24 



BJ0RN HELLAND-HANSEN 



(REP. OF THE "MICHAEL SARS" NORTH 



The values found for the variation in depth are very 

 uncertain. They may indicate that variations of this kind 

 upon the whole are rather insignificant in the North Atlantic 

 Ocean except in regions near the continental slope (Stats. 

 10 and 25 B). 



The observations recorded above show no definite 

 connection with the variations in stability. It is true that 

 repeated observations have not been made within those 

 water-layers where the stability has had a maximum and 

 where boundary waves may be most likely to occur. At 

 Stat. 63 near the outskirts of the Sargasso Sea the stability 

 was« very great in the upper water-layers, especially be- 

 tween 10 and 25 metres below the surface where we 

 may speak of a "discontinuity-layer", and also at the 

 depth of 64 metres the stability was very pronounced. 

 The oscillations indicated at the latter depth may be real and 

 suggest a more prominent primary wave at a higher level. 



Our observations from the North Atlantic in 1910 

 offer only a meagre material for studying the problem of 

 vertical oscillations or quasi-oscillations. Later on more 

 observations have been obtained from the eastern North 

 Atlantic, though not at all satisfactory for our purpose. 

 After a thorough discussion of the various data available, 

 Professor Nansen and the present author [1926] have come 

 to the conclusion that considerable vertical oscillations 

 may occur in some regions especially near the continental 

 shelf and banks, and that these oscillations are possibly, 

 or even probably, connected with the tidal phenomenon, 

 strong evidence being found for 12 hour (lunar) and 

 24 hour periods. The semi-diurnal period seems to do- 

 minate near the banks, at any rate in some water-layers, 

 while the diurnal period is predominant farther out in the 

 sea. The o.scillations at some depths may be inverse to 

 those at other depths (difference of phase 180°). 



It is probable that some of the "Michael Sars" stations 



in the North Atlantic have been taken at places and times 

 when vertical oscillations or quasi-oscillations have occur- 

 red, so that the serial observations do not represent the 

 average conditions. For the greater number of the stations, 

 however, this eventuality is not likely to be of any con- 

 sequence. 



22. Experiments in the Faeroe-Shetland 

 Channel. 



In the Faeroe-Shetland Channel special observations 

 were made for a study of possible short-period variations 

 in the vertical distribution of temperature, salinity and 

 density. After a discussion of the results obtained from 

 the Norwegian Sea, at a meeting in Copenhagen in August 

 1909 of the International Council for the Exploration of 

 the Sea, it was agreed that investigations of submarine 

 waves etc. should be performed if possible in the Faeroe- 

 Shetland Channel, by means of the Danish, Scottish 

 and Norwegian research ships. From the Danish side 

 such investigations were made during 67 hours on May 

 23rd to 26th at 61° 27' N. Lat. and 4° 33' W. Long. 

 where the depth to the bottom was 780 metres [M. Knud- 

 SEN, 1911]. In August 1910 a collaboration was established 

 between the Scottish explorations in the "Goldseeker" 

 and the Norwegian in the "Michael Sars". Relatively 

 many stations were worked by the two ships along four 

 sectional lines between Shetland and the Faeroes (see 

 the chart of stations, p. 95*). At two stations repeated 

 observations were made during more than 24 hours on 

 August 13th and 14th. The Scottish station (marked 

 Sc. in the chart just mentioned) was situated at 61° 32' 

 N. Lat., 4° 19' W. Long., bottom-depth 725 metres. The 

 corresponding observations from the "Michael Sars" 

 were made at Stat. 115, at 61" 0' N. Lat., 2° 41' W. 

 Long., bottom-depth 580 metres. At all three stations in 

 question the place was marked by means of an anchored 

 buoy, the ship being kept close to the buoy when the 

 observations were taken. 



The observations at the "Michael Sars" station 115 

 are recorded in detail in Table II, and are represented in 

 the upper figures on pp. 84^'' (temperature) and 85* (den- 

 sity). In some cases determinations of salinity and con- 

 sequently also of density are missing, while the tempera- 

 ture observations are so numerous that the curves for 

 every hundred metres from the surface to 500 metres 

 (incl.) may be drawn fairly safely. The vertical variations 

 of salinity are frequently so slight that small errors in the 

 determinations may have an appreciable effect upon the 

 apparent results with regard to the oscillations. We shall, 

 therefore, in the following especially pay attention to the 

 temperature variations. 



