scholarly journals A structural glaciological analysis of the 2002 Larsen B ice-shelf collapse

2008 ◽  
Vol 54 (184) ◽  
pp. 3-16 ◽  
Author(s):  
N.F. Glasser ◽  
T.A. Scambos
Keyword(s):  
Surface Structures ◽  
Velocity Mapping ◽  
Ice Shelf ◽  
Lateral Shear ◽  
Source Areas ◽  
Flow Units ◽  
Zone Velocity ◽  
Break Up ◽  
Glacier Flow ◽  
The Antarctic

AbstractThis study provides a detailed structural glaciological analysis of changes in surface structures on the Larsen B ice shelf on the Antarctic Peninsula prior to its collapse in February–March 2002. Mapped features include the ice-shelf front, rifts, crevasses, longitudinal linear surface structures and meltwater features. We define domains on the ice shelf related to glacier source areas and demonstrate that, prior to collapse, the central Larsen B ice shelf consisted of four sutured flow units fed by Crane, Jorum, Punchbowl and Hektoria/Green/Evans glaciers. Between these flow units were ‘suture zones’ of thinner ice where the feeder glaciers merged. Prior to collapse, large open-rift systems were present offshore of Foyn Point and Cape Disappointment. These rifts became more pronounced in the years preceding break-up, and ice blocks in the rifts rotated because of the strong lateral shear in this zone. Velocity mapping of the suture zones indicates that the major rifts were not present more than about 20 years ago. We suggest that the ice shelf was preconditioned to collapse by partial rupturing of the sutures between flow units. This, we believe, was the result of ice-shelf front retreat during 1998–2000, reducing the lateral resistive stress on the upstream parts of the shelf and glacier flow units, ice-shelf thinning and pre-shelf-break-up glacier acceleration.

scholarly journals Longitudinal surface structures (flowstripes) on Antarctic glaciers

2012 ◽  
Vol 6 (2) ◽  
pp. 383-391 ◽  
Author(s):  
N. F. Glasser ◽  
G. H. Gudmundsson
Keyword(s):  
Ross Sea ◽  
Extensional Flow ◽  
Surface Expression ◽  
Surface Structures ◽  
Schematic Model ◽  
Shelf Area ◽  
Ice Shelf ◽  
Flow Units ◽  
Glacier Flow ◽  
Optical Satellite Images

Abstract. Longitudinal surface structures ("flowstripes") are common on many glaciers but their origin and significance are poorly understood. In this paper we present observations of the development of these longitudinal structures from four different Antarctic glacier systems; the Lambert Glacier/Amery Ice Shelf area, the Taylor and Ferrar Glaciers in the Ross Sea sector, Crane and Jorum Glaciers (ice-shelf tributary glaciers) on the Antarctic Peninsula, and the onset zone of a tributary to the Recovery Glacier Ice Stream in the Filchner Ice Shelf area. Mapping from optical satellite images demonstrates that longitudinal surface structures develop in two main situations: (1) as relatively wide flow stripes within glacier flow units and (2) as relatively narrow flow stripes where there is convergent flow around nunataks or at glacier confluence zones. Our observations indicate that the confluence features are narrower, sharper, and more clearly defined features. They are characterised by linear troughs or depressions on the ice surface and are much more common than the former type. Longitudinal surface structures within glacier flow units have previously been explained as the surface expression of localised bed perturbations but a universal explanation for those forming at glacier confluences is lacking. Here we propose that these features are formed at zones of ice acceleration and extensional flow at glacier confluences. We provide a schematic model for the development of longitudinal surface structures based on extensional flow that can explain their ridge and trough morphology as well as their down-ice persistence.

scholarly journals Longitudinal surface structures (flowstripes) on Antarctic glaciers

2011 ◽  
Vol 5 (6) ◽  
pp. 3085-3112 ◽  
Author(s):  
N. F. Glasser ◽  
G. H. Gudmundsson
Keyword(s):  
Ross Sea ◽  
Extensional Flow ◽  
Surface Expression ◽  
Surface Structures ◽  
Schematic Model ◽  
Shelf Area ◽  
Ice Shelf ◽  
Flow Units ◽  
Glacier Flow ◽  
Optical Satellite Images

Abstract. Longitudinal surface structures (''flowstripes'') are common on many glaciers but their origin and significance are poorly understood. In this paper we present observations of the development of these longitudinal structures from four different Antarctic glacier systems (the Lambert Glacier/Amery Ice Shelf area, outlet glaciers in the Ross Sea sector, ice-shelf tributary glaciers on the Antarctic Peninsula, and the onset zone of a tributary to the Recovery Glacier Ice Stream in the Filchner Ice Shelf area). Mapping from optical satellite images demonstrates that longitudinal surface structures develop in two main situations: (1) as relatively wide flow stripes within glacier flow units and (2) as relatively narrow flow stripes where there is convergent flow around nunataks or at glacier confluence zones. Our observations indicate that the confluence features are narrower, sharper, and more clearly defined features. They are characterised by linear troughs or depressions on the ice surface and are much more common than the former type. Longitudinal surface structures within glacier flow units have previously been explained as the surface expression of localised bed perturbations but a universal explanation for those forming at glacier confluences is lacking. Here we propose that these features are formed at zones of ice acceleration and extensional flow at glacier confluences. We provide a schematic model for the development of longitudinal surface structures based on extensional flow that can explain their ridge and trough morphology as well as their down-ice persistence.

scholarly journals Changes of Wilkins Ice Shelf over the past 15 years and inferences on its stability

2009 ◽  
Vol 3 (1) ◽  
pp. 41-56 ◽  
Author(s):  
M. Braun ◽  
A. Humbert ◽  
A. Moll
Keyword(s):  
Sar Interferometry ◽  
Tidal Effects ◽  
Ice Shelf ◽  
Structural Mapping ◽  
Ice Shelves ◽  
Ice Surface ◽  
Melt Ponds ◽  
Elevation Data ◽  
Break Up ◽  
The Antarctic

Abstract. The Wilkins Ice Shelf is situated on the Antarctic Peninsula, a region where seven ice shelves disintegrated or retreated between 1995 and 2002. This study combines various remote sensing datasets from Wilkins Ice Shelf, with the aim of detecting its present and recent dynamics as well as recent changes. The survey includes structural mapping, ERS-1/2 SAR interferometry and analysis of ICESat GLAS ice surface elevation data. Ice front retreat rates from 1986 to 2008 showed several distinct break-up events, including one in February 2008, when 40% of a part of the ice shelf that connected two islands broke off. Surface elevations have been used to study tidal effects, crack formation and to estimate the ice thickness over the floating area. The derived interferometric velocities cover the south-eastern part of the ice shelf as well as major tributaries and reveal maximum inflow speeds of up to 330 m a−1. We show that drainage of melt ponds into crevasses were of no relevance for the break-up at Wilkins Ice Shelf. Buoyancy forces caused rift formation before the break-up in February 2008. Additionally, the evolution of failure zones of the order of tenths of kilometres in length in pre-conditioned locations at ice rises is shown. Investigation of the current (February 2009) situation shows that about 3100 km2 at the Northern Wilkins Ice Shelf are endangered, however, there is no visible signature that the remaining 8000 km2 are at risk.

scholarly journals Recent dynamic changes on Fleming Glacier after the disintegration of Wordie Ice Shelf, Antarctic Peninsula

2017 ◽  
Author(s):  
Peter Friedl ◽  
Thorsten C. Seehaus ◽  
Anja Wendt ◽  
Matthias H. Braun ◽  
Kathrin Höppner
Keyword(s):  
Antarctic Peninsula ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Glacier Tongue ◽  
Bedrock Topography ◽  
Grounding Line ◽  
Glacier Flow ◽  
Western Side ◽  
Continuous Dynamic ◽  
The Antarctic

Abstract. The Antarctic Peninsula is one of the world`s most affected regions by Climate Change. Several ice shelves retreated, thinned or completely disintegrated during recent decades, leading to acceleration and increased calving of their tributary glaciers. Wordie Ice Shelf, located at the south-western side of the Antarctic Peninsula, completely disintegrated in a series of events between the early 1970s and the late 1990s. We investigate the long-term response (1994–2016) of Fleming Glacier after the disintegration of Wordie Ice Shelf by analysing various multi-sensor remote sensing datasets. Our analysis reveals that after two decades of accelerated glacier flow and dynamic thinning the glacier tongue partially ungrounded between January and March 2008. From 2010 to 2011 a further phase of gradual grounding line recession was observed. In total, the retreat of the grounding line between 2008 and 2014 amounted to ~ 6–9 km and caused ~ 68 km2 of the glacier tongue to go afloat. We attribute this to continuous dynamic thinning and pronounced basal melt at the grounding line, probably by a south-western Antarctic Peninsula wide oceanic warming. The bedrock topography revealed that a deep subglacial trough facilitated the grounding line retreat. In response to the ungrounding of the Fleming Glacier tongue we observed an upstream propagation of the acceleration of surface velocities and corresponding to a median speedup along the glacier's centreline of ~ 1.4 m d−1 (~ 29 %) between 2007 and 2011. The propagation of high velocities has not yet affected regions far upstream (~ 50 km) of the glacier. Current ice thinning rates (2011–2014) in areas below 1000 m altitude range between ~ 2.6 to 3.1 m a−1 and are 60–70 % higher than between 2004 and 2008. Our study shows that Fleming Glacier is far away from approaching a new equilibrium and that the glacier dynamics are not primarily controlled by the loss of the ice shelf anymore. Currently, the Fleming Glacier tongue is grounded in a zone of bedrock elevation of ~ −400 m, however, about 3–4 km upstream modelled bedrock topography indicates a retrograde bed which transitions into a deep trough of up to −1000 m at ~ 10 km upstream. Hence, this endangers much larger ice masses in the future and a huge potential for an increase in sea level rise contribution.

scholarly journals The link between climate warming and break-up of ice shelves in the Antarctic Peninsula

2000 ◽  
Vol 46 (154) ◽  
pp. 516-530 ◽  
Author(s):  
Ted A. Scambos ◽  
Christina Hulbe ◽  
Mark Fahnestock ◽  
Jennifer Bohlander
Keyword(s):  
Antarctic Peninsula ◽  
Remote Sensing Data ◽  
Element Model ◽  
Flow Speed ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Melt Ponds ◽  
Break Up ◽  
The Antarctic

AbstractA review of in situ and remote-sensing data covering the ice shelves of the Antarctic Peninsula provides a series of characteristics closely associated with rapid shelf retreat: deeply embayed ice fronts; calving of myriad small elongate bergs in punctuated events; increasing flow speed; and the presence of melt ponds on the ice-shelf surface in the vicinity of the break-ups. As climate has warmed in the Antarctic Peninsula region, melt-season duration and the extent of ponding have increased. Most break-up events have occurred during longer melt seasons, suggesting that meltwater itself, not just warming, is responsible. Regions that show melting without pond formation are relatively unchanged. Melt ponds thus appear to be a robust harbinger of ice-shelf retreat. We use these observations to guide a model of ice-shelf flow and the effects of meltwater. Crevasses present in a region of surface ponding will likely fill to the brim with water. We hypothesize (building on Weertman (1973), Hughes (1983) and Van der Veen (1998)) that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat. A thermodynamic finite-element model is used to evaluate ice flow and the strain field, and simple extensions of this model are used to investigate crack propagation by meltwater. The model results support the hypothesis.

Implications of the break-up of Wordie Ice Shelf, Antarctica for sea level

1993 ◽  
Vol 5 (4) ◽  
pp. 403-408 ◽  
Author(s):  
David G. Vaughan
Keyword(s):  
Sea Level ◽  
Antarctic Peninsula ◽  
Complete Removal ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Mountain Glaciers ◽  
West Antarctic ◽  
Relative Contribution ◽  
Break Up ◽  
The Antarctic

Temperature records in the Antarctic Peninsula have shown a climatic warming of 1.5°C over the past 30 years and a number of ice shelves have retreated. The most dramatic retreat has been that of Wordie Ice Shelf which has undergone a catastrophic disintegration since the 1960s. Understanding the cause and mechanism of the break-up may provide important clues to the fate of ice shelves farther south which, it has been suggested, help to stabilize the West Antarctic Ice Sheet. The break-up of Wordie Ice Shelf has been analysed using Landsat and SPOT imagery. These observations show that the relative contribution of the various input glaciers to the grounding line flux has not altered during the break-up. This means that the effect of the rapid and almost complete removal of the ice shelf has not been transmitted upstream and is not causing a rapid increase in velocities on the input glaciers. The volume of grounded ice in the catchment of Wordie Ice Shelf will thus, be largely unaffected by the break-up and there will be no significant contribution to sea level change. Since other ice shelves around the Antarctic Peninsula are also fed by relatively steep mountain glaciers the effect of the loss of the ice shelves on sea level would be likely to be similarly small.

scholarly journals Evaluation of the AMPS Boundary Layer Simulations on the Ross Ice Shelf, Antarctica, with Unmanned Aircraft Observations

2017 ◽  
Vol 56 (8) ◽  
pp. 2239-2258 ◽  
Author(s):  
Jonathan D. Wille ◽  
David H. Bromwich ◽  
John J. Cassano ◽  
Melissa A. Nigro ◽  
Marian E. Mateling ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Relative Humidity ◽  
High Wind ◽  
Ice Shelf ◽  
High Wind Speed ◽  
Near Surface ◽  
Ross Ice Shelf ◽  
Low Cloud ◽  
The Antarctic

AbstractAccurately predicting moisture and stability in the Antarctic planetary boundary layer (PBL) is essential for low-cloud forecasts, especially when Antarctic forecasters often use relative humidity as a proxy for cloud cover. These forecasters typically rely on the Antarctic Mesoscale Prediction System (AMPS) Polar Weather Research and Forecasting (Polar WRF) Model for high-resolution forecasts. To complement the PBL observations from the 30-m Alexander Tall Tower! (ATT) on the Ross Ice Shelf as discussed in a recent paper by Wille and coworkers, a field campaign was conducted at the ATT site from 13 to 26 January 2014 using Small Unmanned Meteorological Observer (SUMO) aerial systems to collect PBL data. The 3-km-resolution AMPS forecast output is combined with the global European Centre for Medium-Range Weather Forecasts interim reanalysis (ERAI), SUMO flights, and ATT data to describe atmospheric conditions on the Ross Ice Shelf. The SUMO comparison showed that AMPS had an average 2–3 m s−1 high wind speed bias from the near surface to 600 m, which led to excessive mechanical mixing and reduced stability in the PBL. As discussed in previous Polar WRF studies, the Mellor–Yamada–Janjić PBL scheme is likely responsible for the high wind speed bias. The SUMO comparison also showed a near-surface 10–15-percentage-point dry relative humidity bias in AMPS that increased to a 25–30-percentage-point deficit from 200 to 400 m above the surface. A large dry bias at these critical heights for aircraft operations implies poor AMPS low-cloud forecasts. The ERAI showed that the katabatic flow from the Transantarctic Mountains is unrealistically dry in AMPS.

Antarctic ice sheet response to upper-bound scenarios

2021 ◽  
Author(s):  
Sainan Sun ◽  
Frank Pattyn
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Upper Bound ◽  
Ice Sheet ◽  
Climate Forcing ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
Basal Sliding ◽  
The Antarctic

<p>Mass loss of the Antarctic ice sheet contributes the largest uncertainty of future sea-level rise projections. Ice-sheet model predictions are limited by uncertainties in climate forcing and poor understanding of processes such as ice viscosity. The Antarctic BUttressing Model Intercomparison Project (ABUMIP) has investigated the 'end-member' scenario, i.e., a total and sustained removal of buttressing from all Antarctic ice shelves, which can be regarded as the upper-bound physical possible, but implausible contribution of sea-level rise due to ice-shelf loss. In this study, we add successive layers of ‘realism’ to the ABUMIP scenario by considering sustained regional ice-shelf collapse and by introducing ice-shelf regrowth after collapse with the inclusion of ice-sheet and ice-shelf damage (Sun et al., 2017). Ice shelf regrowth has the ability to stabilize grounding lines, while ice shelf damage may reinforce ice loss. In combination with uncertainties from basal sliding and ice rheology, a more realistic physical upperbound to ice loss is sought. Results are compared in the light of other proposed mechanisms, such as MICI due to ice cliff collapse.</p>

scholarly journals Melting and freezing under Antarctic ice shelves from a combination of ice-sheet modelling and observations

2017 ◽  
Vol 63 (240) ◽  
pp. 731-744 ◽  
Author(s):  
JORGE BERNALES ◽  
IRINA ROGOZHINA ◽  
MAIK THOMAS
Keyword(s):  
Mass Balance ◽  
Ice Sheet ◽  
Model Parameters ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Continental Scale ◽  
Model Set ◽  
Set Up ◽  
Basal Melting ◽  
The Antarctic

ABSTRACTIce-shelf basal melting is the largest contributor to the negative mass balance of the Antarctic ice sheet. However, current implementations of ice/ocean interactions in ice-sheet models disagree with the distribution of sub-shelf melt and freezing rates revealed by recent observational studies. Here we present a novel combination of a continental-scale ice flow model and a calibration technique to derive the spatial distribution of basal melting and freezing rates for the whole Antarctic ice-shelf system. The modelled ice-sheet equilibrium state is evaluated against topographic and velocity observations. Our high-resolution (10-km spacing) simulation predicts an equilibrium ice-shelf basal mass balance of −1648.7 Gt a−1 that increases to −1917.0 Gt a−1 when the observed ice-shelf thinning rates are taken into account. Our estimates reproduce the complexity of the basal mass balance of Antarctic ice shelves, providing a reference for parameterisations of sub-shelf ocean/ice interactions in continental ice-sheet models. We perform a sensitivity analysis to assess the effects of variations in the model set-up, showing that the retrieved estimates of basal melting and freezing rates are largely insensitive to changes in the internal model parameters, but respond strongly to a reduction of model resolution and the uncertainty in the input datasets.

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