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



23 



an important phenomenon as the Great Atlantic Current 

 between America and Europe is probably very different 

 from what is now generally believed, but the real conditions 

 cannot be cleared up properly unless special investigations 

 are made, with a very close net of stations. The "Michael 



Sars" observations from the North Atlantic are much too 

 scattered to solve important problems, and the graphical 

 representation of them in charts and sections, as well as 

 the discussion, must for the greater part necessarily be 

 rather schematic. 



V. SHORT-PERIOD OSCILLATIONS. 



21. Observations from the North Atlantic. 



Earlier observations in the North Polar Basin and the 

 Norwegian Sea had shown that even in the deep sea the 

 repetition of a vertical series of observations sometimes gave 

 results which differed from the first series with regard to 

 the distribution of temperature, salinity and density [cf. 

 Helland-Hansen and Nansen, 1909]. A certain tempera- 

 ture or salinity might be observed at a somewhat different 

 level than found a relatively short while before. The phe- 

 nomenon appears as a vertical displacement of the water- 

 layers and may represent real vertical oscillations, caused 

 by internal waves or other motions with a vertical com- 

 ponent. In those places where the horizontal variations 

 are great a purely horizontal displacement may, however, 

 have the same effect upon the values observed. It may 

 also be mentioned that it is not unlikely that the flowing 

 water-masses occasionally are heterogeneous, showing 

 variations in temperature and salinity with constant density. 

 In such cases repeated observations at a fixed station may 

 exhibit variations in the two first named elements without 

 any dynamic significance. 



In the "Michael Sars" Expedition observations at 

 different depths were repeated at several stations, though 

 not systematically except at Stat. 115 in the Faeroe-Shetland 

 Channel. The observations are recorded in Table II. 

 From the North Atlantic we have the following obser- 

 vations of this kind: 



Stat. 10 in the Bay of Biscay, N. of Cape Finisterre. — 

 At 193 metres practically no variations in 3 hours. — At 

 640 metres in 1-7 hours: no variation in salinity, which 

 had the same value as at 457 metres. The last temperature 

 observation was made by means of a Nansen-thermometer 

 in an insulated Pettersson-Nansen water-bottle, showing an 

 increase of temperature of 0-23° C and accordingly a de- 

 crease in (/, of 0-04 units. The observations may indicate 

 a considerable sinking of the water-layers (about 65 metres 

 calculated from a,). — At 914 metres in 1-3 hours: decrease 

 of salinity and density, corresponding to some 20 metres' 

 sinking of the water-layers when calculated from the 

 ff, variations. 



Stat. 25 B in the Cadiz Bay, S. of Cape St. Vincent. 



— At 366 metres in 3-2 hours: increase of temperature 

 and salinity, a^ practically constant. The vertical variations 

 are rather small, especially in o-^. The observations may 

 indicate a sinking of the water-layers of some 15 metres 

 at this depth. 



Stat. 51, more than 500 naut. miles SW. of Fayal 

 (the Azores). — At 400 metres in 0-8 hours: no variation 

 in f/^, but a small decrease of temperature and salinity 

 (corresponding to a lifting of the water-layers of about 

 3 metres only). 



Stat. 63, in the outskirts of the Sargasso Sea. — At 

 64 metres: at first, in 4-1 hours, an increase of temperature 

 (0-28° C, corresponding to a sinking of the water-layers 

 of about 6 metres), a decrease of salinity and density 

 (doubtful), and then, in 1-8 hours, a decrease of tempera- 

 ture (0-13° C, corresponding to a lifting of about 3 metres). 



— At 457 metres: in the first 4-8 hours small variations 

 in temperature and density, none in salinity. In the 

 following 1-8 hours decrease of temperature and salinity, 

 increase of density (about 13 metres' lifting of the water). 



— At 732 metres : no variations in the first 2-8 hours. 

 In the following 1-8 hours increase of temperature and 

 salinity, constant density. 



Stat. 68, about 450 naut. miles SE. of Cape Race. 



— Several measurements were made at about 900 metres, 

 but nothing definitely can be deduced from them. Due 

 to strong wind and current the wire could not be brought 

 in a vertical position; the depths recorded in Table II as 

 896, 901 and 905 metres are reduced from 914 metres on 

 account of the inclination of the line. The 5 observations 

 in question were made during 4-3 hours. Vertical oscil- 

 lations of the water-layers have probably been quite in- 

 significant if occurring at all. 



Stat. 92, SW. of Ireland. — At 1006 metres in 2-9 

 hours: a small decrease of temperature and salinity in- 

 dicates a lifting of the water-layers, while a simultaneous 

 decrease of density indicates a sinking, so that nothing 

 definite can be deduced from the observations. 



The various data given above together with the ap- 

 proximate values of 10^ £, are here brought together: 



