Table 2. — Properties of water masses in the Weddell Sea Coastal Current during IWSOE-70. 



P04P, NOsp = Preformed phosphate and nitrate. 



(fig. 6). This feature has not been described 

 before and its origin is unknown. 



Past investigations have rarely found water 

 temperatures below — 1.8 °C in the Antarctic 

 Surface Water east of 35°W (Lusquinos, 1963). 

 However, low temperatures were observed in 

 two different areas east of 35°W during 1970. 

 In the Halley Bay area (stations 9 through 17), 

 temperatures as low as — 1.98 °C were ob- 

 served with salinities ranging between 34.0 and 

 34.4%o (figs. 4 and 5). This cold water was 

 evident from the surface to the bottom suggest- 

 ing formation at the surface, probably by in- 

 tense cooling and evaporation imposed on the 

 surface by gradient winds. During the occupa- 

 tion of the stations at Halley Bay, continuous 

 winds of 40 knots were measured. 



The area sampled near Halley Bay was in a 

 polynya extending over 600 miles, which is a 

 seasonal feature of the Weddell Sea. In the 

 summer, southwesterly winds predominate in 

 the area (Gordon, 1970). Since the direction of 

 ice drift is approximately 45° to the left in the 

 southern hemisphere, the pack ice would con- 

 centrate to the north leaving open the polynya 

 in the eastern portion of the Weddell Sea. The 

 mechanism which prevents the closing of the 

 polynya by freezing is unknown. The heat con- 

 tent of the subsurface shelf water is not suf- 

 ficient to prevent ice formation if it were 

 brought to the surface by some upward process 

 (convection, diffusion) . The probable answer is 

 that the surface water does freeze but the ac- 

 tion of wind and currents removes the ice. The 

 southward flowing average surface current in 

 the area of Halley Bay is quite slow (Kvinge, 

 1969) and probably does not play a major role 

 in removal of ice. 



Another possible mechanism preventing the 

 closing of the polynya by freezing is the forma- 

 tion of ice in small crystals kept separate and 

 in suspension in the water by turbulence from 

 the action of the wind. The formation of ice 

 crystals in the surface layers has been studied 

 by Littlepage (1965) and Zubov (1945). They 

 found that the ice crystals were carried by ver- 

 tical mixing to a depth where they would melt 

 because of lowered freezing point (due to pres- 

 sure). The heat required for melting the ice 

 would come from the surrounding water, low- 

 ering its temperature further, possibly explain- 

 ing the colder temperatures near the bottom at 

 Halley Bay. 



Sea water with temperatures near the freez- 

 ing point was observed in the southeastern 

 Weddell Sea at stations 5, 6, and 7 (fig. 6). 

 Water temperatures below the freezing point 

 were recorded at 19 subsurface levels (below 

 250 meters) at the three stations. All three sta- 

 tions are located near the Filchner Ice Shelf in 

 a deep depression on the continental shelf. The 

 greatest depth measured in the depression was 

 1200 meters with a sill depth of 400 meters 

 (Kvinge, 1969). The underside of the edge of 

 the ice shelf is approximately 250 meters below 

 sea level, increasing to over 500 meters be- 

 fore the ice contacts the sea floor shoreward 

 (Zumberge and Swithinbank, 1965). The sa- 

 linity of the upper 250 meters at the three sta- 

 tions was less than 34.40%o, which is less than 

 the salinity of the deeper cold water. Since no 

 advection of near freezing water at depth in 

 the Coastal Current was observed, it is reason- 

 able to conclude that the very cold water was 

 derived by freezing either at the surface or at 

 the underside of the ice shelf. 



S 



