed by Vapour Deposition in Cold Environments
No full textIce formed by water vapour deposition has been identified in different terrestrial environments: 1) in the atmosphere; 2) at the ground’s surface; 3) in caves; 4) in seasonally frozen ground; and 5) in perennially frozen ground (permafrost). Thus far, ground ice formed by diffusion and deposition of vapour in soils (types 4 and 5) has rarely been studied in a natural setting and remains one of the most poorly described ice types on Earth. This thesis focuses on the dynamics of deposition and sublimation of atmospheric water vapour into permafrost and the isotopic signature (D/H and 18O/16O) of the emplaced ground ice under different experimental conditions. Ground ice was produced in sediments with different thermo-physical characteristics (glass beads, JSC Mars-1 simulant). After a two-month growth period, the higher porosity sediments (JSC) had more than 7x the gravimetric water content than the lower porosity soil. Ground ice profiles had a distinct concave downwards shape due to the decrease in saturation vapour pressure with depth. Results also indicate that vapour deposited ground ice has a distinct δD-δ18O composition that plots near regression slope value of 8. Pore water isotopes plot below the global meteoric water line (GMWL) when the source of moisture is directly on top of the sediments. If an air gap is introduced between the source of moisture and the sediments, the pore water isotopes shift above the GMWL due to re-sublimation at the ground surface. Overall, this thesis addressed some fundamental knowledge gaps required to better understand the growth and isotopic evolution of ground ice emplaced by vapour deposition.
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