By C.A.M. TABER.
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° 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
waters extend. Especially will this be the case where the snowfall is
great.
Under such conditions, it appears that the only extensive body of
shallow water extending from the ice-clad southern continent is the
shoal channel which separates the South Shetlands from Cape Horn,
which is a region of great snowfall. Therefore, should the antarctic
ice gain sufficient thickness to rest on the bottom of this shallow
sea, it would move into the Cape Horn channel, and eventually close
it. The ice growth would not be entirely from the southern continent,
but also from lands in the region of Cape Horn. Thus the antarctic
continent and South America would be connected by an isthmus of ice,
and consequently the independent circulation of the Southern Ocean
arrested. Hence it will be seen that the westerly winds, instead of
blowing the surface waters of the Southern Ocean constantly around the
globe, as they are known to do to-day, would instead blow the surface
waters away from the easterly side of the ice-formed isthmus, which
would cause a low sea level along its Atlantic side, and this low sea
level would attract the tropical waters from their high level against
Brazil well into the southern seas, and so wash the antarctic
continent to the eastward of the South Shetlands.
The tropical waters thus attracted southward would be cooler than the
tropical waters of to-day, owing to the great extension of cold in the
southern latitudes. Still they would begin the slow process of raising
the temperature of the Southern Ocean, and would in time melt the ice
in all southern lands. Not only the Brazil currents would penetrate
the southern seas, as we have shown, but also the waters from the high
level of the tropical Indian Ocean which now pass down the Mozambique
Channel would reach a much higher latitude than now.
The ice-made isthmus uniting South America to the antarctic continent
would on account of its location be the last body of ice to melt from
the southern hemisphere, it being situated to windward of the tropical
currents and also in a region where the fall of snow is great; yet it
would eventually melt away, and the independent circulation of the
Southern Ocean again be established. But it would require a long time
for ice sheets to again form on southern lands, because of the lack of
icebergs to cool the southern waters. Still, their temperature would
gradually lower with the exclusion of the tropical waters, and
consequently ice would slowly gather on the antarctic lands.
The above theory thus briefly presented to account for the climatic
changes of the high southern latitudes is in full accord with the
simple workings of nature as carried on to-day; and it is probable
that the formation of continents and oceans, as well as the earth's
motions in its path around the sun, have met with little change since
the cold era iced the lands of the high latitudes.
At an early age, previous to the appearance of frigid periods, the
ocean waters of the high latitudes probably did not possess an
independent circulation sufficient to lower the temperature so that
glaciers could form. This may have been owing to the shallow sea
bottom south of Cape Horn having been above the surface of the water,
the channel having since been formed by a comparatively small change
in the ocean's level. For, while considering this subject, it is well
to keep in mind that whenever the western continent extended to the
antarctic circle it prevented the independent circulation of the
Southern Ocean waters, consequently during such times ice periods
could not have occurred in the southern hemisphere.
It will be noticed that according to the views given above, the
several theories which have been published to account for great
climatic changes neglect to set forth the only efficacious methods
through which nature works for conveying and withdrawing tropical heat
sufficient to cause temperate and frigid periods in the high
latitudes. While lack of space forbids an explanation of the causes
which would perfect an ice period in the northern hemisphere, I will
say that it could be mainly brought about through the independent
circulation of the arctic waters, which now largely prevent the
tropical waters of the North Atlantic from entering the arctic seas,
thus causing the accumulation of ice sheets on Greenland. But before a
northern ice period can be perfected, it seems that it will need to
co-operate with a cold period in the southern hemisphere; and in order
to have the ice of a northern frigid period melt away, it would
require the assistance of a mild climate in the high southern
latitudes.--_Science_.
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