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  • 1.
    Braun, Matthias
    et al.
    University of Alaska.
    Pohjola, Veijo A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Möller, Marco
    Finkelnburg, Roman
    Falk, Ulrike
    Scherer, Dieter
    Schneider, Christoph
    Changes of glacial front positions of Vestfonna (Nordaustlandet, Svalbard)2011In: Geografiska Annaler. Series A, Physical Geography, ISSN 0435-3676, E-ISSN 1468-0459, Vol. 93, no 4, p. 301-310Article in journal (Refereed)
    Abstract [en]

    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.

  • 2. Campbell, Ian
    et al.
    Jacobel, Robert
    Welch, Brian
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    The evolution of surface flow stripes and stratigraphic folds within Kamb Ice Stream: why don't they match?2008In: Journal of Glaciology, ISSN 0022-1430, E-ISSN 1727-5652, Vol. 54, no 186, p. 421-427Article in journal (Refereed)
    Abstract [en]

    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.

  • 3. Dow, Christine F.
    et al.
    Kulessa, B.
    Rutt, I.C.
    Tsai, V. C.
    Pimentel, S.
    Doyle, S. H.
    van As, D.
    Lindbäck, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Jones, G. A.
    Hubbard, A.
    Modeling of subglacial hydrological development following rapid supraglacial lake drainage2015In: Journal of Geophysical Research - Earth Surface, ISSN 2169-9003, E-ISSN 2169-9011, Vol. 120, no 6, p. 1127-1147Article in journal (Refereed)
    Abstract [en]

    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.

  • 4. Doyle, Sam H
    et al.
    Hubbard, Alun H
    Dow, Christine F
    Jones, Glenn A
    Fitzpatrick, Andrew
    Gusmeroli, Alessio
    Kulessa, Bernd
    Lindbäck, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Box, Jason E
    Ice tectonic deformation during the rapid in situ drainage of a supraglacial lake on the Greenland Ice Sheet2013In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 7, no 1, p. 129-140Article in journal (Refereed)
    Abstract [en]

    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.

  • 5. Doyle, Samuel H.
    et al.
    Hubbard, Alun
    Fitzpatrick, Andrew A. W.
    van As, Dirk
    Mikkelsen, Andreas B.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Hubbard, Bryn
    Persistent flow acceleration within the interior of the Greenland ice sheet2014In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 41, no 3, p. 899-905Article in journal (Refereed)
    Abstract [en]

    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 <list list-type="bulleted" id="grl51335-list-0001"> <list-item id="grl51335-li-0001">Ice flow in the accumulation area accelerated year-on-year between 2009 and 2012 <list-item id="grl51335-li-0002">The acceleration correlates with the inland expansion of supraglacial lakes <list-item id="grl51335-li-0003">This dynamic response contrasts with observations from the ablation zone

  • 6.
    Fuerst, Johannes J.
    et al.
    Univ Erlangen Nurnberg, Inst Geog, Erlangen, Germany.
    Navarro, Francisco
    Univ Politecn Madrid, Dept Matemat Aplicada Tecnol Informac & Comunicac, ETSI Telecomunicac, Madrid, Spain.
    Gillet-Chaulet, Fabien
    Inst Geosci Environm, Grenoble, France;Univ Grenoble Alpes, CNRS, IRD, Grenoble INP,IGE, Grenoble, France.
    Huss, Matthias
    Univ Fribourg, Dept Geosci, Fribourg, Switzerland;Swiss Fed Inst Technol, Lab Hydraul Hydrol & Glaciol, Zurich, Switzerland.
    Moholdt, Geir
    Norwegian Polar Res Inst, Fram Ctr, Tromso, Norway.
    Fettweis, Xavier
    Univ Liege, Dept Geog, Liege, Belgium.
    Lang, Charlotte
    Univ Liege, Dept Geog, Liege, Belgium.
    Seehaus, Thorsten
    Univ Erlangen Nurnberg, Inst Geog, Erlangen, Germany.
    Ai, Songtao
    Wuhan Univ, Chinese Antarctic Ctr Surveying & Mapping, Wuhan, Hubei, Peoples R China.
    Benham, Toby J.
    Univ Cambridge, Scott Polar Res Inst, Cambridge, England.
    Benn, Douglas I.
    Univ St Andrews, St Andrews Glaciol, Sch Geog & Sustainable Dev, St Andrews, Fife, Scotland.
    Bjornsson, Helgi
    Univ Iceland, Inst Earth Sci, Reykjavik, Iceland.
    Dowdeswell, Julian A.
    Univ Cambridge, Scott Polar Res Inst, Cambridge, England.
    Grabiec, Mariusz
    Univ Silesia Katowice, Fac Earth Sci, Katowice, Poland.
    Kohler, Jack
    Norwegian Polar Res Inst, Fram Ctr, Tromso, Norway.
    Lavrentiev, Ivan
    Russian Acad Sci, Inst Geog, Moscow, Russia.
    Lindback, Katrin
    Norwegian Polar Res Inst, Fram Ctr, Tromso, Norway.
    Melvold, Kjetil
    Univ Erlangen Nurnberg, Inst Geog, Erlangen, Germany;Univ Fribourg, Dept Geosci, Fribourg, Switzerland;Norwegian Water Resources & Energy Directorate NV, Oslo, Norway.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Rippin, David
    Univ York, Dept Environm, York, N Yorkshire, England.
    Saintenoy, Albane
    Univ Paris Saclay, Univ Paris Sud, GEOPS, CNRS, Orsay, France.
    Sanchez-Gamez, Pablo
    Departamento de Matemática Aplicada a las Tecnologías de la Información y las Comunicaciones, ETSI de Telecomunicación, Universidad Politécnica de Madrid, , Madrid, Spain.
    Schuler, Thomas V.
    Univ Oslo, Dept Geosci, Oslo, Norway;UNIS Univ Ctr Svalbard, Dept Arctic Geophys, Longyearbyen, Norway.
    Sevestre, Heidi
    Univ St Andrews, St Andrews Glaciol, Sch Geog & Sustainable Dev, St Andrews, Fife, Scotland.
    Vasilenko, Evgeny
    Acad Sci Uzbek, Inst Ind Res Akadempribor, Tashkent, Uzbekistan.
    Braun, Matthias H.
    Univ Erlangen Nurnberg, Inst Geog, Erlangen, Germany.
    The Ice-Free Topography of Svalbard2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 21, p. 11760-11769Article in journal (Refereed)
    Abstract [en]

    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.

  • 7.
    Fuerst, Johannes Jakob
    et al.
    University of Erlangen-Nuremberg, Institute of Geography.
    Gillet-Chaulet, Fabien
    University of Grenoble Alpes, CNRS, IRD, Institut des Géosciences de l’Environnement (IGE).
    Benham, Toby J.
    University of Cambridge, Scott Polar Research Institute.
    Dowdeswell, Julian A.
    University of Cambridge, Scott Polar Research Institute.
    Grabiec, Mariusz
    University of Silesia in Katowice, Faculty of Earth Sciences.
    Navarro, Francisco
    Universidad Politécnica de Madrid, Departamento de Matemática Aplicada a las Tecnologías de la Información y las Comunicaciones, desp. A302-4, ETSI de Telecomunicación .
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Moholdt, Geir
    Norwegian Polar Institute, Fram Centre.
    Nuth, Christopher
    University of Oslo, Department of Geoscience.
    Sass, Björn
    University of Erlangen-Nuremberg, Institute of Geography.
    Aas, Kjetil
    University of Oslo, Department of Geoscience.
    Fettweis, Xavier
    University of Liège, Department of Geography.
    Lang, Charlotte
    University of Liège, Department of Geography.
    Seehaus, Thorsten
    University of Erlangen-Nuremberg, Institute of Geography.
    Braun, Matthias
    University of Erlangen-Nuremberg, Institute of Geography.
    Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard2017In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 11, no 5, p. 2003-2032Article in journal (Refereed)
    Abstract [en]

    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.

  • 8.
    Gusmeroli, Alessio
    et al.
    University of Fairbanks.
    Jansson, Peter
    Stockholm University.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Murray, Tavi
    University of Swansea.
    Twenty years of cold surface layer thinning at Storglaciären, sub-Arctic Sweden, 1989-20092012In: Journal of Glaciology, ISSN 0022-1430, E-ISSN 1727-5652, Vol. 58, no 207, p. 3-10Article in journal (Refereed)
    Abstract [en]

    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.

  • 9. Gusmeroli, Alessio
    et al.
    Murray, Tavi
    Jansson, Peter
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Aschwanden, Andy
    Booth, Adam D.
    Vertical distribution of water within the polythermal Storglaciären, Sweden2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, no F4, p. F04002-Article in journal (Refereed)
    Abstract [en]

    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.

  • 10.
    Hedfors, Jim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Peyaud, Vincent
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Pohjola, Veijo A
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Jansson, Peter
    Department of Physical Geogr aphy and Quaternary Geology , Stockholm University .
    Pettersson, Rickard
    Department of Physical Geogr aphy and Quaternary Geology , Stockholm University .
    Investigating the ratio of basal drag and driving stress in relation to bedrock topography during a melt season on Storglaciären, Sweden, using force budget analysis2003In: Annals of Glaciology, ISSN 0260-3055, Vol. 37, no 1, p. 263-268Article in journal (Refereed)
    Abstract [en]

    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.

  • 11.
    Ingvander, Susanne
    et al.
    Institutionen för för naturgeografi och kvartärgeologi, Stockholms universitet.
    Johansson, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Jansson, Peter
    Institutionen för för naturgeografi och kvartärgeologi, Stockholms universitet.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Comparison of digital and manual methods of snow particle size estimation2012In: Hydrology Research, ISSN 0029-1277, Vol. 43, no 3, p. 192-202Article in journal (Refereed)
    Abstract [en]

    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.

  • 12. Jansson, Peter
    et al.
    Linderholm, Hans
    Pettersson, Rickard
    Karlin, Torbjörn
    Mörth, Carl-Magnus
    Assessing the possibility to couple the chemical signal in winter snow on Storglaciären to atmospheric climatology2007In: Annals of Glaciology, ISSN 0260-3055, E-ISSN 1727-5644, Vol. 46, no 1, p. 335-341Article in journal (Refereed)
    Abstract [en]

    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.

  • 13. Jansson, Peter
    et al.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Spatial and Temporal Characteristics of a Long Mass Balance Record, Storglaciären, Sweden2007In: Arctic, Antarctic and Alpine research, ISSN 1523-0430, E-ISSN 1938-4246, Vol. 39, no 3, p. 432-437Article in journal (Refereed)
    Abstract [en]

    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.

  • 14.
    Kulessa, Bernd
    et al.
    Swansea Univ, Glaciol Grp, Coll of Sci.
    Hubbard, Alun L.
    UiT Arctic Univ Norway, Ctr Arctic Gas Hydrate Environm & Climate, Dept Geosci.; Aberystwyth Univ, Ctr Glaciol, Dept Geog & Earth Sci.
    Booth, Adam D.
    Univ Leeds, Inst Appl Geosci, Sch Earth & Environm.
    Bougamont, Marion
    Univ Cambridge, Scott Polar Res Inst, Dept Geog.
    Dow, Christine F.
    Swansea Univ, Glaciol Grp, Coll Sci, Singleton Pk.; Univ Waterloo, Dept Geog & Environm Management.
    Doyle, Samuel H.
    Aberystwyth Univ, Ctr Glaciol, Dept Geog & Earth Sci.
    Christoffersen, Poul
    Univ Cambridge, Scott Polar Res Inst, Dept Geog.
    Lindback, Katrin
    Norwegian Polar Res Inst, Fram Ctr.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Fitzpatrick, Andrew A. W.
    Aberystwyth Univ, Ctr Glaciol, Dept Geog & Earth Sci.
    Jones, Glenn A.
    Swansea Univ, Glaciol Grp, Coll of Sci.; Aberystwyth Univ, Ctr Glaciol, Dept Geog & Earth Sci.
    Seismic evidence for complex sedimentary control of Greenland Ice Sheet flow2017In: Science Advances, ISSN 0036-8156, E-ISSN 2375-2548, Vol. 3, no 8, article id e1603071Article in journal (Refereed)
    Abstract [en]

    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.

  • 15.
    Levy, J. S.
    et al.
    Colgate Univ, Dept Geol, 13 Oak Ave, Hamilton, NY 13346 USA.
    Fountain, A. G.
    Portland State Univ, Dept Geol, Portland, OR 97201 USA.
    Obryk, M. K.
    US Geol Survey, Cascades Volcano Observ, Vancouver, WA 98683 USA.
    Telling, J.
    Univ Houston, Dept Civil & Environm Engn, Natl Ctr Airborne Laser Mapping, Houston, TX 77004 USA.
    Glennie, C.
    Univ Houston, Dept Civil & Environm Engn, Natl Ctr Airborne Laser Mapping, Houston, TX 77004 USA.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Gooseff, M.
    Univ Colorado, Dept Civil Environm & Architectural Engn, Boulder, CO 80303 USA.
    Van Horn, Dj.
    Univ New Mexico, Dept Biol, Albuquerque, NM 87131 USA.
    Decadal topographic change in the McMurdo Dry Valleys of Antarctica: Thermokarst subsidence, glacier thinning, and transfer of water storage from the cryosphere to the hydrosphere2018In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 323, p. 80-97Article in journal (Refereed)
    Abstract [en]

    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.

  • 16.
    Lindbäck, Katrin
    et al.
    Norwegian Polar Res Inst, Framsentret, Postboks 6606, N-9296 Tromso, Norway.
    Kohler, Jack
    Norwegian Polar Res Inst, Framsentret, Postboks 6606, N-9296 Tromso, Norway.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Nuth, Christopher
    Univ Oslo, Postboks 1047 Blindern, N-0316 Oslo, Norway.
    Langley, Kirsty
    Asiaq Greenland Survey, Postboks 1003, Nuuk 3900, Greenland.
    Messerli, Alexandra
    Norwegian Polar Res Inst, Framsentret, Postboks 6606, N-9296 Tromso, Norway.
    Vallot, Dorothée
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Matsuoka, Kenichi
    Norwegian Polar Res Inst, Framsentret, Postboks 6606, N-9296 Tromso, Norway.
    Brandt, Ola
    Norwegian Coastal Adm, Kystveien 30, N-4841 Arendal, Norway.
    Subglacial topography, ice thickness, and bathymetry of Kongsfjorden, northwestern Svalbard2018In: Earth System Science Data, ISSN 1866-3508, E-ISSN 1866-3516, Vol. 10, no 4, p. 1769-1781Article in journal (Refereed)
    Abstract [en]

    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.

  • 17.
    Lindbäck, Katrin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Spectral roughness and glacial erosion of a land-terminating section of the Greenland Ice Sheet2015In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 238, p. 149-159Article in journal (Refereed)
    Abstract [en]

    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.

  • 18.
    Lindbäck, Katrin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Doyle, S. H.
    Helanow, C.
    Jansson, P.
    Kristensen, S. S.
    Stenseng, L.
    Forsberg, R.
    Hubbard, A. L.
    High-resolution ice thickness and bed topography of a land-terminating section of the Greenland Ice Sheet2014In: Earth System Science Data, ISSN 1866-3508, E-ISSN 1866-3516, Vol. 6, no 2, p. 331-338Article in journal (Refereed)
    Abstract [en]

    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 ~12 000 km2 and cover the whole ablation area of the outlet glaciers of Isunnguata Sermia, Russell, Leverett, Ørkendalen and Isorlersuup up to the long-term mass balance equilibrium line altitude at ~1600 m 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 ~500 m 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.

  • 19.
    Lindbäck, Katrin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Hubbard, Alun L.
    Doyle, Sam H.
    van As, Dirk
    Mikkelsen, Andreas B.
    Fitzpatrick, Andrew A.
    Subglacial water drainage, storage, and piracy beneath the Greenland Ice Sheet2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 18, p. 7606-7614Article in journal (Other academic)
    Abstract [en]

    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.

  • 20.
    Lindbäck, Katrin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Svensson, Anna
    Origin of englacial features in radio-echo sounding data from the Greenland Ice SheetManuscript (preprint) (Other academic)
  • 21.
    Marchenko, Sergey
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Cheng, Gong
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Lötstedt, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Pohjola, Veijo
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    van Pelt, Ward
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Reijmer, Carleen
    Thermal conductivity of firn at Lomonosovfonna, Svalbard, derived from subsurface temperature measurements2019In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 13, p. 1843-1859Article in journal (Refereed)
  • 22.
    Marchenko, Sergey
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Univ Ctr Svalbard, Dept Geophys, Longyearbyen, Norway..
    Pohjola, Veijo A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    van Pelt, Ward J. J.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Vega, Carmen P.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Machguth, Horst
    Univ Zurich, Dept Geog, Zurich, Switzerland..
    Bøggild, Carl
    Tech Univ Denmark, Ctr Arctic Technol, Copenhagen, Denmark..
    Isaksson, Elisabeth
    Norwegian Polar Res Inst, Tromso, Norway..
    A plot-scale study of firn stratigraphy at Lomonosovfonna, Svalbard, using ice cores, borehole video and GPR surveys in 2012–142017In: Journal of Glaciology, ISSN 0022-1430, E-ISSN 1727-5652, Vol. 63, no 237, p. 67-78Article in journal (Refereed)
    Abstract [en]

    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.

  • 23.
    Marchenko, Sergey
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Department of Geophysics, The University Centre in Svalbard, Longyearbyen, Norway.
    Van Pelt, Ward
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Carlsson, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pohjola, Veijo
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Machguth, Horst
    Reijmer, Carleen
    Parameterizing deep water percolation improves subsurface temperature simulations by a multilayer firn model2017In: Frontiers in Earth Science, ISSN 2296-6463, Vol. 5, no 16Article in journal (Refereed)
    Abstract [en]

    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.

  • 24.
    Mikkelsen, Andreas Bech
    et al.
    Univ Copenhagen, Dept Geosci & Nat Resource Management, Copenhagen, Denmark.;Univ Copenhagen, Ctr Permafrost CENPERM, Oster Voldgade 10, DK-1350 Copenhagen, Denmark..
    Hubbard, Alun
    Univ Tromso, Ctr Arctic Gas Hydrate Environm & Climate, Dept Geol, Dramsveien 201, N-9037 Tromso, Norway.;Aberystwyth Univ, Dept Geog & Earth Sci, Ctr Glaciol, Aberystwyth SY23 3DB, Dyfed, Wales..
    MacFerrin, Mike
    Univ Colorado, Cooperat Inst Res Environm Sci CIRES, Boulder, CO 80309 USA..
    Box, Jason Eric
    Geol Survey Denmark & Greenland, Dept Glaciol & Climate, Copenhagen, Denmark..
    Doyle, Sam H.
    Aberystwyth Univ, Dept Geog & Earth Sci, Ctr Glaciol, Aberystwyth SY23 3DB, Dyfed, Wales..
    Fitzpatrick, Andrew
    Aberystwyth Univ, Dept Geog & Earth Sci, Ctr Glaciol, Aberystwyth SY23 3DB, Dyfed, Wales..
    Hasholt, Bent
    Univ Copenhagen, Dept Geosci & Nat Resource Management, Copenhagen, Denmark..
    Bailey, Hannah L.
    Helmholtz Ctr Polar & Marine Res, Alfred Wegener Inst, Periglacial Res Sect, D-14473 Potsdam, Germany..
    Lindbäck, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Extraordinary runoff from the Greenland ice sheet in 2012 amplified by hypsometry and depleted firn retention2016In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 10, no 3, p. 1147-1159Article in journal (Refereed)
    Abstract [en]

    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.

  • 25. Nuth, C.
    et al.
    Kohler, J.
    Konig, M.
    von Deschwanden, A.
    Hagen, J. O.
    Kaab, A.
    Moholdt, G.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Decadal changes from a multi-temporal glacier inventory of Svalbard2013In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 7, no 5, p. 1603-1621Article in journal (Refereed)
    Abstract [en]

    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.

  • 26.
    Pettersson, Rickard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Christoffersen, Poul
    Dowdeswell, Julian A.
    Pohjola, Veijo A
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Hubbard, Alun
    Strozzi, Tazio
    Ice thickness and basal conditions of Vestfonna ice cap, eastern Svalbard2011In: Geografiska Annaler. Series A, Physical Geography, ISSN 0435-3676, E-ISSN 1468-0459, Vol. 93A, no 4, p. 311-322Article in journal (Refereed)
    Abstract [en]

    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.

  • 27. Pettersson, Rickard
    et al.
    Jansson, Peter
    Huwald, Hendrik
    Blatter, Heinz
    Spatial pattern and stability of the cold surface layer of Storglaciären, Sweden2007In: Journal of Glaciology, ISSN 0022-1430, E-ISSN 1727-5652, Vol. 53, no 180, p. 99-109Article in journal (Refereed)
    Abstract [en]

    The mechanisms controlling the spatial distribution and temporal fluctuations of the thermal structure in polythermal glaciers have, to date, been poorly investigated and are not fully understood. We have investigated the sensitivity of the cold surface layer thickness to different forcing parameters and the causes for an observed thinning of the cold surface layer on Storglaciären, northern Sweden, between 1989 and 2001 using a one-dimensional thermomechanical model and measurements of ice surface temperature, vertical velocity and net mass balance. Similarities between the spatial patterns of the cold surface layer, net mass balance and emergence velocity together with modelled high sensitivity to variations in emergence velocities suggest that the net ablation and vertical ice advection are the dominant forcing parameters. Results from transient model experiments suggest that the cold surface layer reaches a new equilibrium after a perturbation in the forcing within a few decades. No significant change in ice flow or mass balance has been observed at Storglaciären in recent decades. Instead, an increase of 1°C in winter air temperature since the mid-1980s is probably the cause of the observed thinning of the cold surface layer. Increased winter temperatures at the ice surface result in a reduced formation rate 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 surface. Model results indicate that the cold surface layer is more sensitive to changes in ice surface temperature in areas with lower emergence velocity, which explains the observed complex thinning pattern of the cold surface layer.

  • 28.
    Pohjola, Veijo A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Christoffersen, Poul
    Kolondra, Leszek
    Moore, John C.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Schäfer, Martina
    Strozzi, Tazio
    Reijmer, Carleen H.
    Spatial distribution and change in the surface ice-velocity field of Vestfonna ice cap, Nordaustlandet, Svalbard, 1995-2010 using geodetic and satellite interferometry data2011In: Geografiska Annaler. Series A, Physical Geography, ISSN 0435-3676, E-ISSN 1468-0459, Vol. 93, no 4, p. 323-335Article in journal (Refereed)
    Abstract [en]

    During 2007 we launched a geodetic campaign on the Svalbard ice cap Vestfonna in order to estimate the velocity field of the ice cap. This was done within the frame of the IPY project KINNVIKA. We present here the velocity measurements derived from our campaigns 2007–2010 and compare the geodetic measurements against InSAR velocity fields from satellite platforms from 1995/96 and 2008. We find the spatial distribution of ice speeds from the InSAR is in good agreement within the uncertainty limits with our geodetic measurements. We observe no clear indication of seasonal ice speed differences, but we find a speed-up of the outlet glacier Franklinbreen between the InSAR campaigns, and speculate the outlet is having a surge phase.

  • 29.
    Ruskeeniemi, Timo
    et al.
    Geol Survey Finland, FI-02150 Espoo, Finland.
    Engstrom, Jon
    Geol Survey Finland, FI-02150 Espoo, Finland.
    Lehtimaki, Jukka
    Geol Survey Finland, FI-02150 Espoo, Finland.
    Vanhala, Heikki
    Geol Survey Finland, FI-02150 Espoo, Finland.
    Korhonen, Kimmo
    Geol Survey Finland, FI-02150 Espoo, Finland.
    Kontula, Anne
    Posiva Oy, FI-27160 Eurajoki, Finland.
    Liljedahl, Lillemor Claesson
    Swedish Nucl Fuel & Waste Management Co, Box 3091, SE-16903 Solna, Sweden.
    Naslund, Jens-Ove
    Swedish Nucl Fuel & Waste Management Co, Box 3091, SE-16903 Solna, Sweden.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala Univ, Dept Earth Sci, SE-75236 Uppsala, Sweden.
    Subglacial permafrost evidencing re-advance of the Greenland Ice Sheet over frozen ground2018In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 199, p. 174-187Article in journal (Refereed)
    Abstract [en]

    Greenland Ice Sheet (GrIS) covers an area of 1.7 million km(2). It has been an important source of climate information and the air temperature history of Greenland is well known. However, the thermal history and temperature conditions of the Greenland bedrock are poorly known. There are only few records on the temperature of the proglacial bedrock and no records on bedrock temperature underneath the ice sheet. The Greenland Analogue Project (GAP) recently investigated hydrological, hydrogeological and geochemical processes in Kangerlussuaq, West Greenland. Because permafrost has a major hydrological impact in Arctic regions, the cryogenic structure of the bedrock was an important research topic. From previous studies it was already known that Kangerlussuaq is located within the zone of continuous permafrost. Temperature profiling in a new research borehole, extending horizontally 30 m underneath the ice sheet, revealed that permafrost is 350 m deep at the ice margin. This result raised the question how far the permafrost extends under the ice sheet? In order to investigate the thermal properties, we made a series of electromagnetic (EM) soundings at the ice margin area - on proglacial area and on the ice sheet - and detected, that subglacial permafrost extends at least 2 km from the ice margin to inland. We also observed a patchy unfrozen sediment layer between the ice and the frozen bedrock. Possible existence of subglacial sediments and their role in ice dynamics has been debated in many recent papers. Our successful campaign shows that geophysics can be used for bedrock investigations through thick ice, which is known to be challenging for electromagnetic methods. Our results provide the first direct evidence supporting the proposed Holocene ice re-advance over frozen ground, and contribute to the discussion on the rapid climate changes in past, to the future of the ice sheet under warming climate and hydrogeology at the ice margin.

  • 30. Schafer, M.
    et al.
    Gillet-Chaulet, F.
    Gladstone, R.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pohjola, Veijo A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Strozzi, T.
    Zwinger, T.
    Assessment of heat sources on the control of fast flow of Vestfonna ice cap, Svalbard2014In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 8, no 5, p. 1951-1973Article in journal (Refereed)
    Abstract [en]

    Understanding the response of fast flowing ice streams or outlet glaciers to changing climate is crucial in order to make reliable projections of sea level change over the coming decades. Motion of fast outlet glaciers occurs largely through basal motion governed by physical processes at the glacier bed, which are not yet fully understood. Various subglacial mechanisms have been suggested for fast flow but common to most of the suggested processes is the requirement of presence of liquid water, and thus temperate conditions. We use a combination of modelling, field, and remote observations in order to study links between different heat sources, the thermal regime and basal sliding in fast flowing areas on Vestfonna ice cap. A special emphasis lies on Franklinbreen, a fast flowing outlet glacier which has been observed to accelerate recently. We use the ice flow model Elmer/Ice including a Weertman type sliding law and a Robin inverse method to infer basal friction parameters from observed surface velocities. Firn heating, i.e. latent heat release through percolation of melt water, is included in our model; its parameterisation is calibrated with the temperature record of a deep borehole. We found that strain heating is negligible, whereas friction heating is identified as one possible trigger for the onset of fast flow. Firn heating is a significant heat source in the central thick and slow flowing area of the ice cap and the essential driver behind the ongoing fast flow in all outlets. Our findings suggest a possible scenario of the onset and maintenance of fast flow on the Vestfonna ice cap based on thermal processes and emphasise the role of latent heat released through refreezing of percolating melt water for fast flow. However, these processes cannot yet be captured in a temporally evolving sliding law. In order to simulate correctly fast flowing outlet glaciers, ice flow models not only need to account fully for all heat sources, but also need to incorporate a sliding law that is not solely based on the basal temperature, but also on hydrology and/or sediment physics.

  • 31. Schäfer, M.
    et al.
    Zwinger, T.
    Christoffersen, P.
    Gillet-Chaulet, F.
    Laakso, K.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pohjola, Veijo A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Strozzi, T.
    Moore, John C.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Sensitivity of basal conditions in an inverse model: Vestfonna ice cap, Nordaustlandet/Svalbard2012In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 6, no 4, p. 771-783Article in journal (Refereed)
    Abstract [en]

    The dynamics of Vestfonna ice cap (Svalbard) are dominated by fast-flowing outlet glaciers. Its mass balance is poorly known and affected dynamically by these fast-flowing outlet glaciers. Hence, it is a challenging target for ice flow modeling. Precise knowledge of the basal conditions and implementation of a good sliding law are crucial for the modeling of this ice cap. Here we use the full-Stokes finite element code Elmer/Ice to model the 3-D flow over the whole ice cap. We use a Robin inverse method to infer the basal friction from the surface velocities observed in 1995. Our results illustrate the importance of the basal friction parameter in reproducing observed velocity fields. We also show the importance of having variable basal friction as given by the inverse method to reproduce the velocity fields of each outlet glacier-a simple parametrization of basal friction cannot give realistic velocities in a forward model. We study the robustness and sensitivity of this method with respect to different parameters (mesh characteristics, ice temperature, errors in topographic and velocity data). The uncertainty in the observational parameters and input data proved to be sufficiently small as not to adversely affect the fidelity of the model.

  • 32.
    Sevestre, Heidi
    et al.
    Univ St Andrews, Sch Geog & Sustainable Dev, St Andrews, Fife, Scotland.
    Benn, Douglas I.
    Univ St Andrews, Sch Geog & Sustainable Dev, St Andrews, Fife, Scotland.
    Luckman, Adrian
    Swansea Univ, Dept Geog, Coll Sci, Swansea, W Glam, Wales;Univ Ctr Svalbard, Dept Arctic Geophys, Longyearbyen, Norway.
    Nuth, Christopher
    Univ Oslo, Fac Math & Nat Sci, Dept Geosci, Oslo, Norway.
    Kohler, Jack
    Norwegian Polar Res Inst, Tromso, Norway.
    Lindback, Katrin
    Norwegian Polar Res Inst, Tromso, Norway.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tidewater Glacier Surges Initiated at the Terminus2018In: Journal of Geophysical Research - Earth Surface, ISSN 2169-9003, E-ISSN 2169-9011, Vol. 123, no 5, p. 1035-1051Article in journal (Refereed)
    Abstract [en]

    There have been numerous reports that surges of tidewater glaciers in Svalbard were initiated at the terminus and propagated up-glacier, in contrast with downglacier-propagating surges of land-terminating glaciers. Most of these surges were poorly documented, and the cause of this behavior was unknown. We present detailed data on the recent surges of two tidewater glaciers, Aavatsmarkbreen and Wahlenbergbreen, in Svalbard. High-resolution time series of glacier velocities and evolution of crevasse patterns show that both surges propagated up-glacier in abrupt steps. Prior to the surges, both glaciers underwent retreat and steepening, and in the case of Aavatsmarkbreen, we demonstrate that this was accompanied by a large increase in driving stress in the terminal zone. The surges developed in response to two distinct processes. (1) During the late quiescent phase, internal thermodynamic processes and/or retreat from a pinning point caused acceleration of the glacier front, leading to the development of terminal crevasse fields. (2) Crevasses allowed surface meltwater and rainwater to access the bed, causing flow acceleration and development of new crevasses up-glacier. Upward migration of the surge coincided with stepwise expansion of the crevasse field. Geometric changes near the terminus of these glaciers appear to have led to greater strain heating, water production, and storage at the glacier bed. Water routing via crevasses likely plays an important role in the evolution of surges. The distinction between internally triggered surges and externally triggered speedups may not be straightforward. The behavior of these glaciers can be understood in terms of the enthalpy cycle model.

  • 33. Sjoberg, Y.
    et al.
    Marklund, P.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Lyon, S. W.
    Geophysical mapping of palsa peatland permafrost2015In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 9, no 2, p. 465-478Article in journal (Refereed)
    Abstract [en]

    Permafrost peatlands are hydrological and biogeochemical hotspots in the discontinuous permafrost zone. Non-intrusive geophysical methods offer a possibility to map current permafrost spatial distributions in these environments. In this study, we estimate the depths to the permafrost table and base across a peatland in northern Sweden, using ground penetrating radar and electrical resistivity tomography. Seasonal thaw frost tables (at similar to 0.5 m depth), taliks (2.1-6.7 m deep), and the permafrost base (at similar to 16 m depth) could be detected. Higher occurrences of taliks were discovered at locations with a lower relative height of permafrost landforms, which is indicative of lower ground ice content at these locations. These results highlight the added value of combining geophysical techniques for assessing spatial distributions of permafrost within the rapidly changing sporadic permafrost zone. For example, based on a back-of-the-envelope calculation for the site considered here, we estimated that the permafrost could thaw completely within the next 3 centuries. Thus there is a clear need to benchmark current permafrost distributions and characteristics, particularly in under studied regions of the pan-Arctic.

  • 34. Smeets, C. J. P. P.
    et al.
    Boot, W.
    Hubbard, A.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Wilhelms, F.
    van den Broeke, M. R.
    van de Wal, R. S. W.
    A wireless subglacial probe for deep ice applications2012In: Journal of Glaciology, ISSN 0022-1430, E-ISSN 1727-5652, Vol. 58, no 211, p. 841-848Article in journal (Refereed)
    Abstract [en]

    We present the design and first results from two experiments using a wireless subglacial sensor system (WiSe) that is able to transmit data through 2500 m thick ice. Energy consumption of the probes is minimized, enabling the transmission of data for at least 10 years. In July 2010 the first prototype of the system was used to measure subglacial pressure at the base and a temperature profile consisting of 23 probes in two 600 m deep holes at Russell Glacier, a land-terminating part of the West Greenland ice sheet near Kangerlussuaq. The time series of subglacial pressure show very good agreement between data from the WiSe system and the wired reference system. The wireless-measured temperature data were validated by comparison with the theoretical decrease of melting point with water pressure inside the water-filled hole directly after installation. To test the depth range of the WiSe system a second experiment using three different probe types and two different surface antennas was performed inside the 2537 m deep hole at NEEM. It is demonstrated that, with the proper combination of transmission power and surface antenna type, the WiSe system transmits data through 2500 m thick ice.

  • 35. Tenow, O.
    et al.
    Nilssen, A. C.
    Bylund, H.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Battisti, A.
    Bohn, U.
    Caroulle, F.
    Ciornei, C.
    Csóka, G.
    Delb, H.
    De Prins, W.
    Glavendekić, M.
    Gninenko, Y. I.
    Hrašovec, B.
    Matošević, D.
    Meshkova, V.
    Moraal, L.
    Netoiu, C.
    Pajares, J.
    Rubtsov, V.
    Tomescu, R.
    Utkina, I.
    Geometrid outbreak waves travel across Europe2013In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 82, no 1, p. 84-95Article in journal (Refereed)
    Abstract [en]

    We show that the population ecology of the 9- to 10-year cyclic, broadleaf-defoliating winter moth (Operophtera brumata) and other early-season geometrids cannot be fully understood on a local scale unless population behaviour is known on a European scale. Qualitative and quantitative data on O. brumata outbreaks were obtained from published sources and previously unpublished material provided by authors of this article. Data cover six decades from the 1950s to the first decade of twenty-first century and most European countries, giving new information fundamental for the understanding of the population ecology of O. brumata. Analyses on epicentral, regional and continental scales show that in each decade, a wave of O. brumata outbreaks travelled across Europe. On average, the waves moved unidirectionally ESE-WNW, that is, toward the Scandes and the Atlantic. When one wave reached the Atlantic coast after 9-10 years, the next one started in East Europe to travel the same c. 3000 km distance. The average wave speed and wavelength was 330 km year-1 and 3135 km, respectively, the high speed being incongruous with sedentary geometrid populations. A mapping of the wave of the 1990s revealed that this wave travelled in a straight E-W direction. It therefore passed the Scandes diagonally first in the north on its way westward. Within the frame of the Scandes, this caused the illusion that the wave moved N-S. In analogy, outbreaks described previously as moving S-N or occurring contemporaneously along the Scandes were probably the result of continental-scale waves meeting the Scandes obliquely from the south or in parallel. In the steppe zone of eastern-most and south-east Europe, outbreaks of the winter moth did not participate in the waves. Here, broadleaved stands are small and widely separated. This makes the zone hostile to short-distance dispersal between O. brumata subpopulations and prevents synchronization within meta-populations. We hypothesize that hostile boundary models, involving reciprocal host-herbivore-enemy reactions at the transition between the steppe and the broadleaved forest zones, offer the best explanation to the origin of outbreak waves. These results have theoretical and practical implications and indicate that multidisciplinary, continentally coordinated studies are essential for an understanding of the spatio-temporal behaviour of cyclic animal populations.

  • 36.
    Vallot, Dorothée
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Luckman, Adrien
    Benn, Douglas I.
    Zwinger, Thomas
    van Pelt, Ward J. J.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Kohler, Jack
    Schäfer, Martina
    Claremar, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Hulton, Nick R. J.
    Basal dynamics of Kronebreen, a fast-flowing tidewater glacier in Svalbard: non-local spatio-temporal response to water input2017In: Journal of Glaciology, ISSN 0022-1430, E-ISSN 1727-5652, Vol. 63, no 242, p. 1012-1024Article in journal (Refereed)
    Abstract [en]

    We evaluate the variability in basal friction for Kronebreen, Svalbard, a fast-flowing tidewater glacier. We invert 3 years (2013–15) of surface velocities at high temporal resolution (generally 11 days), to estimate the changing basal properties of the glacier. Our results suggest that sliding behaviour of Kronebreen within a year is primarily influenced by changes in water input patterns during the meltwater season and basal friction is highly variable from a year to another. At present, models usually employ parameterisations to encompass the complex physics of glacier sliding by mathematically simulate their net effect. For such ice masses with strong seasonal variations of surface melt, the spatio-temporal patterns of basal friction imply that it is neither possible nor appropriate to use a parameterisation for bed friction that is fixed in space and/or time, at least in a timescale of a few years. Basal sliding may not only be governed by local processes such as basal topography or summer melt, but also be mediated by factors that vary over a larger distance and over a longer time period such as subglacial hydrology organisation, ice-thickness changes or calving front geometry.

  • 37. van Pelt, W. J. J.
    et al.
    Oerlemans, J.
    Reijmer, C. H.
    Pettersson, Rikard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pohjola, Veijo A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Isaksson, E.
    Divine, D.
    An iterative inverse method to estimate basal topography and initialize ice flow models2013In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 7, no 3, p. 987-1006Article in journal (Refereed)
    Abstract [en]

    We evaluate an inverse approach to reconstruct distributed bedrock topography and simultaneously initialize an ice flow model. The inverse method involves an iterative procedure in which an ice dynamical model (PISM) is run multiple times over a prescribed period, while being forced with space-and time-dependent climate input. After every iteration bed heights are adjusted using information of the remaining misfit between observed and modeled surface topography. The inverse method is first applied in synthetic experiments with a constant climate forcing to verify convergence and robustness of the approach in three dimensions. In a next step, the inverse approach is applied to Nordenskioldbreen, Svalbard, forced with height-and time-dependent climate input since 1300 AD. An L-curve stopping criterion is used to prevent overfitting. Validation against radar data reveals a high correlation (up to R = 0.89) between modeled and observed thicknesses. Remaining uncertainties can mainly be ascribed to inaccurate model physics, in particular, uncertainty in the description of sliding. Results demonstrate the applicability of this inverse method to reconstruct the ice thickness distribution of glaciers and ice caps. In addition to reconstructing bedrock topography, the method provides a direct tool to initialize ice flow models for forecasting experiments.

  • 38.
    Van Pelt, Ward J.J.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pohjola, Veijo A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Ehwald, Lena E.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Reijmer, Carleen H.
    Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, Netherlands.
    Boot, Wim
    Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, Netherlands.
    Jakobs, Constantijn L.
    Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, Netherlands.
    Dynamic response of a High Arctic glacier to melt and runoff variations2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 10, p. 4917-4926Article in journal (Refereed)
    Abstract [en]

    The dynamic response of High Arctic glaciers to increased runoff in a warming climateremains poorly understood. We analyze a 10-year record of continuous velocity data collected atmultiple sites on Nordenskiöldbreen, Svalbard, and study the connec tion between ice flow andrunoff within and between seasons. During the melt season, the sensitivit y of ice motion to runoffat sites in the ablation and lower accumulation zone drops by a fac tor of 3 when cumulative runoff exceedsa local threshold, which is likely associated with a transition from inefficient (distributed) to efficient(channelized) drainage. Average summer (June–August) velocities are found to increase with summerablation, while subsequent fall (September–November) velocities decrease. Spring (March–May)velocities are largely insensitive to summer ablation, which suggests a short-lived impact of summermelt on ice flow during the cold season. The net impact of summer ablation on annual velocities is foundto be insignificant.

  • 39.
    van Pelt, Ward
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Oerlemans, J.
    Reijmer, C. H.
    Pettersson, Rikard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pohjola, Veijo A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Isaksson, E.
    Divine, D.
    An iterative inverse method to estimate basal topography and initialize ice flow models2013In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 7, no 3, p. 987-1006Article in journal (Refereed)
    Abstract [en]

    We evaluate an inverse approach to reconstruct distributed bedrock topography and simultaneously initialize an ice flow model. The inverse method involves an iterative procedure in which an ice dynamical model (PISM) is run multiple times over a prescribed period, while being forced with space-and time-dependent climate input. After every iteration bed heights are adjusted using information of the remaining misfit between observed and modeled surface topography. The inverse method is first applied in synthetic experiments with a constant climate forcing to verify convergence and robustness of the approach in three dimensions. In a next step, the inverse approach is applied to Nordenskioldbreen, Svalbard, forced with height-and time-dependent climate input since 1300 AD. An L-curve stopping criterion is used to prevent overfitting. Validation against radar data reveals a high correlation (up to R = 0.89) between modeled and observed thicknesses. Remaining uncertainties can mainly be ascribed to inaccurate model physics, in particular, uncertainty in the description of sliding. Results demonstrate the applicability of this inverse method to reconstruct the ice thickness distribution of glaciers and ice caps. In addition to reconstructing bedrock topography, the method provides a direct tool to initialize ice flow models for forecasting experiments.

  • 40.
    van Pelt, Ward
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Oerlemans, Johannes
    Reijmer, Carleen
    Pohjola, Veijo
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    van Angelen, Jan
    Simulating melt, runoff and refreezing on Nordenskiöldbreen, Svalbard, using a coupled snow and energy balance model2012In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 6, no 3, p. 641-659Article in journal (Refereed)
    Abstract [en]

    A distributed energy balance model is coupled to a multi-layer snow model in order to study the mass balance evolution and the impact of refreezing on the mass budget of Nordenskioldbreen, Svalbard. The model is forced with output from the regional climate model RACMO and meteorological data from Svalbard Airport. Extensive calibration and initialisation are performed to increase the model accuracy. For the period 1989-2010, we find a mean net mass balance of -0.39 m w.e. a(-1). Refreezing contributes on average 0.27 m w.e. a(-1) to the mass budget and is most pronounced in the accumulation zone. The simulated mass balance, radiative fluxes and subsurface profiles are validated against observations and are generally in good agreement. Climate sensitivity experiments reveal a non-linear, seasonally dependent response of the mass balance, refreezing and runoff to changes in temperature and precipitation. It is shown that including seasonality in climate change, with less pronounced summer warming, reduces the sensitivity of the mass balance and equilibrium line altitude (ELA) estimates in a future climate. The amount of refreezing is shown to be rather insensitive to changes in climate.

  • 41.
    van Pelt, Ward
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pohjola, Veijo
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Marchenko, Sergey
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Claremar, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Oerlemans, Johannes
    Inverse estimation of snow accumulation along a radar transect on Nordenskioldbreen, Svalbard2014In: Journal of Geophysical Research - Earth Surface, ISSN 2169-9003, E-ISSN 2169-9011, Vol. 119, no 4, p. 816-835Article in journal (Refereed)
    Abstract [en]

    We present an inverse modeling approach to reconstruct annual accumulation patterns from ground-penetrating radar (GPR) data. A coupled surface energy balance-snow model simulates surface melt and the evolution of subsurface density, temperature, and water content. The inverse problem consists of iteratively calibrating accumulation, serving as input for the model, by finding a match between modeled and observed radar travel times. The inverse method is applied to a 16km GPR transect on Nordenskioldbreen, Svalbard, yielding annual accumulation patterns for 2007-2012. Accumulation patterns with a mean of 0.75meter water equivalent (mwe)a(-1)contain substantial spatial variability, with a mean annual standard deviation of 0.17mwea(-1), and show only partial consistency from year to year. In contrast to traditional methods, accounting for melt water percolation, refreezing, and runoff facilitates accurate accumulation reconstruction in areas with substantial melt. Additionally, accounting for horizontal density variability along the transect is shown to reduce spatial variability in reconstructed accumulation, whereas incorporating irreducible water storage lowers accumulation estimates. Correlating accumulation to terrain characteristics in the dominant wind direction indicates a strong preference of snow deposition on leeward slopes, whereas weaker correlations are found with terrain curvature. Sensitivity experiments reveal a nonlinear response of the mass balance to accumulation changes. The related negative impact of small-scale accumulation variability on the mean net mass balance is quantified, yielding a negligible impact in the accumulation zone and a negative impact of -0.09mwea(-1)in the ablation area.

  • 42.
    Van Pelt, Ward
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pohjola, Veijo
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Marchenko, Sergey
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Kohler, Jack
    Luks, Bartek
    Hagen, Jon Ove
    Schuler, Thomas
    Dunse, Thorben
    Noël, Brice
    Reijmer, Carleen
    A long-term dataset of climatic mass balance, snow conditions, and runoff in Svalbard (1957–2018)2019In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 13, p. 2259-2280Article in journal (Refereed)
    Abstract [en]

    The climate in Svalbard is undergoing amplified change compared to the global mean. This has major implications for runoff from glaciers and seasonal snow on land. We use a coupled energy balance–subsurface model, forced with downscaled regional climate model fields, and apply it to both glacier-covered and land areas in Svalbard. This generates a long-term (1957–2018) distributed dataset of climatic mass balance (CMB) for the glaciers, snow conditions, and runoff with a 1 km×1 km spatial and 3-hourly temporal resolution. Observational data including stake measurements, automatic weather station data, and subsurface data across Svalbard are used for model calibration and validation. We find a weakly positive mean net CMB (+0.09 m w.e. a−1) over the simulation period, which only fractionally compensates for mass loss through calving. Pronounced warming and a small precipitation increase lead to a spatial-mean negative net CMB trend (−0.06 m w.e. a−1 decade−1), and an increase in the equilibrium line altitude (ELA) by 17 m decade−1, with the largest changes in southern and central Svalbard. The retreating ELA in turn causes firn air volume to decrease by 4 % decade−1, which in combination with winter warming induces a substantial reduction of refreezing in both glacier-covered and land areas (average −4 % decade−1). A combination of increased melt and reduced refreezing causes glacier runoff (average 34.3 Gt a−1) to double over the simulation period, while discharge from land (average 10.6 Gt a−1) remains nearly unchanged. As a result, the relative contribution of land runoff to total runoff drops from 30 % to 20 % during 1957–2018. Seasonal snow on land and in glacier ablation zones is found to arrive later in autumn (+1.4 d decade−1), while no significant changes occurred on the date of snow disappearance in spring–summer. Altogether, the output of the simulation provides an extensive dataset that may be of use in a wide range of applications ranging from runoff modelling to ecosystem studies.

  • 43.
    Vega, Carmen P.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Björkman, M. P.
    Pohjola, Veijo A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Isaksson, E.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Martma, T.
    Marca, A.
    Kaiser, J.
    Nitrate stable isotopes and major ions in snow and ice samples from four Svalbard sites2015In: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 34, article id 23246Article, review/survey (Refereed)
    Abstract [en]

    Increasing reactive nitrogen (N-r) deposition in the Arctic may adversely impact N-limited ecosystems. To investigate atmospheric transport of N-r to Svalbard, Norwegian Arctic, snow and firn samples were collected from glaciers and analysed to define spatial and temporal variations (1 10 years) in major ion concentrations and the stable isotope composition (delta N-15 and delta O-18) of nitrate (NO3-) across the archipelago. The delta N-15(NO3-) and delta O-18(NO3-) averaged -4 parts per thousand and 67 parts per thousand in seasonal snow (2010-11) and -9 parts per thousand and 74 parts per thousand in firn accumulated over the decade 2001-2011. East-west zonal gradients were observed across the archipelago for some major ions (non-sea salt sulphate and magnesium) and also for delta N-15(NO3-) and delta O-18(NO3-) in snow, which suggests a different origin for air masses arriving in different sectors of Svalbard. We propose that snowfall associated with long-distance air mass transport over the Arctic Ocean inherits relatively low delta N-15(NO3-) due to in-transport N isotope fractionation. In contrast, faster air mass transport from the north-west Atlantic or northern Europe results in snowfall with higher delta N-15(NO3-) because in-transport fractionation of N is then time-limited.

  • 44.
    Vega, Carmen P.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Pohjola, Veijo A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Beaudon, Emilie
    Univ Lapland, Arctic Ctr, Rovaniemi 96101, Finland; Byrd Polar & Climate Res Ctr, 082A Scott Hall,1090 Carmack Rd, Columbus, OH 43210 USA.
    Claremar, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    van Pelt, Ward J. J.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Isaksson, Elisabeth
    Norwegian Polar Res Inst, Fram Ctr, N-9296 Tromso, Norway.
    Martma, Tonu
    Schwikowski, Margit
    Paul Scherrer Inst, CH-5232 Villigen, Switzerland.
    Bøggild, Carl E.
    UNIS, Univ Ctr Svalbard, Pb 156, N-9171 Longyearbyen, Norway;Tech Univ Denmark, Arctic Technol Ctr, Bygning 204, DK-2800 Lyngby, Denmark.
    A synthetic ice core approach to estimate ion relocation in anice field site experiencing periodical melt: a case study onLomonosovfonna, Svalbard2016In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 10, p. 961-976Article in journal (Refereed)
    Abstract [en]

    Physical and chemical properties of four different ice cores (LF-97, LF-08, LF-09 and LF-11) drilled at Lomonosovfonna, Svalbard, were compared to investigate the effects of meltwater percolation on the chemical and physical stratigraphy of these records. A synthetic ice core approach was employed as reference record to estimate the ionic relocation and meltwater percolation length at this site during the period 2007-2010. Using this method, a partial ion elution sequence obtained for Lomonosovfonna was NO(3)(-)aEuro-> aEuro-SO42-, Mg2+, Cl-, K+, Na+ with nitrate being the most mobile within the snowpack. The relocation length of most of the ions was on the order of 1aEuro-m during this period. In addition, by using both a positive degree day (PDD) and a snow-energy model approaches to estimate the percentage of melt at Lomonosovfonna, we have calculated a melt percentage (MP) of the total annual accumulation within the range between 48 and 70aEuro-%, for the period between 2007 and 2010, which is above the MP range suggested by the ion relocation evidenced in the LF-syn core (i.e., MPaEuro-aEuro parts per thousand= aEuro-30aEuro-%). Using a firn-densification model to constrain the melt range, a MP of 30aEuro-% was found over the same period, which is consistent with the results of the synthetic ice core approach, and a 45aEuro-% of melt for the last 60 years. Considering the ionic relocation lengths and annual melt percentages, we estimate that the atmospheric ionic signal remains preserved in recently drilled Lomonosovfonna ice cores at an annual or bi-annual resolution when weather conditions were similar to those during the 2007-2010 period.

  • 45.
    Vega, Carmen P.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pohjola, Veijo A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Samyn, Denis
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Isaksson, E.
    Björkman, M. P.
    Martma, T.
    Marca, A.
    Kaiser, J.
    First Ice Core Records of NO3- Stable Isotopes from Lomonosovfonna, Svalbard2015In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, no 1, p. 313-330Article in journal (Refereed)
    Abstract [en]

    Samples from two ice cores drilled at Lomonosovfonna, Svalbard, covering the period 1957-2009, and 1650-1995, respectively, were analyzed for NO(3)(-)concentrations, and NO3- stable isotopes (N-15 and O-18). Post-1950 N-15 has an average of (-6.91.9), which is lower than the isotopic signal known for Summit, Greenland but agrees with values observed in recent Svalbard snow and aerosol. Pre-1900 N-15 has an average of (4.21.6)parts per thousand suggesting that natural sources, enriched in the N-15 isotope, dominated before industrialization. The post-1950 O-18 average of (75.1 +/- 4.1)parts per thousand agrees with data from low and polar latitudes, suggesting similar atmospheric NOy (NOy=NO+NO2+HNO3) processing pathways. The combination of anthropogenic source N-15 and transport isotope effect was estimated as -29.1 parts per thousand for the last 60years. This value is below the usual range of NOx (NOx=NO+NO2) anthropogenic sources which is likely the result of a transport isotope effect of -32 parts per thousand. We suggest that the N-15 recorded at Lomonosovfonna is influenced mainly by fossil fuel combustion, soil emissions, and forest fires; the first and second being responsible for the marked decrease in N-15 observed in the post-1950s record with soil emissions being associated to the decreasing trend in N-15 observed up to present time, and the third being responsible for the sharp increase of N-15 around 2000.

  • 46. Walter, Jacob I.
    et al.
    Brodsky, Emily E.
    Tulaczyk, Slawek
    Schwartz, Susan Y.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Transient slip events from near-field seismic and geodetic data on a glacier fault, Whillans Ice Plain, West Antarctica2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, no F1, p. F01021-Article in journal (Refereed)
    Abstract [en]

    Bidaily, tidally modulated stick-slip speed-ups of the Whillans Ice Plain (WIP) provide insight into glacier dynamics and failure at a naturally repeating fault asperity. We installed a network of continuously operating GPS receivers in 2007 and deployed on-ice broadband seismometers during the austral summer of 2008 on Whillans Ice Stream (WIS), West Antarctica, and recorded 26 glacier speed-up events. Previous work during the 2004 field season suggested that these speed-ups initiate as failure of an asperity on or near "ice raft A" that triggers rupture across the entire WIP. Our results for 2008 locate the slip initiation farther to the south of this feature, closer to the grounding line and the southernmost extent of the Ross Ice Shelf. The initiation may be controlled by a discontinuity in basal boundary conditions at the suture between two ice streams. A strong correlation between the amplitude of seismic waves generated at the rupture front and the total slip achieved over the duration of the slip event (similar to 30 min) suggests slip-predictable behavior, i.e., the ability to forecast the eventual slip based on the first minute of seismic radiation. Successive slip events propagate with different rupture speeds (100-300 m/s) that strongly correlate (R-2 = 0.73) with the interevent duration. In addition, the amount of slip achieved during each event appears to be correlated with the rupture speed. We use these observations to constrain basal shear stress to be 4 kPa by calculating conditions for basal freezing. Our observations yield information regarding mechanics and dynamics of ice streambeds at the scale of tens to hundreds of kilometers. Subglacial processes are notoriously difficult to constrain on these large scales, which are relevant to the understanding of regional and continental ice motion.

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