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Fortnightly variations in the flow velocity of Rutford Ice Stream, West Antarctica


Most of the ice lost from the Antarctic ice sheet passes through a few fast-flowing and highly dynamic ice streams1. Quantifying temporal variations in flow in these ice streams, and understanding their causes, is a prerequisite for estimating the potential contribution of the Antarctic ice sheet to global sea-level change2,3. Here I show that surface velocities on a major West Antarctic Ice Stream, Rutford Ice Stream, vary periodically by about 20 per cent every two weeks as a result of tidal forcing. Tidally induced motion on ice streams has previously been thought to be limited to diurnal or even shorter-term variations4,5,6,7,8,9. The existence of strong fortnightly variations in flow demonstrates the potential pitfalls of using repeated velocity measurements over intervals of days to infer long-term change.

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Figure 1: Map of Rutford Ice Stream, West Antartica.
Figure 2: Surface speed and tidal amplitudes as a function of time.
Figure 3: Tidal components.

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I thank R. C. A. Hindmarsh for discussions and E. McGough for assistance with field work. This work was supported by a grant from the NERC GEF.

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Correspondence to G. Hilmar Gudmundsson.

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Gudmundsson, G. Fortnightly variations in the flow velocity of Rutford Ice Stream, West Antarctica. Nature 444, 1063–1064 (2006).

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