scholarly journals Investigations of DInSAR derived grounding line migration in Antarctica induced by ocean tides

2021 ◽  
Author(s):  
Yin Ying Ip ◽  
Lukas Krieger ◽  
Dana Floricioiu
Keyword(s):  
Sea Water ◽  
Qualitative Description ◽  
Double Difference ◽  
Ocean Tide ◽  
Line Position ◽  
Ice Shelf ◽  
Important Indicator ◽  
Catchment Areas ◽  
Grounding Line ◽  
Tide Level

<p>The migration of the glacier grounding line, the boundary between grounded ice and floating ice, is an important indicator of tice sheet stability in a warming climate. Ice-shelf thinning induces grounding line retreat, and potentially leads to the collapse of the inland catchment areas in centennial time periods. Therefore, a continuous observation of the grounding line position is of interest for ice sheet modelling also to predict future sea level rise. However, grounding line in nature is not static in position and it is subject to short-term fluctuations which are influenced by changes in ocean tide level and atmospheric pressure. Investigating tidal influence to the grounding line helps separating the tidal signal from the long-term migration because of ice shelf thinning. Also, it helps quantifying ice discharge and ice flow, as well as potential melting underneath the ice, due to intrusion of sea water.</p><p>In this study, the correlation between the time series of grounding line, derived from Sentinel-1 double difference interferograms and the ocean tide level computed from CATS2008 tide model and air pressure corrected with NCEP reanalysis data  are investigated. Study regions are chosen at the Filchner-Ronne Ice Shelf, the Amery Ice Shelf and Dronning Maud Land based on the availability of coherent interferograms and the large tidal amplitude at these locations. The result is expected to be presented as qualitative description of changes in the fringe belt pattern in double difference interferograms and statistical analysis of the derived changes in grounding line position, depending on the complexity of the grounding line structure and the topography of the bed rock.</p>

scholarly journals Properties of a marine ice layer under the Amery Ice Shelf, East Antarctica

2009 ◽  
Vol 55 (192) ◽  
pp. 717-728 ◽  
Author(s):  
Mike Craven ◽  
Ian Allison ◽  
Helen Amanda Fricker ◽  
Roland Warner
Keyword(s):  
Sea Water ◽  
Average Rate ◽  
East Antarctica ◽  
Ice Shelf ◽  
Closure Rate ◽  
Southern Limit ◽  
Amery Ice Shelf ◽  
Average Porosity ◽  
Grounding Line ◽  
Ocean Properties

AbstractThe Amery Ice Shelf, East Antarctica, undergoes high basal melt rates near the southern limit of its grounding line where 80% of the ice melts within 240 km of becoming afloat. A considerable portion of this later refreezes downstream as marine ice. This produces a marine ice layer up to 200 m thick in the northwest sector of the ice shelf concentrated in a pair of longitudinal bands that extend some 200 km all the way to the calving front. We drilled through the eastern marine ice band at two locations 70 km apart on the same flowline. We determine an average accretion rate of marine ice of 1.1 ± 0.2 m a−1, at a reference density of 920 kg m−3 between borehole sites, and infer a similar average rate of 1.3 ± 0.2 m a−1 upstream. The deeper marine ice was permeable enough that a hydraulic connection was made whilst the drill was still 70–100 m above the ice-shelf base. Below this marine close-off depth, borehole video imagery showed permeable ice with water-filled cavities and individual ice platelets fused together, while the upper marine ice was impermeable with small brine-cell inclusions. We infer that the uppermost portion of the permeable ice becomes impermeable with the passage of time and as more marine ice is accreted on the base of the shelf. We estimate an average closure rate of 0.3 m a−1 between the borehole sites; upstream the average closure rate is faster at 0.9 m a−1. We estimate an average porosity of the total marine ice layer of 14–20%, such that the deeper ice must have even higher values. High permeability implies that sea water can move relatively freely through the material, and we propose that where such marine ice exists this renders deep parts of the ice shelf particularly vulnerable to changes in ocean properties.

New ice thickness maps of Filchner–Ronne Ice Shelf, Antarctica, with specific focus on grounding lines and marine ice

2007 ◽  
Vol 19 (4) ◽  
pp. 521-532 ◽  
Author(s):  
A. Lambrecht ◽  
H. Sandhäger ◽  
D.G. Vaughan ◽  
C. Mayer
Keyword(s):  
Surface Elevation ◽  
Small Scale ◽  
Ice Thickness ◽  
Line Position ◽  
Ice Shelf ◽  
Ice Surface ◽  
Seismic Sounding ◽  
Grounding Line ◽  
Data Coverage

AbstractFor the Filchner–Ronne Ice Shelf we have compiled measurements of meteoric ice thickness from many institutions, and several different techniques (e.g. radar and seismic sounding) to produce an improved digital map of meteoric ice thickness. This map has high-resolution compared to previous compilations and serves to highlight small-scale geographic features (e.g. ice plains, grounding-line regions). We have also produced a map of the thickness of marine ice bodies beneath the ice shelf by using borehole density data to calibrate an ice thickness to surface-elevation relation, and then comparing maps of ice surface elevation and meteoric ice thickness to infer marine ice thickness. Due to denser data coverage and the improved density-depth relation, the resulting map is a significant improvement on its predecessors and allows insight into the glaciological context of the ice shelf, in particular, into the location of the grounding lines on the southern Ronne Ice Shelf. Here the data were supplemented with barometric determination of surface elevation, which were used to locate the grounding line position. The final delineation of the grounding line position was confirmed by reference to satellite imagery, and revealed that earlier estimates were substantially in error, especially in the area of Foundation Ice Stream and Möllereisstrom.

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.

scholarly journals A Coupled Marine Ice-Stream – Ice-Shelf Model

1987 ◽  
Vol 33 (113) ◽  
pp. 3-15 ◽  
Author(s):  
Isabelle Muszynski ◽  
G. E. Birchfield
Keyword(s):  
Sea Water ◽  
Two Dimensions ◽  
Scale Analysis ◽  
Sliding Velocity ◽  
Ice Shelf ◽  
Ice Stream ◽  
Grounding Line ◽  
Basal Sliding ◽  
Ice Flows ◽  
Shearing Deformation

AbstractEvidence as to the potential roles of marine ice flows in the dramatic climatological changes which have occurred from the late Pleistocene to the present is reviewed, indicating the need for careful modeling studies to evaluate several crucial hypotheses. A scale analysis of the flow of a marine ice stream coupled to a freely floating ice shelf is presented, in two dimensions and ignoring thermodynamic effects. With these limitations, the most important control of the dynamics of the ice stream is associated with first-order buoyancy effects related to the density contrast ∆ρ/ρw between ice and sea-water. It is shown that longitudinal stretching, arising from large gradients in basal sliding velocity, dominates shearing deformation provided the aspect ratio ω2 « ∆ρ/ρw. The buoyancy control is established through the necessity of having continuously varying longitudinal strain-rates in the neighborhood of the grounding line.The scale analysis is the basis for derivation of a simplified model of a fast-flowing ice stream coupled to a freely floating ice shelf. The distance in the ice stream up-stream from the grounding line over which the above dynamic regime extends is estimated and found to be relatively insensitive to the basal sliding velocity and to the rheological constant of ice. A further potentially important feed-back mechanism between ice stream and ice shelf is associated with buoyancy corrections to the longitudinal deviatoric stress field.

scholarly journals The use of tiltmeters to study the dynamics of Antarctic ice-shelf grounding lines

1991 ◽  
Vol 37 (125) ◽  
pp. 51-58 ◽  
Author(s):  
A. M. Smith
Keyword(s):  
Elastic Beam ◽  
Ice Thickness ◽  
Elastic Model ◽  
Beam Model ◽  
Line Position ◽  
Stream Data ◽  
Ice Shelf ◽  
Ice Stream ◽  
Grounding Line ◽  
Data Coverage

Abstract New tiltmeter data are presented from Doake Ice Rumples on Ronne Ice Shelf, Antarctica. Five sites which showed a tidal ice-shelf flexure have been analysed using an elastic beam model to investigate the variation of flexure amplitude with distance from the grounding line. An earlier study on Rutford Ice Stream which also used an elastic model required an ice thickness much less than that observed. Reworking the Rutford Ice Stream data suggests that this greatly reduced ice thickness is not required, given the current sparse data coverage. The elastic model is used to improve the estimated grounding-line position on Rutford Ice Stream. Some of the difficulties in modelling ice-shelf flexure and locating grounding lines are discussed.

scholarly journals Internal and basal ice changes near the grounding line derived from radio-echo sounding

1996 ◽  
Vol 42 (140) ◽  
pp. 103-109 ◽  
Author(s):  
Seiho Uratsuka ◽  
Fumihiko Nishio ◽  
Shinji Mae
Keyword(s):  
Sea Water ◽  
Major Change ◽  
Internal Layer ◽  
Shelf Area ◽  
Echo Signal ◽  
Ice Shelf ◽  
Basal Ice ◽  
Grounding Line ◽  
Radio Echo Sounding ◽  
Strong Scattering

AbstractEvidence of changing basal and internal ice properties near the grounding line was derived from airborne radio-echo-sounder observations of the ice sheet around the Sør Rondane Mountains, Antarctica. From the trailing figure of the bottom-echo signal, the roughness of the ice bottom near the grounding line was inferred. Results show that the specular components of scattering begin to appear on the ice-shelf side of the grounding line. Furthermore, double-trip echoes were observed with a strong scattering in the shelf area, and their boundary of occurrence was very close to the grounding line. This is evidence of interaction between ice and sea water at the bottom of the ice shelf. We also examined the occurrence of internal layered echoes. In most of the area around the mountains, internal echoes were observed continously, but they were not found at or close to the ice shelf. The boundary between the appearance and disappearance of internal-layer echoes is distinct, and occurs 20–30 km inland from the grounding line. These results suggest that some major change may occur in the internal ice on the inland side of the grounding line.

scholarly journals Katabatic wind influence on meltwater supply to fuel glacier–substrate interactions at the grounding line, Terra Nova Bay, East Antarctica

1999 ◽  
Vol 28 ◽  
pp. 272-276 ◽  
Author(s):  
A. Bouzette ◽  
R. Souchez
Keyword(s):  
Sea Water ◽  
Double Diffusion ◽  
Katabatic Wind ◽  
Local Production ◽  
Ice Shelf ◽  
Rock Outcrops ◽  
Katabatic Winds ◽  
Terra Nova Bay ◽  
Grounding Line ◽  
Wind Influence

AbstractThe co-isotopic composition, both in δDand in δ18O, of interbedded debris-rich and clear ice layers, thought to have been formed at the grounding line of Hells Gate Ice Shelf, indicates freezing by a double-diffusion effect between continental meltwater and sea water within a subglacial sediment. A source of meltwater is required to sustain the process, since the temperature of the bed is below the freshwater melting point. The most likely source is a surficially frozen meltwater lake.Rock outcrops, kept mostly snow-free by the action of katabatic winds, absorb solar radiation so local production of liquid water becomes possible in an area with year-round subfreezing air-temperature conditions. The meltwater accumulated in a marginal lake can eventually reach the subglacial substratum near a pinning point where the ice is relatively thin and fractured.

scholarly journals Grounding-line basal melt rates determined using radar-derived internal stratigraphy

2010 ◽  
Vol 56 (197) ◽  
pp. 545-554 ◽  
Author(s):  
Ginny Catania ◽  
Christina Hulbe ◽  
Howard Conway
Keyword(s):  
Spatial Pattern ◽  
Large Amplitude ◽  
Radar Data ◽  
Line Position ◽  
Ice Shelf ◽  
Regional Circulation ◽  
Circulation Patterns ◽  
Siple Dome ◽  
Grounding Line ◽  
Basal Melting

AbstractWe use ice-penetrating radar data across grounding lines of Siple Dome and Roosevelt Island, Antarctica, to measure the spatial pattern, magnitude and duration of sub-ice-shelf melting at these locations. Stratigraphic layers across the grounding line show, in places, a large-amplitude downwarp at, or slightly downstream of, the grounding line due to sub-ice-shelf basal melting. Localized downwarping indicates that melting is transient; melt rates, or the grounding line position, have changed within a few hundred years in order to produce the observed stratigraphy. Elsewhere, no melt-related stratigraphic signature is preserved. In part, heterogeneity in the amount of sub-ice-shelf melt is due to regional circulation patterns in the sub-shelf cavity, but local (on the order of tens of kilometers) heterogeneity in the melt pattern may reflect small differences in the shape of the ice-shelf base at the grounding line. We find that all of the grounding lines crossed have been in place for at most ∼400 years.

scholarly journals Internal and basal ice changes near the grounding line derived from radio-echo sounding

1996 ◽  
Vol 42 (140) ◽  
pp. 103-109 ◽  
Author(s):  
Seiho Uratsuka ◽  
Fumihiko Nishio ◽  
Shinji Mae
Keyword(s):  
Sea Water ◽  
Major Change ◽  
Internal Layer ◽  
Shelf Area ◽  
Echo Signal ◽  
Ice Shelf ◽  
Basal Ice ◽  
Grounding Line ◽  
Radio Echo Sounding ◽  
Strong Scattering

AbstractEvidence of changing basal and internal ice properties near the grounding line was derived from airborne radio-echo-sounder observations of the ice sheet around the Sør Rondane Mountains, Antarctica. From the trailing figure of the bottom-echo signal, the roughness of the ice bottom near the grounding line was inferred. Results show that the specular components of scattering begin to appear on the ice-shelf side of the grounding line. Furthermore, double-trip echoes were observed with a strong scattering in the shelf area, and their boundary of occurrence was very close to the grounding line. This is evidence of interaction between ice and sea water at the bottom of the ice shelf. We also examined the occurrence of internal layered echoes. In most of the area around the mountains, internal echoes were observed continously, but they were not found at or close to the ice shelf. The boundary between the appearance and disappearance of internal-layer echoes is distinct, and occurs 20–30 km inland from the grounding line. These results suggest that some major change may occur in the internal ice on the inland side of the grounding line.

scholarly journals The effect of bottom boundary conditions in the ice-sheet to ice-shelf transition zone problem

2007 ◽  
Vol 53 (182) ◽  
pp. 363-367 ◽  
Author(s):  
Alexander V. Wilchinsky
Keyword(s):  
Transition Zone ◽  
Multiple Solutions ◽  
Vertical Motion ◽  
Separation Mechanism ◽  
Line Position ◽  
Rigid Substrate ◽  
Ice Shelf ◽  
Bottom Boundary ◽  
Bottom Boundary Condition ◽  
Grounding Line

AbstractUniqueness of the transition zone solution is discussed. It is argued that when it is assumed that the stresses are continuous at the grounding line, the ice-shelf solution at the grounding line should possess a zero slope. In order to avoid issues caused by the mathematical singularity of the solution, the same technique as that used to study the transition zone is applied to a similar problem of lifting an elastic sheet from a rigid substrate, which allows a better physical understanding. This exemplifies the effect of the bottom boundary condition of no vertical motion imposed up to a fixed grounding line position, while the forcing parameters, such as the flow rate, vary. Its effect is to produce multiple solutions due to suppression of the separation mechanism.

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