Rutford and Evans Ice Streams investigated using satellite radar interferometry and modelling

• Main Author: Sykes, Helena Juliet
• Published: Swansea University 2009
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.752184

The Rutford and Evans Ice Streams together drain over 150,000 km2 of the West Antarctic Ice Sheet, a marine ice sheet with much of its bed below sea level. Ice streams make up only 13% of the Antarctic coastline, but are responsible for 90% of the discharge across the grounding line, where the ice starts to float. The Rutford and Evans Ice Streams were investigated using the remote sensing method of interferometry, which uses the phase difference between successive Synthetic Aperture Radar (SAR) satellite images to derive displacement in the line-of-sight (LOS) direction of the satellite and topography, which can be separated with further processing. The grounding zones of both ice streams were mapped from clearly defined changes in vertical tidal motion visible in the interferograms. The Rutford grounding zone is dominated by a central pinning point, and the Evans grounding zone has a complex shape so that for much of the main trunk of the ice stream the east side is grounded and the west side is floating. The tidal signal for each ice stream was reconstructed, and the tidal ranges of the Rutford and Evans grounding zones are more than 6 m and 5 m respectively, both well above average for Antarctica. Vertical displacement observed in both single and double difference interferograms correlated well to changing tidal height. The width of the grounding zone modelled using an elastic beam was close to the observed grounding zone width for both ice streams. Successful differential interferometry relies on the validity of the Constant Velocity Assumption (CVA), which states that interferograms differenced to derive topographic phase must contain the same displacement phase. However, due to the large tidal ranges at the grounding lines both ice streams, this assumption, which would be better termed the Constant Displacement Assumption (CDA), was violated to an extent which may be unprecedented in the literature. The Rutford Ice Stream reached velocities of approximately 400 m a-1 at its grounding line between 1992 and 1996, and the Evans Ice Stream appears to have decreased in speed from 750 m a-1 in 1992 to 540 m a-1 in 1996. This would have a significant effect on mass balance. The behaviour of this ice stream up to the present day clearly requires further investigation.