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4. Radar derived subglacial properties and landforms beneath Rutford Ice Stream, West Antarctica

Author

Schlegel, Rebecca, Murray, Tavi, Smith, Andrew M., Brisbourne, Alex M., Booth, Adam D., King, Edward C., Clark, Roger A., Schlegel, Rebecca, Murray, Tavi, Smith, Andrew M., Brisbourne, Alex M., Booth, Adam D., King, Edward C., and Clark, Roger A.

Abstract

Basal properties beneath ice streams and glaciers are known to be a control for ice flow dynamics, hence knowledge of them is crucial for predicting sea level due to changes in glacial dynamics. Basal properties, processes and topography also drive the formation of subglacial landforms. Bed properties beneath Rutford Ice Stream (West Antarctica) have previously been described using seismic acoustic impedance measurements at a sparse spatial coverage. Here, we derive bed properties in a 15 x 17 km grid of surface radar data with coverage and sampling much higher than previous seismic studies. Bed reflection amplitudes in surface radar data were calibrated using sediment porosities (ranging from 0.4 – 0.5) derived from seismic acoustic impedance. We find the bed properties are spatially variable, consisting of low porosity material in some areas and soft sediment in other areas. Comparison of seismic and surface radar data imply the low porosity material to be a consolidated sediment or sedimentary rock. Mega-scale glacial lineations (MSGLs) are ubiquitous on the bed and consist of soft, high porosity, probably deforming sediment, consistent with previous interpretations of MSGLs. We find some MSGLs have high reflectivity on their crest, interpreted as water bodies overlying high porosity sediment, whereas the trough around and the upstream end of some landforms consist of low porosity material. Integrating these different observations, we place constraints on possible explanations for the occurrence of water on the crest of landforms.

Published
2022

6. Inland thinning of West Antarctic Ice Sheet steered along subglacial rifts

Author

Bingham, Robert G., Ferraccioli, Fausto, King, Edward C., Larter, Robert D., Pritchard, Hamish D., Smith, Andrew M., and Vaughan, David G.

Subjects
Geodynamics -- Research, Faults (Geology) -- Environmental aspects, Surface-ice melting -- Environmental aspects, Ice sheets -- Environmental aspects, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Current ice loss from the West Antarctic Ice Sheet (WAIS) accounts for about ten per cent of observed global sea-level rise (1). Losses are dominated by dynamic thinning, in which [...]

Published
2012
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9. The precision of radar-derived subglacial bed topography: a case study from Pine Island Glacier, Antarctica

Author

King, Edward C. and King, Edward C.

Abstract

Recent advances in the measurement of bedforms beneath active ice streams have been made using ground-based grid profiling using impulse radar systems operating with centre frequencies in the 3–5 MHz range. Surveys of Rutford Ice Stream and Pine Island Glacier have shown that features such as mega-scale glacial lineations with topographic relief of as little as 3 m can be traced for many kilometres downstream under more than 2 km of fast-moving ice. In the discussion of these data, it is often asked ‘How is it possible to map such fine-scale topography with such a low-frequency radar’. In answering that question, the key point is the distinction between the precision of a radar range measurement to a single, isolated reflective interface and the ability to resolve the presence of two closely-spaced interfaces of similar reflectivity (commonly referred to as the vertical resolution). This paper will discuss and illustrate this distinction and use the case study of data acquired over Pine Island Glacier to examine the limits of precision of the radar range measurement.

Published
2020

13. Diverse landscapes beneath Pine Island Glacier influence ice flow

Author

Bingham, Robert G., Vaughan, David G., King, Edward C., Davies, Damon, Cornford, Stephen L., Smith, Andrew M., Arthern, Robert J., Brisbourne, Alex M., De Rydt, Jan, Graham, Alastair G. C., Spagnolo, Matteo, Marsh, Oliver J., and Shean, David E.

Subjects
Science, lcsh:Q, lcsh:Science, Article
Abstract

The retreating Pine Island Glacier (PIG), West Antarctica, presently contributes ~5–10% of global sea-level rise. PIG’s retreat rate has increased in recent decades with associated thinning migrating upstream into tributaries feeding the main glacier trunk. To project future change requires modelling that includes robust parameterisation of basal traction, the resistance to ice flow at the bed. However, most ice-sheet models estimate basal traction from satellite-derived surface velocity, without a priori knowledge of the key processes from which it is derived, namely friction at the ice-bed interface and form drag, and the resistance to ice flow that arises as ice deforms to negotiate bed topography. Here, we present high-resolution maps, acquired using ice-penetrating radar, of the bed topography across parts of PIG. Contrary to lower-resolution data currently used for ice-sheet models, these data show a contrasting topography across the ice-bed interface. We show that these diverse subglacial landscapes have an impact on ice flow, and present a challenge for modelling ice-sheet evolution and projecting global sea-level rise from ice-sheet loss., Projecting the future retreat and thus global sea level contributions of Antarctica’s Pine Island Glacier is hampered by a poor grasp of what controls flow at the ice base. Here, via high-resolution ice-radar imaging, the authors show diverse landscapes beneath the glacier fundamentally influence ice flow.

Published
2017

17. The internal structure of the Brunt Ice Shelf from ice-penetrating radar analysis and implications for ice shelf fracture

Author

King, Edward C., De Rydt, Jan, Gudmundsson, G. Hilmar, King, Edward C., De Rydt, Jan, and Gudmundsson, G. Hilmar

Abstract

The rate and direction of rift propagation through ice shelves depends on both the stress field and the heterogeneity, or otherwise, of the physical properties of the ice. The Brunt Ice Shelf in Antarctica has recently developed new rifts which are being actively monitored as they lengthen and interact with the internal structure of the ice shelf. Here we present the results of a ground-penetrating radar survey of the Brunt Ice Shelf aimed at understanding variations in the internal structure. We find that there are flow bands composed mostly of thick meteoric ice interspersed with thinner sections of ice shelf that have a large proportion of sea ice and sea-water-saturated firn. Therefore the ice shelf is, in essence, a series of ice tongues cemented together with ice mélange. The changes in structure are related both to the thickness and flow speed of ice at the grounding line and to subsequent processes of firn accumulation and brine infiltration as the ice shelf flows towards the calving front. It is shown that rifts propagating through the Brunt Ice Shelf preferentially skirt the edges of blocks of meteoric ice and slow their rate of propagation when forced by the stress field to break through them.

Published
2018

18. Evidence for the long-term sedimentary environment in an Antarctic subglacial lake

Author

Smith, Andrew M., Woodward, John, Ross, Neil, Bentley, Michael J., Hodgson, Dominic A., Siegert, Martin J., King, Edward C., Smith, Andrew M., Woodward, John, Ross, Neil, Bentley, Michael J., Hodgson, Dominic A., Siegert, Martin J., and King, Edward C.

Abstract

Lakes beneath the Antarctic Ice Sheet are of fundamental scientific interest for their ability to contain unique records of ice sheet history and microbial life in their sediments. However, no records of subglacial lake sedimentation have yet been acquired from beneath the interior of the ice sheet, and understanding of sediment pathways, processes and structure in subglacial lake environments remains uncertain. Here we present an analysis of seismic data from Subglacial Lake Ellsworth, showing that the lake bed comprises very fine-grained sediments deposited in a low energy environment, with low water- and sediment-fluxes. Minimum sediment thickness is 6 m, the result of prolonged low sedimentation rates. Based on the few available analogues, we speculate this sediment age range is a minimum of 150 ka, and possibly >1 Ma. Sediment mass movements have occurred, but they are rare and have been buried by subsequent sedimentation. We present a new conceptual model of subglacial lake sedimentation, allowing a framework for evaluating processes in subglacial lake environments, and for determining future lake access locations and interpreting subglacial lake samples.

Published
2018

19. How dynamic are ice-stream beds?

Author

Davies, Damon, Bingham, Robert G., King, Edward C., Smith, Andrew M., Brisbourne, Alex M., Spagnolo, Matteo, Graham, Alastair G. C., Hogg, Anna E., Vaughan, David G., Davies, Damon, Bingham, Robert G., King, Edward C., Smith, Andrew M., Brisbourne, Alex M., Spagnolo, Matteo, Graham, Alastair G. C., Hogg, Anna E., and Vaughan, David G.

Abstract

Projections of sea-level rise contributions from West Antarctica's dynamically thinning ice streams contain high uncertainty because some of the key processes involved are extremely challenging to observe. An especially poorly observed parameter is sub-decadal stability of ice-stream beds. Only two previous studies have made repeated geophysical measurements of ice-stream beds at the same locations in different years, but both studies were limited in spatial extent. Here, we present the results from repeat radar measurements of the bed of Pine Island Glacier, West Antarctica, conducted 3–6 years apart, along a cumulative ~ 60 km of profiles. Analysis of the correlation of bed picks between repeat surveys show that 90 % of the ice-stream bed displays no significant change despite the glacier increasing in speed by up to 40 % over the last decade. We attribute the negligible detection of morphological change at the bed of Pine Island Glacier to the ubiquitous presence of a deforming till layer, wherein sediment transport is in steady state, such that sediment is transported along the basal interface without inducing morphological change to the radar-sounded bed. Significant change was only detected in one 500 m section of the bed where a change in bed morphology occurs with a difference in vertical amplitude of 3–5 m. Given the precision of our measurements, the maximum possible erosion rate that could go undetected along our profiles is 500 mm a-1, far exceeding erosion rates reported for glacial settings from proglacial sediment yields, but substantially below subglacial erosion rates of 1000 mm a-1 previously reported from repeat geophysical surveys in West Antarctica.

Published
2018

20. Recent rift formation and impact on the structural integrity of the Brunt Ice Shelf, East Antarctica

Author

De Rydt, Jan, Gudmundsson, G. Hilmar, Nagler, Thomas, Wuite, Jan, King, Edward C., De Rydt, Jan, Gudmundsson, G. Hilmar, Nagler, Thomas, Wuite, Jan, and King, Edward C.

Abstract

We report on the recent reactivation of a large rift in the Brunt Ice Shelf, East Antarctica, in December 2012 and the formation of a 50 km long new rift in October 2016. Observations from a suite of ground-based and remote sensing instruments between January 2000 and July 2017 were used to track progress of both rifts in unprecedented detail. Results reveal a steady accelerating trend in their width, in combination with alternating episodes of fast ( > 600 m day−1) and slow propagation of the rift tip, controlled by the heterogeneous structure of the ice shelf. A numerical ice flow model and a simple propagation algorithm based on the stress distribution in the ice shelf were successfully used to hindcast the observed trajectories and to simulate future rift progression under different assumptions. Results show a high likelihood of ice loss at the McDonald Ice Rumples, the only pinning point of the ice shelf. The nascent iceberg calving and associated reduction in pinning of the Brunt Ice Shelf may provide a uniquely monitored natural experiment of ice shelf variability and provoke a deeper understanding of similar processes elsewhere in Antarctica.

Published
2018

23. How dynamic are ice-stream beds?

Author

Davies, Damon, primary, Bingham, Robert G., additional, King, Edward C., additional, Smith, Andrew M., additional, Brisbourne, Alex M., additional, Spagnolo, Matteo, additional, Graham, Alastair G. C., additional, Hogg, Anna E., additional, and Vaughan, David G., additional

Published
2018
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25. Overview of the JET results in support to ITER

Author

Litaudon, X., Abduallev, S., Abhangi, M., Abreu, P., Afzal, M., Aggarwal, K.M., Ahlgren, T., Ahn, Jong Hyun, Aho-Mantila, L., Aiba, N., Airila, M., Albanese, R., Aldred, V., Alegre, D., Alessi, E., Aleynikov, P., Alfier, A., Alkseev, A., Allinson, M., Alper, B., Alves, E., Ambrosino, G., Ambrosino, R., Amicucci, L., Amosov, V., Andersson Sundén, E., Angelone, M., Anghel, M., Angioni, C., Appel, L., Appelbee, C., Arena, P., Ariola, M., Arnichand, H., Arshad, S.A., Ash, A., Ashikawa, N., Aslanyan, V., Asunta, O., Auriemma, F., Austin, Y., Avotina, L., Axton, M.D., Ayres, C., Bacharis, M., Baciero, A., Baião, D., Bailey, Stephen, Baker, A., Balboa, I., Balden, M., Balshaw, N., Bament, R., Banks, J.W., Baranov, Y.F., Barnard, M.A., Barnes, D., Barnes, M., Barnsley, R., Baron Wiechec, A., Barrera Orte, L., Baruzzo, M, Basiuk, V., Bassan, M., Bastow, R., Batista, A., Batistoni, P., Baughan, R., Bauvir, B., Baylor, L., Bazylev, B., Beal, J., Beaumont, P.S., Beckers, M., Beckett, B., Becoulet, A., Bekris, N., Beldishevski, M., Bell, Karen, Belli, F., Bellinger, M., Belonohy, E., Ben Ayed, N., Benterman, N.A., Bergsåker, H., Bernardo, J., Bernert, M., Berry, Philippa A. M., Bertalot, L., Besliu, C., Beurskens, M., Bieg, B., Bielecki, J., Biewer, T., Bigi, M., Bílková, P., Binda, F., Bisoffi, A., Bizarro, J P S, Björkas, C., Blackburn, J. A., Blackman, K., Blackman, T.R., Blanchard, P., Blatchford, P., Bobkov, V., Boboc, A., Bodnár, G., Bogar, O., Bolshakova, I., Bolzonella, T., Bonanomi, N., Bonelli, F., Boom, J., Booth, T. J., Borba, D., Borodin, D., Borodkina, I., Botrugno, A., Bottereau, C., Boulting, P., Bourdelle, C., Bowden, M., Bower, C., Bowman-Collin, C., Boyce, T., Boyd, P. C., Boyer, H.J., Bradshaw, J.M.A., Braic, V., Bravanec, R., Breizman, B., Bremond, S., Brennan, P.D., Breton, Simon-Philippe, Brett, A., Brezinsek, S., Bright, M.D.J., Brix, M., Broeckx, W., Brombin, M., Brosławski, A., Brown, Paul D., Brown, M., Bruno, E., Bucalossi, J., Buch, Martin Jensen, Buchanan, F.J., Buckley, M.A., Budny, R., Bufferand, H., Bulman, M., Bulmer, N., Bunting, P., Buratti, P., Burckhart, A., Buscarino, A., Busse, A., Butler, N.K., Bykov, Ioury, Byrne, J., Cahyna, P., Calabro, G., Calvo, J. I, Camenen, Y., Camp, P., Campling, D.C., Cane, J., Cannas, B., Capel, A.J., Card, P.J., Cardinali, A., Carman, P., Carr, Meghan, Carralero, D., Carraro, L., Carvalho, J. L. B., Carvalho, I. S., Carvalho, P., Casson, F.J., Castaldo, C., Catarino, Nuno, Caumont, J., Causa, F., Cavazzana, R., Cave-Ayland, K., Cavinato, M., Cecconello, M., Ceccuzzi, S., Cecil, E., Cenedese, A., Cesario, R., Challis, C.D., Chandler, M., Chandra, Deepak, Chang, C.S., Chankin, A., Chapman, I.T., Chapman, S.C., Chernyshova, M., Chitarin, G., Ciraolo, G., Ciric, D., Citrin, J, Clairet, F., Clark, E. G., Clark, M., Clarkson, R B, Clatworthy, D., Clements-Croome, Derek, Cleverly, M., Coad, J.P., Coates, P.A., Cobalt, A., Coccorese, V., Cocilovo, V., Coda, S., Coelho, R., Coenen, J.W., Coffey, I., Colas, L., Collins, S. P., Conka, D., Conroy, S., Conway, N., Coombs, D., Cooper, D A, Cooper, S.R., Corradino, C., Corre, Y., Corrigan, G., Cortes, S., Coster, D., Couchman, A.S., Cox, M.P., Craciunescu, T., Cramp, S., Craven, R. A., Crisanti, F, Croci, Gabriele, Croft, D., Crombe, K., Crowe, R., Cruz, N., Cseh, G., Cufar, A., Cullen, A., Curuia, M., Czarnecka, A., Dabirikhah, H., Dalgliesh, P., Dalley, S., Dankowski, J., Darrow, D., Davies, O., Davis, W., Day, C., Day, I.E., De Bock, M.F.M., de Assis Castro, Rafael Cunha, de la Cal, E., de la Luna, E., De Masi, G., de Pablos, J. L., De Temmerman, G., De Tommasi, G., de Vries, P., Deakin, K., Deane, Jonathan H.B., Degli Agostini, F., Dejarnac, R., Delabie, E., den Harder, N., Dendy, R.O., Denis, J., Denner, P., Devaux, S., Devynck, P., Di Maio, Francesco, Di Siena, A., Di Troia, C., Dinca, M. P., D’Inca, R., Ding, B., Dittmar, T., Doerk-Bendig, H., Doerner, R.P., Donné, T., Dorling, S.E., Dormido-Canto, S., Doswon, S., Douai, D., Doyle, P.T., Drenik, A., Drewelow, P., Drews, P., Duckworth, Ph, Dumont, R., Dumortier, P., Dunai, D., Dunne, M., Ďuran, Ivan, Durodie, F., Dutta, Partha Sharathi, Duval, B. P., Dux, R., Dylst, K., Dzysiuk, N., Edappala, P.V., Edmond, J., Edwards, A.M., Edwards, Emily S. J., Eich, Th, Ekedahl, A., El-Jorf, R., Elsmore, C.G., Enachescu, M., Ericsson, G., Eriksson, F., Eriksson, J., Eriksson, L.-G., Esposito, B., Esquembri, S., Esser, H.G., Esteve-Gassent, M. D., Evans, B., Evans, G.E., Evison, G., Ewart, G.D., Fagan, D., Faitsch, M., Falie, D., Fanni, A., Fasoli, A., Faustin, J. M., Fawlk, N., Fazendeiro, L., Fedorczak, N., Felton, R.C., Fenton, K., Fernades, A., Fernandes, H., Ferreira, J.S., Fessey, J.A., Février, O., Ficker, O., Field, Robert A., Fietz, S., Figueiredo, A., Figueiredo, Joana, Fil, A., Finburg, P., Firdaouss, M., Fischer, U., Fittill, L., FitzGerald, Michael, Flammini, D., Flanagan, J., Fleming, C., Flinders, K., Fonnesu, N., Fontdecaba, J. M., Formisano, A., Forsythe, L., Fortuna, L., Fortuna-Zalesna, E., Fortune, M., Foster, S.J., Franke, T., Franklin, T., Frasca, M., Frassinetti, L., Freisinger, M., Fresa, R., Frigione, D., Fuchs, V., Fuller, S.D., Futatani, S., Fyvie, J., Gal, K., Galassi, D., Gałązka, K., Galdon-Quiroga, J., Gallagher, Austin J., Gallart, D., Galvao, R.M.O., Gao, X., Gao, Y., Garcia, Jeronimo, Garcia-Carrasco, A., García-Muñoz, M., Gardarein, J.-L., Garzotti, L., Gaudio, P., Gauthier, E., Gear, D.F., Gee, S.J., Geiger, B., Gelfusa, M., Gerasimov, S., Gervasini, G., Gethins, M., Ghani, Z., Ghate, M., Gherendi, M., Giacalone, J.C., Giacomelli, L., Gibson, C.S., Giegerich, T., Gil, C., Gil de Sola , L., Gilligan, S., Gin, D., Giovannozzi, E., Girardo, J.-B., Giroud, C., Giruzzi, G., Glöggler, S., Godwin, J., Goff, J.P., Gohil, P., Goloborod’ko, V., Gomes, J.R.B., Gonçalves, B., Goniche, M., Goodliffe, M., Goodyear, A., Gorini, G., Gosk, M., Goulding, R., Goussarov, A., Gowland, R., Graham, B., Graham, M.E., Graves, J.P., Grazier, N., Grazier, P., Green, Nick R., Greuner, H., Grierson, B.A., Griph, F.S., Grisolia, C., Grist, D., Groth, M.V., Grove, R., Grundy, C.N., Grzonka, J., Guard, D., Guérard, C., Guillemaut, C., Guirlet, R., Gurl, C., Utoh, H.H., Hackett, L.J., Hacquin, S., Hagar, A., Hager, R., Hakola, A.H., Halitovs, M., Hall, S.J., Hallworth Cook, S.P., Hamlyn-Harris, C., Hammond, K.D., Harrington, C., Harrison, J.M., Harting, D., Hasenbeck, F., Hatano, Y., Hatch, D.R., Haupt, T.D.V., Hawes, J., Hawkes, N.C., Hawkins, Gary J., Hawkins, P., Haydon, P.W., Hayter, N., Hazel, S., Heesterman, P.J.L., Heinola, K., Hellesen, C., Hellsten, T., Helou, W., Hemming, O.N., Hender, T.C., Henderson, M., Henderson, S.S., Henriques, Romina, Hepple, D., Hermon, G., Hertout, P., Hidalgo, C., Highcock, E.G., Hill, M., Hillairet, J., Hillesheim, J., Hillis, D., Hizanidis, K., Hjalmarsson, A., Hobirk, J, Hodille, E., Hogben, C.H.A., Hogeweij, G.M.D., Hollingsworth, Michael A., Hollis, S., Homfray, D.A., Horáček, J., Hornung, G., Horton, A.R., Horton, D. L., Horvath, L., Hotchin, S.P., Hough, M.R., Howarth, P.J., Hubbard, A., Huber, Andreas, Huber, Kilian V. M., Huddleston, T.M., Hughes, Mike, Huijsmans, G.T.A., Hunter, C.L., Huynh, P., Hynes, A.M., Iglesias, D., Imazawa, N., Imbeaux, F., Imríšek, M., Incelli, M., Innocente, P., Irishkin, M., Ivanova-Stanik, I., Jachmich, S., Jacobsen, Asger Schou, Jacquet, P., Jansons, J., Jardin, A., Järvinen, A., Jaulmes, F., Jednoróg, S., Jenkins, I., Jeong, C., Jepu, I., Joffrin, E., Johnson, R., Johnson, T., Johnston, Jane, Joita, L., Jones, G., Jones, T.T.C., Hoshino, K.K., Kallenbach, A., Kamiya, K., Kaniewski, J., Kantor, A., Kappatou, A., Karhunen, J., Karkinsky, D., Karnowska, I., Kaufman, M., Kaveney, G., Kazakov, Y., Kazantzidis, V., Keeling, D.L., Keenan, T., Keep, J., Kempenaars, M., Kennedy, C., Kenny, G. D., Kent, A.J.R., Kent, O.N., Khilkevich, E., Kim, H.T., Kim, H.S., Kinch, A., King, Edward C., King, D. P., King, R.F., Kinna, D.J., Kiptily, V., Kirk, A., Kirov, K., Kirschner, A., Kizane, G., Klepper, C., Klix, A., Knight, P., Knipe, S.J., Knott, S., Kobuchi, T., Köchl, F., Kocsis, G., Kodeli, I., Kogan, L., Kogut, D., Koivuranta, S., Kominis, Y., Köppen, M., Kos, B., Koskela, T., Koslowski, H R, Koubiti, M., Kovari, M., Kowalska-Strzęciwilk, E., Krasilnikov, A., Krasilnikov, V., Krawczyk, N., Kresina, M., Krieger, K., Krivska, A., Kruezi, U., Książek, I., Kukushkin, A., Kundu, A., Kurki-Suonio, T., Kwak, S., Kwiatkowski, R., Kwon, O-joung, Laguardia, L., Lahtinen, Annukka M, Laing, W.A., Lam, Nguyen Ngoc, Lambertz, H.T., Lane, C., Lang, P.T., Lanthaler, S., Lapins, J., Lasa, A., Last, J.R., Łaszyńska, E., Lawless, R., Lawson, M. A., Lawson, K.D., Lazaros, A., Lazzaro, Enzo, Leddy, J., Lee, S., Lefebvre, X., Leggate, H.J., Lehmann, J., Lehnen, M., Leichtle, D., Leichuer, P., Leipold, Frank, Lengar, Igor, Lennholm, M., Lerche, E., Lescinskis, A., Lesnoj, S., Letellier, E., Leyland, M., Leysen, W., Li, L., Liang, Y., Likonen, J., Linke, J., Linsmeier, Ch., Lipschultz, B., Liu, G., Liu, Y., Lo Schiavo, V.P., Loarer, T., Loarte, A., Lobel, R.C., Lomanowski, B., Lomas, P.J., Lönnroth, J., Lopez, M. J., López-Razola, J., Lorenzini, R., Losada, U., Lovell, J.J., Loving, A.B., Lowry, C., Luce, T., Lucock, R.M.A., Lukin, A., Luna, C., Lungaroni, M., Lungu, C.P., Lungu, M., Lunniss, A., Lupelli, I., Lyssoivan, A., MacDonald, Ewen N., Macheta, P., Maczewa, K., Magesh, B., Maget, P., Maggi, C., Maier, H., Mailloux, J., Makkonen, T., Makwana, R., Malaquias, A., Malizia, A., Manas, P., Manning, A., Manso, M.-E., Mantica, P., Mantsinen, M., Manzanares, A., Maquet, Ph, Marandet, Y., Marcenko, N., Marchetto, C., Marchuk, O., Marinelli, M., Marinucci, M., Markovič, Tomáš, Marocco, D., Marot, L., Marren, C.A., Marshal, R., Martin, A. A., Martin, Y., Martín de Aguilera, A., Martínez, J. F., Martín-Solís, J. R., Martynova, Y., Maruyama, S., Masiello, A., Maslov, M., Matejcik, S., Mattei, M., Matthews, G.F., Maviglia, F., Mayer, M., Mayoral, M.-L., May-Smith, T., Mazon, D., Mazzotta, C., McAdams, R., McCarthy, P.J., McClements, K.G., McCormack, O., McCullen, P.A., McDonald, D., McIntosh, Steven, McKean-Cowdin, Roberta, McKehon, J., Meadows, R.C., Meakins, A., Medina, Pablo F., Medland, M., Medley, S., Meigh, S., Meigs, A.G., Meisl, G., Meitner, S., Meneses, L., Menmuir, S., Mergia, K., Merrigan, I.R., Mertens, Ph, Meshchaninov, S., Messiaen, A., Meyer, H., Mianowski, S., Michling, R., Middleton-Gear, D., Miettunen, J., Militello, F., Militello-Asp, E., Miloshevsky, G., Mink, F., Minucci, S., Miyoshi, Y., Mlynář, J., Molina, Daniel R., Monakhov, I., Moneti, M., Mooney, R., Moradi, S., Mordijck, S., Moreira-Neto , S.L., Moreno, R., Moro, F., Morris, A.W., Morris, J., Moser, Mary L., Mosher, S., Moulton, D., Murari, A., Muraro, Andrea, Murphy, S., Asakura, N.N., Na, Y.S., Nabais, F., Naish, R., Nakano, T., Nardon, E., Naulin, Volker, Nave, M. F. F., Nedzelski, I., Nemtsev, G., Nespoli, F., Neto, A., Neu, R., Neverov, V.S., Newman, M. 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R., Martynova, Y., Maruyama, S., Masiello, A., Maslov, M., Matejcik, S., Mattei, M., Matthews, G.F., Maviglia, F., Mayer, M., Mayoral, M.-L., May-Smith, T., Mazon, D., Mazzotta, C., McAdams, R., McCarthy, P.J., McClements, K.G., McCormack, O., McCullen, P.A., McDonald, D., McIntosh, Steven, McKean-Cowdin, Roberta, McKehon, J., Meadows, R.C., Meakins, A., Medina, Pablo F., Medland, M., Medley, S., Meigh, S., Meigs, A.G., Meisl, G., Meitner, S., Meneses, L., Menmuir, S., Mergia, K., Merrigan, I.R., Mertens, Ph, Meshchaninov, S., Messiaen, A., Meyer, H., Mianowski, S., Michling, R., Middleton-Gear, D., Miettunen, J., Militello, F., Militello-Asp, E., Miloshevsky, G., Mink, F., Minucci, S., Miyoshi, Y., Mlynář, J., Molina, Daniel R., Monakhov, I., Moneti, M., Mooney, R., Moradi, S., Mordijck, S., Moreira-Neto , S.L., Moreno, R., Moro, F., Morris, A.W., Morris, J., Moser, Mary L., Mosher, S., Moulton, D., Murari, A., Muraro, Andrea, Murphy, S., Asakura, N.N., Na, Y.S., Nabais, F., Naish, R., Nakano, T., Nardon, E., Naulin, Volker, Nave, M. F. F., Nedzelski, I., Nemtsev, G., Nespoli, F., Neto, A., Neu, R., Neverov, V.S., Newman, M. J., Nicholls, K.J., Nicolas, T., Nielsen, Anders Henry, Nielsen, P., Nilsson, E., Nishijima, D., Noble, C., Nocente, M., Nodwell, D., Nordlund, K., Nordman, H, Nouailletas, R., Nunes, I., Oberkofler, M., Odupitan, T., Ogawa, M.T., O’Gorman, T., Okabayashi, M., Olney, R., Omolayo, O., O’Mullane, M., Ongena, J., Orsitto, F., Orszagh, J., Oswuigwe, B.I., Otin, R., Owen, R.A., Paccagnella, R., Pace, N., Pacella, D., Packer, L.W., Page, Ashley, Pajuste, E., Palazzo, Gaetano S., Pamela, S., Panja, S., Papp, P., Paprok, R., Parail, V., Park, M., Parra Diaz, F., Parsons, A.M., Pasqualotto, R., Patel, A., Pathak, S., Paton, David, Patten, H., Pau, A., Pawelec, E., Paz Soldan, C., Peackoc, A., Pearson, I.J., Pehkonen, S.-P., Peluso, E., Penot, C., Puglia, P.P Pereira, Pereira, R., Pereira Puglia, P.P., Perez von Thun, C., Peruzzo, S., Peschanyi, S., Peterka, M, Petersson, P., Petravich, G., Petre, A., Petrella, N., Petržilka, V., Peysson, Y., Pfefferlé, D., Philipps, V., Pillon, M., Pintsuk, G., Piovesan, P., Pires dos Reis, A., Piron, L., Pironti, A., Pisano, F., Pitts, R., Pizzo, F., Plyusnin, V., Pomaro, N., Pompilian, O.G., Pool, P.J., Popovichev, S., Porfiri, M.T., Porosnicu, C., Porton, M., Possnert, G., Potzel, S., Powell, Thomas L, Pozzi, J., Prajapati, V., Prakash, R., Prestopino, G., Price, D., Price, M., Price, R., Prior, P., Proudfoot, R., Pucella, Gianluca, Puglia, P., Puiatti, M.E., Pulley, D., Purahoo, K., Pütterich, Th, Rachlew, E., Rack, M., Ragona, R., Rainford, M.S.J., Rakha, K. A., Ramogida, G., Ranjan, S., Rapson, C.J., Rasmussen, Jens Juul, Rathod, K., Rattá, G., Ratynskaia, S., Ravera, G., Rayner, J. W.C., Rebai, Marica, Reece, D., Reed, A., Réfy, D., Regan, B., Regaña, J., Reich, M., Reid, N., Reimold, F., Reinhart, M., Reinke, M., Reiser, D., Rendell, D., Reux, C., Reyes Cortes, S.D.A., Reynolds, Christopher S., Riccardo, V., Richardson, N., Riddle, K., Rigamonti, Davide, Rimini, F.G., Risner, J., Riva, M., Roach, C., Robins, R.J., Robinson, S.A., Robinson, T., Robson, D.W., Roccella, R., Rodionov, R., Rodrigues, P., Rodriguez, J., Rohde, V., Romanelli, F., Romanelli, M., Romanelli, S., Romazanov, J., Rowe, S., Rubel, M., Rubinacci, G., Rubino, G., Ruchko, L., Ruiz, M, Ruset, C., Rzadkiewicz, Jacek, Saarelma, S., Sabot, R., Safi, E., Sagar, P., Saibene, G., Saint-Laurent, F., Salewski, Mirko, Salmi, A., Salmon, R., Salzedas, F., Samaddar, D., Samm, U., Sandiford, D., Santa, P., Santala, M.I.K., Santos, M. B. L., Santucci, A., Sartori, F., Sartori, R., Sauter, O., Scannell, R., Schlummer, T., Schmid, K., Schmidt, V., Schmuck, S., Schneider, M., Schoepf, K., Schwörer, D., Scott, S.D., Sergienko, G., Sertoli, M., Shabbir, A., Sharapov, S.E., Shaw, A, Shaw, R.G., Sheikh, H., Shepherd, A., Shevelev, A.E., Shumack, A., Sias, G., Sibbald, M.J., Sieglin, B., Silburn, S., Silva, A., Silva, C., Simmons, P.A., Simpson, James J., Simpson-Hutchinson, J., Sinha, Avinash K., Sipilä, S.K., Sips, A.C.C., Sirén, P., Sirinelli, A., Sjöstrand, H., Skiba, M., Skilton, R., Slabkowska, K., Slade, B., Smith, N., Smith, P.G., Smith, R., Smith, T.J., Smithies, M., Snoj, L., Soare, S., Solano, E. R., Somers, A., Sommariva, C., Sonato, P., Sopplesa, A., Sousa, Jorge, Sozzi, C., Spagnolo, S., Spelzini, T., Spineanu, F., Stables, G., Stamatelatos, I., Stamp, M.F., Staniec, P., Stankūnas, G., Stan-Sion, C., Stead, M.J., Stefanikova, E., Stepanov, I., Stephen, A.V., Stephen, A. M., Stevens, A. A., Stevens, B.D., Strachan, Clare J., Strand, P, Strauss, H.R., Ström, P., Stubbs, G., Studholme, W., Subba, F., Summers, H.P., Svensson, J., Świderski, Ł., Szabolics, T., Szawlowski, M., Szepesi, G., Suzuki, T, Tál, B., Tala, T., Talbot, A.R., Talebzadeh, S., Taliercio, C., Tamain, P., Tame, C., Tang, W., Tardocchi, M., Taroni, L.L., Taylor, D., Taylor, K.A., Tegnered, D., Telesca, G., Teplova, N., Terranova, D., Testa, D., Tholerus, E., Thomas, J., Thomas, J.D., Thomas, P., Thompson, A., Thompson, R. C. A., Thompson, V.K., Thorne, Lucy, Thornton, A., Thrysøe, Alexander Simon, Tigwell, P.A., Tipton, N., Tiseanu, I., Tojo, H., Tokitani, M., Tolias, P., Tomeš, M., Tonner, P., Towndrow, M., Trimble, P., Tripsky, M., Tsalas, M., Tsavalas, P., Tskhakaya jun, D., Turner, I., Turner, MK, Turnyanskiy, M.R., Tvalashvili, G., Tyrrell, S.G.J., Uccello, A., Ul-Abidin, Z., Uljanovs, J., Ulyatt, D., Urano, H., Uytdenhouwen, I., Vadgama, A.P., Valcarcel, D., Valentinuzzi, M., Valisa, M., Vallejos Olivares, P., Valovic, M., Van De Mortel, M., Van Eester, D., Van Renterghem, W., van Rooij, G.J., Varje, J., Varoutis, S., Vartanian, S., Vasava, K., Vasilopoulou, T., Vega-Castillo, Jesús, Verdoolaege, G., Verhoeven, R., Verona, C., Verona Rinati, G., Veshchev, E., Vianello, N., Vicente, J., Viezzer, E., Villari, S., Villone, F., Vincenzi, P., Vinyar, I., Viola, B., Vitins, A., Vizvary, Z., Vlad, M., Voitsekhovitch, I., Vondráček, P., Vora, N., Vu, T., Pires de Sa, W.W., Wakeling, B., Waldon, C.W.F., Walkden, N. R., Walker, Lynn M., Walker, R., Walsh, M.J., Wang, E., Wang, N., Warder, S.E.V., Warren, R.A.J., Waterhouse, J., Watkins, N.W., Watts, C., Wauters, T., Weckmann, A., Weiland, J, Weisen, H., Weiszflog, M., Wellstood, Frederick C., West, A.T., Wheatley, M.R., Whetham, S., Whitehead, A.M., Whitehead, B.D., Widdowson, A.M., Wiesen, S., Wilkinson, J., Williams, J., Williams, M., Wilson, A.R., Wilson, Daniel J, Wilson, Richard H., Wilson, J., Wischmeier, M., Withenshaw, G., Withycombe, A., Witts, D.M., Wood, D., Wood, R., Woodley, C., Wray, S., Wright, J., Wright, J.C., Wu, J., Wukitch, S., Wynn, A., Xu, Can T., Yadikin, D., Yanling, W., Yao, Li, Yavorskij, V., Yoo, M.G., Young, P. C., Young, D., Young, I.D., Young, R., Zacks, J., Zagorski, R., Zaitsev, F.S., Zanino, R., Zarins, A., Zastrow, K.-D., Zerbini, M., Zhang, W., Zhou, Y., Zilli, E., Zoita, V., Zoletnik, S., and Zychor, Izabella

Abstract

The 2014–2016 JET results are reviewed in the light of their significance for optimising the ITER research plan for the active and non-active operation. More than 60 h of plasma operation with ITER first wall materials successfully took place since its installation in 2011. New multi-machine scaling of the type I-ELM divertor energy flux density to ITER is supported by first principle modelling. ITER relevant disruption experiments and first principle modelling are reported with a set of three disruption mitigation valves mimicking the ITER setup. Insights of the L–H power threshold in Deuterium and Hydrogen are given, stressing the importance of the magnetic configurations and the recent measurements of fine-scale structures in the edge radial electric. Dimensionless scans of the core and pedestal confinement provide new information to elucidate the importance of the first wall material on the fusion performance. H-mode plasmas at ITER triangularity (H = 1 at βN ~ 1.8 and n/nGW ~ 0.6) have been sustained at 2 MA during 5 s. The ITER neutronics codes have been validated on high performance experiments. Prospects for the coming D–T campaign and 14 MeV neutron calibration strategy are reviewed.

Published
2017

26. Bed conditions of Pine Island Glacier, West Antarctica

Author

Brisbourne, Alex M., Smith, Andy M., Vaughan, David G., King, Edward C., Davies, D., Bingham, R.G., Smith, E.C., Nias, I.J., Rosier, Sebastian H.R., Brisbourne, Alex M., Smith, Andy M., Vaughan, David G., King, Edward C., Davies, D., Bingham, R.G., Smith, E.C., Nias, I.J., and Rosier, Sebastian H.R.

Abstract

Although 90% of Antarctica's discharge occurs via its fast-flowing ice streams, our ability to project future ice sheet response has been limited by poor observational constraints on the ice-bed conditions used in numerical models to determine basal slip. We have helped address this observational deficit by acquiring and analyzing a series of seismic reflection profiles to determine basal conditions beneath the main trunk and tributaries of Pine Island Glacier (PIG), West Antarctica. Seismic profiles indicate large-scale sedimentary deposits. Combined with seismic reflection images, measured acoustic impedance values indicate relatively uniform bed conditions directly beneath the main trunk and tributaries, comprising a widespread reworked sediment layer with a dilated sediment lid of minimum thickness 1.5 ± 0.4 m. Beneath a slow-moving intertributary region, a discrete low-porosity sediment layer of 7 ± 3 m thickness is imaged. Despite considerable basal topography, seismic observations indicate that a till layer at the ice base is ubiquitous beneath PIG, which requires a highly mobile sediment body to maintain an abundant supply. These results are compatible with existing ice sheet models used to invert for basal shear stress: existing basal conditions upstream will not inhibit further rapid retreat of PIG if the high-friction region currently restraining flow, directly upstream of the grounding line, is breached. However, small changes in the pressure regime at the bed, as a result of stress reorganization following retreat, may result in a less-readily deformable bed and conditions which are less likely to maintain high ice-flow rates.

Published
2017

27. The periodic topography of ice stream beds: insights from the Fourier spectra of mega-scale glacial lineations

Author

Spagnolo, Matteo, Bartholomaus, Timothy C., Clark, Chris D., Stokes, Chris R., Atkinson, Nigel, Dowdeswell, Julian A., Ely, Jeremy C., Graham, Alistair G.C., Hogan, Kelly A., King, Edward C., Larter, Robert D., Livingstone, Stephen J., Pritchard, Hamish D., Spagnolo, Matteo, Bartholomaus, Timothy C., Clark, Chris D., Stokes, Chris R., Atkinson, Nigel, Dowdeswell, Julian A., Ely, Jeremy C., Graham, Alistair G.C., Hogan, Kelly A., King, Edward C., Larter, Robert D., Livingstone, Stephen J., and Pritchard, Hamish D.

Abstract

Ice stream bed topography contains key evidence for the ways ice streams interact with, and are potentially controlled by, their beds. Here we present the first application of two–dimensional Fourier analysis to 22 marine and terrestrial topographies from 5 regions in Antarctica and Canada, with and without mega-scale glacial lineations (MSGLs). We find that the topography of MSGL-rich ice stream sedimentary beds is characterized by multiple, periodic wavelengths between 300 and 1200 m and amplitudes from decimeters to a few meters. This periodic topography is consistent with the idea that instability is a key element to the formation of MSGL bedforms. Dominant wavelengths vary among locations and, on one paleo ice stream bed, increase along the direction of ice flow by 1.7±0.52% km-1. We suggest that these changes are likely to reflect pattern evolution via downstream wavelength coarsening, even under potentially steady ice stream geometry and flow conditions. The amplitude of MSGLs is smaller than that of other fluvial and glacial topographies, but within the same order of magnitude. However, MSGLs are a striking component of ice stream beds because the topographic amplitude of features not aligned with ice flow is reduced by an order of magnitude relative to those oriented with the flow direction. This study represents the first attempt to automatically derive the spectral signatures of MSGLs. It highlights the plausibility of identifying these landform assemblages using automated techniques and provides a benchmark for numerical models of ice stream flow and subglacial landscape evolution.

Published
2017

28. Inferring the viscous and elastic properties of a suture zone in Larsen C

Author

O'Leary, Martin, Kulessa, Bernd, Booth, Adam D., Holland, Paul, Jansen, Daniela, King, Edward C., Luckman, Adrian J., McGrath, Daniel, and Zwinger, T.

Abstract

After the collapse of its neighbours, Larsen A and B, the Larsen C ice shelf is widely considered at risk of future climate-driven instability. Recent work has shown that the ice shelf is stabilized by soft melange in its suture zones, where adjacent flow units merge. Little is known about the mechanical properties of melange however, so that the quantification of its effect on the stability of Larsen C Ice Shelf has remained challenging. To identify the structural and elastic properties of the Joerg Peninsula suture zone in Larsen C Ice Shelf, we integrate seismic reflection and ground-penetrating radar (GPR) geophysical measurements. GPR transects reveal the presence of a stiff layer of meteoric ice, trapped between the softer melange beneath and the firn layer above. Monte Carlo analysis reveals that the seismic velocity of this melange is noticeably reduced compared to meteoric ice. By applying Hashin-Shtrikman bounds on the elastic moduli of a two-phase mixture of ice and water to the velocities, we are able to derive the elastic properties of the melange. We ascertain, significantly, that the melange is softer than meteoric ice because it contains a substantial volume fraction of water. The meteoric ice layer is buckling due to compressive lateral stresses. We suggest this process is analogous to fold buckling in sedimentary rocks. Using the ice flow model Elmer/Ice we are able to replicate this process, and thereby derive bounds on the rheological properties of the suture zone melange.

Published
2016

29. How dynamic are ice-stream beds?

Author

Davies, Damon, primary, Bingham, Robert G., additional, King, Edward C., additional, Smith, Andrew M., additional, Brisbourne, Alex M., additional, Spagnolo, Matteo, additional, Graham, Alastair G. C., additional, Hogg, Anna E., additional, and Vaughan, David G., additional

Published
2017
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31. The periodic topography of ice stream beds: Insights from the Fourier spectra of mega‐scale glacial lineations

Author

Spagnolo, Matteo, primary, Bartholomaus, Timothy C., additional, Clark, Chris D., additional, Stokes, Chris R., additional, Atkinson, Nigel, additional, Dowdeswell, Julian A., additional, Ely, Jeremy C., additional, Graham, Alastair G. C., additional, Hogan, Kelly A., additional, King, Edward C., additional, Larter, Robert D., additional, Livingstone, Stephen J., additional, and Pritchard, Hamish D., additional

Published
2017
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32. Uplift rates from a new high-density GPS network in Palmer Land indicate significant late Holocene ice loss in the southwestern Weddell Sea

Author

Wolstencroft, Martin, King, Matt A., Whitehouse, Pippa L., Bentley, Michael J., Nield, Grace A., King, Edward C., McMillan, Malcolm, Shepherd, Andrew, Barletta, Valentina, Bordoni, Andrea, Riva, Riccardo E.M., Didova, Olga, and Gunter, Brian C.

Subjects
Antarctica, Space geodetic surveys, Glaciology, Sea level change, Global change from geodesy
Abstract

The measurement of ongoing ice-mass loss and associated melt water contribution to sea-level change from regions such as West Antarctica is dependent on a combination of remote sensing methods. A key method, the measurement of changes in Earth's gravity via the GRACE satellite mission, requires a potentially large correction to account for the isostatic response of the solid Earth to ice-load changes since the Last Glacial Maximum. In this study, we combine glacial isostatic adjustment modelling with a new GPS dataset of solid Earth deformation for the southern Antarctic Peninsula to test the current understanding of ice history in this region. A sufficiently complete history of past ice-load change is required for glacial isostatic adjustment models to accurately predict the spatial variation of ongoing solid Earth deformation, once the independently-constrained effects of present-day ice mass loss have been accounted for. Comparisons between the GPS data and glacial isostatic adjustment model predictions reveal a substantial misfit. The misfit is localized on the southwestern Weddell Sea, where current ice models under-predict uplift rates by approximately 2 mm yr-1. This under-prediction suggests that either the retreat of the ice sheet grounding line in this region occurred significantly later in the Holocene than currently assumed, or that the region previously hosted more ice than currently assumed. This finding demonstrates the need for further fieldwork to obtain direct constraints on the timing of Holocene grounding line retreat in the southwestern Weddell Sea and that GRACE estimates of ice sheet mass balance will be unreliable in this region until this is resolved.

Published
2015

33. Full-depth englacial vertical ice-sheet velocities measured using phase-sensitive radar

Author

Kingslake, Jonathan, Hindmarsh, Richard C. A., Aoalgeirsdottir, Guofinna, Conway, Howard, Corr, Hugh F. J., Gillet-Chaulet, Fabien, Martin, Carlos, King, Edward C., Mulvaney, Robert, and Pritchard, Hamish D.

Subjects
Geophysics, Glaciology--Methodology, Ice sheets, Hydrology, Ice--Dynamics
Abstract

We describe a geophysical technique to measure englacial vertical velocities through to the beds of ice sheets without the need for borehole drilling. Using a ground-based phase-sensitive radio-echo sounder (pRES) during seven Antarctic field seasons, we measure the temporal changes in the position of englacial reflectors within ice divides up to 900 m thick on Berkner Island, Roosevelt Island, Fletcher Promontory and Adelaide Island. Recorded changes in reflector positions yield 'full-depth' profiles of vertical ice velocity that we use to examine spatial variations in ice flow near the divides. We interpret these variations by comparing them to the results of a full-Stokes simulation of ice-divide flow, qualitatively validating the model and demonstrating that we are directly detecting an ice-dynamical phenomenon called the Raymond Effect. Using pRES, englacial vertical ice velocities can be measured in higher spatial resolution than is possible using instruments installed within the ice. We discuss how these measurements could be used with inverse methods to measure ice rheology, and to improve ice-core dating by incorporating pRES-measured vertical velocities into age modelling.

Published
2014
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34. Ice-flow reorganization in West Antarctica 2.5 kyr ago dated using radar-derived englacial flow velocities

Author

Kingslake, Jonathan, Martin, Carlos, Arthern, Robert J., Corr, Hugh F.J., King, Edward C., Kingslake, Jonathan, Martin, Carlos, Arthern, Robert J., Corr, Hugh F.J., and King, Edward C.

Abstract

We date a recent ice-flow reorganization of an ice divide in the Weddell Sea Sector, West Antarctica, using a novel combination of inverse methods and ice-penetrating radars. We invert for two-dimensional ice flow within an ice divide from data collected with a phase-sensitive ice-penetrating radar while accounting for the effect of firn on radar propagation and ice flow. By comparing isochronal layers simulated using radar-derived flow velocities with internal layers observed with an impulse radar, we show that the divide's internal structure is not in a steady state but underwent a disturbance, potentially implying a regional ice-flow reorganization, 2.5 (1.8–2.9) kyr B.P. Our data are consistent with slow ice flow in this location before the reorganization and the ice divide subsequently remaining stationary. These findings increase our knowledge of the glacial history of a region that lacks dated constraints on late-Holocene ice-sheet retreat and provides a key target for models that reconstruct and predict ice-sheet behavior

Published
2016

35. Subglacial landforms beneath Rutford Ice Stream, Antarctica: detailed bed topography from ice-penetrating radar

Author

King, Edward C., Pritchard, Hamish D., Smith, Andy M., King, Edward C., Pritchard, Hamish D., and Smith, Andy M.

Abstract

We present a digital elevation model of the bed of Rutford Ice Stream, Antarctica, derived from radio-echo sounding data. The data cover an 18 × 40 km area immediately upstream of the grounding line of the ice stream. This area is of particular interest because repeated seismic surveys have shown that rapid erosion and deposition of subglacial sediments has taken place. The bed topography shows a range of different subglacial landforms including mega-scale glacial lineations, drumlins and hummocks. This data set will form a baseline survey which, when compared to future surveys, should reveal how active subglacial landscapes change over time. These data also allow comparison between subglacial landforms in an active system with those observed in deglaciated areas in both polar regions. The data set comprises observed ice thickness data, an interpolated bed elevation grid, observed surface elevation data and a surface elevation grid. The data set is available at http://doi.org/269.

Published
2016

36. Size, shape and spatial arrangement of mega-scale glacial lineations, and implications for ice stream basal processes

Author

Spagnolo, Matteo, Clark, Chris D., Ely, Jeremy C., Stokes, Chris R., Anderson, John B., Andreassen, Karin, Graham, Alastair G.C., and King, Edward C.

Abstract

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 characterisation 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 characterised by an exceptional parallel conformity (80% of all mapped MSGLs have an azimuth within 5 degrees 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-organised 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 to 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.

Published
2014

37. Marine ice regulates the future stability of a large Antarctic ice shelf

Author

Kulessa, Bernd, Jansen, Daniela, Luckman, Adrian J., King, Edward C., and Sammonds, Peter R.

Subjects
Article
Abstract

The collapses of the Larsen A and B ice shelves on the Antarctic Peninsula in 1995 and 2002 confirm the impact of southward-propagating climate warming in this region. Recent mass and dynamic changes of Larsen B’s southern neighbour Larsen C, the fourth largest ice shelf in Antarctica, may herald a similar instability. Here, using a validated ice-shelf model run in diagnostic mode, constrained by satellite and in situ geophysical data, we identify the nature of this potential instability. We demonstrate that the present-day spatial distribution and orientation of the principal stresses within Larsen C ice shelf are akin to those within pre-collapse Larsen B. When Larsen B’s stabilizing frontal portion was lost in 1995, the unstable remaining shelf accelerated, crumbled and ultimately collapsed. We hypothesize that Larsen C ice shelf may suffer a similar fate if it were not stabilized by warm and mechanically soft marine ice, entrained within narrow suture zones., Signs of instability in the Antarctic Larsen C ice shelf have raised concerns that it might soon collapse like its northern neighbour Larsen B. Kulessa et al. combine an ice-shelf model with satellite and geophysical data to show that despite dynamic similarities, Larsen C is presently stabilized by marine ice.

Published
2014
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40. Widespread low rates of Antarctic glacial isostatic adjustment revealed by GPS observations

Author

Thomas, Ian D., King, Matt A., Bentley, Michael J., Whitehouse, Pippa L., Penna, Nigel T., Williams, Simon D. P., Riccardo, E. M. Riva, Lavallee, David A., Clarke, Peter J., King, Edward C., Hindmarsh, Richard C.A., and Koivula, Hannu

Subjects
Marine Sciences, Antarctica, glacial isostatic adjustment, GPS velocity
Abstract

Bedrock uplift in Antarctica is dominated by a combination of glacial isostatic adjustment (GIA) and elastic response to contemporary mass change. Here, we present spatially extensive GPS observations of Antarctic bedrock uplift, using 52% more stations than previous studies, giving enhanced coverage, and with improved precision. We observe rapid elastic uplift in the northern Antarctic Peninsula. After considering elastic rebound, the GPS data suggests that modeled or empirical GIA uplift signals are often over?estimated, par t icularly the magnitudes of the signal maxima. Our observation that GIA uplift is misrepresented by modeling (weighted root?meansquares of observation?model differences: 4.9–5.0 mm/yr) suggests that, apart from a few regions where large ice mass loss is occurring, the spatial pattern of secular ice mass change derived from Gravity Recovery and Climate Experiment (GRACE) data and GIA models may be unreliable, and that several recent secular Antarctic ice mass loss estimates are systematically biased, mainly too high.

Published
2011

41. In-situ quantification of ice rheology and direct measurement of the Raymond Effect at Summit, Greenland using a phase-sensitive radar

Author

Gillet-Chaulet, Fabien, Hindmarsh, Richard C. A., Corr, Hugh F. J., King, Edward C., and Jenkins, Adrian

Subjects
F700, F800
Abstract

[1] The Glen exponent ncharacterizes the stress‐dependence of ice deformation, directly influencing the rate at which ice masses respond to external forcing. The slow deformation in large ice‐sheets makes laboratory rheometry at representative strain‐rates difficult. We develop a new technique to estimaten in‐situ, deploying a phase‐sensitive radar to measure vertical strain rates of around 10−4 yr−1within the top 1000 m of ice across ice divides at Summit and NEEM, Greenland. A fluid‐dynamical feature, the Raymond Effect, predicts strong vertical strain‐rate variation across divides over distances of a few ice‐thicknesses. We achieve sufficient resolution to show this pattern, enabling us to estimaten= 4.5 by inverting our observations with flow modelling. This is higher than values previously used but consistent with other indirect measurements, implying laboratory measurements do not explore the full range of ice rheology and the consequent possibility of a greater sensitivity and responsiveness in ice‐sheet dynamics.

Published
2011

42. Looking through drumlins: testing the application of ground-penetrating radar

Author

Spagnolo, Matteo, King, Edward C., Ashmore, David W., Rea, Brice R., Ely, Jeremy C., Clark, Chris D., Spagnolo, Matteo, King, Edward C., Ashmore, David W., Rea, Brice R., Ely, Jeremy C., and Clark, Chris D.

Abstract

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 �12m was achieved when using a 50MHz antenna, with a separation of 1 m, trace spacing of 1m 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 �4m 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.

Published
2014

44. Modelling of Kealey Ice Rise, Antarctica, reveals stable ice-flow conditions in East Ellsworth Land over the millennia

Author

Martín, Carlos, Gudmundsson, G. Hilmar, King, Edward C., Martín, Carlos, Gudmundsson, G. Hilmar, and King, Edward C.

Abstract

Flow at ice divides, their shape, size and internal structure depend not only on local conditions, but also on the flow regimes and past histories of the surrounding ice masses. Here we use field data from Kealey Ice Rise, Ellsworth Land, West Antarctica, in combination with flow modelling to investigate any possible signs of transients in the flow of the surrounding ice masses. Kealey Ice Rise shows linear surface features running parallel to its ridge in satellite imagery and a conspicuous layering in the ground-penetrating radar data known as double-peaked Raymond bumps. Through numerical modelling, by using an anisotropic full-Stokes thermomechanical flow solver, we analyse the evolution of Kealey Ice Rise and the timescales involved. We conclude that the features observed in the stratigraphy of Kealey Ice Rise require at least 3 ka of near-stationary flow conditions. However, we cannot exclude the possibility of a recent flow reorganization in the last century. We stress that the signs of stationary flow in radar stratigraphy observed in Kealey Ice Rise have been observed in other ice divides in the East Ellsworth Land area, suggesting stationary flow conditions over a millennial timescale in the region.

Published
2014

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