Tidal motion of the Ross Ice Shelf and its interaction with the Siple Coast ice streams, Antarctica.

摘要

Three stations near the calving front of the Ross Ice Shelf, Antarctica, recorded GPS data through a full spring-to-neap tidal cycle in November 2005. The data reveal a diurnal cycle of horizontal motion which varies both along and transverse to the long-term average velocity direction, similar to tidal signals observed in other ice shelves and ice streams. Based on its periodicity, it is hypothesized that the signal is related to the tides, which are strongly diurnal in the Ross Sea. To assess the influence of the tide on the ice-shelf motion, two hypotheses are developed and a finite element model is created, based on creep flow, to test these hypotheses and to determine the mechanism, or combination of mechanisms, generating the velocity variations at the front of the Ross Ice Shelf. The first hypothesis addresses the direct response of the ice shelf to tidal forcing, such as forces due to sea-surface slopes or forces due to sub-ice-shelf currents and associated basal drag. The second hypothesis involves the indirect response of the ice-shelf flow to the tidal response of the Siple Coast ice streams, which feed the ice shelf. The diurnal, horizontal velocity variations previously observed in the ice streams have been described as either sinusoidal (similar to the smooth signal recorded in the GPS record at the front of the Ross Ice Shelf), or as an abrupt, tidally triggered, stick-slip motion, where most of the forward flow happens in short durations (on the order of 10 to 30 minutes) to velocities on the order of 10,000 m a-1. The quasi-static creep-flow model developed to investigate the two hypotheses provides a relative sense of the significance of the direct and indirect forcings, but fails to simultaneously predict both the magnitude and the smooth, periodic nature of the signal observed at the front of the ice shelf.