scholarly journals On the link between surface and basal structures of the Jelbart Ice Shelf, Antarctica

2015 ◽  
Vol 61 (229) ◽  
pp. 975-986 ◽  
Author(s):  
Angelika Humbert ◽  
Daniel Steinhage ◽  
Veit Helm ◽  
Sebastian Hoerz ◽  
Jacqueline Berendt ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Accumulation Rate ◽  
Surface Displacement ◽  
Maxwell Model ◽  
Relevant Information ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Radio Echo Sounding ◽  
Radar Imagery ◽  
Viscoelastic Modelling

AbstractTo understand the dynamics of ice shelves, a knowledge of their internal and basal structure is very important. As the capacity to perform local surveys is limited, remote sensing provides an opportunity to obtain the relevant information. We must prove, however, that the relevant information can be obtained from remote sensing of the surface. That is the aim of this study. The Jelbart Ice Shelf, Antarctica, exhibits a variety of surface structures appearing as stripe-like features in radar imagery. We performed an airborne geophysical survey across these features and compared the results to TerraSAR-X imagery. We find that the stripe-like structures indicate surface troughs coinciding with the location of basal channels and crevasse-like features, revealed by radio-echo sounding. HH and VV polarizations do not show different magnitude. In surface troughs, the local accumulation rate is larger than at the flat surface. Viscoelastic modelling is used to gain an understanding of the surface undulations and their origin. The surface displacement, computed with a Maxwell model, matches the observed surface reasonably well. Our simulations show that the surface troughs develop over decadal to centennial timescales.

scholarly journals Basal melt of the southern Filchner Ice Shelf, Antarctica

2021 ◽  
Author(s):  
Ole Zeising ◽  
Daniel Steinhage ◽  
Keith W. Nicholls ◽  
Hugh F. J. Corr ◽  
Craig L. Stewart ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Velocity Fields ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Grounding Line ◽  
Key Factor ◽  
Radio Echo Sounding ◽  
Support Force ◽  
The Antarctic ◽  
Factor Governing

Abstract. Basal melt of ice shelves is a key factor governing discharge of ice from the Antarctic Ice Sheet as a result of its effects on buttressing. Here, we use radio echo sounding to determine the spatial variability of the basal melt rate of the southern Filchner Ice Shelf, Antarctica along the inflow of Support Force Glacier. We find moderate melt rates with a maximum of 1.13 m a−1 about 50 km downstream of the grounding line. The variability of the melt rates over distances of a few kilometres is low (all but one < 0.15 m a−1 at < 2 km distance), indicating that measurements on coarse observational grids are able to yield a representative melt rate distribution. A comparison with remote sensing based melt rates revealed that, for the study area, large differences were due to inaccuracies in the estimation of vertical strain rates from remote sensing velocity fields. These inaccuracies can be overcome by using modern velocity fields.

scholarly journals Significant submarine ice loss from the Getz Ice Shelf, Antarctica

2018 ◽  
Author(s):  
David M. Rippin
Keyword(s):  
Mass Loss ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Shelves ◽  
Warming Climate ◽  
Circulation Patterns ◽  
Direct Measurements ◽  
Radio Echo Sounding ◽  
The Impact

Abstract. We present the first direct measurements of changes taking place at the base of the Getz Ice Shelf (GzIS) in West Antarctica. Our analysis is based on repeated airborne radio-echo sounding (RES) survey lines gathered in 2010 and 2014. We reveal that while there is significant variability in ice shelf behaviour, the vast majority of the ice shelf (where data is available) is undergoing basal thinning at a mean rate of nearly 13 m a−1, which is several times greater than recent modelling estimates. In regions of faster flowing ice close to where ice streams and outlet glaciers join the ice shelf, significantly greater rates of mass loss occurred. Since thinning is more pronounced close to faster-flowing ice, we propose that dynamic thinning processes may also contribute to mass loss here. Intricate sub-ice circulation patterns exist beneath the GzIS because of its complex sub-ice topography and the fact that it is fed by numerous ice streams and outlet glaciers. It is this complexity which we suggest is also responsible for the spatially variable patterns of ice-shelf change that we observe. The large changes observed here are also important when considering the likelihood and timing of any potential future collapse of the ice shelf, and the impact this would have on the flow rates of feeder ice streams and glaciers, that transmit ice from inland Antarctica to the coast. We propose that as the ice shelf continues to thin in response to warming ocean waters and climate, the response of the ice shelf will be spatially diverse. Given that these measurements represent changes that are significantly greater than modelling outputs, it is also clear that we still do not fully understand how ice shelves respond to warming ocean waters. As a result, ongoing direct measurements of ice shelf change are vital for understanding the future response of ice shelves under a warming climate.

scholarly journals A synthesis of remote sensing data on Wilkins Ice Shelf, Antarctica

1993 ◽  
Vol 17 ◽  
pp. 211-218 ◽  
Author(s):  
D.G. Vaughan ◽  
D.R. Mantripp ◽  
J. Sievers ◽  
C.S.M. Doake
Keyword(s):  
Mass Balance ◽  
Antarctic Peninsula ◽  
Accumulation Rate ◽  
Remote Sensing Data ◽  
Dynamic Effect ◽  
Remotely Sensed Data ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Limit Of Viability ◽  
The Antarctic

Wilkins Ice Shelf has an area of 16000 km2 and lies off the west coast of the Antarctic Peninsula bounded by Alexander, Latady, Charcot and Rothschild islands. Several ice shelves, including Wilkins, exist close to a climatic limit of viability. The recent disintegration of the neighbouring Wordie Ice Shelf has been linked to atmopsheric warming observed on the Antarctic Peninsula. The limit of ice-shelf viability thus appears to have migrated south. Should this continue, the question arises; how long will Wilkins Ice Shelf survive?Compared with the other ice shelves on the Antarctic Peninsula, few surface glaciological data have been collected on Wilkins Ice Shelf. We compare, contrast and combine a variety of remotely sensed data: the recently declassified GEOSAT Geodetic Mission altimetry, Landsat MSS and TM imagery, and radio-echo sounding data (RES), to study its structure and mass balance regime.We find that this shelf has an unusual mass balance regime and relies heavily for sustenance on in situ accumulation. Its response to a continued atmospheric warming may be significantly different from that of Wordie Ice Shelf. Wordie Ice Shelf was fed by several dynamic outlet glaciers which accelerated the disintegration process when the ice shelf fractured. Wilkins Ice Shelf by contrast is almost stagnant and is expected to respond by normal calving at the ice front. Changes in the accumulation rate or basal melt-rate may, however, dominate any dynamic effect. Over the last two decades the ice front positions have remained stable.

scholarly journals Automation of Ice Fractures and Calving Events Monitoring Using Medical Imaging Ridge Detection Algorithms

2021 ◽  
Author(s):  
Quentin Glaude ◽  
Stéphane Lizin ◽  
Christian Barbier ◽  
Frank Pattyn ◽  
Anne Orban
Keyword(s):  
Remote Sensing ◽  
Medical Imaging ◽  
Hessian Matrix ◽  
Ice Sheet ◽  
Active Role ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Detection Techniques ◽  
Ridge Detection ◽  
Sar Remote Sensing

&lt;p&gt;&lt;em&gt;Ice shelves, i.e. the floating extension of the AIS, are playing an active role in controlling ice loss from the Antarctic ice sheet. Laterally constraint in embayment or by ice rises, they are participating as regulators of the ice discharge, by exerting a back stress to the ice flow. When losing mass, these ice shelves lose their gatekeeper property, with potential local destabilization of the AIS. Losing mass from calving is a sophisticated process that is rarely coupled with observations in ice sheet models. However, calving and damages are visible in SAR remote sensing products. In this study, we built the hypothesis that state-of-the-heart ridge detection techniques from the medical imaging field can be transposed to the cryosphere field. Looking at the local Hessian matrix in SAR acquisitions, we analyzed the eigenvectors that indicate the presence of ridges. Over ice shelves, these edges correspond to the calving front of the ice shelf, or crevasses. Using time series, we can monitor the evolution of crack propagation and calving events. Results over Pine Island Glacier and the Brunt Ice Shelf show a precise delineation of calving events, as well as the damaged areas. These encouraging results support the idea of the integration of ice damage detection from SAR remote sensing into ice sheet models.&lt;/em&gt;&lt;/p&gt;

scholarly journals A synthesis of remote sensing data on Wilkins Ice Shelf, Antarctica

1993 ◽  
Vol 17 ◽  
pp. 211-218 ◽  
Author(s):  
D.G. Vaughan ◽  
D.R. Mantripp ◽  
J. Sievers ◽  
C.S.M. Doake
Keyword(s):  
Mass Balance ◽  
Antarctic Peninsula ◽  
Accumulation Rate ◽  
Remote Sensing Data ◽  
Dynamic Effect ◽  
Remotely Sensed Data ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Limit Of Viability ◽  
The Antarctic

Wilkins Ice Shelf has an area of 16000 km2 and lies off the west coast of the Antarctic Peninsula bounded by Alexander, Latady, Charcot and Rothschild islands. Several ice shelves, including Wilkins, exist close to a climatic limit of viability. The recent disintegration of the neighbouring Wordie Ice Shelf has been linked to atmopsheric warming observed on the Antarctic Peninsula. The limit of ice-shelf viability thus appears to have migrated south. Should this continue, the question arises; how long will Wilkins Ice Shelf survive? Compared with the other ice shelves on the Antarctic Peninsula, few surface glaciological data have been collected on Wilkins Ice Shelf. We compare, contrast and combine a variety of remotely sensed data: the recently declassified GEOSAT Geodetic Mission altimetry, Landsat MSS and TM imagery, and radio-echo sounding data (RES), to study its structure and mass balance regime. We find that this shelf has an unusual mass balance regime and relies heavily for sustenance on in situ accumulation. Its response to a continued atmospheric warming may be significantly different from that of Wordie Ice Shelf. Wordie Ice Shelf was fed by several dynamic outlet glaciers which accelerated the disintegration process when the ice shelf fractured. Wilkins Ice Shelf by contrast is almost stagnant and is expected to respond by normal calving at the ice front. Changes in the accumulation rate or basal melt-rate may, however, dominate any dynamic effect. Over the last two decades the ice front positions have remained stable.

scholarly journals A model of viscoelastic ice-shelf flexure

2015 ◽  
Vol 61 (228) ◽  
pp. 635-645 ◽  
Author(s):  
Douglas R. MacAyeal ◽  
Olga V. Sergienko ◽  
Alison F. Banwell
Keyword(s):  
Thin Plate ◽  
Initial Step ◽  
Maxwell Model ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Supraglacial Lakes ◽  
In Series ◽  
Iceberg Calving ◽  
Power Law Creep ◽  
Creep Deformations

AbstractWe develop a formal thin-plate treatment of the viscoelastic flexure of floating ice shelves as an initial step in treating various problems relevant to ice-shelf response to sudden changes of surface loads and applied bending moments (e.g. draining supraglacial lakes, iceberg calving, surface and basal crevassing). Our analysis is based on the assumption that total deformation is the sum of elastic and viscous (or power-law creep) deformations (i.e. akin to a Maxwell model of viscoelasticity, having a spring and dashpot in series). The treatment follows the assumptions of well-known thin-plate approximation, but is presented in a manner familiar to glaciologists and with Glen’s flow law. We present an analysis of the viscoelastic evolution of an ice shelf subject to a filling and draining supraglacial lake. This demonstration is motivated by the proposition that flexure in response to the filling/drainage of meltwater features on the Larsen B ice shelf, Antarctica, contributed to the fragmentation process that accompanied its collapse in 2002.

scholarly journals On nonlinear strain theory for a viscoelastic material model and its implications for calving of ice shelves

2019 ◽  
Vol 65 (250) ◽  
pp. 212-224 ◽  
Author(s):  
JULIA CHRISTMANN ◽  
RALF MÜLLER ◽  
ANGELIKA HUMBERT
Keyword(s):  
Finite Deformation ◽  
Maxwell Model ◽  
Material Model ◽  
Stress And Strain ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Nonlinear Viscosity ◽  
Linearized Strain ◽  
Long Timescales

ABSTRACTIn the current ice-sheet models calving of ice shelves is based on phenomenological approaches. To obtain physics-based calving criteria, a viscoelastic Maxwell model is required accounting for short-term elastic and long-term viscous deformation. On timescales of months to years between calving events, as well as on long timescales with several subsequent iceberg break-offs, deformations are no longer small and linearized strain measures cannot be used. We present a finite deformation framework of viscoelasticity and extend this model by a nonlinear Glen-type viscosity. A finite element implementation is used to compute stress and strain states in the vicinity of the ice-shelf calving front. Stress and strain maxima of small (linearized strain measure) and finite strain formulations differ by ~ 5% after 1 and by ~ 30% after 10 years, respectively. A finite deformation formulation reaches a critical stress or strain faster, thus calving rates will be higher, despite the fact that the exact critical values are not known. Nonlinear viscosity of Glen-type leads to higher stress values. The Maxwell material model formulation for finite deformations presented here can also be applied to other glaciological problems, for example, tidal forcing at grounding lines or closure of englacial and subglacial melt channels.

scholarly journals Investigations of the Oxygen-18 Content of Samples from Snow Pits and Ice Cores from the Filchner-Ronne Ice Shelves and Ekström Ice Shelf

1985 ◽  
Vol 7 ◽  
pp. 49-53 ◽  
Author(s):  
O. Reinwarth ◽  
W. Graf ◽  
W. Stichler ◽  
H. Moser ◽  
H. Oerter
Keyword(s):  
Accumulation Rate ◽  
Ice Cores ◽  
Research Programme ◽  
Ice Shelf ◽  
Annual Average ◽  
Ice Shelves ◽  
Antarctic Research ◽  
Isotope Studies ◽  
The Mean ◽  
Ice Edge

Since 1979–80, isotope studies with oxygen-18 (18O) have been carried out at several snow pits and ice cores near the German Georg-von-Neumayer station (Ekström ice shelf, Atka Bay), as well as from the Filchner-Ronne ice shelves, in the framework of the German Antarctic research programme. The investigations of snow pits on the Filchner-Ronne ice shelves yield a standard deviation for the annual average δ18O values of approximately 1‰ over the last five years, and a decrease of δ18O with distance from the ice edge of about 1‰ per 50 km. The variation of δ18O for stratigraphically matching snow layers from snow pits at the same location in different years is about 0.3‰ on the Filchner-Ronne ice shelves, and 0.8‰ at Georg-von-Neumayer station. The mean annual accumulation rate in the surroundings of Georg-von-Neumayer station was determined to be 34 g cm-2 for the years 1977–81. On the Filchner-Ronne ice shelves the mean annual accumulation rate (1979–83) decreases from 22 g cm−2 at Filchner station to 15 g cm−2 at traverse point T340, located 200 km southeast of Filchner station.

scholarly journals Investigations of the Oxygen-18 Content of Samples from Snow Pits and Ice Cores from the Filchner-Ronne Ice Shelves and Ekström Ice Shelf

1985 ◽  
Vol 7 ◽  
pp. 49-53 ◽  
Author(s):  
O. Reinwarth ◽  
W. Graf ◽  
W. Stichler ◽  
H. Moser ◽  
H. Oerter
Keyword(s):  
Accumulation Rate ◽  
Ice Cores ◽  
Research Programme ◽  
Ice Shelf ◽  
Annual Average ◽  
Ice Shelves ◽  
Antarctic Research ◽  
Isotope Studies ◽  
The Mean ◽  
Ice Edge

Since 1979–80, isotope studies with oxygen-18 (18O) have been carried out at several snow pits and ice cores near the German Georg-von-Neumayer station (Ekström ice shelf, Atka Bay), as well as from the Filchner-Ronne ice shelves, in the framework of the German Antarctic research programme. The investigations of snow pits on the Filchner-Ronne ice shelves yield a standard deviation for the annual average δ18O values of approximately 1‰ over the last five years, and a decrease of δ18O with distance from the ice edge of about 1‰ per 50 km. The variation of δ18O for stratigraphically matching snow layers from snow pits at the same location in different years is about 0.3‰ on the Filchner-Ronne ice shelves, and 0.8‰ at Georg-von-Neumayer station. The mean annual accumulation rate in the surroundings of Georg-von-Neumayer station was determined to be 34 g cm-2 for the years 1977–81. On the Filchner-Ronne ice shelves the mean annual accumulation rate (1979–83) decreases from 22 g cm−2 at Filchner station to 15 g cm−2 at traverse point T340, located 200 km southeast of Filchner station.

scholarly journals Creep deformation and buttressing capacity of damaged ice shelves: theory and application to Larsen C ice shelf

2013 ◽  
Vol 7 (6) ◽  
pp. 1931-1947 ◽  
Author(s):  
C. P. Borstad ◽  
E. Rignot ◽  
J. Mouginot ◽  
M. P. Schodlok
Keyword(s):  
Remote Sensing ◽  
Creep Deformation ◽  
Damage Mechanics ◽  
Structural Integrity ◽  
Ice Sheet ◽  
Remote Sensing Data ◽  
Analytical Relation ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Grounding Line

Abstract. Around the perimeter of Antarctica, much of the ice sheet discharges to the ocean through floating ice shelves. The buttressing provided by ice shelves is critical for modulating the flux of ice into the ocean, and the presently observed thinning of ice shelves is believed to be reducing their buttressing capacity and contributing to the acceleration and thinning of the grounded ice sheet. However, relatively little attention has been paid to the role that fractures play in the ability of ice shelves to sustain and transmit buttressing stresses. Here, we present a new framework for quantifying the role that fractures play in the creep deformation and buttressing capacity of ice shelves. We apply principles of continuum damage mechanics to derive a new analytical relation for the creep of an ice shelf that accounts for the softening influence of fractures on longitudinal deformation using a state damage variable. We use this new analytical relation, combined with a temperature calculation for the ice, to partition an inverse method solution for ice shelf rigidity into independent solutions for softening damage and stabilizing backstress. Using this new approach, field and remote sensing data can be utilized to monitor the structural integrity of ice shelves, their ability to buttress the flow of ice at the grounding line, and thus their indirect contribution to ice sheet mass balance and global sea level. We apply this technique to the Larsen C ice shelf using remote sensing and Operation IceBridge data, finding damage in areas with known crevasses and rifts. Backstress is highest near the grounding line and upstream of ice rises, in agreement with patterns observed on other ice shelves. The ice in contact with the Bawden ice rise is weakened by fractures, and additional damage or thinning in this area could diminish the backstress transmitted upstream. We model the consequences for the ice shelf if it loses contact with this small ice rise, finding that flow speeds would increase by 25% or more over an area the size of the former Larsen B ice shelf. Such a perturbation could potentially destabilize the northern part of Larsen C along pre-existing lines of weakness, highlighting the importance of the feedback between buttressing and fracturing in an ice shelf.

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