226 DISCOVERY REPORTS 



and maximum oxygen content were the first to increase its speed in the general increase 

 in velocity towards the north. 



At the depth of minimum salinity the average velocity of the water in the layer in- 

 creases from about 1-3 miles a day in 40° S to 2-5 miles a day in 7° S. The increase in 

 velocity may be caused by the narrowing of the South Atlantic Ocean towards the 

 north, as well as to the decreasing thickness of the layer, which becomes more confined 

 between sub-tropical water and North Atlantic deep water. 



In addition to this movement towards the north, there are easterly and westerly 

 movements in the layer; but about these little is known. The layer is deepest in about 

 30° S between the region of west and east winds. South of 30" S there will probably 

 be a movement in the layer towards the east, which is partly responsible for the slope 

 of the isotherms and isohalines downwards towards the north, and north of 30° S a 

 weaker movement towards the west. These zonal movements will aftect the curves in 

 Fig. 22, but not enough to destroy them. 



The velocity of the Antarctic intermediate current towards the north has recently 

 been measured on the eastern side of the South Atlantic, and similar results have been 

 obtained to those already described. A preliminary account of the measurement of 

 these velocities (Deacon, 1931) has also been confirmed by Castens (i93i),who obtained 

 a similar result from the changes in temperature with latitude. The movement north- 

 wards can be considered as a series of waves of water of different properties moving 

 outwards from the Antarctic regions, each of which, in the Atlantic Ocean, takes about 

 4^ years to travel from the Antarctic convergence to the Equator. 



The salinity of the water at the level of minimum salinity only increases from 34- 1 5 

 to 34-56°/ CO between 47° S and the Equator. The temperature increases from 3-2 to 

 4-85° C. over the same distance, and the oxygen content decreases from 6-o to 3-3 cc./litre. 

 North of the Equator the increase of temperature and salinity is more rapid, and the 

 most northerly observations which show the minimum salinity typical of the layer are 

 those of the ' Planet ' (1909) in 24° 20' N, 22° 37' W, and the ' Mowe ' (1914) in 26° 10' N, 

 16° 42' W. Antarctic intermediate water will reach this point about six or seven years 

 after it left the surface in the Antarctic. 



THE WARM DEEP WATER 



STRUCTURE AND DEPTH OF THE WARM DEEP LAYER, AND THE ORIGIN 



AND MOVEMENTS OF THE WARM DEEP WATER, THE NORTH ATLANTIC 



DEEP WATER AND THE PACIFIC DEEP WATER 



The movement of Antarctic surface water away from the Antarctic regions towards 

 the north is known to take place all round the pole, and it is also known that there is a 

 similar movement of Antarctic bottom water towards the north near the sea-bottom. 

 To make up for this transport of water away from the Antarctic regions in the surface 

 and bottom layers there must be a movement towards the pole in the intermediate layer. 

 This is supplied by a movement southwards in the warm deep layer. 



