| 1. |
- Liakka, Johan, 1981-
(författare)
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The mutual interaction between the time-mean atmospheric circulation and continental-scale ice sheets
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Geomorphological evidence of glaciations exist for the Last Glacial Maximum (about 20 kyr ago). At this time, both North America and Eurasia were covered by extensive ice sheets which are both absent today. However, the temporal and spatial evolution of the ice sheets from the previous interglacial up to the fully-glaciated conditions at LGM is still unresolved and remains a vexing question in climate dynamics. The evolution of ice sheets is essentially controlled by the prevailing climate conditions. On glacial time-scales, the climate is shaped the by the orbital variations of the Earth, but also by internal feedbacks within the climate system. In particular, the ice sheets themselves have the potential to change the climate within they evolve. This thesis focuses on the interactions between ice sheets and the time-mean atmospheric circulation (stationary waves). It is studied how the stationary waves, which are forced by the ice-sheet topography, influence ice-sheet evolution through changing the near-surface air temperature. In this thesis, it is shown that the degree of linearity of the atmospheric response controls to what extent the stationary waves can reorganise the structure of ice sheet. Provided that the response is linear, the stationary waves constitute a leading-order feedback, which serves to increase the volume and deform the shape of ice sheets. If the stationary-wave response to ice-sheet topography is nonlinear in character, the impact on the ice-sheet evolution tends to be weak. However, it is further shown that the amplitude of the nonlinear topographical response, and hence its effect on the ice-sheet evolution, can be significantly enhanced if thermal cooling over the ice sheets is taken into account.
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| 2. |
- Kleman, Johan, et al.
(författare)
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Pre-LGM Northern Hemisphere ice sheet topography
- 2013
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 9, s. 2365-2378
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Kleman, Johan, et al.
(författare)
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Rubbat förtroende för forskarna
- 2010
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Ingår i: Svenska Dagbladet. - 1101-2412. ; :25 maj
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 4. |
- Löfverström, Marcus, et al.
(författare)
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Evolution of the large-scale atmospheric circulation in response to changing ice sheets over the last glacial cycle
- 2014
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 10:4, s. 1453-1471
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Löfverström, Marcus, et al.
(författare)
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The North American Cordillera-An Impediment to Growing the Continent-Wide Laurentide Ice Sheet
- 2015
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Ingår i: Journal of Climate. - 0894-8755 .- 1520-0442. ; 28:23, s. 9433-9450
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
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| 7. |
- De Angelis, Hernán, et al.
(författare)
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Palaeo-ice stream onsets: examples from the north-eastern Laurentide Ice Sheet
- 2008
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Ingår i: Earth Surface Processes and Landforms. - : Wiley. - 0197-9337 .- 1096-9837. ; 33:4, s. 560-572
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- De Angelis, Hernán, et al.
(författare)
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Palaeo-ice streams in the Foxe/Baffin sector of the Laurentide Ice Sheet
- 2007
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 26:9-10, s. 1313-1331
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- De Angelis, Hernán, 1974-
(författare)
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Palaeo-ice streams in the north-eastern Laurentide Ice Sheet
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a palaeoglaciological study aimed to determine the location, geometry and temporal evolution of palaeo-ice streams of the north-easternmost Laurentide Ice Sheet. The work was accomplished through the geomorphological interpretation of satellite imagery over 3.19 x 106 km2 of the Canadian Arctic, using a glaciological inversion scheme. Ice streams were active in this region during most of the time between the Last Glacial Maximum and the last deglaciation. A web of ice streams and inter-ice stream areas existed. Three major ice stream networks are identified: the M'Clintock Channel, Gulf of Boothia – Lancaster Sound and Hudson Strait. The M'Clintock Channel bears the most complex landform record, comprising three generations of palaeo-ice streams. Their location was weakly controlled by the subglacial topography and their geometry was determined by frozen-bed portions of the ice sheet, thus providing evidence for pure ice streams in the Laurentide Ice Sheet. In contrast, the more pronounced relief of the Gulf of Boothia – Lancaster Sound corridor supported topographically controlled ice streams. The landform record on emerged land along Hudson Strait is insufficient to support the existence of ice streams. It is therefore proposed that ice streams were constrained within the deep parts of the strait while flanked by cold-based zones on the margins. Small transient ice streams on Baffin and Prince of Wales islands drained local remnant ice caps during the collapse of the ice sheet. Analysis of the controls on the location and flow of palaeo-ice streams suggests that the interaction between the subglacial topography and thermal state of the substrate plays a more fundamental role than the geology. It is concluded that the behaviour of ice streams cannot be explained in terms of environmental controls alone, but the complex dynamics of ice stream shear margins and onset zones must be considered.
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| 10. |
- De Angelis, Hernán, et al.
(författare)
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Palaeo-ice streams in the northern Keewatin sector of the Laurentide Ice Sheet
- 2005
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Ingår i: Annals of Glaciology. - : International Glaciological Society. - 0260-3055 .- 1727-5644. ; 42, s. 135-144
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 11. |
- Dessie, Gessesse, et al.
(författare)
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Pattern and Magnitude of Deforestation in the South Central Rift Valley Region of Ethiopia
- 2007
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Ingår i: Mountain Research And Development. ; 27:2, s. 162-168
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 12. |
- Ebert, Karin, et al.
(författare)
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Factors determining the impact of glacial erosion on shield surfaces
- 2013
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Ingår i: 8th International Conference (AIG) on Geomorphology. ; , s. 272-272
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 13. |
- Ebert, Karin, 1976-, et al.
(författare)
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Ice sheet erosional impacts in the low-relief shield terrain of northern Fennoscandia
- 2014
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Ingår i: 44th international Arctic Workshop, Program & Abstracts 2014. Institute of Arctic and Alpine Research (INSTAAR), University of Colorado at Boulder, 131 pp.. ; , s. 42-
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 14. |
- Ebert, Karin, et al.
(författare)
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The impact of glacial erosion on northern shields
- 2012
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Ingår i: 42nd International Arcitc Workshop, Program and Abstracts 2012. Institute of Arctic and Alpine Research (INSTAAR), University of Colorado at Boulder, 115pp..
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 15. |
- Ebert, Karin, 1976-, et al.
(författare)
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Unequal ice-sheet erosional impacts across low-relief shield terrain in northern Fennoscandia
- 2015
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 233:SI, s. 64-74
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 16. |
- Fabel, D., et al.
(författare)
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Retreat rate of the northern Fennoscandian Ice Sheet margin
- 2007
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Ingår i: Geophysical Research Abstracts.
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Konferensbidrag (refereegranskat)abstract
- 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
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| 17. |
- Fredin, Ola, 1972-
(författare)
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Mountain centered icefields in northern Scandinavia
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mountain centered glaciers have played a major role throughout the last three million years in the Scandinavian mountains. The climatic extremes, like the present warm interglacial or cold glacial maxima, are very short-lived compared to the periods of intermediate climate conditions, characterized by the persistence of mountain based glaciers and ice fields of regional size. These have persisted in the Scandinavian mountains for about 65% of the Quaternary. Mountain based glaciers thus had a profound impact on large-scale geomorphology, which is manifested in large-scale glacial landforms such as fjords, glacial lakes and U-shaped valleys in and close to the mountain range.Through a mapping of glacial landforms in the northern Scandinavian mountain range, in particular a striking set of lateral moraines, this thesis offers new insights into Weichselian stages predating the last glacial maximum. The aerial photograph mapping and field evidence yield evidence that these lateral moraines were overridden by glacier ice subsequent to their formation. The lateral moraines were dated using terrestrial cosmogenic nuclide techniques. Although the terrestrial cosmogenic nuclide signature of the moraines is inconclusive, an early Weichselian age is tentatively suggested through correlations with other landforms and stratigraphical archives in the region. The abundance and coherent spatial pattern of the lateral moraines also allow a spatial reconstruction of this ice field. The ice field was controlled by topography and had nunataks protruding also where it was thickest close to the elevation axis of the Scandinavian mountain range. Outlet glaciers discharged into the Norwegian fjords and major valleys in Sweden.The process by which mountain based glaciers grow into an ice sheet is a matter of debate. In this thesis, a feedback mechanism between debris on the ice surface and ice sheet growth is presented. In essence, the growth of glaciers and ice sheets may be accelerated by an abundance of debris in their ablation areas. This may occur when the debris cover on the glacier surface inhibits ablation, effectively increasing the glaciers mass balance. It is thus possible that a dirty ablation area may cause the glacier to advance further than a clean glacier under similar conditions. An ice free period of significant length allows soil production through weathering, frost shattering, and slope processes. As glaciers advance through this assemblage of sediments, significant amounts of debris end up on the surface due to both mass wastage and subglacial entrainment. Evidence that this chain of events may occur, is given by large expanses of hummocky moraine (local name Veiki moraine) in the northern Swedish lowlands. Because the Veiki moraine has been correlated with the first Weichselian advance following the Eemian, it implies a heavily debris charged ice sheet emanating from the mountain range and terminating in a stagnant fashion in the lowlands.
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| 18. |
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| 19. |
- Gessesse Dessie, , 1963-
(författare)
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Forest decline in South Central Ethiopia : Extent, history and process
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This study presents the extent, history and process of forest decline in Awassa watershed, south central Ethiopia. By combining different data sources such as satellite images, social surveys and historical documents, forest decline is described quantitatively and qualitatively and the main causes behind this process are identified. Forest decline in the study area is interpreted as the result of a combination of socio-political changes, economic activities, population growth, cultural patterns and agricultural developments while local conflicts over resources also play an important role. The findings of this study reveal forest decline to be a continuous process associated with spatial fragmentation and location specific losses. The recent increase in production of the cash crop khat has made a significant impact on the forest through several mechanisms: it relocates the agricultural/forest frontier; it causes intrusion and permanent settlement within forests; and fragments remaining forest. The analysis of human-spatial boundaries indicates unsystematic management of the natural forests by several administrative units. As a result, multiple claims have been made on the forests simultaneously as weak control and accountability conditions have negatively affected forest management. The main conclusions are as follows: Forest decline in the study area has a long history, spanning at least one century. The causes are identifiable as both temporally spaced individual events as well as chains of events. These interact with each other at different levels and scales as well as with the geographical properties of the study area. Land users’ rationale in weighing the advantages between keeping and replacing the forest is affected by economic gain, market conditions and transport facilities. Multiple claims to the forest land and weak accountability contribute to inefficient management, which accelerates forest decline.
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| 20. |
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| 21. |
- Glasser, Neil, et al.
(författare)
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The glacial geomorphology and Pleistocene history of South America between 38 degrees S and 56 degrees S
- 2008
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Ingår i: QUATERNARY SCIENCE REVIEWS. - : Elsevier. - 0277-3791. ; 27:3-4, s. 365-390
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 22. |
- Goodfellow, Bradley, et al.
(författare)
-
Deciphering a non-glacial/glacial landscape mosaic in the northern Swedish mountains
- 2008
-
Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X. ; 93:3-4, s. 213-232
-
Tidskriftsartikel (refereegranskat)abstract
- 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
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| 23. |
- Goodfellow, Bradley, et al.
(författare)
-
Relict non-glacial surfaces in formerly glaciated landscapes: dynamic landform systems?
- 2007
-
Ingår i: Geophysical Research Abstracts.
-
Konferensbidrag (refereegranskat)abstract
- Relict non-glacial surfaces occur within many formerly glaciated landscapes and containimportant information on past surface processes and long-term landscape evolution(Goodfellow, 2007). While cosmogenic dating has confirmed the antiquity ofrelict non-glacial surfaces, the processes that contribute to their evolution and, consequently,the time scales over which they develop remain poorly understood. Of particularimportance is the possibility that relict non-glacial surfaces may provide geomorphicmarkers for the reconstruction of preglacial landscapes, which would allowsubsequent glacial erosion to be quantified. Furthermore, relict non-glacial surfacesmay 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 cosmogenicdating-, grain size-, X-ray diffraction-, and X-ray fluorescence analyses. Onthe basis of these on-going studies, we show that depending on spatial variables suchas bedrock lithology, slope, regolith thickness, and the abundance of fine matrix andwater some surfaces are denuding very slowly, while others display more rapid denudation.High spatial variability in denudation rates results in changing surface morphologiesover time. Rather than being static preglacial remnants, relict non-glacialsurfaces are dynamic features that have evolved during the Quaternary. While reconstructionsof preglacial landscapes and subsequent quantifications of glacial erosionfrom relict non-glacial surfaces remain valid, the Quaternary evolution of these surfacesshould also be considered.Goodfellow B.W., 2007. Relict non-glacial surfaces in formerly glaciated landscapes.Earth-Science Reviews, 80(1-2): 47-73.
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| 24. |
- Goodfellow, Bradley, et al.
(författare)
-
Relict non-glacial surfaces in formerly glaciated landscapes: dynamic landform systems?
- 2007
-
Ingår i: Quaternary International.
-
Konferensbidrag (refereegranskat)abstract
- Relict non-glacial surfaces occur within many formerly glaciated landscapesand contain important information on past surface processes and long-term landscape evolution. While cosmogenic dating has confirmedthe 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 importanceis 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 preglacialand 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 involvingcosmogenic dating-, grain size-, X-ray diffraction-, and X-ray fluorescenceanalyses. 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 preglacialremnants, relict non-glacial surfaces are dynamic features that have evolved during the Quaternary. While reconstructions of preglaciallandscapes and subsequent quantifications of glacial erosion from relict non-glacial surfaces remain valid, the Quaternary evolution of these surfaces should also be considered.
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| 25. |
- Goodfellow, Bradley W., 1971-
(författare)
-
Relict non-glacial surfaces and autochthonous blockfields in the northern Swedish mountains
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Relict non-glacial surfaces occur in many formerly glaciated landscapes, where they represent areas that have escaped significant glacial modification. Frequently distinguished by blockfield mantles, relict non-glacial surfaces are important archives of long-term weathering and landscape evolution processes. The aim of this thesis is to examine the distribution, weathering, ages, and formation of relict non-glacial surfaces in the northern Swedish mountains. Mapping of surfaces from aerial photographs and analysis in a GIS revealed five types of relict non-glacial surfaces that reflect differences in surface process types or rates according to elevation, gradient, and bedrock lithology. Clast characteristics and fine matrix granulometry, chemistry, and mineralogy reveal minimal chemical weathering of the blockfields. Terrestrial cosmogenic nuclides were measured in quartz samples from two blockfield-mantled summits and a numerical ice sheet model was applied to account for periods of surface burial beneath ice sheets and nuclide production rate changes attributable to glacial isostasy. Total surface histories for each summit are almost certainly, but not unequivocally, confined to the Quaternary. Maximum modelled erosion rates are as low as 4.0 mm/kyr, which is likely to be near the low extreme for relict non-glacial surfaces in this landscape. The blockfields of the northern Swedish mountains are Quaternary features formed through subsurface physical weathering processes. While there is no need to appeal to Neogene chemical weathering to explain blockfield origins, these surfaces have remained continuously regolith-mantled and non-glacial since their inception. Polygenetic surface histories are therefore indicated, where the large-scale surface morphologies are potentially older than their regolith mantles.
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| 26. |
- Greenwood, Sarah L., et al.
(författare)
-
Glacial landforms of extreme size in the Keewatin sector of the Laurentide Ice Sheet
- 2010
-
Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 29:15-16, s. 1894-1910
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 27. |
- Hall, Adrian M., et al.
(författare)
-
Glacial and periglacial buzzsaws : fitting mechanisms to metaphors
- 2014
-
Ingår i: Quaternary Research. - : Cambridge University Press (CUP). - 0033-5894 .- 1096-0287. ; 81:2, s. 189-192
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 28. |
- Hall, Adrian, et al.
(författare)
-
Selective glacial erosion on the Norwegian passive margin
- 2013
-
Ingår i: Geology. - 0091-7613 .- 1943-2682. ; 41:12, s. 1203-1206
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 29. |
- Hellström, Maria, et al.
(författare)
-
Artificial light quality changes colonization ability of biocontrol agents under greenhouse conditions
- 2023
-
Ingår i: Acta Horticulturae. - 0567-7572 .- 2406-6168. ; , s. 299-306
-
Konferensbidrag (refereegranskat)abstract
- Integrated pest control measures are important in order to cope with fungal foliar pathogens in greenhouse settings. Biocontrol agents (BCA) play an important role in this context, but disease control results obtained in laboratory experiments cannot always be repeated in larger greenhouse settings. Impaired dispersal and establishment of BCAs on leaves and sites of action may be among the causes for failing efficacy. We studied the role of basic mechanisms for BCAs’ efficacy under greenhouse conditions, namely dispersal and establishment. In the first experiment three BCAs from three commercial products were applied by foliar spray to greenhouse-grown tomatoes (Solanum lycopersicum L.) and begonias (Begonia × hiemalis). Leaves were harvested according to a pre-determined time schedule and the viable BCA cells were quantified by plate count. In the second experiment tomatoes were sprayed and exposed to an array of wavelengths (full spectrum, 420, 530 and 660 nm) and followed during 48 h post inoculation (hpi). We found that the BCAs lifestyle choices varied depending on light quality and target crop. These appear to be decisive parameters for BCA dispersal and establishment on leaves.
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| 30. |
- Hopkins, Nathan R., et al.
(författare)
-
An anisotropy of magnetic susceptibility (AMS) fabric record of till kinematics within a Late Weichselian low Baltic till, southern Sweden
- 2016
-
Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 45:4, s. 846-860
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 31. |
- Jakobsson, Martin, et al.
(författare)
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Glacial geomorphology of the Central Arctic Ocean : The Chukchi Borderland and the Lomonosov Ridge
- 2008
-
Ingår i: Earth Surface Processes and Landforms. - : Wiley. - 0197-9337 .- 1096-9837. ; 33:4, s. 526-545
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 32. |
- Jansen, John D., et al.
(författare)
-
Inner gorges cut by subglacial meltwater during Fennoscandian ice sheet decay
- 2014
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 3815-
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 33. |
- Johansson, A. Malin
(författare)
-
Remote sensing of supra-glacial lakes on the west Greenland Ice Sheet
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Greenland Ice Sheet is the largest ice sheet in the northern hemisphere. Ongoing melting of the ice sheet, resulting in increased mass loss relative to the longer term trend, has raised concerns about the stability of the ice sheet. Melt water generated at the surface is temporarily stored in supra-glacial lakes on the ice sheet. Connections between melt water generation, storage and ice sheet dynamics highlight the importance of the surface hydrological system.In this thesis different methods are used that improve our ability to observe the supra-glacial lake system on the west Greenland Ice Sheet. This region of the Greenland Ice Sheet has the most extensive supra-glacial hydrological system with a dense network of streams connecting lakes that can exceed several square kilometres in area. Synthetic Aperture Radar (SAR) and visible-near infrared (VNIR) images are used to explore the potential of different sensor systems for regular observations of the supra-glacial lakes. SAR imagery is found to be a useful complement to VNIR data. VNIR data from moderate resolution sensors are preferred as these provide high temporal resolution data, ameliorating problems with cloud cover.The dynamic nature of the lakes makes automated classification difficult and manual mapping has been widely used. Here a new method is proposed that improves on existing methods by automating the identification and classification of lakes, and by introducing a flexible system that can capture the full range of lake forms. Applying our new method we are better able to analyse the evolution of lakes over a number of melt seasons. We find that lakes initiate after approximately 40 positive degree days. Most lakes exist for less than 20 days before draining, or later in the season, and less often, freezing over. Using the automated method developed in this thesis lakes have been mapped in imagery from 2001–2010 at approximately five day intervals.
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| 34. |
- Kleman, Johan, et al.
(författare)
-
Age and duration of a MIS 3 interstadial in the Fennoscandian Ice Sheet core area-Implications for ice sheet dynamics
- 2021
-
Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 264
-
Tidskriftsartikel (refereegranskat)abstract
- Previous assumptions of continuous ice cover of the core area of the Fennoscandian Ice Sheet, from Marine Isotope Stage 4 (ca. 70 ka) to the end of MIS 2 (ca. 12 ka), have been challenged by the discovery of several sites in central and northern Scandinavia with interstadial sediments of assumed MIS 3 age. The sequences have often been dated by Optically Stimulated Luminescence (OSL) and dates of around 55 ka are present at most sites, indicating ice-free conditions at this time. There is less consensus about the timing of the build-up and advance of the last (Late Weichselian) ice sheet after this ice-free stage. To address the duration of MIS 3 ice-free conditions in central Scandinavia, we reviewed available dating evidence. At the few sites where multiple OSL dates are available, ages indicate around 15 ka of ice-free conditions. Two studies employing cosmogenic nuclide dating of preserved interstadial ground surfaces both indicate a 20 ka long period of ice-free conditions during the last ice-free period before the Holocene. Our interpretation is that central Scandinavia became ice-free around 55 ka and remained so until c. 35 ka, when the Scandinavian Ice Sheet started to expand once again. Expansion started from a small-sized remnant ice sheet, or from separate remnant ice caps in Norway. Available data limits the size of any Scandinavian ice sheet remnant surviving the MIS 3 interstadial to less than 1 m of global sea-level equivalent.
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| 35. |
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| 36. |
- Kleman, Johan, et al.
(författare)
-
Durations and propagation patterns of ice sheet instability events
- 2014
-
Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 92, s. 32-39
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 37. |
- Kleman, Johan
(författare)
-
Geomorphology : Where glaciers cut deep
- 2008
-
Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 1:6, s. 343-344
-
Tidskriftsartikel (populärvet., debatt m.m.)abstract
- 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.
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| 38. |
- Kleman, Johan, et al.
(författare)
-
Landscape evolution and landform inheritance in tectonically active regions : The case of the Southwestern Peloponnese, Greece
- 2016
-
Ingår i: Zeitschrift für Geomorphologie. - : Schweizerbart. - 0372-8854. ; 60:2, s. 171-193
-
Tidskriftsartikel (refereegranskat)abstract
- The Peloponnese in southwestern Greece fronts the Hellenic Arc at the boundary between the European and African plates. The relief is developed across deeply eroded nappes and folds that represent the roots of Alpine mountains developed during Early Miocene collision. During the Plio-Pleistocene, the geomorphological development of the region was affected by both large-amplitude climatic swings and neotectonic uplift/subsidence of individual blocks. Combined tectonic and climatic forcing acting on existing mountain, piedmont and basin terrains developed across diverse low grade metamorphic and sedimentary rocks, including thick carbonate units, led to a geomorphological evolution that was both area-specific and highly variable over time. We here identify and analyse landforms of the southwestern Peloponnese and the climatic and tectonic events that have been driving the geomorphic evolution during the Plio-Pleistocene. The observational database consists of studies of river profiles, spatial landform distribution and genetic classification of landforms, some of them not previously described from the area. We observe that some important landforms and landscape elements can only be understood in the context of a long Plio-Pleistocene time perspective and reflect particular tectonic trends and events. We examine a partly dissected and southward-tilted pediment surface along the west side of the Mani Peninsula. The seaward truncation of this surface is interpreted to reflect Late Pliocene rifting and uplifting of the edge of Taygetos horst. Analysis of the spatial relations between landforms suggests that before the onset of rifting and the late-Pliocene-Pleistocene phase of uplift, a mature mountain-piedmont morphology already existed in the Taygetos-Mani block. The along-crest elevation differences were less pronounced than they are today, and the central part of the massif was fluvially dissected to a lesser depth than today. The pre-rifting elevation of the highest Taygetos summits is inferred to have been 1800-2000 m. Despite active neotectonics, the Peloponnese retains major landforms that have persisted through 1-3 Myr of slow erosion, due to partial exhumation, karstification and remoteness from drainage lines. A coherent inherited or relict surface comprising the highest summit of the Taygetos Mountains and a disjunct high-elevation, low-gradient valley is identified. We infer that this older morphology formed at considerably lower elevation and has since been uplifted to its present position. It is indicative of locally low summit erosion rates throughout Plio-Pleistocene uplift of the Taygetos horst. The impact of climate changes is most obvious at the lowest and highest elevations (<500 m and >2000 m). At the lowest elevations, eustatic sea level changes influenced the spatial location of erosion and sedimentation, and ravine systems developed in uplifted marine sediments. At the highest elevations, glaciation has during the last few glacial cycles left a diagnostic imprint. At intermediate elevations, the landscape can be described as a continuously evolving fluvial landscape in which climatic changes have left few or no diagnostic landforms. Our results have implications for interpretation of other mountainous carbonate areas, particularly in the climatically distinctive Mediterranean region. Tectonics appears to have been the first-order driver for geomorphic evolution, the effects of which must be clarified before study of climate impact on landform development can be possible or meaningful. The Taygetos Mountains and Mani Peninsula provide a case study that illuminates how a multiple age landscape can result from spatially extremely uneven erosional impacts, where tectonic isolation, remoteness from drainage lines, and karstification are important processes for creating inherited and only slowly changing landscape elements.
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| 39. |
- Kleman, Johan, et al.
(författare)
-
North American Ice Sheet build-up during the last glacial cycle, 115-21 kyr
- 2010
-
Ingår i: Quaternary Science Reviews. - : Elsevier. - 0277-3791 .- 1873-457X. ; 29:17-18, s. 2036-2051
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 40. |
- Kleman, Johan, et al.
(författare)
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Patterns of Quaternary ice sheet erosion and deposition in Fennoscandia and a theoretical framework for explanation
- 2008
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Ingår i: Geomorphology. ; 97:1-2, s. 73-90
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- It has long been recognised that the formerly glaciated area of Fennoscandia shows large spatial differences in thicknesses ofQuaternary deposits (mainly tills), and exhibits distinct patterns of glacial scouring and deep linear erosion. The reasons for thisstriking zonation have been elusive, and in particular the relative roles of mountain ice sheets (MIS) and full-sized Fennoscandianice sheets (FIS) in shaping the landscape surface need clarification. On the basis of current advances in our understanding of theclimate evolution and basal thermal organisation of ice sheets, we perform spatio-temporal qualitative modelling of ice sheet extentand migration of erosion and deposition zones through the entire Quaternary, and proceed to suggest an explanatory model for thecurrent spatial pattern of Quaternary deposits and the two different types of erosion zones. We use the spatial distribution of fjordsand deep non-tectonic lakes for delineating zones of deep glacial erosion, and relict landscapes as markers for frozen-bedconditions. 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 northernSweden) zone of thick drift cannot be explained by deposition under FIS style ice sheets, but is instead likely to be the combinedresult of marginal deposition of fluctuating MIS style ice sheets, primarily during the early and middle Quaternary, and theinefficiency of later east-centered FIS style ice sheets in evacuating this drift from underneath their central low-velocity andpossibly frozen-bed areas. The western (fjord) zone of deep glacial erosion formed underneath both MIS- and FIS style ice sheetsduring the entire Quaternary, while the eastern (lake) zone of deep glacial erosion is exclusively related to MIS style ice sheets, andformed largely during the early and middle Quaternary. The scouring zones formed under conditions of rapid ice flow towardsbathymetrically-defined calving margins of FIS style ice sheets. They likely reflect process patterns of the last two or three FISstyle ice sheets. The three landscape zones differ in their degree of permanence, with the deep erosion zones being a long-lastinglegacy in the landscape, more likely to be enhanced than obliterated by subsequent glacial events. The thick drift cover zone, onceestablished, appears to have been surprisingly robust to erosion by subsequent glacial events. The scouring zones appear to be themost recent and ephemeral of the three zones, with possible major alterations during single glacial events.
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| 41. |
- Kleman, Johan, et al.
(författare)
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Spatial domains of the trimline, nunatak and frozen-bed concepts
- 2007
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Ingår i: Geophysical Research Abstracts.
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 42. |
- Kleman, Johan
(författare)
-
Subglacial processes and the geomorphological impact of cold-based ice sheets
- 2007
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A continuously growing body of literature describes "relict" landforms, such as tors,blockfields and patterned ground, in areas formerly glaciated by ice sheets. In almostall cases where former ice cover can be convincingly demonstrated or safelyassumed, this surprising preservation of often small-scale and fragile landforms isascribed to frozen-bed conditions sustained throughout the last glacial event. Duringthe last decade, the antiquity of many of these landforms has been demonstratedthrough cosmogenic dating, and the overriding by an ice sheet (as opposed to preservationon nunataks) demonstrated by cosmogenic dating of "young" erratics on thelandforms. Based on these observations, a widely held view is that cold-based icecover essentially preserves any pre-existing landform, and that the erosion potential ofcold-based ice is zero or minimal. However, contradictory glaciological field evidenceexists from cold-based valley glaciers, where significant basal sliding, and/or deformationin sandy-silty substrata has been observed. Sliding and deformation are processesintrinsically linked to change of preexisting morphology and landform production. Atface value, these two sets of observations are therefore contradictory.We here review the glaciological context of the different data sets that have a bearingon the issue of landform production under cold-based parts of ice sheets, payingparticular attention to factors such as ice thickness, type of substratum, position alongflowline, temperature and probable thermal history. It is found that no significant contradictionexists between the two sets of observations because of important differencesin the glaciological context. In addition, we describe a datset that allows a closer anlysisof a "minimal disturbance" case where a relict surface on a formerly frozen-bedupland in Sweden is of such a layout and degree of preservation that it allows identificationof horisontal change (transport) rates on the order of 1m/1000yrs with minimalvertical changes. Based on the observations and considerations above, a scheme formore detailed classification of "relict" landforms and surfaces is presented, with theaim that it shall be useful in an inversion context, i.e. for deducing probable formativeglaciological conditions and evolution from preserved landform assemblages.
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| 43. |
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| 44. |
- Kleman, Johan, 1953-
(författare)
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The spectral reflectance of coniferous tree stands and of barley influenced by stress : an analysis of field measured spectral data
- 1985
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on the spectral signatures for vegetation. Knowledge about the spectral characteristics of different vegetation types is imperative for an efficient use of existing remote sensing systems, and also to provide guidelines for sensor development. In this work the relationship between the spectral reflectance factor and the object type, or the state of the object, is analyzed. Two different vegetation types have been studied, coniferous forest stands and barley fields. The spectral reflectance in the wavelength range 0.4—2.3 /tm for differently irrigated and fertilized plots of barley were measured during three years. The relationships between different spectral parameters and water status, biomass and grain yield are analyzed. A spectral parameter strongly related to the water status, but not to the biomass, is presented. The information content in the 1.3—2.3 µm range is discussed and it was found that the water content is only one of several factors governing canopy reflectance at these wavelengths. A method for making spectral reflectance measurements of forest stands from helicopter is described, and the spectral characteristics of stands of Norway spruce and Scotch pine with different ages, crown densities and field layers are discussed. The relationship between measurement geometry and spectral reflectance has also been studied.
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| 45. |
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| 46. |
- Kleman, Johan, et al.
(författare)
-
Trimlines, nunataks, and frozen-bed concepts valid within restricted spatial domains
- 2007
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Ingår i: Quaternary International.
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 47. |
- Margold, Martin, 1981-, et al.
(författare)
-
Glacial meltwater landforms of central British Columbia
- 2011
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Ingår i: Journal of Maps. - : Informa UK Limited. - 1744-5647. ; , s. 486-506
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 48. |
- Margold, Martin, et al.
(författare)
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Ice streams in the Laurentide Ice Sheet : a new mapping inventory
- 2015
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Ingår i: Journal of Maps. - : Informa UK Limited. - 1744-5647. ; 11:3, s. 380-395
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 49. |
- Margold, Martin, 1981-, et al.
(författare)
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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 record
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 50. |
- Margold, Martin, 1981-, et al.
(författare)
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Late-glacial retreat pattern of the Cordilleran Ice Sheet in central British Columbia reconstructed from glacial meltwater landforms
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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