Julian A. Dowdeswell

University of Cambridge

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Co-Authors

Dag Ottesen

Norwegian Geological Survey

Kelly Hogan

British Antarctic Survey

CÓ

Colm Ó Cofaigh

Durham University

Robert D Larter

British Antarctic Survey

Christine L. Batchelor

Newcastle University

Martín J. Siegert

University of Exeter

Toby Benham

University of Cambridge

Riko Noormets

Centre for Arctic Gas Hydrate, Environment and Climate

Jeffrey Evans

Loughborough University

E. K. Dowdeswell

University of Cambridge

Cooperative Institutions

University of Cambridge

British Antarctic Survey

Natural Environment Research Council

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

University of Bristol

Centre National de la Recherche Scientifique

Stockholm University

UiT The Arctic University of Norway

National Oceanography Centre

University of Edinburgh

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Structural evolution of a surge-type polythermal glacier: Hessbreen, Svalbard

Annals of Glaciology (1997)

Michael J. Hambrey Julian A. Dowdeswell

Hessbreen is a small valley glacier which last surged in 1974, and is typical of many polythermal glaciers in Svalbard. The present ice surface displays a wide range of structures that can be attributed to either quiescent-phase or surge-phase deformation. During quiescent-phase flow, primary stratification becomes slightly deformed into low-amplitude open folds, while a completely new structure, longitudinal foliation, develops in axial-planar relationship to these folds. The propagation of a surge front is associated with the formation of thrusts; however, not all of these break through to the surface. As the surge progresses, and the ice behind the surge front becomes extensional, the surface of the glacier breaks up into numerous crevasses, of which several hundred metre long transverse crevasses, convex up-glacier, are dominant. After a period of quiescence, these become degraded into crevasse traces, planar structures which are steeply dipping and have many different orientations. Overall, most ice which reaches the snout has not undergone significant cumulative strain, as indicated by the lack of deformation of both the primary structures and the later crevasse traces. The distribution of debris in Hessbreen is controlled strongly by the development of some of these structures. Angular supraglacial debris is intimately associated with stratification, while basal debris is lifted to en- and supraglacial positions in association with thrusting.

Crevasse

Glacier terminus

Glacier ice accumulation

Stratification (seeds)

10.3189/s0260305500012477

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Citations (16)

Structural evolution of a surge-type polythermal glacier: Hessbreen, Svalbard

Annals of Glaciology (1997)

Michael J. Hambrey Julian A. Dowdeswell

Crevasse

Glacier terminus

Glacier ice accumulation

Stratification (seeds)

10.1017/s0260305500012477

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Citations (27)

Physiographic influences on dense shelf-water cascading down the Antarctic continental slope

Earth-Science Reviews (2018)

David Amblàs Julian A. Dowdeswell

Antarctic Bottom Water

Continental Margin

10.1016/j.earscirev.2018.07.014

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Citations (39)

Morphology and Late Quaternary sedimentation on the North Faeroes slope and abyssal plain, North Atlantic

Marine Geology (2000)

J. Taylor Julian A. Dowdeswell N. H. Kenyon Richard J. Whittington Tj.C.E. van Weering

Continental Margin

Contourite

Abyssal plain

10.1016/s0025-3227(00)00055-4

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Citations (30)

Water Mass Characteristics and Distribution Adjacent to Larsen C Ice Shelf, Antarctica

Katherine Hutchinson Julie Deshayes Jean‐Baptiste Sallée Julian A. Dowdeswell Casimir de Lavergne

<p>The physical oceanographic environment, water mass mixing and transformation in the area adjacent to Larsen C Ice Shelf (LCIS) are investigated using hydrographic data collected during the Weddell Sea Expedition 2019. The results shed light on the ocean conditions adjacent to a thinning LCIS, on a continental shelf that is a source region for the globally important water mass, Weddell Sea Deep Water (WSDW). Modified Weddell Deep Water (MWDW), a comparatively warmer water mass of circumpolar origin, is identified on the continental shelf and is observed to mix with local shelf waters, such as Ice Shelf Water (ISW), which is a precursor of WSDW. Oxygen measurements enable the use of a linear mixing model to quantify contributions from source waters revealing high levels of mixing in the area, with much spatial and temporal variability. Heat content anomalies indicate an introduction of heat, presumed to be associated with MWDW, into the area via Jason Trough. Furthermore, candidate parent sources for ISW are identified in the region, indicating the potential for the circulation of continental shelf waters into the ice shelf cavity. This highlights the possibility that offshore climate signals are conveyed under LCIS. ISW is observed within Jason Trough, likely exiting the sub-ice shelf cavity en route to the Slope Current. This onshore-offshore flux of water masses links the region of the Weddell Sea adjacent to northern LCIS to global ocean circulation and Bottom Water characteristics via its contribution to ISW and hence WSDW properties.&#160;</p><p>What remains to be clarified is whether MWDW found in Jason Trough has a direct impact on basal melting and thus thinning of LCIS. More observations are required to investigate this, in particular direct observations of ocean circulation in Jason Trough and underneath LCIS. Modelling experiments could also shed light on this, and so preliminary results based on NEMO global simulations explicitly representing the circulation in under-ice shelf seas, will be presented.&#160;</p>

Circumpolar deep water

Antarctic Bottom Water

Iceberg

Trough (economics)

10.5194/egusphere-egu2020-112

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The saturation of LANDSAT MSS detectors over large ice masses

International Journal of Remote Sensing (1986)

Julian A. Dowdeswell Neil F. McIntyre

Abstract LANDSAT provides synoptic imagery for the study of large ice masses in the inaccessible polar regions. Even minor ice surface topographic detail can be identified as differences in relative brightness. However, radiance from such surfaces can be greater than the maximum MSS detector calibration. This results in detector saturation and consequent loss of information. Using MSS digital data from snow surfaces in both polar regions, corrected to radiance values to account for detector calibration changes, a model relating detector saturation in each MSS band to changes in Sun elevation is presented. Band 5 becomes saturated at the lowest Sun angles whereas band 7 remains unsaturated in all imagery examined. Secondary factors affecting detector saturation are atmospheric haze, the magnitude and orientation of surface slopes, variations in detector calibration and the character of the surface. Given a knowledge of the Sun elevation at which each band becomes saturated over large ice masses (of low gradient and snow-covered surface), and information on variations in Sun elevation with latitude and time of year, the spatial and temporal pattern of detector saturation can be predicted. This information is useful in the selection of MSS images for future glaciological studies, and in the scheduling by NASA of the optimum periods to acquire unsaturated MSS data of the polar regions.

Saturation (graph theory)

10.1080/01431168608954667

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Citations (30)

The Marine Geophysical Signature of Past Ice Sheets

Proceedings (2012)

Julian A. Dowdeswell

areas. Landforms, including subglacially formed channel systems in inner- and mid-shelf areas, and the lack of them on sedimentary outer shelves, allow inferences to be made about subglacial hydrology. The distribution of grounding-zone wedges and other transverse moraine ridges also provides evidence on the nature of ice-sheet retreat – whether by rapid collapse, episodic retreat or by the slow retreat of grounded ice. Such information can be used to test the predictive capability of ice-sheet numerical models. These marine geophysical and geological observations of submarine glacial landforms enhance our understanding of the form and flow of past ice masses at scales ranging from ice sheets (1000s of km in flow-line and margin length), through ice streams (100s of km long), to surge-type glaciers (10s of km long).

Ice divide

Glacial landform

Landform

Ground-Penetrating Radar

10.3997/2214-4609.20148833

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Citations (0)

Long-Range Side-Scan Sonar Imagery of the North Faeroes Margin

Springer eBooks (2003)

J. Taylor Julian A. Dowdeswell N. H. Kenyon Richard J. Whittington J. Mienert

Side-scan sonar

Margin (machine learning)

Passive margin

Dominance (genetics)

10.1007/978-3-642-55846-7_21

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Citations (3)

Glaciology

Routledge eBooks (2019)

Martín J. Siegert Julian A. Dowdeswell

Glaciers and ice sheets occur in the Arctic because of the climatic conditions that prevail there and those which predominated in the past. This chapter outlines the scale and distribution of glaciers and ice sheets within the Arctic and discusses the mechanisms by which the ice masses move. There are several forms of ice mass which contribute to the ice cover of the Arctic. The majority of ice within the Eurasian Arctic is located in the high Arctic archipelagos of Norwegian Svalbard, and the Russian islands of Franz Josef Land, Novaya Zemlya and Severnaya Zemlya. Field investigations of glacier motion and laboratory studies of ice rheology have identified three main mechanisms by which glaciers and ice sheets move. These are by internal deformation of the ice itself, and through two process which take place at the base of the glacier; basal sliding and the deformation of water-saturated sediments.

Glaciology

10.4324/9780429340475-2

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Citations (0)

A new bed elevation dataset for Greenland

The cryosphere (2013)

J. L. Bamber J. A. Griggs R. T. W. L. Hurkmans Julian A. Dowdeswell S. Gogineni

Abstract. We present a new bed elevation dataset for Greenland derived from a combination of multiple airborne ice thickness surveys undertaken between the 1970s and 2012. Around 420 000 line kilometres of airborne data were used, with roughly 70% of this having been collected since the year 2000, when the last comprehensive compilation was undertaken. The airborne data were combined with satellite-derived elevations for non-glaciated terrain to produce a consistent bed digital elevation model (DEM) over the entire island including across the glaciated–ice free boundary. The DEM was extended to the continental margin with the aid of bathymetric data, primarily from a compilation for the Arctic. Ice thickness was determined where an ice shelf exists from a combination of surface elevation and radar soundings. The across-track spacing between flight lines warranted interpolation at 1 km postings for significant sectors of the ice sheet. Grids of ice surface elevation, error estimates for the DEM, ice thickness and data sampling density were also produced alongside a mask of land/ocean/grounded ice/floating ice. Errors in bed elevation range from a minimum of ±10 m to about ±300 m, as a function of distance from an observation and local topographic variability. A comparison with the compilation published in 2001 highlights the improvement in resolution afforded by the new datasets, particularly along the ice sheet margin, where ice velocity is highest and changes in ice dynamics most marked. We estimate that the volume of ice included in our land-ice mask would raise mean sea level by 7.36 m, excluding any solid earth effects that would take place during ice sheet decay.

Elevation (ballistics)

Greenland ice sheet

10.5194/tc-7-499-2013

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Citations (389)