Surface undulations of Antarctic ice streams tightly controlled by bedrock topography

Full Stokes flow-line models predict that fast-flowing ice streams transmit information about their bedrock topography most efficiently to the surface for basal undulations with length scales between 1 and 20 times the mean ice thickness. This typical behaviour is independent of the precise values of the flow law and sliding law exponents, and should be universally observable. However, no experimental evidence for this important theoretical prediction has been obtained so far, hence ignoring an important test for the physical validity of current-day ice flow models. In our work we use recently acquired airborne radar data for the Rutford Ice Stream and Evans Ice Stream, and we show that the surface response of fast-flowing ice is highly sensitive to bedrock irregularities with wavelengths of several ice thicknesses. The sensitivity depends on the slip ratio, i.e. the ratio between mean basal sliding velocity and mean deformational velocity. We find that higher values of the slip ratio generally lead to a more efficient transfer, whereas the transfer is significantly dampened for ice that attains most of its surface velocity by creep. Our findings underline the importance of bedrock topography for ice stream dynamics on spatial scales up to 20 times the mean ice thickness. Our results also suggest that local variations in the flow regime and surface topography at this spatial scale cannot be explained by variations in basal slipperiness.

[1]  Eric Rignot,et al.  Antarctic grounding line mapping from differential satellite radar interferometry , 2011 .

[2]  G. Gudmundsson Analytical solutions for the surface response to small amplitude perturbations in boundary data in the shallow-ice-stream approximation , 2008 .

[3]  K. Hutter Theoretical Glaciology: Material Science of Ice and the Mechanics of Glaciers and Ice Sheets , 1983 .

[4]  William H. Press,et al.  Numerical Recipes 3rd Edition: The Art of Scientific Computing , 2007 .

[5]  T. Murray,et al.  Rapid erosion, drumlin formation, and changing hydrology beneath an Antarctic ice stream , 2007 .

[6]  H. Corr,et al.  Airborne radio-echo sounding of the Wilkes Subglacial Basin, the Transantarctic Mountains and the Dome C region , 2007 .

[7]  D. Thomson,et al.  Spectrum estimation and harmonic analysis , 1982, Proceedings of the IEEE.

[8]  G. A. Prieto,et al.  A Fortran 90 library for multitaper spectrum analysis , 2009, Comput. Geosci..

[9]  G. Gudmundsson Ice-stream response to ocean tides and the form of the basal sliding law , 2010 .

[10]  Edward C. King,et al.  Formation of mega-scale glacial lineations observed beneath a West Antarctic ice stream , 2009 .

[11]  O. Sergienko The effects of transverse bed topography variations in ice‐flow models , 2012 .

[12]  P. Welch The use of fast Fourier transform for the estimation of power spectra: A method based on time averaging over short, modified periodograms , 1967 .

[13]  S. Tulaczyk,et al.  Positive Mass Balance of the Ross Ice Streams, West Antarctica , 2002, Science.

[14]  R. Alley,et al.  Till beneath ice stream B: 1. Properties derived from seismic travel times , 1987 .

[15]  D. Macayeal,et al.  Basal friction of Ice Stream E, West Antarctica , 1995, Journal of Glaciology.

[16]  Ian Joughin,et al.  Basal shear stress of the Ross ice streams from control method inversions , 2004 .

[17]  G. Gudmundsson,et al.  On the relationship between surface and basal properties on glaciers, ice sheets, and ice streams , 2005 .

[18]  W. Paterson,et al.  The Physics of Glaciers Ed. 4 , 2010 .

[19]  A. Vieli,et al.  Application of control methods for modelling the flow of Pine Island Glacier, West Antarctica , 2003, Annals of Glaciology.

[20]  R. Armstrong,et al.  The Physics of Glaciers , 1981 .

[21]  D. Vaughan,et al.  The basal roughness of Pine Island Glacier, West Antarctica , 2011, Journal of Glaciology.

[22]  John W. Holt,et al.  New boundary conditions for the West Antarctic ice sheet: Subglacial topography beneath Pine Island Glacier , 2006 .

[23]  A. Gades,et al.  Bed properties of Siple Dome and adjacent ice streams, West Antarctica, inferred from radio-echo sounding measurements , 2000, Journal of Glaciology.

[24]  W. Budd,et al.  Ice Flow Over Bedrock Perturbations , 1970, Journal of Glaciology.

[25]  David M. Holland,et al.  Sensitivity of 21st century sea level to ocean‐induced thinning of Pine Island Glacier, Antarctica , 2010 .

[26]  Matt A. King,et al.  Continued deceleration of Whillans Ice Stream, West Antarctica , 2005 .

[27]  R. Alley,et al.  Seismic measurements reveal a saturated porous layer beneath an active Antarctic ice stream , 1986, Nature.

[28]  S. Tulaczyk,et al.  Estimates of effective stress beneath a modern West Antarctic ice stream from till preconsolidation and void ratio , 2001 .

[29]  R. Arthern,et al.  Initialization of ice-sheet forecasts viewed as an inverse Robin problem , 2010, Journal of Glaciology.

[30]  R. Alley,et al.  Influence of subglacial geology on the position of a West Antarctic ice stream from seismic observations , 1998, Nature.

[31]  B. Kamb Basal Zone of the West Antarctic Ice Streams and its Role in Lubrication of Their Rapid Motion , 2013 .

[32]  Charles R. Bentley,et al.  Timing of stagnation of Ice Stream C, West Antarctica, from short-pulse radar studies of buried surface crevasses , 1993, Journal of Glaciology.

[33]  G. Gudmundsson,et al.  Transmission of basal variability to a glacier surface , 2003 .

[34]  G. Gudmundsson,et al.  Estimating basal properties of ice streams from surface measurements: a non-linear Bayesian inverse approach applied to synthetic data , 2009 .

[35]  Richard B. Alley,et al.  In search of ice-stream sticky spots , 1993, Journal of Glaciology.

[36]  Bamber,et al.  Widespread complex flow in the interior of the antarctic ice sheet , 2000, Science.

[37]  Mélanie Raymond Pralong,et al.  Bayesian estimation of basal conditions on Rutford Ice Stream, West Antarctica, from surface data , 2011, Journal of Glaciology.

[38]  H. Wills,et al.  The Motion of Ice Sheets and Glaciers , 1959, Journal of Glaciology.

[39]  Jonathan L. Bamber,et al.  Basal conditions beneath enhanced-flow tributaries of Slessor Glacier, East Antarctica , 2006 .

[40]  S. Tulaczyk,et al.  Integrating satellite observations with modelling: basal shear stress of the Filcher-Ronne ice streams, Antarctica , 2006, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[41]  Robert N. Swift,et al.  Accelerating ice loss from the fastest Greenland and Antarctic glaciers , 2011 .

[42]  C. Bentley,et al.  Radar reflections reveal a wet bed beneath stagnant Ice Stream C and a frozen bed beneath ridge BC, West Antarctica , 1998 .

[43]  S. Tulaczyk Scale independence of till rheology , 2006, Journal of Glaciology.

[44]  D. Vaughan,et al.  Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets , 2009, Nature.

[45]  G. Gudmundsson,et al.  Estimating basal properties of glaciers from surface measurements , 2006 .

[46]  Eric Rignot,et al.  Recent Antarctic ice mass loss from radar interferometry and regional climate modelling , 2008 .

[47]  T. Murray,et al.  Bedform topography and basal conditions beneath a fast-flowing West Antarctic ice stream , 2009 .

[48]  D. Vaughan,et al.  The internal layering of Pine Island Glacier, West Antarctica, from airborne radar-sounding data , 2009, Annals of Glaciology.