Seasonal dynamic thinning at Helheim Glacier

• Published in: Earth and Planetary Science Letters
• Main Authors: Bevan, Suzanne L., Luckman, Adrian, Khan, Shfaqat Abbas, Murray, Tavi
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2015
• Subjects: Dynamics; Glaciology; Helheim Glacier; Mass balance; TanDEM-X; East Greenland; glacier; Greenland
• Online Access: https://orbit.dtu.dk/en/publications/7425b425-2e02-46fe-b089-2284e50e212b; https://doi.org/10.1016/j.epsl.2015.01.031; https://backend.orbit.dtu.dk/ws/files/106096731/1_s2.0_S0012821X15000588_main.pdf

We investigate three annual mass-balance cycles on Helheim Glacier in south-east Greenland using TanDEM-X interferometric digital elevation models (DEMs), bedrock GPS measurements, and ice velocity from feature-tracking. The DEMs exhibit seasonal surface elevation cycles at elevations up to 800 m.a.s.l. with amplitudes of up to 19 m, from a maximum in July to a minimum in October or November, concentrated on the fast-flowing areas of the glacier indicating that the elevation changes have a mostly dynamic origin. By modelling the detrended bedrock loading/unloading signal we estimate a mean density for the loss of 671±70kgm -3 and calculate that total water equivalent volume loss from the active part of the glacier (surface flow speeds >1 m day -1 ) ranges from 0.5 km 3 in 2011 to 1.6 km 3 in 2013. A rough ice-flux divergence analysis shows that at lower elevations (<200 m) mass loss by dynamic thinning fully explains seasonal elevation changes. In addition, surface elevations decrease by a greater amount than field observations of surface ablation or surface-energy-balance modelling predict, emphasising the dynamic nature of the mass loss. We conclude, on the basis of ice-front position observations through the time series, that melt-induced acceleration is most likely the main driver of the seasonal dynamic thinning, as opposed to changes triggered by retreat.