scholarly journals Glacial Geodetic Contributions to the Mass Balance and Dynamics of Ice Shelves

1988 ◽  
Vol 11 ◽  
pp. 89-94 ◽  
Author(s):  
D. Möller ◽  
B. Ritter
Keyword(s):  
Mass Balance ◽  
Collocation Method ◽  
Ice Shelf ◽  
Absolute Position ◽  
Ice Flow ◽  
Ice Shelves ◽  
Rotation Rates ◽  
Deformation Parameters ◽  
Satellite Methods ◽  
The Absolute

The glacial geodetic contribution to the mass balance and dynamics of ice shelves includes repeated determinations of the absolute position (ϕ,λ,Η) of selected points (using satellite methods), the establishment of relative positions (y,x,Δh) in deformation figures, and height measurements. The results are used to establish ice-flow velocities and directions, strain and rotation rates, and changes in height. Modelling of deformation parameters at a few points over a large ice shelf is made possible by the collocation method. Results of these observations and analysis of Ekström Ice Shelf for the period 1979–87 are reported.

scholarly journals Glacial Geodetic Contributions to the Mass Balance and Dynamics of Ice Shelves

1988 ◽  
Vol 11 ◽  
pp. 89-94 ◽  
Author(s):  
D. Möller ◽  
B. Ritter
Keyword(s):  
Mass Balance ◽  
Collocation Method ◽  
Ice Shelf ◽  
Absolute Position ◽  
Ice Flow ◽  
Ice Shelves ◽  
Rotation Rates ◽  
Deformation Parameters ◽  
Satellite Methods ◽  
The Absolute

The glacial geodetic contribution to the mass balance and dynamics of ice shelves includes repeated determinations of the absolute position (ϕ,λ,Η) of selected points (using satellite methods), the establishment of relative positions (y,x,Δh) in deformation figures, and height measurements. The results are used to establish ice-flow velocities and directions, strain and rotation rates, and changes in height. Modelling of deformation parameters at a few points over a large ice shelf is made possible by the collocation method. Results of these observations and analysis of Ekström Ice Shelf for the period 1979–87 are reported.

scholarly journals Climatic conditions, mass balance and dynamics of Larsen B ice shelf, Antarctic Peninsula, prior to collapse

2004 ◽  
Vol 39 ◽  
pp. 557-562 ◽  
Author(s):  
Pedro Skvarca ◽  
Hernán De Angelis ◽  
Andrés F. Zakrajsek
Keyword(s):  
Mass Balance ◽  
Antarctic Peninsula ◽  
Satellite Image ◽  
Climatic Conditions ◽  
Strain Rates ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Shelves ◽  
Additional Information ◽  
Significant Acceleration

AbstractFollowing the collapse of Larsen A in 1995, about 3200 km2 of Larsen B ice shelf disintegrated in early 2002 during the warmest summer recorded on the northeastern Antarctic Peninsula. Immediately prior to disintegration the last field campaign was carried out on Larsen B. Measurements included surface net mass balance, velocity and strain rate on a longitudinal transect along Crane Glacier flowline and over a remnant section confined within Seal Nunataks that survived the collapse. In addition, an automatic weather station located nearby allowed derivation of melt days relevant to the formation and extent of surface meltwater. Repeated surveys allowed us to detect a significant acceleration in ice-flow velocity and associated increasing strain rates along the longitudinal transect. It may be possible to use this acceleration as a predictor of imminent ice-shelf collapse, applicable to ice shelves subject to similar climatic conditions. Additional information on recent ongoing changes was provided by a visible satellite image acquired in early 2003.

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.

scholarly journals Tabular Icebergs: Implication from Geophysical Studies of Ice Shelves

1980 ◽  
Vol 1 ◽  
pp. 55-55
Author(s):  
Sion Shabtaie ◽  
Charles R. Bentley
Keyword(s):  
Mass Balance ◽  
Sea Water ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Frictional Drag ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Rift Zones ◽  
Different Characteristics ◽  
Ice Water

Recent geophysical and glaciological investigations of the Ross Ice Shelf have revealed many complexities in the ice shelf that can be important factors in iceberg structure. The presence of rift zones, surface and bottom crevasses, corrugations, ridges and troughs, and other features could substantially modify the hydraulics of iceberg towing and lead to disintegration of the berg in the course of transport.The relationships between the elevation above sea-level and total ice thickness for three ice shelves (Ross, Brunt, and McMurdo) are given; from them, expressions for the thickness/freeboard ratios of tabular icebergs calved from these ice shelves are obtained. The relationships obtained from the measured values of surface elevation and ice thickness are in agreement with models derived assuming hydrostatic equilibrium.Areas of brine infiltration into the Ross Ice Shelf have been mapped. Examples of radar profiles in these zones are shown. Absorption from the brine layers results in a poor or absent bottom echo. It is probable that little saline ice exists at the bottom of the Ross Ice Shelf front due to a rapid bottom melting near the ice front, and that the thickness of the saline ice at the bottom of icebergs calving from the Ross Ice Shelf is no more than a few meters, if there is any at all.We have observed many rift zones on the ice shelf by airborne radar techniques, and at one site the bottom and surface topographies of (buried) rift zones have been delineated. These rift zones play an obvious role in iceberg formation and may also affect the dynamics of iceberg transport. Bottom crevasses with different shapes, sizes, and spacings are abundant in ice shelves; probably some are filled with saline ice and others with unfrozen sea-water. Existence of these bottom crevasses could lead to a rapid disintegration of icebergs in the course of transport, as well as increasing the frictional drag at the ice-water boundary.Radar profiles of the ice-shelf barrier at four sites in flow bands of very different characteristics are shown. In some places rifting upstream from the barrier shows regular spacings, suggesting a periodic calving. Differential bottom melting near the barrier causes the icebergs to have an uneven surface and bottom (i.e. dome-shaped).Electrical resistivity soundings on the ice shelf can be applied to estimate the temperature-depth function, and from that the basal mass-balance rate. With some modifications, the technique may also be applied to estimating the basal mass-balance rates of tabular icebergs.

scholarly journals Recent ice-surface-elevation changes of Fleming Glacier in response to the removal of the Wordie Ice Shelf, Antarctic Peninsula

2010 ◽  
Vol 51 (55) ◽  
pp. 97-102 ◽  
Author(s):  
J. Wendt ◽  
A. Rivera ◽  
A. Wendt ◽  
F. Bown ◽  
R. Zamora ◽  
...  
Keyword(s):  
Antarctic Peninsula ◽  
Regional Climate ◽  
Airborne Lidar ◽  
Similar Data ◽  
Ice Shelf ◽  
International Polar Year ◽  
Ice Flow ◽  
Ice Shelves ◽  
Elevation Changes ◽  
The Antarctic

AbstractRegional climate warming has caused several ice shelves on the Antarctic Peninsula to retreat and ultimately collapse during recent decades. Glaciers flowing into these retreating ice shelves have responded with accelerating ice flow and thinning. The Wordie Ice Shelf on the west coast of the Antarctic Peninsula was reported to have undergone a major areal reduction before 1989. Since then, this ice shelf has continued to retreat and now very little floating ice remains. Little information is currently available regarding the dynamic response of the glaciers feeding the Wordie Ice Shelf, but we describe a Chilean International Polar Year project, initiated in 2007, targeted at studying the glacier dynamics in this area and their relationship to local meteorological conditions. Various data were collected during field campaigns to Fleming Glacier in the austral summers of 2007/08 and 2008/09. In situ measurements of ice-flow velocity first made in 1974 were repeated and these confirm satellite-based assessments that velocity on the glacier has increased by 40–50% since 1974. Airborne lidar data collected in December 2008 can be compared with similar data collected in 2004 in collaboration with NASA and the Chilean Navy. This comparison indicates continued thinning of the glacier, with increasing rates of thinning downstream, with a mean of 4.1 ± 0.2 m a−1 at the grounding line of the glacier. These comparisons give little indication that the glacier is achieving a new equilibrium.

scholarly journals Tabular Icebergs: Implications from Geophysical Studies of Ice Shelves

1982 ◽  
Vol 28 (100) ◽  
pp. 413-430 ◽  
Author(s):  
Sion Shabtaie ◽  
Charles R. Bentley
Keyword(s):  
Mass Balance ◽  
Sea Water ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Frictional Drag ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Rift Zones ◽  
Different Characteristics ◽  
Ice Water

AbstractRecent geophysical and glaciological investigations of the Ross Ice Shelf have revealed many complexities in the ice shelf that can be important factors in iceberg structure. The presence of rift zones, surface and bottom crevasses, corrugations, ridge/troughs, and other features could substantially modify the hydraulics of iceberg towing and lead to disintegration in the course of transport.The relationships between the elevation above sea-level and total ice thickness for three ice shelves (Ross, Brunt, and McMurdo) are given; from them, expressions for the thickness/freeboard ratios of tabular icebergs calved from these ice shelves are obtained. The relationships obtained from the measured values of surface elevation and ice thickness are in agreement with models derived assuming hydrostatic equilibrium.Areas of brine infiltration into the Ross Ice Shelf have been mapped. Examples of radar profiles in these zones are shown. Absorption from the brine layers results in a poor or absent bottom echo. It is probable that little saline ice exists at the bottom of the Ross Ice Shelf front due to a rapid bottom melting near the ice front, and that the thickness of the saline ice at the bottom of icebergs calving from the Ross Ice Shelf is no more than a few meters, if there is any at all.We have observed many rift zones on the ice shelf by airborne radar techniques, and at one site the bottom and surface topographies of (buried) rift zones have been delineated. These rift zones play an obvious role in iceberg formation and may also affect the dynamics of iceberg transport. Bottom crevasses with different shapes, sizes, and spacings are abundant in ice shelves; probably some are filled with saline ice and others with unfrozen sea-water. Existence of these bottom crevasses could lead to a rapid disintegration of icebergs in the course of transport, as well as increasing the frictional drag at the ice-water boundary.Radar profiles of the ice shelf front at four sites in flow bands of very different characteristics are shown. In some places rifting up-stream from the front shows regular spacings, suggesting a periodic calving. Differential bottom melting near the front causes the icebergs to have an uneven surface and bottom (i.e. dome shaped).Electrical resistivity soundings on the ice shelf can be applied to estimate the temperature-depth function, and from that the basal mass-balance rate. With some modifications, the technique may also be applied to estimating the basal mass balance rates of tabular icebergs.

Constraining ice shelf basalt melting rates from isochrone data

2021 ◽  
Author(s):  
Vjeran Visnjevic ◽  
Reinhard Drews ◽  
Clemens Schannwell ◽  
Inka Koch
Keyword(s):  
Ocean Circulation ◽  
Radar Data ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Ice Shelves ◽  
Inverse Approach ◽  
History Of ◽  
Forward And Inverse Modeling ◽  
Basal Melting

<p>Ice shelves buttress ice flow from the continent towards the ocean, and their disintegration results in increased ice discharge.  Ice-shelf evolution and integrity is influenced by surface accumulation, basal melting, and ice dynamics. We find signals of all of these processes imprinted in the ice-shelf stratigraphy that can be mapped using isochrones imaged with radar.</p><p>Our aim is to develop an inverse approach to infer ice shelf basal melt rates using radar isochrones as observational constraints. Here, we investigate the influence of basalt melt rates on the shape of isochrones using combined insights from both forward and inverse modeling. We use the 3D full Stokes model Elmer/Ice in our forward simulations, aiming to reproduce isochrone patterns observed in our data. Moreover we develop an inverse approach based on the shallow shelf approximating, aiming to constrain basal melt rates using isochronal radar data and surface velocities. Insights obtained from our simulations can also guide the collection of new radar data (e.g., profile lines along vs. across-flow) in a way that ambiguities in interpreting the ice-shelf stratigraphy can be minimized. Eventually, combining these approaches will enable us to better constrain the magnitude and history of basal melting, which will give valuable input for ocean circulation and sea level rise projections.</p>

The effect of Antarctic ice-shelf extent on ice discharge

2021 ◽  
Author(s):  
Jim Jordan ◽  
HIlmar Gudmundsson ◽  
Adrian Jenkins ◽  
Chris Stokes ◽  
Stewart Jamiesson ◽  
...  
Keyword(s):  
Mass Loss ◽  
Recent Work ◽  
Flow Model ◽  
Ice Shelf ◽  
Geophysical Research ◽  
Ice Flow ◽  
Ice Shelves ◽  
Grounding Line ◽  
Natural Variance ◽  
Observational Record

<div>The buttressing strength of Antarctic ice shelves directly effects the amount of ice discharge across the grounding line, with buttressing strength affected by both the thickness and extent of an ice shelf. Recent work has shown that a reduction in ice-shelf buttressing due to ocean induced ice-shelf thinning is responsible for a significant portion of increased Antarctic ice discharge (Gudmundsson et al., 2019, but few studies have attempted to show the effect of variability in ice-shelf extent on ice discharge. This variability arises due to ice-shelf calving following a cycle of long periods of slow, continuous calving interposed with calving of large, discrete sections.  These discrete calving events tend to occur on a comparative timeframe to that of the observational record. As such, when determining observed changes in ice discharge it is crucial that this natural variability is separated from any observed trends.  </div><div> </div><div>In this work we use the numerical ice-flow model Úa in combination with observations of ice shelf extent to diagnostically calculate Antarctic ice discharge. These observations primarily date back to the 1970s, though for some ice shelves records exist back to the 1940s. We assemble an Antarctic wide model for two scenarios: 1) with ice shelves at their maximum observed extent and 2) with ice shelves at their minimum observed extent. We then compare these two scenarios to differences in the observed changes in Antarctic ice-discharge to determine how much can be attributed to natural variance .</div><p> </p><p><span>Gudmundsson, G. H.</span><span>, Paolo, F. S., Adusumilli, S., & Fricker, H. A. (2019). </span>Instantaneous Antarctic ice‐ sheet mass loss driven by thinning ice shelves. <em>Geophysical Research Letters</em>, 46, 13903– 13909. </p>

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 Calving cycle of the Brunt Ice Shelf, Antarctica, driven by changes in ice shelf geometry

2019 ◽  
Vol 13 (10) ◽  
pp. 2771-2787 ◽  
Author(s):  
Jan De Rydt ◽  
Gudmundur Hilmar Gudmundsson ◽  
Thomas Nagler ◽  
Jan Wuite
Keyword(s):  
Large Scale ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Shelves ◽  
Flow Models ◽  
Speed Up ◽  
The Antarctic ◽  
Detrimental Impact ◽  
Natural Laboratory

Abstract. Despite the potentially detrimental impact of large-scale calving events on the geometry and ice flow of the Antarctic Ice Sheet, little is known about the processes that drive rift formation prior to calving, or what controls the timing of these events. The Brunt Ice Shelf in East Antarctica presents a rare natural laboratory to study these processes, following the recent formation of two rifts, each now exceeding 50 km in length. Here we use 2 decades of in situ and remote sensing observations, together with numerical modelling, to reveal how slow changes in ice shelf geometry over time caused build-up of mechanical tension far upstream of the ice front, and culminated in rift formation and a significant speed-up of the ice shelf. These internal feedbacks, whereby ice shelves generate the very conditions that lead to their own (partial) disintegration, are currently missing from ice flow models, which severely limits their ability to accurately predict future sea level rise.

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