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  • 1.
    De Angelis, Hernán
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Palaeo-ice stream onsets: examples from the north-eastern Laurentide Ice Sheet2008In: Earth Surface Processes and Landforms, ISSN 0197-9337, Vol. 33, no 4, 560-572 p.Article in journal (Refereed)
    Abstract [en]

    In this paper we report on observations of glacial landscapes at the head of geomorphologically interpreted palaeo-ice streams, i.e. palaeo-ice-stream onsets. Our work is based on the results of systematic palaeoglaciological mapping of the portion of north-eastern Canada formerly covered by the Laurentide Ice Sheet. Four different cases are considered and analysed in detail: one is the Dubawnt Lake Ice Stream and the others are smaller (<70 km long) palaeo-ice streams. We found that in this region onset zones are generally characterized by a heterogeneous landform record and are more easily recognized when landscapes typical of partially frozen beds are present. Based on publicly available topographical and geological data as well as theoretical developments, we discuss the conditions and controls on the location of these onset zones and their potential stability. Except for the Dubawnt Lake Ice Stream, we found that, although topography and geology are important conditioning factors, the geomorphological imprint of palaeo-ice-stream onsets cannot be explained without invoking the role of the basal thermal boundary between cold- and warm-based ice. Finally, we observed that, except for the Dubawnt Lake Ice Stream, the onset zones of large ice streams are rarely preserved, and we suggest two possible explanations for this. We conclude that although the same qualitative processes are present under the majority of ice streams, conditions for the preservation of the onset zones are more likely to be met in the case of relatively small ice streams because these are more rapidly deglaciated.

  • 2.
    De Angelis, Hernán
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Palaeo-ice streams in the Foxe/Baffin sector of the Laurentide Ice Sheet2007In: Quaternary Science Reviews, ISSN 0277-3791, Vol. 26, no 9-10, 1313-1331 p.Article in journal (Refereed)
    Abstract [en]

    In this paper, we describe mapping of palaeo-ice streams in the Foxe/Baffin sector of the Laurentide Ice Sheet by means of geomorphological interpretation of high-resolution satellite images. Our interpretations were guided by a glaciological inversion scheme, aided by digital elevation models, publicly available sonar surveys and field studies. As a result, we produced a map depicting the location, geometry and relative temporal changes of palaeo-ice streams and analysed their palaeoglaciological implications for the Foxe/Baffin sector. We conclude that in the period between the Last Glacial Maximum and approximately 7.0 kyr BP, the Foxe/Baffin sector was largely drained by topographically controlled outlet glaciers and ice streams, which were organized in a relatively stable pattern. During this time, large areas of Melville Peninsula and central Baffin Island were subject to cold-based conditions. Between 7.0 and 6.0 kyr BP, the Foxe/Baffin sector collapsed catastrophically in the Foxe Basin, after which its remnant portion became confined to Baffin Island. During this collapse, rapid successions of small transient ice streams occurred along wide, loosely defined topographical corridors in two sectors of Baffin Island. The presently available landform archive on emerged land is not sufficient to conclusively support the existence of fully scaled ice streams along the whole length of Hudson Strait. As an alternative solution, we propose that topographically controlled ice streams might have occurred along the deepest parts of Hudson Strait, with attendant cold-based ice zones on marginal areas and islands at the head of the strait.

  • 3.
    De Angelis, Hernán
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Palaeo-ice streams in the northern Keewatin sector of the Laurentide Ice Sheet2005In: Annals of Glaciology, ISSN 0260-3055, Vol. 42, 135-144 p.Article in journal (Refereed)
    Abstract [en]

    Evidence for ice streams in the Laurentide ice sheet is widespread. In the region of northern Keewatin and the Boothia Peninsula, Nunavut, Canada, palaeo-ice streams have been recognized, but their location, size and potential role in ice-sheet dynamics are poorly constrained. Based on the interpretation of satellite imagery, we produce a palaeo-ice-stream map of this region. Glacial directional landforms, eskers and moraines were mapped and integrated into landform assemblages using a glacial geological inversion model. Palaeo-frozen bed areas were also identified. Relative age of the geomorphic swarms was assessed by cross-cutting relationships and radiocarbon ages where available. Using this information we obtained a glaciologically plausible picture of ice-stream evolution within the northernmost Laurentide ice sheet. On the M'Clintock Channel corridor, three generations of pure ice streams are found. On Baffin Island and the Gulf of Boothia, glaciation was dominated by frozen-bed zones located on high plateaus and ice streams running along the troughs, i.e. topographic ice streams. A massive convergent pattern at the head of Committee Bay drained ice from both the Keewatin and Foxe sectors and was probably one of the main deglaciation channels of the Laurentide ice sheet. Finally, our results indicate that streaming flow was present in the deep interior of the Laurentide ice sheet, as recently shown for the Greenland and Antarctic ice sheets.

  • 4.
    Dessie, Gessesse
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Pattern and Magnitude of Deforestation in the South Central Rift Valley Region of Ethiopia2007In: Mountain Research And Development, Vol. 27, no 2, 162-168 p.Article in journal (Refereed)
    Abstract [en]

    The pattern and magnitude of deforestation that occurred from 1972 to 2000 in the south central Rift Valley of Ethiopia were analyzed using remote sensing change detection techniques. The results show that natural forest cover declined from 16% in 1972 to 2.8% in 2000. The total natural forest cleared between 1972 and 2000 amounted to 40,324 ha, corresponding to an annual loss of 1440 ha. The total loss was 82% of the 1972 forest cover and the annual loss was equivalent to 0.9% of the national figure. The forest decline in the area involved proximate causal factors as well as causal factors that are more spatially diffuse and are part of the long-term evolution of a region much larger than the study area. In order of importance, the major causes of change were small-scale agriculture, commercial logging, and commercial farms. Two major modes of change were observed: 1) internal, ie openings created by small farm plots, grazing lands, and villages; and 2) external, ie expansion of agriculture from the exterior into the forests. The main consequences of deforestation were habitat destruction and decline of water availability.

  • 5.
    Ebert, Karin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hall, Adrian
    University of St Andrews, UK.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    The impact of glacial erosion on northern shields2012In: 42nd International Arcitc Workshop, Program and Abstracts 2012. Institute of Arctic and Alpine Research (INSTAAR), University of Colorado at Boulder, 115pp., 2012Conference paper (Refereed)
    Abstract [en]

    The long-term geomorphic evolution of shield surfaces is poorly understood, especially of glaciated shields where saprolites and correlative sediments have been removed by glacial erosion. We know the rough picture of land uplift and erosional unloading during the Cenozoic and we know of the existence of stepped surfaces on the shield. However for further studies of the long term geomorphology of glaciated shields, we first need to assess the patterns and depth of glacial erosion on the shield bedrock landforms in order to reconstruct the preglacial land surface.

    Large scale topography controls ice inception on that surface and influences ice dynamics during glaciation. Large-scale relief is a trigger for selective erosion and for ice streaming and bed materials affect the ice flow and the composition of tills. Yet the quantitative impact of glacial erosion on shield bedrock is barely known.

    The patterns of erosion, deposition and redistribution of loose material on the shield surface are well known. The interesting question is if the bedrock surface of the northern shields only was the surface for redistribution, largely unaffected, or if the surface itself was modified and to what degree?

    A detailed and convincing quantification of removal of bedrock by ice does not exist. Studies show that the ice erosional impact can be modest. However these are results of regional studies and wider studies of the northern shields are desirable, with the final aim of a quantification of the glacial erosional removal of bedrock for entire cratons.

    Field investigations on the basis of identification of promising field localities in a digital elevation model (DEM), and in combination of GIS-analysis of combinations of the DEM with databases of bedrock geology and tectonics, are a new and powerful tool to identify patterns of glacial erosion over large areas and eventually to quantify the depths of glacial erosion on glaciated shield surfaces.

    The presentation will show current results for northern Fennoscandia and future possibilities to assess patterns and quantities of glacial erosion in glaciated shield areas, with a focus on DEM-analysis.

  • 6.
    Ebert, Karin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hall, Adrian M.
    University of St Andrews, Scotland, UK.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Factors determining the impact of glacial erosion on shield surfaces2013In: 8th International Conference (AIG) on Geomorphology: Abstracts Volume, 2013, 272-272 p.Conference paper (Refereed)
    Abstract [en]

    The erosional effect of ice sheets on shield bedrock surfaces has been debated for many decades. Whilst there seems to be agreement that ice sheet erosion of the bedrock landforms was generally modest, and that many preglacial landscape elements remain, we need to know which factors influence ice sheet dynamics and erosional impact on the shield. Using GIS-analysis and field observations, combined with cosmogenic exposure ages, we investigate areas with a similar ice cover history but with greatly different degrees of glacial erosional impact. On two transects with an area of ~35 000km2 each across the shield, we examine why glacially eroded areas exist adjacent to areas of negligible glacial erosion.  Firstly, a E-W transect, identifies two areas of exceptional glacial preservation, the Parkajoki area in Sweden and the so-called ice shed zone in Finland, each with large tors and deep saprolite covers. Secondly a NW-SE transect, overlapping in the northern part with the first transect, includes areas of intense glacial streamlining, with bedrock areas stripped of loose material and barely any weathering remnants. For areas of negligible and advanced glacial erosion, we investigate geology, elevation, topography, hydrology and duration of ice cover in an attempt to identify factors leading to ice sheet erosion/preservation of the underlying shield landscape. We estimate the duration of ice cover from the known ice cover history. We use a single flow path and thereby use steady glaciological parameters. Our results point to glacial bedrock erosion of flat shield surfaces in the range of tens of meters. Erosion only happens in areas where the ice is forced to flow around obstacles or into basins. These preglacial landscape properties are in turn determined by bedrock geology and long-term geomorphic and tectonic evolution. Consequently, a combination of bedrock type and topography determines ice sheet properties and thereby effects of ice erosion on shield surfaces.

  • 7.
    Ebert, Karin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hall, Adrian M
    University of StAndrews, Scotland, UK.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Ice sheet erosional impacts in the low-relief shield terrain of northern Fennoscandia2014In: 44th international Arctic Workshop, Program & Abstracts 2014. Institute of Arctic and Alpine Research (INSTAAR), University of Colorado at Boulder, 131 pp., 2014, 42- p.Conference paper (Refereed)
    Abstract [en]

    Much previous work on Late Cenozoic glacial erosion patterns in bedrock has focussed on mountain areas. We here identify varying impacts of ice sheet erosion on the low-relief bedrock surface of the Fennoscandian shield, and examine the geological, topographical and glaciological controls on these patterns.

    We combine GIS-mapping of topographical, hydrological and weathering data with field observations. We identify and investigate areas with similar geology and general low relief that show different degrees of ice sheet erosional impact, despite similar ice cover histories. On two transects with a total area of ~84 000km2 across the northern Fennoscandian shield, we first establish patterns of glacial erosion and then examine why glacially streamlined areas exist adjacent to areas of negligible glacial erosion.  The northern transect includes two areas of exceptional glacial preservation, the Parkajoki area in Sweden and the so-called ice divide zone in Finland, each of which preserve tors and deep saprolite covers. The southern transect, overlapping in the northern part with the first transect, includes areas of intense glacial streamlining, with bedrock areas stripped of loose material and barely any weathering remnants.

    For both areas, we firstly present the indicators we have availabe for ice sheet erosional impact: streamlined and non-streamlined inselbergs; parallel and dendritic/rectangular drainage patterns; the absence and presence of Neogene weathering remnants. This is  followed by an investigation of factors that possibly influence ice sheet erosional impact: (pre-glacial) land surface elevation and topography, bedrock type and structure, and the ice cover history.

    We find that the extreme preservation of pre-glacial relief in certain parts of the study area is likely explained by repeatedly divergent flow and frozen-based conditions, and that the most likely control causing glacial streamlining and strong erosion was acceleration of flow around major obstacles and convergence towards major bed depressions. No direct impact of rock type on glacial erosion patterns was found, but an indirect control appears clear.  Bedrock geology and long-term differential weathering and tectonic evolution determined the topography of the pre-glacial landscape, and these topographic differences subsequently influenced ice sheet dynamics and thereby partly controlled ice sheet erosion on the Northern Fennoscandian shield.

  • 8.
    Ebert, Karin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hall, Adrian M.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. University of St Andrews, Scotland. UK.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Andersson, Jannike
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Unequal ice-sheet erosional impacts across low-relief shield terrain in northern Fennoscandia2015In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 233, no SI, 64-74 p.Article in journal (Refereed)
    Abstract [en]

    Much previous work on Late Cenozoic glacial erosion patterns in bedrock has focussed on mountain areas. Here we identify varying impacts of ice sheet erosion on the low-relief bedrock surface of the Fennoscandian shield, and examine the geological, topographical and glaciological controls on these patterns.

    We combine GIS-mapping of topographical, hydrological and weathering data with field observations. We identify and investigate areas with similar geology and general low relief that show different degrees of ice sheet erosional impact, despite similar ice cover histories. On two transects with a total area of ~ 84 000 km2 across the northern Fennoscandian shield, we first establish patterns of glacial erosion and then examine why glacially streamlined areas exist adjacent to areas of negligible glacial erosion. The northern transect includes two areas of exceptional glacial preservation, the Parkajoki area in Sweden and the so-called ice divide zone in Finland, each of which preserve tors and deep saprolite covers. The southern transect, overlapping in the northern part with the first transect, includes areas of well developed glacial streamlining, with bedrock areas stripped of loose material and barely any weathering remnants.

    For both areas, we firstly present contrasting indicators for ice sheet erosional impact: streamlined and non-streamlined inselbergs; parallel and dendritic/rectangular drainage patterns; and the absence and presence of Neogene weathering remnants. This is followed by an investigation of factors that possibly influence ice sheet erosional impact: ice cover history, ice cover duration and thickness, bedrock type and structure, and topography.

    We find that the erosional impact of the Fennoscandian ice sheet has varied across the study area. Distinct zones of ice sheet erosion are identified in which indicators of either low or high erosion coexist in the same parts of the transects. No direct impact of rock type on glacial erosion patterns was found, but an indirect control appears clear. Bedrock geology and long-term differential weathering and tectonic evolution determined the topography of the pre-glacial landscape, and these topographic differences subsequently influenced ice sheet dynamics and thereby partly controlled patterns of ice sheet erosion. Ice cover duration and former ice thickness were not significant controls on glacial erosion patterns. Extensive preservation of pre-glacial relief through low glacial erosion is attributed to the maintenance throughout the Pleistocene of divergent flow and frozen-bed conditions in the Fennoscandian ice sheet. In contrast, glacial streamlining and strong glacial erosion were caused mainly by acceleration of flow around major obstacles and flow towards major depressions on the ice sheet bed. The relatively strong ice sheet erosion towards the Gulf of Bothnia is the result of a combination of favourable factors: bedrock structure and river valleys aligned sub-parallel to ice sheet flow and convergent ice flow towards the Baltic.

  • 9. Fabel, D.
    et al.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harbor, J.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Dahlgren, K.I.T.
    Retreat rate of the northern Fennoscandian Ice Sheet margin2007In: Geophysical Research Abstracts, 2007Conference paper (Refereed)
    Abstract [en]

    The deglaciation chronologies of the northern and north-eastern margins of the Fennoscandian Ice Sheet are relatively poorly constrained. This is because the principal methodological tool to trace and date the deglaciation pattern, the occurrence of deglaciation varves, does not apply in the northernmost regions of Fennoscandia. Moreover, a paucity of radiocarbon dates allows for only a most generalised pattern for the post-Younger Dryas shrinkage of the ice sheet to its final deglaciation configuration in the northern Swedish mountains. We are tracing the deglaciation of the Fennoscandian Ice Sheet from its Younger Dryas terminal moraines in northern Norway and eastern Finland towards the northern Swedish mountains, using cosmogenic nuclide apparent exposure ages of depositional and erosional features related to the former ice sheet margin. Because the ice sheet had initially warm-based conditions close to its margin, the dominant morphology is one of eskers and aligned lineation systems such as crag-and-tails. Abundant meltwater has locally eroded bedrock to considerable depth and deposited fans or deltas perched above current local base levels. Subglacial conditions during final deglaciation close to the mountain range were cold-based, thus inhibiting the formation of eskers and lineation systems. However, there is a ubiquity of meltwater erosional imprints and occasional plucking scars where, locally, pressure-melting conditions were reached. Surface exposure ages from these different geomorphological settings should yield true deglaciation ages provided the following conditions are met, (i) erosion on crags of crag-and-tails, across transverse erosional scarps, and in meltwater channels has exposed bedrock surfaces without a prior exposure history, and (ii) depositional features contain exposed boulders without a prior exposure history. Results show that transverse erosional scarps and erratics yield reliable deglaciation ages, but that bedrock samples from meltwater channels and crag-and-tails and sediment samples from eskers occasionally yield unreliable deglaciation ages due to cosmogenic nuclide inheritance and potential shielding by snow. Apparent deglaciation ages range from _14 ka at the Younger Dryas moraine to _8 ka approximately 500 km to the south in the northern Swedish Mountains. The spread of ages do not deviate from what would be expected for a regular uninterrupted retreat by the ice margin

  • 10. Glasser, Neil
    et al.
    Jansson, Krister
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harrison, Stephan
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    The glacial geomorphology and Pleistocene history of South America between 38 degrees S and 56 degrees S2008In: QUATERNARY SCIENCE REVIEWS, ISSN 0277-3791, Vol. 27, no 3-4, 365-390 p.Article in journal (Refereed)
    Abstract [sv]

    This paper presents new mapping of the glacial geomorphology of southern South America between latitudes 38 degrees S and 56 degrees S, approximately the area covered by the former Patagonian Ice Sheets. Glacial geomorphological features, including glacial lineations, moraines, meltwater channels, trimlines, sandur and cirques, were mapped from remotely sensed images (Landsat 7 ETM +, pan-sharpened Landsat 7 and ASTER). The landform record indicates that the Patagonian Ice Sheets consisted of 66 main outlet glaciers, together with numerous local cirque glaciers and independent ice domes in the surrounding mountains. In the northern part of the mapped area, in the Chilean Lake District (38-42 degrees S), large piedmont glaciers developed on the western side of the Andes and the maximum positions of these outlet glaciers are, in general, marked by arcuate terminal moraines. To the east of the Andes between 38 degrees S and 42 degrees S, outlet glaciers were more restricted in extent and formed "alpine-style" valley glaciers. Along the eastern flank of the Andes south of similar to 45 degrees S a series of large fast-flowing outlet glaciers drained the ice sheet. The location of these outlet glaciers was topographically controlled and there was limited scope for interactions between individual lobes. West of the Andes at this latitude, there is geomorphological evidence for an independent ice cap close to sea level on the Taitao Peninsula. The age of this ice cap is unclear but it may represent evidence of glacier growth during the Antarctic Cold Reversal and/or Younger Dryas Chronozone. Maximum glacier positions are difficult to determine along much of the western side of the Andes south of 42 degrees S because of the limited land there, and it is assumed that most of these glaciers had marine termini. In the south-east of the mapped area, in the Fuegan Andes (Cordillera Darwin), the landform record provides evidence of ice-sheet initiation. By adding published dates for glacier advances from the literature we present maps of pre-Last Glacial Maximum (LGM) glacier extent, LGM extent and the positions of other large mapped moraines younger than LGM in age. A number of large moraines occur within the known LGM limits. The age of these moraines is unknown but, since many of them lie well outside the established maximum Neoglacial positions, the possibility that they reflect a return to glacial climates during the Younger Dryas Chronozone or Antarctic Cold Reversal cannot be discounted.

  • 11.
    Goodfellow, Bradley
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Deciphering a non-glacial/glacial landscape mosaic in the northern Swedish mountains2008In: Geomorphology, Vol. 93, no 3-4, 213-232 p.Article in journal (Refereed)
    Abstract [en]

    Relict surfaces contain information on past surface processes and long-term landscape evolution. A detailed investigation of relict non-glacial surfaces in a formerly glaciated mountain landscape of northern Sweden was completed, based on interpretation of colour infrared aerial photographs, analysis in a GIS, and fieldwork. Working backwards from landscape to process, surfaces were classified according to large- and small-scale morphologies that result from the operation of non-glacial processes, the degree of weathering, regolith characteristics, and the style of glacial modification. Surfaces were also compared in the GIS according to elevation, slope angle, and bedrock lithology. The study revealed five types of relict non-glacial surfaces but also two types of extensively weathered glacial surfaces that were transitional to relict non-glacial surfaces, illustrating spatially variable processes and rates of non-glacial and glacial landscape evolution. Rather than being static preglacial remnants, relict non-glacial surfaces are dynamic features that have continued to evolve during the Quaternary. The classification provides hypotheses for landscape evolution that can be field tested through, for example, terrestrial cosmogenic nuclide studies and geochemical analyses of fine matrix materials. The classification may be applicable to relict non-glacial surfaces in other formerly glaciated landscapes

  • 12.
    Goodfellow, Bradley
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Fabel, Derek
    Fredin, Ola
    Derron, M.-H.
    Relict non-glacial surfaces in formerly glaciated landscapes: dynamic landform systems?2007In: Quaternary International, 2007Conference paper (Refereed)
    Abstract [en]

    Relict non-glacial surfaces occur within many formerly glaciated landscapes

    and contain important information on past surface processes and long-term landscape evolution. While cosmogenic dating has confirmed

    the antiquity of relict non-glacial surfaces, the processes that contribute to their evolution and, consequently, the time scales over which they develop remain poorly understood. Of particular importance

    is the possibility that relict non-glacial surfaces may provide geomorphic markers for the reconstruction of preglacial landscapes, which would allow subsequent glacial erosion to be quantified. Furthermore,

    relict non-glacial surfaces may also hold information on preglacial

    and interglacial environmental conditions. An investigation of relict non-glacial surfaces was undertaken through remote sensing, mapping and analysis of surfaces in a GIS, and regolith studies involving

    cosmogenic dating-, grain size-, X-ray diffraction-, and X-ray fluorescence

    analyses. On the basis of these on-going studies, we show that depending on spatial variables such as bedrock lithology, slope, regolith thickness, and the abundance of fine matrix and water some surfaces are denuding very slowly, while others display more rapid denudation. High spatial variability in denudation rates results in changing surface morphologies over time. Rather than being static preglacial

    remnants, relict non-glacial surfaces are dynamic features that have evolved during the Quaternary. While reconstructions of preglacial

    landscapes and subsequent quantifications of glacial erosion from relict non-glacial surfaces remain valid, the Quaternary evolution of these surfaces should also be considered.

  • 13.
    Goodfellow, Bradley
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Fabel, Derek
    Fredin, Ola
    Derron, M.-H.
    Relict non-glacial surfaces in formerly glaciated landscapes: dynamic landform systems?2007In: Geophysical Research Abstracts, 2007Conference paper (Refereed)
    Abstract [en]

    Relict non-glacial surfaces occur within many formerly glaciated landscapes and contain

    important information on past surface processes and long-term landscape evolution

    (Goodfellow, 2007). While cosmogenic dating has confirmed the antiquity of

    relict non-glacial surfaces, the processes that contribute to their evolution and, consequently,

    the time scales over which they develop remain poorly understood. Of particular

    importance is the possibility that relict non-glacial surfaces may provide geomorphic

    markers for the reconstruction of preglacial landscapes, which would allow

    subsequent glacial erosion to be quantified. Furthermore, relict non-glacial surfaces

    may also hold information on preglacial and interglacial environmental conditions.

    An investigation of relict non-glacial surfaces was undertaken through remote sensing,

    mapping and analysis of surfaces in a GIS, and regolith studies involving cosmogenic

    dating-, grain size-, X-ray diffraction-, and X-ray fluorescence analyses. On

    the basis of these on-going studies, we show that depending on spatial variables such

    as bedrock lithology, slope, regolith thickness, and the abundance of fine matrix and

    water some surfaces are denuding very slowly, while others display more rapid denudation.

    High spatial variability in denudation rates results in changing surface morphologies

    over time. Rather than being static preglacial remnants, relict non-glacial

    surfaces are dynamic features that have evolved during the Quaternary. While reconstructions

    of preglacial landscapes and subsequent quantifications of glacial erosion

    from relict non-glacial surfaces remain valid, the Quaternary evolution of these surfaces

    should also be considered.

    Goodfellow B.W., 2007. Relict non-glacial surfaces in formerly glaciated landscapes.

    Earth-Science Reviews, 80(1-2): 47-73.

  • 14.
    Greenwood, Sarah L.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Glacial landforms of extreme size in the Keewatin sector of the Laurentide Ice Sheet2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 15-16, 1894-1910 p.Article in journal (Refereed)
    Abstract [en]

    Assemblages of glacial landforms of a 'mega-scale' are here identified in the Keewatin sector of the Laurentide Ice Sheet. Large till 'belts' or 'ridges', apparent only on satellite imagery and lying beneath the drumlins, flutes and ribbed moraine which comprise the known regional glacial landform record, form extensive and coherent patterns throughout the Keewatin region. Planform and crestline mapping from remotely sensed imagery yields a mapped population of >2500 individual landforms, whose dimensions are on average similar to 10 km long and similar to 1.5 km wide. Based on analysis of their morphology and morphometry, their spatial arrangement and pattern, and comparison with analogues and reference populations of glacial landform types, we interpret three morphological groups of different genetic origin. Two of these are examples of currently known landform types: i) a set of heavily overprinted, i.e. non-pristine, mega-scale glacial lineations, feeding from the heart of the Keewatin region north into Queen Maud Gulf; and ii) a 350 km long moraine zone, overrun by later ice flow paths, and likely associated with the terminal position of an ice sheet prior to the final deglacial episode. A third group, comprising a significant number of the Keewatin population, does not fit any existing category of glacial landforms. Here we report a major new finding: subglacial bedforms, of a mega-scale, transverse to the palaeo-ice flow direction. Mega-scale transverse bedforms have not been previously reported from any palaeo-(or contemporary) ice sheet. Close spatial integration with the ribbed moraine population in Keewatin suggests a similar mode of genesis. The Keewatin landforms indicate there is a fundamental transverse organisation of till at a scale beyond that of conventional transverse bedforms (ribbed moraine), and with as yet unknown implications for our understanding of subglacial processes and ice-bed coupling.

  • 15.
    Hall, Adrian
    et al.
    University of St Andrews, Scotland, UK.
    Ebert, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Nesje, Atle
    Ottesen, Dag
    Selective glacial erosion on the Norwegian passive margin2013In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 41, no 12, 1203-1206 p.Article in journal (Refereed)
    Abstract [en]

    Glaciated passive margins display dramatic fjord coasts, but also commonly retain plateau fragments inland. It has been proposed recently that such elevated, low-relief surfaces on the Norwegian margin are products of highly efficient and extensive glacial and periglacial erosion (the glacial buzzsaw) operating at equilibrium line altitudes (ELAs). We demonstrate here that glacial erosion has acted instead to dissect plateaus in western Norway. Low-relief surfaces are not generally spatially associated with cirques, and do not correlate regionally with modern and Last Glacial Maximum ELAs. Glacier dynamics require instead that glacial erosion is selective, with low-relief surfaces representing islands of limited Pleistocene erosion. Deep glacial erosion of the coast and inner shelf has provided huge volumes of sediment (70,000 km3), largely resolving apparent mismatches (65–100,000 km3) between fjord and valley volumes and Pliocene–Pleistocene sediment wedges offshore. Nonetheless, as Pleistocene glacial valleys and cirques are cut into preexisting mountain relief, tectonics rather than isostatic compensation for glacial erosion have been the main driver for late Cenozoic uplift on the Norwegian passive margin.

  • 16.
    Hall, Adrian M.
    et al.
    University of St Andrews, Scotland, UK.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Glacial and periglacial buzzsaws: fitting mechanisms to metaphors2014In: Quaternary Research, ISSN 0033-5894, E-ISSN 1096-0287, Vol. 81, no 2, 189-192 p.Article in journal (Refereed)
    Abstract [en]

    The buzzsaw hypothesis refers to the potential for glacial and periglacial processes to rapidly denude mountains at and above glacier Equilibrium Line Altitudes (ELAs), irrespective of uplift rates, rock type or pre-existing topography. Here the appropriateness of the buzzsaw metaphor is examined alongside questions of the links between glacial erosion and ELAs, and whether the glacial system can produce low-relief surfaces or limit summit heights. Plateau fragments in mountains on both active orogens and passive margins that have been cited as products of glacial and periglacial buzzsaw erosion instead generally represent dissected remnants of largely inherited, pre-glacial relief. Summit heights may correlate with ELAs but no causal link need be implied as summit erosion rates are low, cirque headwalls may not directly abut summits and, on passive margins, cirques are cut into pre-existing mountain topography. Any simple links between ELAs and glacial erosion break down on passive margins due to topographic forcing of ice-sheet growth, and to the km-scale vertical swaths through which ELAs have shifted through the Quaternary. Glaciers destroy rather than create low-relief rock surfaces through the innate tendency for ice flow to be faster, thicker and warmer along valleys. The glacial buzzsaw cuts down.

  • 17.
    Hopkins, Nathan R.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Evenson, Edward B.
    Kodama, Kenneth P.
    An anisotropy of magnetic susceptibility (AMS) fabric record of till kinematics within a Late Weichselian low Baltic till, southern Sweden2016In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 45, no 4, 846-860 p.Article in journal (Refereed)
    Abstract [en]

    Herein we report on the results of an anisotropy of magnetic susceptibility (AMS) fabric case-study of two Late Weichselian tills exposed in a bedrock quarry in Dalby, Skane, southern Sweden. The region possesses a complex glacial history, reflecting alternating and interacting advances of the main body of the Scandinavian Ice Sheet (SIS) and its ice lobes from the Baltic basin, perhaps driven by streaming ice. AMS till fabrics are robust indicators of ice-flow history and till kinematics, and provide a unique tool to investigate till kinematics within and amongst till units. The till section investigated here contains similar to 8m of the Dalby Till - a dark grey silt-clay rich till deposited during one or more Baltic advance - overlain by similar to 1.5m of the regional surface diamicton. AMS fabrics within the lower part of the Dalby Till conform to the regional surface fluting, and reflect sustained flow from the ENE with progressive increases in basal strain. A boulder-rich horizon approximately 3m from the base of the till marks a restricted excursion in till fabric direction, fabric strength and style of strain. Ice flow is from the SW and W in the upper section. We interpret these fabrics to record shifting ice flow and bed conditions at the margins of the Young Baltic Advance ice lobe in southern Sweden, prior to a short-lived re-advance of the main body of the SIS over mainland Sweden recorded by the surface diamicton.

  • 18.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Polyak, L.
    Edwards, M.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Coakley, B.
    Glacial geomorphology of the Central Arctic Ocean: The Chukchi Borderland and the Lomonosov Ridge2008In: Earth Surface Processes and Landforms, ISSN 0197-9337, E-ISSN 1096-9837, Vol. 33, no 4, 526-545 p.Article in journal (Refereed)
    Abstract [en]

    The last decade of geophysical seafloor mapping in the Arctic Ocean from nuclear submarines and icebreakers reveals a wide variety of glaciogenic geomorphic features at water depths reaching 1000 in. These findings provide new and intriguing insights into the Quaternary glacial history of the Northern Hemisphere. Here we integrate multi- and single beam bathymetric data, chirp sonar profiles and sidescan images from the Chukchi Borderland and Lomonosov Ridge to perform a comparative morphological seafloor study. This investigation aims to elucidate the nature and provenance of ice masses that impacted the Arctic Ocean sea floor during the Quaternary. Mapped glaciogenic bedforms include iceberg keel scours, most abundant at water depths shallower than similar to 350-400 m, flutes and megascale glacial lineations extending as deep as similar to 1000 m below the present sea level, small drumlin-like features and morainic ridges and grounding-zone wedges. The combination of these features indicates that very large glacial ice masses extended into the central Arctic Ocean from surrounding North American and Eurasian ice sheets several times during the Quaternary. Ice shelves occupied large parts of the Arctic Ocean during glacial maxima and ice rises were formed over the Chukchi Borderland and portions of the Lomonosov Ridge. More geophysical and sediment core data combined with modeling experiments are needed to reconstruct the timing and patterns of these events.

  • 19.
    Jansen, John D.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. University of Wollongong, Australia.
    Codilean, A. T.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Fabel, D.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harbor, Jon M.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Purdue University, USA.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kubik, P. W.
    Xu, S.
    Inner gorges cut by subglacial meltwater during Fennoscandian ice sheet decay2014In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 5, 3815- p.Article in journal (Refereed)
    Abstract [en]

    The century-long debate over the origins of inner gorges that were repeatedly covered by Quaternary glaciers hinges upon whether the gorges are fluvial forms eroded by subaerial rivers, or subglacial forms cut beneath ice. Here we apply cosmogenic nuclide exposure dating to seven inner gorges along similar to 500 km of the former Fennoscandian ice sheet margin in combination with a new deglaciation map. We show that the timing of exposure matches the advent of ice-free conditions, strongly suggesting that gorges were cut by channelized subglacial meltwater while simultaneously being shielded from cosmic rays by overlying ice. Given the exceptional hydraulic efficiency required for meltwater channels to erode bedrock and evacuate debris, we deduce that inner gorges are the product of ice sheets undergoing intense surface melting. The lack of postglacial river erosion in our seven gorges implicates subglacial meltwater as a key driver of valley deepening on the Baltic Shield over multiple glacial cycles.

  • 20.
    Kleman, J.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Destouni, G.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Gustafsson, Ö.
    Holmgren, K.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Svensson, G.
    Presentation of the Bert Bolin Centre for Climate Research for the Environmental Committee of Swedish Parliament, Stockholm, May 3, 2011.2011Other (Other (popular science, discussion, etc.))
  • 21.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Geomorphology: Where glaciers cut deep2008In: Nature Geoscience, ISSN 1752-0894, Vol. 1, no 6, 343-344 p.Article in journal (Other (popular science, discussion, etc.))
    Abstract [sv]

    Stunning images of fjords are familiar to geologists, but their origins are less well known. A simple model suggests that topographic steering of ice and erosion proportional to ice discharge are sufficient to explain fjord formation during the Quaternary period.

  • 22.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Subglacial processes and the geomorphological impact of cold-based ice sheets2007Conference paper (Other academic)
    Abstract [en]

    A continuously growing body of literature describes "relict" landforms, such as tors,

    blockfields and patterned ground, in areas formerly glaciated by ice sheets. In almost

    all cases where former ice cover can be convincingly demonstrated or safely

    assumed, this surprising preservation of often small-scale and fragile landforms is

    ascribed to frozen-bed conditions sustained throughout the last glacial event. During

    the last decade, the antiquity of many of these landforms has been demonstrated

    through cosmogenic dating, and the overriding by an ice sheet (as opposed to preservation

    on nunataks) demonstrated by cosmogenic dating of "young" erratics on the

    landforms. Based on these observations, a widely held view is that cold-based ice

    cover essentially preserves any pre-existing landform, and that the erosion potential of

    cold-based ice is zero or minimal. However, contradictory glaciological field evidence

    exists from cold-based valley glaciers, where significant basal sliding, and/or deformation

    in sandy-silty substrata has been observed. Sliding and deformation are processes

    intrinsically linked to change of preexisting morphology and landform production. At

    face value, these two sets of observations are therefore contradictory.

    We here review the glaciological context of the different data sets that have a bearing

    on the issue of landform production under cold-based parts of ice sheets, paying

    particular attention to factors such as ice thickness, type of substratum, position along

    flowline, temperature and probable thermal history. It is found that no significant contradiction

    exists between the two sets of observations because of important differences

    in the glaciological context. In addition, we describe a datset that allows a closer anlysis

    of a "minimal disturbance" case where a relict surface on a formerly frozen-bed

    upland in Sweden is of such a layout and degree of preservation that it allows identification

    of horisontal change (transport) rates on the order of 1m/1000yrs with minimal

    vertical changes. Based on the observations and considerations above, a scheme for

    more detailed classification of "relict" landforms and surfaces is presented, with the

    aim that it shall be useful in an inversion context, i.e. for deducing probable formative

    glaciological conditions and evolution from preserved landform assemblages.

  • 23.
    Kleman, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Applegate, Patrick J.
    Durations and propagation patterns of ice sheet instability events2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, 32-39 p.Article in journal (Refereed)
    Abstract [en]

    Continued atmospheric and ocean warming places parts of the West Antarctic Ice Sheet at risk for collapse through accelerated ice flow and grounding line retreat over reversed bed slopes. However, understanding of the speed and duration of ice sheet instability events remains incomplete, limiting our ability to include these events in sea level rise projections. Here, we use a first-order, empirical approach, exploring past instability events in the Fennoscandian (FIS) and Laurentide (LIS) ice sheets to establish a relationship between catchment size and the duration of instability events. We also examine how instabilities propagate through ice sheet catchments, and how this propagation is controlled by topography and existing flow organisation at the onset of an event. We find that the fastest documented paleo-collapses involved streaming or surging in corridors that are wide compared to their length, and in which fast flow did not resume after the event. Distributed ice stream networks, in which narrow ice streams were intertwined with slow-flow interstream ridges, are not represented among the fastest documented events. For the FIS and LIS, there is geological evidence for instability events covering areas of similar to 100,000 km(2), with durations between 100 and 300 yr. Comparison of the spatial patterns and topographic contexts of Lateglacial collapse events in former Northern Hemisphere ice sheets and the current WAIS suggest that only a minor part of the WAIS area may be at risk for unimpeded collapse, and that negative feedbacks will likely slow or halt ice drawdown in remaining areas. The Pine Island Glacier (PIG) and Thwaites Glacier (TG) catchments in West Antarctica are likely to respond in very different ways to possible further grounding line retreat. The PIG may experience a minor collapse over its main trunk, but the bed topography favours a less dramatic retreat thereafter. The TG is probably not as close to a threshold as PIG, but once efficient drainage has progressed inwards to reach the Bentley Subglacial Basin (BSB) and Bentley Subglacial Trench (BST), a full collapse of the area may occur. The likely time perspective for a BSB BST collapse is the time required for 100-200 km of grounding line retreat in the TG system plus 100-300 years for an actual collapse event.

  • 24.
    Kleman, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Fastook, Jim
    Ebert, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Caballero, Rodrigo
    Stockholm University, Faculty of Science, Department of Meteorology .
    Pre-LGM Northern Hemisphere ice sheet topography2013In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 9, 2365-2378 p.Article in journal (Refereed)
    Abstract [en]

    We here reconstruct the paleotopography of Northern Hemisphere ice sheets during the glacial maxima of marine isotope stages (MIS) 5b and 4.We employ a combined approach, blending geologically based reconstruction and numerical modeling, to arrive at probable ice sheet extents and topographies for each of these two time slices. For a physically based 3-D calculation based on geologically derived 2-D constraints, we use the University of Maine Ice Sheet Model (UMISM) to calculate ice sheet thickness and topography. The approach and ice sheet modeling strategy is designed to provide robust data sets of sufficient resolution for atmospheric circulation experiments for these previously elusive time periods. Two tunable parameters, a temperature scaling function applied to a spliced Vostok–GRIP record, and spatial adjustment of the climatic pole position, were employed iteratively to achieve a good fit to geological constraints where such were available. The model credibly reproduces the first-order pattern of size and location of geologically indicated ice sheets during marine isotope stages (MIS) 5b (86.2 kyr model age) and 4 (64 kyr model age). From the interglacial state of two north–south obstacles to atmospheric circulation (Rocky Mountains and Greenland), by MIS 5b the emergence of combined Quebec–central Arctic and Scandinavian–Barents-Kara ice sheets had increased the number of such highland obstacles to four. The number of major ice sheets remained constant through MIS 4, but the merging of the Cordilleran and the proto-Laurentide Ice Sheet produced a single continent-wide North American ice sheet at the LGM.

  • 25.
    Kleman, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Glasser, Neil
    The subglacial thermal organisation (STO) of ice sheets2007In: Quaternary Science Reviews, Vol. 26, 585-597 p.Article in journal (Refereed)
  • 26.
    Kleman, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    de Angelis, Hernán
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Alm, Göran
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Glasser, Neil
    Aberystwyth University.
    North American Ice Sheet build-up during the last glacial cycle, 115-21 kyr2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 17-18, 2036-2051 p.Article in journal (Refereed)
    Abstract [en]

    The last glacial maximum (LGM) outline and subsequent retreat pattern (21e7 kyr) of North Americanice sheets are reasonably well established. However, the evolution of the ice sheets during their build-upphase towards the LGM between 115 and 21 kyr has remained elusive, making it difficult to verifynumerical ice sheet models for this important time interval. In this paper we outline the pre-LGM icesheet evolution of the Laurentide and Cordilleran ice sheets by using glacial geological and geomorphologicalrecords to make a first-order reconstruction of ice sheet extent and flow pattern. We mappedthe entire area covered by the Laurentide and Cordilleran ice sheets in Landsat MSS images andapproximately 40% of this area in higher resolution Landsat ETMþ images. Mapping in aerial photographsadded further detail primarily in Quebec-Labrador, the Cordilleran region, and on Baffin Island.Our analysis includes the recognition of approximately 500 relative-age relationships from crosscuttinglineations. Together with previously published striae and till fabric data, these are used as the basis forrelative-age assignments of regional flow patterns. For the reconstruction of the most probable ice sheetevolution sequence we employ a stepwise inversion scheme with a clearly defined strategy for delineatingcoherent landforms swarms (reflecting flow direction and configuration), and linking these topreviously published constraints on relative and absolute chronology. Our results reveal that icedispersalcentres in Keewatin and Quebec were dynamically independent for most of pre-LGM time andthat a massive Quebec dispersal centre, rivalling the LGM in extent, existed at times when the SW sectorof the ice sheet had not yet developed. The oldest flow system in eastern Quebec-Labrador (Atlanticswarm had an ice divide closer to the Labrador coast than later configurations). A northern Keewatin-Central Arctic Ice Sheet existed prior to the LGM, but is poorly chronologically constrained. There is alsoevidence for older and more easterly Cordilleran Ice Sheet divide locations than those that prevailedduring the Late Wisconsinan. In terms of ice sheet build-up dynamics, it appears that “residual” ice capsafter warming phases may have played an important role. In particular, the location and size of remnantice masses at the end of major interstadials, i.e. OIS 5c and 5a, must have been critical for subsequentbuild-up patterns, because such remnant “uplands” may have fostered much more rapid ice sheetgrowth than what would have occurred on a fully deglaciated terrain. The ice-sheet configuration duringstadials would also be governed largely by the additional topography that such “residual” ice constitutesbecause of inherent mass balance-topography feedbacks.

  • 27.
    Kleman, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Källén, Erland
    Stockholm University, Faculty of Science, Department of Meteorology .
    Rodhe, Henning
    Stockholm University, Faculty of Science, Department of Meteorology .
    Bern förnekar fysikens grunder2008Other (Other (popular science, discussion, etc.))
  • 28.
    Kleman, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Rodhe, Henning
    Stockholm University, Faculty of Science, Department of Meteorology .
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Svensson, Gunilla
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tjernström, Michael
    Stockholm University, Faculty of Science, Department of Meteorology .
    Rubbat förtroende för forskarna2010In: Svenska Dagbladet, ISSN 1101-2412, no 25 majArticle in journal (Other (popular science, discussion, etc.))
  • 29.
    Kleman, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Spatial domains of the trimline, nunatak and frozen-bed concepts2007In: Geophysical Research Abstracts, 2007Conference paper (Refereed)
    Abstract [en]

    Relict upland morphology has been reported from most glaciated areas, typically forming a dramatic contrast to conventional glacial morphology at lower elevations. The topographical and geographical setting is diverse, ranging from fjord landscapes, such as in Greenland, Norway and Canada, to the hilly hinterland landscapes of, for example, Sweden, Scotland and Baffin Island. The morphological boundary between glacial landscapes and relict landscapes is often so distinct that it has been interpreted to mark a former trimline which, by definition, marks the upper ice-sheet surface. The inference of trimlines, therefore, forms the basis for pinpointing specific uplands and summits as nunataks, and inferring maximum ice sheet elevations. In a different school of thought the same morphological contrast is interpreted to represent topographically-induced subglacial thermal boundaries, i.e frozen-bed conditions under the thinner ice over uplands and thawed-bed basal sliding conditions across intervening lowlands. We review key relationships related to the concepts of trimlines, nunataks, and frozenbed patches. We pay particular attention to (i) the glaciological environment in which trimlines form, (ii) how uplands can be demonstrated to have been nunataks, and (iii) how relict surfaces can be demonstrated to have been ice-overriden, thus justifying a frozen-bed interpretation. We find that “trimline-and-nunatak” interpretations may be valid in coastal high-relief domains, but that it is exceedingly difficult to reliably demonstrate that a certain upland has remained uninterruptedly ice free. The “frozen-bed” interpretations are valid primarily for hinterland domains, where direct evidence (erratics, slight glacial modifications) or circumstantial evidence (isostatic uplift patterns, numerical ice sheet modelling) irrefutably indicate complete ice overriding. The application of terrestrial cosmogenic nuclide studies has recently revived studies of relict surfaces and glacial landscapes. Whereas such studies have convincingly shown the antiquity and subglacial preservation of relict hinterland domains (through studies of bedrock-erratic pairs), it has been impossible to convincingly demonstrate subglacial preservation for some coastal domains in the absence of erratics. It has been equally difficult to demonstrate the presence of nunataks in the coastal domain during maximum glaciation, primarily because the effect of relatively short-lived (< 10,000 years) overriding events are undetectable given current analytical and systematic uncertainties in the cosmogenic nuclide method, and can therefore not be distinguished from a full-exposure scenario.

  • 30.
    Kleman, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Trimlines, nunataks, and frozen-bed concepts valid within restricted spatial domains2007In: Quaternary International, 2007Conference paper (Refereed)
    Abstract [en]

    Relict upland morphology has been reported from most glaciated areas, typically forming a dramatic contrast to conventional glacial morphology at lower elevations. The topographical and geographical setting is diverse, ranging from fjord landscapes, such as in Greenland, Norway and Canada, to the hilly hinterland landscapes of, for example, Sweden, Scotland and Baffin Island. The morphological boundary between glacial landscapes and relict landscapes is often so distinct that it has been interpreted to mark a former trimline which, by definition, marks the upper ice-sheet surface. The inference of trimlines, therefore, forms the basis for pinpointing specific uplands and summits as nunataks, and inferring maximum ice sheet elevations. In a different school of thought the same morphological contrast is interpreted to represent topographically-induced subglacial thermal boundaries, i.e frozen-bed conditions under the thinner ice over uplands and thawed-bed basal sliding conditions across intervening lowlands. We review key relationships related to the concepts of trimlines, nunataks, and frozen-bed patches. We pay particular attention to (i) the glaciological environment in which trimlines form, (ii) how uplands can be demonstrated to have been nunataks, and (iii) how relict surfaces can be demonstrated to have been ice-overriden, thus justifying a frozen-bed interpretation. We find that “trimline-and-nunatak” interpretations may be valid in coastal high-relief domains, but that it is exceedingly difficult to reliably demonstrate that certain uplands have remained uninterruptedly ice free. The “frozen-bed” interpretations are valid primarily for hinterland domains, where direct evidence (erratics, slight glacial modifications) or circumstantial evidence (isostatic uplift patterns, numerical ice sheet modelling) irrefutably indicate complete ice overriding. The application of terrestrial cosmogenic nuclide studies has recently revived studies of relict surfaces and glacial landscapes. Whereas such studies have convincingly shown the antiquity and subglacial preservation of relict hinterland domains (through studies of bedrock-erratic pairs), it has been impossible to convincingly demonstrate subglacial preservation for some coastal domains in the absence of erratics. It has been equally difficult to demonstrate the presence of nunataks in the coastal domain during maximum glaciation, primarily because the effect of relatively short-lived (< 10,000 years) overriding events are undetectable given current analytical and systematic uncertainties in the cosmogenic nuclide method, and can therefore not be distinguished from a full-exposure scenario.

  • 31.
    Kleman, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lundqvist, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Patterns of Quaternary ice sheet erosion and deposition in Fennoscandia and a theoretical framework for explanation2008In: Geomorphology, Vol. 97, no 1-2, 73-90 p.Article in journal (Other (popular science, discussion, etc.))
    Abstract [en]

    It has long been recognised that the formerly glaciated area of Fennoscandia shows large spatial differences in thicknesses of

    Quaternary deposits (mainly tills), and exhibits distinct patterns of glacial scouring and deep linear erosion. The reasons for this

    striking zonation have been elusive, and in particular the relative roles of mountain ice sheets (MIS) and full-sized Fennoscandian

    ice sheets (FIS) in shaping the landscape surface need clarification. On the basis of current advances in our understanding of the

    climate evolution and basal thermal organisation of ice sheets, we perform spatio-temporal qualitative modelling of ice sheet extent

    and migration of erosion and deposition zones through the entire Quaternary, and proceed to suggest an explanatory model for the

    current spatial pattern of Quaternary deposits and the two different types of erosion zones. We use the spatial distribution of fjords

    and deep non-tectonic lakes for delineating zones of deep glacial erosion, and relict landscapes as markers for frozen-bed

    conditions. On the basis of the amount of exposed bedrock, the landscape was classified into a tripartite system of drift thickness

    (thick drift, intermediate drift thickness, absence of drift/scoured zones). It is found that a centrally placed (central and northern

    Sweden) zone of thick drift cannot be explained by deposition under FIS style ice sheets, but is instead likely to be the combined

    result of marginal deposition of fluctuating MIS style ice sheets, primarily during the early and middle Quaternary, and the

    inefficiency of later east-centered FIS style ice sheets in evacuating this drift from underneath their central low-velocity and

    possibly frozen-bed areas. The western (fjord) zone of deep glacial erosion formed underneath both MIS- and FIS style ice sheets

    during the entire Quaternary, while the eastern (lake) zone of deep glacial erosion is exclusively related to MIS style ice sheets, and

    formed largely during the early and middle Quaternary. The scouring zones formed under conditions of rapid ice flow towards

    bathymetrically-defined calving margins of FIS style ice sheets. They likely reflect process patterns of the last two or three FIS

    style ice sheets. The three landscape zones differ in their degree of permanence, with the deep erosion zones being a long-lasting

    legacy in the landscape, more likely to be enhanced than obliterated by subsequent glacial events. The thick drift cover zone, once

    established, appears to have been surprisingly robust to erosion by subsequent glacial events. The scouring zones appear to be the

    most recent and ephemeral of the three zones, with possible major alterations during single glacial events.

  • 32.
    Löfverström, Marcus
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Caballero, Rodrigo
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Evolution of the large-scale atmospheric circulation in response to changing ice sheets over the last glacial cycle2014In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 10, no 4, 1453-1471 p.Article in journal (Refereed)
    Abstract [en]

    We present modelling results of the atmospheric circulation at the cold periods of marine isotope stage 5b (MIS 5b), MIS 4 and the Last Glacial Maximum (LGM), as well as the interglacial. The palaeosimulations are forced by ice-sheet reconstructions consistent with geological evidence and by appropriate insolation and greenhouse gas concentrations. The results suggest that the large-scale atmospheric winter circulation remained largely similar to the interglacial for a significant part of the glacial cycle. The proposed explanation is that the ice sheets were located in areas where their interaction with the mean flow is limited. However, the LGM Laurentide Ice Sheet induces a much larger planetary wave that leads to a zonalisation of the Atlantic jet. In summer, the ice-sheet topography dynamically induces warm temperatures in Alaska and central Asia that inhibits the expansion of the ice sheets into these regions. The warm temperatures may also serve as an explanation for westward propagation of the Eurasian Ice Sheet from MIS 4 to the LGM.

  • 33.
    Löfverström, Marcus
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Liakka, Johan
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    The North American Cordillera - an impediment to growing the Laurentide Ice SheetManuscript (preprint) (Other academic)
  • 34. Löfverström, Marcus
    et al.
    Liakka, Johan
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    The North American Cordillera-An Impediment to Growing the Continent-Wide Laurentide Ice Sheet2015In: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 28, no 23, 9433-9450 p.Article in journal (Refereed)
    Abstract [en]

    This study examines the evolution of a continental-scale ice sheet on a triangular representation of North America, with and without the influence of the Cordilleran region. Simulations are conducted using a comprehensive atmospheric general circulation model asynchronously coupled to a three-dimensional thermomechanical ice-sheet model. The atmospheric state is updated for every 2 x 10(6) km(3) increase in ice volume, and the coupled model is integrated to steady state. In the first experiment a flat continent with no background topography is used. The ice sheet evolves fairly zonally symmetric, and the equilibrium state is continent-wide and has the highest point in the center of the continent. This equilibrium ice sheet forces an anticyclonic circulation that results in relatively warmer (cooler) summer surface temperatures in the northwest (southeast), owing to warm (cold) air advection and radiative heating due to reduced cloudiness. The second experiment includes a simplified representation of the Cordilleran region. The ice sheet's equilibrium state is here structurally different from the flat continent case; the center of mass is strongly shifted to the east and the interior of the continent remains ice freean outline broadly resembling the geologically determined ice margin in Marine Isotope Stage 4. The limited glaciation in the continental interior is the result of warm summer surface temperatures primarily due to stationary waves and radiative feedbacks.

  • 35.
    Margold, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Glacial meltwater landforms of central British Columbia2011In: Journal of Maps, ISSN 1744-5647, 486-506 p.Article in journal (Refereed)
    Abstract [en]

    The Cordilleran Ice Sheet (CIS), which grew and melted repeatedly across the mountain ranges of westernmost Canada during the late Cenozoic, has imprinted its legacy in the form of glacial landforms, such as meltwater landforms. However, despite their abundance, a coherent effort to map meltwater landforms has been lacking. Here, we present a first regional geomorphological map of glacial meltwater landforms of central British Columbia. Series of well-developed meltwater channels occur at higher elevations on the Interior Plateau, in marginal ranges east of the Coast Mountains, in the Skeena and Omineca mountains, and, in much lower abundances, in the Rocky Mountains. Single-ridged eskers, that in direction are consistent with the regional ice flow direction from glacial lineations, occur in elevated areas of the Interior Plateau. Multiple-ridged larger eskers and esker complexes are, on the other hand, confined to the main topographic lows. The geographical distribution of meltwater landforms is a new reliable dataset for use in palaeoglaciological reconstructions and inference of late glacial ice sheet dynamics in central British Columbia.

  • 36.
    Margold, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Late-glacial ice dynamics of the Cordilleran Ice Sheet in northern British Columbia and southern Yukon Territory: retreat pattern of the Liard Lobe reconstructed from the glacial landform recordManuscript (preprint) (Other academic)
    Abstract [en]

    The Liard Lobe formed a part of the northeastern sector of the Cordilleran Ice Sheet and drained ice from accumulation areas in the Selwyn, Pelly, Cassiar and Skeena mountains. This study reconstructs the ice retreat pattern of the Liard Lobe during the last deglaciation from the glacial landform record that is comprised of glacial lineations and landforms of the meltwater system such as eskers, meltwater channels, perched deltas and outwash fans. The spatial distribution of these landforms defines the successive configurations of the ice sheet during the deglaciation. The Liard Lobe retreated to the west and southwest across the Hyland Highland from its local Last Glacial Maximum position in the southeastern Mackenzie Mountains where it coalesced with the Laurentide Ice Sheet. The retreat across the Liard Lowland and a subsequent splitting of the thus far uniform ice surface into several ice lobes is evidenced by large esker complexes that stretch across the Liard Lowland cutting across the contemporary drainage network. Ice margin positions from the late stage of deglaciation are reconstructed locally at the foot of the Cassiar Mountains and farther up-valley in an eastern facing valley of the Cassiar Mountains. The presented landform record indicates that the deglaciation of the Liard Lobe was accomplished mainly by active ice retreat and that ice stagnation did not play a significant role in the deglaciation of this region.

  • 37.
    Margold, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Clague, John
    Simon Fraser University, Department of Earth Sciences.
    Late-glacial retreat pattern of the Cordilleran Ice Sheet in central British Columbia reconstructed from glacial meltwater landformsArticle in journal (Refereed)
    Abstract [en]

    The Cordilleran Ice Sheet (CIS) covered much of the mountainous northwestern part of North America during Pleistocene glaciations. In contrast to other ephemeral Pleistocene ice sheets, the pattern and timing of growth and decay of the CIS are poorly understood. Here, we present a reconstruction of the pattern of late-glacial ice sheet retreat in central British Columbia based on a palaeoglaciological interpretation of ice-marginal meltwater channels, eskers, and deltas mapped from satellite imagery and digital elevation models. A consistent spatial pattern of high-elevation ice-marginal meltwater channels (1600-2400 m a.s.l.) occurs across central British Columbia. They indicate the presence of ice domes over the Skeena Mountains and the central Coast Mountains early during deglaciation. Ice sourced in the Coast Mountains remained dominant over the southern and east-central parts of the Interior Plateau during late-glacial time. Our reconstruction shows a successive westward retreat of the ice margin away from the western foot of the Rocky Mountains, accompanied by the formation and rapid evolution of a glacial lake in the upper Fraser River basin. Final stages of deglaciation were characterized by the frontal retreat of ice lobes through the valleys of the Skeena and Omineca mountains and by the formation of large esker systems in the most prominent topographic lows of the Interior Plateau. We conclude that the CIS underwent a large-scale reconfiguration early during deglaciation and subsequently diminished by thinning and complex frontal retreat towards the Coast Mountains.

  • 38.
    Margold, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister N.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Clague, John J.
    Retreat pattern of the Cordilleran Ice Sheet in central British Columbia at the end of the last glaciation reconstructed from glacial meltwater landforms2013In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 42, no 4, 830-847 p.Article in journal (Refereed)
    Abstract [en]

    The Cordilleran Ice Sheet (CIS) covered much of the mountainous northwestern part of North America at least several times during the Pleistocene. The pattern and timing of its growth and decay are, however, poorly understood. Here, we present a reconstruction of the pattern of ice-sheet retreat in central British Columbia at the end of the last glaciation based on a palaeoglaciological interpretation of ice-marginal meltwater channels, eskers and deltas mapped from satellite imagery and digital elevation models. A consistent spatial pattern of high-elevation (1600-2400m a.s.l.), ice-marginal meltwater channels is evident across central British Columbia. These landforms indicate the presence of ice domes over the Skeena Mountains and the central Coast Mountains early during deglaciation. Ice sourced in the Coast Mountains remained dominant over the southern and east-central parts of the Interior Plateau during deglaciation. Our reconstruction shows a successive westward retreat of the ice margin from the western foot of the Rocky Mountains, accompanied by the formation and rapid evolution of a glacial lake in the upper Fraser River basin. The final stage of deglaciation is characterized by the frontal retreat of ice lobes through the valleys of the Skeena and Omineca Mountains and by the formation of large esker systems in the most prominent topographic lows of the Interior Plateau. We conclude that the CIS underwent a large-scale reconfiguration early during deglaciation and was subsequently diminished by thinning and complex frontal retreat towards the Coast Mountains.

  • 39.
    Margold, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister N.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lateglacial ice dynamics of the Cordilleran Ice Sheet in northern British Columbia and southern Yukon Territory: retreat pattern of the Liard Lobe reconstructed from the glacial landform record2013In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 28, no 2, 180-188 p.Article in journal (Refereed)
    Abstract [en]

    The Liard Lobe formed a part of the north-eastern sector of the Cordilleran Ice Sheet and drained ice from accumulation areas in the Selwyn, Pelly, Cassiar and Skeena mountains. This study reconstructs the ice retreat pattern of the Liard Lobe during the last deglaciation from the glacial landform record that comprises glacial lineations and landforms of the meltwater system such as eskers, meltwater channels, perched deltas and outwash fans. The spatial distribution of these landforms defines the successive configurations of the ice sheet during the deglaciation. The Liard Lobe retreated to the west and south-west across the Hyland Highland from its local Last Glacial Maximum position in the south-eastern Mackenzie Mountains where it coalesced with the Laurentide Ice Sheet. Retreat across the Liard Lowland is evidenced by large esker complexes that stretch across the Liard Lowland cutting across the contemporary drainage network. Ice margin positions from the late stage of deglaciation are reconstructed locally at the foot of the Cassiar Mountains and further up-valley in an eastern-facing valley of the Cassiar Mountains. The presented landform record indicates that the deglaciation of the Liard Lobe was accomplished mainly by active ice retreat and that ice stagnation played a minor role in the deglaciation of this region.

  • 40. Margold, Martin
    et al.
    Stokes, Chris R.
    Clark, Chris D.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Ice streams in the Laurentide Ice Sheet: a new mapping inventory2015In: Journal of Maps, ISSN 1744-5647, E-ISSN 1744-5647, Vol. 11, no 3, 380-395 p.Article in journal (Refereed)
    Abstract [en]

    Rapidly flowing ice streams dominate the drainage of continental ice sheets and are a key component of their mass balance. Due to their potential impact on sea level, their activity in the Antarctic and Greenland Ice Sheets has undergone detailed scrutiny in recent decades. However, these observations only cover a fraction of their 'life-span' and the subglacial processes that facilitate their rapid flow are very difficult to observe. To circumvent these problems, numerous workers have highlighted the potential of investigating palaeo-ice streams tracks, preserved in the landform and sedimentary record of former ice sheets. As such, it is becoming increasingly important to know where and when palaeo-ice streams operated. In this paper, we present a new map of ice streams in the North American Laurentide Ice Sheet (LIS; including the Innuitian Ice Sheet), which was the largest of the ephemeral Pleistocene ice sheets and where numerous ice streams have been identified. We compile previously published evidence of ice stream activity and complement it with new mapping to generate the most complete and consistent mapping inventory to date. The map depicts close to three times as many ice streams (117 in total) compared to previous inventories, and categorises them according to the evidence they left behind, with some locations more speculative than others. The map considerably refines our understanding of LIS dynamics, but there is a clear requirement for improved dating of ice stream activity.

  • 41. Napieralski, Jacob
    et al.
    Hubbard, Alun
    Li, Yingkui
    Harbor, Jon
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Alm, Göran
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Towards a GIS assessment of numerical ice sheet model performance using geomorphological data2007In: Journal of Glaciology, Vol. 53, no 180, 71-83 p.Article in journal (Refereed)
    Abstract [en]

    A major difficulty in assimilating geomorphological information with ice-sheet models is the lack of a consistent methodology to systematically compare model output and field data. As an initial step in establishing a quantitative comparison methodology, automated proximity and conformity analysis (APCA) and automated flow direction analysis (AFDA) have been developed to assess the level of correspondence between modelled ice extent and ice-marginal features such as end moraines, as well as between modelled basal flow directions and palaeo-flow direction indicators, such as glacial lineations. To illustrate the potential of such an approach, an ensemble suite of 40 numerical simulations of the Fennoscandian ice sheet were compared to end moraines of the Last Glacial Maximum and the Younger Dryas and to glacial lineations in northern Sweden using APCA and AFDA. Model experiments evaluated in this manner were ranked according to level of correspondence. Such an approach holds considerable promise for optimizing the parameter space and coherence of ice-flow models by automated, quantitative assessment of multiple ensemble experiments against a database of geological or glaciological evidence.

  • 42. Näslund, Jens-Ove
    et al.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Alexanderson, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Helmens, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Martina
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lundqvist, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Brandefelt, Jenny
    Houmark-Nielsen, Michael
    Kjellström, Erik
    Strandberg, Gustav
    Knudsen, Karen-Luise
    Krog Larsen, Nikolai
    Ukkonen, Pirkko
    Mangerud, Jan
    Fennoscandian paleo-environment and ice sheet dynamics during Marine Isotope Stage (MIS) 3: Report of a workshop held September 20–21, 2007 in Stockholm, Sweden2008Report (Other academic)
  • 43.
    Seguinot, Julien
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. ETH Zürich, Switzerland; GFZ German Research Centre for Geosciences, Germany.
    Rogozhina, Irina
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Margold, Martin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Numerical simulations of the Cordilleran ice sheet through the last glacial cycle2016In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 10, no 2, 639-664 p.Article in journal (Refereed)
    Abstract [en]

    After more than a century of geological research, the Cordilleran ice sheet of North America remains among the least understood in terms of its former extent, volume, and dynamics. Because of the mountainous topography on which the ice sheet formed, geological studies have often had only local or regional relevance and shown such a complexity that ice-sheet-wide spatial reconstructions of advance and retreat patterns are lacking. Here we use a numerical ice sheet model calibrated against field-based evidence to attempt a quantitative reconstruction of the Cordilleran ice sheet history through the last glacial cycle. A series of simulations is driven by time-dependent temperature offsets from six proxy records located around the globe. Although this approach reveals large variations in model response to evolving climate forcing, all simulations produce two major glaciations during marine oxygen isotope stages 4 (62.2-56.9 ka) and 2 (23.2-16.9 ka). The timing of glaciation is better reproduced using temperature reconstructions from Greenland and Antarctic ice cores than from regional oceanic sediment cores. During most of the last glacial cycle, the modelled ice cover is discontinuous and restricted to high mountain areas. However, widespread precipitation over the Skeena Mountains favours the persistence of a central ice dome throughout the glacial cycle. It acts as a nucleation centre before the Last Glacial Maximum and hosts the last remains of Cordilleran ice until the middle Holocene (6.7 ka).

  • 44.
    Stroeven, Arjen
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Harbor, Jon
    Li, Yingkui
    Zhou, Liping
    Caffee, Marc
    Alexanderson, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Ma, Haizhou
    Liu, Gengnian
    Landscape analysis of the Huang He headwaters, NE Tibetan Plateau — Patterns of glacial and fluvial erosion2009In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 103, no 2, 212-226 p.Article in journal (Refereed)
    Abstract [en]

    The large-scale geomorphology of the Huang He (Yellow River) headwaters, centered around the Bayan Har Shan (5267 m asl) in the northeastern part of the Tibetan Plateau, is dominated by an uplifted remnant of a low-relief relict plateau with several mountain ranges. We have performed geomorphological mapping using SRTM topographic data and Landsat 7 ETM+ satellite imagery to evaluate landscape characteristics and patterns, and to investigate the relative importance of different erosional processes in the dissection of this plateau remnant. The distribution of valley morphologies indicates that the eastern and southern margins of the plateau remnant have been extensively dissected by the Huang He and Chang Jiang (Yangtze) rivers and associated tributaries, while the mountain ranges have valley morphologies with U-shaped cross-sections that indicate large impacts from glacial erosion during Quaternary glaciations.

    An east-west decrease in the abundance of glacial valleys in mountains above 4800 m asl suggests that the diminishing size of the mountain blocks, coupled with increased continentality, resulted in more restricted glaciations to the west. Glacial valleys in mountain blocks on the plateau remnant are wider and deeper than adjacent fluvial valleys. This indicates that, integrated over time, the glacial system has been more effective in eroding the mountains of the relict upland surface than the fluvial system. This erosion relationship is reversed, however, on the plateau margin where dramatic fluvial rejuvenation in valleys that are part of the Huang He and Chang Jiang watersheds has consumed whatever glacial morphology existed. A remarkable correspondence exists between the outline of the relict plateau remnant and the outline that has been proposed for the Huang He Ice Sheet. This coincidence could mean that the Huang He Ice Sheet was larger than originally proposed, but that evidence for this has been consumed by fluvial incision at the plateau margin. Alternatively, this coincidence could indicate that what has been described as an ice sheet border is merely the outline of a relict plateau landscape.

    In apparent support of the latter, the absence of large-scale glacial geomorphological evidence on the plains of the relict plateau surface is not consistent with the hypothesis of a Huang He Ice Sheet.

  • 45.
    Stroeven, Arjen
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Fabel, Derek
    Clague, John
    Chronology and dynamics of the Yukon sector of the northern Cordilleran ice sheet2007In: Quaternary International, 2007Conference paper (Refereed)
    Abstract [en]

    The history of the Cordilleran ice sheet (CIS) of western North Amer¬ica is relatively poorly understood despite over one hundred years of field studies. In contrast to other ice sheets, except for the West Antarc¬tic ice sheet, the CIS was largely resting on mountainous terrain. Due to its physiographic characteristics, of having been fed by confluent flow from both the Coast Range and the Rocky Mountains, it appears to have been one of the most dynamic ice age features on Earth. There is a reasonably good understanding of the timing of maximum glacia¬tion for the last glacial cycle (LGM) and for the almost instantaneous onset of postglacial conditions, based on radiocarbon dates. This gen¬eralized picture is better-documented for the southern than for the northern CIS. We focus on the succession of flow patterns of the CIS by mapping glacial lineation systems and ribbed moraine. These land¬forms define the spatial flow organisation, and give insight into the subglacial thermal regime. In addition to the dominating Late Wiscon¬sinan flow pattern, we discovered numerous fragments of older, over¬ridden and partially destroyed lineation systems. These shed light on older, albeit undated, ice sheet configurations with more easterly ice divide locations than during the late Wisconsinan ice sheet configura¬tion. Mapping in the Pelly Mountains region, Yukon Territory, shows remnant relict glacial lineation systems, relict upland surfaces, well-defined end- and lateral moraine systems and abundant LGM lineation systems in the major glacial troughs. We test the hypothesis that sub¬glacial preservation of relict lineation systems and relict uplands define the subglacial temperature distribution of subsequent ice sheets (i.e LGM), particularly the potential occurrence of frozen bed conditions. We will present cosmogenic 10Be ages on end- and lateral moraines that define the upper/distal limit of the CIS in this region, to test wheth¬er mountain summits were likely overridden (and preserved beneath cold-based ice) or were in effect nunataks during maximum of glacia¬tion. A preliminary study of fabric of two superimposed till sheets ex¬posed in a section along the Nisutin River, in an area inferred to have relict lineation systems, showed consistency with inferred ice flow di¬rections from satellite imagery. The presence of a till sheet above the till sheet which, based on till fabric analysis, forms the relict lineations in the area, potentially shows that preservation may have been under influence of slow-flowing ice rather than (just) cold-based conditions.

  • 46.
    Stroeven, Arjen
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Fabel, Derek
    Clague, John
    Dynamics of the Yukon sector of the northern Cordilleran ice sheet2007In: Geophysical Research Abstracts, 2007Conference paper (Refereed)
    Abstract [en]

    The history of the Cordilleran ice sheet (CIS) of western North America is relatively poorly understood despite over one hundred years of field studies. In contrast to other ice sheets, except for the West Antarctic ice sheet, the CIS was largely resting on mountainous terrain. Due to its physiographic characteristics, of having been fed by confluent flow from both the Coast Range and the Rocky Mountains, it appears to have been one of the most dynamic ice age features on Earth. There is a reasonably good understanding of the timing of maximum glaciation for the last glacial cycle (LGM) and for the almost instantaneous onset of postglacial conditions, based on radiocarbon dates. This generalized picture is better-documented for the southern than for the northern CIS. We focus on the succession of flow patterns of the CIS by mapping glacial lineation systems and ribbed moraine. These landforms define the spatial flow organisation, and give insight into the subglacial thermal regime. In addition to the dominating Late Wisconsinan flow pattern, we discovered numerous fragments of older, overridden and partially destroyed lineation systems. These shed light on older, albeit undated, ice sheet configurations with more easterly ice divide locations than during the late Wisconsinan ice sheet configuration. Mapping in the Pelly Mountains region, Yukon Territory, shows remnant relict glacial lineation systems, relict upland surfaces, well-defined end- and lateral moraine systems and abundant LGM lineation systems in the major glacial troughs. We test the hypothesis that subglacial preservation of relict lineation systems and relict uplands define the subglacial temperature distribution of subsequent ice sheets (i.e. LGM), particularly the potential occurrence of frozen bed conditions. We will present cosmogenic beryllium ages on end- and lateral moraines that define the upper/distal limit of the CIS in this region, to test whether mountain summits were likely overridden (and preserved beneath cold-based ice) or were in effect nunataks during maximum of glaciation. A preliminary study of fabric of two superimposed till sheets exposed in a section along the Nisutin River, in an area inferred to have relict lineation systems, showed consistency with inferred ice flow directions from satellite imagery. The presence of a till sheet above the till sheet which, based on till fabric analysis, forms the relict lineations in the area, potentially shows that preservation may have been under influence of slow-flowing ice rather than (just) cold-based conditions.

  • 47.
    Stroeven, Arjen P.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Purdue University .
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Morén, Björn M.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Glacial geomorphology of the Tian Shan2013In: Journal of Maps, ISSN 1744-5647, E-ISSN 1744-5647, Vol. 9, no 4, 505-512 p.Article in journal (Refereed)
    Abstract [en]

    The glacial geomorphology of the Tian Shan has been mapped, with the study area covering almost 638,000km(2). The map, designed to be printed at A0 size due to the elongated shape of the mountain range, is presented at a scale of 1:1,100,000. Five glacial landform categories are presented; glacial valleys, marginal moraines, glacial lineations, hummocky terrain and meltwater channels. These landform categories were mapped using the Shuttle Radar Topography Mission (SRTM) digital elevation model (90m resolution), Landsat 7 ETM+ satellite imagery (30m resolution), and images contained in Google Earth. The mapped landforms were created by glaciers that were restricted to mountain areas and their immediate surroundings.

  • 48.
    Stroeven, Arjen P.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Fabel, Derek
    Fredin, Ola
    Goodfellow, Bradley W.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Lund University, Sweden.
    Harbor, Jonathan M.
    Stockholm University, Faculty of Science, Department of Physical Geography. Purdue University, USA.
    Jansen, John D.
    Stockholm University, Faculty of Science, Department of Physical Geography. University of Potsdam, Germany.
    Olsen, Lars
    Caffee, Marc W.
    Fink, David
    Lundqvist, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Rosqvist, Gunhild C.
    Stockholm University, Faculty of Science, Department of Physical Geography. University of Bergen, Norway.
    Strömberg, Bo
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Jansson, Krister N.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Deglaciation of Fennoscandia2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 147, no SI, 91-121 p.Article in journal (Refereed)
    Abstract [en]

    To provide a new reconstruction of the deglaciation of the Fennoscandian Ice Sheet, in the form of calendar-year time-slices, which are particularly useful for ice sheet modelling, we have compiled and synthesized published geomorphological data for eskers, ice-marginal formations, lineations, marginal meltwater channels, striae, ice-dammed lakes, and geochronological data from radiocarbon, varve, optically-stimulated luminescence, and cosmogenic nuclide dating. This is summarized as a deglaciation map of the Fennoscandian Ice Sheet with isochrons marking every 1000 years between 22 and 13 cal kyr BP and every hundred years between 11.6 and final ice decay after 9.7 cal kyr BP. Deglaciation patterns vary across the Fennoscandian Ice Sheet domain, reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins. For example, the ice sheet margin in the high-precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice-marginal deposits in many fjords and coastal valleys. Retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern Sweden and rapid retreat of the calving ice margin in the Baltic Basin. Our reconstruction is consistent with much of the published research. However, the synthesis of a large amount of existing and new data support refined reconstructions in some areas. For example, the LGM extent of the ice sheet in northwestern Russia was located far east and it occurred at a later time than the rest of the ice sheet, at around 17-15 cal kyr BP. We also propose a slightly different chronology of moraine formation over southern Sweden based on improved correlations of moraine segments using new LiDAR data and tying the timing of moraine formation to Greenland ice core cold stages. Retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet, with the lowest rates on the high-elevation and maritime Norwegian margin. Retreat rates compared to the climatic information provided by the Greenland ice core record show a general correspondence between retreat rate and climatic forcing, although a close match between retreat rate and climate is unlikely because of other controls, such as topography and marine versus terrestrial margins. Overall, the time slice reconstructions of Fennoscandian Ice Sheet deglaciation from 22 to 9.7 cal kyr BP provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the Fennoscandian Ice Sheet, and are an important resource for testing and refining ice sheet models.

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