Observations on rate of accumulation, compaction, density, petrography, and differential motion of the firn in the upper levels of the Ross Shelf ice in the vicinity of Little America III were made during the Antarctic summer of 1946–1947. Studies were conducted in an enclosed pit dug to a depth of 23 feet by members of the expedition of 1939–1941. The bottom of this pit is now about 36 feet below the surface. The present observations project our knowledge of the physical characedge of the physical characteristics of the Ross Shelf ice to a greater depth than heretofore investigated.
Eighteen feet of firn accumulated during the period 1940–1947. The annual rate of 31 inches thus indicated must have been greater originally as subsequent compaction has taken place. The compaction was greatest in the upper, more porous layers. Petrographic examination indicates that the density increases were primarily the result of this compaction. No evidence of recrystallization was observed, except for occasional interpenetration of grains at the deepest level. This would seem to restrict recrystallization to depths greater than 36 feet. There was no evidence of differential motion of the firn to this depth.