Twelve years of ice velocity change in Antarctica observed by RADARSAT-1 and -2 satellite radar interferometry

Abstract. We report changes in ice velocity of a 6.5 million km2 region around South Pole encompassing the Ronne/Filchner and Ross Ice Shelves and a significant portion of the ice streams and glaciers that constitute their catchment areas. Using the first full interferometric synthetic-aperture radar (InSAR) coverage of the region completed in 2009 and partial coverage acquired in 1997, we process the data to assemble a comprehensive map of ice velocity changes with a nominal precision of detection of ±3–4 m yr–1. The largest observed changes, an increase in speed of 100 m yr–1 in 12 yr, are near the frontal regions of the large ice shelves and are associated with the slow detachment of large tabular blocks that will eventually form icebergs. On the Ross Ice Shelf, our data reveal a slow down of Mercer and Whillans Ice Streams with a 12 yr velocity difference of 50 m yr–1 (16.7 %) and 100 m yr–1 (25.3 %) at their grounding lines. The slow down spreads 450 km upstream of the grounding line and more than 500 km onto the shelf, i.e., far beyond what was previously known. Also slowing in the Ross Ice Shelf sector are MacAyeal Ice Stream and Byrd Glacier with a 12 yr velocity difference near their grounding lines of 30 m yr–1 (6.7 %) and 35 m yr–1 (4.1 %), respectively. Bindschadler Ice Stream is faster by 20 m yr–1 (5 %). Most of these changes in glacier speed extend on the Ross Ice Shelf along the ice streams' flow lines. At the mouth of the Filchner/Ronne Ice Shelves, the 12 yr difference in glacier speed is below the 8 % level. We detect the largest slow down with a 12 yr velocity difference of up to 30 m yr–1 on Slessor and Recovery Glaciers, equivalent to 6.7 % and 3.3 %, respectively. Foundation Ice Stream shows a modest speed up (30 m yr–1 or 5 %). No change is detected on Bailey, Rutford, and Institute Ice Streams. On the Filchner Ice Shelf proper, ice slowed down rather uniformly with a 12 yr velocity difference of 50 m yr–1, or 5 % of its ice front speed, which we attribute to an 12 km advance in its ice front position. Overall, we conclude that the ice streams and ice shelves in this broad region, in contrast with their counterparts in the Amundsen and Bellingshausen seas, exhibit changes in ice dynamics that have almost no impact on the overall ice balance of the region.