ATLANT. DEEP-SEA EXPED. 1910. VOL. i] PHYSICAL OCEANOGRAPHY AND METEOROLOGY 



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the single currents ("dynamical variations", in relation to 

 geographical co-ordinates) or the individual seasonal varia- 

 tions of temperature within them ("physical variations", 

 in relation to "oceanographical co-ordinates", cf. above 

 p. 47). The difficulties arise from the local variations 

 which are so often met with. 



In the deeper strata below 200 metres, where the 

 surface exerts next to no influence apart from the winter 

 convection in some areas, seasonal variations in tempe- 

 rature may occur as a result solely of variations in the 

 course and velocity of the currents. 



The current system of the eastern North Atlantic 

 seems to be rather complicated. In our discussion of all 



of temperature". The different marks have the same 

 significance as in Figs. 11, 12 and 15. The dispersion 

 of the marks is rather great, on account of the local 

 variations. There is no definite indication of any seasonal 

 variations at this depth. It may also be referred to Figs. 

 21—23. 



33. Variations from One Year to Another 

 (Annual Variations). 



In the preceding section we have discussed the varia- 

 tions of temperature which, on an average, take place in 

 the course of one year within different areas. Within one 



Fig. 19. Temperatures observed (vipper part of the figure) and tlie corresponding 

 "anomalies of temperature" at 400 metres in area "B". 



modern observations made in this part of the sea up to 

 the year 1922 Professor Nansen and 1 came to the con- 

 clusion [1926] that a number of vortices arise and reveal 

 their presence by great variations of temperature and 

 salinity within short distances (local variations i. This 

 holds good on the assumption that the observations may 

 be directly combined in sections and charts, and that the 

 variations are not caused to any great extent by vertical 

 oscillations. At about 1000 metres below the surface, 

 water from the Mediterranean makes itself felt in a vari- 

 able degree. The salinities and temperatures are, relati- 

 vely, very high at this depth in the Atlantic near the 

 Straits of Gibraltar. Here we find very high positive 

 values of salinity-anomaly (or negative values of "anomaly 

 of temperature"). These anomalies gradually decrease in 

 all directions as one moves away from the outlet from 

 the Mediterranean. The local variations are so great that 

 it is not worth while to try to use the same method for 

 these intermediate depths that we have adopted in the 

 above discussion of the upper water-layers. 



At 400 metres the conditions are much more uniform 

 than at about 1000 metres. Fig. 19 shows the tempera- 

 tures observed at 400 metres within our area "B" (the 

 upper part of the Fig.) and the corresponding "anomalies 



and the same area considerable changes may, however, 

 occur from one year to another, in the manner which 

 is so familiar in meteorology. A certain month or season 

 may be warmer or colder in one year than in another, 

 and in most cases we find positive or negative departures 

 from the mean temperature of the epoch. For the sake 

 of brevity we shall term these variations annual variations 

 in contradistinction to the average changes from season 

 to season. 



When discussing oceanographic observations which 

 had been made in the Norwegian Sea during a number 

 of years, Professor Nansen and the present author found 

 [1909] that the temperature of the Atlantic water (S :> 

 35 7oo) in this sea in May was subject to considerable 

 annual variations. The Atlantic water entering the Faeroe- 

 Shetland Channel becomes mixed with Arctic water, and 

 the annual variations exhibited farther to the north may 

 be explained either by the different proportions in which 

 the water-masses are mixed or by variations in the 

 temperature of the single constituents. In order to decide 

 this question we have tried to examine the annual varia- 

 tions in the North Atlantic, but for want of more adequate 

 material we had to confine ourselves merely to a study 

 of the surface temperatures towards the end of the winter 



