Bed Roughness Impact on Streaming Ice-Flow Persistence

Abstract:

Paleo-subglacial beds reveal detailed records of former ice-flow and grounding-line behavior, particularly since the Last Glacial Maximum, and constrain subglacial processes and conditions that influence ice behavior. Here, we utilize high-resolution bathymetry from Pine Island Bay, Antarctica to explore spatial variability in bed roughness (i.e., vertical changes in bed topography across a given area or horizontal distance) in locations where sufficient bedforms allow for the determination of ice-flow direction and the continuity of flow paths.

We quantify bed roughness along 1-D transects using standard deviation and Fast Fourier Transform methods. Additionally, 2-D bathymetric grids allow continuous quantification of bed roughness. We assess the impact of transect orientation and spacing and spatial resolution to determine the scales of topography and orientation with respect to ice-flow direction that are important for roughness values.

Streamlined bedforms occur where bed roughness is relatively minimal, which has implications for the relationship between bed roughness and bedform occurrence, as well as the persistence of streaming ice flow pathways across relatively smooth beds. Higher roughness for orthogonal versus parallel transects suggest that bed roughness is modulated by glacial erosion and sediment deposition in the along ice-flow direction. This supports the potential for enhanced basal friction when ice flow deviates from dominant ice-flow pathways.

We assess the systematic impact of bed roughness on ice flow by comparing findings from Pine Island Bay with other paleo-subglacial beds on the Antarctic continental shelf. The persistence (or lack thereof) in ice-flow pathways across beds with contrasting topography will be a valuable test of whether spatially variable basal drag should be parameterized in numerical ice-sheet models.