Subglacial bed form morphology controlled by ice speed and sediment thickness

Barchyn, Thomas E.; Dowling, Thomas; Stokes, Chris R.; Hugenholtz, Chris H.

doi:10.1002/2016gl069558

Cited by 41 publications

(54 citation statements)

References 45 publications

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“…An observed MSGL pattern could be created by many different ice stream characteristics. This challenges the assertion that MSGL characteristics may, at some point, be inverted for paleo ice‐flow characteristics [ Barchyn et al , ]. MSGL evolution may be affected by pattern coarsening, a phenomenon already suggested for the formation of dunes [e.g., Fourrière et al , ].…”

Section: Discussionmentioning

confidence: 97%

“…MSGLs could also be the product of sediment deformation [ Boulton , ; Clark , ]. The pressure‐gradient hypothesis suggests that MSGLs are formed through gradients in ice pressure over deforming sediment, with MSGLs emerging from an uneven bed as a result of stoss side erosion and lee side deposition into cavities [ Barchyn et al , ]. Finally, the groove‐plowing hypothesis invokes erosion via basal ice keels plowing through soft sediment [ Tulaczyk et al , ; Clark et al , ].…”

Section: Discussionmentioning

confidence: 99%

“…Whereas the lack of a topographical break between adjacent MSGLs is evident in ice stream bed topography (Figure ), the extent to which MSGLs are spatially organized (i.e., regular) remains unclear. Spatial organization can have important implications for hypotheses of their formation [ Barchyn et al , ], with some predicting that MSGLs evolve via the amplification of initial perturbations that leads to a topography characterized by dominant wavelengths [ Fowler , ; Fowler and Chapwanya , ].…”

Section: Introductionmentioning

confidence: 99%

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The periodic topography of ice stream beds: Insights from the Fourier spectra of mega‐scale glacial lineations

et al. 2017

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Ice stream bed topography contains key evidence for the ways ice streams interact with, and are potentially controlled by, their beds. Here we present the first application of two‐dimensional Fourier analysis to 22 marine and terrestrial topographies from 5 regions in Antarctica and Canada, with and without mega‐scale glacial lineations (MSGLs). We find that the topography of MSGL‐rich ice stream sedimentary beds is characterized by multiple, periodic wavelengths between 300 and 1200 m and amplitudes from decimeters to a few meters. This periodic topography is consistent with the idea that instability is a key element to the formation of MSGL bedforms. Dominant wavelengths vary among locations and, on one paleo ice stream bed, increase along the direction of ice flow by 1.7 ± 0.52% km−1. We suggest that these changes are likely to reflect pattern evolution via downstream wavelength coarsening, even under potentially steady ice stream geometry and flow conditions. The amplitude of MSGLs is smaller than that of other fluvial and glacial topographies but within the same order of magnitude. However, MSGLs are a striking component of ice stream beds because the topographic amplitude of features not aligned with ice flow is reduced by an order of magnitude relative to those oriented with the flow direction. This study represents the first attempt to automatically derive the spectral signatures of MSGLs. It highlights the plausibility of identifying these landform assemblages using automated techniques and provides a benchmark for numerical models of ice stream flow and subglacial landscape evolution.

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The periodic topography of ice stream beds: Insights from the Fourier spectra of mega‐scale glacial lineations

et al. 2017

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“…Explicit comparisons have rarely been made, but the ice–bed interface is analogous to the ‘boundary layer’ in fluvial and aeolian environments, where shear stresses (both basal and lateral in the case of ice streams) oppose the flow of the overlying medium. This analogy extends further because processes within the boundary layer create a distinctive geomorphology that is characterised by subglacial bedforms that resemble features created in fluvial and aeolian environments (Shaw ; Fisher and Shaw, ; Shaw et al ., ; Clark, ; Barchyn et al ., ; Ely et al ., ).…”

Section: Introductionmentioning

confidence: 99%

Geomorphology under ice streams: Moving from form to process

Stokes

2017

Earth Surf Processes Landf

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Ice streams are integral components of an ice sheet's mass balance and directly impact on sea level. Their flow is governed by processes at the ice-bed interface which create landforms that, in turn, modulate ice stream dynamics through their influence on bed topography and basal shear stresses. Thus, ice stream geomorphology is critical to understanding and modelling ice streams and ice sheet dynamics. This paper reviews developments in our understanding of ice stream geomorphology from a historical perspective, with a focus on the extent to which studies of modern and palaeo-ice streams have converged to take us from a position of near-complete ignorance to a detailed understanding of their bed morphology. During the 1970s and 1980s, our knowledge was limited and largely gleaned from geophysical investigations of modern ice stream beds in Antarctica. Very few palaeo-ice streams had been identified with any confidence. During the 1990s, however, glacial geomorphologists began to recognise their distinctive geomorphology, which included distinct patterns of highly elongated mega-scale glacial lineations, ice stream shear margin moraines, and major sedimentary depocentres. However, studying relict features could say little about the time-scales over which this geomorphology evolved and under what glaciological conditions. This began to be addressed in the early 2000s, through continued efforts to scrutinise modern ice stream beds at higher resolution, but our current understanding of how landforms relate to processes remains subject to large uncertainties, particularly in relation to the mechanisms and time-scales of sediment erosion, transport and deposition, and how these lead to the growth and decay of subglacial bedforms. This represents the next key challenge and will require even closer cooperation between glaciology, glacial geomorphology, sedimentology, and numerical modelling, together with more sophisticated methods to quantify and analyse the anticipated growth of geomorphological data from beneath active ice streams.

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“…Conversely, the latter is consistent with a 'sitespecific' view whereby each drumlin forms in isolation from its neighbours. Data and findings answering these questions should guide the development of theory or could be used to test numerical process-models that are both starting to make quantitative predictions and to yield three-dimensional model simulation movies of bedform organization, evolution and migration (Chapwanya et al, 2011;Barchyn et al, 2016). Do we need to explain the development of the individual bump (the drumlin) or the wavelength (spacing) and relief of the undulating surface; the drumlin field?…”

Section: Introductionmentioning

confidence: 99%

Spatial organization of drumlins

Clark

Ely

Spagnolo

et al. 2017

Earth Surf Processes Landf

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Ice-sheets flowing over soft sediments produce undulations in the bed, typically of metres in relief, of which drumlins are the most abundant and widely investigated. Consensus regarding their mechanism of formation has yet to be achieved. In this paper we examine the spatial organization of drumlins in order to provide an improved description of the phenomenon and to guide hypotheses of their formation. We review the literature highlighting contradictory findings regarding drumlin spatial organization and then use this to motivate our study based on a large sample (42 488) of drumlins from Canada, Britain and Norway. Are there typical arrangements in drumlin positioning and are they organized in a regular spatial manner (patterned) or are they distributed randomly? We recognize that drumlin fields are inherently patchy and therefore apply inhomogeneous spatial statistics in order to study their distribution. This shows that whilst drumlins are occasionally randomly placed, their main state is non-random. They exhibit a strong and statistically significant signal of regularity across lengths scales of 100 to 1200 m. We conclude that patterning is a near ubiquitous property of drumlins. This finding of regularity demonstrates spatial self-organization in the bedforming process with drumlins as an emergent manifestation of sub-glacial sediment mobility. Kilometre-scale interactions between drumlins must occur as they evolve, or interactions may arise as a consequence of growth or migration. Hypotheses or models are required that can explain the regular spacing of drumlins. We highlight three suggestions for such self-organization: instability in the coupling of ice flowsediment flux-bed shape; local feedback between sediment mobility and relief; and coarsening by growth or migration.

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Subglacial bed form morphology controlled by ice speed and sediment thickness

Cited by 41 publications

References 45 publications

The periodic topography of ice stream beds: Insights from the Fourier spectra of mega‐scale glacial lineations

The periodic topography of ice stream beds: Insights from the Fourier spectra of mega‐scale glacial lineations

Geomorphology under ice streams: Moving from form to process

Spatial organization of drumlins

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