scholarly journals A Cross-Sectional Model for West Antarctica

1984 ◽  
Vol 5 ◽  
pp. 95-99 ◽  
Author(s):  
B. J. McInnes ◽  
W. F. Budd
Keyword(s):  
Ross Sea ◽  
Dynamic State ◽  
Ice Thickness ◽  
Cross Sectional ◽  
West Antarctic Ice Sheet ◽  
Ross Ice Shelf ◽  
West Antarctic ◽  
Mass Fluxes ◽  
Ice Stream B ◽  
The One

The dynamic state of the West Antarctic ice sheet has been termed the grand problem of glaciology. An attempt is presented to assess it by simulating the observed ice thickness and ice velocities along a cross-section from ice stream B (Ross Sea) to Pine Island Glacier (Pine Island Bay) with a numerical model developed from the one described by Budd and McInnes (1978). A kinematic analysis with topographical and regime data from various sources shows the mass fluxes observed near the grounding line of the Ross Ice Shelf to be of the order expected for steady-state balance. Deformation of the ice accounts for only a small fraction of the observed flow there. Simulations (to be described in detail elsewhere) with the Budd/McInnes surging mechanism can approximate the existing ice thickness as a post-surge feature but fail to reproduce the high balance velocities. Both these velocities and the existing ice-thickness profile are simulated successfully as a state of steady sliding, with parameterizations involving the ice thickness above that corresponding to buoyancy and realistically assumed longitudinal strain-rates. A range of results is presented to illustrate the sensitivity of the simulation to changes in various parameters.

scholarly journals A Cross-Sectional Model for West Antarctica

1984 ◽  
Vol 5 ◽  
pp. 95-99 ◽  
Author(s):  
B. J. McInnes ◽  
W. F. Budd
Keyword(s):  
Ross Sea ◽  
Dynamic State ◽  
Ice Thickness ◽  
Cross Sectional ◽  
West Antarctic Ice Sheet ◽  
Ross Ice Shelf ◽  
West Antarctic ◽  
Mass Fluxes ◽  
Ice Stream B ◽  
The One

The dynamic state of the West Antarctic ice sheet has been termed the grand problem of glaciology. An attempt is presented to assess it by simulating the observed ice thickness and ice velocities along a cross-section from ice stream B (Ross Sea) to Pine Island Glacier (Pine Island Bay) with a numerical model developed from the one described by Budd and McInnes (1978). A kinematic analysis with topographical and regime data from various sources shows the mass fluxes observed near the grounding line of the Ross Ice Shelf to be of the order expected for steady-state balance. Deformation of the ice accounts for only a small fraction of the observed flow there. Simulations (to be described in detail elsewhere) with the Budd/McInnes surging mechanism can approximate the existing ice thickness as a post-surge feature but fail to reproduce the high balance velocities. Both these velocities and the existing ice-thickness profile are simulated successfully as a state of steady sliding, with parameterizations involving the ice thickness above that corresponding to buoyancy and realistically assumed longitudinal strain-rates. A range of results is presented to illustrate the sensitivity of the simulation to changes in various parameters.

scholarly journals Electromagnetic Sounding of Bottom Crevasses on the Ross Ice Shelf, Antarctica

1979 ◽  
Vol 24 (90) ◽  
pp. 321-330 ◽  
Author(s):  
Kenneth C. Jezek ◽  
Charles R. Bentley ◽  
John W. Clough
Keyword(s):  
Flow Direction ◽  
Ice Shelf ◽  
Electromagnetic Sounding ◽  
West Antarctic Ice Sheet ◽  
North West ◽  
Ross Ice Shelf ◽  
North East ◽  
West Antarctic ◽  
Ice Stream B ◽  
Folded Dipole

AbstractDuring the 1976—77 season of the Ross Ice Shelf Geophysical and Glaciological Survey, a series of vertical electromagnetic sounding profiles of subsurface features was completed at station J-9. The survey comprised three five-kilometer north-west-south-east profiles separated by one kilometer and six two-kilometer north-east-south-west profiles, and was carried out on the surface using 35 MHz and 50 MHz radar systems. Folded-dipole antennae were used and oriented to detect reflectors both along and perpendicular to the profile path. This was done to facilitate the interpretation of the data, which indicated a complex system of bottom crevasses. Measurements of the positions, heights, and shapes of these crevasses showed at least two sets of crevasses varying in both strike and size. The larger crevasses, about 120 m high and oriented more or less normal to the flow direction, are probably associated with the movement of ice stream B across the grounding line between the West Antarctic ice sheet and the Ross Ice Shelf. A satisfactory explanation for the secondary set of crevasses, about 60 m high and forming an angle of 60° ±10° with the first set, has not yet been found.

scholarly journals Ice-Thickness Map of the West Antarctic Ice Streams by Radar Sounding

1988 ◽  
Vol 11 ◽  
pp. 126-136 ◽  
Author(s):  
S. Shabtaie ◽  
C. R. Bentley
Keyword(s):  
Transient Behavior ◽  
Ice Thickness ◽  
Ice Streams ◽  
Cross Sectional ◽  
Ross Ice Shelf ◽  
Bed Topography ◽  
West Antarctic ◽  
Ice Stream ◽  
Adjacent Part ◽  
Thickness Variations

Extensive radar ice-thickness sounding of ice streams A, B, and C, and the ridges between them, has been carried out. Closely spaced flight lines, as well as ties to numerous ground stations, have enabled us to compile a detailed ice-thickness map of the area. The map reveals a highly complex pattern of ice-thickness variations, which, because they are much larger than the surface relief, largely reflect the subglacial topography. Several cross-sectional profiles across the ice streams and ridges are shown, and a new configuration for Ice Stream A is presented. Ice Stream A is connected to Reedy Glacier and Horlick Ice Stream by subglacial troughs that converge down-stream. The single trough continues, at a depth of more than 1000 m below sea-level, beneath the entire length of the ice stream and adjacent part of Ross Ice Shelf. Ridge AB (part of which may be a remanent ice stream) overlies a deep bed with pronounced troughs at its headward end; the bed shoals rapidly down-stream to a height more than 500 m above the beds of the adjacent ice streams. Ice stream B1 overlies a subglacial trough that is deep inland and also shoals markedly toward the grounding line. Near its head. Ice Stream B2 is as much as 1000 m thinner than Ice Stream Bl, but then remains much more nearly constant in thickness along its length. Ridge BC is characterized by a smoother bed and less variation in bed depth than ridge AB. Ice Stream C, which is inactive, is particularly marked by uncorrelated maxima and minima in surface and bed topography. There are no distinct topographical steps that demarcate the transition from sheet to streaming flow at the head of the ice streams, and the ice streams are placed asymmetrically in some places with respect to their subglacial troughs. This may reflect a relative impermanence or transient behavior of the “Ross” ice streams.

scholarly journals Field Studies of Bottom Crevasses in the Ross Ice Shelf, Antarctica (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 341 ◽  
Author(s):  
Kenneth C. Jezek ◽  
Charles R. Bentley
Keyword(s):  
Bottom Topography ◽  
Field Studies ◽  
Airborne Radar ◽  
Ice Thickness ◽  
Ice Shelf ◽  
The West ◽  
West Antarctic Ice Sheet ◽  
Ross Ice Shelf ◽  
West Antarctic ◽  
Grounding Line

Surface and airborne radar sounding data were used to identify and map fields of bottom crevasses on the Ross Ice Shelf. Two major concentrations of crevasses were found, one along the grid-eastern grounding line and another, made up of eight smaller sites, grid-west of Crary Ice Rise. Based upon an analysis of bottom crevasse heights and locations, and of the strength of radar waves diffracted from the apex and bottom corners of the gridcrevasses, we conclude that the crevasses are formed at discrete locations on the ice shelf. By comparing the locations of crevasse formation with ice thickness and bottom topography, we conclude that most of the crevasse sites are associated with grounding. Hence we have postulated that six grounded areas, in addition to Crary Ice Rise and Roosevelt Island, exist in the grid-western sector of the ice shelf. These pinning points may be important for interpreting the dynamics of the West Antarctic ice sheet.

scholarly journals Field Studies of Bottom Crevasses in the Ross Ice Shelf, Antarctica

1983 ◽  
Vol 29 (101) ◽  
pp. 118-126 ◽  
Author(s):  
Kenneth C. Jezek ◽  
Charles R. Bentley
Keyword(s):  
Bottom Topography ◽  
Field Studies ◽  
Airborne Radar ◽  
Ice Thickness ◽  
Ice Shelf ◽  
The West ◽  
West Antarctic Ice Sheet ◽  
Ross Ice Shelf ◽  
West Antarctic ◽  
Grounding Line

AbstractSurface and airborne radar sounding data were used to identify and map fields of bottom crevasses on the Ross Ice Shelf. Two major concentrations of crevasses were found, one along the grid-eastern grounding line and another, made up of eight smaller sites, grid west of Crary Ice Rise. Based upon an analysis of bottom crevasse heights and locations, and of the strength of radar waves diffracted from the apex and bottom corners of the crevasses, we conclude that the crevasses are formed at discrete locations on the ice shelf. By comparing the locations of crevasse formation with ice thickness and bottom topography, we conclude that most of the crevasse sites are associated with ice rises. Hence we have postulated that six ice rises, in addition to Crary Ice Rise and Roosevelt Island, exist in the grid-western sector of the ice shelf. These “pinning points” may be important for interpreting the dynamics of the West Antarctic ice sheet.

scholarly journals Lateral Density Differences from Seismic Measurements at a Site on the Ross Ice Shelf, Antarctica

1979 ◽  
Vol 24 (90) ◽  
pp. 309-312 ◽  
Author(s):  
Joseph F. Kirchner ◽  
Charles R. Bentley ◽  
James D. Robertson
Keyword(s):  
High Stress ◽  
Maximum Velocity ◽  
Compressional Wave ◽  
Stress System ◽  
Ice Shelf ◽  
West Antarctic Ice Sheet ◽  
Depth Profiles ◽  
Ross Ice Shelf ◽  
West Antarctic ◽  
Ice Stream B

AbstractSeismic compressional-wave data from short refraction shooting carried out during the 1974–75 and 1976–77 seasons at J-9, the site of the Ross Ice Shelf Drilling Project, have been compared. Significant dissimilarities were found to exist between the two sets of data. The measurements were made at locations about 2 km apart, with three unreversed profiles 60° apart recorded during the 1976–77 season and one unreversed profile during the 1974–75 season. The resulting velocity–depth profiles, and hence the derived density–depth profiles, differ by as much as 8%, with the 1976–77 results indicating a maximum velocity, corresponding to solid ice, at a shallower depth than the 1974–75 data. Both profiles were subjected to the same analysis, and a comparison of travel-time curves shows the differences to be real. Densities measured on cores from a 100 m bore hole drilled in 1974–75 about 50 m from the center of the 1974–75 profile agree well with densities computed from that profile. The density difference is believed to be due to the passage of the ice through the high-stress system associated with the interaction between Ice Stream B, flowing in from the West Antarctic ice sheet, and the Ross Ice Shelf. A reversed refraction profile carried out at station B.C. about 30 km up-stream, shows evidence of dipping layers that may be similarly caused.

Effects of giant icebergs on two emperor penguin colonies in the Ross Sea, Antarctica

2007 ◽  
Vol 19 (1) ◽  
pp. 31-38 ◽  
Author(s):  
Gerald L. Kooyman ◽  
David G. Ainley ◽  
Grant Ballard ◽  
Paul J. Ponganis
Keyword(s):  
Ross Sea ◽  
Emperor Penguin ◽  
Ice Shelf ◽  
West Antarctic Ice Sheet ◽  
North West ◽  
Ross Ice Shelf ◽  
The North ◽  
West Antarctic ◽  
South West ◽  
Wintering Areas

The arrival in January 2001 in the south-west Ross Sea of two giant icebergs, C16 and B15A, subsequently had dramatic affects on two emperor penguin colonies. B15A collided with the north-west tongue of the Ross Ice Shelf at Cape Crozier, Ross Island, in the following months and destroyed the penguins' nesting habitat. The colony totally failed in 2001, and years after, with the icebergs still in place, exhibited reduced production that ranged from 0 to 40% of the 1201 chicks produced in 2000. At Beaufort Island, 70 km NW of Crozier, chick production declined to 6% of the 2000 count by 2004. Collisions with the Ross Ice Shelf at Cape Crozier caused incubating adults to be crushed, trapped in ravines, or to abandon the colony and, since 2001, to occupy poorer habitat. The icebergs separated Beaufort Island from the Ross Sea Polynya, formerly an easy route to feeding and wintering areas. This episode has provided a glimpse of events which have probably occurred infrequently since the West Antarctic Ice Sheet began to retreat 12 000 years ago. The results allow assessment of recovery rates for one colony decimated by both adult and chick mortality, and the other colony by adult abandonment and chick mortality.

scholarly journals Electromagnetic Sounding of Bottom Crevasses on the Ross Ice Shelf, Antarctica

1979 ◽  
Vol 24 (90) ◽  
pp. 321-330 ◽  
Author(s):  
Kenneth C. Jezek ◽  
Charles R. Bentley ◽  
John W. Clough
Keyword(s):  
Flow Direction ◽  
Ice Shelf ◽  
Electromagnetic Sounding ◽  
West Antarctic Ice Sheet ◽  
North West ◽  
Ross Ice Shelf ◽  
North East ◽  
West Antarctic ◽  
Ice Stream B ◽  
Folded Dipole

AbstractDuring the 1976—77 season of the Ross Ice Shelf Geophysical and Glaciological Survey, a series of vertical electromagnetic sounding profiles of subsurface features was completed at station J-9. The survey comprised three five-kilometer north-west-south-east profiles separated by one kilometer and six two-kilometer north-east-south-west profiles, and was carried out on the surface using 35 MHz and 50 MHz radar systems. Folded-dipole antennae were used and oriented to detect reflectors both along and perpendicular to the profile path. This was done to facilitate the interpretation of the data, which indicated a complex system of bottom crevasses. Measurements of the positions, heights, and shapes of these crevasses showed at least two sets of crevasses varying in both strike and size. The larger crevasses, about 120 m high and oriented more or less normal to the flow direction, are probably associated with the movement of ice stream B across the grounding line between the West Antarctic ice sheet and the Ross Ice Shelf. A satisfactory explanation for the secondary set of crevasses, about 60 m high and forming an angle of 60° ±10° with the first set, has not yet been found.

scholarly journals Implications for the Late Wisconsin-holocene Extent of the West Antarctic Ice Sheet from Regional Free-air Gravity Anomalies in the Ross Embayment (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 340-340
Author(s):  
Larry L. Greischar ◽  
Charles R. Bentley
Keyword(s):  
Continental Shelf ◽  
Ross Sea ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
West Antarctic Ice Sheet ◽  
Ross Ice Shelf ◽  
West Antarctic ◽  
Low Pass ◽  
Free Air Gravity ◽  
Gravity Map

Gravity data from cruises 32, 51, and 52 of the USNS Eltanin (Hayes and Davey 1975), approximately adjusted to the new gravity datura (IGSN 71) and reference system (GRS 67), have been used to extend the Ross Ice Shelf gravity map to the edge of the Ross Sea continental shelf. Various regional gravity anomaly fields obtained by applying low-pass filters to these data are strongly negative over the entire Ross embayment; values increase gradually from approximately -300 gu (-30 mgal) near the Siple Coast to -150 gu (-15 mgal) near the edge of the Ross Sea continental shelf.

scholarly journals Field Studies of Bottom Crevasses in the Ross Ice Shelf, Antarctica

1983 ◽  
Vol 29 (101) ◽  
pp. 118-126 ◽  
Author(s):  
Kenneth C. Jezek ◽  
Charles R. Bentley
Keyword(s):  
Bottom Topography ◽  
Field Studies ◽  
Airborne Radar ◽  
Ice Thickness ◽  
Ice Shelf ◽  
The West ◽  
West Antarctic Ice Sheet ◽  
Ross Ice Shelf ◽  
West Antarctic ◽  
Grounding Line

AbstractSurface and airborne radar sounding data were used to identify and map fields of bottom crevasses on the Ross Ice Shelf. Two major concentrations of crevasses were found, one along the grid-eastern grounding line and another, made up of eight smaller sites, grid west of Crary Ice Rise. Based upon an analysis of bottom crevasse heights and locations, and of the strength of radar waves diffracted from the apex and bottom corners of the crevasses, we conclude that the crevasses are formed at discrete locations on the ice shelf. By comparing the locations of crevasse formation with ice thickness and bottom topography, we conclude that most of the crevasse sites are associated with ice rises. Hence we have postulated that six ice rises, in addition to Crary Ice Rise and Roosevelt Island, exist in the grid-western sector of the ice shelf. These “pinning points” may be important for interpreting the dynamics of the West Antarctic ice sheet.

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