1870.] 



Deep-sea Researches. 



189 



ever, in No. III., the temperature undergoes so extraordinarily rapid a de- 

 pression, that it is reduced nine degrees within the next 200 fathoms ; the 

 water at 994 fathoms being only 2° warmer than it is at 1000 fathoms 

 in No. I. A slight further reduction of temperature is noticeable in the 

 two deepest Soundings taken in the Atlantic Cruise of 1870, the tempe- 

 rature found at nearly 1 1 00 fathoms being just 2° higher than that found 

 at 1250 in No. I. 



80. Considering these facts in the light thrown upon the Temperature 

 phenomena of the Atlantic Basin by those of the " Cold Area " explored in 

 1869, it appears clear that we have in the Latitude of Lisbon the same 

 distinct separation between an upper warm and a lower cold stratum as 

 presented itself in the channel between the Shetland and the Faroe Islands ; 

 but whilst the " stratum of intermixture " in the latter lies between 1 50 and 

 300 fathoms, it lies in the former between 800 and 1000 fathoms. It 

 seems perfectly clear that the lower stratum must have had a Polar source ; 

 but there is at present no distinct evidence that the upper stratum is de- 

 rived from any source nearer the Equator. Its temperature, indeed, is lower 

 by 4 or 5 degrees than that of the Mediterranean in the same parallel of 

 Latitude at corresponding depths ; and since the temperature of the latter 

 may be considered as the normal of the Latitude, — this great Inland Sea 

 being virtually excluded from participation in the general Oceanic Cir- 

 culation, — it would seem that the effect of that circulation is rather to 

 lower than to raise the temperature of the upper stratum of this portion 

 of the Atlantic. Its swr/#ce-temperature also, as already shown (§ 45), 

 is decidedly lower than that of the Mediterranean under the same parallel ; 

 and the limitation of the superheating to its most superficial layer is in 

 entire accordance with our Mediterranean observations upon this point 

 (§ 87). — Hence it seems a justifiable conclusion that neither the super- 

 ficial layer nor any portion of the upper stratum of the Atlantic water 

 that laves the coasts of Spain and Portugal receives any accession of heat 

 from the extension of the Gulf-stream into its area*. 



81. "When, however, we compare the Temperatures of this upper stratum 

 at different depths with those which are met with at Stations much further 

 North (as tabulated in Par. 110 of the Report for 1869), there is found to 

 be a remarkable correspondence in the general rate of reduction with depth, 

 except in this particular, — that the influence of the cold stratum beneath 

 begins to be decidedly marked much nearer the surface; so that instead of a 

 very slight reduction between 500 and 800 fathoms, and then a very rapid 

 passage through a "stratum of intermixture" of 200 fathoms, as in the 



* It may be said that this conclusion, though it may be true as regards the summer 

 temperature of this marine area, is " not proven" as regards its winter temperature. 

 The data furnished, however, by the comparison of the Winter climates of stations 

 along the Atlantic Sea-bord, with those of Mediterranean Stations in corresponding 

 Latitudes, indicate that it is as true for "Winter as for Summer. (See • Proceedings of 

 the Eoyal Geographical Society' for Jan. 9, 1871.) 



