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- Reinardy, Benedict T. I., et al.
(author)
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Pervasive cold ice within a temperate glacier : implications for glacier thermal regimes, sediment transport and foreland geomorphology
- 2019
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In: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 13:3, s. 827-843
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Journal article (peer-reviewed)abstract
- This study suggests that cold-ice processes may be more widespread than previously assumed, even within temperate glacial systems. We present the first systematic mapping of cold ice at the snout of the temperate glacier Midtdalsbreen, an outlet of the Hardangerjøkulen icefield (Norway), from 43 line kilometres of ground-penetrating radar data. Results show a 40m wide cold-ice zone within the majority of the glacier snout, where ice thickness is < 10 m. We interpret ice to be cold-based across this zone, consistent with basal freeze-on processes involved in the deposition of moraines. We also find at least two zones of cold ice up to 15m thick within the ablation area, occasionally extending to the glacier bed. There are two further zones of cold ice up to 30m thick in the accumulation area, also extending to the glacier bed. Cold-ice zones in the ablation area tend to correspond to areas of the glacier that are covered by late-lying seasonal snow patches that reoccur over multiple years. Subglacial topography and the location of the freezing isotherm within the glacier and underlying subglacial strata likely influence the transport and supply of supraglacial debris and formation of controlled moraines. The wider implication of this study is the possibility that, with continued climate warming, temperate environments with primarily temperate glaciers could become polythermal in forthcoming decades with (i) persisting thinning and (ii) retreat to higher altitudes where subglacial permafrost could be and/or become more widespread. Adversely, the number and size of late-lying snow patches in ablation areas may decrease and thereby reduce the extent of cold ice, reinforcing the postulated change in the thermal regime.
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| 2. |
- Gjerde, M., et al.
(author)
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Holocene glacier variability and Neoglacial hydroclimate at Alfotbreen, western Norway
- 2016
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 133, s. 28-47
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Journal article (peer-reviewed)abstract
- Glaciers and small ice caps respond rapidly to climate perturbations (mainly winter precipitation, and summer temperature), and the mass-balance of glaciers located in western Norway is governed mainly by winter precipitation (Pw). Records of past Pw can offer important insight into long-term changes in atmospheric circulation, but few proxies are able to accurately capture winter climate variations in Scandinavia. Reconstructions of equilibrium-line-altitude (ELA) variations from glaciers that are sensitive to changes in Pw therefore provide a unique opportunity to quantify past winter climate in this region. Here we present a new, Holocene glacier activity reconstruction for the maritime ice cap Alfotbreen in western Norway, based on investigations of distal glacier-fed lake sediments and modern mass balance measurements (1963-2010). Several lake sediment cores have been subject to a suite of laboratory analyses, including measurements of physical parameters such as dry bulk density (DBD) and loss-on-ignition (LOI), geochemistry (XRF), surface magnetic susceptibility (MS), and grain size distribution, to identify glacial sedimentation in the lake. Both radiocarbon (AMS C-14) and Pb-210 dating were applied to establish age-depth relationships in the sediment cores. A novel approach was used to calibrate the sedimentary record against a simple ELA model, which allowed reconstruction of continuous ELA changes for Alfotbreen during the Neoglacial (when Alfotbreen was present, i.e. the last similar to 1400 years). Furthermore, the resulting ELA variations were combined with an independent summer temperature record to calculate Neoglacial Pw using the 'Liestol equation'. The resulting Pw record is of higher resolution than previous reconstructions from glaciers in Norway and shows the potential of glacier records to provide high-resolution data reflecting past variations in hydroclimate. Complete deglaciation of the Alfotbreen occurred similar to 9700 cal yr BP, and the ice cap was subsequently absent or very small until a short-lived glacier event is seen in the lake sediments similar to 8200 cal yr BP. The ice cap was most likely completely melted until a new glacier event occurred around similar to 5300 cal yr BP, coeval with the onset of the Neoglacial at several other glaciers in southwestern Norway. Alfotbreen was thereafter absent (or very small) until the onset of the Neoglacial period similar to 1400 cal yr BP. The 'Little Ice Age' (LIA) similar to 650-50 cal yr BP was the largest glacier advance of Alfotbreen since deglaciation, with a maximum extent at similar to 400-200 cal yr BP, when the ELA was lowered approximately 200 m relative to today. The late onset of the Neoglacial at Alfotbreen is suggested to be a result of its low altitude relative to the regional ELA. A synthesis of Neoglacial ELA fluctuations along the coast of Norway indicates a time transgressive trend in the maximum extent of the LIA, which apparently seems to have occurred progressively later as we move northwards. We suggest that this trend is likely due to regional winter precipitation differences along the coast of Norway. (C) 2015 The Authors. Published by Elsevier Ltd.
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| 3. |
- Hormes, Anne, et al.
(author)
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Radiocarbon wiggle-match dating of proglacial lake sediments : Implications for the 8.2 ka event
- 2009
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In: Quaternary geochronology. - : Elsevier BV. - 1871-1014. ; 4:4, s. 267-277
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Research review (peer-reviewed)abstract
- The problem of insufficient age-control limits the utilisation of the 8.2 ka BP event for modelling freshwater forcing in climate change studies. High-resolution radiocarbon dates, magnetic susceptibility and lithostratigraphic evidence from a lake sediment core from Nedre Hervavatnet located at Sygnefjell in western Norway provide a record of the early Holocene. We use the method of radiocarbon wiggle-match dating of the lake sediments using the non-linear relationship between the C-14 calibration curve and the consecutive accumulation order of the sample series in order to build a high-resolution age-model. The timing and duration of Holocene environmental changes is estimated using 38 AMS radiocarbon dates on terrestrial macrofossils, insects and chironomids covering the time period from 9750 to 1180 cal BP. Chironomids, Salix and Betula leaves produce the most consistent results. Sedimentological and physical properties of the core suggest that three meltwater events with high sedimentation rates are superimposed on a long-term trend with glacier retreat between 9750 and 8000 cal BP. The lake sediment sequence of Nedre Hervavatnet demonstrates the following: only a reliable high-resolution geochronology based on carefully selected terrestrial macrofossils allows the reconstruction of a more refined and complex environmental change history before and during the 8.2 ka event.
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| 5. |
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| 6. |
- Nesje, M, et al.
(author)
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Genetic variability in peregrine falcons (Falco peregrinus) analysed by microsatellites.
- 2002
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In: Raptors in the new Millenium, eds. Yosef,R., Miller, M.L. & Pepler D. International Birding & Research Center in Eilat, Israel.. ; , s. 206-210
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Journal article (peer-reviewed)abstract
- Genetic variability and population structure in the endangered Peregrine Falcon (Falco peregrinus) were studied using DNA microsatellite markers. Special emphasis was placed on the subspecies F.p.peregrinus living in Scandinavia and Scotland. The species was almost extirpated as a breeding bird in southeastern Norway and southwestern Sweden in the 1970´s before a recovery programme was initiated. We compared the level of genetic variability of peregrines from the southern area to those found in the northern part of Scandinavia where the decline was less severe. For comparative purposes, three North American peregrine subspecis (F.p.tundrius, F.p.pealei, F.p. anatum) and one Tasmania subspecies (F.p. macropus) were included in this analyses. Twelve DNA microsatellite loci (developed from the peregrine falcon) were analysed across a total of 146 individuals. The amount of genetic variation did not differ in the peregrine populations, except for Tasmania with a significant lower genetic variability. Significant genetic differentiation was found between populations in northern and southern Scandinavia and between the Scandinavian and Scottish populations, while the populations in south-western Norway and south-eastern Sweden did not differ significantly. Analysis of cliff nesting peregrines in northern Sweden and bog nesting peregrines in northern Finland/Sweden suggests that the difference in nesting habitat is not associated with genetic differentiation. Population structuring in F.p.peregrinus is further supported by an assignment test, wherein simulated genotypes are correctly assigned to the northern and southern Scandinavian and Scottish populations with relatively high probabilities, and by analysis of allele-sharing among individuals. Cluster analyses of genetic distances grouped populations of peregrines in accordance with their subspecific designation. F.p.macropus clusters distinctly from the other four subspecies, and peregrines on either side of the Atlantic Ocean were clearly separated. Except for the Tasmanian population, the markers show a high resolving power for parentage and identity analysis, confirming their usefulness as a tool for various research and management purposes over a range of populations and subspecies.
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| 7. |
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| 8. |
- Watts, Hannah, et al.
(author)
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An Assessment of Geophysical Survey Techniques for Characterising the Subsurface Around Glacier Margins, and Recommendations for Future Applications
- 2022
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In: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 10
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Journal article (peer-reviewed)abstract
- Geophysical surveys provide an efficient and non-invasive means of studying subsurface conditions in numerous sedimentary settings. In this study, we explore the application of three geophysical methods to a proglacial environment, namely ground penetrating radar (GPR), seismic refraction and multi-channel analysis of surface waves (MASW). We apply these geophysical methods to three glacial landforms with contrasting morphologies and sedimentary characteristics, and we use the various responses to assess the applicability and limitations of each method for these proglacial targets. Our analysis shows that GPR and seismic (refraction and MASW) techniques can provide spatially extensive information on the internal architecture and composition of moraines, but careful survey designs are required to optimise data quality in these geologically complex environments. Based on our findings, we define a number of recommendations and a potential workflow to guide future geophysical investigations in analogous settings. We recommend the initial use of GPR in future studies of proglacial environments to inform (a) seismic survey design and (b) the selection of seismic interpretation techniques. We show the benefits of using multiple GPR antenna frequencies (e.g., 25 and 100 MHz) to provide decimetre scale imaging in the near surface (e.g., < 15 m) while also enabling signal penetration to targets at up to ∼40 m depth (e.g., bedrock). This strategy helps to circumvent changes in radar signal penetration resulting from variations in substrate conductivity or abundant scatterers. Our study also demonstrates the importance of combining multiple geophysical methods together with ground-truthing through sedimentological observations to reduce ambiguity in interpretations. Implementing our recommendations will improve geophysical survey practice in the field of glacial geology and allow geophysical methods to play an increasing role in the interpretation of glacial landforms and sediments.
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