76 



BJ0RN HELLAND-HANSEN 



[REP. OF THE "MICHAEL SARS" NORTH 



ranean is indicated quite distinctly at higher levels, as 

 shown by the charts on p. 97*. In this respect there is 

 a marked difference between the area near Stat. 10 A 

 and that around Stat. 91, where the temperatures of the 

 bottom-water seem to be considerably lower. 



The conclusion to be drawn from this is, .then, that 

 the apparent increase of im with increasing depth in the 

 eastern regions is due to regional variations, and does 

 not represent the distribution of temperature along a 

 vertical. 



Fig. 27 and the small table above indicate that, 

 generally speaking, r™ as well as decrease with in- 

 creasing depth in the western North Atlantic. It may be 

 that the deep water is actually more stable in this part 

 of the sea than on the eastern side of the central ridge. 

 It is very doubtful, however, whether the apparent result 

 of the "Challenger" observations corresponds to the real 

 conditions. We see, for instance, that the observations 

 at all "Challenger" stations between 30 and 39, at depths 

 between 4480 and 5212 metres, show exactly the same 

 temperature in situ, 2-50" C, with the exception of Stat. 

 32, where the depth is 4214 metres only and rm = 2.61° C. 



It is possible that a minimum of temperature may 

 occur at about 4500 metres in this area. Analogous 

 conditions may be indicated in other areas too. In other 

 words, it is possible that there may be a rise of temperature 

 in the bottom-water in the western North Atlantic as well 

 as in the eastern. The observations at the "Michael Sars" 

 Stat. 63 actually show a slight increase of temperature 

 between 4000 and 4850 metres. However this may be, 

 it seems to be a fairly well established fact that the 

 temperature of the bottom-water is higher, on an average, 

 in the eastern than in the western North Atlantic. 



The potential temperatures calculated from obser- 

 vations near the bottom at depths below 4000 metres are set 

 out in the chart. Fig. 26. Most of them are due to the 

 "Challenger" Expedition and are, therefore, as stated 

 above, of doubtful reliability. They are apt to be too 

 low, unless the minimum temperatures registered by the 

 Miller-Casella thermometers are subject to systematic errors 

 tending to give too high values. In any case, however, 

 the data recorded by the "Challenger" in both parts of 

 the North Atlantic are probably valid for mutual compa- 

 rison and may serve to demonstrate the essential features 

 of the local geographic variations in the bottom-water. 

 The data procured by other expeditions and inserted on 

 the chart, Fig. 26, seem to fit in quite well with the 

 "Challenger" observations. Besides the deepest of the 

 "Michael Sars" observations mentioned above, these data 

 are as shown in the following table: 



Some of the depths recorded for the "Deutschland" 

 observations are uncertain, as the sounding wire was in 

 some cases deflected rather far from the vertical. 



Our chart (Fig. 26) demonstrates appreciable local 

 variations of temperature in the bottom-water. In the 

 eastern North Atlantic potential temperatures are found to 

 be mostly above 2-0'' C. In the southernmost parts, near 

 the equator, some observations show lower values, with 

 a minimum of =^ 1-70^ C. at the "Planet" Stat. 17. 

 At the "Challenger" Stat. 103, where m =. 4526 metres 

 and T„ = 2-22° C, is 1-80° C The low temperatures 

 are due to water which comes from the western South 

 Atlantic by way of a deep passage cutting through the 

 central longitudinal ridge (the Romanche Deep), as sugge- 

 sted by ScHOTT and Schulz [1914] and proved by Bshnecke 

 [1927]. 



The "Challenger" station 104 {in = 4572 metres) was 

 situated about 180 naut. miles W. of Stat. 103. The 

 depths were nearly the same at both stations, but the 

 temperatures observed near the bottom were different. 

 At Stat. 104 Tm was = 2-55° C, the corresponding po- 

 tential temperature being 2-12° C. At Stat. 102, about 

 132 miles E. of Stat. 103, we have m = 4480 metres, 

 im — 2.50° C ai;d ---:: 2-08° C, or nearly the same 

 temperature as at Stat. 104 on the other side of Stat. 

 103. Provided that the observations are fairly correct, 

 we arrive at the important conclusion that the temperature 

 in situ of the bottom-water as well as the corresponding 

 potential temperature may exhibit considerable variations 

 in a horizontal direction even if the depth is greater 

 than 4000 metres. Similar examples are found by com- 

 paring, for instance, the "Challenger" stations 80 and 81, 

 or Stats. 6 and 353 (cf. also the "Deutschland" station 



