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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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.
Reprints and permissions information is available at www.nature.com/reprints. The author declares no competing financial interests.
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Gudmundsson, G. Fortnightly variations in the flow velocity of Rutford Ice Stream, West Antarctica. Nature 444, 1063–1064 (2006). https://doi.org/10.1038/nature05430
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