scholarly journals The Equilibrium State of the Eastern Half of the Ross Ice Shelf

1978 ◽  
Vol 20 (84) ◽  
pp. 509-518 ◽  
Author(s):  
Robert H. Thomas ◽  
Charles R. Bentley
Keyword(s):  
Indirect Evidence ◽  
Melting Rate ◽  
Snow Accumulation ◽  
Surface Strain ◽  
The South ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Average Value ◽  
West Antarctic ◽  
Flow Band

AbstractMeasurements of ice thickness, velocity, snow accumulation rates, and surface strain-rates are used to examine the state of equilibrium of three flow bands of the Ross Ice Shelf. The analysis gives the rate of thickening of the ice shelf in terms of the basal freezing rate, which is unknown. However, indirect evidence suggests that the basal flux ranges from a small value of freezing in the south to a melting rate of about one meter of ice per year at the ice front. If these values are correct then the flow band in the south-east corner of the ice shelf appears to be thickening at an average value of (34 ± 15) cm of ice per year. Persistent thickening at this rate must lead to grounding of large areas of the ice shelf. This would restrict drainage from West Antarctic ice streams which feed this part of the ice shelf and these would tend to thicken and advance their grounding lines into the ice shelf. Further north, near the RISP bore-hole site, the ice shelf is probably in equilibrium. The largest flow band is to the south and east of Roosevelt Island, and this also may be in equilibrium if there is significant bottom melting from ice shelf that is more than 100 km from the ice front.

scholarly journals The Equilibrium State of the Eastern Half of the Ross Ice Shelf

1978 ◽  
Vol 20 (84) ◽  
pp. 509-518 ◽  
Author(s):  
Robert H. Thomas ◽  
Charles R. Bentley
Keyword(s):  
Indirect Evidence ◽  
Melting Rate ◽  
Snow Accumulation ◽  
Surface Strain ◽  
The South ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Average Value ◽  
West Antarctic ◽  
Flow Band

AbstractMeasurements of ice thickness, velocity, snow accumulation rates, and surface strain-rates are used to examine the state of equilibrium of three flow bands of the Ross Ice Shelf. The analysis gives the rate of thickening of the ice shelf in terms of the basal freezing rate, which is unknown. However, indirect evidence suggests that the basal flux ranges from a small value of freezing in the south to a melting rate of about one meter of ice per year at the ice front. If these values are correct then the flow band in the south-east corner of the ice shelf appears to be thickening at an average value of (34 ± 15) cm of ice per year. Persistent thickening at this rate must lead to grounding of large areas of the ice shelf. This would restrict drainage from West Antarctic ice streams which feed this part of the ice shelf and these would tend to thicken and advance their grounding lines into the ice shelf. Further north, near the RISP bore-hole site, the ice shelf is probably in equilibrium. The largest flow band is to the south and east of Roosevelt Island, and this also may be in equilibrium if there is significant bottom melting from ice shelf that is more than 100 km from the ice front.

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 Sources And Movement of Icebergs in the South-West Ross Sea, Antarctica

1989 ◽  
Vol 12 ◽  
pp. 85-88 ◽  
Author(s):  
Harry Keys ◽  
Dennis Fowler
Keyword(s):  
Small Proportion ◽  
Ross Sea ◽  
The South ◽  
Ice Shelf ◽  
Sea Floor ◽  
Ross Ice Shelf ◽  
South West ◽  
Fast Ice ◽  
Western Side ◽  
Coastal Strip

The shape, surface features, composition, and thickness of icebergs trapped annually in a 200 km long coastal strip of fast ice have been examined to determine their sources and movement. The thin western ice front of the Ross Ice Shelf seems to produce about 40% of the icebergs while local glaciers produce the remainder. The ice-shelf icebergs are carried west towards Ross Island then north up the western side of the Ross Sea. A small proportion of them gets trapped mainly by grounding on shallow areas of the sea floor which protrude across the regional long-shore currents.

scholarly journals Enhanced Moisture Delivery into Victoria Land, East Antarctica During the Early Last Interglacial: Implications for West Antarctic Ice Sheet Stability

2021 ◽  
Author(s):  
Yuzhen Yan ◽  
Nicole E. Spaulding ◽  
Michael L. Bender ◽  
Edward J. Brook ◽  
John A. Higgins ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Cores ◽  
Snow Accumulation ◽  
East Antarctica ◽  
Ice Age ◽  
Accumulation Rates ◽  
Last Interglacial ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Victoria Land

Abstract. The S27 ice core, drilled in the Allan Hills Blue Ice Area of East Antarctica, is located in Southern Victoria Land ~80 km away from the present-day northern edge of the Ross Ice Shelf. Here, we utilize the reconstructed accumulation rate of S27 covering the Last Interglacial (LIG) period between 129 and 116 thousand years before present (ka) to infer moisture transport into the region. The accumulation rate is based on the ice age-gas age differences calculated from the ice chronology, which is constrained by the stable water isotopes of the ice, and an improved gas chronology based on measurements of oxygen isotopes of O2 in the trapped gases. The peak accumulation rate in S27 occurred at 128.2 ka, near the peak LIG warming in Antarctica. Even the most conservative estimate yields a six-fold increase in the accumulation rate in the LIG, whereas other Antarctic ice cores are typically characterized by a glacial-interglacial difference of a factor of two to three. While part of the increase in S27 accumulation rates must originate from changes in the large-scale atmospheric circulation, additional mechanisms are needed to explain the large changes. We hypothesize that the exceptionally high snow accumulation recorded in S27 reflects open-ocean conditions in the Ross Sea, created by reduced sea ice extent and increased polynya size, and perhaps by a southward retreat of the Ross Ice Shelf relative to its present-day position near the onset of LIG. The proposed ice shelf retreat would also be compatible with a sea-level high stand around 129 ka significantly sourced from West Antarctica. The peak in S27 accumulation rates is transient, suggesting that if the Ross Ice Shelf had indeed retreated during the early LIG, it would have re-advanced by 125 ka.

scholarly journals Large-scale rheology of the Ross Ice Shelf, Antarctica, computed by a control method

1997 ◽  
Vol 24 ◽  
pp. 43-48 ◽  
Author(s):  
Vincent Rommelaere ◽  
Douglas R. MacAyeal
Keyword(s):  
Large Scale ◽  
Control Method ◽  
Equilibrium Equations ◽  
Ice Shelf ◽  
The West ◽  
Ross Ice Shelf ◽  
Stress Equilibrium ◽  
West Antarctic ◽  
Flow Law ◽  
Basal Melting

Measurements made during the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS, 1973–78) are used to determine the large-scale rheological conditions of the Ross Ice Shelf, Antarctica. Our method includes a numerical ice-shelf model based on the stress-equilibrium equations and control theory. We additionally perform a few tests on simplified geometries to investigate the precision of our method. Our results consist of a map of the depth-averaged viscosity of the central part of the Ross Ice Shelf to within an uncertainty of 20%. We find that the viscosity variations are consistent with Glen’s flow law. Application of a more realistic flow law in our study provides little enhancement of ice-shelf model accuracy until uncertainties associated with basal melting conditions and with temperature profiles at inflow boundaries are addressed. Finally, our results suggest a strong viscosity anomaly in the west-central part of the ice shelf, which is interpreted to be associated with changes in the dynamics of Ice Stream A or B at least 1000 years ago. This feature conforms to the prevailing notion that the West Antarctic ice streams are unsteady.

scholarly journals The Unsteady State of The Ross Ice Shelf (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 339
Author(s):  
Charles R. Bentley
Keyword(s):  
Ice Cores ◽  
Secular Change ◽  
Supporting Evidence ◽  
Ice Shelf ◽  
Outlet Glacier ◽  
Thickness Change ◽  
Ross Ice Shelf ◽  
Input Flux ◽  
Entire Flow ◽  
Flow Band

According to our present picture, the Ross Ice Shelf is subject to relatively rapid changes, perhaps constantly out of steady state, but not undergoing a long-term secular change. Recent supporting evidence comes from a flow band of ice extending from the edges of Beardmore Glacier as far as Nimrod Glacier. The boundaries of that band and of ice stemming from several individual glaciers within it have been traced on airborne radar records. Using measurements made as part of the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS) program, mass-flux variations along the bands have been calculated. The band from Nimrod Glacier, a major outlet glacier from the East Antarctic inland ice sheet, shows no significant deviations from zero for the sum of thence thickness change rate ∂H/∂t and bottom melt rate. ḃH. We interpret this to mean that ∂H/∂t and ḃH are separately small. Significant flux variations in the entire flow band are then attributed to relatively large variations in input flux from the alpine glaciers of the Transantarctic Mountains, and from zones between the glaciers. Although flux variations are not coherent between individual glacier bands, the average strengths of internal reflections (from bottom crevasses and/or included moraine), exhibit a semi-coherent variation with a period of 400 a that correlates with 180 variations in ice cores from Dome C and Byrd station.

scholarly journals The Recent Advance of the Ross Ice Shelf Antarctica

1986 ◽  
Vol 32 (112) ◽  
pp. 464-474 ◽  
Author(s):  
S. S. Jacobs ◽  
D. R. Macayeal ◽  
J. L. Ardai
Keyword(s):  
Large Scale ◽  
Melting Rate ◽  
Spreading Rate ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Front Position ◽  
Iceberg Calving ◽  
Basal Melting ◽  
Available Information

AbstractThe seaward edge of the Ross Ice Shelf advanced northward at a minimum average velocity of 0.8 km a–1 between 1962 and 1985. That advance approximated velocities that have been obtained from glaciological data, indicating little recent wastage by iceberg calving. West of long. 178° E., the ice shelf has attained its most northerly position in the past 145 years, and has not experienced a major calving episode for at least 75 years. Since 1841 the ice-front position has advanced and retreated within a zone from about lat. 77° 10’S. (near long. 171° E.) to lat. 78° 40’ S. (near long. 164° W.). The central ice front is now farthest south but has the highest advance rate. Calving may occur at more frequent intervals in that sector, which also overlies the warmest ocean currents that flow into the sub-ice-shelf cavity. Available information on ice-shelf advance, thickness, spreading rate, and surface accumulation indicates a basal melting rate around 3 m a–1 near the ice front. These data and independent estimates imply that basal melting is nearly as large a factor as iceberg calving in maintaining the ice-shelf mass balance. In recent years, the Ross, Ronne, and Filchner Ice Shelves have contributed few icebergs to the Southern Ocean, while projections from a contemporaneous iceberg census are that circumpolar calving alone may exceed accumulation on the ice sheet. Large-scale ice-shelf calving may have preceded historical sightings of increased numbers of icebergs at sea.

scholarly journals Force, Mass, and Energy Budgets of the Crary Ice Rise Complex, Antarctica

1987 ◽  
Vol 33 (114) ◽  
pp. 218-230 ◽  
Author(s):  
D.R. Macayeal ◽  
R.A. Bindschadler ◽  
S. Shabtaie ◽  
S. Stephenson ◽  
C.R. Bentley
Keyword(s):  
Potential Energy ◽  
Snow Accumulation ◽  
Back Pressure ◽  
Surface Strain ◽  
Surface Velocity ◽  
Pressure Force ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Stream ◽  
Work Done

AbstractResistive force exerted by the Crary Ice Rise on its ice-shelf/ice-stream environment and back-pressure force transmitted across the grounding lines of Ice Streams A and B are calculated from airborne radio echo-sounding data and measurements of surface strain-rates. Resistance generated by the ice rise ranges in magnitude between 45 and 51% of the back-pressure force on the ice streams (depending on the flow law). The mechanical-energy budget of the ice rise is computed by considering work done against frictional forces at the perimeter of the ice rise and gravitational potential energy fluxes associated with changing mass distribution in the ice/ocean system. Energy dissipated by flow surrounding the ice rise is balanced by potential energy released within Ice Streams A and B, and accounts for between 15 and 49% of the work done by the ice streams against ice-shelf back pressure at their grounding lines. Mass balance of the ice rise, and the discharge of Ice Streams A and B, are calculated from surface-velocity and snow-accumulation measurements. The ice rise and its immediate environment gain mass by advection and snowfall at a rate equivalent to an area-averaged thickening rate of 0.44 ± 0.06 m/year. This mass gain may be balanced by regional basal melting (which we do not measure), or could contribute to ice-rise expansion through regional thickening and ice-shelf grounding. Approximately 1/4 to 1/2 of the excess volume discharged by Ice Streams A and B above snow accumulation in their catchment areas is deposited in the vicinity of the ice rise (or melted from the bottom of the ice shelf). This suggests that the ice rise may have formed as a consequence of recent ice-stream acceleration, and that its continued growth may eventually reverse this trend of ice-stream discharge.

scholarly journals A Reconsideration of the Mass Balance of a Portion of the Ross Ice Shelf, Antarctica

1984 ◽  
Vol 30 (106) ◽  
pp. 381-384 ◽  
Author(s):  
Kenneth C. Jezek ◽  
Charles R. Bentley
Keyword(s):  
Mass Balance ◽  
Small Region ◽  
Volume Element ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
The North ◽  
Ice Velocity ◽  
Flow Band ◽  
Input Gate ◽  
North Western

AbstractThe identification of a small region of grounded ice in the north-western sector of the Ross Ice Shelf has forced a re-evaluation of the mass-balance calculations carried out by Thomas and Bentley (1978). Those authors concluded that the Ross Ice Shelf up-stream of Crary Ice Rise was thickening, but they did not take into account the effects on the velocity field of grounded ice (of which they were unaware), which is located near the input gate to their volume element. Reasonable estimates of the degree to which the ice velocity just up-stream of the grounded ice is diminished indicate that it is no longer possible to conclude that the ice shelf is thickening using Thomas and Bentley’s original flow band. Therefore, a new flow band was chosen which was grid east of Thomas and Bentley’s band and unaffected by any nearby grounded areas. The mass balance in this flow band was found to be zero within experimental error; a difference exceeding about 0.2 m a−1 in magnitude between the thickening and bottom freeze-on rates is unlikely.

scholarly journals Isostatic Equilibrium Grounding Line Between The West Antarctic Ice Sheet And The Ross Ice Shelf

1979 ◽  
Vol 24 (90) ◽  
pp. 500 ◽  
Author(s):  
C. R. Bentley ◽  
L. Greischar
Keyword(s):  
Ice Sheet ◽  
Shelf Area ◽  
Ice Shelf ◽  
Ice Streams ◽  
West Antarctic Ice Sheet ◽  
Ross Ice Shelf ◽  
Isostatic Rebound ◽  
West Antarctic ◽  
Grounding Line ◽  
Eastern Half

Abstract Taking various retreat-rates for the presumed grounded ice sheet in the Ross embayment during Wisconsin time, as calculated by Thomas (Thomas and Bentley, 1978), and assuming a time constant of 4400 years for isostatic rebound, a sea-floor uplift of 100±50 m still to be expected in the grid western part of the Ross Ice Shelf can be calculated. The expected uplift diminishes from grid west to grid east, and is probably negligible in the eastern half of the shelf area. There are extensive areas near the present grounding line where the water depth beneath the shelf is less than 100 m, so that uplift would lead to grounding. As grounding occurred, the neighboring ice shelf would thicken, causing grounding to advance farther. This process would probably extend the grounding line to a position running grid north-eastward across the shelf from the seaward end of Roosevelt Island, deeply indented by the extensions of the present ice streams. Floating ice would remain in the grid south-eastern half of the shelf.

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