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

Echelmeyer, Κ. A.; Harrison, W. D.; Larsen, Curtis E.; Mitchell, J. E.

doi:10.3189/s0022143000012417

Cited by 68 publications

(121 citation statements)

References 34 publications

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“…Several studies indicate that longitudinal coupling at the grounding line is less important than previously supposed [Hindmarsh, 1993;Whillans and Van der Veen, 1993;Echelmeyer et al, 1994;Bentley, 1997]. A further argument for ignoring the ice shelf is that if the grounded part of a marine ice sheet is sufficiently described by the shallow ice approximation (SIA [Hutter, 1983]), in which the gravitational driving stresses are exclusively balanced by local vertical stress gradients, then longitudinal stresses are not significant and coupling with the shelf can not be important .…”

Section: Introductionmentioning

confidence: 95%

Assessing the ability of numerical ice sheet models to simulate grounding line migration

2005

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[1] Grounding line migration is a key process affecting the stability of marine ice sheets such as the West Antarctic ice sheet (WAIS). Grounding line motion is often included in numerical models simulating the past and future evolution of the WAIS; however, little attention has been paid to the numerical consistency of these models. The aim of this paper is to assess the ability of simple versions of existing marine ice sheet models to simulate grounding line migration. In particular, we investigate the response of the grounding line to external forcing and the sensitivity of the models' predictions to their numerics and the mechanical coupling between ice sheet and shelf. From the model comparison, there is no consensus on how the grounding line should react to changes in boundary conditions. A crucial finding is the strong dependency of models using a fixed grid on numerical details such as the horizontal grid size. This implies that we should be very wary about grounding line predictions from such models. Including mechanical coupling at the grounding line does not seem to change the qualitative behavior of the models. This suggests that the way the grounding line is treated in marine ice sheet models dominantly determines the grounding line dynamics. We find that models that employ a moving grid to explicitly track the grounding line do not share many of the deficiencies of the fixed grid models. We conclude that at present, no reliable model of the grounding line is available, and further model development is urgently needed.Citation: Vieli, A., and A. J. Payne (2005), Assessing the ability of numerical ice sheet models to simulate grounding line migration,

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Section: Introductionmentioning

confidence: 95%

Assessing the ability of numerical ice sheet models to simulate grounding line migration

2005

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“…In order to take account of the effects of crystal orientation, a flow enhancement factor was incorporated in our calculations of ice deformation within the enhanced flow tributaries [Dahl-Jensen, 1985;Jacka and Budd, 1989;Van der Veen, 1999]. Estimates of enhancement factors vary widely [e.g., Dahl-Jensen, 1985;Echelmeyer et al, 1994;Van der Veen and Whillans, 1994]. Here, we assume a maximum reasonable enhancement factor of 8 in the enhanced flow tributaries, in order to put a minimum bound on basal motion occurring there [Jacka and Budd, 1989;Van der Veen, 1999].…”

Section: Discussionmentioning

confidence: 99%

Basal topography and ice flow in the Bailey/Slessor region of East Antarctica

et al. 2003

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An airborne radio‐echo sounding campaign carried out in the upper reaches of Bailey Ice Stream and Slessor Glacier, in Coats Land, East Antarctica, has revealed that tributaries of enhanced flow lie within well‐defined basal troughs and are separated from each other by bed highs. These new data indicate significant differences in ice thickness compared with those estimated in the Bedmap database. A numerical modeling study has revealed that driving stresses are high enough to account for flow by ice deformation alone in intertributary areas. Most flow in the enhanced flow tributaries of Slessor Glacier may also be explained by ice deformation alone. However, although ice deformation is also significant in the Bailey Ice Stream tributary, a large amount of basal motion is also required to fully explain flow velocities here. It is proposed that the trough in which Bailey tributary lies is sufficiently deep that marine sediments may have accumulated here in preglacial times. Along with water produced by geothermal heating, frictional heating, and through a reduction in the pressure melting point, basal motion may therefore be facilitated by the presence of a deformable, saturated till layer at the bed.

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“…In some places off the Unicorn, bottom crevasses offer the most viable explanation for deep diffractions [Novick and Bentley, 1990;Jacobel et al, 2000]; perhaps they could also form (or have formed before the margin shift) on the Unicorn, although the conditions are less than ideal. In some cases, it may be that strain heating within a shear margin caused a core of temperate ice with a small percentage of internal water to form [Echelmeyer et al, 1994;Jacobson and Raymond, 1998]; we believe this is the most likely explanation for the asymmetric amplitude.…”

Section: Morainal Debrismentioning

confidence: 99%

Evidence for a recently abandoned shear margin adjacent to ice stream B2, Antarctica, from ice‐penetrating radar measurements

Clarke¹,

Liu²,

Lord³

et al. 2000

J. Geophys. Res.

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Abstract. Satellite imagery of the area between ice streams B1 and B2, Antarctica, shows a lineation on the surface of the ice sheet of uncertain origin. Ice motion in the area (2 m yr-•) is 2 orders of magnitude slower than that of the surrounding streams and shows no significant variation that could explain the feature. A low-power, high-resolution radar system was used to image the upper 80 m of the ice sheet between the two ice streams; the survey shows that the lineation is associated with what is likely an abandoned shear margin. The radar data show that a set of chaotic diffractors lies buried beneath two thirds of the area, while the remaining one third is undisturbed to 80 m depth. The chaotic ice ends abruptly along a boundary that is parallel to, but offset 2.5 km from, the surface lineation. Also, isolated linear diffractors are commonly observed in the otherwise undisturbed ice immediately adjacent to the boundary. The depth, location, orientation, and curved form of the diffractors strongly suggest they are the tops of crevasses that were active at the time the chaotic ice was being strained and that they were formed by leftlateral shear. This is the same sense of shear that is presently active in the B2 margin, 6 km away. The depth to the chaotic diffractors suggests that the shear margin abandoned its prior position -190 years B.P.; the burial depth decreases toward the B2 margin and suggests a migration rate of -100 m yr -•. In addition, a separate high-power radar system was used to image the entire thickness of the ice sheet (-1 km) in the same area. These data show numerous linear diffractors near the base of the ice sheet. It is very likely that at least some of these diffractors are entrained morainal debris. Others may be bottom crevasses or zones of wet, reflective ice that developed in the high-strain environment of the now-abandoned shear margin. IntroductionThe ice streams that drain West Antarctica into the Ross Ice Shelf carry 20-25% of the total outflow and thus form an important ingredient to understanding the dynamics and stability of the West Antarctic ice sheet as a whole (Figure 1 Figures 2a and 2b). The interstream ridge is commonly referred to as the "Unicorn" (Figures 1 and 2 Two separate radar systems were used to image the ice sheet. The first was a low-power impulse-type system that provided high-resolution images of the upper 80 m of the ice sheet. The second was a high-power modulated-type system, which provided images of the entire depth of the kilometerthick ice sheet at low resolution. The purpose of the highresolution radar survey was to image both near-surface and 13,409

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

Cited by 68 publications

References 34 publications

Assessing the ability of numerical ice sheet models to simulate grounding line migration

Assessing the ability of numerical ice sheet models to simulate grounding line migration

Basal topography and ice flow in the Bailey/Slessor region of East Antarctica

Evidence for a recently abandoned shear margin adjacent to ice stream B2, Antarctica, from ice‐penetrating radar measurements

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