This study examines the
δ
18O and
δ
13C composition of cryogenic carbonate deposits in relation to the initial
δ
18O,
δ
13C
DIC and chemical composition of the water from which it precipitated. This ...study focuses on cryogenic calcites precipitated in relation to aufeis aggradation since it offers the possibility of examining the chemical and isotopic partitioning that occurs during freezing. The studied aufeis are located in the western Canadian Arctic (YT and NWT), a region underlain mostly by limestone bedrock, and southern Baffin Island (NU), an area of crystalline bedrock. The results indicate that the
δ
18O composition of cryogenic calcite from a carbonated environment are slightly depleted over that of the initial
δ
18O of the parent water, while those from a non-carbonated environment are strongly depleted over the initial
δ
18O of the parent water as a result of the lower calcite saturation state of the parent water. This suggest that the
δ
18O of cryogenic carbonates not only depends on the initial
δ
18O composition of the parent water and the temperature at which the carbonate precipitated, but also on the calcite saturation state of the parent water and kinetic inhibitions during calcite precipitation. Given that the aggradation of aufeis occurs under closed-system freezing, the residual water will become progressively depleted in
δ
18O as a result of the removal of heavier isotopes in the ice. In addition, freezing imparts a concentration of solutes in the residual water, which leads to an increase in calcite saturation index. Therefore, carbonate precipitated in equilibrium from water that has a low calcite saturation index will have a highly depleted
δ
18O composition over that of the initial
δ
18O values of the parent water since the calcite saturation state will only be exceeded in the late stage of freezing. By contrast, solute and isotopic partitioning during freezing has little effect on the
δ
13C of the cryogenic carbonates as it tends to reflect that of the initial
δ
13C
DIC value of the parent water. These findings have significant implications in the use of cryogenic carbonates in paleoclimate studies. Care must be taken when interpreting the
δ
18O signature preserved in cryogenic carbonates since their signature might be modified by freezing prior to their precipitation, which will lead to a lighter
δ
18O composition of the cryogenic carbonates. Therefore, it would be difficult to use the
δ
18O composition of cryogenic carbonates as a direct proxy in paleoclimatic reconstruction unless details about the chemical composition of parent waters are known. Nevertheless, the
δ
13C composition of the cryogenic carbonates that precipitated under closed-system conditions can allow insights into the different water sources contributing to carbonate precipitation.
A tree-ring analysis of 764 western white spruce (Picea albertiana) in the Takhini Valley of southwest Yukon was conducted to assess short- and long-term variation in growth and local climate. The ...resulting chronology spanned the period from AD 1763 to 2013. A polynomial regression (R = 0.720, p < 0.001) indicated that the pre-1840 segment of the chronology had below-normal tree ring-width index (RWI) values (average 0.64, with modest variation), but the subsequent segment had greater variation and a steady increase in RWI values (average 0.89) until ~1920. After 1930, RWI values began to increase again (average 1.06) with 51% more variation than had previously occurred. Peak RWI values after 1930 were double those of the early 1800s. RWI values were uncorrelated with air temperature variables (except September minima), but weakly and positively correlated (r < 0.35) with precipitation variables. RWI values were moderately correlated with annual heat-moisture index values (r = −0.415, p < 0.001), although more strongly with RWI values less than 1.1 (R = −0.631, p < 0.001). Therefore, the RWI chronology was interpreted from an ecological moisture-balance perspective, with possible long-term temperature changes estimated from archival sources. The latter suggested a 2.1°–3.1°C rise since the early 1800s. Extreme RWI values and portions of the chronology were associated with known environmental events.
L’analyse des anneaux de croissance de 764 épinettes blanches de l’Ouest (Picea albertiana) de la vallée Takhini, dans le sud-ouest du Yukon, a été effectuée dans le but d’évaluer les variations à court et à long termes en matière de croissance et de climat local. La chronologie qui en a découlé s’étend sur la période allant de 1763 à 2013 de notre ère. La régression polynomiale (R = 0,720, p < 0,001) a permis de déterminer que les valeurs des largeurs d’anneaux de croissance du segment chronologique précédant 1840 étaient en bas de la normale (moyenne de 0,64, avec de modestes variations), mais que les valeurs des largeurs d’anneaux du segment subséquent affichaient de plus grandes variations et une augmentation continue des valeurs des largeurs d’anneaux de croissance (moyenne de 0,89) jusque vers 1920. Après 1930, ces valeurs ont recommencé à augmenter (moyenne de 1,06) pour afficher une variation 51 % plus élevée que celle enregistrée auparavant. Après 1930, les valeurs maximales des largeurs d’anneaux correspondaient au double de celles du début des années 1800. Les valeurs des largeurs d’anneaux n’ont pas été corrélées avec les variables des températures de l’air (à l’exception des minimums de septembre), mais ont fait l’objet d’une corrélation faible et positive (r < 0,35) avec les variables des précipitations. Les valeurs des largeurs d’anneaux de croissance ont fait l’objet d’une corrélation modérée avec les valeurs annuelles des indices de chaleur et d’humidité (r = −0,415, p < 0,001), et d’une corrélation plus forte avec les valeurs des largeurs d’anneaux de moins de 1,1 (R = −0,631, p < 0,001). Par conséquent, la chronologie des largeurs d’anneaux de croissance a été interprétée à partir de la perspective du bilan d’eau du sol et les changements possibles de températures à long terme ont été évalués à partir de sources archivées. Ces dernières ont permis de suggérer une augmentation de 2,1°à 3,1 °C depuis le début des années 1800. Les valeurs extrêmes et les segments chronologiques des largeurs d’anneaux de croissance ont été associés à des événements environnementaux connus.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Glaciers in the Yukon, NW Canada, lost 22% of their surface area during the 50 years following the 1957–58 International Geophysical Year, coincident with increases in average winter and summer air ...temperatures and decreases in winter precipitation. Scaling these results to ice volume change, we obtain a total mass loss of 406 ± 177 Gt, which accounts for 1.12 ± 0.49 mm of global sea‐level rise. Yukon glaciers thinned by 0.78 ± 0.34 m yr−1 water equivalent, a regional thinning rate exceeded only by mountain glaciers in Patagonia and Alaska. Our scaling analysis suggests the remaining glaciers have the capacity to contribute a further 5.02 mm to global sea‐level rise.
1. Climate is an important factor influencing the population dynamics of large herbivores operating directly on individuals or through its effect on forage characteristics. However, the seasonal ...effect of climate may differ between forage- and predator-limited populations because of a climatic influence on predation rates. The influence of climate on predator-limited large herbivores is less well known than on forage-limited populations. Further, the effect of Pacific-based climate on large herbivore populations has been rarely assessed. 2. We investigated the effect of the Pacific Decadal Oscillation (PDO), across different seasons, on recruitment in 10 populations (herds) of mountain-dwelling caribou Rangifer tarandus caribou L. in the Yukon Territory, Canada. These low-density populations occur in highly seasonal environments and are considered predator-limited with high neonatal calf mortality. Hence, in most years females do not spend resources through lactational support during the summer and resource intake is devoted to self-maintenance. We predicted that climate affecting environmental conditions at calving would have a strong effect on recruitment via its influence on predation rates. We also predicted that climatic conditions prior to conception could have an effect on recruitment through its influence on female fecundity. We modelled recruitment (n = 165) by seasonal PDO values using generalized linear mixed-effects models with herd-varying coefficients. 3. We found that recruitment variability was best explained by variation in winter climate (β = 0·110, SE = 0·007) prior to birth (in utero) and May climate (β = 0·013, SE = 0·006) at calving. There was little support for a pre-conception climate effect influencing female body condition and hence fecundity. These results confirm that recruitment in these populations is limited by predation and that forage-limitation is not a significant factor in their population dynamics. There was considerable variability in herd-specific relationships between the PDO and recruitment. Incorporating herd-specific characteristics, such as variable predator densities or terrain characteristics within a herd range, may shed greater light on the complex relationship between climate and ungulate population dynamics.
At least five Middle to Late Pleistocene advances of the northern Cordilleran Ice Sheet are preserved at Silver Creek, on the northeastern edge of the St Elias Mountains in southwest Yukon, Canada. ...Silver Creek is located 100 km up‐ice of the Marine Isotope Stage (MIS) 2 McConnell glacial limit of the St Elias lobe. This site contains ~3 km of nearly continuous lateral exposure of glacial and non‐glacial sediments, including multiple tills separated by thick gravel, loess and tilted lake beds. Infrared‐stimulated luminescence (IRSL) and AMS radiocarbon dating constrain the glacial deposits to MIS 2, 4, either MIS 6 or mid‐MIS 7, and two older Middle Pleistocene advances. This chronology and the tilt of the lake beds suggest Pleistocene uplift rates of up to 1.9 mm a−1 along the Denali Fault since MIS 7. The non‐glacial sediment consists of sand, gravel, loess and organic beds from MIS 7, MIS 3 and the early Holocene. The MIS 3 deposits date to between 30–36 14C ka BP, making Silver Creek one of the few well‐constrained MIS 3‐aged sites in Yukon. This confirms that ice receded close to modern limits in MIS 3. Pollen and macrofossil analyses show that a meadow‐tundra to steppe‐tundra mosaic with abundant herbs and forbs and few shrubs or trees, dominated the environment at this time. The stratigraphy at Silver Creek provides a palaeoclimatic record since at least MIS 8 and comprises the oldest direct record of Pleistocene glaciation in southwest Yukon.
This paper describes the first synthesis method of yukonite, its thorough molecular and structural analysis along with natural specimens originating from Tagish Lake (Canada) and Grotta della Monaca ...(Italy) for comparison, and its structural relation to arseniosiderite. The synthetic and natural yukonites were found to have a range of composition according to the general formula Ca
2Fe
3–5(AsO
4)
3(OH)
4–10·
xH
2O where
x
=
2–11. The synthetic yukonite was found to be equivalent at the atomic, molecular and structural level to the Tagish Lake yukonite. At the molecular level, arseniosiderite, via vibrational spectroscopy, was found to have a H-bonding system as in scorodite and exhibit an extra arsenate mode indicative of
HAsO
4
2
-
groups. Heating experiments along with ATR-IR analysis indicated the presence of structural water and hydroxyl units in arseniosiderite. In yukonite in contrast, a wide diffuse H-bonding environment was observed with only arsenate groups. The presence of both structural water and hydroxyl groups was further verified via ATR-IR spectroscopy. The As K, Fe 2p and Ca 2p XANES spectra of yukonite and arseniosiderite were found to be identical, confirming that the local nature of the As, Fe and Ca atoms in these structures is the same. Diffraction analysis (X-ray and electron) showed that yukonite consist of nano-crystalline domains while in the case of arseniosiderite micro-size single crystal domains exist.
Roads affect the ecosystems they traverse: road construction and maintenance constitute substantial disturbance, while roads and vehicles have hydrological, thermal, and other abiotic effects. ...Arthropod communities respond to these abiotic effects of roads, as well as to the indirect effects of vegetation changes. The Dempster Highway is a year-round gravel highway that travels 737 km through the Subarctic and Arctic ecosystems of Yukon and the Northwest Territories, Canada. In July 2016, in a Subarctic region of Yukon, we established nine transects spaced at 4 - 12 km intervals along a 56 km segment of the Dempster Highway and sampled arthropods at 1, 10, and 100 m from the highway on each transect. Our objective was to determine the effect of road proximity on the diversity, abundance, and composition of arthropod communities, with a special focus on the functionally and phylogenetically diverse group, Hymenoptera. We found that total arthropod abundance was lowest at the intermediate distance from the road, a pattern driven by high Diptera abundance close to the road and high Collembola abundance far from the road. We suggest that Diptera may be responding to increased moisture and plant biomass near the road, while Collembola may be responding to changes in soil characteristics. Hymenoptera abundance was greater close to the road than farther away, a pattern that may be driven by high Diptera parasitoid abundance near the road. Our results suggest that arthropods are good indicators of ecosystem function and that roads may have important effects on Subarctic ecosystem services (e.g., pollination, pest control). As infrastructural development continues in the Canadian North, it is of vital importance to anticipate and predict the effects of this development on the unique and diverse fauna of the Subarctic ecosystem.
Les routes ont des effets sur les écosystèmes qu’elles traversent. La construction et l’entretien des routes sont une source importante de perturbation, et en soi, les routes et les véhicules ont des incidences de nature hydrologique et thermique ainsi que d’autres effets abiotiques. Les populations d’arthropodes réagissent aux effets abiotiques des routes de même qu’aux effets indirects des changements de la végétation. La route Dempster est une route de gravier utilisée à l’année. Elle s’étend sur 737 km dans les écosystèmes subarctiques et arctiques du Yukon et des Territoires du Nord-Ouest, au Canada. En juillet 2016, dans une région subarctique du Yukon, nous avons établi neuf transects à intervalles de quatre à 12 km sur un segment de 56 km de la route Dempster, ce qui nous a permis de prélever des échantillons d’arthropodes à des distances de un, dix et 100 m de la route sur chacun des transects. Notre objectif consistait à déterminer l’effet de la proximité de la route sur la diversité, l’abondance et la composition des populations d’arthropodes, en portant une attention particulière au groupe fonctionnellement et phylogénétiquement divers des hyménoptères. Cette étude nous a permis de constater que l’abondance d’arthropodes était à son niveau le plus bas à distance intermédiaire de la route, tendance attribuable à la forte abondance de diptères à proximité de la route et à la forte abondance de collemboles loin de la route. Nous suggérons que les diptères répondent peut-être au degré d’humidité plus élevé et à la biomasse végétale plus grande le long de la route, tandis que les collemboles répondent peut-être aux changements des caractéristiques du sol. L’abondance d’hyménoptères était plus grande à proximité de la route que loin de celle-ci, une tendance susceptible de découler de la forte abondance de diptères parasitoïdes près de la route. Nos résultats suggèrent que les arthropodes sont de bons indicateurs de la fonction de l’écosystème et que les routes peuvent avoir des effets importants sur les services écosystémiques subarctiques (c’est-à-dire la pollinisation, la lutte antiparasitaire). Au fur et à mesure que la mise en place d’infrastructures se poursuit dans le Nord canadien, il est d’une importance capitale de pouvoir prévoir et prédire les effets de ces infrastructures sur la faune unique et diverse de l’écosystème subarctique.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The large and variable riverine inflow to Arctic continental shelves strongly influences their chemical, biological, and optical properties. The Beaufort Sea receives the largest amount of suspended ...sediments amongst all Arctic shelves, with sediment-laden Mackenzie river waters strongly influencing bio-optical properties on the shelf. Here, we developed two regional algorithms for the estimation of total suspended matter (TSM) concentration using Medium Resolution Imaging Spectrometer (MERIS) spectral bands, based on in situ optical and suspended particulate data collected in the summer during the Canadian Arctic Shelf Exchange Study (CASES) in 2004 and during the Arctic Coastal Ecosystem Study (ACES) in 2010. The band ratio (where Rᵣₛ is remote-sensing reflectance) Rᵣₛ,₅₆₀/Rᵣₛ,₄₉₀ was best correlated with low TSM concentrations (less than 3.0 g m⁻³), while higher TSM concentrations were well correlated to Rᵣₛ,₆₈₁/Rᵣₛ,₅₆₀. An empirical piecewise algorithm is thus proposed with the switch between the ratios being triggered by Rᵣₛ,₆₈₁/Rᵣₛ,₅₆₀ at a threshold value of 0.6. The second algorithm made use of support vector machines (SVMs) as a nonlinear transfer function between TSM concentrations and remote-sensing reflectance ratios Rᵣₛ,₆₈₁/Rᵣₛ,₅₆₀, Rᵣₛ,₆₆₅/Rᵣₛ,₅₆₀, and Rᵣₛ,₅₆₀/Rᵣₛ,₄₉₀. Results show that both algorithms perform better (31% and 25%, respectively) than other published TSM algorithms including the MERIS Case 2 water processor (C2R) neural network algorithm in the study area.
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