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



77 



15), or the "Michael Sars" stations 10 A and 91. These 

 e.xamples are taken from the eastern region, but some- 

 thing similar holds good for the western Nortii Atlantic 

 as well (of. for instance tlie "Challenger" stations 19 — 

 21). We have not yet a sufficient number of determinations 

 to examine the variations in salinity in the bottom-water. It 

 is highly probable that the salinity exiiibits horizontal 

 differences which correspond to the differences of temp- 

 erature, and that, accordingly, the densities are prac- 

 tically uniform. If not, there must be a field of force, 

 which would mean that the velocity of the bottom-water 

 is subject to vertical variations. 



Bottom-water from the South Atlantic with relatively 

 low temperatures spreads northwards on the western side 

 of the North Atlantic. At the "Challenger" station 1 10 at the 

 equator in about 30"^ W. the depth was 4160 metres and 

 the temperature observed near the bottom 1-55° C. (© 

 — 1-20" C). The temperature in situ and the potential 

 temperature increase northwards as is seen from the chart, 

 Fig. 26. The "Challenger" observations in abouth 20° N. 

 (Stats. 15—21) seem to indicate that the cold bottom- 

 water from the south exerts itself more strongly on the 

 American side of the deep basin than along the central 

 ridge. It is, however, impossible to draw safe conclusions 

 from our material in this regard, on account of the inad- 

 equacy of the Miller-Casella thermometers and the lack of 

 observations between 2743 metres (1500 fathoms) and the 

 bottom. The depth to the bottom is less than 4500 

 metres at Stats. 15—17, but about 5500 metres at Stats. 

 19—21, and a water layer with a minimum of tempera- 

 ture may exist between these levels, as already stated. 



It deserves notice that the apparent bottom-tempe- 

 rature observed was everywhere 2-5° C. or more at the 

 "Challenger" stations between 30 and 43 where the depth 

 to the bottom exceeded 4000 metres. Temperatures as 

 high as these were observed at no other stations below 

 4000 metres in the western North Atlantic, with the excep- 

 tion of Stats. 17 and 66 and one of the "Deufschland" 

 stations. They correspond to the potential temperatures 

 above 2-0° C. (at Stat. 39:1-98°) shown in the chart. 

 Fig. 26. It seems natural to infer that the bottom-water 

 below 4000 metres in an area west of about 65° W. Long, 

 and north of about 33° N. Lat. is influenced by the Sar- 

 gasso Sea in the same way that the bottom-water in the 

 eastern North Atlantic appears to be affected by the Medi- 

 terranean. 



We have hitherto chiefly discussed the temperature 

 of the bottom-water at depths below 4000 metres. This 

 water has to a great extent come from the northernmost 

 part of the North Atlantic where the depths are smaller, 

 and it must have, so to say, moved down hill. As men- 

 tioned above, the bottom-water of northern origin is 



mainly formed by the cooling of the sea surface in a 

 limited area near Greenland, but partly also by a flow 

 of cold water from the Norwegian Sea across the Faeroe 

 — Iceland— Greenland Ridge at depths of, broadly speaking, 

 about 500 metres. The latter water gets mixed with the 

 water in the Atlantic in a similar way to the water coming 

 from the Mediterranean across the ridge at Gibraltar. 



The water near the bottom in the northernmost part 

 of the North Atlantic exhibits great local variations in 

 temperature and salinity, even at depths of 3000 metres 

 and more. In the eastern part of the region in question, 

 the temperatures in situ near the bottom at such depths 

 are relatively high, between 2-5 and 3° C. This is evi- 

 dently due to the influence of the Mediterranean even 

 in these high latitudes. Some observations made during 

 the "Armauer Hansen" Expeditions in 1913 and 1914 

 are quite illuminating. Stat. 6 in 1913 was taken in 

 54° 2' N. and 24° 34' W. The depth sounded was 3368 

 metres and the salinity of the water at the very bottom 

 was 34-98"/oo. The lowest observation of temperature was 

 secured from 3000 metres, where /„ — 2-83° C, 5 -- 

 34-97 °/oo and ,r, 27.90. In 1914 a station (62) was worked 

 in 52° 47' N. and 16° 39' W. The deepest observation 

 was taken at 3200 metres and gave Tm = 2-77°, 5 = 

 34-98 "/oo and o-/ = 27-91. No sounding was made, but 

 in all probability this observation was from a level not 

 far above the bottom, to judge from the charts, r^ = 

 2-83° at 3000 metres correspond to (■) — 2-57° and r^ — 

 2-77° at 3200 metres to H ^ 2-49° C. These potential 

 temperatures are, however, decidedly higher than those 

 computed for the bottom -water at depths below 4000 

 metres in the eastern North Atlantic, so the water near 

 the bottom at these two stations cannot directly form the 

 bottom-water farther south in the ocean. The poten- 

 tial densities found from the observations in question 

 are 27-920 and 27-934 respectively. At the "Michael 

 Sars" Stat. 91 in about 4772' N. the observations from 

 3500 metres gave: /„, =^ 2-63°, 5 = 34-965 Vo, n, = 

 27-91, B = 2-33° and o-g = 27-937. This fits in very 

 well with the observations from 3200 metres at the "Ar- 

 mauer Hansen" Stat. 62, when the difference of depth is 

 taken into account. This water does not belong to what 

 we have called the bottom-water in our discussion above, 

 but to a higher layer in the deep water. At the "Mi- 

 chael Sars" station 91, 4750 metres, the salinity observed 

 was just what must be expected for the bottom-water in 

 the eastern North Atlantic, 34-915 "/o". w't'i a temperature 

 /// situ estimated at 2-27 ° C. and a corresponding poten- 

 tial temperature of l-82« {,r(j =- 27-94). Water of the 



same salinity and potential temperature was not observed 

 at the above-mentioned stations 6 and 62 of the "Ar- 



