Ice sheet grounding zone stabilization due to till compaction

Abstract

[1] Based on modeling motivated by new GPS and radioecho sounding surveys, a few-kilometers-long zone of Whillans Ice Stream, West Antarctica, just inland of the grounding line has higher basal shear stress than the ice farther upstream or the freely slipping ice shelf downstream. Data from this zone show a few-meter-high upwarp of the surface overlying a large fold extending through all internal radar layers observed. Flowband modeling shows that the fold can be generated by decreased basal lubrication beneath the upwarp. Basal topography alone cannot create this fold. Physical modeling and available data suggest that lowamplitude tidal flexure of the ice shelf extends a few kilometers inland. Downward flexing of this grounded ice from the rising tide would compact subglacial till, resulting in higher basal shear stress. This result suggests that important processes influencing grounding line stability are not included in modern whole-ice-sheet models. Citation: Christianson,

Active subglacial lakes and channelized water flow beneath the Kamb Ice Stream

“…The KIS trunk estuary shows some similarities to the WIS trunk estuary reported by Horgan et al (2013) and Christianson et al (2013), i.e., similarities in the shapes of the estuaries, potential saddles dividing the estuaries from upstream potential lows and upstream subglacial lakes which probably supply subglacial water into the estuaries. However, the KIS trunk estuary is located on the upstream side of the current grounding line and has higher hydraulic potentials (300-500 kPa), indicating that it is entirely grounded at present; whereas the estuary downstream of the WIS, with almost 0 kPa potential, is probably exchanging water and sediment across the grounding zone through viscoelastic flexure induced by tidal forcing.…”

Radiostratigraphy and age structure of the Greenland Ice Sheet

“…Low bed slopes in these regions are qualitatively consistent with observations of lower bed roughness there, particularly for Petermann Glacier [ Rippin , ]. The lack of bed‐conforming radiostratigraphy in these regions suggests strong and long‐term organization of ice flow that is consistent with pattern of surface velocity [ Joughin et al ., ] and may be further modulated by spatiotemporal variation in basal friction [e.g., Hindmarsh et al ., ; Christianson et al ., , ]. This pattern is distinct from observations of some Antarctic glaciers that contain disrupted radiostratigraphy, which has been interpreted as evidence of fast ice flow in the past [e.g., Catania et al ., ; Rippin et al ., ].…”

“…Having traced the radiostratigraphy using the methods described above, we then seek to date these observed reflections. While inferences regarding ice sheet dynamics from reflection morphology alone are valuable [e.g., Conway et al ., ; Catania et al ., ; Hindmarsh et al ., ; Rippin et al ., ; Catania and Neumann , ; Campbell et al ., ; Christianson et al ., ; Sime et al ., ], the value of traced reflections can increase substantially if they are also dated [e.g., Whillans , ; Fahnestock et al ., ; Baldwin et al ., ; Dahl‐Jensen et al ., ; Buchardt , ; Medley et al ., ]. Hence, we seek to date as many traced reflections as possible, even those that do not intersect an ice core and are not continuous.…”

Projections of Future Sea Level Contributions from the Greenland and Antarctic Ice Sheets: Challenges Beyond Dynamical Ice Sheet Modeling

“…Higher order (HO) models include additional stresses to allow stress transmission across floating and grounded ice, while Full-Stokes (FS) models resolve all stresses. Adapted from Pattyn et al (2006) of the nature of the underlying bed (Christianson et al, 2013) and the evolution in properties of basal conditions (Gillet-Chaulet et al, 2016). Such processes and understanding are starting to be implemented in regional ISMs and should be more systematically included in future simulations.…”