Northwestern Canada Research Articles

Quantified growth and possible heterochronic development of two corynexochid trilobites from the middle Cambrian (Miaolingian Series, Wuliuan Stage) Mount Cap Formation, eastern Mackenzie Mountains, northwestern Canada

Abstract The ontogeny of two species of corynexochid trilobites from the middle Cambrian Mount Cap Formation of the eastern Mackenzie Mountains, northern Canada, is documented. Sahtuia carcajouensis (Dolichometopidae) and Mackenzieaspis parallelispinosa (Zacanthoididae) are both endemic to this formation and only known from one locality. They, along with several other corynexochid taxa, occur in a succession of mudstone with scattered carbonate interbeds, deposited in a weakly storm-agitated setting near the flank of a semi-enclosed basin. The ontogeny of both species is characterized by mainly normal cranidial development, but a unique distribution of segments in their thoraxes and pygidia. The number of trunk segments was typical for their respective families, whereas the final number of segments released into the thorax was reduced. This occurred in both species through timing modifications to segment release, indicating heterochrony. Sahtuia carcajouensis and Mackenzieaspis parallelispinosa are likely derived from two separate clades, and heterochrony probably arose separately but synchronously. The endemicity of both species probably reflects unique paleoecological conditions in this part of the basin. Preliminary results indicate that the fossil-bearing mudstone was deposited under well-oxygenated conditions that underwent high nutrient flux and possibly experienced varying salinity. These factors may have affected the organisms’ physiology, or perhaps provoked an adaptation to achieve early maturation.

Elucidating the sustainability of 700 y of Inuvialuit beluga whale hunting in the Mackenzie River Delta, Northwest Territories, Canada

Beluga whales play a critical role in the subsistence economies and cultural heritage of Indigenous communities across the Arctic, yet the effects of Indigenous hunting on beluga whales remain unknown. Here, we integrate paleogenomics, genetic simulations, and stable δ13C and δ15N isotope analysis to investigate 700 y of beluga subsistence hunting in the Mackenzie Delta area of northwestern Canada. Genetic identification of the zooarchaeological remains, which is based on radiocarbon dating, span three time periods (1290 to 1440 CE; 1450 to 1650 CE; 1800 to 1870 CE), indicates shifts across time in the sex ratio of the harvested belugas. The equal number of females and males harvested in 1450 to 1650 CE versus more males harvested in the two other time periods may reflect changes in hunting practices or temporal shifts in beluga availability. We find temporal shifts and sex-based differences in δ13C of the harvested belugas across time, suggesting historical adaptability in the foraging ecology of the whales. We uncovered distinct mitochondrial diversity unique to the Mackenzie Delta belugas, but found no changes in nuclear genomic diversity nor any substructuring across time. Our findings indicate the genomic stability and continuity of the Mackenzie Delta beluga population across the 700 y surveyed, indicating the impact of Inuvialuit subsistence harvests on the genetic diversity of contemporary beluga individuals has been negligible.

Changing climatic controls on the greenhouse gas balance of thermokarst bogs during succession after permafrost thaw.

Permafrost thaw in northern peatlands causes collapse of permafrost peat plateaus and thermokarst bog development, with potential impacts on atmospheric greenhouse gas exchange. Here, we measured methane and carbon dioxide fluxes over 3 years (including winters) using static chambers along two permafrost thaw transects in northwestern Canada, spanning young (~30 years since thaw), intermediate and mature thermokarst bogs (~200 years since thaw). Young bogs were wetter, warmer and had more hydrophilic vegetation than mature bogs. Methane emissions increased with wetness and soil temperature (40 cm depth) and modelled annual estimates were greatest in the young bog during the warmest year and lowest in the mature bog during the coolest year (21 and 7 g C-CH4 m-2 year-1, respectively). The dominant control on net ecosystem exchange (NEE) in the mature bog (between +20 and -54 g C-CO2 m-2 year-1) was soil temperature (5 cm), causing net CO2 loss due to higher ecosystem respiration (ER) in warmer years. In contrast, wetness controlled NEE in the young and intermediate bogs (between +55 and -95 g C-CO2 m-2 year-1), where years with periodic inundation at the beginning of the growing season caused greater reduction in gross primary productivity than in ER leading to CO2 loss. Winter fluxes (November-April) represented 16% of annual ER and 38% of annual CH4 emissions. Our study found NEE of thermokarst bogs to be close to neutral and rules out large CO2 losses under current conditions. However, high CH4 emissions after thaw caused a positive net radiative forcing effect. While wet conditions favouring high CH4 emissions only persist for the initial young bog period, we showed that continued climate warming with increased ER, and thus, CO2 losses from the mature bog can cause net positive radiative forcing which would last for centuries after permafrost thaw.

Rate of permafrost thaw and associated plant community dynamics in peatlands of northwestern Canada

Abstract The most rapid climate warming is occurring in northern, permafrost environments. Peatlands of these regions are particularly sensitive to climate warming, with the high ground ice content of peat plateaux resulting in the formation of collapse scars as ground temperatures warm. To quantify the rates of permafrost thaw and associated vegetation changes, we sampled the plant and lichen communities in transects spanning actively thawing collapse scar margins at sites from mid‐Boreal to Low Subarctic conditions, within Canada's Northwest Territories. Seventeen transects were sampled in 2007/08 and 14 of these were resampled 10 years later. The rate of lateral permafrost thaw of collapse scar margins ranged from −6 to 63 cm year−1 (mean: 22.0 cm ± 4.7 cm year−1 (SE)); variability was high and no trends with respect to latitude or temperature gradients were detected. Plant communities displayed a clear gradient from lichen‐ and ericaceous shrub‐dominated peat plateaux, to collapse scars primarily characterized by Sphagnum mosses and graminoids. Both space‐for‐time (distance from collapsing margin) and direct measurement of 10‐year changes showed a successional sequence following permafrost thaw; floating mat communities characterized by Sphagnum riparium or S. balticum proceeded to lawn communities of S. angustifolium and, finally, to hummock communities with Mylia anomala or S. fuscum. This successional sequence was associated with increased water table depth and lower soil water content in plant communities farther from the actively collapsing front, illustrating that peat growth above the water table was driving plant community successional changes. The most rapid plant community succession occurred in recently thawed environments as peat growth propelled the ground surface above the water table while the slowest succession occurred in the collapse scar hummock communities located farthest from the actively collapsing peat plateau margin. Synthesis. In just 10 years, significant vegetation change was detected, in association with both permafrost thaw and subsequent plant community succession. These changes occurred across a broad climatic and latitudinal gradient, from mid‐Boreal to Low Subarctic and have implications for wildlife, global C cycle and indigenous communities who depend on this landscape for harvesting, spiritual and cultural practices.

Settler colonialism and the administrative state: The transfer of the Government of the Northwest Territories to Yellowknife in 1967

AbstractIn September 1967, the federal government transferred the Government of the Northwest Territories from Ottawa to Yellowknife. While the transfer brought the machinery of government closer to the governed, it also established settler institutions in the homelands of Dene, Métis, and Inuit peoples. Using the tools of administrative history and settler colonial theory, this article reconstructs the transfer using newly released archival papers of NWT Commissioner Stuart Hodgson, who oversaw the transfer and the development of government in the NWT until 1979. It analyzes the role federal public servants played in facilitating settler colonial development in northwestern Canada and, in turn, how that development affected the structure and work of the federal public service in Ottawa. While the transfer entrenched Westminster parliamentary government in the NWT, it also served as a focal point for Indigenous resurgence and resistance that has remade contemporary governance in the territory.

Surface-atmosphere energy exchanges and their effects on surface climate and atmospheric boundary layer characteristics in the forest-tundra ecotone in northwestern Canada

The circumpolar forest-tundra ecotone is experiencing rapid changes in vegetation composition and structure. Collectively, these changes modify surface-atmosphere energy exchanges and thus characteristics of the atmospheric boundary layer (ABL). Here, we characterize differences in bulk surface properties and resulting energy balance components using multi-year eddy covariance and supporting measurements made at a mineral upland tundra and a nearby subarctic woodland site between 2013 and 2022. The two sites are characteristic of the forest-tundra ecotone of northwestern Canada. A mixed-layer slab model, in combination with radiosonde observations, was used to gain more insights into differences in ABL characteristics. Compared to the tundra, the tree cover of the woodland led to an enhanced ability to transfer heat into the atmosphere, a higher resistance to evapotranspiration and a stronger coupling between surface and atmosphere. Sensible heat flux (H) was generally higher at the woodland than at the tundra. The largest difference in daily mean H was observed in late winter and spring when the albedo of the snow-covered landscape at the woodland was reduced by 45% compared to the tundra. Both sites experienced similar latent heat flux throughout the year. At the woodland, modelled afternoon air temperature in the mixed layer was up to 9 °C higher in spring and up to 3 °C higher in summer compared to the tundra. In accordance with model results, radiosonde observations indicated a deeper ABL and higher air temperature at the woodland. The presence of trees in the southern part of the forest-tundra ecotone increases air temperature throughout the year and has a drying effect in spring. Consequently, vegetation shifts in the forest-tundra ecotone can be expected to modify local surface climate change patterns, which must be considered when assessing climate change impacts in the region.

A Comprehensive Survey of Population Ecology in Insects

Population ecology focuses on studying populations and their relationship with the environment, including parameters such as birth, death, migration, density, and age distribution. Population ecology involves laboratory work, field observations, and the use of mathematical and statistical models to study groups of organisms. By studying populations, researchers gain insights into population dynamics, growth, distribution, density, and age structure. Insects play a vital role in population ecology by influencing ecosystems and human societies. They contribute to ecological processes such as decomposition, pollination, and nutrient cycling. In addition, some insects produce valuable substances, and predatory insects help control pests. Understanding population dynamics and interactions is crucial for conserving and managing natural resources effectively. Population ecology is a branch of ecology that focuses on studying the lives of organisms within populations and their interactions with the environment and other populations. Different species have developed various strategies to deal with organisms of their species or other species. Some species compete directly with individuals of the same species, while others form social groups and cooperate to secure resources. Population ecologists examine complex interactions between organisms and their environment, which lead to different selective pressures for animals that compete with individuals of the same species. Humans, for example, have been successful in part because of their social nature and ability to cooperate to obtain vital resources. The field of population ecology seeks to answer questions about the carrying capacity of the environment, the optimal population size, the causes and mechanisms of population growth, and population distribution. Insects play a significant role in biodiversity, accounting for 64% of the world's biodiversity. They have diverse functional roles in ecosystems, including herbivores, hunting, parasitism, decomposition, and pollination. Various factors influence the number, population, and survival of insects, including insect diversity, abundance, evolution, and habitats. Population ecology studies these factors to understand the survival and current population dynamics of insects. The distribution of insects is an important indicator of species diversity and is influenced by factors such as time, conditions, and food resources. For example, the leopard beetle Cicindela longilabris is found at higher latitudes and elevations, with populations ranging from northwestern Canada to the coastal states of eastern Canada. Ecologists believe that historical climate changes, such as the last Ice Age, have influenced the current distribution of this species. In studying insect populations, ecologists use sampling techniques to estimate population size and abundance. Statistical methods, such as the rarefaction method, are employed to compare species abundance in different areas and estimate the number of species present in a sample. Understanding changes in insect population density over time is important, and ecologists study population life cycles and population explosions to gain insights into these fluctuations. By comprehending and predicting changes in insect populations, ecologists can mitigate potential damage and obtain valuable information about insect abundance. Certain species of locusts, including the desert locust, migratory locust, tree locust, and Australian locust, experience periodic population eruptions. In South America, various species of desert locusts are also significant pests. Climatic factors play a significant role in the formation and migration of locust swarms. Locust eggs can remain dormant in the soil until rain triggers their hatching. The rainy season is optimal for egg development, and rainfall also promotes the growth of green plants, which serve as food for nymphs and adult grasshoppers. The El Nino phenomenon, characterized by periodic changes in flight patterns, has a significant impact on locust populations, causing substantial damage every few years. Satellite imagery is commonly used to identify locust groups by detecting areas of new plant growth following rain. Once the nymphs have exhausted their food sources, the locust swarm enters the migratory phase, guided by wind direction. These swarms can persist for months or even years under favorable weather conditions, but population declines occur when dry weather or significant temperature drops occur. In conclusion, population explosions in migratory locusts are primarily influenced by density-independent factors like climate change, rather than density-dependent factors.

A female woolly mammoth's lifetime movements end in an ancient Alaskan hunter-gatherer camp.

Woolly mammoths in mainland Alaska overlapped with the region's first people for at least a millennium. However, it is unclear how mammoths used the space shared with people. Here, we use detailed isotopic analyses of a female mammoth tusk found in a 14,000-year-old archaeological site to show that she moved ~1000 kilometers from northwestern Canada to inhabit an area with the highest density of early archaeological sites in interior Alaska until her death. DNA from the tusk and other local contemporaneous archaeological mammoth remains revealed that multiple mammoth herds congregated in this region. Early Alaskans seem to have structured their settlements partly based on mammoth prevalence and made use of mammoths for raw materials and likely food.

Hydrothermal Mineralization and Mineral Chemistry of Arsenides and Sulfarsenides in the Fe-Co-Ni-As-S System and Introduction of Three Unique Minerals, Port Radium Deposit, Canada

The Port Radium U-Cu-Ni-Co-Ag deposit in northwestern Canada is hosted within a mineral system that has generated a variety of mineralization styles from iron oxide-copper-gold to iron oxide-apatite, porphyry, skarn, and epithermal. Their genesis is linked to an extensive subduction-related magmatism that formed widespread dacite-rhyodacite-andesite volcanic and volcanoclastic sequences (~1.87 Ga), which have been intruded by their equivalent intrusive plutons. Pervasive and intensive hydrothermal alterations, including albitic, magnetite-actinolite-apatite, potassic ± albitic, phyllic, and propylitic occurred before the main sulfide, sulfarsenide, and uraninite vein-type mineralization. Although scarce sulfide minerals formed at the beginning of the hydrothermal activity, the main polymetallic arsenide-sulfarsenide-sulfide ± uraninite vein-type mineralization occurred during the epithermal stage. In addition to the common arsenides and sulfarsenides including nickeline, cobaltite, rammelsbergite, safflorite, skutterudite, gersdorffite, and arsenopyrite, three unique sulfarsenides were also found: Co0.67Ni0.32Fe0.02S0.19As2.80, which could be a sulfur-rich skutterudite, Ni0.85Co0.15S0.39As1.60, and Ni0.69Co0.31S0.47As1.52, which are chemically comparable to the Port Radium rammelsbergite with substantial addition of S and Co; they could be the solid solution product of gersdorffite-cobaltite or safflorite-rammelsbergite.

Wild Smoke: Managing Forest Pollution in Northern British Columbia since 1950

Almost every year, ash drifts from forest fires in north-western Canada into northern Europe, altering forecasts on both continents, settling in Antarctic ice and turning the skies over the world’s major cities an apocalyptic orange. As smoke drifts from the forests into nearby communities and distant urban centres, it becomes the medium through which most people experience forest fire, leaving traces on memories and bodies. Although wildfires and their associated plumes are getting worse, people have a long and dynamic relationship with forest fire smoke which can be understood through the lens of air pollution and forestry history. Using British Columbia, Canada as a case study, I argue that the difficulty of separating wildfire smoke from other types of air pollution has worked to the advantage of land managers interested in supporting the forestry industry, with negative impacts for northern communities.

Late Holocene glacier and climate fluctuations in the Mackenzie and Selwyn mountain ranges, northwestern Canada

Abstract. Over the last century, northwestern Canada experienced some of the highest rates of tropospheric warming globally, which caused glaciers in the region to rapidly retreat. Our study seeks to extend the record of glacier fluctuations and assess climate drivers prior to the instrumental record in the Mackenzie and Selwyn mountains of northwestern Canada. We collected 27 10Be surface exposure ages across nine cirque and valley glacier moraines to constrain the timing of their emplacement. Cirque and valley glaciers in this region reached their greatest Holocene extents in the latter half of the Little Ice Age (1600–1850 CE). Four erratic boulders, 10–250 m distal from late Holocene moraines, yielded 10Be exposure ages of 10.9–11.6 ka, demonstrating that by ca. 11 ka, alpine glaciers were no more extensive than during the last several hundred years. Estimated temperature change obtained through reconstruction of equilibrium line altitudes shows that since ca. 1850 CE, mean annual temperatures have risen 0.2–2.3 ∘C. We use our glacier chronology and the Open Global Glacier Model (OGGM) to estimate that from 1000 CE, glaciers in this region reached a maximum total volume of 34–38 km3 between 1765 and 1855 CE and had lost nearly half their ice volume by 2019 CE. OGGM was unable to produce modeled glacier lengths that match the timing or magnitude of the maximum glacier extent indicated by the 10Be chronology. However, when applied to the entire Mackenzie and Selwyn mountain region, past millennium OGGM simulations using the Max Planck Institute Earth System Model (MPI-ESM) and the Community Climate System Model 4 (CCSM4) yield late Holocene glacier volume change temporally consistent with our moraine and remote sensing record, while the Meteorological Research Institute Earth System Model 2 (MRI-ESM2) and the Model for Interdisciplinary Research on Climate (MIROC) fail to produce modeled glacier change consistent with our glacier chronology. Finally, OGGM forced by future climate projections under varying greenhouse gas emission scenarios predicts 85 % to over 97 % glacier volume loss by the end of the 21st century. The loss of glaciers from this region will have profound impacts on local ecosystems and communities that rely on meltwater from glacierized catchments.

Variations of Crustal Thickness in Alaska and Northwestern Canada: Implications for Crustal Modification and Accretion of Tectonic Units

AbstractThe northwestern part of North America has recorded multiple tectonic events, such as terrane accretion, strike‐slip motion, and subduction of the Pacific and Yakutat plates, providing an iconic setting to investigate the tectonic evolution of the continental crust. In this study we analyze the receiver functions at seismic stations deployed during 1999–2022 to estimate the crustal thickness, as well as possible slab signature, in Alaska and northwestern Canada. The Moho signal can be clearly detected within the continental region. Specifically, in northwestern Canada, the thickest crust is observed beneath the Cordilleran Deformation Front, which marks the structural boundary between the North American Craton and the North American Margin. We observe a few distinct offsets in the Moho depth located both within the tectonic units and approximately across the major faults between the tectonic units. We provide a first‐order estimate of the depth gradient of the Moho offsets based on the horizontal distance of the two closest seismic stations across the offsets. We propose that the Moho offsets reflect the cumulative impact of the accretionary orogenies and post‐orogenic tectonic events on crustal modification. The continental Moho signal is weak or obscure in Aleutian and southcentral Alaska, and the oceanic Moho within the subducting plates is likely detected. This study provides new seismic insights into understanding the impacts of the tectonic events on continental formation and evolution.

Icing and aufeis in cold regions II: consequences and mitigation

The process of icing and the resulting layered ice masses, called aufeis, are caused by the freezing of overflow originating from groundwater or surface water. Aufeis can directly impact infrastructure and property, most commonly through winter ice formation and spring flooding within, against, and on the surface of hydraulic structures and transportation infrastructure. They also represent a safety concern for drivers. This geohazard often needs to be managed proactively and efficiently to mitigate associated risks. This paper provides an overview of the consequences of aufeis in northwestern Canada. A total of 50 existing and novel icing and aufeis mitigation approaches are described and classified. The context of applicability for each approach is identified, considering the source of water, the type of infrastructure, and its role in the formation of aufeis. Finally, future research avenues to support the development or improvement of aufeis risk reduction techniques are presented.

Recent peat and carbon accumulation on changing permafrost landforms along the Mackenzie River valley, Northwest Territories, Canada

Northwestern Canada is currently warming nearly four times faster than the global average, driving accelerated permafrost thaw and changes to ecosystem vegetation, hydrology and landscape structure across the landscape. While permafrost peatlands constitute a large carbon reservoir, there is no consensus yet on the direction and magnitude of changes to their vulnerable carbon balance. Here, we assessed changes in peatland ecosystems following permafrost thaw at three sites located along a 1000 km long climate and permafrost gradient along the Mackenzie River valley, Canada. Specifically, we examined vegetation succession over the last few decades to evaluate the possible impact of climate warming on peat and carbon accumulation. Results from the palaeoecological analysis of 20 surficial peat cores, supported by robust chronologies, show a return to Sphagnum accumulation since ca. 1980 CE in the sporadic and discontinuous permafrost zones and ca. 2000 CE in the continuous permafrost zone. The average rates of peat and carbon accumulation reached 4 mm yr−1 and 134 g C m−2 yr−1 at the northernmost site in the continuous permafrost zone. In contrast, peat and carbon accumulation reached 3 mm yr−1 and 81 g C m−2 yr−1, respectively, in the sporadic and discontinuous permafrost zones. This study highlights the need for a net carbon budget that integrates the recent accelerated Sphagnum growth and carbon uptake from the atmosphere to better assess the potential carbon emissions offset following permafrost thaw. High-resolution palaeoecological studies can offer insights into decadal-scale patterns of vegetation and carbon balance changes to improve model predictions of peat climate-carbon cycle feedbacks.

Evaluating the inclusion of Inuvialuktun place names in online maps

Place names, also known as toponyms, are a fundamental part of our cultural and geographical environment. Like many Indigenous groups, Inuvialuit in what is now northwestern Canada use place names to describe the landscape, guide and warn travellers, and convey important cultural information (Hart 2011, 9). Many efforts are underway to document, restore and promote the use of Indigenous toponyms in Canada, including their submission to provincial and territorial naming authorities (Inuit Heritage Trust 2016). A related means of raising the profile of Inuvialuit place names is their inclusion on maps that are readily accessible to the public. In their ten calls to action for natural science researchers working in Canada, Wong et al. (2020) underscore the need for Indigenous place names to be incorporated, with permission, in maps and text associated with scientific research to recognize the stories and Indigenous Knowledge behind the names (777). This paper is a step in addressing this call to action by presenting the results of an analysis of Inuvialuktun-language place names in the Tuktoyaktuk area. The analysis examines how readily the names are identified in official, and popular non-official sources and discusses implications for promoting Indigenous Knowledge more broadly.

The Northwest Territories Thermokarst Mapping Collective: A northern-driven mapping collaborative toward understanding the effects of permafrost thaw

This paper documents the first comprehensive inventory of thermokarst and thaw-sensitive terrain indicators for a 2 million km2 region of northwestern Canada. This is accomplished through the Thermokarst Mapping Collective (TMC), a research collaborative to systematically inventory indicators of permafrost thaw sensitivity by mapping and aerial assessments across the Northwest Territories (NT), Canada. The increase in NT-based permafrost capacity has fostered science leadership and collaboration with government, academic, and community researchers to enable project implementation. Ongoing communications and outreach have informed study design and strengthened Indigenous and stakeholder relationships. Documentation of theme-based methods supported mapper training, and flexible data infrastructure facilitated progress by Canada-wide researchers throughout the COVID-19 pandemic. The TMC inventory of thermokarst and thaw-sensitive landforms agree well with fine-scale empirical mapping (69% to 84% accuracy) and aerial inventory (74% to 96% accuracy) datasets. National- and circumpolar-scale modelling of sensitive permafrost terrain contrasts significantly with TMC outputs, highlighting their limitations and the value of empirically-based mapping approaches. We demonstrate that the multi-parameter TMC outputs support a holistic understanding and refined depictions of permafrost terrain sensitivity, provide novel opportunities for syntheses, and inform future modelling approaches, which are urgently required to comprehend better what permafrost thaw means for Canada’s North.

Modeling 3D crustal velocities in the vicinities of Alaska and the Bering sea

Abstract This document introduces Version 0.4 of the TRANS4D software, where TRANS4D is short for Transformations in Four Dimensions. TRANS4D enables geospatial professionals and others to transform three-dimensional positional coordinates across time and among several popular terrestrial reference frames. Version 0.4 introduces new crustal velocity models for the vicinities of Alaska and the Bering Sea, including parts of northwestern Canada and eastern Russia. These new models supplement existing velocity models for the continental United States as well as for most of Canada and for a neighborhood of the Caribbean plate. This document also provides evidence for the existence of a Bering tectonic plate, and it presents estimates for the Euler-pole parameters of this hypothesized plate. Moreover, estimated horizontal velocities computed at several geodetic stations located in Alaska provide evidence for the existence of part of the plate boundary separating the North American plate and the hypothesized Bering plate.

Permafrost thaw induces short-term increase in vegetation productivity in northwestern Canada.

Over the past several decades, various trends in vegetation productivity, from increases to decreases, have been observed throughout Arctic-Boreal ecosystems. While some of this variation can be explained by recent climate warming and increased disturbance, very little is known about the impacts of permafrost thaw on productivity across diverse vegetation communities. Active layer thickness data from 135 permafrost monitoring sites along a 10° latitudinal transect of the Northwest Territories, Canada, paired with a Landsat time series of normalized difference vegetation index from 1984 to 2019, were used to quantify the impacts of changing permafrost conditions on vegetation productivity. We found that active layer thickness contributed to the observed variation in vegetation productivity in recent decades in the northwestern Arctic-Boreal, with the highest rates of greening occurring at sites where the near-surface permafrost recently had thawed. However, the greening associated with permafrost thaw was not sustained after prolonged periods of thaw and appeared to diminish after the thaw front extended outside the plants' rooting zone. Highest rates of greening were found at the mid-transect sites, between 62.4° N and 65.2° N, suggesting that more southernly sites may have already surpassed the period of beneficial permafrost thaw, while more northern sites may have yet to reach a level of thaw that supports enhanced vegetation productivity. These results indicate that the response of vegetation productivity to permafrost thaw is highly dependent on the extent of active layer thickening and that increases in productivity may not continue in the coming decades.

Integrated Litho-, Chemo- and Sequence Stratigraphy of the Ediacaran Gametrail Formation Across a Shelf-Slope Transect in the Wernecke Mountains, Yukon, Canada

The Ediacaran Gametrail Formation of northwestern Canada chronicles the evolution of a complex carbonate ramp system in response to fluctuations in relative sea level and regional tectonic subsidence alongside exceptional global change associated with the Shuram carbon isotope excursion (CIE). Here, we use extensive outcrop exposures of the Gametrail Formation in the Wernecke Mountains of Yukon, Canada, to construct a shelf-slope transect across the Shuram CIE. Twelve stratigraphic sections of the Gametrail Formation are combined with geological mapping and a suite of geochemical analyses to develop an integrated litho-, chemo-, and sequence stratigraphic model for these strata. In the more proximal Corn/Goz Creek region, the Gametrail Formation represents a storm-dominated inner to outer ramp depositional setting, while slope depositional environments in the Nadaleen River region are dominated by hemipelagic sedimentation, turbidites, and debris flows. The magnitude of the Shuram CIE is largest in slope limestones which underwent sediment-buffered diagenesis, while the CIE is notably smaller in the inner-outer ramp dolostones which experienced fluid-buffered diagenesis. Our regional mapping identified a distinct structural panel within the shelf-slope transect that was transported ~30 km via strike-slip motion during the Mesozoic–Cenozoic Cordilleran orogeny. One location in this transported structural block contains a stromatolite reef complex with extremely negative carbon isotope values down to ~ -30‰, while the other location contains an overthickened ooid shoal complex that does not preserve the characteristic negative CIE associated with the Shuram event. These deviations from the usual expression of the Shuram CIE along the shelf-slope transect in the Wernecke Mountains, and elsewhere globally, provide useful examples for how local tectonic, stratigraphic, and/or geochemical complexities can result in unusually large or completely absent expressions of a globally recognized CIE.

Interactions within the climate-vegetation-fire nexus may transform 21st century boreal forests in northwestern Canada

Dry and warm conditions have exacerbated the occurrence of large and severe wildfires over the past decade in Canada's Northwest Territories (NT). Although temperatures are expected to increase during the 21st century, we lack understanding of how the climate-vegetation-fire nexus might respond. We used a dynamic global vegetation model to project annual burn rates, as well as tree species composition and biomass in the NT during the 21st century using the IPCC's climate scenarios. Burn rates will decrease in most of the NT by the mid-21st century, concomitant with biomass loss of fire-prone evergreen needleleaf tree species, and biomass increase of broadleaf tree species. The southeastern NT is projected to experience enhanced fire activity by the late 21st century according to scenario RCP4.5, supported by a higher production of flammable evergreen needleleaf biomass. The results underlie the potential for major impacts of climate change on the NT's terrestrial ecosystems.