On the Temperature and Animal Life of the Deep Sea*

Abstract

DURTNG the first and second cruises of the Porcupine, the temperature of the eastern border of the great North Atlantic basin was examined at various depths between from 54 to 2,435 fathoms, and in widely different localities, ranging from lat. 47° to lat. 55°. The bottom-temperature was ascertained at thirty stations, and serial soundings were taken at seven stations; making the total number of observations eighty-four. (Table II., p. 20.) Amongst all these the coincidence of temperatures, at corresponding depths is extraordinarily close; the chief differences showing themselves in the temperature of the surface and of the stratum immediately beneath it. A decided superheating is observable in this superficial stratum, not. extending to a depth of much more than 70 or 80 fathoms, and more considerable at the southern than at the northern stations. Whether this “superheating” is entirely due to the direct influence of solar heat, or depends in any degree on an extension of the Gulf Stream as far as the southern part of the area examined, is a question which can only be resolved by the determination of its relative amount at.different seasons. Between 100 and 500 fathoms, the rate of decrement is very slow, averaging Only about 3° in the whole, or three-fourths of a degree for every 100 fathoms; and this body of water has a temperature so much above the isotherm of the northern stations at which the observations were made, as decidedly to indicate that it must have found its way thither from a southern source. Between 500 and 750 fathoms, however, the rate of decrease becomes much more rapid, the reduction being 5.4° or above 2° per 100 fathoms; while between 750 and 1000 fathoms it amounts to 3.1°, bringing down the temperature at the latter depth to an average of 38.6°. Beneath this there is still a slow progressive reduction with increase of depth, the temperature falling a little more than 2° between loop and 2,435 fathoms; so that at the last-named depth, the greatest at which it was ascertained, it was 36.5°.—Thus it is obvious either that the vast body of water occupying the deeper half of the Atlantic basin has been itself derived from a colder region, or that its temperature has been reduced by the diffusion through it of frigid water from a Polar source, The latter supposition best accords with the gradual depression of temperature exhibited between 500 and 1000 fathoms, which corresponds with the “stratum of intermixture” of the cold area.