Elastic dynamics and tidal migration of grounding lines modify subglacial lubrication and melting

Sayag, Roiy; Worster, M. Grae

doi:10.1002/2013gl057942

Cited by 57 publications

(98 citation statements)

References 30 publications

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“…The model does not take into account feedback between ice flexure and water pressure. water pressure and it has been suggested that this mechanism could pump brackish water upstream (Walker et al, 2013;Sayag and Worster, 2013). This flexure may have the additional effect of opening crevasses beneath the ice or dilating the subglacial till, leading to changes in local water storage and thereby altering the distribution of water.…”

Section: Discussionmentioning

confidence: 99%

Temporal variations in the flow of a large Antarctic ice stream controlled by tidally induced changes in the subglacial water system

2015

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Abstract. Observations show that the flow of Rutford IceStream (RIS) is strongly modulated by the ocean tides, with the strongest tidal response at the 14.77-day tidal period (M sf ). This is striking because this period is absent in the tidal forcing. A number of mechanisms have been proposed to account for this effect, yet previous modelling studies have struggled to match the observed large amplitude and decay length scale. We use a nonlinear 3-D viscoelastic fullStokes model of ice-stream flow to investigate this open issue. We find that the long period M sf modulation of icestream velocity observed in data cannot be reproduced quantitatively without including a coupling between basal sliding and tidally induced subglacial water pressure variations, transmitted through a highly conductive drainage system at low effective pressure. Furthermore, the basal sliding law requires a water pressure exponent that is strongly nonlinear with q = 10 and a nonlinear basal shear exponent of m = 3. Coupled model results show that sub-ice shelf tides result in a ∼ 12 % increase in mean horizontal velocity of the adjoining ice stream. Observations of tidally induced variations in flow of ice streams provide stronger constraints on basal sliding processes than provided by any other set of measurements.

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Section: Discussionmentioning

confidence: 99%

Temporal variations in the flow of a large Antarctic ice stream controlled by tidally induced changes in the subglacial water system

2015

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“…, representing a relatively stiff bed (Sayag and Worster, 2013) to avoid complicating our results with soft till effects. At the GL ice is pinned to the bed such that the GL cannot migrate, in accordance with DInSAR analysis that shows no GL migration at this site (Wild and others, 2017).…”

Section: Methodsmentioning

confidence: 99%

On the interpretation of ice-shelf flexure measurements

et al. 2017

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ABSTRACT. Tidal flexure in ice shelf grounding zones has been used extensively in the past to determine grounding line position and ice properties. Although the rheology of ice is viscoelastic at tidal loading frequencies, most modelling studies have assumed some form of linear elastic beam approximation to match observed flexure profiles. Here we use density, radar and DInSAR measurements in combination with full-Stokes viscoelastic modelling to investigate a range of additional controls on the flexure of the Southern McMurdo Ice Shelf. We find that inclusion of observed basal crevasses and density dependent ice stiffness can greatly alter the flexure profile and yet fitting a simple elastic beam model to that profile will still produce an excellent fit. Estimates of the effective Young's modulus derived by fitting flexure profiles are shown to vary by over 200% depending on whether these factors are included, even when the local thickness is well constrained. Conversely, estimates of the grounding line position are relatively insensitive to these considerations for the case of a steep bed slope in our study region. By fitting tidal amplitudes only, and ignoring phase information, elastic beam theory can provide a good fit to observations in a wide variety of situations. This should, however, not be taken as an indication that the underlying rheological assumptions are correct.

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“…Sayag and Worster (2013) explored this process using elastic beam theory and found that changes in overburden pressure of the ice over a tidal cycle could lead to a hydrological barrier that acts as a control on subglacial hydrology.…”

Section: Overview Of Previous Studiesmentioning

confidence: 99%

Insights into ice stream dynamics through modelling their response to tidal forcing

2014

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Abstract. The tidal forcing of ice streams at their ocean boundary can serve as a natural experiment to gain an insight into their dynamics and constrain the basal sliding law. A nonlinear 3-D viscoelastic full Stokes model of coupled ice stream ice shelf flow is used to investigate the response of ice streams to ocean tides. In agreement with previous results based on flow-line modelling and with a fixed grounding line position, we find that a nonlinear basal sliding law can qualitatively reproduce long-period modulation of tidal forcing found in field observations. In addition, we show that the inclusion of lateral drag, or allowing the grounding line to migrate over the tidal cycle, does not affect these conclusions. Further analysis of modelled ice stream flow shows a varying stress-coupling length scale of boundary effects upstream of the grounding line. We derive a viscoelastic stresscoupling length scale from ice stream equations that depends on the forcing period and closely agrees with model output.

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Elastic dynamics and tidal migration of grounding lines modify subglacial lubrication and melting

Cited by 57 publications

References 30 publications

Temporal variations in the flow of a large Antarctic ice stream controlled by tidally induced changes in the subglacial water system

Temporal variations in the flow of a large Antarctic ice stream controlled by tidally induced changes in the subglacial water system

On the interpretation of ice-shelf flexure measurements

Insights into ice stream dynamics through modelling their response to tidal forcing

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