![]() ![]() Over the 1946–2018 period, the cumulative mass balances diverged. We reanalyzed mass balance records at Taku and Lemon Creek Glaciers to better understand the relative roles of hypsometry, local climate and dynamics as mass balance drivers. ![]() 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. 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. 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. Both profiles also show substantial local variability. 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. 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. ![]() Direct measurements of spatially distributed vertical strain within ice masses are scientifically valuable but challenging to acquire. ![]()
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