22 



BJ0RN HELLAND-HANSEN 



[REP. OF THE "MICHAEL SARS" NORTH 



horizontal variations in salinity and temperature may take 

 place within astonishingly short distances. There are 

 strong indications that also the Great Atlantic Current off 

 the coast of North America and across the Ocean towards 

 Europe, with its chief branches, is narrower than has hitherto 

 been assumed, the mere surface current being excepted. The 

 main Polar Currents along the east coast of Greenland and 

 off Newfoundland seem likewise to have a great velocity 

 only within a very narrow belt, which upon the whole is 

 confined to a stretch just outside the edge of the con- 

 tinental slope. 



In the "Michael Sars" Expedition we crossed the 

 Great Atlantic Current near America south of the New- 

 foundland banks and east of the Flemish Cap. The dis- 

 tribution of temperature and salinity is illustrated by the 

 sections pp. 91* (the lower section), 92* and 93*. The 

 physical and dynamical conditions in this area will be 

 discussed later on in this paper, and we shall here only draw 

 attention to some features connected with what has been 

 said above. The sections just mentioned show very steep 

 inclinations of isohalines and isotherms. The distance 

 from one station to the next within the area in question is 

 between 90 and 250 kilometres, being so great that 

 important variations may have escaped observation, or 

 that the inclination may have been considerably steeper 

 than shown in the sections. We shall here consider 

 especially the last section, from the Flemish Cap eastwards 

 (p. 93*). Stat. 81 was worked in the forenoon, July 12th. 

 After some hours of tow-netting the observations were 

 repeated at several depths, the new series being numbered 

 81 A. As far as it can be made out, the horizontal distance 

 between the two series was only 10—12 kilometres, but 

 the vertical distribution of temperature, salinity and den- 

 sity was very different. At Stat. 81 we observed at 549 

 metres 9-46° C, 35-16''/oo of salinity, and o-,=27-19. At 

 Stat. 81 A much the same values were found at 457 metres 

 (9-45° C, 35-147oo, (T,=:27-18). Allowing for small errors 

 in the determinations of salinity we may safely say that 

 the water found at 549 metres in the first series of ob- 

 servations was situated nearly 90 metres higher in the last 

 series. There is a possibility that these variations may be 

 due to vertical oscillations, but such an explication is not 

 at all likely to be the right one. Both series have been 

 used for the construction of the isohalines and isotherms 

 in the section, with the result that a steep inclination of 

 the curves appears at this place. It is, now, interesting to 

 notice that the shape of the curves thus obtained fits 

 remarkably well with the surface observations on both 

 sides of Stats. 81—81 A. Between Stat. 80 and Stat. 81 

 we met with a maximum of temperature at the surface 

 corresponding to the downward bend of the curves in the 

 section. East of Stat. 81 A we encountered a minimum 



of surface temperature corresponding to the convexity of 

 the curves in the section. In this case we may corroborate 

 the surface observations with vertical series and obtain a 

 somewhat safe construction of the curves also for the 

 intervals between the stations. It is very doubtful whether 

 a similar construction would have been accepted when 

 based upon the surface observations only. Now the con- 

 sequence is that the section exhibits a deep and marked 

 bulk of water with high temperatures and salinities, evid- 

 ence that the Great Atlantic Current makes a curious 

 serpentine bend in this region (it is not visible in the small- 

 scale charts as for instance that on p. 96*). Such details 

 may be of the greatest importance to our understanding 

 of the physical and dynamical conditions in the ocean, 

 but may easily escape observation through the generally 

 much too open-meshed net of stations. 



Large eddies and horizontal vortex movements are very 

 conspicuous in the Norwegian Sea, and are probably quite 

 common in many parts of the Ocean [Helland-Hansen 

 and Nansen, 1909]. In August 1910 a number of stations 

 were taken in the Faeroe-Shetland Channel from the "Mi- 

 chael Sars" and the Scottish exploration ship "Goldseeker". 

 Leaving the discussion of the results to a subsequent chap- 

 ter, I shall here only mention that the distribution of tem- 

 perature, salinity and density was very complicated, great 

 horizontal variations being observed within short distances. 

 The observations may, however, be combined in such a way 

 that a plausible series of vortices is indicated, which makes 

 the intricate variations quite intelligible. Similar studies 

 have not previously been made in the North Atlantic 

 except in some small areas. When working up the results of 

 the "Armauer Hansen" cruises. Professor Nansen and I 

 [1926] have found great and numerous variations in those 

 parts of the eastern North Atlantic where many stations 

 have been taken in the course of time. The variations 

 may to a great extent be accounted for in a reasonable 

 way on the assumption of vertical oscillations, but it is 

 most likely that eddies also enter as an ordinary part in 

 the features of these regions. 



Great and rather abrupt local variations due to cur- 

 rents and eddies make the utilization of serial obser- 

 vations from stations far apart very limited and many 

 apparent results quite illusory. Even a short displacement 

 may alter the results very appreciably. In those places 

 where relatively many stations have been worked, an error 

 in the determination of the ship's position may cause 

 considerable error in the deduction of results. For further- 

 ing our knowledge of the physical and dynamical condi- 

 tions in such oceans as the North Atlantic, observations 

 scattered over the greater part of the ocean are now, upon 

 the whole, of comparatively little value. What is needed 

 is a detailed survey of the different regions. Even such 



