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

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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Tabular Icebergs: Implication from Geophysical Studies of Ice Shelves

Annals of Glaciology ◽

10.3189/s0260305500016967 ◽

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.

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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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Tabular Icebergs: Implications from Geophysical Studies of Ice Shelves

Journal of Glaciology ◽

10.1017/s0022143000005037 ◽

1982 ◽

Vol 28 (100) ◽

pp. 413-430 ◽

Cited By ~ 45

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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A Case Study of a Ross Ice Shelf Airstream Event: A New Perspective*

Monthly Weather Review ◽

10.1175/2009mwr2880.1 ◽

2009 ◽

Vol 137 (11) ◽

pp. 4030-4046 ◽

Cited By ~ 31

Author(s):

Daniel F. Steinhoff ◽

Saptarshi Chaudhuri ◽

David H. Bromwich

Keyword(s):

Large Scale ◽

Model Performance ◽

Thermal Infrared ◽

Integrated Approach ◽

Cloud Formation ◽

Synoptic Scale ◽

Ice Shelf ◽

Low Level ◽

Ross Ice Shelf

Abstract A case study illustrating cloud processes and other features associated with the Ross Ice Shelf airstream (RAS), in Antarctica, is presented. The RAS is a semipermanent low-level wind regime primarily over the western Ross Ice Shelf, linked to the midlatitude circulation and formed from terrain-induced and large-scale forcing effects. An integrated approach utilizes Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery, automatic weather station (AWS) data, and Antarctic Mesoscale Prediction System (AMPS) forecast output to study the synoptic-scale and mesoscale phenomena involved in cloud formation over the Ross Ice Shelf during a RAS event. A synoptic-scale cyclone offshore of Marie Byrd Land draws moisture across West Antarctica to the southern base of the Ross Ice Shelf. Vertical lifting associated with flow around the Queen Maud Mountains leads to cloud formation that extends across the Ross Ice Shelf to the north. The low-level cloud has a warm signature in thermal infrared imagery, resembling a surface feature of turbulent katabatic flow typically ascribed to the RAS. Strategically placed AWS sites allow assessment of model performance within and outside of the RAS signature. AMPS provides realistic simulation of conditions aloft but experiences problems at low levels due to issues with the model PBL physics. Key meteorological features of this case study, within the context of previous studies on longer time scales, are inferred to be common occurrences. The assumption that warm thermal infrared signatures are surface features is found to be too restrictive.

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

Journal of Glaciology ◽

10.1017/s0022143000000502 ◽

1990 ◽

Vol 36 (124) ◽

pp. 350-351

Author(s):

G. Delisle

Keyword(s):

Recent Change ◽

Ice Thickness ◽

Ice Shelf ◽

Ross Ice Shelf

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An ice-shelf model test based on the Ross Ice Shelf, Antarctica

Annals of Glaciology ◽

10.1017/s0260305500013240 ◽

1996 ◽

Vol 23 ◽

pp. 46-51 ◽

Cited By ~ 47

Author(s):

D. R. MacAyeal ◽

V. Rommelaere ◽

P. Huybrechts ◽

C. L. Hulbe ◽

J. Determann ◽

...

Keyword(s):

Finite Element ◽

Finite Difference ◽

Large Scale ◽

Finite Difference Methods ◽

Equilibrium Equations ◽

Ice Shelf ◽

Ross Ice Shelf ◽

Stress Equilibrium ◽

Flow Features ◽

Large Scale Flow

A standard numerical experiment featuring the Ross Ice Shelf, Antarctica, is presented as a test package for the development and intercomparison of ice-shelf models. The emphasis of this package is solution of stress-equilibrium equations for an ice-shelf velocity consistent with present observations. As a demonstration, we compare five independently developed ice-shelf models based on finite-difference and finite-element methods. Our results suggest that there is little difference between finite-element and finite-difference methods in capturing the basic, large-scale flow features of the ice shelf. We additionally show that the fit between model and observed velocity depends strongly on the ice-shelf temperature field, for which there is presently little observational control. The main differences between model results are due to the equations being solved, the boundary conditions at the ice from and the discretization method (finite element vs finite difference).

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

Annals of Glaciology ◽

10.3189/s0260305500011915 ◽

1997 ◽

Vol 24 ◽

pp. 43-48 ◽

Cited By ~ 13

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.

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The Effects of Basal Melting on the Present Flow of the Ross Ice Shelf, Antarctica

Journal of Glaciology ◽

10.1017/s0022143000006900 ◽

1986 ◽

Vol 32 (110) ◽

pp. 72-86 ◽

Cited By ~ 46

Author(s):

D.R. MacAyeal ◽

R.H. Thomas

Keyword(s):

Large Scale ◽

Oceanic Circulation ◽

Ice Shelf ◽

Ice Streams ◽

Ross Ice Shelf ◽

Flow And Heat Transfer ◽

Improve Model ◽

Dependent Flow ◽

Basal Melting ◽

Shelf Flow

AbstractWe use a hybrid finite-element/finite-difference model of ice-shelf flow and heat transfer to investigate the effects of basal melting on the present observed flow of the Ross Ice Shelf, Two hypothetical basal melting scenarios are compared: (i) zero melting everywhere and (ii) melting sufficient to balance any large-scale patterns of ice-shelf thickening that would otherwise occur. As a result of the temperature-dependent flow law (which we idealize as having a constant activation energy of 120 kJ mol−1, a scaling coefficient of 1.3 N m−2s1/3, and an exponent of 3), simulated ice-shelf velocities for the second scenario are reduced by up to 20% below those of the first. Our results support the hypothesis that melting patterns presently maintain ice thickness in steady state and conform to patterns of oceanic circulation presently thought to ventilate the sub-ice cavity. Differences between the simulated and observed velocities are too large in the extreme south-eastern quarter of the ice shelf to permit verification of either basal melting scenario. These differences highlight the need to improve model boundary conditions at points where ice streams feed the ice shelf and where the ice shelf meets stagnant grounded ice.

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