Resolving the internal and basal geometry of ice masses using imaging phase-sensitive radar

Young, Tun Jan; Schroeder, Dustin M.; Christoffersen, Poul; Lok, Lai Bun; Nicholls, Keith W.; Brennan, Paul V.; Doyle, Samuel; Hubbard, Bryn; Hubbard, Alun

doi:10.1017/jog.2018.54

Cited by 31 publications

(39 citation statements)

References 68 publications

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“…With an ice column consisting of Holocene as well as softer Wisconsin‐aged ice, enhanced deformation in the latter, thought to occupy the lowest 150 m of the ice column, should be expected for a glacier flowing over a relatively nondeforming strong bed. The suggestion of highly deformable ice may also explain why internal layers within these regions were difficult to track (Figure ; Young et al, ). The vertical velocity profiles observed in this study are consistent with a high concentration of strain within this highly deforming layer, with colder ice higher up the ice column resembling a “stiff beam,” resisting these stresses (Ryser, Lüthi, Andrews, Catania, et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…Data collected from each deployment were collapsed into one dimension. Further information of the array design used in the field deployments are detailed in supporting information S1 and in Young et al ().…”

Section: Methodsmentioning

confidence: 99%

“…In 2014, the development of a low‐power autonomous pRES (ApRES) allowed long‐term, unattended monitoring of ice‐shelf and ice‐sheet thinning (Nicholls et al, ). Importantly, this new instrument allowed measurement of vertical strain rates on fast‐flowing glaciers and ice streams due to its ability to track unambiguously and continuously the vertical movement of deforming internal layers at sufficiently short time steps (Young et al, ).…”

Section: Introductionmentioning

confidence: 99%

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Physical Conditions of Fast Glacier Flow: 3. Seasonally‐Evolving Ice Deformation on Store Glacier, West Greenland

et al. 2019

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Temporal variations in ice sheet flow directly impact the internal structure within ice sheets through englacial deformation. Large‐scale changes in the vertical stratigraphy within ice sheets have been previously conducted on centennial to millennial timescales; however, intra‐annual changes in the morphology of internal layers have yet to be explored. Over a period of 2 years, we use autonomous phase‐sensitive radio‐echo sounding to track the daily displacement of internal layers on Store Glacier, West Greenland, to millimeter accuracy. At a site located ∼30 km from the calving terminus, where the ice is ∼600 m thick and flows at ∼700 m/a, we measure distinct seasonal variations in vertical velocities and vertical strain rates over a 2‐year period. Prior to the melt season (March–June), we observe increasingly nonlinear englacial deformation with negative vertical strain rates (i.e., strain thinning) in the upper half of the ice column of approximately −0.03 a−1, whereas the ice below thickens under vertical strain reaching up to +0.16 a−1. Early in the melt season (June–July), vertical thinning gradually ceases as the glacier increasingly thickens. During late summer to midwinter (August–February), vertical thickening occurs linearly throughout the entire ice column, with strain rates averaging 0.016 a−1. We show that these complex variations are unrelated to topographic setting and localized basal slip and hypothesize that this seasonality is driven by far‐field perturbations in the glacier's force balance, in this case generated by variations in basal hydrology near the glacier's terminus and propagated tens of kilometers upstream through transient basal lubrication longitudinal coupling.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Physical Conditions of Fast Glacier Flow: 3. Seasonally‐Evolving Ice Deformation on Store Glacier, West Greenland

et al. 2019

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“…Much of the meltwater will ultimately end up in the ocean (Enderlin et al, 2014;Andersen et al, 2015). Along the way, subglacial water and temporal variations in subglacial water flux can significantly influence ice advection by modulating basal sliding resistance (e.g., Zwally et al, 2002;Schoof, 2010;Shannon et al, 2013;Tedstone et al, 2014). (Howat et al, 2014;Morlighem et al, 2017a).…”

Section: Introductionmentioning

confidence: 99%

Basal control of supraglacial meltwater catchments on the Greenland Ice Sheet

2018

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Abstract. Ice surface topography controls the routing of surface meltwater generated in the ablation zones of glaciers and ice sheets. Meltwater routing is a direct source of ice mass loss as well as a primary influence on subglacial hydrology and basal sliding of the ice sheet. Although the processes that determine ice sheet topography at the largest scales are known, controls on the topographic features that influence meltwater routing at supraglacial internally drained catchment (IDC) scales (<10s of km) are less well constrained. Here we examine the effects of two processes on ice sheet surface topography: transfer of bed topography to the surface of flowing ice and thermal–fluvial erosion by supraglacial meltwater streams. We implement 2-D basal transfer functions in seven study regions of the western Greenland Ice Sheet ablation zone using recent data sets for bed elevation, ice surface elevation, and ice surface velocities. We find that ∼1–10 km scale ice surface features can be explained well by bed topography transfer in regions with different multiyear-averaged ice flow conditions. We use flow-routing algorithms to extract supraglacial stream networks from 2 to 5 m resolution digital elevation models and compare these with synthetic flow networks calculated on ice surfaces predicted by bed topography transfer. Multiple geomorphological metrics calculated for these networks suggest that bed topography can explain general ∼1–10 km supraglacial meltwater routing and that thermal–fluvial erosion thus has a lesser role in shaping ice surface topography on these scales. We then use bed topography transfer functions and flow routing to conduct a parameter study predicting how supraglacial IDC configurations and subglacial hydraulic potential would change under varying multiyear-averaged ice flow and basal sliding regimes. Predicted changes to subglacial hydraulic flow pathways directly caused by changing ice surface topography are subtle, but temporal changes in basal sliding or ice thickness have potentially significant influences on IDC spatial distribution. We suggest that changes to IDC size and number density could affect subglacial hydrology primarily by dispersing the englacial–subglacial input of surface meltwater.

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“…These layers are passively advected with flow, recording cumulative deformation of the ice mass (e.g. Ng and Conway, 2004; Siegert and others, 2013; Bingham and others, 2015; Winter and others, 2015; Bons and others, 2016; Young and others, 2018). Isochrones have been interpreted as tracers at ice divides to confirm theoretical ice deformation mechanisms in a relatively simple deformational regime (Raymond, 1983; Vaughan and others, 1999).…”

Section: Introductionmentioning

confidence: 99%

Interpreting englacial layer deformation in the presence of complex ice flow history with synthetic radargrams

2020

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Fast ice flow on the Antarctic continent constitutes much of the mass loss from the ice sheet. However, geophysical methods struggle to constrain ice flow history at depth, or separate the signatures of topography, ice dynamics and basal conditions on layer structure. We develop and demonstrate a methodology to compare layer signatures in multiple airborne radar transects in order to characterize ice flow at depth, or improve coverage of existing radar surveys. We apply this technique to generate synthetic, along-flow radargrams and compare different deformation regimes to observed radargram structure. Specifically, we investigate flow around the central sticky spot of Whillans Ice Stream, West Antarctica. Our study suggests that present-day velocity flowlines are insufficient to characterize flow at depth as expressed in layer geometry, and streaklines provide a better characterization of flow around a basal sticky spot. For Whillans Ice Stream, this suggests that ice flow wraps around the central sticky spot, supported by idealized flow simulations. While tracking isochrone translation and rotation across survey lines is complex, we demonstrate that our approach to combine radargram interpretation and modeling can reveal critical details of past ice flow.

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Resolving the internal and basal geometry of ice masses using imaging phase-sensitive radar

Cited by 31 publications

References 68 publications

Physical Conditions of Fast Glacier Flow: 3. Seasonally‐Evolving Ice Deformation on Store Glacier, West Greenland

Physical Conditions of Fast Glacier Flow: 3. Seasonally‐Evolving Ice Deformation on Store Glacier, West Greenland

Basal control of supraglacial meltwater catchments on the Greenland Ice Sheet

Interpreting englacial layer deformation in the presence of complex ice flow history with synthetic radargrams

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