Scientific American Supplement No. 819, September 12, 1891Various
Science
Scientific American Supplement No. 819, September 12, 1891
Various
Science -- Periodicals
Having had occasion to cruise a considerable time over the Southern
Ocean, I have had my attention directed to its prevailing winds and
currents, and the way in which they affect its temperature, and also
to the ice-worn appearance of its isolated lands.
It is now generally conceded that the lands situated in the high
latitudes of the southern hemisphere have in the remote past been
covered with ice sheets, similar to the lands which lie within the
antarctic circle. The shores of Southern Chile, from latitude 40 deg. to
Cape Horn, show convincing evidence of having been overrun by heavy
glaciers, which scoured out the numerous deep channels that separate
the Patagonian coast from its islands. The Falkland Islands and South
Georgia abound with deep friths; New Zealand and Kerguelen Land also
exhibit the same evidence of having been ice-laden regions; and it is
said that the southern lands of Africa and Australia show that ice
accumulated at one time to a considerable extent on their shores. At
this date we find the southern ice sheets mostly confined to regions
within the antarctic circle; still the lands of Chile, South Georgia,
and New Zealand possess glaciers reaching the low lands, which are
probably growing in bulk; for it appears that the antarctic cold is
slowly on the increase, and the reasons for its increase are the same
as the causes which brought about the frigid period which overran with
ice all lands situated in the high southern latitudes.
Why there should be a slow increase of cold on this portion of the
globe is because of the independent circulation of the waters of the
Southern Ocean. The strong westerly winds of the southern latitudes
are constantly blowing the surface waters of the sea from west to east
around the globe. This causes an effectual barrier, which the warm
tropical currents cannot penetrate to any great extent. For instance,
the tropical waters of the high ocean levels, which lie abreast Brazil
in the Atlantic and the east coast of Africa in the Indian Ocean, are
not attracted far into the southern sea, because the surface waters of
the latter sea are blown by the westerly winds from west to east
around the globe. Consequently the tropical waters moving southward
are turned away by the prevailing winds and currents from entering the
Southern Ocean. Thus the ice is accumulating on its lands, and the
temperature of its waters slowly falling through their contact with
the increasing ice; and such conditions will continue until the lands
of the high southern latitudes are again covered with glaciers, and a
southern ice period perfected. But while this gathering of ice is
being brought about, the antarctic continent, now nearly covered with
an ice sheet, will, through the extension of glaciers out into its
shallow waters, cover a larger area than now; for where the waters are
shoal the growing glaciers, resting on a firm bottom, will advance
into the sea, and this advancement will continue wherever the shallow
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