Desarrollo de la Antártica

Takesi Nagata / THE ADVANCEMENT ~F SCIENTIFIC RESEARCH .•• colder water tends to subside beneath the warmer water mass. In substitution, the sea water of 2,000 _ 4000 m in depth coming from the north comes upwards and southwards in the south side of the Antarctic convergence, thus forming the Antarctic circumpolar water. The most particular dharacteristic of the Antarctic sea water is the production of Antarctic bottlom water in Weddell Sea, Ross Se:t and other Antarctic bays. The sea /Water remaining after tlhe fOTma– tion of fast ice at cold temperature in comparatively shallow sea water areas suoh as Weddell Sea or Ross Sea should have a higher salinity and colder temperature. Thus, tihe cold (about -1.9°C) and high– salinity (>34.6 %) water mass subsides down along the ocean bot– tam and flow out northwards. It is believed that tihe bottom water in the Atlantic, lndian and ¡Pacific Oceans originates in this Antarctic bottom water. b) Geochemist1"Y 01 the Antarctic ocean As described in § 4, about 2 X 10 12 tons of Antarctic ice come out into the ocean water every year. Since about 1 % or less of t:hese ice masses are O'ccupied by silicate dusts which the ice sheet or glaciers nave scraped from the Antarctic bed rocks, the melting, of Antarctic ice is considered to be che source of fine suspensions of silicate dusts in the ocean, approximately in the rate of 2 x 10 10 tans/year. Actually, the observed content of suspensions in the sea :water amounts to 200~500 mgjI in the neighbourhood of AntartictÍc coast, decreases with an increase of distance from che coast and becomes less than 1 ¡mil in the north of 60 0 S latitude cirde. § 8. SOLlO STATE GEOPHYSICS IN ANTARCTICA Main results of researches of gravity and geomagnetic field distribu– tions and seismology in Antarctica will be briefly summarized here under the title of "Solid State Geophysics". a) Earthquakes in Antarctz"ca Since the IGY period, more than 10 seismological stations have been set up in IAntarctica. This Antarctic seismological network is particu– larIy important, because the major parts of t'he lS'outhern hemisphere are occupied by tihe oceans so that the precise seismological observa– tions in the Antarctic continent can mpply extremely impoTtant data to accurately determine Lhe earthguake foci. rrhe seismological data thus obstained indicate that earthquakes very 101