the water masses j7s 



Stability of the water masses 

 To obtain some further comparison of the characteristics of the upper water layers on the two surveys 

 the vertical stability of the water columns has been determined. This has been calculated approxi- 

 mately as io 5 datjdz for the layers 0-50 m. and 0-100 m., and is set out in Table 6. 



In spite of the instability of the water at WS 976 the great stability of the upper 50 m. at all the 

 other stations on survey I contrasts most vividly with the generally lower stability on survey II. This 

 pronounced difference, the whole region being some ten times more stable in the upper 50 m. on the 

 first than on the second survey, reflects clearly the difference in the meteorological conditions on the 

 two surveys. 



THE WATER MASSES 

 Water masses of the South Atlantic 

 Wiist (1935) plotted T-S curves for three more or less meridional lines of 'Meteor' stations in the 

 Atlantic Ocean. The remarkable similarity of these curves within the South Atlantic is at once apparent 

 from his diagram (his p. 216). Excepting the upper layers where external factors come into play, 

 the curves all fall within a regular pattern. A typical T-S curve for the South-east Atlantic is shown 

 in Fig. 31. 



The ' Bottom ' water is a cold dense mass of water lying in the deeper basins. It originates in the 

 Antarctic, where cooling processes in the proximity of the continent cause the water there to sink 

 down the continental slope, and being very dense it spreads out across the ocean floor. The main 

 centre of this sinking appears to be the Weddell Sea, but it probably also occurs at other points along 

 the Antarctic coast. The water thus formed can be traced by its low temperature and salinity, and it 

 describes a northward flow into the South Atlantic. Partly under the influence of the earth's rotation, 

 but probably mainly owing to the bottom topography, the principal flow takes place up the western 

 side of the South Atlantic. A certain amount of the water flows up into the Cape Basin, but this does 

 not go far north since its passage is interrupted by the Walvis Ridge, a connecting ridge between the 

 African continent and the Central Atlantic Ridge. Wiist (1935) demonstrated that the potential 

 temperature of the bottom water south of the Walvis Ridge was about 1 ° C. lower than that to the 

 north of the ridge where it was over 2 C. He suggests that the flow up the western side of the ocean 

 infiltrates in a cyclonic movement through a gap in the Central Atlantic Ridge (the Romanche gap) 

 and enters the Angola Basin from the north. 



Lying above the bottom water, and extending up to nearly 1000 m. from the surface, there lies 

 a great mass of water called the ' North Atlantic deep water '. Owing to its great homogeneity it 

 occupies relatively little space on the T-S diagram (Fig. 31), the observations within it being clustered 

 around an intermediate maximum of salinity. Taking other factors into account, however, Wust has 

 shown that the deep water is, in actual fact, composed of three separate layers. As far as we are con- 

 cerned the three deep water layers can all be taken together, and considered as having a general 

 southward flow. The water leaving the North Atlantic does so principally on the western side, so that 

 the best-defined flow in the South Atlantic is found down the South American coast, the movement 

 in the eastern part of the ocean being much less well defined. On reaching higher latitudes the whole 

 mass of deep water becomes directed to the east. 



Above the deep water, there is a layer of minimum salinity. This characterizes the main axis of 

 northward flow of the ' Antarctic intermediate water '. Formed by the sinking of antarctic surface- 

 water, from the antarctic convergence in about 50 S., this layer moves northward at a depth of 

 between 600 and 800 m. Again the strongest movement is on the western side of the ocean, and indeed 



