Abstract
Englacial radar reflectors in the ablation zone of the Greenland Ice Sheet are derived from layering deposited in the accumulation zone over past millennia. The original layer structure is distorted by ice flow toward the margin. In a simplified case, shear and normal strain incurred between the ice divide and terminus should align depositional layers such that they closely approximate particle paths through the ablation zone where horizontal motion dominates. It is unclear, however, if this relationship holds in western Greenland where complex bed topography, three dimensional ice flow, and historical changes to ice sheet mass and geometry since layer deposition may promote a misalignment between present-day layer orientation and the modern ice flow field. We investigate this problem using a suite of analyses that leverage ice sheet models and observational datasets. Our findings suggest that across a study sector of western Greenland, the radiostratigraphy of the ablation zone is closely aligned with englacial particle paths, and is not far departed from a state of balance. The englacial radiostratigraphy thus provides insight into the modern, local, internal flow field, and may serve to further constrain ice sheet models that simulate ice dynamics in this region.
Highlights
As ice sheets accumulate mass, surfaces are buried which define discrete internal layers
See Supplementary Material for visualizations of the deformed strain ellipsoid in the transverse vertical plane and map view, which further emphasize how ice deformation yields structures aligned with ice flow near the margin (Supplementary Figure 1)
The subhorizontal layers of the ablation zone correspond to initially subhorizontal layering in the accumulation zone, but elements reaching the ablation zone have been rotated counter-clockwise by nearly 90◦ and stretched out one and a half times
Summary
As ice sheets accumulate mass, surfaces are buried which define discrete internal layers. Buried surfaces have contrasting dielectric permittivity, which are revealed by ice penetrating radar due to discrete acid layers from volcanic aerosol deposition (Millar, 1981; Hempel et al, 2000), density contrasts, and differing crystal fabric orientation (Fujita et al, 1999). The hundreds of thousands of kilometers of airborne radar data collected over the Greenland Ice Sheet (GrIS) (Leuschen, 2011), document this internal architecture, the radiostratigraphy, providing insights into historical and current ice sheet conditions. Radargrams have been used to calculate historical accumulation rates (Waddington et al, 2007; Karlsson et al, 2014), illuminate strain history (MacGregor et al, 2016), characterize englacial drainage (Catania et al, 2008), quantify geothermal heat flux (Fahnestock et al, 2001) and constrain
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