Tide induced velocity fluctuations in the grounding zone of Darwin Glacier, Antarctica, Revealed by GNSS and SAR satellite data.

Flow velocities and flow variations of Antarctic glaciers play an important role in Antarctica's mass balance and global sea level change. Oceanic tides are known to influence ice dynamics of outlet glaciers where they become afloat. The Darwin Glacier in the Transantarctic Mountains (TAM), Antarctica, experiences tidal forcing downstream of its grounding line (GL) which modulates its flow velocity primarily over the grounding zone (GZ). In comparison to other large glaciers in the TAM, the Darwin flows relatively slowly at less than 100 m a⁻¹. Field work was carried out to locally measure small scale velocity fluctuations and ice deflection over three weeks at high temporal resolution using GNSS stations. The data are used to research the ability of radar remote sensing techniques to detect ice dynamics in 35 COSMO-SkyMed and TerraSAR-X synthetic aperture radar (SAR) satellite images from an eight month period in 2016. Tidal forcing is derived from a regional model, validated against local field measurements and used to remove tidal distortion from the SAR imagery. Flow velocities in the Darwin GZ are found to be influenced by diurnal tidal cycles with fluctuations of ±52% and weaker fortnightly variations of ±9%. This study shows that uncertainties from tidal contaminations can override the accuracy of remotely sensed information and the constellation of satellite orbit path and incidence angle affects the ability to remotely discern small scale ice dynamics. Average ice velocity is well represented in the SAR scenes and short term ice flexure reveals a tidally induced GL migration of up to 2000 m over the eight month period. Flow velocity variations at the Darwin are similar to other glaciers feeding the Ross Ice Shelf. Tide induced flow fluctuations are different at other Antarctic outlet glaciers and without a buttressing ice shelf. The unique pattern of ice dynamics in the embayment of the Darwin GZ shows that this glacier is additionally buttressed by the underlying topography and may therefore be less susceptible to environmental changes