scholarly journals Brief Communication: Thwaites Glacier cavity evolution

2021 ◽  
Author(s):  
Suzanne L. Bevan ◽  
Adrian J. Luckman ◽  
Douglas I. Benn ◽  
Susheel Adusumilli ◽  
Anna Crawford
Keyword(s):  
Large Cavity ◽  
Western Margin ◽  
Grounding Line ◽  
Modelling Studies ◽  
Cavity Evolution ◽  
Thinning Rate

Abstract. Between 2014 and 2017, ocean melt eroded a large cavity beneath and along the western margin of the fast-flowing core of Thwaites Glacier. Here we show that from 2017 to the end of 2020 the cavity persisted but did not expand. This behaviour, of melt concentrated at the grounding line within confined sub-shelf cavities, fits with prior observations and modelling studies. We also show that acceleration and thinning of Thwaites Glacier grounded ice continue, with an increase in speed of 400 ma−1 and a thinning rate of 1.5 ma−1, between 2012 and 2020.

scholarly journals Brief communication: Thwaites Glacier cavity evolution

2021 ◽  
Vol 15 (7) ◽  
pp. 3317-3328
Author(s):  
Suzanne L. Bevan ◽  
Adrian J. Luckman ◽  
Douglas I. Benn ◽  
Susheel Adusumilli ◽  
Anna Crawford
Keyword(s):  
Large Cavity ◽  
Western Margin ◽  
Grounding Line ◽  
Modelling Studies ◽  
Cavity Evolution ◽  
Thinning Rate

Abstract. Between 2014 and 2017, ocean melt eroded a large cavity beneath and along the western margin of the fast-flowing core of Thwaites Glacier. Here we show that from 2017 to the end of 2020 the cavity persisted but did not expand. This behaviour, of melt concentrated at the grounding line within confined sub-shelf cavities, fits with prior observations and modelling studies. We also show that acceleration and thinning of Thwaites Glacier grounded ice continued, with an increase in speed of 400 m a−1 and a thinning rate of at least 1.5 m a−1, between 2012 and 2020.

scholarly journals Changes in ice-shelf buttressing following the collapse of Larsen A Ice Shelf, Antarctica, and the resulting impact on tributaries

2016 ◽  
Vol 62 (235) ◽  
pp. 905-911 ◽  
Author(s):  
SAM ROYSTON ◽  
G. HILMAR GUDMUNDSSON
Keyword(s):  
Antarctic Peninsula ◽  
Surface Velocity ◽  
Ice Shelf ◽  
Mass Redistribution ◽  
Grounding Line ◽  
Modelling Studies ◽  
Speed Up ◽  
Stringent Test ◽  
The Antarctic ◽  
The Impact

ABSTRACTThe dominant mass-loss process on the Antarctic Peninsula has been ice-shelf collapse, including the Larsen A Ice Shelf in early 1995. Following this collapse, there was rapid speed up and thinning of its tributary glaciers. We model the impact of this ice-shelf collapse on upstream tributaries, and compare with observations using new datasets of surface velocity and ice thickness. Using a two-horizontal-dimension shallow shelf approximation model, we are able to replicate the observed large increase in surface velocity that occurred within Drygalski Glacier, Antarctic Peninsula. The model results show an instantaneous twofold increase in flux across the grounding line, caused solely from the reduction in backstress through ice shelf removal. This demonstrates the importance of ice-shelf buttressing for flow upstream of the grounding line and highlights the need to explicitly include lateral stresses when modelling real-world settings. We hypothesise that further increases in velocity and flux observed since the ice-shelf collapse result from transient mass redistribution effects. Reproducing these effects poses the next, more stringent test of glacier and ice-sheet modelling studies.

scholarly journals An Ice-shelf Moraine, George VI Sound, Antarctica

1981 ◽  
Vol 2 ◽  
pp. 135-141 ◽  
Author(s):  
D. E. Sugden ◽  
C. M. Clapperton
Keyword(s):  
Conceptual Model ◽  
Fresh Water ◽  
Antarctic Peninsula ◽  
Sea Water ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Western Margin ◽  
Grounding Line ◽  
Double Ridge

The morphology, sediments, and processes associated with the construction of a moraine along the western margin of the ice shelf in George VI Sound, Antarctica, are discussed. The moraine occurs as a double ridge where the ice sheet grounds against promontories on Alexander Island and is approximately horizontal over a distance of 120 km. It consists of exotic rock debris carried into the ice shelf by Antarctic Peninsula glaciers and local rock debris derived from the grounding line on Alexander Island. As the coast steepens, so the proportion of exotic rocks increases. The transport of basal material from the peninsula implies that there can be little bottom melting beneath this part of the ice shelf. The moraine is modified by streams and marginal lakes which periodically drain into and through the ice shelf. Tidal lakes are impounded against the ice shelf in shallower embayments and consist of fresh water overlying sea-water. A conceptual model of the moraine is developed and may help to explain some features of puzzling horizontal moraines found in formerly glaciated areas.

The Nastapoka drift belt, eastern Hudson Bay: implications of a stillstand of the Quebec–Labrador ice margin in the Tyrrell Sea at 8 ka BP

2003 ◽  
Vol 40 (1) ◽  
pp. 65-76 ◽  
Author(s):  
Patrick Lajeunesse ◽  
Michel Allard
Keyword(s):  
Water Depth ◽  
Laurentide Ice Sheet ◽  
Hudson Bay ◽  
James Bay ◽  
Western Margin ◽  
Submarine Fans ◽  
Grounding Line ◽  
Rapid Drop ◽  
Reduced Water ◽  
Lake Ojibway

During deglaciation of eastern Hudson Bay, the western margin of the Québec–Labrador sector of the Laurentide Ice Sheet came to a stillstand about 8 14C ka BP along the Nastapoka Hills, a series of topographic highs along the bay. These hills are the northward continuation of the eastern Hudson Bay cuesta system. It left a drift belt consisting of ice-contact submarine fans along the western slopes of the hills, small frontal moraines on hilltops, and grounding-line deposits on sills between the hills. Geomorphological, sedimentary, and radiometric evidence suggest that the stillstand responsible for deposition of the Nastapoka drift belt was either entirely or partly synchronous with the deposition of the Sakami moraine farther south. There was a period when these two morainic systems marked a continuous ice margin. These stillstands occurred due to reduction of ablation at the ice margin. In the Nastapoka Hills, ablation slowed down when the ice margin was anchored on higher relief and stood at a regional break of slope that grounded the ice margin and reduced water depth at the ice terminus, therefore, putting an end to intensive calving. In eastern James Bay and southeastern Hudson Bay, stabilization of the ice margin was caused by a reequilibrium of the ice terminus after a rapid drop of water level due to the drainage of Glacial Lake Ojibway. The new data improves the resolution of the position ice margin in eastern Hudson Bay at 8 ka BP.

scholarly journals Changes in the ice plain of Whillans Ice Stream, West Antarctica

2005 ◽  
Vol 51 (175) ◽  
pp. 620-636 ◽  
Author(s):  
Robert Bindschadler ◽  
Patricia Vornberger ◽  
Laurence Gray
Keyword(s):  
West Antarctica ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Ice Stream ◽  
Whillans Ice Stream ◽  
Grounding Line ◽  
Local Areas ◽  
The Mean ◽  
Geometric Changes ◽  
Thinning Rate

AbstractData from the mouth of the decelerating Whillans Ice Stream (WIS), West Antarctica, spanning 42 years are reviewed. Deceleration has continued, with local areas of both thinning and thickening occurring. The mean thinning rate is 0.48 ± 0.77 ma–1. No consistent overall pattern is observed. Ice thickens immediately upstream of Crary Ice Rise where deceleration and divergence are strongest, suggesting expanded upstream influence of the ice rise. Thinning is prevalent on the Ross Ice Shelf. Grounding-line advance at a rate of 0.3 km a–1 is detected in a few locations. Basal stresses vary across an ice-stream transect with a zone of enhanced flow at the margin. Marginal shear is felt at the ice-stream center. Mass-balance values are less negative, but larger errors of earlier measurements mask any possible temporal pattern. Comparisons of the recent flow field with flow stripes suggest WIS contributes less ice to the deep subglacial channel carved by Mercer Ice Stream and now flows straighter. The general lack of geometric changes suggests that the regional velocity decrease is due to changing basal conditions.

scholarly journals Processes and Models of Antarctic Glaciomarine Sedimentation

1981 ◽  
Vol 2 ◽  
pp. 117-122 ◽  
Author(s):  
D. J. Drewry ◽  
A. P. R. Cooper
Keyword(s):  
Open Ocean ◽  
Ocean Modelling ◽  
Ice Shelves ◽  
Grounding Line ◽  
Modelling Studies ◽  
Iceberg Calving ◽  
Glaciomarine Sediments ◽  
High Sediment ◽  
Marine Zone ◽  
Line Zone

Glaciomarine sediments (GMS) comprise detrital, biogenic, and authigenic materials of two principal facies: laminated deposits and massive aqueous till. The processes governing sedimentation of the ice-rafted debris (IRD) component of GMS are investigated in the marine zone around Antarctica. Four controlling factors are identified: nature and disposition of sediments at the grounding line, transition from grounded to floating ice (ice shelves, outlet glaciers, and ice cliffs), processes of under-side melting and freezing of these ice masses, and, finally, mechanisms of iceberg calving, fragmentation, and melt-release of debris in the open ocean. Modelling studies of Brunt and Ross ice shelves suggest two main conclusions. (1) Ice shelves are of major importance for sedimentation on the continental shelf. Bulk •debris release occurs within the grounding-line zone which may frequently oscillate, producing pronounced diachronism. Bottom melting removes all debris prior to calving at the ice front so that ice shelves do not play a part in deposition in the open ocean. (2) Outlet glaciers, in contrast, have high sediment content, calve rapidly, and produce debris-rich icebergs which contribute the major portion of IRD in the ocean.

scholarly journals Subglacial sediment transport upstream of a basal channel in the ice shelf of Support Force Glacier (West Antarctica), identified by reflection seismics

2020 ◽  
Author(s):  
Coen Hofstede ◽  
Sebastian Beyer ◽  
Hugh Corr ◽  
Olaf Eisen ◽  
Tore Hattermann ◽  
...  
Keyword(s):  
Rapid Change ◽  
West Antarctica ◽  
Seismic Profiles ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Reflection Seismics ◽  
Grounding Line ◽  
Support Force ◽  
Modelling Studies ◽  
Basal Melting

Abstract. Flow stripes on the surface of an ice shelf indicate the presence of large channels at the base. Modelling studies have shown that where these surface expressions intersect the groundling line, they coincide with the likely outflow of subglacial water. An understanding of the initiation and the ice–ocean evolution of the basal channels is required to understand the present behaviour and future dynamics of ice sheets and ice shelves. Here, we present focused active seismic and radar surveys of a basal channel and its upstream continuation on Support Force Glacier which feeds into the Filchner Ice Shelf, West Antarctica. We map the structure of the basal channel at the ice base in the grounded and floating part and identify the subglacial material within the grounded part of the channel and also along the seafloor. Several kilometers upstream of the grounding line we identify a landform, consisting at least in part of sediments, that forms the channel at the ice base. Immediately seaward of the grounding line, the seismic profiles show a 200 m thick partly disturbed, stratified sediment sequence at the seafloor, which we interpret as grounding line deposits. We conclude that the landform hosts the subglacial transport of sediments entering Support Force Glacier at the eastern side of the basal channel. In contrast to the standard perception of a rapid change in ice shelf thickness just downstream of the grounding line, we find a very flat topography of the ice shelf base with an almost constant ice thickness gradient along flow, indicating only little basal melting, but an initial widening of the basal channel, which we ascribe to melting along its flanks. Our findings provide a detailed view of a more complex interaction of grounded landforms, ice stream shear margins and subglacial hydrology to form basal channels in ice shelves.

scholarly journals On the interpretation of ice-shelf flexure measurements

2017 ◽  
Vol 63 (241) ◽  
pp. 783-791 ◽  
Author(s):  
SEBASTIAN H. R. ROSIER ◽  
OLIVER J. MARSH ◽  
WOLFGANG RACK ◽  
G. HILMAR GUDMUNDSSON ◽  
CHRISTIAN T. WILD ◽  
...  
Keyword(s):  
Elastic Beam ◽  
Beam Theory ◽  
Beam Model ◽  
Line Position ◽  
Ice Shelf ◽  
Study Region ◽  
Grounding Line ◽  
Modelling Studies ◽  
Bed Slope ◽  
Viscoelastic Modelling

ABSTRACTTidal flexure in ice shelf grounding zones has been used extensively in the past to determine grounding line position and ice properties. Although the rheology of ice is viscoelastic at tidal loading frequencies, most modelling studies have assumed some form of linear elastic beam approximation to match observed flexure profiles. Here we use density, radar and DInSAR measurements in combination with full-Stokes viscoelastic modelling to investigate a range of additional controls on the flexure of the Southern McMurdo Ice Shelf. We find that inclusion of observed basal crevasses and density dependent ice stiffness can greatly alter the flexure profile and yet fitting a simple elastic beam model to that profile will still produce an excellent fit. Estimates of the effective Young's modulus derived by fitting flexure profiles are shown to vary by over 200% depending on whether these factors are included, even when the local thickness is well constrained. Conversely, estimates of the grounding line position are relatively insensitive to these considerations for the case of a steep bed slope in our study region. By fitting tidal amplitudes only, and ignoring phase information, elastic beam theory can provide a good fit to observations in a wide variety of situations. This should, however, not be taken as an indication that the underlying rheological assumptions are correct.

scholarly journals Evidence for a grounding line fan at the onset of a basal channel under the ice shelf of Support Force Glacier, Antarctica, revealed by reflection seismics

2021 ◽  
Vol 15 (3) ◽  
pp. 1517-1535
Author(s):  
Coen Hofstede ◽  
Sebastian Beyer ◽  
Hugh Corr ◽  
Olaf Eisen ◽  
Tore Hattermann ◽  
...  
Keyword(s):  
Rapid Change ◽  
West Antarctica ◽  
Seismic Profiles ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Reflection Seismics ◽  
Grounding Line ◽  
Support Force ◽  
Modelling Studies ◽  
Basal Melting

Abstract. Curvilinear channels on the surface of an ice shelf indicate the presence of large channels at the base. Modelling studies have shown that where these surface expressions intersect the grounding line, they coincide with the likely outflow of subglacial water. An understanding of the initiation and the ice–ocean evolution of the basal channels is required to understand the present behaviour and future dynamics of ice sheets and ice shelves. Here, we present focused active seismic and radar surveys of a basal channel, ∼950 m wide and ∼200 m high, and its upstream continuation beneath Support Force Glacier, which feeds into the Filchner Ice Shelf, West Antarctica. Immediately seaward from the grounding line, below the basal channel, the seismic profiles show an ∼6.75 km long, 3.2 km wide and 200 m thick sedimentary sequence with chaotic to weakly stratified reflections we interpret as a grounding line fan deposited by a subglacial drainage channel directly upstream of the basal channel. Further downstream the seabed has a different character; it consists of harder, stratified consolidated sediments, deposited under different glaciological circumstances, or possibly bedrock. In contrast to the standard perception of a rapid change in ice shelf thickness just downstream of the grounding line, we find a flat topography of the ice shelf base with an almost constant ice thickness gradient along-flow, indicating only little basal melting, but an initial widening of the basal channel, which we ascribe to melting along its flanks. Our findings provide a detailed view of a more complex interaction between the ocean and subglacial hydrology to form basal channels in ice shelves.

Residual Gas Reactions in the Electron Microscope: I. Qualitative Observations on the Water Gas Reaction

1968 ◽  
Vol 26 ◽  
pp. 292-293
Author(s):  
Richard E. Hartman ◽  
Roberta S. Hartman ◽  
Peter L. Ramos
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Gas Phase ◽  
Absolute Temperature ◽  
Residual Gas ◽  
Gas Reactions ◽  
Image Position ◽  
The Right ◽  
Water Gas ◽  
Thinning Rate

The action of water and the electron beam on organic specimens in the electron microscope results in the removal of oxidizable material (primarily hydrogen and carbon) by reactions similar to the water gas reaction .which has the form:The energy required to force the reaction to the right is supplied by the interaction of the electron beam with the specimen.The mass of water striking the specimen is given by:where u = gH2O/cm2 sec, PH2O = partial pressure of water in Torr, & T = absolute temperature of the gas phase. If it is assumed that mass is removed from the specimen by a reaction approximated by (1) and that the specimen is uniformly thinned by the reaction, then the thinning rate in A/ min iswhere x = thickness of the specimen in A, t = time in minutes, & E = efficiency (the fraction of the water striking the specimen which reacts with it).

Sign in / Sign up

Export Citation Format

Share Document