Book Description

Cores obtained to the bottom of the Antarctic Ice Sheet at Byrd Station were used to analyze the physical properties of air bubbles trapped in the ice. Parameters measured were the sizes, shapes, abundances, spatial distributions, gas volumes and pressure of bubbles, and their variations with depth in the ice sheet. Bubbles occur abundantly in the top 800 m of ice but then gradually disappear until they can no longer be detected optically below 1100 m. This disappearance is not accompanied by any significant loss of air from the ice and all available evidence indicates that the air actually diffuses into the ice in response to increasing overburden pressure. Bubble pressure measurements show that (1) bubbles with pressures exceeding about 16 bars begin to relax back to this value soon after in situ pressures are relieved by drilling, (2) further slow decompression occurs with time, and (3) the rate of decompression is controlled to some extent by the intrinsic structural properties of the ice and its thermal and deformational history. Only small variations were observed in the entrapped air content of the ice cores; they probably reflect variations in the temperature and/or pressure of the air at the time of its entrapment, but the data are not sufficient to draw any firm conclusions regarding past variations in ice sheet thickness. Only ice from the bottom 4.83 m was found to lack any detectable trace of air.