1869.] 



on the Scientific Exploration of the Deep Sea. 



473 



(IV.) That the Frigid stream which imparts to our Cold area, in the 

 latitude of the Shetland Islands, a Bottom-temperature helow 30°, may in 

 like maimer he considered as an intensification of the ordinary flow of deep 

 water from the Polar to the Equatorial area, this intensification being due 

 to the peculiar local conditions which limit the flow into the Atlantic basin 

 of the water that has been cooled in the Polar basin, and thus keep it from 

 intermixture with warmer water, whilst, by the narrowing of its channel, it 

 is forced up nearer to the surface. 



(V.) That as the temperature of the Gulf-stream is reduced, and the 

 depth of its stratum diminished, the further it diffuses itself over the sur- 

 face-water of the Atlantic, so the temperature of the Frigid Stream is 

 raised by admixture with the warmer water through which it diffuses itself 

 in the Atlantic basin, whilst it descends deeper and deeper beneath the 

 surface with the increasing depth of the floor on which it rests. 



120. It may be questioned, however, whether the low temperature thus 

 shown to prevail, not only over the deepest portion of the North-Atlantic 

 sea-bed, but throughout the enormous mass of water which lies below the 

 "stratum of intermixture" (§ 117), is attributable solely, or even prin- 

 cipally, to the cooling effect of the comparatively small quantity of frigid 

 water discharged from the Arctic basin into this vast area, through the 

 narrow channels previously indicated (§ 104). For it is to be remembered 

 that the converse heating-action exerted by the solar rays over the southern 

 portion is continually pumping up this cold water (so to speak) from the 

 depths to the surface ; and that this movement will be aided from below 

 by the heat continually imparted from the solid ocean-bed to the colder 

 water which rests upon it. Now as the most trustworthy observations on 

 Deep-seaTemperatures under the Equator, though few in number *, indicate 

 that even there a temperature not much above 32° prevails, it seems pro- 

 bable that part of the cooling effect is due to the extension of a flow of 

 frigid water from the Antarctic area, even to the north of the Tropic of 

 Cancer. It seems impossible to give any other explanation of the low 

 temperatures observed in the 'Hydra' soundings across the Arabian Gulf f, 

 since no frigid water from the Arctic basin could be supposed to find its 

 way to that locality. 



121. The unrestricted communication which exists between the Antarctic 

 area and the great Southern Ocean-basins would involve, if the doctrine 

 of a general Oceanic circulation be admitted, (1) a much more considerable 

 interchange of waters between the Atlantic and the Equatorial areas than 

 is possible in the Northern hemisphere ; and (2) a reduction in the tem- 



* See ' Lightning ' Report, p. 186. 



t ' Lightning ' Report, p. 187, note: — The lowest Temperature actually observed in 

 these Soundings, with Thermometers protected on Admiral Fitzroy's plan, was 36£°. The 

 temperature of 33£° given in the « Lightning ' Report as existing below 1800 fathoms, 

 proves to have been only an estimate formed by Captain Shortland, under the idea that 

 the rate of reduction observed at smaller depths would continue uniform to the bottom, 

 which the Serial soundings of the ' Porcupine ' prove to be by no means the case. 



