HYDROLOGY OF THE BRANSFIELD STRAIT 9 



of warm deep water and the lowest layer of Antarctic bottom water. The effect of the 

 relatively warmer middle layer is to produce a temperature inversion below the cold 

 nucleus of the surface layer. 



If we consider firstly the temperature-salinity curve for St. WS 400 it can be seen 

 that it consists of three distinct portions AB, BC and CD. The line AB represents the 

 effect of summer conditions on Antarctic surface water, which has come from the 

 Bellingshausen Sea and has been warmed by the sun and diluted by melting ice in its 

 upper portion. The point B represents the relation of temperature and salinity at the 

 cold nucleus of this layer. Between B and C both the temperature and salinity increase 

 rapidly with depth and this portion of the curve represents the mixtures between these 

 depths of Antarctic surface water and warm deep water, the latter water being of Pacific 

 origin. At B only Antarctic surface water and at C only warm deep water is present and 

 the proportion of each type of water in the mixture represented by the line BC may easily 

 be calculated. From the point C the temperature commences to fall rapidly to the lowest 

 observation and the salinity increases very slowly as far as 1000 m., where it remains 

 constant until 1500 m., below which it decreases very slightly to the two lowest 

 observations at 2000 and 3000 m. If the warm deep water were a homogeneous layer 

 the portion CD would accurately represent the mixtures of this layer with Antarctic 

 bottom water. The latter, however, does not commence to influence the salinity until a 

 depth between 1500 and 2000 m. is reached. Thus only below 1500-2000 m. does the 

 amount of Antarctic bottom water in the mixture commence to be appreciable. At this 

 station there is a very smooth transition from the warm deep water to the bottom water 

 of the southern part of the Drake Passage. 



The temperature-salinity curve for St. WS 384 shows essentially the same features 

 as that for St. WS 400, with, however, some modifications, due to the fact that St. WS 

 400 is situated outside and WS 384 inside the strait. The summer warming and dilution 

 of the surface layer is seen between o and 200 m. The cold nucleus of the Antarctic 

 surface water is, however, deeper than usual and the salinity at this point is high, which 

 indicates the effect of vertical mixing in winter. Between 200 and 300 m. both salinity 

 and temperature increase, but the temperature does not rise beyond — 0-31° C, which 

 is found at 300 m. Compared with the corresponding temperature at St. WS 400 this 

 temperature is 2-03° lower and is situated 300 m. nearer the surface. Thus a large 

 difference is found in the temperature and depth of the maximum temperature of the 

 warm deep water at stations inside and outside the Bransfield Strait. This is perhaps the 

 chief effect of the topography of the sea-bottom of the strait. The flow of warm deep 

 water into the strait is restricted by submarine ridges, and as a consequence the circula- 

 tion with the warm deep water of the outside sea is greatly modified. At the majority of 

 the stations inside the strait the temperature inversion due to the presence of the warm 

 deep water is either absent or very weak. Between 300 m. and the lowest observation 

 the warm deep water at St. WS 384 is mixed with increasing amounts of Antarctic 

 bottom water until at 1500 m. the temperature reaches the low value of — 1-56° C. 



St. WS 385 was selected as one of the many stations inside the Bransfield Strait at 



