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Glacier Ice Motion in Antarctica using ERS-1/2 InSAR: 10 years of study.

Eric Rignot(1)

(1) Jet Propulsion Laboratory, MS 300-227, Pasadena CA 91109-8099, United States


We have been using ERS-1/2 InSAR from 1992, 1995/96 and 2000 to study ice motion in Antarctica. The interferograms have been employed to map ice velocity in vector form, map the precise location of the line of grounding of glaciers, and detect changes over time of the velocity field and of the grounding lines. These studies were complemented by ice velocity maps generated from Radarsat InSAR data, especially for those areas further south not covered by ERS-1/2. Mass balance estimates for 33 Antarctic glaciers, covering 75% of West Antarctica and 55% of East Antarctica were summarized by Rignot and Thomas, Science (2002). While the glaciers discharging ice into the Weddell Sea appear to be close to balance, those discharging ice into the Ross Sea are thickening (Joughin and Tulacyzk, Science, 2002), and those draining into the Amundsen Sea are thinning (Rignot et al., Ann. Glaciol. 2002). Overall, the West Antarctic Ice Sheet is losing mass. Additional InSAR processing in the Amundsen Sea, combined with recent ice thickness data collected by Centro de Estudios Cientificos and NASA, suggest an even larger imbalance in the Amundsen Sea sector, equivalent to a sea level rise of 0.25 mm/yr alone. This is the largest contribution to sea level reported todate from land ice. Most of this sector has eluded glaciological observations until the advent of ERS satellites. It is now becoming the focus of future glaciology research. All the glaciers in this sector are thinning several meters per year along the coast, their ice shelves are thinning, the grounding lines are retreating, and the glacier velocities are increasing with time. This behavior cannot be attributed to warmer air temperatures, as no surface melt occurs at those latitudes; but is attributed to enhanced bottom melting from warm ocean waters (Jacobs et al. Science, 2002), which thins the ice shelves, reduces buttressing of the ice streams, and in turn increases mass discharge. Analysis of InSAR data near grounding lines indeed revealed that high bottom melt rates are observed widespread in Antarctica, especially in the Amundsen Sea (Rignot and Jacobs, Science, 2002). These studies thereby reveal the essential role of ice-ocean interactions in the evolution of the ice sheet. More recent analysis has been conducted in the Antarctic Peninsula, where several glaciers are exhibiting large imbalances and flow acceleration, which suggest that those glaciers are retreating and contributing to sea level rise as well. It is likely that ocean warming also plays a significant role in the evolution of land ice in the Antarctic Peninsula. All these observations challenge the traditional view of ice sheets changing with glacial slowness.


Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry