230 DISCOVERY REPORTS 



mediate water and sub-Antarctic water and picks up from them a large concentration 

 of phosphate and nitrate in its upper stratum. 



Not much is known of the origin of Pacific deep water, but when it is in the Atlantic 

 it differs very little in properties from North Atlantic deep water. 



The warm deep water which flows westwards in the south of the Weddell Sea, and 

 eventually out of the Weddell Sea as the cold deep current, flows from the Indian Ocean. 

 It cannot yet be definitely stated whether it flows into the Indian Ocean from the 

 Atlantic or whether it has its origin in the north of the Indian Ocean. 



TEMPERATURE, SALINITY AND OXYGEN CONTENT OF THE WARM 



DEEP WATER 



The upper stratum of warm deep water is characterized by a secondary temperature 

 maximum and it is warmer than the bottom stratum of Antarctic, sub-Antarctic, and 

 Antarctic intermediate waters. The temperature in the warm deep layer decreases with 

 depth, but its salinity increases with depth until it reaches a maximum at a level which 

 can be considered the nucleus of the layer — just as the minimum salinity level was 

 considered to be the nucleus of the north-going Antarctic intermediate water. 



The depth interval between the depths of maximum temperature and maximum 

 salinity in the layer is a measure of the thickness of the layer. The thickness can be 

 obtained from Table IX (p. 222), and it will be seen that it is not uniform. The depth 

 of the level of the maximum salinity, and the thickness of the layer, are greatest in the 

 deep basins and least above the zonal ridges and rises which cross the West Atlantic 

 basin. 



The temperature and salinity in the nucleus of the layer decrease towards the south, 

 and their decrease is due to vertical mixing with the Antarctic intermediate and bottom 

 waters. The decrease is not regular, partly because the North Atlantic deep water which 

 supplies the current must vary in just the same way as the water supplying the Antarctic 

 intermediate current. The rate of decrease also shows some dependence on the thickness 

 of the layer, owing to the changing speed of the water, or because of lateral inflow of 

 water in the basins. Attempts to measure the speed of flow of the water are rendered 

 diflicult by these changes, which are fortunately not communicated to the layer above. 



In 50° S and 30° W the depth between the maximum temperature and maximum salinity 

 of the warm deep water is about 1000 m., but in 55^ S it is only 40 m. This is probably 

 because the lower strata of warm deep water, whether their origin is Atlantic or Pacific, 

 have been changed or deflected by the strong flow of Antarctic bottom water, or of cold 

 deep water, from the Weddell Sea towards the Argentine Basin past the north-east coast 

 of South Georgia. 



The depth between the maximum temperature and the maximum salinity generally 

 decreases in the direction of movement, or as the temperature itself decreases. The 

 maximum temperatures of the layer in the Falkland Sector have been shown in Fig. 24 

 The maximum salinity varies from about 3473 or 3474 °l^^ below the Antarctic con- 

 vergence to 34-67 7 00 ii^ the cold deep water of the Weddell Sea. 



