Deglaciation since the Last Glacial Maximum
What has happed in the Antarctica recently? Referring to the long history of our planet over 46 billions years, we refer the last twenty thousands years as the recent. The upper panel of the left figure shows the current shape of the ice sheet measured by satellite altimeter (J. Bamber, Univ. Bristol), while the lower panel shows a reconstructed Antarctic ice sheet by an ice-flow model (P. Huybrechts, AWI) with 10x exaggeration in the vertical (image courtesy: Bob Bindschadler, NASA). Antarctic Transaction Mountains divides the ice sheet into the East Antarctic Ice Sheet (EAIS) and the West Antarctic Ice Sheet (WAIS). You can see a huge deglaciation in inland regions of the Ross Embayment, where large efforts of the U.S. Antarctic Program has been made to understand its past, present, and future of this region as well as physical mechanisms underlined it. This area includes many fast-ice-flow channels ("ice streams") and inter-stream ridges, which constitute a highly variable system that interacts with sediment and ocean as well as atmosphere. One of the most important question from a global point of view is how ice volume in this dynamic region has changed and will change in the future.
Reconstruction of the ice sheet in the past using computer models relies on our incomplete understanding of the physics that controls ice. Various kinds of evidence collected from Antarctica have been used to constrain the past ice sheet. Rock not covered with ice and ocean sediment can provide rich information on the evolution of the ice sheet, while such constraints in the current ice-covered region is unavailable. Even if the margin of the ice sheet is constrained by geological evidence, thickness of the past ice (i.e. elevation of the ice sheet surface) is necessary to estimate the volume of the ice there. More information about how ice flowed can help understand the role of the ice in the entire Antarctic system including geosphere, atmosphere and ocean. The central region of the WAIS, marked with the red circle in the figure, is currently covered by more than 3000 m of ice. Our projects peer into this deep ice using ice-penetrating radar.
Remote sensing of ice characteristics using ice-penetrating radar
Our projects primary use ice-penetrating radar to peer into the ice and the bed beneath the ice. Radio wave can penetrate into the ice and reflect at interfaces where ice characteristics are slightly altered. This radargram show a clear reflection from the ice/bed interface where the largest difference in dielectric properties are expected (horizontal distance: about 350 km; vertical distance: about 3000 m). Besides the bedrock, the radar detected layered structure (isochrones) within the ice. Since 1960's, glaciologists have used the radar to map geometry of the bedrock, as well as internal layers. Furthermore, radar studies can potentially reveal much more than simply the geometry of the bed rock and internal layers. Our projects investigate the echo intensity from these layers and its spatial variations over the inland WAIS. Radar data in the left image was collected by Supports Office of Aerogeophysical Research (SOAR) located at University of Texas, Austin, in the 2000-2001 season. We are analyzing this airborne radar data set together with the SOAR scientists. The airborne measurements can cover a wide area, while ground-based measurements can provide more detail information with various radio-wave characteristics (frequency, polarization, vertical and horizontal resolutions). We'll make extended ground-based radar sounding for the 2005-6 and 2006-7 seasons.This complements interpretation of the airborne radar data collected various areas.