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.
Factors affecting changes in the floating Ross Ice Shelf in the vicinity of the 1957–1958 IGY Little America Station are examined. From direct measurements, the amount of snow accumulation was 67 cm annually, or 26 cm ice equivalent. The principal horizontal strain rates, determined from repeated transit surveys, were 129 and 81×10−5 per year, with the minimum values in the approximate direction of motion. The maximum strain rate may be deduced from Weertman's formula for the creep of floating ice, using acceptable flow law constants. Vertical strain accompanying the horizontal strains should reduce the ice thickness by 54 cm/yr. From the known variations in ice shelf temperature with depth, 80 cm of melting at the ice‐water interface is deduced. The net change for these factors would be an annual thinning of the ice shelf of 108 cm, equivalent to a decrease in surface elevations of 18 cm/yr. For the average surface slope in the Little America area of 65 cm/km, a forward ice shelf motion of 277 m/yr would be required, if elevations at fixed points remain constant with time. This velocity is comparable to that which has been deduced from the movement of Kainan Bay since it was first observed in 1912 by the Japanese Antarctic Expedition. Extrapolation of the creep rates and amounts of bottom melting south from the barrier edge give ice thinning that would result in somewhat higher ice movement values. Although the validity of the extrapolation to thicker ice is questionable, it appears likely that the ice west of Roosevelt Island is moving northward 3 to 4 times faster than the ice east of the island.
Summarizes some physical characteristics of ice island T-3 and its presumed source, the ice shelf off northern Ellesmere. Investigations since 1952 are described, results tabulated and graphed. The maximum ice thickness of the ice shelf was 60 m and that of T-3, 68 m (averaging 0.905 gm/cm³ in density from the surface to a depth of 16 m). Dust from dirt layers (collecting in small holes) on T-1 and T-3 appears to have originated from a land mass underlain partly by volcanic rock and partly by metamorphic and plutonic types and to have been wind-deposited. Deep cores on T-3 revealed a sequence of dirt layers to 28 m with clear ice below, the composition and grain size the same in all the layers; the heaviest were near the surface (amounting to 114-122 gm/m²) and at depths of 25 and 28 m (80 gm/m²). Four types of ice were observed on Ellesmere ice shelf and on T-3 in 1953 and 1954: iced firn, glacier, lake and sea ice; in 1955 only iced firn and lake ice were identified on the island. Temperatures recorded below the depth of annual change at the ice rise near Ward Hunt Island were -17.7 °C at 12.2 m and -17.3 °C at 18.0 m. Rocks, and plant and animal specimens found on T-3 are examined in relation to the possible origin of the island. Strand cracks at the junction between floating and grounded ice on the Ward Hunt ice shelf are also considered. From SIPRE [Snow, Ice, and Permafrost Research Establishment].
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