The Whitehorse trough is an Early to Middle Jurassic marine sedimentary basin that overlaps the Intermontane terranes in the northern Cordillera. Detrital zircon dates from eight Laberge Group ...sandstones from various parts of the trough all display a major Late Triassic-Early Jurassic peak (220-180 Ma) and a minor peak in the mid-Paleozoic (340-330 Ma), corresponding exactly with known igneous ages from areas surrounding the trough. Source regions generally have Early Jurassic (ca. 200-180 Ma) mica cooling dates, and the petrology of metamorphic rocks and Early Jurassic granitoid plutons flanking the trough suggests rapid exhumation during emplacement. These data suggest that subsidence and coarse clastic sedimentation in the trough occurred concurrently with rapid exhumation of the shoulders. Isolated occurrences of sandstone and conglomerate units with similar detrital zircon signatures occur west and east of the trough, as well as overlapping the Cache Creek terrane, indicating that either the trough was once more extensive, or isolated basins tapped similar sources. Development of these sedimentary basins and accompanying rapid exhumation in the northern Cordillera were coeval with the onset of orogenic activity in the hinterland of the southern Canadian Cordillera, and subsidence in the western Canada foreland sedimentary basin. The Whitehorse trough is interpreted as a forearc basin that progressively evolved into a collisional, synorogenic piggyback basin developed atop the nascent Cordilleran orogen. Upper Jurassic-Lower Cretaceous fluvial deposits overlapping the Whitehorse trough have detrital zircons that were mainly derived from recycling of the Laberge Group, but they also contain zircons exotic to the northern Intermontane terranes that are interpreted to reflect windblown detritus from the Late Jurassic-Early Cretaceous magmatic arc that developed either atop the approaching Insular terranes to the west or southern Stikinia.
Erosion of permafrost coasts has received increasing scientific attention since 1990s because of rapid land loss and the mobilisation potential of old organic carbon. The majority of permafrost ...coastal erosion studies are limited to time periods from a few years to decades. Most of these studies emphasize the spatial variability of coastal erosion, but the intensity of inter-annual variations, including intermediate coastal aggradation, remains poorly documented. We used repeat airborne Light Detection And Ranging (LiDAR) elevation data from 2012 and 2013 with 1m horizontal resolution to study coastal erosion and accompanying mass-wasting processes in the hinterland. Study sites were selected to include different morphologies along the coast of the Yukon Coastal Plain and on Herschel Island. We studied elevation and volume changes and coastline movement and compared the results between geomorphic units. Results showed simple uniform coastal erosion from low coasts (up to 10m height) and a highly diverse erosion pattern along coasts with higher backshore elevation. This variability was particularly pronounced in the case of active retrogressive thaw slumps, which can decrease coastal erosion or even cause temporary progradation by sediment release. Most of the extremes were recorded in study sites with active slumping (e.g. 22m of coastline retreat and 42m of coastline progradation). Coastline progradation also resulted from the accumulation of slope collapse material. These occasional events can significantly affect the coastline position on a specific date and can affect coastal retreat rates as estimated in long term by coastline digitalisation from air photos and satellite imagery. These deficiencies can be overcome by short-term airborne LiDAR measurements, which provide detailed and high-resolution information about quickly changing elevations in coastal areas.
•Low-elevation ice-rich coasts erode uniformly by up to 20ma−1.•Mass wasting causes high erosion variability of high-elevation permafrost coasts.•Intensive slumping can result in coastline progradation by up to 40ma−1.•Of all slump-activated material, 5.5% is re-accumulated and exposed to carbon loss.•Short-term coastline movements can impact erosion estimates from aerial imagery.
The paper provides a comparison of minimum air temperature (TN), maximum air temperature (TX), mean air temperature (T mean) and a few derived temperature indices for Herschel Island (Qikiqtaruk) in ...the Yukon Territory, Canada for the periods 1899–1905 and 2008–2014. A significant increase in the TN was noted at +4.2°C, which was a larger increase than that for both T mean (+3.7°C) and TX (+3.5°C). Air temperature increased the most in October, November, and December. In addition, the length of the frost-free season increased by 26 days and the length of the growing season increased by 25 days from the early 20th century to the early 21st century. The increase in the TN also triggered a change in the plant hardiness zone where Herschel Island is located. However, the daily air temperature range declined over the course of the study period as well as the annual total of heating degree days and the number of exceptionally cold days. No statistically significant change in the number of freeze-thaw days was found for the studied periods.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Permafrost thaw in the Arctic enables the biogeochemical transformation of vast stores of organic carbon into carbon dioxide (CO2). This CO2 release has significant implications for climate ...feedbacks, yet the potential counterbalance from CO2 fixation via chemical weathering of minerals exposed by thawing permafrost is entirely unstudied. We show that thermokarst in the western Canadian Arctic can enable rapid weathering of carbonate tills, driven by sulfuric acid from sulfide oxidation. Unlike carbonic acid‐driven weathering, this caused significant and previously undocumented CO2 production and outgassing in headwater streams. Increasing riverine solute fluxes correspond with long‐term intensification of thermokarst and reflect the regional predominance of sulfuric acid‐driven carbonate weathering. We conclude that thermokarst‐enhanced mineral weathering has potential to profoundly disrupt Arctic freshwater carbon cycling. While thermokarst and sulfuric acid‐driven carbonate weathering in the western Canadian Arctic amplify CO2 release, regional variation in sulfide oxidation will moderate the effects on the permafrost carbon‐climate feedback.
Plain Language Summary
In the Arctic, perennially frozen ground (permafrost) in previously glaciated regions stores abundant minerals and is often ice‐rich. Therefore, this permafrost can rapidly thaw and collapse, resulting in thermokarst and exposing minerals to breakdown by chemical weathering. Mineral weathering by carbonic acid fixes CO2, making it less likely to enter the atmosphere. However, the effect of thermokarst on mineral weathering, carbon cycling, and rising atmospheric CO2 levels is unknown. We show thermokarst enhances weathering in streams in the western Canadian Arctic can rapidly produce significant and previously undocumented CO2 because carbonate weathering in this region is driven by sulfuric acid (from weathering of sulfide minerals) instead of carbonic acid. Long‐term river chemistry reveals that this weathering is intensifying as thermokarst accelerates. Across the Arctic, increasing thermokarst will profoundly impact freshwater carbon cycling, yet the influence of weathering on climate feedbacks will depend on regional variation in the mineral composition of permafrost soils.
Key Points
Permafrost thaw‐driven ground collapse (thermokarst) in the western Canadian Arctic enhances carbonate weathering locally and regionally
This weathering is driven by sulfuric acid and rapidly produces significant, previously undocumented CO2
Carbonic acid‐driven weathering elsewhere can consume CO2, yet thermokarst effects on weathering, carbon cycle, and climate are unstudied
Where present, permafrost exerts a primary control on water fluxes, flowpaths, and distribution. Climate warming and related drivers of soil thermal change are expected to modify the distribution of ...permafrost, leading to changing hydrologic conditions, including alterations in soil moisture, connectivity of inland waters, streamflow seasonality, and the partitioning of water stored above and below ground. The field of permafrost hydrology is undergoing rapid advancement with respect to multiscale observations, subsurface characterization, modeling, and integration with other disciplines. However, gaining predictive capability of the many interrelated consequences of climate change is a persistent challenge due to several factors. Observations of hydrologic change have been causally linked to permafrost thaw, but applications of process-based models needed to support and enhance the transferability of empirical linkages have often been restricted to generalized representations. Limitations stem from inadequate baseline permafrost and unfrozen hydrogeologic characterization, lack of historical data, and simplifications in structure and process representation needed to counter the high computational demands of cryohydrogeologic simulations. Further, due in part to the large degree of subsurface heterogeneity of permafrost landscapes and the nonuniformity in thaw patterns and rates, associations between various modes of permafrost thaw and hydrologic change are not readily scalable; even trajectories of change can differ. This review highlights promising advances in characterization and modeling of permafrost regions and presents ongoing research challenges toward projecting hydrologic and ecologic consequences of permafrost thaw at time and spatial scales that are useful to managers and researchers.
Surface energy balance (SEB) strongly influences the thermal state of permafrost, cryohydrological processes, and infrastructure stability. Road construction and snow accumulation affect the energy ...balance of underlying permafrost. Herein, we use an experimental road section of the Alaska Highway to develop a SEB model to quantify the surface energy components and ground surface temperature (GST) for different land cover types with varying snow regimes and properties. Simulated and measured ground temperatures are in good agreement, and our results show that the quantity of heat entering the embankment center and slope is mainly controlled by net radiation, and less by the sensible heat flux. In spring, lateral heat flux from the embankment center leads to earlier disappearance of snowpack on the embankment slope. In winter, the insulation created by the snow cover on the embankment slope reduces heat loss by a factor of three compared with the embankment center where the snow is plowed. The surface temperature offsets are 5.0°C and 7.8°C for the embankment center and slope, respectively. Furthermore, the heat flux released on the embankment slope exponentially decreases with increasing snow depth, and linearly decreases with earlier snow cover in fall and shorter snow‐covered period in spring.
In northern regions, transportation infrastructure can experience severe structural damages due to permafrost degradation. Water infiltration and subsurface water flow under an embankment affect the ...energy balance of roadways and underlying permafrost. However, the quantification of the processes controlling these changes and a detailed investigation of their thermal impacts remain largely unknown due to a lack of available long‐term embankment temperature data in permafrost regions. Here, we report observations of heat advection linked to surface water infiltration and subsurface flow based on a 9‐year (from 2009 to 2017) thermal monitoring at an experimental road test site built on ice‐rich permafrost conditions in southwestern Yukon, Canada. Our results show that snowmelt water infiltration in the spring rapidly increases temperature in the upper portion of the embankment. The earlier disappearance of snow deposited at the embankment slope increases the thawing period and the temperature gradient in the embankment compared with the natural ground. Infiltrated summer rainfall water lowered the near‐surface temperatures and subsequently warmed embankment fill materials down to 3.6‐m depth. Heat advection caused by the flow of subsurface water produced warming rates at depth in the embankment subgrade up to two orders of magnitude faster than by atmospheric warming (heat conduction). Subsurface water flow promoted permafrost thawing under the road embankment and led to an increase in active layer thickness. We conclude that the thermal stability of roadways along the Alaska Highway corridor is not maintainable in situations where water is flowing under the infrastructure unless mitigation techniques are used. Severe structural damages to the highway embankment are expected to occur in the next decade.
Our manuscript presents three important novel findings:
The infiltration of spring snowmelt causes a very rapid temperature increase in the road embankment, within just a few days.
The infiltration of summer rainfall lowers near‐surface temperatures while simultaneously warming embankment fill materials at depth.
The advection of heat due to porewater flow through subsurface water flow leads to warming rates that can be up to two orders of magnitude faster than by just atmospheric warming.
The Selwyn fold-and-thrust belt between the Stewart and Nadaleen rivers, Yukon, Canada, has several features that are rare in thrust belts, such as steep oppositely-dipping thrusts and ...steeply-plunging folds, the latter of which are important controls on Au-mineralization in the area. This paper describes fold and fault geometries and cross-cutting relationships to determine how the steeply-plunging folds formed. Fold analysis and field cross-cutting relationships indicate that the folds formed through buckling and pre-date thrusts. Earlier buckle folds with hinge lines oblique to the bulk shortening direction back-rotated on later thrust imbricates to their steep geometry. We suggest that the geometry of early folds was partly controlled by vertical axis rotations in the fold train caused by shortening against an irregular basin margin. The basin margin also acted as a backstop against which the thrust system shortened. This shortening resulted in over-steepening of the thrusts until they were too misoriented for further slip, at which point back thrusts formed and cut the fore thrusts. Continued shortening steepened both fore and back thrusts.
•Steeply-plunging fold formation in the Selwyn fold-and-thrust belt formed is investigated.•The folds pre-date thrust faults and were back-rotated and shortened to their steep geometry.•The irregular basin margin acted as a backstop to shortening.
Introduction
This study describes the legal recreational cannabis market across Canada over the 2 years following legalisation. We compared changes in access to the legal cannabis retail market for ...all provinces and territories (jurisdictions) in Canada and explored differences between jurisdictions.
Methods
We collected data for all legal cannabis stores in Canada over five time periods following legalisation in October 2018. We examined the following measures by jurisdiction and retail model (public vs. private operation): absolute and per capita store numbers, hours of operation and store access across neighbourhoods.
Results
Two years following legalisation, there were a total of 1183 legal cannabis stores open across Canada (3.7 stores per 100 000 individuals aged 15+). There was wide variation between jurisdictions in access to retail stores, with the lowest stores per capita in Quebec and Ontario (0.6 and 1.6 per 100 000), and the highest in Alberta and Yukon (14.3 per 100 000 in both). Jurisdictions with private retail models had more stores (4.8 vs. 1.0 per 100 000), held greater median weekly hours (80 vs. 69) and experienced greater store growth over time compared to public models. After adjusting for confounders, there were 1.96 times (95% confidence intervals: 1.84, 2.09) more cannabis stores within 1000 m of the lowest‐ compared to the highest‐income quintile neighbourhoods.
Discussion and Conclusions
While access to the recreational cannabis retail market has increased following legalisation, there is substantial variation in access between jurisdictions and evidence of concentration in lower‐income neighbourhoods. These differences may contribute to disparities in cannabis use and harms.
Sustained oxidation of sulfide minerals in waste rock generates acid mine drainage for time frames of hundreds to thousands of years. Management to minimize long-term degradation of water supplies ...and ecosystem health requires a thorough understanding of geochemical processes occurring within the waste rock. A comprehensive field investigation was conducted on sulfide and carbonate-rich waste-rock dumps at the Faro Mine Complex, south-central Yukon Territory, Canada. This investigation included installation of three highly instrumented boreholes, in situ measurements of physical and geochemical parameters (e.g., water content, temperature, air permeability, and pore-gas O2 and CO2 concentration), and collection of pore-water, pore-gas, and solid-phase samples. Field and laboratory measurements indicate the waste rock is lithologically and mineralogically segregated, with sulfide-rich (>20 wt% S) waste rock dominating in the lower benches (20–50 mbgs) and carbonate-bearing waste rock dominating in the upper benches and other parts of the dumps. The observed segregation strongly influences spatial variability of geochemical parameters. Three distinct geochemical zones are observed within the waste-rock dumps, including a rapid O2-supply zone, with near-atmospheric concentrations of O2 (0–30 mbgs); a strong O2-depletion zone (30–50 mbgs), characterized by abundant sulfide minerals and significant O2 depletion to <5 vol%; and a thermally-induced O2-enriched zone (50 mbgs to the pre-mining surface), where thermally-driven gas transport results in replenishment of O2 concentrations (7–18 vol%). These observations indicate sulfide-mineral oxidation and pH neutralization via dissolution of carbonate and aluminosilicate minerals influence pore-water pH and concentrations of dissolved sulfate and metal(loid)s. High concentrations of dissolved metal(loid)s (e.g., up to Fe 36,900 mg L−1, Zn 14,200 mg L−1, Pb 6.16 mg L−1, Al 8,750 mg L−1, As 63.6 mg L−1, Mn 2,170 mg L−1, Cd 21.7 mg L−1, and Cr 1.53 mg L−1) and SO4 (up to 114,000 mg L−1) in pore water correlate with extreme values of pH (as low as 1.4). In the absence of an effective remediation strategy, the oxidation of still-abundant un-oxidized sulfide minerals will continue through vast portions of the waste-rock dumps.
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•Lithological segregation of the waste rock affects spatial variability of pore-water geochemistry.•Pore-gas transport is caused by diffusion, wind-induced advection, and thermally driven convection.•Site-specific geochemical investigation can facilitate decision-making related to remediation.
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