Streamlined subglacial bedform sensitivity to bed characteristics across the deglaciated Northern Hemisphere

Streamlined subglacial bedforms observed in deglaciated landscapes provide the opportunity to assess the sensitivity of glacier dynamics to bed characteristics across broader spatiotemporal scales than is possible for contemporary glacial systems. While many studies of streamlined subglacial bedforms rely on manual mapping and qualitative (i.e., visual) assessment, we semi-automatically identify 11,628 sedimentary and bedrock bedforms, created during and following the Last Glacial Maximum across nine geologically and topographically diverse deglaciated sites in the Northern Hemisphere. Using this large dataset of landforms and associated morphometrics, we empirically test the importance of subglacial terrain on bedform morphology and ice-flow behavior. A minimum bedform length-width ratio threshold provides a constraint on minimum morphometrics needed for streamlined bedforms to develop. Similarities in bedform metric distribution regardless of bed properties indicate that all bed types may support similar distributions of warm-based ice flow conditions. Ice flow within valleys with easily erodible beds host the most elongate bedforms yet the widest range in bedform elongation and bedform surface relief. The presence of these highly elongate bedforms suggest high ice-flow velocities occur within valley settings despite spatially heterogeneous landform-generating processes. In contrast, lithified sedimentary beds within regions not constrained by topography on the scale of 1-10(2) km contain bedforms with high density and packing, low change in surface relief and low elongation, indicating spatially uniform and organized interactions at the ice-bed interface and consistency in ice-flow velocity. Regardless of genesis, we find a sensitivity of bedform elongation (i.e., used to interpret ice-flow speed or persistence) to topographic conditions on the scale of 1-10(2) km, while bedform density is sensitive to bed lithology. The findings presented in this study provide analogues for processes of subglacial erosion and deposition, ice-bed interactions and warm-based ice flow within contemporary glacial systems.

Automated summary

Streamlined subglacial bedforms in deglaciated landscapes provide insights into glacier dynamics across larger spatial and temporal scales. This study uses a large dataset to examine the importance of subglacial terrain on bedform morphology and ice-flow behavior. The results indicate that the characteristics of the subglacial terrain have an influence on the morphology and velocity of ice flow.