PHYSICAL OCEANOGRAPHY 223 



three belong to the Atlantic proper; Stations 87, loi, and 106 

 all lie within the precincts of the " Gulf Stream." At all four 

 stations the temperature is highest at the surface : 22°-23*' C. in 

 the Sargasso Sea (24th June), over 18° C. at Station 87 (17th 

 July), 13°- 1 4° C. westward of Scotland (7th August), and 13° C. 

 at the station west of Shetland (loth August). It is worthy of 

 note that a temperature of about 13° C. was observed at the 

 surface near Scotland, while the same temperature occurred at 

 a depth greater than 500 metres in the Sargasso Sea. 



From the surface downwards the temperature falls very 

 rapidly for the first 50 or 100 metres; at 100 metres it is from 

 4" to 6° C. colder than at the surface. Beyond 100 metres the 

 temperature decreases at first much more slowly, then rapidly 

 again, and then very slowly until the great depths are reached, 

 where the temperature changes very little. The layers in Discontinuity 

 which the temperature changes very rapidly are called " dis- ^^y^^^- 

 continuity-layers" (by the Americans " thermocline," and by 

 the Germans " Sprungschicht "). They are particularly marked 

 at Station 106, where there is such a layer immediately below 

 the surface, and another extending from 450 to 750 metres. 

 Between the two (from 50 to 450 metres) there is a fairly 

 uniform stratum, and another one under the deeper layer, from 

 750 metres to the bottom. At the other three stations the 

 upper discontinuity-layer is also very strongly marked, but the 

 lower one is not so sharply distinguished from the adjoining 

 water-strata. 



It will be noticed that the temperatures in the deep strata 

 (below 800 or 900 metres) were, at the same depths, nearly 

 identical at the three stations in the Atlantic proper, the differ- 

 ences not exceeding 1° C, although these stations are situated 

 far apart ; but at Station 106 in the Norwegian Sea the temper- 

 ature was 7°-8° C. colder. This is due to the form of the 

 bottom, the Wyville Thomson Ridge separating the deep layers wyviiie 

 of the Atlantic from the deep layers of the Norwegian Sea, so ^1^°™^°" 

 that at a depth of 1000 metres the temperature is 6'-7° C. in 

 the Atlantic Ocean, and below o" C. in the Norwegian Sea. 

 That implies two widely different deep-sea regions : a warm 

 one south of the ridge, and a cold one to the north of it, with 

 great differences in the deep-sea fauna of the two regions. 

 The influence of the Wyville Thomson Ridge is very clearly 

 seen in a section across the ridge (see Fig. 106, p. 124), from 

 Station loi to Station 106 ; in the upper strata, down to 500 

 metres, there is little difference, but the deeper strata are like 



