The Geographical Journal (Journal of the Royal Geographical Society): Volume XII, No. 2 [‎267r] (36/154)

OCEAN, AND ITS RELATION TO OTHER OCEANOGRAPHICAL PHENOMENA. 127
in the polar regions is in the end similar to that of evaporation in
warmer latitudes. The lighter ice is separated from the denser mother-
liquor, which sinks to the greater depths, leaving the ice on the surface.
These statements as to the effects of range of temperature might be
illustrated by reference to many parts of the ocean. It will be sufficient
to refer to the most striking example, in the southern hemisphere,
where there is a band of large range of temperature right round the
world. 1 he warm tropical waters, which are driven southwards along
the eastern coasts of South America, Africa, and Australia, into the
threat Southern Ocean, there become cooled as they flow to the east
before the strong westerly winds. On account of their high salinity,
these tropical waters can suffer much dilution with antarctic water, and
still be denser than water from these higher latitudes at the same
temperature. Here the density observations and the seawater gases
indicate that a large part of the cold water found at the greater depths
of the ocean probably leaves the surface, and sinks towards the bottom
of the Southern Ocean, between the latitudes of 45° and 56° S.
At a depth of 100 fathoms, the temperature in one part of the ocean
may differ from that to be found in some other part at the same depth
by as much as 42° Fahr.; and at 500 fathoms there may be between one
part and another a range of as much as 20° Fahr.; at 1000 fathoms, a range
not exceeding 11° Fahr.; and at 1500 fathoms, not exceeding 8° Fahr. A
consideration, however, of all the available observations shows that there
is no evidence of any annual variation of temperature at any one spot
in the ocean at a depth of 100 fathoms; and at a depth of 50 fathoms
no annual range greater than 2° Fahr. appears to be indicated. This
remark applies especially to the open ocean; but, although we have
no direct observations, still it is most probable that along certain
coasts a wide range of temperature is occasionally produced at the
bottom in depths of 50 and even 100 fathoms, due to the lateral
shifting of large bodies of water from different sources. The evidence
of movements like these comes especially from regions where polar and
equatorial currents meet, or run alongside of each other in different
directions, as, for instance, in the case of the Gulf Stream and Labrador
current off the eastern coasts of North America,* to which reference
will presently be made in connection with the destruction of the tile-
fish. Those areas, where currents of different temperatures meet, cor
respond with the areas of greatest annual range, indicated on the map
by the deepest shades of blue, and they become the theatre of some
remarkable phenomena, specially interesting to the biologist and
geologist.
II a comparison be made between the map accompanying this paper
and the maps showing the isobrric lines and prevailing winds for
^ . Libbey, Junr., “ ihe Relations of the Gulf Stream and the Labrador Current,”
Report Sixth Intern. Geogr. Congress, London, 1895.