High-resolution distributed vertical strain and velocity from repeat borehole logging by optical televiewer: Derwael Ice Rise, Antarctica

• Published in: Journal of Glaciology
• Main Authors: Bryn Hubbard, Morgane Philippe, Frank Pattyn, Reinhard Drews, Tun Jan Young, Carine Bruyninx, Nicolas Bergeot, Karen Fjøsne, Jean-Louis Tison
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press 2020
• Subjects: Accumulation; ice shelves; ice thickness measurements; mass-balance reconstruction; polar firn; Environmental sciences; GE1-350; Meteorology. Climatology; QC851-999; Antarc*; Antarctica; Ice Shelves; Journal of Glaciology
• Online Access: https://doi.org/10.1017/jog.2020.18; https://doaj.org/article/8a4485fcac1948a9ac58f888bf97bc46

Direct measurements of spatially distributed vertical strain within ice masses are scientifically valuable but challenging to acquire. We use manual marker tracking and automatic cross correlation between two repeat optical televiewer (OPTV) images of an ~100 m-long borehole at Derwael Ice Rise (DIR), Antarctica, to reconstruct discretised, vertical strain rate and velocity at millimetre resolution. The resulting profiles decay with depth, from −0.07 a−1 at the surface to ~−0.002 a−1 towards the base in strain and from −1.3 m a−1 at the surface to ~−0.5 m a−1 towards the base in velocity. Both profiles also show substantial local variability. Three coffee-can markers installed at different depths into adjacent boreholes record consistent strain rates and velocities, although averaged over longer depth ranges and subject to greater uncertainty. Measured strain-rate profiles generally compare closely with output from a 2-D ice-flow model, while the former additionally reveal substantial high-resolution variability. We conclude that repeat OPTV borehole logging represents an effective means of measuring distributed vertical strain at millimetre scale, revealing high-resolution variability along the uppermost ~100 m of DIR, Antarctica.