Evidence for non-tidal diurnal velocity variations of Helheim Glacier, East Greenland | Glaciological instruments and methods

12 pages, 9 figures, 1 table, 1 appendix

We have used tide-gauge data from near Helheim Glacier, East Greenland, and GPS data acquired on the glacier to investigate the spectra of tidal forcing and flow response. For both the tidegauge and GPS time series, we calculated amplitudes and phases for a harmonic expansion using a limited set of harmonic constituents. We find that the semidiurnal constituents of the glacier flow are well modeled using a single admittance and lag with respect to the tide-gauge data. However, diurnal variations in the glacier flow cannot be simply described using this model. We find an additional signal in glacier position, in phase with the S1 solar tide, with some modulations at other frequencies. These non-tidal variations account for a peak-to-peak variation in glacier flow speed at a site close to the terminus of ~0.7md-1, compared with a mean flow rate at this location of ~22md-1. The speed variations reach their daily maximum value ~6 hours after local noon. We hypothesize that these additional diurnal variations are associated with peaks in lubrication of the glacier bed due to surface melting driven by diurnal solar heating

We thank members of the Helheim Project for collecting the datasets used in this analysis. This work was supported by US National Science Foundation grants ARC-0713970, ARC-07131749 and ARC-1110322, the Gary Comer Science and Education Foundation, the Spanish Ministry of Science and Innovation (MICINN; now MINECO), the Danish Commission for Scientific Research in Greenland (KVUG), the Geological Survey of Denmark and Greenland (GEUS), Geocenter Copenhagen, the Danish National Space Center and NASA. GPS equipment and technical support were provided by UNAVCO, Inc.

Peer Reviewed