Desarrollo de la Antártica

EL DESARROLLO DE LA ANTÁRTICA Sea water is frozen at -1.9°C and ,becomes ice. The sea ices couId therefore be defined as the ice masses produced from the sea water. 1s is widely accepted at present, however, Ihat the sea ices represent all ices on the ocean area comprising rhe fast ices, the pack ices and icebergs. i. Fast ices The fast ice which is extented outwards from tobe Antarctic coast line is originally produced from tihe sea water by a freezing mechanism. Since me fast ices thus produced contain not only pure ice crystals but also air bulbhles, brines (the concentrated sea water among ice crystals) and various kinds 'Of salt, their physical properties are much complicated. The mecha1nical and tihermal properties of fast ice, however, have been reasonably welI examined to date. The growth rate of fast ice is now experimentally and tJheoretically known. Namely, the thickness 'Of fast ice (h) is approximately proportíonal t'O a square root of the product of t'he negative temperature deviation from the freezing point and tihe duratíon time of temperature below the freezing (Ei) , Le. h ,..., 2.5 ylEi (cm), where Ei is represented in unit of degrees x days. For example, Ei in the neigfubourhood of Syowa Station is about 4 x lOs degrees days so that h becomes about 160 cm, which is in agreement with observed data. ii. Pack ices The >Antarctic continent is surrounded by pack ices. rrho&e pack ices which originate in the fast ice are extended as shown in Fig. 5. As mentioned in § 3 the albedo by such an extented white area in Antarctica canno! help seriously affecting the world dimate. As suggested in Fig. 5, tihe main sources of Antarctic pack ices are mostly Ross Sea and Weddell Sea. The drifting motion of these pack ices is subjected strongly to the wind speed and direction, but also to ocean currents, mutual actions among padk ices themselves as well as the Corioli's force. Thus, these pack ice area is gradualIy expanded northwards. iii.lcebergs The Antarctic icebergs ongmate in the Antarctic ice sheet or ice shelves, so that their majority are in shape of the tablular icebergs. 'I1he total number of Antarctic icebergs amounts to as many as 2 x 10 5 , which is in remarkable eontrast to ATetic ieebergs of aboct 9 0