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  • 1
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    The periodic topography of ice stream beds: Insights from the Fourier spectra of mega‐scale glacial lineations
    American Geophysical Union (AGU) ; 2017
    In:  Journal of Geophysical Research: Earth Surface Vol. 122, No. 7 ( 2017-07), p. 1355-1373
    Details
    In: Journal of Geophysical Research: Earth Surface, American Geophysical Union (AGU), Vol. 122, No. 7 ( 2017-07), p. 1355-1373
    Kurzfassung: MSGL topography consists of superimposed periodic wavelengths as expected in the instability theory of subglacial bedform formation Most of the dominant wavelengths present within one extensive MSGL field increase downstream, suggesting that MSGLs evolve via pattern coarsening For MSGLs to generate periodic topography, sediment must be able to accumulate or erode (freely move) without fixed anchor points
    Materialart: Online-Ressource
    ISSN: 2169-9003 , 2169-9011
    URL: Issue
    URL: Article
    DOI: 10.1002/jgrf.v122.7
    DOI: 10.1002/2016JF004154
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 2017
    ZDB Id: 3094104-0
    ZDB Id: 2130824-X
    ZDB Id: 2138320-0
    SSG: 16,13
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  • 2
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    Growth and retreat of the last British–Irish Ice Sheet, 31 000 to 15 000 years ago: the BRITICE‐CHRONO reconstruction
    Wiley ; 2022
    In:  Boreas Vol. 51, No. 4 ( 2022-10), p. 699-758
    Details
    In: Boreas, Wiley, Vol. 51, No. 4 ( 2022-10), p. 699-758
    Kurzfassung: The BRITICE‐CHRONO consortium of researchers undertook a dating programme to constrain the timing of advance, maximum extent and retreat of the British–Irish Ice Sheet between 31 000 and 15 000 years before present. The dating campaign across Ireland and Britain and their continental shelves, and across the North Sea included 1500 days of field investigation yielding 18 000 km of marine geophysical data, 377 cores of sea floor sediments, and geomorphological and stratigraphical information at 121 sites on land; generating 690 new geochronometric ages. These findings are reported in 28 publications including synthesis into eight transect reconstructions. Here we build ice sheet‐wide reconstructions consistent with these findings and using retreat patterns and dates for the inter‐transect areas. Two reconstructions are presented, a wholly empirical version and a version that combines modelling with the new empirical evidence. Palaeoglaciological maps of ice extent, thickness, velocity, and flow geometry at thousand‐year timesteps are presented. The maximum ice volume of 1.8 m sea level equivalent occurred at 23 ka. A larger extent than previously defined is found and widespread advance of ice to the continental shelf break is confirmed during the last glacial. Asynchrony occurred in the timing of maximum extent and onset of retreat, ranging from 30 to 22 ka. The tipping point of deglaciation at 22 ka was triggered by ice stream retreat and saddle collapses. Analysis of retreat rates leads us to accept our hypothesis that the marine‐influenced sectors collapsed rapidly. First order controls on ice‐sheet demise were glacio‐isostatic loading triggering retreat of marine sectors, aided by glaciological instabilities and then climate warming finished off the smaller, terrestrial ice sheet. Overprinted on this signal were second order controls arising from variations in trough topographies and with sector‐scale ice geometric readjustments arising from dispositions in the geography of the landscape. These second order controls produced a stepped deglaciation. The retreat of the British–Irish Ice Sheet is now the world’s most well‐constrained and a valuable data‐rich environment for improving ice‐sheet modelling.
    Materialart: Online-Ressource
    ISSN: 0300-9483 , 1502-3885
    URL: Issue
    URL: Article
    DOI: 10.1111/bor.v51.4
    DOI: 10.1111/bor.12594
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2022
    ZDB Id: 2028632-6
    ZDB Id: 185110-X
    SSG: 14
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  • 3
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    Size, shape and spatial arrangement of mega‐scale glacial lineations from a large and diverse dataset
    Wiley ; 2014
    In:  Earth Surface Processes and Landforms Vol. 39, No. 11 ( 2014-09-15), p. 1432-1448
    Details
    In: Earth Surface Processes and Landforms, Wiley, Vol. 39, No. 11 ( 2014-09-15), p. 1432-1448
    Kurzfassung: Mega‐scale glacial lineations (MSGLs) are a characteristic landform on ice stream beds. Solving the puzzle of their formation is key to understanding how ice interacts with its bed and how this, in turn, influences the dynamics of ice streams. However, a comprehensive and detailed characterization of this landform's size, shape and spatial arrangement, which might serve to test and refine formational theories, is largely lacking. This paper presents a detailed morphometric analysis and comparison of 4043 MSGLs from eight palaeo‐ice stream settings: three offshore (Norway and Antarctica), four onshore (Canada), and one from under a modern ice stream in West Antarctica. The length of MSGLs is lower than previously suggested (mode 1000–2000 m; median 2892 m), and they initiate and terminate at various locations on an ice stream bed. Their spatial arrangement reveals a pattern that is characterized by an exceptional parallel conformity (80% of all mapped MSGLs have an azimuth within 5° from the mean values), and a fairly constant lateral spacing (mode 200–300 m; median 330 m), which we interpret as an indication that MSGLs are a spatially self‐organized phenomenon. Results show that size, shape and spatial arrangement of MSGLs are consistent both within and also generally between different ice stream beds. We suggest this results from a common mechanism of formation, which is largely insensitive to local factors. Although the elongation of MSGLs (mode 6–8; median 12.2) is typically higher than features described as drumlins, these values and those of their width (mode 100–200 m; median 268 m) overlap, which suggests the two landforms are part of a morphological continuum and may share a similar origin. We compare their morphometry with explicit predictions made by the groove‐ploughing and rilling instability theories of MSGL formation. Although the latter was most compatible, neither is fully supported by observations. © 2014 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.
    Materialart: Online-Ressource
    ISSN: 0197-9337 , 1096-9837
    URL: Issue
    URL: Article
    DOI: 10.1002/esp.v39.11
    DOI: 10.1002/esp.3532
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2014
    ZDB Id: 1479188-2
    SSG: 14
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  • 4
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    Recent progress on combining geomorphological and geochronological data with ice sheet modelling, demonstrated using the last British–Irish Ice Sheet
    Wiley ; 2021
    In:  Journal of Quaternary Science Vol. 36, No. 5 ( 2021-07), p. 946-960
    Details
    In: Journal of Quaternary Science, Wiley, Vol. 36, No. 5 ( 2021-07), p. 946-960
    Kurzfassung: Palaeo‐ice sheets are important analogues for understanding contemporary ice sheets, offering a record of ice sheet behaviour that spans millennia. There are two main approaches to reconstructing palaeo‐ice sheets. Empirical reconstructions use the available glacial geological and chronological evidence to estimate ice sheet extent and dynamics but lack direct consideration of ice physics. In contrast, numerically modelled simulations implement ice physics, but often lack direct quantitative comparison with empirical evidence. Despite being long identified as a fruitful scientific endeavour, few ice sheet reconstructions attempt to reconcile the empirical and model‐based approaches. To achieve this goal, model‐data comparison procedures are required. Here, we compare three numerically modelled simulations of the former British–Irish Ice Sheet with the following lines of evidence: (a) position and shape of former margin positions, recorded by moraines; (b) former ice‐flow direction and flow‐switching, recorded by flowsets of subglacial bedforms; and (c) the timing of ice‐free conditions, recorded by geochronological data. These model–data comparisons provide a useful framework for quantifying the degree of fit between numerical model simulations and empirical constraints. Such tools are vital for reconciling numerical modelling and empirical evidence, the combination of which will lead to more robust palaeo‐ice sheet reconstructions with greater explicative and ultimately predictive power.
    Materialart: Online-Ressource
    ISSN: 0267-8179 , 1099-1417
    URL: Issue
    URL: Article
    DOI: 10.1002/jqs.v36.5
    DOI: 10.1002/jqs.3098
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2021
    ZDB Id: 2031875-3
    SSG: 13
    SSG: 14
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  • 5
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    Looking through drumlins: testing the application of ground-penetrating rada
    International Glaciological Society ; 2014
    In:  Journal of Glaciology Vol. 60, No. 224 ( 2014), p. 1126-1134
    Details
    In: Journal of Glaciology, International Glaciological Society, Vol. 60, No. 224 ( 2014), p. 1126-1134
    Kurzfassung: Ground-penetrating radar (GPR) is becoming a commonly applied technique in geomorphology. However, its use in the study of subglacial bedforms has yet to be fully explored and exploited. This paper presents the results of a GPR feasibility study conducted on a drumlinized terrain in Cumbria, UK, where five drumlins were investigated using multiple radar antenna frequencies. The site was selected for the presence of nearby bedrock outcrops, suggesting a shallow drumlinized diamict–bedrock contact and a permeable lithology. Despite the clayey sediment and unfavourable weather conditions, a considerable penetration depth of ~12 m was achieved when using a 50 MHz antenna, with a separation of 1 m, trace spacing of 1 m and 128-fold vertical stack. Results indicate that the drumlinized diamict is in direct erosional contact with the bedrock. While the internal drumlin geometry is generally chaotic on the stoss side, evidence of layering dipping downflow at an angle greater than the drumlin surface profile was found on the lee side. The inter-drumlin areas comprise ~4 m of infill sediment that masks part of the original drumlin profile. Overall, this study indicates that GPR can be deployed successfully in the study of glacial bedform sedimentary architecture.
    Materialart: Online-Ressource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.3189/2014JoG14J110
    Sprache: Englisch
    Verlag: International Glaciological Society
    Publikationsdatum: 2014
    ZDB Id: 2140541-4
    SSG: 14
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  • 6
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    BRITICE Glacial Map, version 2: a map and GIS database of glacial landforms of the last British–Irish Ice Sheet
    Wiley ; 2018
    In:  Boreas Vol. 47, No. 1 ( 2018-01), p. 11-
    Details
    In: Boreas, Wiley, Vol. 47, No. 1 ( 2018-01), p. 11-
    Kurzfassung: During the last glaciation, most of the British Isles and the surrounding continental shelf were covered by the British–Irish Ice Sheet ( BIIS ). An earlier compilation from the existing literature ( BRITICE version 1) assembled the relevant glacial geomorphological evidence into a freely available GIS geodatabase and map (Clark et al . 2004: Boreas 33, 359). New high‐resolution digital elevation models, of the land and seabed, have become available casting the glacial landform record of the British Isles in a new light and highlighting the shortcomings of the V.1 BRITICE compilation. Here we present a wholesale revision of the evidence, onshore and offshore, to produce BRITICE version 2, which now also includes Ireland. All published geomorphological evidence pertinent to the behaviour of the ice sheet is included, up to the census date of December 2015. The revised GIS database contains over 170 000 geospatially referenced and attributed elements – an eightfold increase in information from the previous version. The compiled data include: drumlins, ribbed moraine, crag‐and‐tails, mega‐scale glacial lineations, glacially streamlined bedrock (grooves, roches moutonnées, whalebacks), glacial erratics, eskers, meltwater channels (subglacial, lateral, proglacial and tunnel valleys), moraines, trimlines, cirques, trough‐mouth fans and evidence defining ice‐dammed lakes. The increased volume of features necessitates different map/database products with varying levels of data generalization, namely: (i) an unfiltered GIS database containing all mapping; (ii) a filtered GIS database, resolving data conflicts and with edits to improve geo‐locational accuracy (available as GIS data and PDF maps); and (iii) a cartographically generalized map to provide an overview of the distribution and types of features at the ice‐sheet scale that can be printed at A0 paper size at a 1:1 250 000 scale. All GIS data, the maps (as PDFs) and a bibliography of all published sources are available for download from: https://www.sheffield.ac.uk/geography/staff/clark_chris/britice .
    Materialart: Online-Ressource
    ISSN: 0300-9483 , 1502-3885
    URL: Issue
    URL: Article
    DOI: 10.1111/bor.2018.47.issue-1
    DOI: 10.1111/bor.12273
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2018
    ZDB Id: 2028632-6
    ZDB Id: 185110-X
    SSG: 14
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  • 7
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    ATAT 1.1, the Automated Timing Accordance Tool for comparing ice-sheet model output with geochronological data
    Copernicus GmbH ; 2019
    In:  Geoscientific Model Development Vol. 12, No. 3 ( 2019-03-12), p. 933-953
    Details
    In: Geoscientific Model Development, Copernicus GmbH, Vol. 12, No. 3 ( 2019-03-12), p. 933-953
    Kurzfassung: Abstract. Earth's extant ice sheets are of great societal importance given their ongoing and potential future contributions to sea-level rise. Numerical models of ice sheets are designed to simulate ice-sheet behaviour in response to climate changes but to be improved require validation against observations. The direct observational record of extant ice sheets is limited to a few recent decades, but there is a large and growing body of geochronological evidence spanning millennia constraining the behaviour of palaeo-ice sheets. Hindcasts can be used to improve model formulations and study interactions between ice sheets, the climate system and landscape. However, ice-sheet modelling results have inherent quantitative errors stemming from parameter uncertainty and their internal dynamics, leading many modellers to perform ensemble simulations, while uncertainty in geochronological evidence necessitates expert interpretation. Quantitative tools are essential to examine which members of an ice-sheet model ensemble best fit the constraints provided by geochronological data. We present the Automated Timing Accordance Tool (ATAT version 1.1) used to quantify differences between model results and geochronological data on the timing of ice-sheet advance and/or retreat. To demonstrate its utility, we perform three simplified ice-sheet modelling experiments of the former British–Irish ice sheet. These illustrate how ATAT can be used to quantify model performance, either by using the discrete locations where the data originated together with dating constraints or by comparing model outputs with empirically derived reconstructions that have used these data along with wider expert knowledge. The ATAT code is made available and can be used by ice-sheet modellers to quantify the goodness of fit of hindcasts. ATAT may also be useful for highlighting data inconsistent with glaciological principles or reconstructions that cannot be replicated by an ice-sheet model.
    Materialart: Online-Ressource
    ISSN: 1991-9603
    URL: Article
    URL: Article
    DOI: 10.5194/gmd-12-933-2019
    DOI: 10.5194/gmd-12-933-2019-supplement
    Sprache: Englisch
    Verlag: Copernicus GmbH
    Publikationsdatum: 2019
    ZDB Id: 2456725-5
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  • 8
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    Exploring controls of the early and stepped deglaciation on the western margin of the British Irish Ice Sheet
    Wiley ; 2021
    In:  Journal of Quaternary Science Vol. 36, No. 5 ( 2021-07), p. 833-870
    Details
    In: Journal of Quaternary Science, Wiley, Vol. 36, No. 5 ( 2021-07), p. 833-870
    Kurzfassung: New optically stimulated luminescence dating and Bayesian models integrating all legacy and BRITICE‐CHRONO geochronology facilitated exploration of the controls on the deglaciation of two former sectors of the British–Irish Ice Sheet, the Donegal Bay (DBIS) and Malin Sea ice‐streams (MSIS). Shelf‐edge glaciation occurred ~27 ka, before the global Last Glacial Maximum, and shelf‐wide retreat began 26–26.5 ka at a rate of ~18.7–20.7 m a –1 . MSIS grounding zone wedges and DBIS recessional moraines show episodic retreat punctuated by prolonged still‐stands. By ~23–22 ka the outer shelf (~25 000 km 2 ) was free of grounded ice. After this time, MSIS retreat was faster (~20 m a –1 vs. ~2–6 m a –1 of DBIS). Separation of Irish and Scottish ice sources occurred ~20–19.5 ka, leaving an autonomous Donegal ice dome. Inner Malin shelf deglaciation followed the submarine troughs reaching the Hebridean coast ~19 ka. DBIS retreat formed the extensive complex of moraines in outer Donegal Bay at 20.5–19 ka. DBIS retreated on land by ~17–16 ka. Isolated ice caps in Scotland and Ireland persisted until ~14.5 ka. Early retreat of this marine‐terminating margin is best explained by local ice loading increasing water depths and promoting calving ice losses rather than by changes in global temperatures. Topographical controls governed the differences between the ice‐stream retreat from mid‐shelf to the coast.
    Materialart: Online-Ressource
    ISSN: 0267-8179 , 1099-1417
    URL: Issue
    URL: Article
    DOI: 10.1002/jqs.v36.5
    DOI: 10.1002/jqs.3315
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2021
    ZDB Id: 2031875-3
    SSG: 13
    SSG: 14
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  • 9
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    Devising quality assurance procedures for assessment of legacy geochronological data relating to deglaciation of the last British-Irish Ice Sheet
    Elsevier BV ; 2017
    In:  Earth-Science Reviews Vol. 164 ( 2017-01), p. 232-250
    Details
    In: Earth-Science Reviews, Elsevier BV, Vol. 164 ( 2017-01), p. 232-250
    Materialart: Online-Ressource
    ISSN: 0012-8252
    URL: Article
    DOI: 10.1016/j.earscirev.2016.11.007
    RVK:
    RA 1000
    Sprache: Englisch
    Verlag: Elsevier BV
    Publikationsdatum: 2017
    ZDB Id: 1792-9
    ZDB Id: 2012642-6
    SSG: 13
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  • 10
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    Rapid accelerations of Antarctic Peninsula outlet glaciers driven by surface melt
    Springer Science and Business Media LLC ; 2019
    In:  Nature Communications Vol. 10, No. 1 ( 2019-09-20)
    Details
    In: Nature Communications, Springer Science and Business Media LLC, Vol. 10, No. 1 ( 2019-09-20)
    Kurzfassung: Atmospheric warming is increasing surface melting across the Antarctic Peninsula, with unknown impacts upon glacier dynamics at the ice-bed interface. Using high-resolution satellite-derived ice velocity data, optical satellite imagery and regional climate modelling, we show that drainage of surface meltwater to the bed of outlet glaciers on the Antarctic Peninsula occurs and triggers rapid ice flow accelerations (up to 100% greater than the annual mean). This provides a mechanism for this sector of the Antarctic Ice Sheet to respond rapidly to atmospheric warming. We infer that delivery of water to the bed transiently increases basal water pressure, enhancing basal motion, but efficient evacuation subsequently reduces water pressure causing ice deceleration. Currently, melt events are sporadic, so efficient subglacial drainage cannot be maintained, resulting in multiple short-lived ( 〈 6 day) ice flow perturbations. Future increases in meltwater could induce a shift to a glacier dynamic regime characterised by seasonal-scale hydrologically-driven ice flow variations.
    Materialart: Online-Ressource
    ISSN: 2041-1723
    URL: Article
    DOI: 10.1038/s41467-019-12039-2
    Sprache: Englisch
    Verlag: Springer Science and Business Media LLC
    Publikationsdatum: 2019
    ZDB Id: 2553671-0
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