Recent change in ice thickness in Windless Bight, Ross Ice Shelf, Antarctica?

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.

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Tabular Icebergs: Implications from Geophysical Studies of Ice Shelves

Journal of Glaciology ◽

10.3189/s0022143000005037 ◽

1982 ◽

Vol 28 (100) ◽

pp. 413-430 ◽

Cited By ~ 6

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.

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Ice Movement Studies on the Skelton Glacier

Journal of Glaciology ◽

10.3189/s0022143000027258 ◽

1961 ◽

Vol 3 (29) ◽

pp. 873-878

Author(s):

Charles R. Wilson ◽

A. P. Crary

Keyword(s):

Ross Sea ◽

Ice Thickness ◽

Strain Rates ◽

Shelf Area ◽

Dry Valleys ◽

Ice Shelf ◽

The West ◽

Ross Ice Shelf ◽

High Plateau ◽

Plateau Area

The volume of ice that flows annually from the Skelton Glacier on the west side of the Ross Ice Shelf between the Worcester and Royal Society Ranges was determined during 1958–59 traverse operations to be approximately 791 × 106 m.3 or 712 × 106 m.3 water equivalent. Annual accumulation on the Skelton névé field and small cirque glaciers is estimated to be 1,018 × 106 m.3 water equivalent, but this figure can be reduced to 712 × 106 m.3 by assuming that 30 per cent of the expected accumulation in the lower slopes of the glacier is lost to adjacent areas of the Ross Ice Shelf by katabatic winds. It is evident that little or no contribution to the nourishment of the Skelton Glacier comes from the high plateau area of East Antarctica. It is suggested that this condition exists generally in the western Ross Sea and Ross Shelf area, and is responsible for the existence of the present “dry” valleys in the McMurdo Sound area.Some estimates of local ice regime are made at two sites on the glacier where ice thickness and strain rates are known.

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A comparison of satellite-altimetry and ice-thickness measurements of the Ross Ice Shelf, Antarctica

Annals of Glaciology ◽

10.1017/s0260305500016694 ◽

1994 ◽

Vol 20 ◽

pp. 357-364 ◽

Cited By ~ 13

Author(s):

Bamber Jonathan ◽

Bentley Charles r

Keyword(s):

Measurement Errors ◽

Satellite Altimetry ◽

Altimeter Data ◽

Ice Thickness ◽

Correlated Errors ◽

Ice Shelf ◽

Height Measurement ◽

Ross Ice Shelf ◽

In Situ Data ◽

Radio Echo Sounding

The launch of ERS-l provides coverage, by satellite altimetry, of a large part of the Ross Ice Shelf ineluding areas of input from Byrd Glacier and Ice Streams D and E. Five 35 d repeats of fast-delivery data, comprising approximately 100000 height estimates, have been used to produce a Digital Elevation Model (DEM) of the Ross Icc Shelf north of 81.5° S. Careful filtering of the altimeter data, which removed about 30% of the measurements, ensured that only valid values were used. The data were grldded to produce a DEM with a cell size of 10km. Repeatability of the data was assessed from an analysis of crossing points of ascending and descending tracks. The rms cross-over difference for the ice shelf was 0.94 m. Using the five repeat tracks gave a random error of 0.30 m for an averaged height measurement. Regionally correlated errors in the orbit and geoid add a systematic long wavelength bias of approximately 2m to the final elevation estimate. Two of the latest geoid models, OSU91-A and JGMI, were compared with the available in situ data and hYdrostatic models based on ice and water densities.The altimetry was compared with ice-thickness data from Ross Icc Shelf Geophysical and Glaciological Survey (RIGGS) stations and Scott Polar Research Institute radio-echo-sounding surveys undertaken in the 1970s. Differences between the DEM and heights calculated from ice thicknesses and a standard density -depth equation lie, in general, within the combined measurement errors. There are, however, several areas where this is not the case. Prominent north-south stripes of different ice thickness shown on a RIGGS map apparently do not exist. Low elevations are associated with high-density ice draining from East Antarctic outlet glaciers. The grounding line of Icc Streams D and E and an ice plain behind it are clearly demarcated by the break in surface slope. Grounded ice north of Steershead is also observed

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Geometry and ice dynamics of the Darwin–Hatherton glacial system, Transantarctic Mountains

Journal of Glaciology ◽

10.1017/jog.2017.60 ◽

2017 ◽

Vol 63 (242) ◽

pp. 959-972

Author(s):

METTE K. GILLESPIE ◽

WENDY LAWSON ◽

WOLFGANG RACK ◽

BRIAN ANDERSON ◽

DONALD D. BLANKENSHIP ◽

...

Keyword(s):

Ice Sheet ◽

Ice Thickness ◽

Ice Shelf ◽

Ice Dynamics ◽

Ross Ice Shelf ◽

Basal Ice ◽

Grounding Line ◽

Ice Flows ◽

Ice Velocity ◽

The Mean

ABSTRACTThe Darwin–Hatherton Glacial system (DHGS) connects the East Antarctic Ice Sheet (EAIS) with the Ross Ice Shelf and is a key area for understanding past variations in ice thickness of surrounding ice masses. Here we present the first detailed measurements of ice thickness and grounding zone characteristics of the DHGS as well as new measurements of ice velocity. The results illustrate the changes that occur in glacier geometry and ice flux as ice flows from the polar plateau and into the Ross Ice Shelf. The ice discharge and the mean basal ice shelf melt for the first 8.5 km downstream of the grounding line amount to 0.24 ± 0.05 km3 a−1 and 0.3 ± 0.1 m a−1, respectively. As the ice begins to float, ice thickness decreases rapidly and basal terraces develop. Constructed maps of glacier geometry suggest that ice drainage from the EAIS into the Darwin Glacier occurs primarily through a deep subglacial canyon. By contrast, ice thins to <200 m at the head of the much slower flowing Hatherton Glacier. The glaciological field study establishes an improved basis for the interpretation of glacial drift sheets at the link between the EAIS and the Ross Ice Sheet.

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The calving and drift of iceberg B-9 in the Ross Sea, Antarctica

Antarctic Science ◽

10.1017/s0954102090000335 ◽

1990 ◽

Vol 2 (3) ◽

pp. 243-257 ◽

Cited By ~ 40

Author(s):

Harry (J.R.) Keys ◽

S.S. Jacobs ◽

Don Barnett

Keyword(s):

Ocean Circulation ◽

Ross Sea ◽

Maximum Velocity ◽

Open Water ◽

Ice Thickness ◽

Ice Shelf ◽

East Central ◽

North West ◽

Ross Ice Shelf ◽

Subsurface Current

Major rifts is the Ross Ice Shelf controlled the October 1987 calving of the 154 × 35 km “B-9” iceberg, one of the longest on record. The 2000 km, 22 month drift of this iceberg and the quite different tracks of smaller bergs that calved with it have extended our understanding of the ocean circulation in the Ross Sea. B-9 initially moved north-west for seven months until deflected southward by a subsurface current which caused it to collide with the ice shelf in August 1988. It then completed a 100 km-radius gyre on the east-central shelf before resuming its north-westerly drift. Based upon weekly locations, derived from NOAA-10 and DMSP satellite and more frequent ARGOS data buoy positions, B-9 moved at an average speed of 2.4 km day−1 over the continental shelf. It was not grounded there at any time, but cast a large shadow of open water or reduced ice thickness during the austral winters. B-9 was captured by the continental slope current in May 1989, and attained a maximum velocity of 13 km day−1 before breaking into three pieces north of Cape Adare in early August 1989.

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Ice-thickness Patterns and the Dynamics of the Ross Ice Shelf, Antarctica

Journal of Glaciology ◽

10.1017/s0022143000014805 ◽

1979 ◽

Vol 24 (90) ◽

pp. 287-294 ◽

Cited By ~ 81

Author(s):

Charles R. Bentley ◽

John W. Glough ◽

Kenneth C. Jezek ◽

Sion Shabtaie

Keyword(s):

Large Scale ◽

Rapid Change ◽

Thickness Variation ◽

Ice Thickness ◽

Ice Shelf ◽

Mountain Glacier ◽

Ross Ice Shelf ◽

Scale Turbulence ◽

Thickness Variations ◽

Ice Water

AbstractAs part of the Ross Ice Shelf Geophysical and Glaciological Survey, a detailed map of ice thickness has been produced from airborne radar measurements closely tied to the network of survey stations on the ice-shelf surface. The map, drawn with a 20 m contour interval, reveals a highly complex pattern of thickness variations reflecting presumably, at least in part, complex ice-shelf dynamics. Many features of the thickness variation pattern appear to be associated with zones of grounded ice, but not all. Features of interest include many ice thickness minima, with closures up to 120m; a narrow, greatly elongated ridge-trough system 450 km or more in length; a few ice thickness maxima; steep regional gradients of 10 m/km in freely floating ice; highly contorted contours suggesting a large-scale “turbulence”; and at least two remarkable step-like changes in ice thickness. The irregularity of many of these features suggests dynamic non-equilibrium, i.e. the existence of transients in the dynamic system, so that the ice shelf as a whole suggests a state of rather rapid change. Flow-bands constructed on the basis of the strengths of the echo from the ice-water interface clearly delineate the outflow from the main East Antarctic outlet glaciers in the grid eastern part of the shelf. A discontinuous flow band originating in a small mountain glacier (Robb Glacier) suggests a variable mesoclimate in the vicinity of the glacier within the last thousand years. Strong reflections near the ice front suggest bottom melting of saline ice previously frozen on to the underside of the ice. Several rifts or incipient rifts in the ice shelf characteristically show two lateral bands of strong reflections with a non-reflecting zone in between.

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

Annals of Glaciology ◽

10.1017/s0260305500003074 ◽

1982 ◽

Vol 3 ◽

pp. 341 ◽

Cited By ~ 1

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.

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Thinning and Grounding-Line Retreat on Ross Ice Shelf, Antarctica

Annals of Glaciology ◽

10.3189/s0260305500006492 ◽

1988 ◽

Vol 11 ◽

pp. 165-172 ◽

Cited By ~ 6

Author(s):

R. H. Thomas ◽

S. N. Stephenson ◽

R. A. Bindschadler ◽

S. Shabtaie ◽

C. R. Bentley

Keyword(s):

Snow Accumulation ◽

Gravity Potential ◽

Ice Thickness ◽

Ice Shelf ◽

Ross Ice Shelf ◽

Major Activity ◽

Ice Stream ◽

Grounding Line ◽

Ice Stream B ◽

Basal Melting

Detailed measurements of surface topography, ice motion, snow accumulation, and ice thickness were made in January 1974 and again in December 1984, along an 8 km stake network extending from the ice sheet, across the grounding line, and on to floating ice shelf in the mouth of slow-moving Ice Stream C, which flows into the eastern side of Ross Ice Shelf, Antarctica. During the 11 years between surveys, the grounding line retreated by approximately 300 m. This was caused by net thinning of the ice shelf, which we believe to be a response to the comparatively recent, major decrease in ice discharge from Ice Stream C. Farther inland, snow accumulation is not balanced by ice discharge, and the ice stream is growing progressively thicker.There is evidence that the adjacent Ice Stream B has slowed significantly over the last decade, and this may be an early indication that this fast-moving ice stream is about to enter a period of stagnation similar to that of Ice Stream C. Indeed, these large ice streams flowing from West Antarctica into Ross Ice Shelf may oscillate between periods of relative stagnation and major activity. During active periods, large areas of ice shelf thicken and run aground on seabed to form extensive “ice plains” in the mouth of the ice stream. Ultimately, these become too large to be pushed seaward by the ice stream, which then slows down and enters a period of stagnation. During this period, the grounding line of the ice plain retreats, as we observe today in the mouth of Ice Stream C, because nearby ice shelf, no longer compressed by ice-stream motion, progressively thins. At the same time, water within the deformable till beneath the ice starts to freeze on to the base of the ice stream, and snow accumulation progressively increases the ice thickness. A new phase of activity would be initiated when the increasing gravity potential of the ice stream exceeds the total resistance of the shrinking ice plain and the thinning layer of deformable till at the bed. This could occur rapidly if the effects of the shrinking ice plain outweigh those of the thinning (and therefore stiffening) till. Otherwise, the till layer would finally become completely frozen, and the ice stream would have to thicken sufficiently to initiate significant heating by internal deformation, followed by basal melting and finally saturation of an adequate thickness of till; this could take some thousands of years.

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