scholarly journals Can Relict Crevasse Plumes on Antarctic Ice Shelves Reveal a History of Ice-Stream Fluctuation?

1988 ◽  
Vol 11 ◽  
pp. 77-82 ◽  
Author(s):  
D. R. MacAyeal ◽  
R. A. Bindschadler ◽  
K. C. Jezek ◽  
S. Shabtaie
Keyword(s):  
Numerical Model ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Shelves ◽  
Stream Discharge ◽  
Ice Stream ◽  
History Of

Configurations of relict surface-crevasse bands and medial moraines that emanate from the shear margins of ice streams are simulated, using a numerical model of an ideal rectangular ice shelf to determine their potential for recording a past ice-stream discharge chronology.

scholarly journals Can Relict Crevasse Plumes on Antarctic Ice Shelves Reveal a History of Ice-Stream Fluctuation?

1988 ◽  
Vol 11 ◽  
pp. 77-82 ◽  
Author(s):  
D. R. MacAyeal ◽  
R. A. Bindschadler ◽  
K. C. Jezek ◽  
S. Shabtaie
Keyword(s):  
Numerical Model ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Shelves ◽  
Stream Discharge ◽  
Ice Stream ◽  
History Of

Configurations of relict surface-crevasse bands and medial moraines that emanate from the shear margins of ice streams are simulated, using a numerical model of an ideal rectangular ice shelf to determine their potential for recording a past ice-stream discharge chronology.

scholarly journals A millennium of variable ice flow recorded by the Ross Ice Shelf, Antarctica

2000 ◽  
Vol 46 (155) ◽  
pp. 652-664 ◽  
Author(s):  
M. A. Fahnestock ◽  
T. A. Scambos ◽  
R. A. Bindschadler ◽  
G. Kvaran
Keyword(s):  
Landsat Imagery ◽  
Ice Shelf ◽  
Ice Streams ◽  
The West ◽  
Northern Margin ◽  
Ross Ice Shelf ◽  
Stream Discharge ◽  
Ice Stream ◽  
History Of ◽  
Ice Stream B

AbstractAn enhanced composite Advanced Very High Resolution Radiometer (AVHRR) image is used to map flow stripes and rifts across the Ross Ice Shelf, Antarctica. The patterns of these flow-related features reveal a history of discharge variations from the ice streams feeding the eastern part of the shelf. The most profound variations are visible in the track of rifts downstream of Crary Ice Rise, flow-stripe bends to the west of this ice rise and adjacent to Steershead ice rise, and changes in the northern margin of Ice Stream B. The track of rifts downstream of Crary Ice Rise indicates that the ice rise has existed for at least 700 years. The character of this track changes about 350 km downstream, indicating a rearrangement of flow patterns about 550 years ago. The large bulge in the flow stripes to the west of Crary Ice Rise is shown in detail, with bent flow stripes extending for several hundred kilometers along flow; this feature formed from the south, possibly due to a change in the discharge of Ice Stream A. The AVHRR image documents a complex history associated with the shutdown of Ice Stream C, with changes in the margins of Ice Stream C and the northern margin of Ice Stream B, and the grounding of Steershead ice rise with an associated bending and truncation of flow stripes. Landsat imagery shows a region that appears to be actively extending just downstream of the ice rise, as the shelf continues to respond to recent changes in ice-stream discharge. We present a four-stage flow history which accounts for the features preserved in the ice shelf.

scholarly journals Grounding-zone flow variability of Priestley Glacier, Antarctica, in a diurnal tidal regime

2021 ◽  
Author(s):  
Reinhard Drews ◽  
Christian Wild ◽  
Oliver Marsh ◽  
Wolfgang Rack ◽  
Todd Ehlers ◽  
...  
Keyword(s):  
Spatial Scales ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Shelves ◽  
Ice Stream ◽  
Grounding Line ◽  
Temporal And Spatial ◽  
Gnss Measurements ◽  
Natural Laboratory

<p>Dynamics of polar outlet glaciers vary with ocean tides, providing a natural laboratory to understand basal processes beneath ice streams, ice rheology and ice-shelf buttressing. We apply Terrestrial Radar Interferometry to close the spatiotemporal gap between localized, temporally well-resolved GNSS and area-wide but sparse satellite observations. Three-hour flowfields collected over an eight day period at Priestley Glacier, Antarctica, validate and provide the spatial context for concurrent GNSS measurements. Ice flow is fastest during falling tides and slowest during rising tides. Principal components of the timeseries prove upstream propagation of tidal signatures $>$ 10 km away from the grounding line. Hourly, cm-scale horizontal and vertical flexure patterns occur $>$6 km upstream of the grounding line. Vertical uplift upstream of the grounding line is consistent with ephemeral re-grounding during low-tide impacting grounding-zone stability. On the freely floating ice shelves, we find velocity peaks both during high- and low-tide suggesting that ice-shelf buttressing varies temporally as a function of flexural bending from tidal displacement. Taken together, these observations identify tidal imprints on ice-stream dynamics on new temporal and spatial scales providing constraints for models designed to isolate dominating processes in ice-stream and ice-shelf mechanics.</p>

scholarly journals Technologies for retrieving sediment cores in Antarctic subglacial settings

2016 ◽  
Vol 374 (2059) ◽  
pp. 20150056 ◽  
Author(s):  
Dominic A. Hodgson ◽  
Michael J. Bentley ◽  
James A. Smith ◽  
Julian Klepacki ◽  
Keith Makinson ◽  
...  
Keyword(s):  
Sediment Cores ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Stream ◽  
Whillans Ice Stream ◽  
History Of ◽  
Subglacial Lakes ◽  
Physical And Chemical ◽  
The Antarctic

Accumulations of sediment beneath the Antarctic Ice Sheet contain a range of physical and chemical proxies with the potential to document changes in ice sheet history and to identify and characterize life in subglacial settings. Retrieving subglacial sediments and sediment cores presents several unique challenges to existing technologies. This paper briefly reviews the history of sediment sampling in subglacial environments. It then outlines some of the technological challenges and constraints in developing the corers being used in sub-ice shelf settings (e.g. George VI Ice Shelf and Larsen Ice Shelf), under ice streams (e.g. Rutford Ice Stream), at or close to the grounding line (e.g. Whillans Ice Stream) and in subglacial lakes deep under the ice sheet (e.g. Lake Ellsworth). The key features of the corers designed to operate in each of these subglacial settings are described and illustrated together with comments on their deployment procedures.

scholarly journals Ice-Shelf Response to Ice-stream Discharge Fluctuations: III. The Effects of Ice-stream Imbalance on the Ross Ice Shelf, Antarctica

1989 ◽  
Vol 35 (119) ◽  
pp. 38-42 ◽  
Author(s):  
Douglas R. Macayeal
Keyword(s):  
Snow Accumulation ◽  
Time Span ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ross Ice Shelf ◽  
Stream Discharge ◽  
Ice Stream ◽  
Discharge Rates ◽  
Short Time Span ◽  
Catchment Areas

AbstractA numerical simulation of the Ross Ice Shelf, Antarctica, in which discharge from Ice Streams A-E is changed suddenly between extreme states, is used to investigate ice-shelf thickness and flow anomalies generated by ice-stream transience. At one extreme, ice-stream discharge rates specified as model boundary conditions are balanced individually with snow accumulation in the ice-stream catchment areas. At the other, discharge rates are fixed at current observed values which widely depart from mass balance. The simulated ice-shelf evolution between initial and final steady states suggests that ice-thickness and velocity fields adjust to new ice-stream conditions over a relatively short time span (approximately 500 years). In contrast, transitory geometrics of medial moraines and relict-crevasse bands persist over a longer time span (up to 2000 years). Contortions of medial moraines and relict-crevasse bands thus may provide a useful long-term history of past ice-stream activity. The past stoppage of Ice Stream C, for example, should be evident today in some medial moraine trajectories even if the stoppage occurred over 1000 years ago. Ice-shelf thickness fluctuations induced by ice-stream activity are generally restricted to the neighborhood of the grounding line. These fluctuations may constitute a trigger for ice-rise formation near ice-stream outlets.

scholarly journals West Antarctic ice-stream discharge variability: mechanism, controls and pattern of grounding-line retreat

2004 ◽  
Vol 50 (171) ◽  
pp. 471-484 ◽  
Author(s):  
Christina L. Hulbe ◽  
Mark A. Fahnestock
Keyword(s):  
Temperature Gradient ◽  
Ice Streams ◽  
West Antarctic Ice Sheet ◽  
Stream Discharge ◽  
West Antarctic ◽  
Basal Ice ◽  
Ice Stream ◽  
Grounding Line ◽  
Downstream Reach ◽  
History Of

AbstractWest Antarctic ice streams show pronounced flow variability in their downstream reaches, with changes stranding formerly fast-flowing ice and redirecting discharge. A simple model, in which the temperature gradient in basal ice provides control of fast sliding in the downstream reach, can explain this behavior. Downstream thinning steepens the temperature gradient near the bed, increasing upward heat flow and the tendency toward basal freezing. The basal temperature gradient is steepest and the tendency toward basal freezing the strongest in ice that has experienced the most rapid downstream thinning, that is, the fastest-flowing ice. The most ‘successful’ rapid outflows are regions where basal water from elsewhere is likely to be consumed. Freezing here leads to episodic slow-downs and redirections of flow, the history of which appears in satellite imagery as ice rises, distorted streaklines, and margin jumps created when discharge migrates to areas with more favorable basal conditions. One compelling consequence of this process is that it makes catastrophic collapse less likely; if discharge currents are forced to slow when they become too fast (thin), then there may be an upper bound on the retreat rate and discharge flux of the West Antarctic ice sheet (WAIS) ice-stream system under the present climate.

scholarly journals Twelve years of ice velocity change in Antarctica observed by RADARSAT-1 and -2 satellite radar interferometry

2012 ◽  
Vol 6 (3) ◽  
pp. 1715-1738 ◽  
Author(s):  
B. Scheuchl ◽  
J. Mouginot ◽  
E. Rignot
Keyword(s):  
Ice Shelf ◽  
Ice Streams ◽  
Velocity Difference ◽  
Velocity Change ◽  
Ice Dynamics ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Ice Stream ◽  
Catchment Areas ◽  
Ice Velocity

Abstract. We report changes in ice velocity of a 6.5 million km2 region around South Pole encompassing the Ronne/Filchner and Ross Ice Shelves and a significant portion of the ice streams and glaciers that constitute their catchment areas. Using the first full interferometric synthetic-aperture radar (InSAR) coverage of the region completed in 2009 and partial coverage acquired in 1997, we process the data to assemble a comprehensive map of ice velocity changes with a nominal precision of detection of ±3–4 m yr–1. The largest observed changes, an increase in speed of 100 m yr–1 in 12 yr, are near the frontal regions of the large ice shelves and are associated with the slow detachment of large tabular blocks that will eventually form icebergs. On the Ross Ice Shelf, our data reveal a slow down of Mercer and Whillans Ice Streams with a 12 yr velocity difference of 50 m yr–1 (16.7 %) and 100 m yr–1 (25.3 %) at their grounding lines. The slow down spreads 450 km upstream of the grounding line and more than 500 km onto the shelf, i.e., far beyond what was previously known. Also slowing in the Ross Ice Shelf sector are MacAyeal Ice Stream and Byrd Glacier with a 12 yr velocity difference near their grounding lines of 30 m yr–1 (6.7 %) and 35 m yr–1 (4.1 %), respectively. Bindschadler Ice Stream is faster by 20 m yr–1 (5 %). Most of these changes in glacier speed extend on the Ross Ice Shelf along the ice streams' flow lines. At the mouth of the Filchner/Ronne Ice Shelves, the 12 yr difference in glacier speed is below the 8 % level. We detect the largest slow down with a 12 yr velocity difference of up to 30 m yr–1 on Slessor and Recovery Glaciers, equivalent to 6.7 % and 3.3 %, respectively. Foundation Ice Stream shows a modest speed up (30 m yr–1 or 5 %). No change is detected on Bailey, Rutford, and Institute Ice Streams. On the Filchner Ice Shelf proper, ice slowed down rather uniformly with a 12 yr velocity difference of 50 m yr–1, or 5 % of its ice front speed, which we attribute to an 12 km advance in its ice front position. Overall, we conclude that the ice streams and ice shelves in this broad region, in contrast with their counterparts in the Amundsen and Bellingshausen seas, exhibit changes in ice dynamics that have almost no impact on the overall ice balance of the region.

scholarly journals Thermal controls on ice stream shear margins

2021 ◽  
pp. 1-15
Author(s):  
Pierce Hunter ◽  
Colin Meyer ◽  
Brent Minchew ◽  
Marianne Haseloff ◽  
Alan Rempel
Keyword(s):  
Steady State ◽  
Stream Velocity ◽  
Viscous Heating ◽  
Ice Streams ◽  
Temperature Dependent Viscosity ◽  
Stream Discharge ◽  
Ice Stream ◽  
Steady State Model ◽  
Slow Moving ◽  
Dependent Viscosity

Abstract Ice stream discharge responds to a balance between gravity, basal friction and lateral drag. Appreciable viscous heating occurs in shear margins between ice streams and adjacent slow-moving ice ridges, altering the temperature-dependent viscosity distribution that connects lateral drag to marginal strain rates and ice stream velocity. Warmer ice deforms more easily and accommodates faster flow, whereas cold ice supplied from ice ridges drives advective cooling that counteracts viscous heating. Here, we present a two-dimensional (three velocity component), steady-state model designed to explore the thermal controls on ice stream shear margins. We validate our treatment through comparison with observed velocities for Bindschadler Ice Stream and verify that calculated temperatures are consistent with results from previous studies. Sweeping through a parameter range that encompasses conditions representative of ice streams in Antarctica, we show that modeled steady-state velocity has a modest response to different choices in forcing up until temperate zones develop in the shear margins. When temperate zones are present, velocity is much more sensitive to changes in forcing. We identify key scalings for the emergence of temperate conditions in our idealized treatment that can be used to identify where thermo-mechanical feedbacks influence the evolution of the ice sheet.

scholarly journals Ice shelf internal reflection horizons reveal ice provenance, dynamics, surface accumulation and oceanic melt

2021 ◽  
Author(s):  
Inka Koch ◽  
Reinhard Drews ◽  
Daniela Jansen ◽  
Steven Franke ◽  
Vjeran Visnjevic ◽  
...  
Keyword(s):  
Shear Zones ◽  
Ultra Wideband ◽  
Internal Layers ◽  
Ice Shelf ◽  
Ice Streams ◽  
Catchment Scale ◽  
Ice Dynamics ◽  
Ice Shelves ◽  
Wideband Radar ◽  
Narrow Belt

<p>Ice shelves are widely known to slow the transfer of Antarctic grounded ice to the ocean, especially if their flow is decelerated by local pinning points. Their longevity is influenced by variations in ice dynamics, surface accumulation and oceanic conditions in the ice shelf cavity. This is reflected in the ice shelf structure, which can be characterized by the shape of internal radar reflection horizons.</p><p>We aim to map the internal ice shelf stratigraphy of ice shelves, starting with the narrow belt of ice-shelves in the Dronning Maud Land area. The final goal will be to evaluate these as a spatiotemporal archive of ice provenance and ice dynamics. The bulk of the data presented here were collected with AWI’s airborne multi frequency ultra-wideband radar and we combine these new observations with airborne and ground-based radar surveys from previous years. We present a consistent set of internal radar isochrones on a catchment scale for the Roi Baudoin area including the Ragnhild ice streams, the grounding-zone, the iceshelf and multiple ice rises.  Using pattern matching technique we can link isochrones across different ice rises in the area, and hence provide first observational constraints on how ice rises jointly react to changes in atmospheric and oceanographic forcings. We also find a number of interesting features including dynamically induced dips in shear zones, truncating layers at the ice-shelf base, and the development of a meteoric ice layer distinguishing advected from newly accumulated ice in the iceshelf. The time series provided by radar observations over the last 10 years also offers the potential to map temporal changes. We use ice-flow modelling to provide age constraints for some internal layers and delineate portions within the shelf as a function of their advection history, hence marking areas of differing rheologies within the shelf. Taken together, this case study on a catchment scale is a primer to unravel the information stored in the isochronal stratigraphy of coastal Antarctica and contributes to international efforts (e.g., SCAR AntArchitecture)  of mapping stratigraphy on ice sheet scales.</p>

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.

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