January 19, 191 1] 



NATURE 



189 



' taken part in these researches, Prof. H. H. Gran, Dr. 

 Helland-Hansen, Mr. E. Koefoed, and Captain Thor 

 Iversen, all signified their utmost willingness to join the 

 '^^ledition. 



)n completing our preparations, we started off from 

 mouth in the beginning of April, 1910, after being 

 joined by Sir John Murray at that port. 



During the four months that the cruise lasted, a great 

 ' I was accomplished. Y<x oceanographic science it can- 

 but be interesting to learn that a little steamer, of 

 226 tons, could carry out so many and such multi- 

 >us researches right across one of the mighty oceans, 

 i I will accordingly give a few* figures to illustrate what 

 was done. 



In the case of hydrc^raphical material, we collected 

 2400 water-samples, more than 900 of which were from 

 below the surface. At no stations we toc^ 937 tempera- 

 ture observations from below the surface, while as many 

 as 1625 observations of the surface temperature were re- 

 corded during the cruise. In addition, we obtained 258 

 measurements of currents and seven measurements of 

 light. For the study of vegetable plankton we made 140 

 ical hauls, and took 38 water-samples for filtering and 

 -amples for examining with the centrifuge. For the 

 _^ r plankton there were 95 vertical hauls with nets of 

 rent sizes, 193 horizontal hauls with silk nets, 80 hori- 

 :al hauls with pelagic trawls, and 18 hauls with a very- 

 large tow-net. Trawlings were undertaken on twenty-four 

 occasions at different depths. 



Our being able to carry out so many investigations, in 

 spite of the fact that the ship traversed a distance of about 

 11.000 miles during the four months the cruise lasted, 

 shows that oceanographic expeditions can be undertaken 

 in small craft and for a relatively moderate expenditure ; 

 and this will most likely be a matter for consideration 

 when future expeditions are planned. 



Hydrographical Investigations. 



At no stations we collected material for determining 

 the temperature and salinity of the sea water. The 

 temperature observations have now been corrected, the 

 water-samples have been titrated, and the results are set 

 down in vertical sections and charts showing the distribu- 

 tion of temperatures and salinities at the different depths. 

 The distribution of temperatures and salinities in the sea 

 between Newfoundland and Ireland in the month of Julv, 

 1910. can be shown in a diagram. Throughout nearly the 

 whole section there is a layer with salinities of 35-5 per 

 mille in the uppermost 150-200 metres. Both salinities 

 and temperatures decrease in fairly regular proportion as 

 we descend, until we reach a uniform layer termed 

 "bottom water," in which the temperature is slightly 

 below 2^° C, and the salinity is about 349 per mille. It 

 is noteworthy that this salinity is exactly the same as 

 has been found in the bottom water of the Norwegian sea 

 during the previous investigations. During the cruise of 

 the Michael Sars in the Atlantic, this same salinity has 

 been discovered both between the Canary- Islands and the 

 .^ores, and between the Azores and Newfoundland, and 

 also outside the Bay of Biscay. 



This uniform bottom water lies deeper in the eastern 

 portion of the North Atlantic, off the south coast of Europe 

 and the north coast of .Africa, than in the western or 

 north-western portion of the coast of America. East of 

 Newfoundland it attains a comparatively high level. This 

 would seem to indicate that the bottom water of the North 

 Atlantic comes from the north-western portion of that 

 ocean. 



\ chart shows clearly the influence of the Mediter- 

 ranean : verv salt and comparatively warm water streams 

 out of the Mediterranean and sinks deeper down ; outside 

 Spain it mainly flows northwards, owing to the effect of 

 the earth's rotation; another portion seems to follow the 

 ordmary stream towards the south-west. . Between the 

 comparatively fresh cold water in the north-west and the 

 relatively warm salt water outside Spain a belt extends 

 from west of the .Azores as far as the Faroes and Iceland, 

 with fairly uniform salinities of -?; to 3^-; per mille, and 

 temperatures of 6° to 8° C. 



^Vhen we compare our temperatures with those of the 

 ^haUenger, we find that they agree most satisfactorily, so 

 NO. 2 15 I, VOL. 85] 



far as the deep layers are concerned, and the temperature 

 observations of the Challenger seem to have been very 

 good. When we look at all the stations from the cruise 

 of the Challenger in the summer of 1873, which are 

 situated in the neighbourhood of the Michael Sars' stations 

 of a summer thirty-seven years later, we find everywhere 

 that the water in the mid-layers was much w'armer in 

 1873 than in 19 10. The differences of temperature go up 

 to about 5° in the mid water-layers, but sink to o-i° and 

 0-4°, respectively, in deep water. This seems to indicate 

 that there are such very great fluctuations from year to 

 year in the degree of warmth in these mid-layers that they 

 even exceed the fluctuations in the seasons. 



It is obvious that fluctuations of this kind in the degree 

 of warmth of the Atlantic Ocean are most important, and 

 need further investigation. In the Norwegian Sea such 

 fluctuations in water flowing in from the Atlantic have 

 been already previously investigated by the Michael Sars. 



These determinations of the temperatures and salinities 

 of salt water will subsequently be utilised for dynamic 

 calculations. It will thus be possible to draw conclusions 

 as to the movements of the different water-layers. These 

 movements the expedition endeavoured also to investigate 

 by means of direct-current measurements with the propeller 

 current-meter which Ekman has constructed. 



In the Strait of Gibraltar we tried first to anchor one 

 of the lifeboats fore and aft, as had often been done 

 previously in Norwegian waters. However, the strong 

 current broke the lines repeatedly. We accordingly 

 anchored the ship itself, with ij-inch steel wire and a 

 warp anchor, in about 200 fathoms. The ship lay thus 

 on April 30 from 2.30 a.m. until 5 p.m. During this time 

 we took seventy measurements at eight different depths. 



A comparison of diagrams representing the conditions at 

 9 a.m., when the inflow into the Mediterranean was at its 

 height, and at 2 o'clock in the morning and 3 o'clock in 

 the afternoon, shows that the effects of the tidal water 

 are very great throughout the whole mass of water from 

 the surface to the bottom. During the inflow, the velocity 

 in the upper instreaming layer was about i metre per 

 second, while in the lowest west-flowing layer it did not 

 exceed one-third metre. During the outflow from the 

 Mediterranean to the Atlantic there was hardly any surface 

 current, whereas the outward current at depth had a 

 velocity of up to 2 metres per second. The real velocities 

 were actually greater, as the current generally ran in a 

 slightly oblique direction to the axis of the strait. 



During our experiments with the large otter trawl on 

 the bank south of the Azores on June 12. our trawl stuck 

 fast on the bottom. Instead of immediately getting it 

 clear, this otherwise unfortunate circumstance was made 

 use of for taking current measurements. The ship was 

 thus anchored to the trawl at a depth of 668 fathoms 

 (1235 metres). In all, we tocJc ninety measurements at 

 various depths down to 800 metres. On a diagram show- 

 ing the current from hour to hour at a depth of 10 metres, 

 the tidal movements can be distinctly seen. The actual 

 main current ran southwards with a velocity of 8-9 cm. 

 per second. Another diagram shows the currents in the 

 different layers at three intervals of time : — (i) at 3.30 

 a.m. ; (2) at 7 a.m. ; (3) at 10.45 a-m- A comparison of 

 the three figures shows that at all the depths down so 

 far as 800 metres there were tidal movements. On the 

 whole, the currents in the dee|>er layers flowed in a con- 

 trary direction to the movements in the upper ones. There 

 was an astonishingly strong current at 800 metres at 

 3.30 a.m., but otherwise w'e found, as a rule, that the 

 current was strongest close to the surface, while at 100 

 metres there was a tendency to a minimum, and a 

 tendency to a maximum at 200 metres. 



The measurements show, accordingly, that there can be 

 ver\- considerable tidal currents even down so low as 800 

 metres. The reason why they were so strong south of the 

 Azores is probably to a great extent that the bottom there 

 forms a large shoal, w-hich the water presses up against. 



Similar investigations w-ith modern methods have never 

 been undertaken before either in deep water or in the 

 Strait of Gibraltar. 



That there are tidal movements in the open sea and 

 such strong currents, even at depths above 400 fathoms 

 (800 metres), is interesting for many reasons, as it assists 

 us in understanding the ocean currents, the tide-wave, the 



