Desarrollo de la Antártica

EL DESARROLLO DE LA ANTÁRTICA to be about 2 x 10 12 tons/year. As the total weight of ice oi rhe A'ntarctic ice sheet is approximately 2 x 10 16 tons. it may be concluded that about 1 JI 0.000 of the Antarctic ice sheet is supplied by the snow accumulation in every year. ii. Loss of ice The ice of Antarctic ice sheet is last in several different ways. The largest 10ss 'Üf ice is due to the calving of outer edges of ice sheet or glaciers into icebergs. As given in the following table (Tablp. 3), the calvings of ice sheet can be further classified into three categories, namely, tt.\e calving of outer edge of ice ~heet itself which has a slow velocity (....... 40 m/year), that of valley gLcicrs or ice streams which have faster velodties (;::: 400 m/year) and that o( ice shelves whose outward veIocity is 511ú ....... 1,000 m/year. TIle second cause oí ice sheet loss is considered as tlhe melting of bottom parts of ice sheet and ice shelves. However, the quantitative estimate of the melting 10ss of ice by tibe sea water at tlhe bottom of ice shelves and by the geothermal heat at the bottom of ice sheet is 110t suffíciently reliable. The estimated 10ss amount in the aboye table may be considered as the maximum possible one. The third cause wilI be the ablation o( ice on the ice sheet surface. The bIue ice (bare ice) area in the outer zone of Antarctic ice sheet is clear evidence of the abIation eHect. The quantitatíve estimate o( the ablation 10ss effect also is difficult. Therefore, tbe TABtE .3 LOSS OF THE ANTARCTIC ICE SHEET (AFTER LOEVE, 1967) rIce shelf Calving of Ice Sheet ~ Glacier l Ice sheet Ablation Melting of Ice shelf bottom and ice sheet bottom 8.80 5.20 0.50 0,10 2.00 (x J01 tons/ year) I Total I 16.60 x Ion tonsfyear I --------------------~------------------ 86