III. BRANSFIEIJ) STRAIT AREA, OCEANOGRAPHT 



A. General 



This comparatively narrow passage to the north of the Palmer 

 Peninsula averages 60 miles in width and extends for approximately 

 200 miles from Brabant Island in the west to D'Urville Island in the 

 east, both islands forming part of the southern boundary of the 

 strait. To the north the strait is bounded by the South Shetland 

 Islands of which the most famous is Deception Island lying to the 

 west. Bransfield Strait has a rfiputation for rough and foggy weather 

 but is almost always free of ice for the greater part of the summer. 

 On very rare occasions ice has blocked Deception Island so that ships 

 have not been able to reach it. The strait has two depressions, the 

 deepest of which lies between Gibbs IslsJid and Deception Island and 

 varies from 1,^00 to 1,800 meters in depth. South of Deception Island 

 is a smaller depression with a maximum depth of 1,300 meters. 



In DraJce Passage to the north, the waters are moving eastward and 

 are much warmer than the water in Bransfield Strait, Some of the Drake 

 Passage water apparently flows south through Boyd Strait and into the 

 smaller depression from which it flows northeastward into the main 

 depression, A bottom stream of cold water from the Weddell Sea also 

 flows westward along the southern shores. This current is the product 

 of the deep cold bottom water which originates in the Weddell Sea, 

 flows down the continental slope and then spreads north and west. 



B, Physical Properties 



Three stations were selected to form a section through the strait 

 (fig. U) which wDu].d show the warm water to the west and possibly the 

 colder Weddell Sea water from the east and south. Hence, the western 

 station (station 8) was located southeast of Boyd Strait and slightly 

 west of Deception Island, station 10 was located north of D'Urville in 

 the southeast comer of Bransfield Strait, and a third station (station 

 9) was located between the other two stations in the middle of the 

 strait. As might be expected, the two eastern stations show simi- 

 larities in the water mass structure and composition, while there is 

 a marked change at the Deception Island station which is influenced by 

 the Drake Passage water flowing southward through Boyd Strait, 



1. Temperature 



VJater having temperatures below 0°C, is present below a depth of 

 100 meters at both easterly stations, but disappears to the west before 

 Deception Island is reached, apparently flovrlng south along the southern 

 shores of the strait. The coldest water observed at the D'Urville 

 Island station was ■^O.J^'^ C, at a depth of just below 100 meters; at 



