Tidal Modulation of a Lateral Shear Margin: Priestley Glacier, Antarctica

Abstract

We use high resolution, ground-based observations of ice displacement to investigate ice deformation across the floating left-lateral shear margin of Priestley Glacier, Terra Nova Bay, Antarctica. Bare ice conditions allow us to fix survey marks directly to the glacier surface. A combination of continuous positioning of a local reference mark, and repeat positioning of a network of 33 stakes installed across a 2 km width of the shear margin are used to quantify shear strain rates and the ice response to tidal forcing over an 18-day period. Along-flow velocity observed at a continuous Global Navigation Satellite Systems (GNSS) station within the network varies by up to ∼30% of the mean speed (±28 m a−1) over diurnal tidal cycles, with faster flow during the falling tide and slower flow during the rising tide. Long-term deformation in the margin approximates simple shear with a small component of flow-parallel shortening. At shorter timescales, precise optical techniques allow high-resolution observations of across-flow bending in response to the ocean tide, including across-flow strains on the order of 10–5. An elastodynamic model informed by the field observations is used to simulate the across-flow motion and deformation. Flexure is concentrated in the shear margin, such that a non-homogeneous elastic modulus is implied to best account for the combined observations. The combined pattern of ice displacement and ice strain also depends on the extent of coupling between the ice and valley sidewall. These conclusions suggest that investigations of elastic properties made using vertical ice motion, but neglecting horizontal displacement and surface strain, will lead to incorrect conclusions about the elastic properties of ice and potentially over-simplified assumptions about the sidewall boundary condition.

A framework for time-dependent ice sheet uncertainty quantification, applied to three West Antarctic ice streams

“…The advection of colder tributary glacier ice onto the ice shelf is well represented by the vast expanses of stiffer ice originating at the grounding line and extending downstream for tens of kilometres (see panels c and d of Fig. 3), whereas observed deformation patterns at the shear margins (Khazendar et al, 2011;Still et al, 2022) suggest the presence of weaker deformable ice, where the prominent formation of crevasses occurs. Thus, we keep an auto-covariance length scale l β(0) for β equal to 1 km in all prior configurations, as crevasses can be present within that length scale.…”

“…From the literature (Pattyn, 2010;Khazendar et al, 2011;Still et al, 2022) we know that the spatial pattern of the ice stiffness is not uncorrelated. The advection of colder tributary glacier ice onto the ice shelf is well represented by the vast expanses of stiffer ice originating at the grounding line and extending downstream for tens of kilometres (see panels c and d of Fig.…”

A framework for time-dependent Ice Sheet Uncertainty Quantification, applied to three West Antarctic ice streams

“…The advection of colder tributary glacier ice onto the ice shelf is well represented by the vast expanses of stiffer ice originating at the grounding line and extending downstream for tens of kilometers (see panels c and d of Fig. 3), whereas observed deformation patterns at the shear margins (Khazendar et al, 2011;Still et al, 2022) suggest the presence of weaker deformable ice, where the prominent formation of crevasses occur. Thus we keep an auto-covariance length scale l β(0) for β equal to 1 km in all prior configurations, as crevasses can be present within that length scale.…”

“…From the literature (Pattyn, 2010;Khazendar et al, 2011;Still et al, 2022) we know that the spatial pattern of the ice stiffness is not uncorrelated. The advection of colder tributary glacier ice onto the ice shelf is well represented by the vast expanses of stiffer ice originating at the grounding line and extending downstream for tens of kilometers (see panels c and d of Fig.…”