Characteristics of the deforming bed: till properties on the deglaciated Antarctic continental shelf

• Published in: Journal of Glaciology
• Main Authors: ANNA RUTH W. HALBERSTADT, LAUREN M. SIMKINS, JOHN B. ANDERSON, LINDSAY O. PROTHRO, PHILIP J. BART
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press 2018
• Subjects: glacial geomorphology; glacial tills; ice dynamics; subglacial processes; Environmental sciences; GE1-350; Meteorology. Climatology; QC851-999; Antarctic; Ross Sea; Antarc*; Ice Sheet; Journal of Glaciology
• Online Access: https://doi.org/10.1017/jog.2018.92; https://doaj.org/article/299ea2abb75a455b8eceaa944c0a32df

Contemporary ice stream flow is directly linked to conditions at the ice/bed interface, yet this environment is logistically difficult to access. Instead, we investigate subglacial processes important for ice stream flow by studying tills on the deglaciated Antarctic continental shelf. We test currently-accepted hypotheses surrounding subglacial processes and till properties with a Ross Sea dataset. Till shear strengths indicate a continuum of simultaneous processes acting at the bed, rather than discrete ‘deformation’ and ‘lodgement’ end-members. We identify a threshold water content representing saturated pore spaces, leading to basal sliding and meltwater channelization. Based on observations of till properties relative to glacial landforms, we challenge the assumption that low shear strength is linked to intense deformation. Spatial variability in landform morphology reflects variability in deforming processes at the sub-ice stream scale and suggests a maximum deforming bed thickness of 2 m at the grounding line. Regional till properties generally correlate with seafloor geology and deglacial history; the western Ross Sea is characterized by higher and more variable shear strengths and water contents, while lower-shear strength till was preserved in the Eastern Basin. These observations inform till interpretation and provide context for deforming beds beneath the modern ice sheet and on glaciated continental shelves.