Old Ice Streams

Abstract

GEOLOGY The size and behavior of past Antarctic ice sheets are essential elements in the quest to understand how and why climate changed in the past and what the consequences may be in the future. Modern observations have shown that Antarctic ice flow is slow and diffuse over most of the interior of the ice sheet but focuses into relatively rapid streams near the edges of the sheet. Canals et al. have found a set of parallel to subparallel ridges and grooves up to 100 kilometers (km) in length at a water depth of 1000 m in the Western Bransfield Basin off Antarctica. They identify this formation, called a “bundle” structure, as material deposited by a giant ice stream during the last glacial maximum. This finding illustrates the importance of rapid ice flow during past glacial maxima that are related to present ice sheet movements. The minimum ice thickness necessary to have formed this bundle is 1000 m. This single stream, which was probably about 340-km long, would have transported approximately 8000 km3 of ice to the ocean—enough to raise sea level slightly more than 2 cm.— HJS Geology 28 , 31 (2000)