Desarrollo de la Antártica

EL DESARROLLO DE LA ANTÁRTICA about 257 m long was drilled at Little America V. The density and temperature of the ice core changes from 0.841 amd -21.7°C respec– tively at 52 m in depth to 0.912 and --I2'.9°C at 255 m in deplJh, where is almost the bottom of the Ross ice shelf. The important findings of this project are evidence of the snow accumulation on the surface (about 22 cm water/year) and the melting of the bottom ice into the sea water. A summary of recent knowledge of the ice shelf structu– re will be dealt with in a later section. b) The structure 01 Antarctic Ice Sheet The total volume of the Antarctíc ice sheet amounts to about 2.35 x 10 7 km 3 which covers 1.251 x 10 7 km 2 of the Antarctic continent area, so that the average thickness of Antarctic ice sheet is 1,880 m. This world largest ice sheet of Antarctica is about ten times as large as the second largest ice sheet of Greenland, where the total volume of ice sheet and Íts average thiohness are about 2.6 x 10 6 km 3 and 1,515 m respectively. A quasi-steady state of an ice sheet is maintained by the snow accumulation on the ice sheet on one hand and the ablation of ice and snow on the orher hand. The snow density at the top surface of an ice sheet is 0.3 '-' 0.4 g/cm 3 , but it gradually increases with depth up to 0.4 '-' 0.8 g/cm 3 (firn) and finally at depths of 50 ,....., 100 m the firn becomes the glacier ice oE 0.80 ,....., 0.90 in den– sity. Even the glader ice in the deep inside of an ice sheet is slowly moving towards the lower level sea coast mostly due to the gravity effect but with the resistance of the elastíco-viscosity of ice. Depending on the bed rock topography, the form of an ice sheet and stream lines oí ice flow wivhin the ice sheet are more or less modified. Fig. 3 illustrates an example of such a dependence of ice sheet profile shape on the bed rock topography. The velocity oí ice flow becomes generally larger in the outer part of an ice sheet, and particularIy in a valley between mountain ranges lJhe ice flow forms an ice stream or a valley glacier which has a considerably larger velocity compared wirh its both sides. rrhe outer dege of a valley glacier forms an ice tongue when it is extended over the sea area. Where the ;valley glacier comes into an ocean bay area, the glacier ice becomes the major souree for maintaining an iee shelf. i. Snow aecumulation The aceumulatio'l1 of snow on fue Antarctic ice sheet has been measured at many places by means of various methods. The mea-