72 THE ANTARCTIC MANUAL. 
Low Ockanic TEMPERATURES: Ick aT SEA AND ON LAND, &c.* 
One of the striking features of the ocean discovered by the 
Challenger expedition, was the extensive area of very cold water 
which occupies the bottom of the sea from the east coast of South 
America to the ridge which runs north and south in the meridian of 
the island of Ascension. Here the bottom temperature was found 
to be 32°'5 Fahr. The existence of this exceptionally cold bottom 
water was discovered on the outward voyage in soundings near the 
Brazilian coast, so that the expedition was prepared to take up the 
study of it on the way home. This was done very thoroughly on a 
line from the mouth of the river Plate along the parallel of 35° to 
the meridian of Ascension. The depth of the water varied from 
1900 to 2900 fathoms, and the distribution of temperature in the 
water was, roughly, a warm surface layer of perhaps 100 to 200 
fathoms, then a thick layer of water of temperature about 36° Fahr. 
down to 1600 fathoms near the coast, and to 2200 fathoms or there- 
abouts at sea. Here was-a steep temperature-gradient falling away 
rapidly from 35° to 33° Fahr., and more slowly to 32°°5 Fahr. The 
occurrence of the steep gradient shows a renewal of the water, and 
therefore a current. The observations of the Valdivia show a similar 
distribution in lat. 60° to 63°S., with this difference—that the surface 
layer is colder than the intermediate one, which is itself colder than the 
former intermediate, being about 34° Fahr. The bottom layer has as 
low a temperature as 31°°5 Fahr. Unfortunately, there are not enough 
determinations of the temperature of the deeper layers to indicate the 
gradient which separates the cold bottom water from the comparatively 
warm intermediate water. The recommendation, therefore, which the 
writer would make is, that in these regions temperature observations 
in the deeper layers should not be spared, and where there is water 
of exceptional coldness at the bottom, the position and steepness of 
the gradient which separates it from the overlying water should be 
accurately determined. Further, as the whole range of temperature 
to be dealt with in Antarctic water is at the most from 28° to 35° or 
36° Fahr., and therefore small differences of temperature are relatively 
of great importance, it is well to have the thermometers constructed 
specially for this work, the scale containing few degrees, but these wide 
apart. In the survey of the Gulf of Guinea in the Buccaneer, the writer 
had such thermometers, and he regularly sounded with one thermo- 
meter at the end of the wire, and another usually 250 fathoms above it. 
* On the Physical and Chemical Work of an Antarctic Expedition, by J. Y. 
Buchanan, F.RWS. Geographicul Journal for November 1809. 
