| 1. |
- Alam, Assad, et al.
(författare)
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Cooperative driving according to Scoop
- 2011
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- KTH Royal Institute of Technology and Scania are entering the GCDC 2011 under the name Scoop –Stockholm Cooperative Driving. This paper is an introduction to their team and to the technical approach theyare using in their prototype system for GCDC 2011.
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| 2. |
- Sepp, Hanna, et al.
(författare)
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Children's nutrient intake at preschool and at home
- 2001
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Ingår i: Acta Paediatrica. - : Wiley. - 0803-5253 .- 1651-2227. ; 90:5, s. 483-491
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Tidskriftsartikel (refereegranskat)abstract
- A preschool-based dietary survey, using 7-d records, was carried out in a suburb of Stockholm. The aim was to assess the intake of food and the quality of the diet of preschool children aged 3-5 y at preschool and at home, and to compare the dietary intake with the Swedish dietary recommendations for preschool children. The respective mean intakes of protein, fat, carbohydrates and sucrose, expressed as a percentage of total energy intake were 14, 38, 50 and 9 at preschool, and at home 14, 36, 52 and 12 on weekdays, 14, 34, 55 and 16 on weekend days. The mean intakes of seven vitamins and minerals were low only for selenium as compared with the recommended level. No differences were found in nutrient density between diet at preschool and diet at home, with the exception of dietary fibre (higher at preschool). On weekdays there was a significantly higher nutrient density for calcium, zinc, selenium, vitamin A, riboflavin, vitamin C and dietary fibre compared with weekend days. Conclusion: The average intakes of energy and nutrients per meal at preschool compared with the recommended levels for children aged 4-6 y were low for all meals (breakfast, lunch and afternoon snack). This, however, was compensated for by home meals.
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| 3. |
- Andersson, Tommy, et al.
(författare)
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Women and men sexually violated by closely related perpetrators over a lifespan : Prevalence, revictimization, and association to adverse childhood conditions and experiences
- 2020
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Ingår i: Children and youth services review. - : Elsevier. - 0190-7409 .- 1873-7765. ; 113
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Tidskriftsartikel (refereegranskat)abstract
- Background: Being sexually violated by a perpetrator to whom one has strong emotional and social ties may be exceedingly traumatic as it involves a serious betrayal and violation of basic trust.Objective: To examine the prevalence and revictimization of this type of sexual violence in childhood, adolescence, and adulthood and its covariance with adverse psychosocial conditions and experiences in childhood.Participants and setting: A representative sample of 10,337 Swedish women and men aged 18–74.Method: A combined online and postal survey. Attrition bias was adjusted for by a calibration and weighting procedure based on official register information. Logistic regression was applied to calculate odds ratios (OR) and adjusted odds ratios (AOR).Results: The results showed that 25% of the women and 7% of the men had been sexually violated by closely related perpetrators at some time in their life. Victimization in childhood generated an OR of 4.3 (p < .001) for revictimization in adulthood. Most psychosocial indicators of an adverse childhood situation were significantly linked (OR) to victimization of sexual violence, but insignificant when controlling for the influence of confounders (AOR). The importance of the total burden of psychosocial childhood adversity was illustrated in that 12% of women and 2% of men without indicators of an adverse childhood situation were sexually victimized in adulthood, while the corresponding figures for those reporting at least nine aspects of an adverse childhood situation were 47% and 15%, respectively.Conclusion: The importance of integrating sexual victimization into a holistic psychosocial context in prevention and treatment was emphasized.
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| 4. |
- Braun, Matthias, et al.
(författare)
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Changes of glacial front positions of Vestfonna (Nordaustlandet, Svalbard)
- 2011
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 93:4, s. 301-310
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Tidskriftsartikel (refereegranskat)abstract
- Glaciers in Svalbard have shown considerable mass loss in recent years with a reported acceleration in the western and southern parts of the archipelago. However, for the ice cap Vestfonna, in northeastern Svalbard, climatic mass balance modelling has suggested almost balanced conditions over a period of nine years (2000–2009). A slightly positive geodetic mass balance (1990–2005) has been reported from a comparison of laser altimetry to older DEMs. A heterogeneous situation has been depicted for the various catchments, and hence changes in glacier extent can reveal additional information of glacier status, in particular when dealing with surge-type glaciers. We analysed a 34-year data record of multi-spectral satellite imagery in order to study changes in glacier frontal positions of the ice cap Vestfonna. A consistent pattern of almost steady retreat of the southern and north-eastern outlet glaciers of the ice cap is observed while Franklinbreen, the only major outlet glacier draining towards the north-west shows re-advance. This is consistent with an observed speed up and potential upcoming surge of this outlet. The glacier retreat on the southern coast also agrees with ICESat elevation change measurements. However, due to the glacier response time no direct relations between frontal retreat and surface mass balance can be drawn from the short observation period. The heterogeneous pattern of changes with on-going dynamic adjustments in some areas make the ice cap Vestfonna an ideal test site for future monitoring activities including novel techniques like differential interferometry from bi-static SAR systems.
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| 5. |
- Campbell, Ian, et al.
(författare)
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The evolution of surface flow stripes and stratigraphic folds within Kamb Ice Stream : why don't they match?
- 2008
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Ingår i: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 54:186, s. 421-427
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Tidskriftsartikel (refereegranskat)abstract
- Flow stripes seen in satellite imagery of ice streams and ice shelves are caused by surface undulations with kilometer-scale spacing and meter-scale relief and generally indicate current or recent fast ice flow. On a similar scale, folding of internal ice stratigraphy depicted in cross-flow icepenetrating radar profiles is also a common occurrence in ice streams, suggesting a possible relationship between the two sets of features. We have traced surface flow stripes in RADARSAT and MODIS imagery on Kamb Ice Stream, West Antarctica, from the onset of streaming flow into the near-stagnant trunk. We compare the morphology and evolution of the surface flow stripes to the folds seen in the internal stratigraphy in cross-ice-stream radar profiles. We find essentially no correspondence in the observed locations or spacings between the radar internal layer folds at depths greater than 100 m and the flow stripes on the surface. The gap in the radar data and the surface mappings in the top 100m of firn prevents a precise depiction of how the flow stripes and fold patterns at depth diverge. We explore hypotheses about how flow stripes and internal stratigraphic folds can originate and evolve differently as ice flows downstream. We suggest that flow stripes are subject to surface processes that can modify their morphology independently of the internal stratigraphy, leading to changes in the pattern of flow stripes relative to the internal layers below.
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| 6. |
- Charalampidis, Charalampos, 1983-
(författare)
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Climatology and firn processes in the lower accumulation area of the Greenland ice sheet
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Greenland ice sheet is the largest Northern Hemisphere store of fresh water, and it is responding rapidly to the warming climate. In situ observations document the changing ice sheet properties in the lower accumulation area, Southwest Greenland. Firn densities from 1840 meters above sea level retrieved in May 2012 revealed the existence of a 5.5-meter-thick, near-surface ice layer in response to the recent increased melt and refreezing in firn. As a consequence, vertical meltwater percolation in the extreme summer 2012 was inefficient, resulting in surface runoff. Meltwater percolated and refroze at six meters depth only after the end of the melt season. This prolonged autumn refreezing under the newly accumulated snowpack resulted in unprecedented firn warming with temperature at ten meters depth increased by more than four degrees Celsius. Simulations confirm that meltwater reached nine meters depth at most. The refrozen meltwater was estimated at 0.23 meters water equivalent, amounting to 25 % of the total 2012 ablation.A surface energy balance model was used to evaluate the seasonal and interannual variability of all surface energy fluxes at that elevation in the years 2009 to 2013. Due to the meltwater presence at the surface in 2012, the summer-averaged albedo was significantly reduced (0.71 in 2012; typically 0.78). A sensitivity analysis revealed that 71 % of the subsequent additional solar radiation in 2012 was used for melt, corresponding to 36 % of the total 2012 surface lowering. This interplay between melt and firn properties highlights that the lower accumulation area of the Greenland ice sheet will be responding rapidly in a warming climate.
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| 7. |
- Clemenzi, Ilaria, et al.
(författare)
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Impact of snow distribution modelling for runoff predictions
- 2023
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Ingår i: Nordic Hydrology. - : IWA Publishing. - 0029-1277 .- 1996-9694. ; 54:5, s. 633-647
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Tidskriftsartikel (refereegranskat)abstract
- Snow in the mountains is essential for the water cycle in cold regions. The complexity of the snow processes in such an environment makes it challenging for accurate snow and runoff predictions. Various snow modelling approaches have been developed, especially to improve snow predictions. In this study, we compared the ability to improve runoff predictions in the Överuman Catchment, Northern Sweden, using different parametric representations of snow distribution. They included a temperature-based method, a snowfall distribution (SF) function based on wind characteristics and a snow depletion curve (DC). Moreover, we assessed the benefit of using distributed snow observations in addition to runoff in the hydrological model calibration. We found that models with the SF function based on wind characteristics better predicted the snow water equivalent (SWE) close to the peak of accumulation than models without this function. For runoff predictions, models with the SF function and the DC showed good performances (median Nash–Sutcliffe efficiency equal to 0.71). Despite differences among the calibration criteria for the different snow process representations, snow observations in model calibration added values for SWE and runoff predictions.
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| 8. |
- Dow, Christine F., et al.
(författare)
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Modeling of subglacial hydrological development following rapid supraglacial lake drainage
- 2015
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Ingår i: Journal of Geophysical Research - Earth Surface. - 2169-9003 .- 2169-9011. ; 120:6, s. 1127-1147
-
Tidskriftsartikel (refereegranskat)abstract
- The rapid drainage of supraglacial lakes injects substantial volumes of water to the bed of the Greenland ice sheet over short timescales. The effect of these water pulses on the development of basal hydrological systems is largely unknown. To address this, we develop a lake drainage model incorporating both (1) a subglacial radial flux element driven by elastic hydraulic jacking and (2) downstream drainage through a linked channelized and distributed system. Here we present the model and examine whether substantial, efficient subglacial channels can form during or following lake drainage events and their effect on the water pressure in the surrounding distributed system. We force the model with field data from a lake drainage site, 70 km from the terminus of Russell Glacier in West Greenland. The model outputs suggest that efficient subglacial channels do not readily form in the vicinity of the lake during rapid drainage and instead water is evacuated primarily by a transient turbulent sheet and the distributed system. Following lake drainage, channels grow but are not large enough to reduce the water pressure in the surrounding distributed system, unless preexisting channels are present throughout the domain. Our results have implications for the analysis of subglacial hydrological systems in regions where rapid lake drainage provides the primary mechanism for surface-to-bed connections.
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| 9. |
- Doyle, Sam H, et al.
(författare)
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Ice tectonic deformation during the rapid in situ drainage of a supraglacial lake on the Greenland Ice Sheet
- 2013
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Ingår i: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 7:1, s. 129-140
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Tidskriftsartikel (refereegranskat)abstract
- We present detailed records of lake discharge, ice motion and passive seismicity capturing the behaviour and processes preceding, during and following the rapid drainage of a 4 km2 supraglacial lake through 1.1-km-thick ice on the western margin of the Greenland Ice Sheet. Peak discharge of 3300 m3 s−1 coincident with maximal rates of vertical uplift indicates that surface water accessed the ice–bed interface causing widespread hydraulic separation and enhanced basal motion. The differential motion of four global positioning system (GPS) receivers located around the lake record the opening and closure of the fractures through which the lake drained. We hypothesise that the majority of discharge occurred through a 3-km-long fracture with a peak width averaged across its wetted length of 0.4 m. We argue that the fracture's kilometre-scale length allowed rapid discharge to be achieved by combining reasonable water velocities with sub-metre fracture widths. These observations add to the currently limited knowledge of in situ supraglacial lake drainage events, which rapidly deliver large volumes of water to the ice–bed interface.
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| 10. |
- Doyle, Samuel H., et al.
(författare)
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Persistent flow acceleration within the interior of the Greenland ice sheet
- 2014
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 41:3, s. 899-905
-
Tidskriftsartikel (refereegranskat)abstract
- We present surface velocity measurements from a high-elevation site located 140km from the western margin of the Greenland ice sheet, and similar to 50km into its accumulation area. Annual velocity increased each year from 51.780.01myr(-1) in 2009 to 52.920.01myr(-1) in 2012a net increase of 2.2%. These data also reveal a strong seasonal velocity cycle of up to 8.1% above the winter mean, driven by seasonal melt and supraglacial lake drainage. Sole et al. (2013) recently argued that ice motion in the ablation area is mediated by reduced winter flow following the development of efficient subglacial drainage during warmer, faster, summers. Our data extend this analysis and reveal a year-on-year increase in annual velocity above the equilibrium line altitude, where despite surface melt increasing, it is still sufficiently low to hinder the development of efficient drainage under thick ice. Key Points Ice flow in the accumulation area accelerated year-on-year between 2009 and 2012 The acceleration correlates with the inland expansion of supraglacial lakes This dynamic response contrasts with observations from the ablation zone
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| 11. |
- Fornell, Rickard, 1976, et al.
(författare)
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Preliminary design and energy efficiency analysis of a kraft pulp mill converted to a biorefinery producing ethanol and DME from softwood
- 2010
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Ingår i: 19th International Congress of Chemical and Process Engineering, CHISA 2010 and 7th European Congress of Chemical Engineering, ECCE-7; Prague; Czech Republic; 28 August 2010 through 1 September 2010.
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Konferensbidrag (refereegranskat)abstract
- A conceptual biorefinery process is evaluated. The process is based on conversion of softwood to biofuels and consists of a digester according to the soda cooking principle, a cellulose to ethanol production line, and a black liquor gasification line. The main products are ethanol and dimethyl ether. Opportunities for heat integration exist. The steam surplus from the gasification plant cannot fully satisfy the steam demand of the balance of the process even if the process is well heat-integrated. However, the demand is considerably lower compared to when pulp is produced. This is an abstract of a paper presented at the 7th European Congress of Chemical Engineering-7 and the 19th International Congress of Chemical and Process Engineering CHISA (Prague, Czech Republic 8/28/2010-9/1/2010).
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| 12. |
- Fornell, Rickard, 1976, et al.
(författare)
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Preliminary Design and Energy Efficiency Analysis of a Kraft Pulp Mill Converted to a Biorefinery Producing Ethanol and DME from Softwood
- 2010
-
Ingår i: Chemical Engineering Transactions. - 2283-9216. - 9788895608051 ; Volume 21, s. 1147-1152
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Tidskriftsartikel (refereegranskat)abstract
- In this study a conceptual biorefinery process is evaluated. The process is based on conversion of softwood to biofuels, and consists of a digester according to the soda cooking principle, a cellulose to ethanol production line, and a black liquor gasification line. The main products are ethanol and DME. The focus of the study is to combine knowledge from previous research in order to generate a preliminary design and energy balance for the process. This information is then used as input in a heat integration analysis in order to assess the potential for energy efficiency measures. Since the gasification leg of the process is a heat source and the ethanol leg, pretreatment and evaporation plant are heat sinks, an important result of the heat integration analysis is to give an indication of whether the process is self sufficient with respect to heat. The study shows that large opportunities for heat integration exist. The results from the study indicate that the steam surplus from the gasification plant cannot fully satisfy the steam demand of the balance of the process, even if the process is well heat-integrated. The demand is however considerably lower compared to when pulp is produced.
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| 13. |
- Fuerst, Johannes Jakob, et al.
(författare)
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Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard
- 2017
-
Ingår i: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 11:5, s. 2003-2032
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Tidskriftsartikel (refereegranskat)abstract
- The basal topography is largely unknown beneath most glaciers and ice caps, and many attempts have been made to estimate a thickness field from other more accessible information at the surface. Here, we present a two-step reconstruction approach for ice thickness that solves mass conservation over single or several connected drainage basins. The approach is applied to a variety of test geometries with abundant thickness measurements including marine-and landterminating glaciers as well as a 2400 km(2) ice cap on Svalbard. The input requirements are kept to a minimum for the first step. In this step, a geometrically controlled, non-local flux solution is converted into thickness values relying on the shallow ice approximation (SIA). In a second step, the thickness field is updated along fast-flowing glacier trunks on the basis of velocity observations. Both steps account for available thickness measurements. Each thickness field is presented together with an error-estimate map based on a formal propagation of input uncertainties. These error estimates point out that the thickness field is least constrained near ice divides or in other stagnant areas. Withholding a share of the thickness measurements, error estimates tend to overestimate mismatch values in a median sense. We also have to accept an aggregate uncertainty of at least 25% in the reconstructed thickness field for glaciers with very sparse or no observations. For Vestfonna ice cap (VIC), a previous ice volume estimate based on the same measurement record as used here has to be corrected upward by 22 %. We also find that a 13% area fraction of the ice cap is in fact grounded below sea level. The former 5% estimate from a direct measurement interpolation exceeds an aggregate maximum range of 6-23% as inferred from the error estimates here.
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| 14. |
- Fuerst, Johannes J., et al.
(författare)
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The Ice-Free Topography of Svalbard
- 2018
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 45:21, s. 11760-11769
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Tidskriftsartikel (refereegranskat)abstract
- We present a first version of the Svalbard ice-free topography (SVIFT1.0) using a mass conserving approach for mapping glacier ice thickness. SVIFT1.0 is informed by more than 1 million point measurements, totalling more than 8,700 km of thickness profiles. SVIFT1.0 is publicly available and represents the geometric state around the year 2010. Our estimate for the total ice volume is 6,199 km(3), equivalent to 1.5-cm sea level rise. The thickness map suggests that 13% of the glacierized area is grounded below sea level. A complementary map of error estimates comprises uncertainties in the thickness surveys as well as in other input variables. Aggregated error estimates are used to define a likely ice-volume range of 5,200-7,300 km(3). The ice front thickness of marine-terminating glaciers is a key quantity for ice loss attribution because it controls the potential ice discharge by iceberg calving into the ocean. We find a mean ice front thickness of 135 m for the archipelago (likely range 123-158 m). Plain Language Summary Svalbard is an archipelago in the Arctic, north of Norway, which is comparable in size to the New York metropolitan area. Roughly half of it is covered by glacier ice. Yet to this day, the ice volume stored in the many glaciers on Svalbard is not well known. Many attempts have been made to infer a total volume estimate, but results differ substantially. This surprises because of the long research activity in this area. A large record of more than 1 million thickness measurements exists, making Svalbard an ideal study area for the application of a state-of-the-art mapping approach for glacier ice thickness. The mapping approach computes an ice volume that will raise global sea level by more than half an inch if instantaneously melted. If spread over the metropolitan area, New York would be buried beneath a 100-m ice cover. The asset of this approach is that it provides not only a thickness map for each glacier on the archipelago but also an error map that defines the likely local thickness range. Finally, we provide the first well-informed estimate of the ice front thickness of all marine-terminating glaciers that loose icebergs to the ocean. The archipelago-wide mean ice front cliff is 135 m.
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| 15. |
- Gusmeroli, Alessio, et al.
(författare)
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Twenty years of cold surface layer thinning at Storglaciaren, sub-Arctic Sweden, 1989-2009
- 2012
-
Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 58:207, s. 3-10
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents the changes in the thermal structure of the polythermal glacier Storglaciaren, northern Sweden, over the 20 year period 1989-2009 derived by comparing maps of the depth of the englacial transition between cold ice (permanently frozen) and temperate ice (which contains water inclusions). The maps are based on interpreted ice-penetrating radar surveys from 1989, 2001 and 2009. Complex thinning of the cold layer, first identified between 1989 and 2001, is still ongoing. A volume calculation shows that Storglaciaren has lost one-third of its cold surface layer volume in 20 years, with a mean thinning rate of 0.80 +/- 0.24 m a(-1). We suggest that the thinning of the cold layer at Storglaciaren is connected to the climatic warming experienced by sub-Arctic Scandinavia since the 1980s and we argue that repeated ice-penetrating radar surveys over the ablation area of polythermal glaciers offer a useful proxy for evaluating glacier responses to changes in climate.
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| 16. |
- Gusmeroli, Alessio, et al.
(författare)
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Vertical distribution of water within the polythermal Storglaciären, Sweden
- 2010
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115:F4, s. F04002-
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of water content and its distribution in polythermal glaciers is required to model their flow and thermal state. However, observ of water content variations with depth in polythermal glaciers are scarce. Water content can be estimated from radio wave speed because they depend on one another. We obtained continuous profiles of radio wave speed variations with depth from zero-offset radar profiles collected in boreholes approximately 80 m deep in the upper ablation area of Storglaciaren, northern Sweden. These profiles show that the microcrystalline water system in the temperate ice is relatively homogeneous. The overall hydrothermal structure at this location is composed of a 20 m thick upper layer of cold, water-free ice, underlain by a temperate ice layer whose average water content is 0.6% +/- 0.3%. These results are corroborated by surface radar and thermistor measurements, which show that the depth of the cold temperate transition is 21 m and the calculated water content at that transition is 0.6% +/- 0.1%. These findings imply that the whole temperate ice layer is from 3 to 4 times softer than the cold ice and, consequently, that realistic ice flow models of polythermal glaciers should include the effect of water content on viscosity.
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| 17. |
- Hedfors, Jim, et al.
(författare)
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Investigating the ratio of basal drag and driving stress in relation to bedrock topography during a melt season on Storglaciären, Sweden, using force budget analysis
- 2003
-
Ingår i: Annals of Glaciology. - : International Glaciological Society. - 0260-3055 .- 1727-5644. ; 37:1, s. 263-268
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Tidskriftsartikel (refereegranskat)abstract
- We apply the force-budget technique using the isothermal block-flow model, on Storglacia« ren, Sweden, to investigate the ratio between basal drag and driving stress in relation to a bedrock ridge in the bed topography during a peak melt season. The input data consist of glacier surface velocities collected using differential global positioning system surveying of a stake net and geometry fromprevious radar soundings and digitized ice surface maps. The study focuses on the effects of transverse bedrock ridges upon basal stress conditions.The pattern of the calculated ratio of basal drag and driving stress shows a rhythmical position of relatively high and lowbasal drags onthe stoss and lee sides, respectively, of the bedrock thresholds. One of the zones of low basal drag corresponds to the location where the highest basal sliding rate has been measured previously by borehode deformation studies. This zone also aligns with the area where the drainage system is suggested to change from englacial to subglacial.
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| 18. |
- Hills, Benjamin H., et al.
(författare)
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Radar attenuation demonstrates advective cooling in the Siple Coast ice streams
- 2022
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Ingår i: Journal of Glaciology. - : Cambridge University Press. - 0022-1430 .- 1727-5652. ; 69:275, s. 566-576
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Tidskriftsartikel (refereegranskat)abstract
- Ice streams are warmed by shear strain, both vertical shear near the bed and lateral shear at the margins. Warm ice deforms more easily, establishing a positive feedback loop in an ice stream where fast flow leads to warm ice and then to even faster flow. Here, we use radar attenuation measurements to show that the Siple Coast ice streams are colder than previously thought, which we hypothesize is due to along-flow advection of cold ice from upstream. We interpret the attenuation results within the context of previous ice-temperature measurements from nearby sites where hot-water boreholes were drilled. These in-situ temperatures are notably colder than model predictions, both in the ice streams and in an ice-stream shear margin. We then model ice temperature using a 1.5-dimensional numerical model which includes a parameterization for along-flow advection. Compared to analytical solutions, we find depth-averaged temperatures that are colder by 0.7°C in the Bindschadler Ice Stream, 2.7°C in the Kamb Ice Stream and 6.2–8.2°C in the Dragon Shear Margin of Whillans Ice Stream, closer to the borehole measurements at all locations. Modelled cooling corresponds to shear-margin thermal strengthening by 3–3.5 times compared to the warm-ice case, which must be compensated by some other weakening mechanism such as material damage or ice-crystal fabric anisotropy.
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| 19. |
- Hofstede, C., et al.
(författare)
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The Subglacial Lake That Wasn't There : Improved Interpretation From Seismic Data Reveals a Sediment Bedform at Isunnguata Sermia
- 2023
-
Ingår i: Journal of Geophysical Research - Earth Surface. - : American Geophysical Union (AGU). - 2169-9003 .- 2169-9011. ; 128:10
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Tidskriftsartikel (refereegranskat)abstract
- Radio Echo Sounding (RES) surveys conducted in May 2010 and April 2011 revealed a 2 km(2) flat area with increased bed reflectivity at the base of Isunnguata Sermia at the western margin of the Greenland Ice Sheet. This flat reflector was located within a localized subglacial hydraulic potential (hydropotential) minimum, as part of a complex and elongated trough system. By analogy with comparable features in Antarctica, the initial interpretation of such a feature was a potential subglacial lake. In September 2013 a co-located seismic survey revealed a 1,750 m by 540 and 37 m thick stratified lens-shaped bedform at the base of a subglacial trough system. Amplitude Versus Angle (AVA) analysis yields a derived reflection coefficient R = 0.09 +/- 0.14 indicative of consolidated sediments possibly overlain by dilatant till. The bed and flank on the northern side of the trough consist of unconsolidated, possibly water-bearing sediments with R = -0.10 +/- 0.08, whereas on the southern side it consists of more consolidated material. We interpret the trough as a key component of the wider subglacial drainage network, for which the sediments on its northern side act as a localized water-storage reservoir. Given the observation of seasonally forming and rapidly draining supraglacial meltwater lakes in this area, we interpret the lens-shaped bedform as deposited by episodically ponding meltwater within the subglacial trough system. Our results highlight the importance of transient subglacial hydrological and sedimentological processes such as drainage events for the interaction of ice sheets and their substrates, to understand ice dynamics in a warming climate. Plain Language Summary A ground based radar survey in West Greenland showed an unusually flat, highly reflective zone in an otherwise rough bed suggesting a possible subglacial lake beneath the ice. The highly reflective zone was part of a drainage system transporting meltwater under the ice sheet. We performed a detailed seismic survey across the area which, unlike radar signals, has the advantage of penetrating through the overlying ice into any rock, sediments and water below it. Analysis of our reflection data reveal that the flat area was in fact an elongated lens-shaped bedform consisting of layered (stratified) sediments. However at a larger angle of incidence, analysis showed the bedform is possibly overlain by a thin layer of water-bearing sediments likely saturated by ponding water. Our interpretation is that episodically draining meltwater from upstream is locally accumulating beneath the ice sheet at this locality, thereby depositing the lens-shaped bedform over many melt seasons.
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| 20. |
- Ignatiuk, Dariusz, et al.
(författare)
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Ground penetrating radar measurement of snow in Svalbard - past, present, future (SnowGPR)
- 2023
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Ingår i: SESS report 2022 - The State of Environmental Science in Svalbard - an annual report. - : Svalbard Integrated Arctic Earth Observing System (SIOS).
-
Bokkapitel (refereegranskat)abstract
- This is chapter 5 of the State of Environmental Science in Svalbard (SESS) report 2022.Snowpack covers 60-100% of all land in Svalbard, depending on the season, and it is very sensitive to changes in climate. Knowledge about the snowpack is important not just in itself, but also to understand how snow cover affects other components of Svalbard’s natural environment – land, sea, permafrost, glaciers, and the ecosystems that they support. Monitoring the evolution of Svalbard’s snow cover will be crucial as the world’s climate continues to warm.Ground-penetrating radars (GPRs) towed by snowmobile across glaciers and snowfields provide vital information about snowpack thickness and structure. Ideally, such surveys should be repeated annually for continuous monitoring of climate-induced change. Three decades ago, a GPR programme catalogued regional variations in snow accumulation. This should be repeated and expanded to cover all of Svalbard. The GPR method should also be further developed e.g. by mounting GPRs on drones, giving access to parts of glaciers that are too dangerous for researchers to visit. Lastly, women are encouraged to join the field of GPR-based research on snow.Most of the GPR data collected so far are not currently available in any data repository. The comprehensive compilation of available studies presented in this report, and the recommendations for metadata and data quality, are important first steps to making GPR data more accessible.
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| 21. |
- Ingvander, Susanne, 1979-, et al.
(författare)
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Comparison between digital and manual methods of snow grain size determination
- 2012
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Ingår i: Hydrology Research. - : IWA Publishing. - 0029-1277 .- 2224-7955. ; 43:3, s. 192-202
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Tidskriftsartikel (refereegranskat)abstract
- Maintaining long time series of observations of the Cryosphere is a key issue in climate research. Long observational time series involve problems due to change in methodology or observers. In order to extend time series and introduce new methods, careful comparisons must be made to ensure homogeneity in the observational data. We have compared an established method for snow grain-size observations used by the Abisko Scientific Research Station (ASRS) in northern Sweden, based on visual interpretation, with a newly developed method for Digital Snow Particle Properties (DSPP) analysis. Transition from subjective visual method into digital reproducible analysis creates less subjective and more comparable results. The ASRS method generates size classifications excluding quantitative analysis size ranges. By determining the sizes of the classified snow using the DSPP-method, actual size ranges for classified snow can be established. By performing a digital analysis of the reference samples and the snow samples classified, we can compare the ASRS classification system to existing official classification systems. The results indicate underestimation of the visual particle size in comparison to the reference samples. Our results show how to quantify the historical data set, which enables us to perform quantitative analysis on the historical data set.
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| 22. |
- Ingvander, Susanne, et al.
(författare)
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Comparison of digital and manual methods of snow particle size estimation
- 2012
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Ingår i: Hydrology Research. - : IWA Publishing. - 0029-1277 .- 2224-7955. ; 43:3, s. 192-202
-
Tidskriftsartikel (refereegranskat)abstract
- Maintaining long time series of observations of the Cryosphere is a key issue in climate research. Long observational time series involve problems due to change in methodology or observers. In order to extend time series and introduce new methods, careful comparisons must be made to ensure homogeneity in the observational data. We have compared an established method for snow grain-size observations used by the Abisko Scientific Research Station (ASRS) in northern Sweden, based on visual interpretation, with a newly developed method for Digital Snow Particle Properties (DSPP) analysis. Transition from subjective visual method into digital reproducible analysis creates less subjective and more comparable results. The ASRS method generates size classifications excluding quantitative analysis size ranges. By determining the sizes of the classified snow using the DSPP method, actual size ranges for classified snow can be established. By performing a digital analysis of the reference samples and the snow samples classified, we can compare the ASRS classification system to existing official classification systems. The results indicate underestimation of the visual particle size in comparison to the reference samples. Our results show how to quantify the historical data set, which enables us to perform quantitative analysis on the historical data set.
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| 23. |
- Jacobel, Robert W., et al.
(författare)
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Spatial variation of radar-derived basal conditions on Kamb Ice Stream, West Antarctica
- 2009
-
Ingår i: Annals of Glaciology. - : International Glaciological Society. - 0260-3055 .- 1727-5644. ; 50:51, s. 10-16
-
Tidskriftsartikel (refereegranskat)abstract
- Radar profiles of bed echo intensity can survey conditions at the ice-bed interface and test for the presence or absence of water. However, extracting information about basal conditions from bed echo intensities requires an estimate of the attenuation loss through the ice. We used the relationship between bed echo intensities from constant-offset radar data and ice thickness to estimate depth-averaged attenuation rates at several locations on and near Kamb Ice Stream (KIS), West Antarctica. We found values varying from 29 dB km−1 at Siple Dome to 15 dB km−1 in the main trunk region of KIS, in agreement with a previous measurement and models. Using these attenuation-rate values, we calculated the relative bed reflectivity throughout our KIS surveys and found that most of the bed in the trunk has high basal reflectivities, similar to those obtained in the location of boreholes that found water at the bed. Areas of lower bed reflectivity are limited to the sticky spot, where a borehole found a dry bed, and along the margins of KIS. These results support previous hypotheses that the basal conditions at locations like the sticky spot on KIS control its stagnation and possible reactivation.
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| 24. |
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| 25. |
- Jansson, Peter, et al.
(författare)
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Assessing the possibility to couple the chemical signal in winter snow on Storglaciären to atmospheric climatology
- 2007
-
Ingår i: Annals of Glaciology. - : International Glaciological Society. - 0260-3055 .- 1727-5644. ; 46:1, s. 335-341
-
Tidskriftsartikel (refereegranskat)abstract
- Winter accumulation on glaciers in temperate to sub-arctic climate regimes is determined by both precipitation and snowdrifting during repeated events during any particular winter. Since glacier mass balance is calculated from the sum of winter and summer balance, and summer balance can be modeled with high accuracy, identification of the coupling between atmospheric circulation and winter balance is essential in order to fully understand the climate information hidden in the glacier mass-balance records. We have sampled snow cores from Storglaciären, Sweden, to examine identifiable chemical signatures to link these with up-wind sources in an attempt to quantify how much accumulation occurs under given atmospheric conditions. The snow samples reveal that several different chemical signatures occur but that identifying their source is not trivial, although only few but distinct sources exist. The relationship between the identified strata of a given signature is difficult to couple to recorded precipitation events because the crucial timing of deposition is lacking in our investigation. If time control on snow deposition is available, the combination of snow chemistry, meteorological and climatological data is a promising tool for evaluating the coupling between snow accumulation and atmospheric circulation.
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| 26. |
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| 27. |
- Jansson, Peter, et al.
(författare)
-
Spatial and Temporal Characteristics of a Long Mass Balance Record, Storglaciären, Sweden
- 2007
-
Ingår i: Arctic, Antarctic and Alpine research. - 1523-0430 .- 1938-4246. ; 39:3, s. 432-437
-
Tidskriftsartikel (refereegranskat)abstract
- Glacier fluctuations constitute an important indicator for climate change, both current and past. Glacier mass balance measurements are made to correctly reflect the state of the glacier. Very few studies have been made to study the representability of each point measurement to the average mass balance of a particular glacier, an exercise that requires a large number of measurements. Such studies are rare due to the practical constraints and costs involved in collecting data. On Storglaciären, Sweden, a very dense system of measurements of both distributed winter (~100 points km-2) and summer (~15 points km-2) balance allows a spatial analysis of the mass balance components. The results show that local summer balance values are strongly correlated to the average summer balance value of the glacier. Local winter balance values are also generally well correlated to the average winter balance value, but small areas on the glacier exhibit no correlation. These areas correspond to wind-eroded areas of low accumulation on the glacier. The local net balance values are also well correlated to the average net balance value, indicating that the effect of the summer balance is strong and, at least partly, counter-balancing the spatial inhomogeneities in the local spatial winter balance values. These results show that detailed knowledge of both mass balance components and their spatial variability may be necessary to safely use a sparse system of measurements points. On Storglaciären, this is especially true for winter balance measurements since the spatial snow distribution is highly variable and not necessarily representative of the glacier average at each measurement point. The results strictly apply to Storglaciären but similar effects should be present on most glaciers in a similar setting; the results thus serve as an example of conditions that can be expected on a typical mid-latitude to subarctic glacier.
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| 28. |
- Kassab, Christine M., et al.
(författare)
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Formation and evolution of an extensive blue ice moraine in central Transantarctic Mountains, Antarctica
- 2020
-
Ingår i: Journal of Glaciology. - : CAMBRIDGE UNIV PRESS. - 0022-1430 .- 1727-5652. ; 66:255, s. 49-60
-
Tidskriftsartikel (refereegranskat)abstract
- Mount Achernar moraine is a terrestrial sediment archive that preserves a record of ice-sheet dynamics and climate over multiple glacial cycles. Similar records exist in other blue ice moraines elsewhere on the continent, but an understanding of how these moraines form is limited. We propose a model to explain the formation of extensive, coherent blue ice moraine sequences based on the integration of ground-penetrating radar (GPR) data with ice velocity and surface exposure ages. GPR transects (100 and 25 MHz) both perpendicular and parallel to moraine ridges at Mount Achernar reveal an internal structure defined by alternating relatively clean ice and steeply dipping debris bands extending to depth, and where visible, to the underlying bedrock surface. Sediment is carried to the surface from depth along these debris bands, and sublimates out of the ice, accumulating over time (>300 ka). The internal pattern of dipping reflectors, combined with increasing surface exposure ages, suggest sequential exposure of the sediment where ice and debris accretes laterally to form the moraine. Subsurface structure varies across the moraine and can be linked to changes in basal entrainment conditions. We speculate that higher concentrations of debris may have been entrained in the ice during colder glacial periods or entrained more proximal to the moraine sequence.
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| 29. |
- Kulessa, Bernd, et al.
(författare)
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Seismic evidence for complex sedimentary control of Greenland Ice Sheet flow
- 2017
-
Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 3:8
-
Tidskriftsartikel (refereegranskat)abstract
- The land-terminating margin of the Greenland Ice Sheet has slowed down in recent decades, although the causes and implications for future ice flow are unclear. Explained originally by a self-regulating mechanism where basal slip reduces as drainage evolves from low to high efficiency, recent numerical modeling invokes a sedimentary control of ice sheet flow as an alternative hypothesis. Although both hypotheses can explain the recent slowdown, their respective forecasts of a long-term deceleration versus an acceleration of ice flow are contradictory. We present amplitude-versus-angle seismic data as the first observational test of the alternative hypothesis. We document transient modifications of basal sediment strengths by rapid subglacial drainages of supraglacial lakes, the primary current control on summer ice sheet flow according to our numerical model. Our observations agree with simulations of initial postdrainage sediment weakening and ice flow accelerations, and subsequent sediment restrengthening and ice flow decelerations, and thus confirm the alternative hypothesis. Although simulated melt season acceleration of ice flow due to weakening of subglacial sediments does not currently outweigh winter slowdown forced by self regulation, they could dominate over the longer term. Subglacial sediments beneath the Greenland Ice Sheet must therefore be mapped and characterized, and a sedimentary control of ice flow must be evaluated against competing self-regulation mechanisms.
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| 30. |
- Kävrestad, Joakim, 1989-, et al.
(författare)
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The language effect in phishing susceptibility
- 2020
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Ingår i: Proceedings of the 6th International Workshop on Socio-Technical Perspective in IS Development (STPIS 2020). - : CEUR-WS. ; , s. 162-167
-
Konferensbidrag (refereegranskat)abstract
- Phishing has been, and remains to be, one of the most common types of social engineering. It is the act of tricking users to perform actions they normally wouldn’t using e-mail. Since phishing involves using technical measures to trick users, it is a social technical phenomenon that must be understood from the technical as well as the social side. While phishing and phishing susceptibility has been researched for decades, the effect of language ability on phishing susceptibility is underresearched. In this paper, we conducted a survey where we had swedes rate their English ability before classifying e-mails in Swedish and English as fraudulent or legitimate. The results shows that the respondents English ability does affect the ability to correctly identify legitimate emails and brings another piece to the puzzle of phishing susceptibility.
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| 31. |
- Levy, J. S., et al.
(författare)
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Decadal topographic change in the McMurdo Dry Valleys of Antarctica : Thermokarst subsidence, glacier thinning, and transfer of water storage from the cryosphere to the hydrosphere
- 2018
-
Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 323, s. 80-97
-
Tidskriftsartikel (refereegranskat)abstract
- Recent local-scale observations of glaciers, streams, and soil surfaces in the McMurdo Dry Valleys of Antarctica (MDV) have documented evidence for rapid ice loss, glacial thinning, and ground surface subsidence associated with melting of ground ice. To evaluate the extent, magnitude, and location of decadal-scale landscape change in the MDV, we collected airborne lidar elevation data in 2014-2015 and compared these data to a 2001-2002 airborne lidar campaign. This regional assessment of elevation change spans the recent acceleration of warming and melting observed by long-term meteorological and ecosystem response experiments, allowing us to assess the response of MDV surfaces to warming and potential thawing feedbacks. We find that locations of thermokarst subsidence are strongly associated with the presence of excess ground ice and with proximity to surface or shallow subsurface (active layer) water. Subsidence occurs across soil types and landforms, in low-lying, low-slope areas with impeded drainage and also high on steep valley walls. Glacier thinning is widespread and is associated with the growth of fine-scale roughness. Pond levels are rising in most closed-basin lakes in the MDV, across all microclimate zones. These observations highlight the continued importance of insolation-driven melting in the MDV. The regional melt pattern is consistent with an overall transition of water storage from the local cryosphere (glaciers, permafrost) to the hydrosphere (dosed basin lakes and ponds as well as the Ross Sea). We interpret this regional melting pattern to reflect a transition to Arctic and alpine-style, hydrologically mediated permafrost and glacial melt.
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| 32. |
- Lindbäck, Katrin, et al.
(författare)
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High-resolution ice thickness and bed topography of a land-terminating section of the Greenland Ice Sheet
- 2014
-
Ingår i: Earth System Science Data. - : Copernicus GmbH. - 1866-3508 .- 1866-3516. ; 6:2, s. 331-338
-
Tidskriftsartikel (refereegranskat)abstract
- We present ice thickness and bed topography maps with a high spatial resolution (250-500 m) of a land-terminating section of the Greenland Ice Sheet derived from ground-based and airborne radar surveys. The data have a total area of similar to 12 000 km(2) and cover the whole ablation area of the outlet glaciers of Isunnguata Sermia, Russell, Leverett, Orkendalen and Isorlersuup up to the long-term mass balance equilibrium line altitude at similar to 1600m above sea level. The bed topography shows highly variable subglacial trough systems, and the trough of Isunnguata Sermia Glacier is overdeepened and reaches an elevation of similar to 500m below sea level. The ice surface is smooth and only reflects the bedrock topography in a subtle way, resulting in a highly variable ice thickness. The southern part of our study area consists of higher bed elevations compared to the northern part. The compiled data sets of ground-based and airborne radar surveys cover one of the most studied regions of the Greenland Ice Sheet and can be valuable for detailed studies of ice sheet dynamics and hydrology. The combined data set is freely available at doi:10.1594/pangaea.830314.
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| 33. |
- Lindbäck, Katrin
(författare)
-
Hydrology and Bed Topography of the Greenland Ice Sheet : Last known surroundings
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increased temperatures in the Arctic accelerate the loss of land based ice stored in glaciers. The Greenland Ice Sheet is the largest ice mass in the Northern Hemisphere and holds ~10% of all the freshwater on Earth, equivalent to ~7 metres of global sea level rise. A few decades ago, the mass balance of the Greenland Ice Sheet was poorly known and assumed to have little impact on global sea level rise. The development of regional climate models and remote sensing of the ice sheet during the past decade have revealed a significant mass loss. To monitor how the Greenland Ice Sheet will affect sea levels in the future requires understanding the physical processes that govern its mass balance and movement. In the southeastern and central western regions, mass loss is dominated by the dynamic behaviour of ice streams calving into the ocean. Changes in surface mass balance dominate mass loss from the Greenland Ice Sheet in the central northern, southwestern and northeastern regions. Little is known about what the hydrological system looks like beneath the ice sheet; how well the hydrological system is developed decides the water’s impact on ice movement. In this thesis, I have focused on radar sounding measurements to map the subglacial topography in detail for a land-terminating section of the western Greenland Ice Sheet. This knowledge is a critical prerequisite for any subglacial hydrological modelling. Using the high-resolution ice thickness and bed topography data, I have made the following specific studies: First, I have analysed the geological setting and glaciological history of the region by comparing proglacial and subglacial spectral roughness. Second, I have analysed the subglacial water drainage routing and revealed a potential for subglacial water piracy between adjacent subglacial water catchments with changes in the subglacial water pressure regime. Finally, I have looked in more detail into englacial features that are commonly observed in radar sounding data from western Greenland. In all, the thesis highlights the need not only for accurate high-resolution subglacial digital elevation models, but also for regionally optimised interpolation when conducting detailed hydrological studies of the Greenland Ice Sheet.
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| 34. |
|
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| 35. |
- Lindbäck, Katrin, et al.
(författare)
-
Spectral roughness and glacial erosion of a land-terminating section of the Greenland Ice Sheet
- 2015
-
Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 238, s. 149-159
-
Tidskriftsartikel (refereegranskat)abstract
- Spectral roughness offers a significant potential for understanding the evolution of glaciated landscapes. Here, we present the first roughness study combining a high-resolution (250 to 500 m) DEM of a large land-terminating section (12,000 km2) of the Greenland Ice Sheet with the topography of the proglacial area. Subglacial roughness shows a directional dependence with consistently lower values in the ice flow direction compared to the across–flow direction. We find a correlation between low basal roughness, fast ice flow, and subglacial troughs. The northern part of the subglacial study area has an undulating topography with variable roughness, resembling the landscape in the proglacial area. In this area, there is a glacially eroded, overdeepened trough with bed elevations 510 m below sea level, consistent with warm ice and a well-lubricated bed. The southern part of the subglacial study area has higher bed elevations and higher roughness than the northern part, possibly because the bedrock consists of hard granitic gneiss as in the adjacent proglacial area. The subglacial troughs, which have been eroded to various extents, are aligned with geological weakness zones suggesting a preglacial origin. In general, there is a major geological control on the distribution of bed variability.
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| 36. |
- Lindbäck, Katrin, et al.
(författare)
-
Subglacial topography, ice thickness, and bathymetry of Kongsfjorden, northwestern Svalbard
- 2018
-
Ingår i: Earth System Science Data. - : COPERNICUS GESELLSCHAFT MBH. - 1866-3508 .- 1866-3516. ; 10:4, s. 1769-1781
-
Tidskriftsartikel (refereegranskat)abstract
- Svalbard tidewater glaciers are retreating, which will affect fjord circulation and ecosystems when glacier fronts become land-terminating. Knowledge of the subglacial topography and bathymetry under retreating glaciers is important to modelling future scenarios of fjord circulation and glacier dynamics. We present high-resolution (150m gridded) digital elevation models of subglacial topography, ice thickness, and ice surface elevation of five tidewater glaciers in Kongsfjorden (1100 km(2)), northwestern Spitsbergen, based on similar to 1700 km airborne and ground-based ice-penetrating radar profiles. The digital elevation models (DEMs) cover the tidewater glaciers Blomstrandbreen, Conwaybreen, Kongsbreen, Kronebreen, and Kongsvegen and are merged with bathymetric and land DEMs for the non-glaciated areas. The large-scale subglacial topography of the study area is characterized by a series of troughs and highs. The minimum subglacial elevation is 180m above sea level (a.s.l.), the maximum subglacial elevation is 1400m a.s.l., and the maximum ice thickness is 740m. Three of the glaciers, Kongsbreen, Kronebreen, and Kongsvegen, have the potential to retreat by similar to 10 km before they become land-terminating. The compiled data set covers one of the most studied regions in Svalbard and is valuable for future studies of glacier dynamics, geology, hydrology, and fjord circulation.
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| 37. |
- Lindbäck, Katrin, et al.
(författare)
-
Subglacial water drainage, storage, and piracy beneath the Greenland Ice Sheet
- 2015
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 42:18, s. 7606-7614
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Meltwater drainage across the surface of the Greenland Ice Sheet (GrIS) is well constrained by measurements and modeling, yet despite its critical role, knowledge of its transit through the subglacial environment remains limited. Here we present a subglacial hydrological analysis of a land-terminating sector of the GrIS at unprecedented resolution that predicts the routing of surface-derived meltwater once it has entered the basal drainage system. Our analysis indicates the probable existence of small subglacial lakes that remain undetectable by methods using surface elevation change or radar techniques. Furthermore, the analysis suggests transient behavior with rapid switching of subglacial drainage between competing catchments driven by seasonal changes in the basal water pressure. Our findings provide a cautionary note that should be considered in studies that attempt to relate and infer future response from surface temperature, melt, and runoff from point measurements and/or modeling with measurements of proglacial discharge and ice dynamics.
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| 38. |
- Marchenko, Sergey, et al.
(författare)
-
A plot-scale study of firn stratigraphy at Lomonosovfonna, Svalbard, using ice cores, borehole video and GPR surveys in 2012–14
- 2017
-
Ingår i: Journal of Glaciology. - : Cambridge University Press (CUP). - 0022-1430 .- 1727-5652. ; 63:237, s. 67-78
-
Tidskriftsartikel (refereegranskat)abstract
- Spatial heterogeneity of snow and firn properties on glaciers introduces uncertainty in interpretation of point and profile observations and complicates modelling of meltwater percolation and runoff. Here we present a study of the temporal and spatial dynamics of firn density and stratigraphy at the plot-scale (approximate to 10 m x 10 m x 10 m) repeated annually during 2012-14 at the Lomonosovfonna ice-field, Svalbard. Results from cores, video inspections in boreholes and radar grid surveys are compared. Ice layers 0.1-50 cm thick comprised approximate to 8% of the borehole length. Most of them are 1-3 cm thick and could not be traced between boreholes separated by 3 m. Large lateral variability of firn structure affects representativeness of observations in single holes and calls for repeated studies in multiple points to derive a representative stratigraphy signal. Radar reflections are poorly correlated with ice layers in individual boreholes. However, the match between the high amplitude peaks in the grid-averaged radar signal and horizons of preferential ice layer formation revealed by averaging the video surveys over multiple boreholes is higher. These horizons are interpreted as buried firn layers previously exposed to melt-freeze or wind-driven densification and several of them are consistently recovered throughout three field campaigns.
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| 39. |
- Marchenko, Sergey A., et al.
(författare)
-
Water content of firn at Lomonosovfonna, Svalbard, derived from subsurface temperature measurements
- 2021
-
Ingår i: Journal of Glaciology. - : Cambridge University Press. - 0022-1430 .- 1727-5652. ; 67:265, s. 921-932
-
Tidskriftsartikel (refereegranskat)abstract
- The potential of capillary forces to retain water in pores is an important property of snow and firn at glaciers. Meltwater suspended in pores does not contribute to runoff and may refreeze during winter, which can affect the climatic mass balance and the subsurface density and temperature. However, measurement of firn water content is challenging and few values have been reported in the literature. Here, we use subsurface temperature and density measured at the accumulation zone of Lomonosovfonna (1200 m a.s.l.), Svalbard, to derive water content of the firn profiles after the 2014 and 2015 melt seasons. We do this by comparing measured and simulated rates of freezing front propagation. The calculated volumetric water content of firn is ~1.0–2.5 vol.% above the depth of 5 m and <0.5 vol.% below. Results derived using different thermistor strings suggest a prominent lateral variability in firn water content. Reported values are considerably lower than those commonly used in snow/firn models. This is interpreted as a result of preferential water flow in firn leaving dry volumes within wetted firn. This suggests that the implementation of irreducible water content values below 0.5 vol.% within snow/firn models should be considered at the initial phase of water infiltration.
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| 40. |
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| 41. |
- Marchenko, Sergey, et al.
(författare)
-
Parameterizing deep water percolation improves subsurface temperature simulations by a multilayer firn model
- 2017
-
Ingår i: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 5:16
-
Tidskriftsartikel (refereegranskat)abstract
- Deep preferential percolation of melt water in snow and firn brings water lower along the vertical profile than a laterally homogeneous wetting front. This widely recognized process is an important source of uncertainty in simulations of subsurface temperature, density, and water content in seasonal snow and in firn packs on glaciers and ice sheets. However, observation and quantification of preferential flow is challenging and therefore it is not accounted for by most of the contemporary snow/firn models. Here we use temperature measurements in the accumulation zone of Lomonosovfonna, Svalbard, done in April 2012-2015 using multiple thermistor strings to describe the process of water percolation in snow and firn. Effects of water flow through the snow and firn profile are further explored using a coupled surface energy balance - firn model forced by the output of the regional climate model WRF. In situ air temperature, radiation, and surface height change measurements are used to constrain the surface energy and mass fluxes. To account for the effects of preferential water flow in snow and firn we test a set of depth-dependent functions allocating a certain fraction of the melt water available at the surface to each snow/firn layer. Experiments are performed for a range of characteristic percolation depths and results indicate a reduction in root mean square difference between the modeled and measured temperature by up to a factor of two compared to the results from the default water infiltration scheme. This illustrates the significance of accounting for preferential water percolation to simulate subsurface conditions. The suggested approach to parameterization of the preferential water flow requires low additional computational cost and can be implemented in layered snow/ firn models applied both at local and regional scales, for distributed domains with multiple mesh points.
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| 42. |
- Marchenko, Sergey, 1988-
(författare)
-
Subsurface fluxes of mass and energy at the accumulation zone of Lomonosovfonna ice cap, Svalbard
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Glaciers cover ca 10% of the Earth's land and are found in the high altitudes and latitudes. They are important components of environmental systems due to the multiple feedbacks linking them with the atmosphere, hydrosphere and periglacial landscapes. The cold sloping surfaces of glaciers change the patterns of atmospheric circulation at different scales and at the same time glaciers are largely controlled by climate. They are commonly used as climatic archives for reconstruction of the past environmental changes based on evidences from the areas affected by glaciation at the moment and in the past. Glaciers are the largest fresh-water reservoirs on our planet and runoff thereof significantly affects the global sea level and life in glaciated catchments. However, melt- and rain-induced runoff from glaciers greatly depends on the subsurface conditions which thus need to be taken into account, particularly in a changing climate.This thesis focuses on the processes of subsurface mass and energy exchange in the accumulation zones of glaciers, which are largely driven by the climate at the surface. Results are largely based on empirical data from Lomonosovfonna ice cap, Svalbard, collected during field campaigns in 2012-2017. Observations of subsurface density and stratigraphy using shallow cores, video records from boreholes and radar surveys returned detailed descriptions of the snow and firn layering. The subsurface temperature data collected using multiple thermistor strings provided insights into several subsurface processes. The temperature values measured during three summer seasons were used to constrain the suggested parameterization of deep preferential water flow through snow and firn. The part of data recorded during the cold seasons was employed for an inverse modelling exercise resulting in optimized values of effective thermal conductivity of the subsurface profile. These results are then used to compute the subsurface water content by comparing the simulated and measured rates of freezing front propagation after the melt season in 2014.The field observations and quantitative estimates provide further empirical evidences of preferential water flow in snow/firn packs at glaciers. Results presented in the thesis call for implementation of description of the process in layered models simulating the subsurface fluxes of energy and mass at glaciers. This will result in a better understanding of glacier response to the past and future climatic changes and more accurate estimates of glacier runoff.
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| 43. |
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| 44. |
- Mikkelsen, Andreas Bech, et al.
(författare)
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Extraordinary runoff from the Greenland ice sheet in 2012 amplified by hypsometry and depleted firn retention
- 2016
-
Ingår i: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 10:3, s. 1147-1159
-
Tidskriftsartikel (refereegranskat)abstract
- It has been argued that the infiltration and retention of meltwater within firn across the percolation zone of the Greenland ice sheet has the potential to buffer up to similar to 3.6aEuro-mm of global sea-level rise (Harper et al., 2012). Despite evidence confirming active refreezing processes above the equilibrium line, their impact on runoff and proglacial discharge has yet to be assessed. Here, we compare meteorological, melt, firn stratigraphy and discharge data from the extreme 2010 and 2012 summers to determine the relationship between atmospheric forcing and melt runoff at the land-terminating Kangerlussuaq sector of the Greenland ice sheet, which drains into the Watson River. The 6.8aEuro-km(3) bulk discharge in 2012 exceeded that in 2010 by 28aEuro-%, despite only a 3aEuro-% difference in net incoming melt energy between the two years. This large disparity can be explained by a 10aEuro-% contribution of runoff originating from above the long-term equilibrium line in 2012 caused by diminished firn retention. The amplified 2012 response was compounded by catchment hypsometry; the disproportionate increase in area contributing to runoff as the melt-level rose high into the accumulation area. Satellite imagery and aerial photographs reveal an extensive supraglacial network extending 140aEuro-km from the ice margin that confirms active meltwater runoff originating well above the equilibrium line. This runoff culminated in three days with record discharge of 3100aEuro-m(3)aEuro-s(-1) (0.27aEuro-GtaEuro-d(-1)) that peaked on 11 July and washed out the Watson River Bridge. Our findings corroborate melt infiltration processes in the percolation zone, though the resulting patterns of refreezing are complex and can lead to spatially extensive, perched superimposed ice layers within the firn. In 2012, such layers extended to an elevation of at least 1840aEuro-m and provided a semi-impermeable barrier to further meltwater storage, thereby promoting widespread runoff from the accumulation area of the Greenland ice sheet that contributed directly to proglacial discharge and global sea-level rise.
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| 45. |
- Nuth, C., et al.
(författare)
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Decadal changes from a multi-temporal glacier inventory of Svalbard
- 2013
-
Ingår i: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 7:5, s. 1603-1621
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Tidskriftsartikel (refereegranskat)abstract
- We present a multi-temporal digital inventory of Svalbard glaciers with the most recent from the late 2000s containing 33 775 km(2) of glaciers covering 57% of the total land area of the archipelago. At present, 68% of the glacierized area of Svalbard drains through tidewater glaciers that have a total terminus width of similar to 740 km. The glacierized area over the entire archipelago has decreased by an average of 80 km(2) a(-1) over the past similar to 30 yr, representing a reduction of 7%. For a sample of similar to 400 glaciers (10 000 km(2)) in the south and west of Spitsbergen, three digital inventories are available from the 1930/60s, 1990 and 2007 from which we calculate average changes during 2 epochs. In the more recent epoch, the terminus retreat was larger than in the earlier epoch, while area shrinkage was smaller. The contrasting pattern may be explained by the decreased lateral wastage of the glacier tongues. Retreat rates for individual glaciers show a mix of accelerating and decelerating trends, reflecting the large spatial variability of glacier types and climatic/dynamic response times in Svalbard. Lastly, retreat rates estimated by dividing glacier area changes by the tongue width are larger than centerline retreat due to a more encompassing frontal change estimate with inclusion of lateral area loss.
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| 46. |
- Pettersson, Rickard, et al.
(författare)
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Cold surface layer thinning on Storglaciären, Sweden, observed by repeated ground penetrating radar surveys
- 2003
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Ingår i: Journal of Geophysical Research. - Washington D.C. : American Geophysical Union. - 0148-0227. ; 108:F1, s. 5.1-5.9
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Tidskriftsartikel (refereegranskat)abstract
- A characteristic feature of ground penetrating radar (GPR) surveys on polythermal glaciers is an internal reflection presumably caused by the cold temperate transition surface (CTS), hence providing a possible tool for mapping thermal structure with high accuracy. Comparison of detailed temperature measurements in bore holes and GPR profiles at 345 MHz and 800 MHz center frequencies on Storglaciären, Sweden, show that the CTS can be detected and mapped with an accuracy of about ±1 m at both frequencies. A comparison between comprehensive GPR surveys of the cold surface layer, separated by 12 years (1989-2001), shows a substantial and complex thinning of the cold layer. An overall decrease of 8.3 m (22% of average thickness) of the CTS depth is much larger than uncertainties in CTS depth determinations. The stability of the cold surface layer depends on the net ice ablation at the surface and the downward migration of CTS. There is no evidence of substantial increased net ablation between the survey dates that could explain the observed thinning. However, small increase in average winter air temperature, a limiting factor for the temperature gradient through the cold surface layer, may provide a partial explanation. The weaker temperature gradient reduces the transport of latent heat from the CTS, thus slowing down its downward migration.
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| 47. |
- Pettersson, Rickard, 1972-
(författare)
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Dynamics of the cold surface layer of polythermal Storglaciären, Sweden
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polythermal glaciers, i.e. glaciers with a combination of ice at and below the freezing point, are widespread in arctic and subarctic environments. The polythermal structure has major implications for glacier hydrology, ice flow and glacial erosion. However, the interplay of factors governing its spatial and temporal variations such as net mass balance, ice advection and water content in the ice is poorly investigated and as yet not fully understood. This study deals with a thorough investigation of the polythermal regime on Storglaciären, northern Sweden, a small valley glacier with a cold surface layer in the ablation area. Extensive field work was performed including mapping of the cold surface layer using ground-penetrating radar, ice temperature measurements, mass balance and ice velocity measurements. Analyses of these data combined with numerical modelling were used specifically to investigate the spatial and temporal variability of the cold surface layer, the spatial distribution of the water content just below the cold surface layer transition, the effect of radar frequency on the detection of the surface layer, and the sensitivity of the cold surface layer to changes in forcing.A comparison between direct temperature measurements in boreholes and ground-penetrating surveys shows that the radar-inferred cold-temperate transition depth is within ±1 m from the melting point of ice at frequencies above ~300 MHz. At frequencies below ~155 MHz, the accuracy degrades because of reduced scattering efficiency that occurs when the scatterers become much smaller compared to the wavelength. The mapped spatial pattern of the englacial cold-temperate transition boundary is complex. This pattern reflects the observed spatial variation in net loss of ice at the surface by ablation and vertical advection of ice, which is suggested to provide the predominant forcing of the cold surface layer thickness pattern. This is further supported by thermomechanical modeling of the cold surface layer, which indicates high sensitivity of the cold surface layer thickness to changes in vertical advection rates.The water content is the least investigated quantity that is relevant for the thermal regime of glaciers, but also the most difficult to assess. Spatial variability of absolute water content in the temperate ice immediately below the cold surface layer on Storglaciären was determined by combining relative estimates of water content from ground-penetrating radar data with absolute determination from temperature measurements and the thermal boundary condition at the freezing front. These measurements indicate large-scale spatial variability in the water content, which seems to arise from variations in entrapment of water at the firn-ice transition. However, this variability cannot alone explain the spatial pattern in the thermal regime on Storglaciären.Repeated surveys of the cold surface layer show a 22% average thinning of the cold surface layer on Storglaciären between 1989 and 2001. Transient thermomechanical modeling results suggest that the cold surface layer adapts to new equilibrium conditions in only a few decades after a perturbation in the forcing is introduced. An increased winter air temperature since mid-1980s seems to be the cause of the observed thinning of the cold surface layer. Over the last decades, mass balance measurements indicate that the glacier has been close to a steady state. The quasi-steady state situation is also reflected in the vertical advection, which shows no significant changes during the last decades. Increased winter temperatures at the ice surface would result in a slow-down of the formation of cold ice at the base of the cold surface layer and lead to a larger imbalance between net loss of ice at the surface and freezing of temperate ice at the cold-temperate transition.
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| 48. |
- Pettersson, Rickard
(författare)
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Frequency dependence in detection of the cold-temperate transition surface in a polythermal glacier
- 2005
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Ingår i: Radio Sience. - Washington D.C. : American Geophysical Union. - 0048-6604. ; 40:RS3007
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Tidskriftsartikel (refereegranskat)abstract
- Radar surveys of the cold-temperate transition in polythermal glaciers have been used to investigate the polythermal structure, as well as the stability of the temperature regime, in glaciers. The mapping is based on the detection of small water-filled pockets present in the temperate ice beneath the cold surface layer. I compare radar profiles recorded at different frequencies on a polythermal glacier to show that the apparent depth to the cold-temperate transition reflection at a center frequency of 155 MHz is significantly greater than that detected at frequencies above 345 MHz. This increase appears to be the result of a reduction of scattering efficiency from the uppermost part of the temperate ice, as the theory of electromagnetic scattering from small objects indicates a strong decrease in scattering efficiency from objects much smaller than the wavelength of the incident wave. Thus I interpret this apparent depth increase to indicate that the average radii of the water pockets of the cold-temperate transition is on a subdecimeter scale. Spatial variation in the difference between cold-temperate transition depths at 155 MHz and higher frequencies may arise from spatial variations in size or the number density of scatterers.
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| 49. |
- Pettersson, Rickard, et al.
(författare)
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Ice thickness and basal conditions of Vestfonna ice cap, eastern Svalbard
- 2011
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 93A:4, s. 311-322
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Tidskriftsartikel (refereegranskat)abstract
- We combined ground-based pulsed radar data collected in 20082009 with airborne radio-echo sounding data acquired in 1983 and 1986 over Vestfonna ice cap, Svalbard. The airborne dataset mainly covers the fast-flowing outlet glaciers and the marginal zone, while the ground-based data explicitly cover the interior part of the ice cap. The data presented here are thus the first complete estimate of bed topography and ice thickness. The subglacial landscape undulates with elevations between -160 and +410 m above sea level. The mean ice thickness is 186 m and the total ice area and volume are 2402 km2 and 442 +/- 0.6 km3, respectively. This is a much smaller volume than those derived from empirical volume-area scaling relationships currently used to estimate regional-to-global glacier volumes. This difference may depend on local conditions for Vestfonna and emphasizes the need to include more volume observations in the derivations of volume-area scaling parameters. We also derive basal reflectivity as a proxy for thermal conditions at the bed. Basal reflectivity values suggest that fast-flowing outlet glaciers are underlain by temperate conditions. The geometric boundaries and basal conditions for Vestfonna will be critical additions to the development of numerical models of the ice cap and to the estimation of more accurate area-volume scaling parameters.
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| 50. |
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