The West Antarctic Ice Sheet: Instability, disintegration, and initiation of Ice Ages

Hughes, Terence J.

doi:10.1029/rg013i004p00502

Cited by 170 publications

(105 citation statements)

References 62 publications

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“…There is considerable disagreement concerning the current state of equilibrium of the West Antarctic ice sheet. Hughes ( 1975) suggested that the ice sheet may be collapsing, and measurements of surface strain-rate that were made near the ice-sheet summit have been interpreted as indicating thinning of perhaps a few centimetres per year (Whillans, 1973(Whillans, , 1977Hughes, 1973;Thomas, 1976) . There is poor agreement between the various estimates of thinning-rate because of lack of information on the behavior of deep ice, and errors are difficult to assess since the result is rather sensitive to errors in the strain-rate measured perpendicular to the flow direction.…”

Section: The Stability Of the West Antarctic Ice Sheetmentioning

confidence: 99%

The Dynamics of Marine Ice Sheets

Thomas

1979

J. Glaciol.

189

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ABSTRACT. Marine ice sh eets rest on land that, for the most part, is below sea-level. Ice that flows across the grounding line, where the ice sheet becomes a float, either calves into icebergs or forms a floating ice shelf joined to the ice sheet. At the grounding line there is a transition from ice-sheet dynamics to ice-shelf dynamics, and the creep-thinning rate in this region is very sensitive to sea depth; rising sea-level causes increased thinning-rates a nd grounding-line retreat, falling sea-level has the reverse effect . If the bedrock slopes down towards the centre of the ice sheet there may be only two stable modes: a freely-floating ice shelf or a ma rine ice sheet that extends to the edge of the continental shelf. Once started, collapse of such an ice sheet to form a n ice shelf may take place extremely rapidly. Ice sh elves which form in embayments of a marine ice sh eet, or which are partially grounded, have a stabilizing influence since ice flowing across the grounding line has to push the ice shelf past its sides. Retreat of the grounding line tends to enlarge the ice shelf, which ultimately may become large enough to prevent excessive outflow from the ice sheet so that a new equilibrium grounding line is established ; removal of the ice shelf would allow r etreat to continue. During the late-Wisconsin glacial maximum there may have been marine ice sheets in the northern hemisphere but the only current exa mple is the W est Antarctic ice sh eet. This is buttressed by the Ross and Ronne Ice Shelves, and if clima tic warming were to prohibit the ex isten ce of these ice shelves then the ice sheet would collapse. Field observations suggest that, a t present, the ice sh eet may be advancing into parts of the R oss I ce Shelf. Such advance, however, would not ensure the secu rity of the ice sh eet since ice streams that dra in to the north appear to fl ow directly into the sea with little or no ice shelf to buttress them. If these ice streams do not flow over a sufficiently high bedrock sill then they provide the most likely avenues for ice-sh eet retreat. R EsuME. La dynamique des calottes glaciaires marines. L es calottes glaciaires marines resposent sur un sol qui, pour la plus gran de part est en dessous du ni veau de la mer. La glace qui s'ecoule a travers la ligne d e decollem ent, lorsq ue la glace commence a flotter, soit vele en icebergs soit form e une cou verture de glace qui se raccorde a la calotte glaciaire. A la lign e de decollement il y a un e transition de la dynamique des calottes a celle des plateformes d e glace, et I'amin cissement dli au mouvement des glaces dans cette region est tres sensible a la profondeur d e la mer; si le niveau marin s'eleve, la vitesse de I'amincissement s'accroit et la ligne d e decollement recul e, un e baisse du niveau des mers a I'effet inverse. Si la pente du lit rocheux descend vers le centre de la calotte gl aciaire il ne peut y avoir que d eux etats stables : une plateforme flottant librement ou une calotte glacia ire marine qui s'etend jusqu'a l...

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Section: The Stability Of the West Antarctic Ice Sheetmentioning

confidence: 99%

The Dynamics of Marine Ice Sheets

Thomas

1979

J. Glaciol.

189

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“…Hughes, 1975) . These ice streams are often highly crevassed and they move at speeds which are 2-3 orders of magnitude greater than the ice sheet in which they are embedded.…”

Section: Introductionmentioning

confidence: 99%

The role of the margins in the dynamics of an active ice stream

et al. 1994

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ABSTRACT. A transverse profile of velocity was measured across Ice Stream B, West Antarctica, in order to determine the role of the margins in the force balance of an active ice stream. The profile extended from near the ice-stream center line, through a marginal shear zone and on to the slow-moving ice sheet. The velocity profile exhibits a high degree of shear d eformation within a marginal zone, where intense, chaotic crevassing occurs. Detailed analysis of the profile, using analytical and numerical models of ice flow, leads to the following conclusions regarding the roles of the bed and the margins in ice-stre a m dynamics: While the exact quantitative values leading to these conclusions are somewhat model and location-dependent, th e overall conclusions are robust. As such, they are likely to have importa nce for ice-strea m dynamics in gen eral.

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“…I). This was attributed by Hughes (1975) to partial uncoupling of the base of the ice stream from its bed in the presence of large amounts of basal melt water. The stress-continuity requirement at the grounding line (Equation (9.2')) can be rewritten as an expression for the surface curvature on the ice-stream side of the grounding line by substitution of Equation (18):…”

Section: Discussionmentioning

confidence: 99%

“…If the bedrock depth increases inland from the grounding line, a rise in sea-level, for example, may lift a part of the ice stream free of its bed and effectively float the marginal zone of the ice stream, causing the grounding line to retreat inland to a region of greater ice thicknesses. Because of the strong dependence of the creep rate at the grounding line on ice thickness (Weertman, 1957), ice discharge at the grounding line will increase, resulting in down-draw of the ice-sheet surface in the drainage basin of the ice stream, a decrease in basal shear stress, and thus an acceleration of the collapse of the marine ice sheet (Hughes, 1975(Hughes, , 1981. These are all positive feed-back mechanisms that will amplify the initial perturbation.…”

Section: Clima Tological Role Of Ice Sheetsmentioning

confidence: 99%

“…Ice shelves are in hydrostatic equilibrium with the ocean; the junction between the ice shelf and the ice stream, where the ice stream first becomes afloat, is the grounding line. It has been suggested (Hughes, 1973(Hughes, , 1975Weertman, 1974) that marine ice sheets are inherently unstable and cannot exist at steady state . While a terrestrial ice sheet interacts directly only with the atmosphere, a marine 'ice sheet is also in contact with the ocean and responds to changes in oceanic temperatures, circulation , and sea-level.…”

Section: Introductionmentioning

confidence: 99%

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A Coupled Marine Ice-Stream – Ice-Shelf Model

Muszynski

Birchfield

1987

J. Glaciol.

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ABSTRACT. Evidence as to the potential roles of marine ice flows in the dramatic climatological changes which have occurred from the late Pleistocene to the present is reviewed, indicating the need for careful modeling studies to evaluate several crucial hypotheses. A scale analysis of the flow of a marine ice stream coupled to a freely floating ice shelf is presented, in two dimensions and ignoring thermodynamic effects. With these limitations, the most important control of the dynamics of the ice stream is associated with first-order buoyancy effects related to the density contrast bp/ pw between ice and sea-water. It is shown that longitudinal stretching, arising from large gradients in basal sliding velocity, dominates shearing deformation provided the aspect ratio w 2 « bp/ pw' The buoyancy control is established through the necessity of having continuously varying longitudinal strain-rates in the neighborhood of the grounding line.The scale analysis is the basis for derivation of a simplified model of a fast-flowing ice stream coupled to a freely floating ice shelf. The distance in the ice stream upstream from the grounding line over which the above dynamic regime extends is estimated and found to be relatively insensitive to the basal sliding velocity and to the rheological constant of ice. A further potentially important feed-back mechanism between ice stream and ice shelf is associated with buoyancy corrections to the longitudinal deviatoric stress field.

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The West Antarctic Ice Sheet: Instability, disintegration, and initiation of Ice Ages

Cited by 170 publications

References 62 publications

The Dynamics of Marine Ice Sheets

The Dynamics of Marine Ice Sheets

The role of the margins in the dynamics of an active ice stream

A Coupled Marine Ice-Stream – Ice-Shelf Model

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