Glaciological regime of the Ross Ice Shelf

Abstract

A description of the floating Ross ice shelf in Antarctica, determined from miscellaneous studies between 1957 and I960, is provided by contoured maps giving values of ice thickness, ocean floor depth, surface snow density, average annual temperature, and average annual snow accumulation. The low surface densities and low average annual surface temperatures encountered in the central part of the shelf are explained by meteorological parameters. The thickness of the ice varies from about 700 meters in the southeastern area of the shelf to about 250 meters near the barrier edge, and it is demonstrated from theoretical strain values for floating ice that the main portion of the shelf must be under abnormally large horizontal stresses which prevent the ice from thinning more rapidly, thus accounting for its presence over such a large area. Snow densities at 40 meters depth, derived from an empirical relation between seismic refraction velocities and densities, vary widely over the shelf areas, and these differences can be explained in part by variations in the strain rates. The horizontal velocity components of the ice particles are obtained from the amount of accumulation and the area of the ‘snowshed,’ on the assumption that elevations are not changing in time. In order for these inferred velocities to conform to observed values near the shelf barrier, considerable melting is required at the ice-water boundary at the bottom of the shelf. This melting is confirmed by local data and is shown to increase from east to west. Vertical velocities of ice particles with respect to the surface are determined from snow accumulation and strain rates. These velocity components are combined in a numerical-integration method to allow the ice particle paths to be followed forward or backward in time or in space. The method is illustrated by reference to the area of Little America station, where a 250-meter hole was drilled in 1957. Ice cores from this hole, which include three large ash layers, have a maximum age of about 4500 years.