TEMPERATURE VARIATIONS IN THE NORTH 



ATLANTIC OCEAN AND IN THE 



ATMOSPHERE ' 



By Bjorn Helland-Hansen and Fridtjof Nansen 



I. THE AIM OF THE INVESTIGATION. THE ASSEMBLY OF THE 

 OBSERVATIONAL MATERIAL 



In 1909 we found that the water-masses in the Atlantic cur- 

 rents of the Norwegian sea (with a salinity of more than 35 

 parts per thousand) experience great temperature variations from 

 year to year. These variations, according to our view, may find 

 their explanation either by different proportions of mixture between 

 the water masses of the Atlantic Ocean current which passes 

 through the Faroe-Shetland Channel (and also northward of the 

 Faroe Islands) and those of the Icelandic- Arctic current — or, on the 

 other hand, by variations in the water-masses in the Atlantic Ocean 

 currents themselves before their entrance into the Norwegian sea. 



In order to decide this question, we held it desirable to study 

 the possible variations from year to year in the temperature of the 

 North Atlantic and their causes. Unfortunately there was not avail- 

 able enough observational material for a long series of years on 

 the temperatures of the deeper water layers of the Atlantic Ocean. 

 It was moreover questionable if the numerous surface observa- 

 tions would answer for our purpose. 



As has been shown by several investigators, the vertical con- 

 vection reaches in the winter in the North Atlantic Ocean to very 

 great depths (see Neilsen, 1907, p. 10, Nansen 1913, p. 18, etc.). 

 Somewhat similar results were found by Helland-Hansen in the 

 Norwegian sea in a February expedition in the year 1903. Altho'ugh 

 apparently the vertical convection there did not reach to so great a 

 depth as in the North Atlantic Ocean, yet he found equal tempera- 

 tures and equal salt contents reaching very considerable depths 

 below the surface. The isotherms and also the lines of equal salt 

 contents in the sections show a very steep almost vertical position, 

 which is partly to be explained because the vertical convection 

 equalizes the differences (see Helland-Hansen and Nansen 1909, 



^Translated from Videnskapsselskapets Skrifter. I. Mat.-Naturv. Klasse. 

 1916. No. 9, with additions by the authors and by Dr. C. G. Abbot, Smith- 

 sonian Institution, Washington, U. S. A. 



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