Terdiurnal Tide rocks Ekstroem Shelf Ice, Antarctica

Vera.Schlindwein [ at ] awi.de


The floating ice shelves surrounding Antarctica stabilize the Antarctic ice sheet and link its ice masses to the dynamic ocean system. The periodic changes of the ocean tides force ice shelf dynamics, influence ice stream velocities, and therefore affect ice mass balance. GPS observations can directly measure changes in ice velocities, but internal causative processes within the ice body remain hidden. However, seismological measurements of ground motion reveal the stress state of ice bodies and hence can give clues about internal ice dynamics. We analyzed seismological data from Neumayer Station III, Dronning Maud Land in East Antarctica, and calculated spectral noise levels using probability power spectral densities. The noise levels in the frequency range of 1-10 Hz change periodically with the ocean tides, but additionally to the major diurnal and semi-diurnal tidal constituents, we observe a strong terdiurnal component (8 hour period) in the noise levels reaching the same magnitude as semi-diurnal noise changes, although the amplitude of the exciting terdiurnal tide is only about a tenth of the semidiurnal amplitude. We speculate that a geometric resonance in shallow cavities near the grounding line might amplify the terdiurnal tide and reduce basal drag. Consequently the ice stream velocity increases and higher stress release leads to the observed elevated noise levels. Linked ice shelf–ocean models therefore underestimate the influence of the terdiurnal tide and require additional processes to explain the strong effect it has on noise levels in seismological data and on the stress-state of the ice body.

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Conference (Poster)
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27th IUGG General Assembly, 08 Jul 2019 - 18 Jul 2019, Montreal, Canada.
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Fromm, T. and Schlindwein, V. (2019): Terdiurnal Tide rocks Ekstroem Shelf Ice, Antarctica , 27th IUGG General Assembly, Montreal, Canada, 8 July 2019 - 18 July 2019 .

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