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Tidal control of ice stream flow at annual and semi-annual frequencies
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Professor Matt King
Murray T, Smith AM, King MA, Nicholls KW, Makinson K, Adalgeirsdottir G, Behar AE
Conference Proceedings (inc. Abstract)
Eos Transactions: Fall Meeting
San Francisco, CA, USA
Year of Conference
11–15 December 2006
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For over a year between December 2004 and December 2005 we ran a GPS receiver located ~ 40 km upstream from the grounding line on Rutford Ice Stream, West Antarctica. Locations were calculated every 5 minutes using a kinematic Precise Point Positioning GPS data processing strategy. The ice stream velocity averages 376.9 m/year (averaged over 372 days) at this location and we examine deviations from mean flow. Although the record is incomplete due to power loss at times during the austral winter, there appears to be modulation of the downstream flow rate of the ice stream at a wide range of frequencies that correspond to known ocean tidal frequencies, but no identifiable modulation of the vertical or lateral position. Modulation at close to semi-diurnal, diurnal and fortnightly frequencies is very clear within the record, and there also appears to be modulation at lower frequencies that probably corresponds to annual and semi-annual tidal frequencies. Comparing to a model of the nearby ocean tidal signal, the ice stream appears to flow fastest at times when the tidal range is largest, but the response is not symmetric suggesting some hysteresis in the system, which may be due to the viscous behaviour of the ice stream at these timescales. This is the first observation of tidal modulation of ice stream flow over such a long period and at such low frequencies. The sensitivity of the ice flow rate to the rather small forcing at these long periods suggests that ice stream velocity may be affected by future changes in sea level. If so, this effect would provide a potential feedback whereby rising sea levels might increase ice stream velocity and discharge more ice into the global oceans.
American Geophysical Union
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