792 REPORT—1899. 
deep-sea thermiometers, from the electric resistance of telegraph cables resting on 
the bed of the great ocean-basins, and from the temperature of large masses of 
mud and ooze brought up by the dredge from great depths. These observations 
are now sufficiently numerous to permit of some general statements as to the 
distribution of temperature over the bottom of the great oceans. 
All the temperatures recorded up to the present time in the sub-surface waters 
of the open ocean indicate that at a depth of about 100 fathoms seasonal variation 
of temperature disappears. Beyond that depth there is a constant, or nearly 
constant, temperature at any one place throughout the year. In some special 
positions, and under some peculiar conditions, a lateral shitting of large bodies of 
water takes place on the floor of the ocean at depths greater than 100 fathoms. 
This phenomenon has been well illustrated by Professor Libbey off the east coast 
of North America, where the Gulf Stream and Labrador Current run side by side 
in opposite directions. This lateral shifting cannot, however, be called seasonal, 
for it appears to be effected by violent storms, or strong off-shore winds bringing 
up colder water from considerable depths to supply the place of the surface 
drift, so that the colder water covers stretches of the ocean’s bed which under 
normal conditions are overlaid by warmer strata of water. Sudden changes of 
temperature like these cause the destruction of innumerable marine animals, and 
produce very marked peculiarities in the deposits over the areas thus affected. 
It is estimated that 92 per cent. of the entire sea-floor has a temperature lower 
than 40° F. This is in striking contrast to the temperature prevailing at the surface 
of the ocean, only 16 per cent. of which has a mean temperature under 40° F. 
The temperature over nearly the whole of the floor of the Indian Ocean in deep 
water is under 35° F. <A similar temperature occurs over a large part of the 
South Atlantic and certain parts of the Pacific, but at the bottom of the North 
Atlantic basin and over a very large portion of the Pacific the temperature is 
higher than 35°F. In depths beyond 2,000 fathoms, the average temperature 
over the floor of the North Atlantic is about 2° F. above the average temperature 
at the bottom of the Indian Ocean and South Atlantic, while the average tempera- 
ture of the bed of the Pacific is intermediate between these. 
It is admitted that the low temperature of the deep sea has been acquired at. 
the surface in Polar and sub-Polar regions, chiefly within the higher latitudes of 
the southern hemisphere, where the cooled surface water sinks to the bottom and 
spreads slowly over the floor of the ocean into equatorial regions. These cold 
waters carry with them into the deep sea the gases of the atmosphere, which are 
everywhere taken up at the surface according to the known laws of gas absorp- 
tion. In this way myriads of living animals are enabled to carry on their exist- 
ence at all depths in the open ocean. The nitrogen remains more or less constant 
at all times and places, but the proportion of oxygen is frequently much reduced in 
deep water, owing to the processes of oxidation and respiration which are there 
oing on. 
5 The deep sea is a region of darkness as well as of low temperature, for the 
direct rays of the sun are wholly absorbed in passing through the superficial layers 
of water. Plant-life is in consequence quite absent over 93 per cent. of the bottom 
of the ocean, or 66 per cent. of the whole surface of the lithosphere. The abundant 
deep-sea fauna, which covers the floor of the ocean, is therefore ultimately dependent 
for food upon organic matter assimilated by plants near its surface, in the shallower 
waters near the coast-lines, and on the surface of the dry land itself. 
As has been already stated, about 7,000,000 square geographical miles of the 
sea-floor lies within the 100-fathom line, and this area is in consequence subject to 
seasonal variations of temperature, to strong currents, to the effects of sunlight, 
and presents a great variety of physical conditions, The planktonic plant-life is 
here reinforced by the littoral seaweeds, and animal-life is very abundant. About 
40 per cent. of the water over the bottom of this shallow-water area has a mean 
temperature under 40° F., while 20 per cent. has a mean temperature between 40° 
and 60° F., and 40 per cent. a temperature of over 60° F. 
It follows from this that only 3 per cent. of the floor of the ocean presents 
conditions of temperature fayourable for the vigorous growth of corals and those 
