| 1. |
- Andin, Caroline, et al.
(författare)
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Synoptic variability of extreme snowfall in the St. Elias Mountains,Yukon, Canada
- 2015
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Konferensbidrag (refereegranskat)abstract
- Glaciers in the Wrangell and St. Elias Mountains (Alaska and Yukon) are presently experiencing some of thehighest regional wastage rates worldwide. While the effect of regional temperatures on glacier melt rates in thisregion has been investigated, comparatively little is known about how synoptic climate variations, for example inthe position and strength of the Aleutian Low, modulate snow accumulation on these glaciers. Such informationis needed to accurately forecast future wastage rates, glacier-water resource availability, and contributions tosea-level rise. Starting in 2000, automated weather stations (AWS) were established in the central St-EliasMountains (Yukon) at altitudes ranging from 1190 to 5400 m asl, to collect climatological data in support ofglaciological research. These data are the longest continuous year-round observations of surface climate everobtained from this vast glaciated region. Here we present an analysis of snowfall events in the icefields of theSt-Elias Mountains based on a decade-long series of AWS observations of snow accumulation. Specifically,we investigated the synoptic patterns and air mass trajectories associated with the largest snowfall events (> 25cm/12 hours) that occurred between 2002 and 2012. Nearly 80% of these events occurred during the cold season(October-March), and in 74 % of cases the precipitating air masses originated from the North Pacific south of50N. Zonal air mass advection over Alaska, or from the Bering Sea or the Arctic Ocean, was comparativelyrare (20%). Somewhat counter-intuitively, dominant surface winds in the St. Elias Mountains during highsnowfall events were predominantly easterly, probably due to boundary-layer frictional drag and topographicfunneling effects. Composite maps of sea-level pressure and 700 mb winds reveal that intense snowfall eventsbetween 2002 and 2012 were associated with synoptic situations characterized by a split, eastwardly-shifted orlongitudinally-stretched Aleutian Low (AL) having an easternmost node near the Kenai Peninsula, conditionsthat drove a strong southwesterly upper airstream across the Gulf of Alaska towards the coast. Situations with asingle-node, westerly-shifted AL were comparatively rare. The spatial configuration of the synoptic AL pressurepattern appears to play a greater role in determining snowfall amount in the central St. Elias Mountains than dopressure anomalies within the AL. The estimated snowfall gradient from coastal Alaska to the central St. EliasMountains during intense snowfall events averaged +2.0 0.7 mm/km (SWE), while the continental-side gradientfrom the mountains towards the Yukon plateau averaged -3.3 0.9 mm/km (SWE). The findings presented herecan better constrain the climatic interpretation of long proxy records of snow accumulation variations developedfrom glacier cores drilled in the St. Elias Mountains or nearby regions.
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| 2. |
- Barbaro, E., et al.
(författare)
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Measurement report: Spatial variations in ionic chemistry and water-stable isotopes in the snowpack on glaciers across Svalbard during the 2015-2016 snow accumulation season
- 2021
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 21:4, s. 3163-3180
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Tidskriftsartikel (refereegranskat)abstract
- The Svalbard archipelago, located at the Arctic sea-ice edge between 74 and 81 degrees N, is similar to 60% covered by glaciers. The region experiences rapid variations in atmospheric flow during the snow season (from late September to May) and can be affected by air advected from both lower and higher latitudes, which likely impact the chemical composition of snowfall. While long-term changes in Svalbard snow chemistry have been documented in ice cores drilled from two high-elevation glaciers, the spatial variability of the snowpack composition across Svalbard is comparatively poorly understood. Here, we report the results of the most comprehensive seasonal snow chemistry survey to date, carried out in April 2016 across 22 sites on seven glaciers across the archipelago. At each glacier, three snowpits were sam- pled along the altitudinal profiles and the collected samples were analysed for major ions (Ca2+, K+, Na+, Mg2+, NH4+, SO42, Br-, Cl-, and NO3-) and stable water isotopes ( ffi18O, delta H-2). The main aims were to investigate the natural and anthropogenic processes influencing the snowpack and to better understand the influence of atmospheric aerosol transport and deposition patterns on the snow chemical composition. The snow deposited in the southern region of Svalbard is characterized by the highest total ionic loads, mainly attributed to sea-salt particles. Both NO3 and NH4+ in the seasonal snowpack reflect secondary aerosol formation and post-depositional changes, resulting in very different spatial deposition patterns: NO3 has its highest loading in northwestern Spitsbergen and NH4+ in the south-west. The Br enrichment in snow is highest in north-eastern glacier sites closest to areas of extensive sea-ice coverage. Spatial correlation patterns between Na+ and delta O-18 suggest that the influence of long-range transport of aerosols on snow chemistry is proportionally greater above 600-700ma.s.l.
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| 3. |
- Baykal, Yunus
(författare)
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Source and age of late Quaternary loess deposits in Europe
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Atmospheric mineral dust is a fundamental component of the Earth’s climate system, with dust both responding to and driving climate change. This close link between dust and climate is recorded in archives of past dust activity, which show that abrupt 101-3 yr shifts in temperature during the last glacial period were accompanied with fluctuations in dust activity. However, the precise mechanism behind this close coupling of dust and climate and the specific role dust plays in modulating rapid climate change remains unclear. Terrestrial wind-blown dust deposits (loess) in Europe serve as source proximal archives of past dust activity. Loess formation chronologies across this region generally indicate greatly enhanced dust deposition during the last glacial cold phases of MIS 4 and, most notably, MIS 2. However, currently chronological precision is not sufficient to constrain more abrupt changes in dust activity and their potential links to climate change. More fundamentally, uncertainties over the sources of loess in Europe limit understanding of the causes of this last glacial dust deposition variability. The four chapters that comprise this thesis address these uncertainties through detailed analysis of the age and sources of loess in the Northern European Plain and English Channel region. Overall, the results demonstrate that abrupt changes in dust deposition during the late last glacial were a function of changes in ice sheet driven sediment supply. Eurasian and Alpine Ice Sheet derived meltwater pulses periodically greatly enhanced sediment availability and dust emission along their drainage routes, as reflected by abrupt dust deposition variability recorded in European loess deposits. Upon discharge into the North Atlantic, these meltwater pulses are also believed to have interacted with ocean circulation, potentially driving abrupt climate fluctuations during the last glacial. This provides a mechanism linking changes in dust, climate and ocean circulation on millennial timescales via ice sheet dynamics and provides the first coherent explanation of the close coupling of millennial scale variation in climate and dust during the Quaternary. Moreover, these findings suggest that meltwater pulses not only affected last glacial climate by changing ocean circulation but also through their impact on the high latitude dust cycle.
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| 4. |
- Beal, Samuel A., et al.
(författare)
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Ice Core Perspective on Mercury Pollution during the Past 600 Years
- 2015
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 49:13, s. 7641-7647
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Tidskriftsartikel (refereegranskat)abstract
- Past emissions of the toxic metal mercury (Fig) persist in the global environment yet these emissions remain poorly constrained by existing data. Ice cores are high-resolution archives of atmospheric deposition that may provide crucial insight into past atmospheric Hg levels during recent and historical time. Here we present a record of total Hg (Hg-T) in an ice core from the pristine summit plateau (5340 m asl) of Mount Logan, Yukon, Canada, representing atmospheric deposition from AD 1410 to 1998. The Colonial Period (similar to 1603-1850) and North American "Gold Rush" (1850-1900) represent minor fractions (8% and 14%, respectively) of total anthropogenic Hg deposition in the record, with the majority (78%) occurring during the 20th Century. A period of maximum HgT fluxes from 1940 to 1975 coincides with estimates of enhanced anthropogenic Hg emissions from commercial sources, as well as with industrial emissions of other toxic metals. Rapid declines in HgT fluxes following peaks during the Gold Rush and the mid-20th Century indicate that atmospheric Hg deposition responds quickly to reductions in emissions. Increasing HgT fluxes from 1993 until the youngest samples in 1998 may reflect the resurgence of Hg emissions from unregulated coal burning and small-scale gold mining.
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| 5. |
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| 6. |
- Beaudoin, Anne, et al.
(författare)
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Palaeoenvironmental history of the last six centuries in the Nettilling Lake area (Baffin Island, Canada) : A multi-proxy analysis
- 2016
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Ingår i: The Holocene. - : Sage Publications. - 0959-6836 .- 1477-0911. ; 26:11, s. 1835-1846
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Tidskriftsartikel (refereegranskat)abstract
- The Baffin Island region in the eastern Canadian Arctic has recently experienced a rapid warming, possibly unprecedented in millennia. To investigate theresponse of freshwater environments to this warming and place it in a secular perspective, we analyzed a 90-cm-long sediment core from Nettilling Lake,the largest lake of the Canadian Arctic Archipelago. The core was taken from a part of the lake basin that receives meltwater and sediment inputs from thenearby Penny Ice Cap. The core time scale, established using 137Cs and palaeomagnetic techniques, spans an estimated 600 years. A multi-proxy approachwas used to document changes in the physical, chemical, and biological properties of the sediments. We found evidence for a relatively warm period (mid/late 15th century to mid/late 16th century) during the early part of the ‘Little Ice Age’ (LIA), characterized by high sedimentation rates and laminations.This was followed by colder, drier, and windier conditions corresponding to the coldest phase of LIA and coinciding with the latest and most extensiveperiod of regional ice cap expansion (early 16th to late 19th centuries). A rapid warming occurred at the beginning of the 20th century. Variations intitanium (Ti) content in the core, a proxy for detrital sediment inputs, showed good agreement with reconstructed secular variations in summer meltrates on Penny Ice Cap between the mid-14th century and the present-day, providing supporting evidence for a climatic–hydrological connection betweenthe ice cap and Nettilling Lake.
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| 7. |
- Beaudoin, Anne, et al.
(författare)
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Paleoenvironmental reconstructions of Nettilling Lake area (Baffin Island, Nunavut) : A multi-proxy analysis
- 2014
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Konferensbidrag (refereegranskat)abstract
- The paleoclimate and paleolimnological history of several Arctic regions remains poorly known. This is the casefor the area around Nettilling Lake (Baffin Island, Nunavut), the largest lake of the Canadian Arctic Archipelago.To reconstruct the past environmental history of this area, a highly innovative multi-proxy approach combiningphysical, magnetic, chemical and biological properties preserved in lake sediments was used. One particular goalof this study was to investigate the possible coupling between sedimentation processes observed in the lake andmelt rates of nearby Penny Ice Cap.A 1-m long sediment core was retrieved from a small bay in the northeastern part of Nettilling Lake duringthe summer of 2010. This sampling area was chosen based on the hypothesis that incoming glacial meltwatersfrom Penny Ice Cap would leave a strong climate-modulated signal that would be reflected in the sedimentarysequence. The core was analyzed by both non-destructive (X-radiography (X-ray), microfluorescence-X (-XRF),magnetic susceptibility) and destructive (Loss On Ignition, grain size, water content, thin sections, diatoms)techniques. Radiometric AMS 14C and 210Pb/137Cs age determinations, as well as paleomagnetic measurements,were used to develop the core chronology, yielding an estimated bottom age of approximately 1365 AD.The sedimentation rate (0.15 cm.yr-1) in Nettilling Lake was found to be high compared to other Arctic lakes,due to inputs of highly turbid meltwaters from Penny Ice Cap with high suspended sediment loads. Significantcorrelations were found between geochemical profiles of elements linked to detrital inputs (Si, Ti, K, Ca) and meltrates from Penny Ice Cap since the 19th century. This suggests that variations in detrital elements in NettillingLake sediments might be used as an indirect indicator of regional climate fluctuations (e.g., summer temperatures) that determine glacier melt rates.
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| 8. |
- Campeau, Audrey, et al.
(författare)
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Controls on the 14C Content of Dissolved and Particulate Organic Carbon Mobilized Across the Mackenzie River Basin, Canada
- 2020
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Ingår i: Global Biogeochemical Cycles. - : AMER GEOPHYSICAL UNION. - 0886-6236 .- 1944-9224. ; 34:12
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Tidskriftsartikel (refereegranskat)abstract
- The Mackenzie River Basin (MRB) delivers large quantities of organic carbon (OC) into the Arctic Ocean, with significant implications for the global C budgets and ocean biogeochemistry. The amount and properties of OC in the Mackenzie River's delta have been well monitored in the last decade, but the spatial variability in OC sources transported by its different tributaries is still unclear. Here we present new data on the radiocarbon (14C) content of dissolved and particulate OC (Δ14C‐DOC and Δ14C‐POC) across the mainstem and major tributaries of the MRB, comprising 19 different locations, to identify factors controlling spatial patterns in riverine OC sources. The Δ14C‐DOC and Δ14C‐POC varied across a large range, from −179.9‰ to 62.9‰, and −728.8‰ to −9.0‰, respectively. Our data reveal a positive spatial coupling between the Δ14C of DOC and POC across the MRB, whereby the most 14C‐depleted waters were issued from the mountainous west bank of the MRB. This 14C‐depleted DOC and POC likely originates from a combination of petrogenic sources, connected with the presence of kerogens in the bedrock, and biogenic sources, mobilized by thawing permafrost. Our analysis also reveals intriguing relationships between Δ14C of DOC and POC with turbidity, water stable isotope ratio and catchment elevation, indicating that hydrology and geomorphology are key to understanding riverine OC sources in this landscape. A closer examination of the specific mechanisms giving rise to these relationships is recommended. For now, this study provides a road map of the key OC sources in this rapidly changing river basin.
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| 9. |
- Campeau, Audrey, et al.
(författare)
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Sources of riverine mercury across the Mackenzie River Basin; inferences from a combined Hg C isotopes and optical properties approach
- 2022
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 806, s. 150808-150808
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Tidskriftsartikel (refereegranskat)abstract
- The Arctic terrestrial environment harbors a complex mosaic of mercury (Hg) and carbon (C) reservoirs, some of which are rapidly destabilizing in response to climate warming. The sources of riverine Hg across the Mackenzie River basin (MRB) are uncertain, which leads to a poor understanding of potential future release. Measurements of dissolved and particulate mercury (DHg, PHg) and carbon (DOC, POC) concentration were performed, along with analyses of Hg stable isotope ratios (incl. ∆199Hg, d202Hg), radiocarbon content (∆14C) and optical properties of DOC of river water. Isotopic ratios of Hg revealed a closer association to terrestrial Hg reservoirs for the particulate fraction, while the dissolved fraction was more closely associated with atmospheric deposition sources of shorter turnover time. There was a positive correlation between the ∆14C-OC and riverine Hg concentration for both particulate and dissolved fractions, indicating that waters transporting older-OC (14C-depleted) also contained higher levels of Hg. In the dissolved fraction, older DOC was also associated with higher molecular weight, aromaticity and humic content, which are likely associated with higher Hg-binding potential. Riverine PHg concentration increased with turbidity and SO4 concentration. There were large contrasts in Hg concentration and OC age and quality among the mountain and lowland sectors of the MRB, which likely reflect the spatial distribution of various terrestrial Hg and OC reservoirs, including weathering of sulfate minerals, erosion and extraction of coal deposits, thawing permafrost, forest fires, peatlands, and forests. Results revealed major differences in the sources of particulate and dissolved riverine Hg, but nonetheless a common positive association with older riverine OC. These findings reveal that a complex mixture of Hg sources, supplied across the MRB, will contribute to future trends in Hg export to the Arctic Ocean under rapid environmental changes.
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| 10. |
- Cardyn, R., et al.
(författare)
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Molar gas ratios of air entrapped in ice : A new tool to determine the origin of relict massive ground ice bodies in permafrost
- 2007
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Ingår i: Quaternary Research. - : Cambridge University Press (CUP). - 0033-5894 .- 1096-0287. ; 68:2, s. 239-248
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Tidskriftsartikel (refereegranskat)abstract
- The molar ratios of atmospheric gases change during dissolution in water due to differences in their relative solubilities. We exploited this characteristic to develop a tool to clarify the origin of ice formations in permafrost regions. Extracted from ice, molar gas ratios can distinguish buried glacier ice from intrasedimental ground ice formed by freezing groundwaters. An extraction line was built to isolate gases from ice by melting and trapping with liquid He, followed by analysis of N2, O2,, Ar, 18OO2 and 15NN2, by continuous flow mass spectrometry. The method was tested using glacier ice, aufeis ice (river icing) and intrasedimental ground ice from sites in the Canadian Arctic. O2/Ar and N2/Ar ratios clearly distinguish between atmospheric gas in glacial ice and gases from intrasedimental ground ice, which are exsolved from freezing water. δ15NN2 and δ18OO2 in glacier ice, aufeis ice and intrasedimental ground ice do not show clear distinguishing trends as they are affected by various physical processes during formation such as gravitational settling, excess air addition, mixing with snow pack, and respiration.
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