Freeze-on limits bed strength beneath sliding glaciers

Area of Science:

• Glaciology
• Earth Science
• Climate Science

Background:

• Glacier discharge from sliding outlet glaciers is a key factor in sea level rise projections.
• Current models often overpredict driving stresses using shear-thinning rheology, particularly in dynamic sliding regions.
• Thermo-mechanical interactions at the glacier bed are crucial for balancing driving stresses in sliding areas.

Purpose of the Study:

• To investigate the factors controlling basal strength in sliding glaciers.
• To explain the observed range of driving stresses in glacial systems.
• To understand the mechanisms of ice-sediment interaction at the glacier bed.

Main Methods:

• Analysis of gravitational driving stresses across glacial areas.
• Comparison of bed strength with threshold effective stress, considering ice-liquid surface energy and till pore size.
• Modeling of thermo-mechanical interactions and basal freeze-on processes.

Main Results:

• Median bed strength is comparable to a threshold effective stress determined by ice-liquid surface energy and till pore size.
• Ice infiltration into sediment occurs above this threshold, forming debris-rich basal ice layers, even during net melting.
• Heterogeneous freeze-on enhances basal roughness, explaining the narrow range of inferred bed strengths and mechanical resistance to sliding.

Conclusions:

• Basal strength, not just ice rheology, is critical for understanding glacier dynamics and sea level contributions.
• Ice-sediment interactions, including debris-rich basal ice formation, are governed by a critical effective stress threshold.
• Heterogeneous freeze-on plays a significant role in regulating basal sliding and overall glacier discharge.