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  • ItemOpen AccessAccepted version Peer-reviewed
    Global glacier dynamics during 100 ka Pleistocene glacial cycles
    (Cambridge University Press (CUP), 2018) Hughes, PD; Gibbard, PL; Gibbard, Philip [0000-0001-9757-7292]
    AbstractIce volume during the last ten 100 ka glacial cycles was driven by solar radiation flux in the Northern Hemisphere. Early minima in solar radiation combined with critical levels of atmospheric CO2drove initial glacier expansion. Glacial cycles between Marine Isotope Stage (MIS) 24 and MIS 13, whilst at 100 ka periodicity, were irregular in amplitude, and the shift to the largest amplitude 100 ka glacial cycles occurred after MIS 16. Mountain glaciers in the mid-latitudes and Asia reached their maximum extents early in glacial cycles, then retreated as global climate became increasingly arid. In contrast, larger ice masses close to maritime moisture sources continued to build up and dominated global glacial maxima reflected in marine isotope and sea-level records. The effect of this pattern of glaciation on the state of the global atmosphere is evident in dust records from Antarctic ice cores, where pronounced double peaks in dust flux occur in all of the last eight glacial cycles. Glacier growth is strongly modulated by variations in solar radiation, especially in glacial inceptions. This external control accounts for ~50–60% of ice volume change through glacial cycles. Internal global glacier–climate dynamics account for the rest of the change, which is controlled by the geographic distributions of glaciers.
  • ItemOpen AccessPublished version Peer-reviewed
    Seismic evidence for complex sedimentary control of Greenland Ice Sheet flow
    (AAAS, 2017-08-02) Kulessa, B; Hubbard, AL; Booth, AD; Bougamont, MH; Dow, C; Doyle, SH; Christoffersen, P; Lindback, K; Pettersson, R; Fitzpatrick, AW; Jones, GA; Bougamont, Marion [0000-0001-7196-4171]; Christoffersen, Poul [0000-0003-2643-8724]
    The land-terminating margin of the Greenland Ice Sheet has slowed down in recent decades, although the causes and implications for future ice flow are unclear. Explained originally by a self-regulating mechanism where basal slip reduces as drainage evolves from low to high efficiency, recent numerical modeling invokes a sedimentary control of ice sheet flow as an alternative hypothesis. Although both hypotheses can explain the recent slowdown, their respective forecasts of a long-term deceleration versus an acceleration of ice flow are contradictory. We present amplitude-versus-angle seismic data as the first observational test of the alternative hypothesis. We document transient modifications of basal sediment strengths by rapid subglacial drainages of supraglacial lakes, the primary current control on summer ice sheet flow according to our numerical model. Our observations agree with simulations of initial postdrainage sediment weakening and ice flow accelerations, and subsequent sediment restrengthening and ice flow decelerations, and thus confirm the alternative hypothesis. Although simulated melt season acceleration of ice flow due to weakening of subglacial sediments does not currently outweigh winter slowdown forced by self-regulation, they could dominate over the longer term. Subglacial sediments beneath the Greenland Ice Sheet must therefore be mapped and characterized, and a sedimentary control of ice flow must be evaluated against competing self-regulation mechanisms.
  • ItemOpen AccessPublished version Peer-reviewed
    A Survey of Arctic Information Provision for the European Union
    (The Scott Polar Research Institute, 2013-12-20) Cronin, GM; Lane, H; Cronin, George [0000-0003-0054-6436]
    A part of the Strategic Environmental Impact Assessment of the Development of the Arctic and preparatory action for a European Union Arctic Information Centre
  • ItemOpen AccessPublished version Peer-reviewed
    Ground-penetrating radar measurements of debris thickness on Lirung Glacier, Nepal
    (Cambridge University Press, 2017-06-01) McCarthy, M; Pritchard, H; Willis, IC; King, E; Willis, Ian [0000-0002-0750-7088]
    Supraglacial debris thickness is a key control on the surface energy balance of debriscovered glaciers, yet debris thickness measurements are sparse due to difficulties of data collection. Here we use ground-penetrating radar (GPR) to measure debris thickness on the ablation zone of Lirung Glacier, Nepal. We observe a strong, continuous reflection, which we interpret as the ice surface, through debris layers of 0.1 to at least 2.3 m thick, provided that appropriate acquisition parameters were used while surveying. GPR measurements of debris thickness correlate well with pit measurements of debris thickness (r = 0.91, RMSE = 0.04 m) and two-way travel times are consistent at tie points (r = 0.97). 33% of measurements are <0.5 m, so sub-debris melting is likely important in terms of mass loss on the debris-covered tongue and debris thickness is highly variable over small spatial scales (of order 10 m), likely due to local slope processes. GPR can be used to make debris thickness measurements more quickly, over a wider debris thickness range, and at higher spatial resolution than any other means and is therefore a valuable tool with which to map debris thickness distribution on Himalayan glaciers.
  • ItemOpen AccessAccepted version Peer-reviewed
    Seafloor geomorphology and glacimarine sedimentation associated with fast-flowing ice sheet outlet glaciers in Disko Bay, West Greenland
    (Elsevier, 2017-08-01) Streuff, K; Ó Cofaigh, C; Hogan, K; Jennings, A; Lloyd, JM; Noormets, R; Nielsen, T; Kuijpers, A; Dowdeswell, JA; Weinrebe, W; Dowdeswell, Julian [0000-0003-1369-9482]
    Fast-flowing outlet glaciers currently drain the Greenland Ice Sheet (GIS), delivering ice, meltwater and debris to the fjords around Greenland. Although such glaciers strongly affect the ice sheet's mass balance, their glacimarine processes and associated products are still poorly understood. This study provides a detailed analysis of lithological and geophysical data from Disko Bay and the Vaigat Strait in central West Greenland. Disko Bay is strongly influenced by Jakobshavn Isbræ, Greenland's fastest-flowing glacier, which currently drains ∼7% of the ice sheet. Streamlined glacial landforms record the former flow of an expanded Jakobshavn Isbræ and adjacent GIS outlets through Disko Bay and the Vaigat Strait towards the continental shelf. Thirteen vibrocores contain a complex set of lithofacies including diamict, stratified mud, interbedded mud and sand, and bioturbated mud deposited by (1) suspension settling from meltwater plumes and the water column, (2) sediment gravity flows, and (3) iceberg rafting and ploughing. The importance of meltwater-related processes to glacimarine sedimentation in West Greenland fjords and bays is emphasised by the abundance of mud preserved in the cores. Radiocarbon dates constrain the position of the ice margin during deglaciation, and suggest that Jakobshavn Isbræ had retreated into central Disko Bay before 10.6 cal ka BP and to beyond Isfjeldsbanken by 7.6–7.1 cal ka BP. Sediment accumulation rates were up to 1.7 cm a −1 for ice-proximal glacimarine mud, and ∼0.007–0.05 cm a −1 for overlying distal sediments. In addition to elucidating the deglacial retreat history of Jakobshavn Isbræ, our findings show that the glacimarine sedimentary processes in West Greenland are similar to those in East Greenland, and that variability in such processes is more a function of time and glacier proximity than of geographic location and associated climatic regime.
  • ItemOpen AccessAccepted version Peer-reviewed
    What colour is penguin guano?
    (Cambridge University Press, 2017-10) Rees, WG; Brown, JA; Fretwell, PT; Trathan, PN; Rees, Gareth [0000-0001-6020-1232]; Brown, Jennifer [0000-0002-7527-2540]
    The identification and quantification of Antarctic Pygoscelis penguin colonies depends increasingly on recognition of the characteristic optical properties of guano deposits, but almost all knowledge of these properties until now has been compromised by resolution and atmospheric propagation effects. Here we present hyperspectral reflectance data in the range 350–2500 nm, collected in situ from fresh guano deposits in Pygoscelis penguin colonies on Signy Island, South Orkney Islands. The period of data collection included the transition from predominantly white guano to the pink coloration characteristic of a krill-rich diet. The main identifiable features in the spectra are a broad absorption feature centred around 550 nm, responsible for the pink coloration and identified with the pigment astaxanthin, as well as several water absorption features. Variations in these features are responsible for differentiation between spectra. From these results we propose two spectral indices suitable for use with satellite data, one of which responds to the presence of astaxanthin in the guano and the other to water. Our results do not allow us to differentiate between penguin species from their guano, but do suggest that the breeding phenology of Pygoscelis penguins could be determined from a time series of multispectral imagery.
  • ItemOpen AccessAccepted version Peer-reviewed
    On the provenance of a historic sledge shoe fragment, said to have been collected by Edward Wilson at the South Pole in 1912
    (Cambridge University Press, 2017-07) Rowe, RSW; Rowe, Rebecca [0000-0001-6693-2394]
    This paper discusses the authentication of a metal sledge shoe fragment, believed by the owner to have been collected by Edward Wilson close to the South Pole on 18 January 1912. Microscopic and elemental analysis show that the object is made from ‘German silver’, a copper alloy used only on Norwegian Nansen-style sledges in the late nineteenth and early twentieth century, and that it was used to clad a tapering sledge runner end about 10 mm thick. By comparing related objects, including sledges used by Amundsen and Scott in their South Pole journeys and a sledge from the Discovery Expedition, we show that the object cannot have come from an English sledge, but would have fitted one of Amundsen's modified sledges. Written sources have been extensively searched, but no direct written provenance for the object exists. However, contemporary Norwegian and British accounts explain specific features of the object and exclude other possible provenances. We conclude that it is most likely that the proposed provenance and history attached to this artefact are correct.
  • ItemOpen AccessPublished version Peer-reviewed
    A Fully Automated Supraglacial lake area and volume Tracking (“FAST”) algorithm: Development and application using MODIS imagery of West Greenland
    (Elsevier, 2017-07-01) Williamson, AG; Arnold, NS; Banwell, AF; Willis, IC; Arnold, Neil [0000-0001-7538-3999]; Banwell, Alison [0000-0001-9545-829X]; Willis, Ian [0000-0002-0750-7088]
    Supraglacial lakes (SGLs) on the Greenland Ice Sheet (GrIS) influence ice dynamics if they drain rapidly by hydrofracture. MODIS data are often used to investigate SGLs, including calculating SGL area changes through time, but no existing work presents a method that tracks changes to individual (and total) SGL volume in MODIS imagery over a melt season. Here, we develop such a method by first testing three automated approaches to derive SGL areas from MODIS images from the MOD09 level-2 surface-reflectance product, by comparing calculated areas for the Paakitsoq and Store Glacier regions in West Greenland with areas derived from Landsat-8 (LS8) images. Second, we apply a physically-based depth-calculation algorithm to the pixels within the SGL boundaries from the best performing area-derivation method, and compare the resultant depths with those calculated using the same method applied to LS8 imagery. Our results indicate that SGL areas are most accurately generated using dynamic thresholding of MODIS band 1 (red) MOD09 data with a 0.640 threshold value; calculated values from MODIS are closely comparable to those derived from LS8. Third, we incorporate the best performing area- and depth-detection methods into a Fully Automated SGL Tracking (“FAST”) algorithm that tracks individual SGLs between successive MODIS images. Finally, we apply the FAST algorithm to the two study regions, where it identifies 43 (Paakitsoq) and 19 (Store Glacier) rapidly draining SGLs during 2014, representing 21% and 15% of the respective total SGL populations, including some clusters of rapidly draining SGLs. The FAST algorithm improves upon existing automatic SGL tracking methods through its calculation of both SGL areas and volumes over large regions of the GrIS on a fully automatic basis. It therefore has the potential to be used for investigating statistical relationships between SGL areas, volumes and drainage events over the whole of the GrIS, and over multiple seasons, which might provide further insights into the factors that trigger rapid SGL drainage.
  • ItemOpen AccessPublished version Peer-reviewed
    Generating synthetic fjord bathymetry for coastal Greenland
    (Copernicus Publications, 2017-02-01) Williams, CN; Cornford, SL; Jordan, TM; Dowdeswell, JA; Siegert, MJ; Clark, CD; Swift, DA; Sole, A; Fenty, I; Bamber, JL; Dowdeswell, Julian [0000-0003-1369-9482]
    Bed topography is a critical boundary for the numerical modelling of ice sheets and ice-ocean interactions. A persistent issue with existing topography products for the bed of the Greenland Ice Sheet and surrounding sea floor is the poor representation of coastal bathymetry, especially in regions of floating ice and near the grounding line. Sparse data coverage, and the resultant coarse resolution at the ice-ocean boundary, poses issues in our ability to model ice flow advance and retreat from the present position. In addition, as fjord bathymetry is known to exert strong control on ocean circulation and ice-ocean forcing, the lack of bed data leads to an inability to model these processes adequately. Since the release of the last complete Greenland bed topography-bathymetry product, new observational bathymetry data have become available. These data can be used to constrain bathymetry, but many fjords remain completely unsampled and therefore poorly resolved. Here, as part of the development of the next generation of Greenland bed topography products, we present a new method for constraining the bathymetry of fjord systems in regions where data coverage is sparse. For these cases, we generate synthetic fjord geometries using a method conditioned by surveys of terrestrial glacial valleys as well as existing sinuous feature interpolation schemes. Our approach enables the capture of the general bathymetry profile of a fjord in north-west Greenland close to Cape York, when compared to observational data. We validate our synthetic approach by demonstrating reduced overestimation of depths compared to past attempts to constrain fjord bathymetry. We also present an analysis of the spectral characteristics of fjord centrelines using recently acquired bathymetric observations, demonstrating how a stochastic model of fjord bathymetry could be parameterised and used to create different realisations.
  • ItemOpen AccessAccepted version Peer-reviewed
    Glaciology: Ice-shelf stability questioned
    (Nature Publishing Group, 2017-04-20) Banwell, AF; Banwell, Alison [0000-0001-9545-829X]
    Surface lakes and streams are forming on Antarctica's ice shelves, making them susceptible to instability and possible collapse. But rivers could mitigate this effect by efficiently exporting meltwater to the ocean.
  • ItemOpen AccessPublished version Peer-reviewed
    Introduction: an $\textit{Atlas of Submarine Glacial Landforms}$
    (Geological Society of London, 2016-12-16) Dowdeswell, JA; Canals, M; Jakobsson, M; Todd, BJ; Dowdeswell, EK; Hogan, K; Dowdeswell, Julian [0000-0003-1369-9482]; Dowdeswell, Evelyn [0000-0001-9256-8776]
    The Atlas of Submarine Glacial Landforms is a comprehensive and timely summary of the current state of knowledge of these high-latitude glacier-influenced systems.
  • ItemOpen AccessPublished version Peer-reviewed
    Quantifying supraglacial meltwater pathways in the Paakitsoq region, West Greenland
    (Cambridge University Press, 2017) Koziol, C; Arnold, N; Pope, A; Colgan, W; Arnold, Neil [0000-0001-7538-3999]
    Increased summer ice velocities on the Greenland ice sheet are driven by meltwater input to the subglacial environment. However, spatial patterns of surface input and partitioning of meltwater between different pathways to the base remain poorly understood. To further our understanding of surface drainage, we apply a supraglacial hydrology model to the Paakitsoq region, West Greenland for three contrasting melt seasons. During an average melt season, crevasses drain ~47% of surface runoff, lake hydrofracture drains ~3% during the hydrofracturing events themselves, while the subsequent surface-to-bed connections drain ~21% and moulins outside of lake basins drain ~15%. Lake hydrofracture forms the primary drainage pathway at higher elevations (above ~850 m) while crevasses drain a significant proportion of meltwater at lower elevations. During the two higher intensity melt seasons, model results show an increase (~5 and ~6% of total surface runoff) in the proportion of runoff drained above ~1300 m relative to the melt season of average intensity. The potential for interannual changes in meltwater partitioning could have implications for how the dynamics of the ice sheet respond to ongoing changes in meltwater production.
  • ItemOpen AccessAccepted version Peer-reviewed
    Antarctic subglacial groundwater: a concept paper on its measurement and potential influence on ice flow
    (Geological Society, 2018) Siegert, MJ; Kulessa, B; Bougamont, MH; Christoffersen, P; Key, K; Andersen, KR; Booth, AD; Smith, AM; Bougamont, Marion [0000-0001-7196-4171]; Christoffersen, Poul [0000-0003-2643-8724]
    Is groundwater abundant in Antarctica and does it modulate ice flow? Answering this question matters because ice streams flow by gliding over a wet substrate of till. Water fed to ice-stream beds thus influences ice-sheet dynamics and, potentially, sea-level rise. It is recognised that both till and the sedimentary basins from which it originates are porous and could host a reservoir of mobile groundwater that interacts with the subglacial interfacial system. According to recent numerical modelling up to half of all water available for basal lubrication, and time lags between hydrological forcing and ice-sheet response as long as millennia, may have been overlooked in models of ice flow. Here, we review evidence in support of Antarctic groundwater and propose how it can be measured to ascertain the extent to which it modulates ice flow. We present new seismoelectric soundings of subglacial till, and magnetotelluric and transient electromagnetic forward models of subglacial groundwater reservoirs. We demonstrate that multi-facetted and integrated geophysical datasets can detect, delineate and quantify the groundwater contents of subglacial sedimentary basins and, potentially, monitor groundwater exchange rates between subglacial till layers. The paper thus describes a new area of glaciological investigation and how it should progress in future.
  • ItemOpen AccessPublished version Peer-reviewed
    Characterizing near-surface firn using the scattered signal component of the glacier surface return from airborne radio-echo sounding
    (Wiley, 2017-01-19) Rutishauser, A; Grima, C; Sharp, M; Blankenship, DD; Young, DA; Cawkwell, F; Dowdeswell, JA; Dowdeswell, Julian [0000-0003-1369-9482]
    We derive the scattered component (hereafter referred to as the incoherent component) of glacier surface echoes from airborne radio-echo sounding measurements over Devon Ice Cap, Arctic Canada, and compare the scattering distribution to firn stratigraphy observations from ground-based radar data. Low scattering correlates to laterally homogeneous firn above 1800m elevation containing thin, flat, and continuous ice layers and below 1200m elevation where firn predominantly consists of ice. Increased scattering between elevations of 1200-1800m corresponds to firn with inhomogeneous, undulating ice layers. No correlation was found to surface roughness and its theoretical incoherent backscattering values. This indicates that the scattering component is mainly influenced by the near-surface firn stratigraphy, whereas surface roughness effects are minor. Our results suggest that analyzing the scattered signal component of glacier surface echoes is a promising approach to characterize the spatial heterogeneity of firn that is affected by melting and refreezing processes.
  • ItemOpen AccessAccepted version Peer-reviewed
    Quaternary evolution of the northern North Sea margin through glacigenic debris-flow and contourite deposition
    (Wiley, 2017) Batchelor, C; Ottesen, D; Dowdeswell, JA; Dowdeswell, Julian [0000-0003-1369-9482]
    The Norwegian Channel Ice Stream of the Scandinavian Ice Sheet extended across the northern North Sea margin during the mid- to late Quaternary, eroding older sediment from the continental shelf. Consequently, little is known about early Quaternary sedimentation on this margin. We use two- and three-dimensional seismic-reflection data to investigate changing sediment volumes and sources in the northern North Sea through the Quaternary. The northern North Sea Basin was infilled during the early Quaternary by intercalated glacigenic debris-flows and contourites, which provide a record of the delivery of glacigenic sediment to the slope and the intensity of North Atlantic thermohaline circulation during early Quaternary glacial-interglacial cycles. The infilling of the basin reduced accommodation and led to the deflection of mid- to late Quaternary sediments into the Norwegian Sea, forming the North Sea Fan. Close to the onset of the mid-Quaternary, the south-western Scandinavian Ice Sheet margin was drained by an ice stream located beneath Måløy Plateau, 60 km east of the Last Glacial Maximum Norwegian Channel Ice Stream. The southward-flowing Norwegian Sea Bottom Water current was directed into the partially filled northern North Sea Basin during the early Quaternary, and deflected progressively northwards as the basin became infilled.
  • ItemOpen AccessAccepted version Peer-reviewed
    Pleistocene iceberg dynamics on the west Svalbard margin: Evidence from bathymetric and sub-bottom profiler data
    (Elsevier, 2017-04-01) Zhao, F; Minshull, TA; Crocker, AJ; Dowdeswell, JA; Wu, S; Soryal, SM; Dowdeswell, Julian [0000-0003-1369-9482]
    Large icebergs leave evidence of their drift via ploughing of the seabed, thereby providing a geological record of episodes of calving from thick ice sheets. We interpret large-scale curvilinear depressions on the western Svalbard margin as ploughmarks produced by the keels of icebergs that grounded on the seafloor as they drifted through this area. Iceberg ploughmarks were identified at modern water depths between 300 m and 1000 m and in two distinct stratigraphic units. Combining data from sediment cores with seismic stratigraphy from sub-bottom profiler data suggests that the ploughmarks developed in two phases: (1) during Marine Isotope Stage (MIS) 6; and (2) during MIS 2, indicating the presence of large drifting icebergs on the western Svalbard margin during both the Late Saalian and Late Weichselian glaciations. Sediment-core data along the western Svalbard margin indicate a sharp increase in mass-transported sediments dated at 23.7 ± 0.2 ka, consistent with the MIS 2 age of the younger iceberg-ploughed surface. The ploughmarks are oriented in two main directions: SW-NE and S-N. S-N oriented ploughmarks, which shallow to the north, indicate iceberg drift from the south with a SW–NE component marking the zone of splitting of the West Spitsbergen Current (WSC) into the Yermak Slope Current (YSC) and North Spitsbergen Current (NSC). Large MIS 6 and MIS 2 icebergs most likely had an Arctic Ocean source. We suggest that these icebergs probably left the Arctic Ocean southward through Fram Strait and circulated within the Norwegian-Greenland Sea before being transported northwards along the Svalbard margin by the WSC. An additional likely source of icebergs to the western Svalbard margin during MIS 2 was the ice-sheet terminating in the western Barents Sea, from which icebergs drifted northward.
  • ItemOpen AccessPublished version Peer-reviewed
    Ice-sheet dynamics through the Quaternary on the mid-Norwegian continental margin inferred from 3D seismic data
    (Elsevier, 2017-02) Montelli, A; Dowdeswell, JA; Ottesen, D; Johansen, SE; Montelli, Aleksandr [0000-0003-4512-2653]; Dowdeswell, Julian [0000-0003-1369-9482]
    Reconstructing the evolution of ice sheets is critical to our understanding of the global environmental system, but most detailed palaeo-glaciological reconstructions have hitherto focused on the very recent history of ice sheets. Here, we present a three-dimensional (3D) reconstruction of the changing nature of ice-sheet derived sedimentary architecture through the Quaternary Ice Age of almost 3 Ma. An extensive geophysical record documents a marine-terminating, calving Fennoscandian Ice Sheet (FIS) margin present periodically on the mid-Norwegian shelf since the beginning of the Quaternary. Spatial and temporal variability of the FIS is illustrated by the gradual development of fast-flowing ice streams and associated intensification of focused glacial erosion and sedimentation since that time. Buried subglacial landforms reveal a complex and dynamic ice sheet, with converging palaeo-ice streams and several flow-switching events that may reflect major changes in topography and basal thermal regime. Lack of major subglacial meltwater channels suggests a largely distributed drainage system beneath the marine-terminating part of the FIS. This palaeo-environmental examination of the FIS provides a useful framework for ice-sheet modelling and shows that fragmentary preservation of buried surfaces and variability of ice-sheet dynamics should be taken into account when reconstructing glacial history from spatially limited datasets.
  • ItemOpen AccessAccepted version Peer-reviewed
    Glacier characteristics and retreat between 1991 and 2014 in the Ladakh Range, Jammu and Kashmir
    (Taylor and Francis Inc., 2017-02-22) Chudley, TR; Miles, ES; Willis, IC; Chudley, Thomas [0000-0001-8547-1132]; Willis, Ian [0000-0002-0750-7088]
    Glaciers in the Ladakh Range lie between the Himalaya, a monsoon-forced region of glacier retreat, and the Karakoram, a region of anomalous glacier stability driven by mid-latitude westerlies. Given this context, glaciers might be expected to display behaviour intermediate to the two adjacent ranges. However, no glacier change data have been compiled for the Ladakh Range itself. Here, we examine 864 glaciers in the central section of the Ladakh Range, covering a number of smaller glaciers not included in alternative glacier inventories. Glaciers in the range are small (median 0.25 km²; maximum 6.58 km²) and largely distributed 5000–6000 m above sea level (a.s.l.). 657 glaciers are available for multitemporal analysis between 1991 to 2014 using data from Landsat multispectral sensors. We find glaciers to have lost 12.8% of their area over the period. Glacier changes are consistent with observations in the Western Himalaya (to the south) and in sharp contrast with the Karakoram (to the north) in spite of its proximity to the latter. We suggest this sharp transition must be explained at least in part by non-climatic mechanisms (such as debris covering or hypsometry), or that the climatic factors responsible for the Karakoram behaviour are extremely localised.
  • ItemOpen AccessPublished version Peer-reviewed
    Moulin density controls drainage development beneath the Greenland ice sheet
    (Wiley, 2016-12-02) Banwell, A; Hewitt, I; Willis, I; Arnold, N; Banwell, Alison [0000-0001-9545-829X]; Willis, Ian [0000-0002-0750-7088]; Arnold, Neil [0000-0001-7538-3999]
    Uncertainty remains about how the surface hydrology of the Greenland ice sheet influences its subglacial drainage system, affecting basal water pressures and ice velocities, particularly over intraseasonal and interseasonal timescales. Here we apply a high spatial (200m) and temporal (1h) resolution subglacial hydrological model to a marginal (extending ~25km inland), land-terminating, ~200km$^{2}$ domain in the Paakitsoq region, West Greenland. The model is based on that by Hewitt (2013) but adapted for use with both real topographic boundary conditions and calibrated modeled water inputs. The inputs consist of moulin hydrographs, calculated by a surface routing and lake-filling/draining model, which is forced with distributed runoff from a surface energy-balance model. Results suggest that the areal density of lake-bottom moulins and their timing of opening during the melt season strongly affects subglacial drainage system development. A higher moulin density causes an earlier onset of subglacial channelization (i.e., water transport through channels rather than the distributed sheet), which becomes relatively widespread across the bed, whereas a lower moulin density results in a later onset of channelization that becomes less widespread across the bed. In turn, moulin density has a strong control on spatial and temporal variations in subglacial water pressures, which will influence basal sliding rates, and thus ice motion. The density of active surface-to-bed connections should be considered alongside surface melt intensity and extent in future predictions of the ice sheet's dynamics.
  • ItemOpen AccessPublished version Peer-reviewed
    Geomorphic and shallow-acoustic investigation of an Antarctic Peninsula fjord system using high-resolution ROV and shipboard geophysical observations: Ice dynamics and behaviour since the Last Glacial Maximum
    (Elsevier, 2016-12-01) Garcia, M; Dowdeswell, JA; Noormets, R; Hogan, KA; Evans, J; Ó Cofaigh, C; Larter, RD; Dowdeswell, Julian [0000-0003-1369-9482]
    Detailed bathymetric and sub-bottom acoustic observations in Bourgeois Fjord (Marguerite Bay, Antarctic Peninsula) provide evidence on sedimentary processes and glacier dynamics during the last glacial cycle. Submarine landforms observed in the 50 km-long fjord, from the margins of modern tidewater glaciers to the now ice-distal Marguerite Bay, are described and interpreted. The landforms are grouped into four morpho-sedimentary systems: (i) glacial advance and full-glacial; (ii) subglacial and ice-marginal meltwater; (iii) glacial retreat and neoglaciation; and (iv) Holocene mass-wasting. These morpho-sedimentary systems have been integrated with morphological studies of the Marguerite Bay continental shelf and analysed in terms of the specific sedimentary processes and/or stages of the glacial cycle. They demonstrate the action of an ice-sheet outlet glacier that produced drumlins and crag-and-tail features in the main and outer fjord. Meltwater processes eroded bedrock channels and ponds infilled by fine-grained sediments. Following the last deglaciation of the fjord at about 9000 yr BP, subsequent Holocene neoglacial activity involved minor readvances of a tidewater glacier terminus in Blind Bay. Recent stillstands and/or minor readvances are inferred from the presence of a major transverse moraine that indicates grounded ice stabilization, probably during the Little Ice Age, and a series of smaller landforms that reveal intermittent minor readvances. Mass-wasting processes also affected the walls of the fjord and produced scars and fan-shaped deposits during the Holocene. Glacier-terminus changes during the last six decades, derived from satellite images and aerial photographs, reveal variable behaviour of adjacent tidewater glaciers. The smaller glaciers show the most marked recent retreat, influenced by regional physiography and catchment-area size.