The effect of sea tides on gravity tidal observations on the Antarctic Ekstrom ice shelf

Simultaneous time series of gravity variations on an ice shelf and sea-level fluctuations in the Antarctic have been analysed. The gravity data was recorded in the observatory of the Georg von Neumayer (GvN) station on the Ekström ice shelf in the Antarctic by an Askania GS-15 earth-tide gravity meter. An Aanderaa pressure recorder was used on a mooring 10 km north of the ice-shelf edge in a water depth of 468 m to measure the sea-level fluctuations. Both time series are approximately one year in length. Amplitudes and phases for the tidal waves and residual spectra, with minimum leakage effects, were obtained using the least-squares method of the HYCON program. The gravity variations on the ice shelf are primarily caused by the local sea tides. The amplitude of the main tidal wave M2 is 80.3 µgal (1 µgal=10−8 ms−2). After removing the effect of the body and load tide the residual signal of 89.7 µgal amplitude corresponds to a tidal height of 33 cm while the tidal acceleration is only 8.3 agal. The vertical movement of the ice shelf is modelled by a simple elastic model. The ice shelf is taken as a uniform elastic beam floating on the sea and clamped on one side. This model constrains the location of the hinge zone of the Ekstrom ice shelf to be about 55 km south of the GvN station and verifies the observed vertical displacements at this station.