Abstract
Abstract. On glaciers and ice sheets, identifying the relationship between velocity and traction is critical to constrain the bed physics that controls ice flow. Yet in Greenland, these relationships remain unquantified. We determine the spatial relationship between velocity and traction in all eight major drainage catchments of Greenland. The basal traction is estimated using three different methods over large grid cells to minimize interpretation biases associated with unconstrained rheologic parameters used in numerical inversions. We find the relationships are consistent with our current understanding of basal physics in each catchment. We identify catchments that predominantly show Mohr–Coulomb-like behavior typical of deforming beds or significant cavitation, as well as catchments that predominantly show rate-strengthening behavior typical of Weertman-type hard-bed physics. Overall, the traction relationships suggest that the flow field and surface geometry of the grounded regions in Greenland is mainly dictated by Weertman-type hard-bed physics up to velocities of approximately 450 m yr−1, except within the Northeast Greenland Ice Stream and areas near floatation. Depending on the catchment, behavior of the fastest-flowing ice (∼ 1000 m yr−1) directly inland from marine-terminating outlets exhibits Weertman-type rate strengthening, Mohr–Coulomb-like behavior, or is not confidently resolved given our methodology. Given the complex basal boundary across Greenland, the relationships are captured reasonably well by simple traction laws which provide a parameterization that can be used to model ice dynamics at large scales. The results and analysis serve as a first constraint on the physics of basal motion over the grounded regions of Greenland and provide unique insight into future dynamics and vulnerabilities in a warming climate.
Highlights
For glaciers and ice sheets the relationship between basal motion, basal traction, and the response to external forcing are fundamental to realistic ice flow modeling
The velocity–traction relationships have a large degree of scatter but show increasing velocities result in increasing traction (Figs. 4, S4 – linear scale)
The R2 is high in catchments 3, 4, and 6 through 8 (0.88–0.99) indicating that the power-law model generally describes most of the variability in the binned relationships (Fig. 4, Supplement Table S1) for the shallow-ice approximation (SIA) and shallow-stream approximation (SSA) tractions
Summary
For glaciers and ice sheets the relationship between basal motion, basal traction, and the response to external forcing are fundamental to realistic ice flow modeling. For hard beds basal traction is related to the viscous drag generated as ice slides around bed roughness (Weertman, 1964). Meltwater modulates friction and sliding over hard beds by occupying cavities on the lee side of bedrock bumps (Gagliardini et al, 2007; Lliboutry, 1968; Schoof, 2005), increasing sliding by reducing the apparent roughness of the bedrock. For deformable till beds the traction and occurrence of basal motion primarily depends on the failure strength of the till which acts as a Mohr–Coulomb material (Iverson et al, 1998; Kamb, 1991; Tulaczyk, 1999; Zoet and Iverson, 2020). Meltwater can weaken deformable beds by increasing pore pressures within the till (Iverson et al, 1998, 2003) and induce bed deformation where there was previously none
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
