[Illustration: No. 1.
THIS MAP SHOWS THE SPREAD OF GLACIERS AND ICEBERGS, AND THE EXTENSION
OF SOUTHERN LANDS DURING ICE AGE AND ALSO THE DIRECTION OF WINDS AND
OCEAN CURRENTS.]
[Illustration: No. 2.
THIS MAP SHOWS THE SPREAD OF GLACIERS AND ICEBERGS AND THE DIRECTION
OF WINDS AND CURRENTS AT THIS DATE.]
THE
COMING ICE AGE.
BY
C. A. M. TABER.
BOSTON:
GEO. H. ELLIS, 141 FRANKLIN STREET.
1896.
COPYRIGHT, 1896.
BY C. A. M. TABER.
GEO. H. ELLIS, PRINTER, 141 FRANKLIN STREET, BOSTON.
PREFACE.
The explanations given in the following pages, in which I have sought
to show the manner in which an ice age is being brought about, is an
extension of a treatise on “The Cause of Warm and Frigid Periods,”
which I published in a small edition in 1894. And, from the small
number of copies circulated, only a few came to the hands of persons
particularly interested in such matter. Yet there were instances of
its having proved of special interest to persons celebrated for their
geological attainments, and also to instructors in physical geography.
Besides, it received considerate notice in some of the leading reviews.
Being thus somewhat encouraged, and thinking that the subject was too
important to be neglected, I have given it further study during the
last year, and meanwhile have obtained additional information from
recent discoveries which has served to corroborate my views. Hence I
have been able to be more explicit in my explanations in the present
volume than in my earlier writings. Still, while acting as a pioneer in
the matter, it will be seen that I have only attempted to expose the
main outlines, as my age and failing health will not permit me to enter
into the voluminous details necessary for a full explanation. In order
to show why my attention has been turned to the great climatic changes
which have taken place during past ages, and now threaten the future, I
will repeat the introduction of my earlier publication, wherein I wrote
that “the reason why I have undertaken to explain the causes which have
brought about the warm and cold epochs is because of my being unable
to harmonize the several theories that have been published with the
general mode of action which nature pursues to-day. Having in the early
part of my life been employed for a score of years in the whaling
service, during which time my sea voyages were passed in cruising over
the North and South Atlantic, and over the Indian Ocean, from latitudes
north of the equator to the southern shores of Kerguelen Land, and
along the seas of Southern Australia, I also, in my searching, cruised
over the Pacific Ocean from the icy seas south of Cape Horn to the
northern latitudes of Alaska, and, from New Zealand in the Western
Pacific to the numerous islands in the tropical zone. And it may be
said that among the chief things to be learned on such voyages was the
direction of the prevailing winds and surface currents of the sea. Thus
the impressions then received were in mind when, in after years, I had
my attention drawn to the several theories advanced for explaining the
causes which produced the warm and frigid epochs. But, so far as my
marine experience goes, such theories have not harmonized with nature’s
mode of operating at this age of the world. Therefore, I have conceived
views which, to my mind, are more agreeable to the simple operations of
nature of which I have long been witness. Consequently, I have written
several short essays on climatic changes since 1880, and also letters
relating to the same subject, which have been published in _Science_
and _Scientific American_. But the space allowed for the introduction of
such matter was necessarily too limited for so wide an explanation as
the subject required. The views then advanced I have again repeated,
with the addition of several facts pertaining to physical geography,
which, so far as I know, have never before been published.”
WAKEFIELD, MASS., U.S.A.
June, 1896.
CONTENTS.
CHAPTER I.
PAGE
CAUSE OF COLD AND MILD PERIODS, 9–36
Traces of ancient glaciers in temperate zones, 9;
prevailing winds the main cause of the circulation of
the ocean waters between the tropical and temperate
zones, 10; general direction of prevailing winds, and
how, in connection with continents, they circulate the
surface waters of the sea, 11; high and low sea-levels;
separation of antarctic lands from South America, 12;
Captain Larsen’s discoveries in antarctic regions,
13; how low lands south of Cape Horn were submerged,
13; how the winds move more surface water southward
than northward, 14; Dr. Croll’s views on winds and
ocean currents, 16; under-currents of the ocean, and
how caused, 16; Gulf Stream currents, 17; antarctic
under-currents, 18; why the winds were able to force
more of the ocean waters southward than northward
at the close of the Tertiary age, 19; Mr. Alfred R.
Wallace’s views on Tertiary seas, 20; how the Cape Horn
channel affects the ocean currents, 21; cause of the
increase of cold in southern latitudes, 22; how the
Cape Horn channel is closed during ice age, and its
effect on ocean currents and temperature of southern
latitudes, 24; the melting of glaciers from southern
lands, 27; a salt sea requisite for circulation during
ice age, 28; direction of surface currents in southern
seas, 29; Humboldt current, 30; Agulhas current, 32;
temperature of arctic ice, 34; movement of southern
icebergs, 35; glaciers south of Cape Horn, 36.
CHAPTER II.
HOW ICE PERIODS IN THE NORTHERN HEMISPHERE ARE BROUGHT
ABOUT, 37–54
Northern seas during Tertiary age, 37; Gulf Stream during
Tertiary times, 38; the origin of a cold period in the
northern hemisphere, 38; remarks on Gulf Stream and
arctic currents, 39; circulation of arctic waters, 40;
arctic channels during ice age, 41; how the weight of
glaciers in the northern hemisphere attracts the waters
of the southern seas during ice age, 42; Professor
Prestwich on the submergence of European lands, 43;
the great Atlantic tide rips the head-waters of the
Gulf Stream, 44; high sea-level of Atlantic calm
region, 45; tropical Atlantic currents, 46; Sargasso
Sea, 48; arctic and Gulf Stream currents, 49; Pacific
Ocean currents, 50; slow growth of an ice period, 52;
reduction of Cape Horn channel, 53; permanence of
antarctic glaciers elevated above the snow-line during
mild periods, 54.
CHAPTER III.
SPREAD OF GLACIERS DURING COLD EPOCHS, 54–61
Spread of glaciers in tropical zone, 54; Professor Agassiz
on the origin of Galapagos Islands, 55; the bowlders
of Hood’s Island and rookery of Albatross, 56; alpine
flora of Galapagos and tropical America, 57; Mr. J.
Crawford on ancient glaciers in Nicaragua, 58; Cuba and
Republic of Colombia during ice age, 58; destruction
of animal life during glacial age, 59; temperature
of North Atlantic and Mediterranean Sea during ice
age, 60; temperature of ocean during warm epochs, 61;
generative age ascribed to warm eras; Professor Wright
on pre-glacial man, 61.
CHAPTER IV.
THE GLACIERS OF THE TEMPERATE ZONE, 62–75
Professor Hitchcock on the early history of North America,
62; glacial deposits of Nantucket and Martha’s
Vineyard, 63; Professor James Geikie on the glacial
deposits of Northern Italy, 64; California coast ranges
the work of Sierra glaciers, 65; ancient glaciers on
the Pacific slope north of California, 67; Professor
Geikie’s views on the ancient glaciers in the Salt
Lake region, 68; Colorado Cañon, 69; the conglomerate
deposits in the Appalachian district, 69; remarks on
the glacial boundaries in United States during ice age,
70; sands of Florida, 71; ancient ice-sheets of the
plains west of the Mississippi River, 73; the driftless
region of Wisconsin, 74; tropical waters of North
Atlantic chilled during ice age, 75; the drifted snow
of British America and Siberia during ice age, 75.
CHAPTER V.
REMARKS ON THEORIES ADVANCED FOR EXPLAINING ICE PERIODS, 76–93
Professor Geikie on supposed causes of the glacial period,
76; change in the relative level of the land and sea
during glacial and post-glacial times, 77; submergence
of northern lands at close of ice age, 78; the main
cause of the movement of water from the northern seas
at the close of glacial age, 79; why the earth-movement
hypothesis should be rejected, 79; glaciers of Europe
and Alaska, 80; North Pacific currents, 81; why the
Pacific waters are growing cool, 82; the lowering
temperature of the northern seas, 83; the increase of
cold in Europe and Asia, 84; falling temperature of
the Andean region, 85; General Drayson’s astronomical
discoveries for explaining the cause of ice periods,
87; why the Gulf Stream was always confined to the
North Atlantic, 89; the improbability of the Indian
Ocean currents entering the arctic seas, 90; why the
increase of glaciers must continue while the Cape Horn
channel maintains its present capacity, 91; comments on
the coming ice age, 92; tropical zone the abode of man
during ice age, 93; preservation of the tropical ocean
fauna through the glacial period, 93.
CHAPTER I.
CAUSE OF COLD AND MILD PERIODS.
It is now generally conceded by those who have given the subject much
attention that the greater portion of North America above the latitude
of 39° north to the shores of the Arctic Ocean has been furrowed and
scoured by the action of ice.
Vast traces of ancient glaciers are also found in Europe; for it is
reported that ice-sheets have left unmistakable marks of having overrun
the greater part of the lands lying between the arctic seas and the
latitude of the Pyrenees.
In Asia evidences of glacial action have been noticed from Northern
Siberia to the mountains of Syria.
The great glaciers of Himalaya have in times past attained gigantic
proportions. In Northern China huge bowlders are found scattered over
the valleys, and a long distance from the mountains.
The southern hemisphere, in proportion to the extent of its land
surface, shows ample traces of former ice action. From the latitude of
38° south to the southern extremity of the western continent there is
said to be the clearest evidence of former glacial action in numerous
bowlders scattered over the land.
On the shores of the South Pacific, from the Island of Chiloe to
Cape Horn, the coast is fringed with deep fiords, which appear to be
channelled out by ice, like the fiords of Norway and Greenland. And at
this date the mountains of that southern region are covered with snow,
and the glaciers which flow down the valleys are said to reach the
tide-water as far north as the latitude of 47° south. The glaciers of
New Zealand, now of Alpine proportions, during the ice age descended
to the sea, and channelled the deep fiords on its south-western coast;
and certain traces of glacial action have been observed in Southern
Australia, and also in the province of Natal, South Africa.
Kerguelen Land is pierced with deep, narrow fiords, which have the
appearance of having been the work of ancient glaciers.
The lands south of the antarctic circle are to-day supposed to be
covered by an ice-sheet, of which the great ice barrier surrounding
that region furnishes ample proof.
While impressed with the above reports of the work of ancient
glaciers, in connection with my own observations along the shores of
the several oceans, I have been led to seek for the physical causes
which brought about the great climatic changes of past geological
ages. And, while having the subject under consideration, I have had my
attention directed to the manner in which the great prevailing winds in
connection with continental lands are able to move the heated surface
waters of the tropical oceans into the colder zones, and also transfer
the cold waters of the higher latitudes into the tropical zones.
And it is through this grand movement of the ocean waters that we are
enabled to account for the difference in the temperature of places now
lying in the same parallels of latitude.
The natural methods for conveying tropical heat into the higher
latitudes, and also for excluding it therefrom, are so simple and
efficient that on due consideration we are able to conceive how epochs
possessing mild climates have been succeeded by periods of frigidity.
It has been admitted by several writers on climatic changes that,
should the tropical surface waters of the ocean be moved into the
high latitudes in large volume, thus adding their warmth to the heat
imparted by the sun, such combined heat would cause a mild climate.
And it has been estimated that the amount of equatorial heat moved
into the temperate and polar regions of the northern hemisphere by
the Gulf Stream alone is equal to one-fourth of all the heat received
from the sun by the North Atlantic from the tropic of Cancer to the
arctic circle. Still, it appears to me, while viewing the subject from
a marine standpoint, that the explainers of climatic changes have never
fully comprehended the manner in which the surface waters of the ocean
are moved from the tropics into the high latitudes, and returned from
the high latitudes to the tropics. Consequently, they have neglected
necessary and efficient natural agents in their explanatory theories,
and with much learning and ingenuity have laboriously sought to show
how great changes of climate could be brought about through other
causes.
But when we notice the simple methods employed by nature to-day for
transferring the heat of the tropics into the higher latitudes, and
also the manner of excluding such heat therefrom, they appear to afford
an explanation for the great changes of climate which have taken place
during past ages; for it appears that the natural manner of proceeding
by which heat is moved from the torrid zone into the high latitudes
sufficient to cause a mild climate is through the ocean currents which
are constantly set in motion by the great prevailing winds of the
globe. These winds, as is well known, blow mostly from the east toward
the west in the tropics, and from the west toward the east in the high
latitudes.
This counter-movement of the winds, in connection with a continent
extending both northward and southward from the equator over many
degrees of latitude, such as obtains on the western continent, is
abundantly able to create extensive depressions and elevations on
the ocean’s surface, and thus cause vast streams of water to move by
gravity from the high sea-levels to the low sea-levels; and in this
way the tropical waters have been moved during past ages, and to a
considerable extent are now moved far into the northern and southern
seas.
This transfer of the ocean waters is the main cause of a temperate
climate being enjoyed by countries situated in the high latitudes at
this age.
But, in order that the tropical currents should be able to flow into
the high latitudes, in quantities sufficient to cause all lands and
seas situated in such latitudes to enjoy a mild climate, it would be
necessary that the land should extend unbroken, or nearly so, from
the arctic to the antarctic circles. Thus, with a continent of such
vast extent, the westerly winds would blow the surface waters of the
ocean away from the eastern shores in the high latitudes, and so cause
extensive low sea-levels; while the easterly winds of the torrid zone
would heap the surface waters of the ocean against the eastern tropical
shores of the continent. Consequently, the warm waters of the tropical
high sea-level would be moved by gravity to the low sea-levels of the
high latitudes, even to the arctic and antarctic regions, and thus
afford them a mild climate. In this way we account for the mild climate
enjoyed on lands and seas within the high latitudes during the warm
epochs anterior to the glacial periods.
As the western continent is the only land that extends unbroken from
the equator to the cold latitudes of both hemispheres, thus affording
an opportunity for the prevailing winds to move the tropical waters
into the high latitudes, I will call attention to that portion of the
continent which extends far southward into the southern ocean, where
the winds and ocean currents have the greatest range and power to
affect the climate on different parts of the globe. Here we see South
America separated from the antarctic continent by a wide channel of
deep water, where the westerly winds blow with great force. The space
now covered by this interesting channel, owing to its being situated in
the high southern latitudes, must have been occupied by a channel of
comparatively small capacity, or else an isthmus of low land uniting
the southern portion of South America with the antarctic continent
during the warm epochs when the beds of the ancient seas of the
northern hemisphere contained a considerable portion of the water now
swelling the southern ocean.
Therefore, the obstructions which separated the Pacific Ocean from
the South Atlantic furnished opportunity for the westerly winds to
force the surface waters of the sea away from the leeward side of such
obstructions, causing a vast low sea-level, sufficient to attract the
tropical waters heaped against Brazil by the trade winds into the
southern seas in adequate quantity to cause a mild climate throughout
the antarctic regions through long periods of time.
Recent discoveries have proved that these high southern latitudes have
been subject to great changes of climate. According to the reports
from the Dundee whalers, while searching for seal in the icy seas that
surround the South Shetlands, they met with the Norwegian ship “Jason,”
Captain Larsen, who had traced the eastern shore of Graham Land to 68°
south latitude, noting two active volcanoes.
The same mariner brought from Seymour Island fossil shells and
coniferous wood of the Tertiary epoch.
These furnish sufficient evidence to show that a warmer climate once
prevailed there.
At the commencement of the glacial age the obstructions which separated
the South Pacific from the South Atlantic had become deeply submerged
by the sea, which may have been caused by a tendency of the ocean’s
waters to move southward or by a comparative small movement in the
earth’s crust. But, on account of the stability of the crust of the
earth during times so late as the glacial epochs, the submergence of
this southern region was probably owing to the movement of the ocean’s
waters from the northern hemisphere into the southern hemisphere,
which appears to have been brought about mostly through the agency of
the great prevailing winds; for it seems to have happened that the
prevailing winds on account of the disposition of the lands and seas
were able to move more of the ocean waters southward than they moved
northward during the age preceding the glacial periods. The waters
thus slowly and gradually forced into the high southern latitudes
must have deprived the northern hemisphere of their heaviness, and
added their weight to the southern hemisphere. Therefore, the waters
moved southward could not all be returned to the seas of the northern
hemisphere by gravity, for the reason that the earth’s centre of
attraction would change in accordance with the weight of water moved
from the northern hemisphere into the southern. It will thus be seen
that, while the northern seas were drained or became shallow, the
augmented southern oceans deeply submerged the region south of Cape
Horn, thus widely separating the western continent from the antarctic
lands.
Although the south-east trade winds on the eastern sides of the
Atlantic and Pacific Oceans extend further northward than the
north-east trade winds extend southward, owing to the heated tropical
shores north of the equator being more extensive than such lands
south of the equator, still, on account of the general weakness of
the south-east trade winds at the equator, and also because of the
obstructing northern lands, they have during remote times, and at this
age, been largely prevented from impelling the surface waters of the
sea into the northern latitudes in opposition to the brisk north-east
trades. Furthermore, on account of the widening of the oceans as they
extend southward, the surface currents setting in the latter direction
have more broad and easy passages than the great currents setting
northward.
Moreover, the great currents setting southward on the western sides
of the oceans south of the equator are also much assisted during the
southern summer months by the strong north-east monsoons which prevail
along the east coast of equatorial Africa and the east coast of South
America as far as the latitude of 30° south.
The South African current is impelled northward by the trade winds down
the south-western coast of Africa; but it is debarred from entering
the northern latitudes by the Guinea currents, and so turned away into
the south equatorial current which flows into the Brazilian stream.
The Gulf Stream is much obstructed in its northern movement by the
narrow Florida channel and the opposing arctic currents, and also
by the trend of the North American coast eastward; while its return
current on the eastern side of the Atlantic has a much less obstructed
passage in its southern movement, and, while on its way past the Azores
and Madeira Islands, is largely assisted by the prevailing winds.
The Brazil current, with the impelling force of a strong north-east
monsoon during the summer season, has no obstruction whatever in its
southern passage until it meets with an offshoot from the great drift
current of the southern ocean.
And the same favorable conditions are obtained by the great currents
setting southward on the western sides of the South Pacific while on
their way to the low sea-levels east of Southern Australia and New
Zealand. That portion of the equatorial stream of the Pacific which
continues west across the Indian Ocean finds no open passage to the
northern seas. Consequently, it turns south along the east coast of
Africa into the southern seas.
Therefore, this current, in connection with the great currents setting
southward east of Australia, offsets the great Humboldt current setting
north along the coast of Peru.
In the North Pacific the Japanese current setting northward is
obstructed by the narrowing of the ocean; while its return current
on the American side has a constantly widening ocean on its passage
southward, and also favorable winds to impel the surface waters toward
the equator. Still, with all the facilities above mentioned for the
movement of the ocean waters into the southern latitudes, it is
probable that since the shallow seas of the northern hemisphere were
drained, or much diminished, the prevailing winds have not possessed
sufficient force to further augment the southern seas, because of the
superior weight of the land in the northern hemisphere compared with
the lands south of the equator.
It will appear to those who attribute the rotation of the earth as
being the main cause of ocean currents that I am too much given
over to the wind theory. But I have reason to believe, as Dr. Croll
has asserted, that “the winds are the principal cause of the ocean
currents, and are not due to the trade winds alone, but to the general
impulse of the prevailing winds of the globe.”
Dr. Croll also declares that “all of the principal currents of the
globe are moving in the exact direction which they ought to move,
assuming the winds to be the sole impelling cause.”
Those who think that the rotation of the earth is the real cause of
the movement of the great surface currents of the sea should explain
in some reasonable way why the Agulhas current turns west into the
Atlantic from the Mozambique stream, and why the Guinea current turns
to the east from the main tropical current of the North Atlantic; for
it seems that these two great currents move in direct opposition to the
rotation theory, while at the same time many things go to show that
they receive their motion from the winds. This view of the question
will receive further attention in succeeding pages.
It is the opinion of some writers that a difference of temperature
and density between the waters of the polar latitudes and the torrid
zone is the principal cause of the movement of the surface waters of
the ocean from the equatorial latitudes toward the polar seas, and
so returned in under-currents; and this is a favorable factor for
assisting the winds on some parts of the sea, especially in aiding the
Brazil current in moving the surface waters from the high sea-levels
abreast Brazil, and the equatorial calm belt of the Atlantic into the
southern ocean, and also for favoring the surface currents setting
southward on the western sides of the South Pacific and Indian Oceans.
Yet, whatever gravitating force it may possess for assisting the
above-named currents, it would also act against the impelling force of
the trade winds, while they were drifting the surface waters northward
toward the equator on the eastern sides of the several oceans, and also
to retard the returning surface currents, while being drifted by the
winds southward on the eastern sides of the North Atlantic and North
Pacific. Therefore, while it would seem to favor the winds in their
work on the one hand, it would act as an opposing agent on other parts
of the ocean. Still, the difference of temperature between the tropical
and antarctic seas probably does act in opposition to the wide and
brisk trade winds on the eastern sides of the great oceans south of the
equator, and so prevents their impelling the surface waters northward
to a great extent; and this seems to be one great cause of there being
less surface water moved northward than southward over the greatest
oceans of the globe.
The theory that the difference of density caused by the difference
of temperature between the polar seas and the equatorial oceans made
under-currents to flow from the polar latitudes, and meet in the
equatorial seas, can only be carried on in the Atlantic Ocean, and in a
comparatively less perfect way in the Pacific Ocean, and not at all in
the Indian Ocean.
The North Atlantic being open to the Arctic Ocean, a portion of the
Gulf Stream waters that enter it from the north-west of Europe do sink
and return southward in under-currents; and the cold waters which pass
down the east and west coast of Greenland also sink under the Gulf
Stream while on their southern movement. The meeting of these arctic
currents with the cold under-currents from the antarctic seas in the
tropical zone is probably one cause of their cold waters rising near
the surface of the sea in the torrid latitudes of the Atlantic; and
the same conditions probably obtain in a somewhat less degree in the
Pacific Ocean.
Yet it appears that the cold waters of the Antarctic occupy the largest
space in the tropical zone, even in the North Atlantic. Dr. Carpenter,
in his lectures on Ocean Currents, speaks of meeting with antarctic
water so far north as the latitudes of the West India Islands; and
he also says that all of the Pacific Ocean at its depths is supplied
from the Antarctic Ocean, as are the cold under-waters of the tropical
Indian Ocean, which extend over twenty degrees north of the equator.
Thus, from what we can learn of the antarctic under-currents, they seem
to show that they are not wholly attracted northward on account of
the difference of temperature between the antarctic and the tropical
oceans, but partly because of more surface water being moved southward
by the prevailing winds than they are able to move northward.
And it appears that, if through the winds, combined with the difference
of temperature between the antarctic seas and the equatorial waters,
and also because of the oceans widening toward the south, more surface
water is being carried southward than northward, the waters of the
under-currents so caused must rise toward the surface in the latitudes
from which they were first removed. Having called attention to the
fact that the prevailing winds are not able at this date to augment
the southern ocean waters from the scanty northern seas, because of
the preponderance of northern lands, still there is reason to believe
that even now, owing to the form of continents and oceans, and the
attraction of the tropical surface waters into the Antarctic Ocean
because of the difference of density between the warm and cold seas,
the prevailing winds of this age are able to force more of the surface
waters of the sea southward than they force northward; but, owing to
the superior weight of the land in the northern hemisphere, the surplus
surface water forced into the southern seas is returned by gravity
after being cooled by the antarctic ice, and so adding to the deep
under-currents which flow with a sluggish movement over the bottom of
the sea into the tropical and northern temperate latitudes. And in this
way the northern oceans are maintained at their present sea-level.
The cold under-currents are probably assisted in their northern
movement by whatever difference there may be in the density of the
antarctic waters over the bottom waters of the equatorial seas. But,
as such currents extend into the northern tropical latitudes of the
northern hemisphere, it seems that the winds are the main cause of the
under-currents which carry so much antarctic cold into the northern
tropical seas, because the winds have forced an undue proportion
of ocean surface water southward, to be attracted northward in
under-currents by the preponderating northern lands.
Yet, notwithstanding the superior weight of land in the northern
hemisphere, it appears that there have been periods when there was
somewhat more water in the oceans of the southern hemisphere than now;
for it is reported that a portion of the low lands of Australia show
traces of having been submerged during late geological times.
This may have happened through an increased weight in the antarctic
glaciers, which have in past ages, and probably may in future epochs,
cause more of the ocean waters to be attracted southward than now
obtains. But it is probable that an increase of southern ice would be
largely counterbalanced by the accumulation of ice on northern lands.
Yet it appears certain that since the Tertiary epoch the waters of
vast shallow seas have been moved from the northern hemisphere into
the southern. The dry beds of the ancient northern seas encourage this
opinion, while the comparatively small area of southern lands serves to
support such views.
Still, during the ages prior to the glacial periods, while the low
lands of the northern hemisphere were covered by the sea, the wide
shoal channels which submerged the lower portion of North America
afforded convenient passages for the surface waters of the ocean in
their northern movement, and so prevented the oceans of the southern
hemisphere from gaining undue preponderance.
Hence long geological ages passed away before the winds were able
to force more of the ocean waters southward than they could move
northward, and thus augment the southern ocean from the waters of the
northern seas. But the slow growth of such immense marine deposits
in the shallow seas as are found in the Florida Peninsula and other
portions of that region was at length sufficient to greatly obstruct
the passage of the Gulf currents in their northern movement, and thus
cause conditions which enabled the winds to force more of the ocean
waters southward than they could move northward after the close of the
Tertiary epoch.
Mr. Alfred R. Wallace says in “Island Life” that the seas in the
northern hemisphere during the Tertiary period covered a much larger
area than now, and extended across Central Europe and portions of
Western Asia, and the Arctic Ocean was enlarged.
As it is not likely that any portion of the waters of the sea have been
absorbed by the earth during the late epochs in the world’s history,
therefore the ocean waters have not diminished except during cold
periods, when the water evaporated from the sea was converted into ice,
and, eventually, again returned to the sea.
Thus it necessarily follows that, when the seas of the northern
hemisphere contained a much larger portion of the waters of the globe
than at this age, the seas of the southern hemisphere must have
contained proportionally less. Consequently, during such times a
portion of the shoal seas of the high southern latitudes must have been
dry land. Therefore, this must have been the condition of the shallow
sea basins in the region of Cape Horn.
Mr. Wallace also says that “many peculiarities in the distribution of
plants and some groups of animals in the southern hemisphere render it
almost certain that there has sometimes been a greater extension of
antarctic lands during Tertiary times.”
And he also asserts that the great ocean basins have not changed, and
that the form of continents has been permanent. It will thus be seen
that it was through the movement of the ocean’s waters southward that
the low lands south of Cape Horn were covered with water previous to
the frigid periods, and so caused the wide separation between the
western continent and the antarctic lands.
The Cape Horn channel thus enlarged, the continuous mildness of the
high southern latitudes which possessed the earlier ages came to an
end, and gave place to alternate epochs of frigid and mild weather.
For it appears that it is owing to the creation or enlargement of the
Cape Horn channel that it is possible for frigid periods to be brought
about, for the reason that its enlarged space of water prevents the
westerly winds from maintaining a great low sea-level in the higher
latitudes of the southern ocean; for, whenever the capacity of the Cape
Horn channel is enlarged, the westerly winds, instead of maintaining a
low sea-level on the South Atlantic, employ their force in impelling
the surface water of the southern seas around the globe. And this work
the strong westerly winds of the high southern latitudes have always
accomplished whenever the Cape Horn channel was widely open, and this
is what the winds are doing at this date.
Therefore, such waters of the torrid zone as are moved southward from
their high sea-level, caused by the trade winds abreast the Brazilian
coast, are largely turned away from the high southern latitudes. It is
true, even with an enlarged Cape Horn channel, they can always flow
along the South American coast to an inferior low sea-level, caused by
the westerly winds blowing the surface waters of the sea away from the
coast of Argentine and Patagonia; but on gaining that region they meet
the cold ice-bearing currents which turn away east of Cape Horn from
the great southern drift current to gain the same low sea-level which
attracts the Brazil water. Consequently, the ice-bearing currents from
the south, which branch off from the great southern drift current, are
able to largely turn away the warm Brazil current from the higher
southern latitudes; and, furthermore, the great southern drift current
which passes through the Cape Horn channel, and so onward around the
globe, also partly turns away the Mozambique current as well as the
East Australian current, and so largely prevents their waters from
warming the southern seas.
Therefore, it is evident that, whenever the Cape Horn channel obtains
sufficient capacity to give an independent circulation to the southern
ocean, the conditions are favorable for the increase of cold in the
southern latitudes. For it is because of the large exclusion of the
tropical waters from the southern seas that ice-sheets have been
able to form in early periods and in later epochs on the antarctic
lands, and store away the annual frosts for thousands of years, and
at the same time furnish icebergs sufficient to chill the waters of
the southern temperate oceans, and consequently make cold such of the
surface waters of the sea as are forced into the southern latitudes by
the winds in surface currents, and so returned to warmer seas in cold
under-currents, and thus with such frigid combinations bring about cold
periods.
Thus it appears, as I have previously shown, that it is owing partly
to there being more of the surface waters of the sea forced southward
by the prevailing winds than they impel northward that the cold
under-currents are maintained; but it also requires an independent
circulation of the southern ocean, such as I have pointed out, to cool
its surface waters before they can sink and form cold under-currents.
And there is reason to believe that such cold under-currents are more
efficient in lowering the temperature of the temperate and tropical
oceans than even the icebergs which such under-currents move into the
temperate seas. And, when it is considered that the cold antarctic
under-currents fill the depths of the Pacific and Indian Oceans in the
northern hemisphere, and also largely the tropical depths of the North
Atlantic, I am led to believe that the frigid conditions of the ice
age were concurrent in the northern and southern hemispheres. The main
reasons for such belief I will explain in the following chapter.
After the foregoing explanations, showing how frigid periods are
brought about through the independent circulation of the southern ocean
surface waters, it is evident that, whenever through a slow natural
process the Cape Horn channel is closed, a great change is wrought in
the circulation of the southern ocean.
For instead of the westerly winds blowing the surface waters of the
southern seas constantly around the globe, and so turning away and
preventing the entrance of the tropical currents into the high southern
latitudes, the strong westerly winds, whenever the Cape Horn channel
is closed or greatly obstructed, would blow the surface waters away
from the Atlantic side of the closed channel, and so cause a great low
sea-level, sufficient to attract the ocean waters of the tropical high
sea-level abreast Brazil well into the southern seas. Therefore, it is
important to trace nature’s slow methods of closing the wide Cape Horn
channel at the perfection of an ice age.
In my previous explanations on the subject I have thought that, should
the southern seas have remained at or near the same sea-level as now,
through an ice period brought about in the manner I have described,
ice-sheets would accumulate on the antarctic continent, and also on the
southern lands of South America, sufficient to flow out into the sea
and close the Cape Horn channel.
But further consideration shows the impossibility of the southern seas
having maintained their present sea-level during the growth of frigid
epochs which have left such ample traces of glaciers having extended
widely over the lands of the high latitudes of both the northern and
southern hemispheres. For it appears that the larger areas of land in
the northern latitudes, embracing wide continents and large islands,
must, during the growth of a frigid age, have increased the spread of
glaciers many times greater in extent than could be obtained on the
smaller lands of the high latitudes of the southern hemisphere.
For it is evident that the water evaporated from the sea and deposited
in snow on the large continents and islands of the high northern
latitudes during the growth of an ice period would, while thus
diminishing the ocean waters, greatly increase the weight of northern
lands. Therefore, the waters of the diminishing seas of the southern
latitudes would be attracted into the northern oceans in opposition to
the prevailing winds.
Thus it appears that the Cape Horn channel would be too much reduced at
the perfection of an ice age to afford an independent circulation for
the southern ocean, even without being filled by glaciers to the extent
I have pointed out in previous essays. Still, to whatever dimensions
the Cape Horn channel might be reduced at the perfection of a frigid
period, the enlarged shores bordering its diminished waters would be
covered by heavy glaciers that would flow into the shrunken strait, and
so close it effectually. Thus the reduction of the Cape Horn channel
during the advance of an ice age seems, on close consideration, to be a
simple operation of nature, which in the normal course of events must
have taken place.
As the closing of the Cape Horn channel has been considered by
reviewers the weak and questionable point in preventing my views from
gaining acceptance, it becomes necessary to be explicit concerning the
manner in which the Cape Horn channel has in past ages been obstructed.
According to the charts prepared by John James Wild, the middle portion
of the strait is represented as being over a thousand fathoms in depth;
but, as far as I know, its true soundings have never been determined.
The deep portion of the mid-channel is described as being narrow
when compared with its whole breadth from Cape Horn to the antarctic
continent.
And, when it is considered, with the growth of an ice age, how much of
the ocean waters would be stored in the vast ice-sheets of the northern
hemisphere, and consequently because of their weight a large portion of
the diminished southern oceans would be attracted into the northern
seas, it seems that the bottom of the shoaler waters of the Cape Horn
channel, which now comprise so large a portion of its breadth, would be
raised above the surface of the sea.
The one-hundred-fathom depth south of Cape Horn, now supposed to extend
from longitude 70° west to 55° west, and southward to the latitude of
57°, would be a land supporting heavy glaciers for six hundred miles
along the north side of the reduced channel during the advanced growth
of a frigid age; and the same conditions would be obtained in the
vicinity of the South Shetland. And when, in addition, we contemplate
the great snow-fall of that region, and the consequent gathering of
glaciers which would occur on the widened shores of the lessened
channel, and the certainty of their flowing into the diminished strait,
together with the immense icebergs of such an age grounding in the
shoaled waters, it seems that the complete obstruction of the reduced
channel would be accomplished.
While contemplating the conditions that would obtain while the Cape
Horn channel was being reduced, it will be seen that the independent
circulation of the icy southern ocean would be carried on to a
considerable extent even after the narrowing strait was no longer
able to afford space for wide drift currents, for the reason of the
strong current that would be caused on account of the high ocean-level
maintained by the westerly winds on the Pacific side of the diminishing
channel, and the great low sea-level that would take place on its
Atlantic side.
Still, as previously shown, it seems that during an advanced stage of
the frigid epoch, the heavy glaciers from the enlarged northern and
southern shores of the shrunken channel, together with the ponderous
icebergs, blocking its waters, the closing process would at last be
speedy and effective.
And on further consideration it might be said that a channel of much
less width and depth would not have been of sufficient capacity to
have caused ice periods so wide-spread as those that have left their
traces on the continents and islands of the globe, for the reason
that the independent circulation of the southern ocean would not have
been sufficiently complete and long continued to have brought such
world-wide cold periods to perfection.
With the Cape Horn channel closed, as above explained, there would be,
as I have asserted, a great change wrought in the circulation of the
southern ocean; for instead of the westerly winds blowing its surface
waters constantly around the globe, and so turning away and preventing
the entrance of tropical currents into the higher latitudes, the strong
prevailing westerly winds would blow the surface waters of the sea from
the Atlantic side of the closed Cape Horn channel, and so cause a great
low sea-level, sufficient to attract the ocean waters of the tropical
high sea-level abreast Brazil well into the southern seas.
The winds of the southern westerly wind-belt being stronger in that
region than on any other portion of the globe, consequently they are
able to do nearly as much work while drifting surface water as the belt
of westerly wind of greater width on other parts of the southern seas.
Thus a person who has had a long experience with the forcible westerly
winds of the southern ocean can well understand their ability for
disturbing the ocean waters in the latitudes of the Cape Horn channel.
The drift currents of this region are moved by the winds and waves
from one to four miles an hour. Therefore, with the Cape Horn channel
closed, there is nothing more certain than that the westerly winds
would be able to cause a vast low sea-level on the Atlantic side of
the closed Cape Horn strait, and that the waters of the high tropical
sea-level abreast Brazil would be attracted to its wide depression, as
shown on map No. 1.
The tropical waters thus attracted far southward would be cooler
than the tropical waters of to-day, owing to the great amount of
cold imparted to the ocean by the numerous icebergs of a frigid age.
Still, they would begin the slow process of raising the temperature
of the southern ocean, and would in time carry sufficient heat into
the southern regions to melt the ice from all southern lands; for, in
addition to the Brazil currents, the waters of the high sea-level of
the tropical Indian Ocean which pass southward down the Mozambique
channel would reach a much higher latitude than during periods when the
Cape Horn channel was open.
The ice periods of the northern and southern hemispheres being
concurrent, a condition which I shall explain in another chapter, makes
it obvious that during the melting of the glaciers from the antarctic
continent and other southern lands the depleted Cape Horn channel
could not gain sufficient capacity to give an independent circulation
to the southern ocean during the melting of the southern ice-sheets,
on account of the diminishing heaviness of the antarctic ice and the
greater weight of the extensive glaciers and augmented seas of the
northern latitudes. Consequently, it seems that the southern seas would
continue in a lessened state while the glaciers were being melted from
the northern hemisphere, as was the case during the melting of the ice
from the southern hemisphere; and, furthermore, during such times the
glaciers which overrun all the low lands and shoal waters of the Cape
Horn region would, on account of their position being to the windward
of the tropical currents, be the last great mass of ice to melt from
the southern hemisphere.
Therefore, it seems that the Cape Horn channel would continue closed
or greatly obstructed while the glaciers were being melted from the
lands of both hemispheres. Thus at length a mild climate would extend
over the globe, and so remain until the prevailing winds slowly forced
the surface waters of the sea into the southern ocean in the manner
explained in previous pages, thus filling the Cape Horn channel to its
present capacity, and again restoring the independent circulation of
the southern ocean.
While contemplating the conditions that would obtain during the melting
of the ice from the antarctic lands, it will be seen that the tropical
waters attracted to the great low sea-level to the leeward of the
closed Cape Horn channel would eventually enter the great bight of
the antarctic continent to the eastward of Graham Land, where Captain
Weddell sailed to the latitude of 74° south. This deep gulf, owing to
its situation, would receive the full impact of the southern movement
of the tropical currents; and, as the warm waters spread over the
wide sea-level, the westerly winds would convert them into a drift
current, and under such conditions would be driven along the shores
of the antarctic continent, past the South Indian and Pacific Oceans,
and eventually, after undergoing a cooling process from the long icy
passage, be forced against the Pacific side of the closed Cape Horn
channel and the western Patagonian coast.
While regarding the circulation of the sea during an ice age, it may
be said that the ocean’s being composed of brine was the cause of its
waters being able to circulate in frigid latitudes where fresh water
would congeal. Consequently, this is one of the reasons why successive
periods of frigidity and mildness have been brought about; for with an
ocean of fresh water, repeated epochs of cold and warmth could not have
occurred, because a sea composed of fresh water would have congealed
while circulating in the high latitudes during a frigid age. Therefore,
it required a sea of brine to maintain a liquid state during the low
temperature of an ice period.
For, while the cold of a glacial age increased, the saltness of the sea
increased also, because of the great amount of fresh water evaporated
from the ocean, and stored in ice-sheets on the great continents and
islands of the globe. Thus the briny sea was maintained in a liquid
state, while washing vast ice-fields and glaciated shores and floating
the numerous icebergs of a freezing age. The cold which radiated
from such ice-bound seas must have been severe; but meanwhile the
evaporation from the ocean was much reduced, while the saltness and
coldness of the sea increased, and so prevented the ice of a glacial
period from gaining invincible proportions before the independent
circulation of the southern ocean was arrested. Therefore, the
remaining warmth of the tropical waters after gaining free access to
the antarctic latitudes was able to overcome the accumulated cold of
that frigid region.
At this date the observant navigators who have visited the antarctic
seas report that the surface currents above the latitude of Cape Horn,
while being drifted eastward by the prevailing westerly winds, also set
toward the antarctic ice cliffs, as shown on map No. 2.
The reason why this southerly set of the surface currents becomes
noticeable above the latitude of 55° south is because the tropical
currents which set southward from the torrid latitudes on the western
sides of the Atlantic, Indian, and Pacific Oceans, although largely
turned away from the high latitudes by the westerly winds and drift
currents, are also able to send sufficient water into the great
belt of westerly winds to furnish water for the deep under-currents
setting northward from the antarctic shores. Thus the surface waters
moving from the north in order to gain the higher latitudes, after
entering the westerly wind-belt, are moved in drift currents by the
impelling winds easterly over many degrees of longitude, and also at
the same time slowly southward among the cooling icebergs, because of
the attraction caused by the difference of temperature and density
between the northern drift waters and the icy seas of the antarctic ice
barrier. Consequently, the gradual movement of the surface waters of
the westerly wind-belt southward before entering the higher latitudes
is not generally apparent; for it is after they enter latitudes where
the globe becomes much reduced in circumference that their southern
movement in the contracted seas becomes more noticeable. The impact of
this southerly current, which finds its outlet in deep under-currents,
and retards somewhat the increase of ice on the southern continent at
this date, also largely prevents the small icebergs and field-ice from
floating northward, away from the antarctic ice barrier; for it is such
large icebergs as penetrate the deep under-currents that are the best
able to move into the more temperate latitudes.
From the above explanations it will be seen that the impact of surface
water against the antarctic ice barrier when the Cape Horn channel
was closed would greatly assist the tropical waters attracted to the
great low sea-level to the leeward of the obstructed strait to wash the
antarctic shores while being drifted eastward by the westerly winds
over the southern ocean against the Patagonian coast and the Pacific
side of the closed channel, and there causing a high sea-level. This
movement of the winds and currents encircling the antarctic continent
is shown on map No. 1.
The vast, high sea-level caused by the westerly winds drifting the
surface waters against the Patagonian coast would obtain a much higher
plain, were it not that so much of the water of the great drift current
was required to feed the antarctic under-current which constantly sets
northward from the antarctic shores; yet it would be sufficient to
greatly increase the volume of the Humboldt current, which would flow
in the same direction it now flows, down the South American coast to
the equatorial latitudes, where it would become the main source of the
great equatorial stream, and thus offset the increased southward flow
of the equatorial waters through the Brazil and Mozambique streams.
The equatorial stream, with its increased volume, would also move, as
it moves to-day, across the Pacific; and, on gaining the western side,
after sending off large streams to the northern and southern latitudes,
it would pass through the East India passages into the Indian Ocean,
where it would be drifted westward by the trade winds and cause a high
sea-level abreast the east coast of Africa, and so become the source
of the great Mozambique current, which would flow southward along the
east coast of Africa, and, with the Cape Horn channel closed, would
gain a much higher latitude than it would with the channel open. At
this age, when the continuation of this great equatorial stream gains
the latitude of the Cape of Good Hope, its waters are largely turned
eastward by the great drift current of the southern ocean.
Still, a considerable portion of its waters turns toward the west,
forming the Agulhas current, which flows around the Cape of Good Hope
into the Atlantic, where it mingles with the cooler currents which
branch off from the great southern drift current; and so, in connection
with the latter, it is attracted to the low sea-level caused by the
south-east trade winds abreast the south-western coast of Africa,
and from thence moved as a drift current by the trade winds to the
equatorial Atlantic and coast of Brazil. Thus it will be seen that the
Agulhas current, even with the Cape Horn channel in possession of its
present wide capacity, serves to retard somewhat the advance of a cold
period.
The Agulhas current at this date also partly serves to replenish the
water which is forced from the South Atlantic by strong westerly winds
into the Southern Indian and Southern Pacific Oceans. For it appears
that more water is now removed by such winds from the South Atlantic
than enters it from the South Pacific, even through the enlarged Cape
Horn channel of this date; and this fact seems to favor an impression
that a portion of this enlarged channel existed prior to the glacial
periods, but with its waters so much reduced as to be unable to give
the southern ocean an independent circulation sufficient to exclude the
tropical currents from reaching the high southern latitudes in adequate
volume to maintain a mild climate in the southern hemisphere.
For previous to the glacial age, with little or no ice gathered on
the antarctic lands, it seems that a strait possessing one-half the
capacity of the Cape Horn channel of the present age could not prevent
the Brazil current and the Agulhas stream from flowing into the
southern ocean in quantities sufficient to make it impossible for
glaciers to form on southern lands.
Thus it is probable that a reduced channel separated the western
continent from the antarctic lands even in the mild eras previous to
the glacial epochs.
The Cape Horn channel, at the present age, with a capacity sufficient
to largely maintain an independent circulation for the southern ocean,
is still only one-third of the breadth of the westerly wind-belt of the
southern seas. Therefore, the drift currents do not all pass through
it from the Pacific into the Atlantic. Consequently, a considerable
portion of the drifted water turns northward west of Cape Horn, and so
forms the Humboldt current.
The Agulhas stream, which even now assists in replenishing the South
Atlantic with tropical water, would, during the perfection of a glacial
period, with the Cape channel closed, be a much stronger stream than
it now obtains with the Cape channel possessing its present enlarged
capacity, for the reason that the South Atlantic waters would continue
as now to be forced eastward by the westerly winds, while they could
not be replenished, as they are to-day, directly from the South Pacific.
Consequently, the waters of the South Atlantic Ocean would be
correspondingly reduced.
Such conditions alone would greatly increase the volume of the Agulhas
stream at the culmination of a frigid age. Therefore, the work of
subduing a frigid period in the southern hemisphere after the Cape Horn
channel was closed would not rest on the Brazil current alone, but also
on the great equatorial stream of the Pacific and Indian Oceans.
Yet during such frigid times the sources of the equatorial stream would
be greatly chilled by its two great feeders, the Humboldt current and
the returning Japanese current, both of which flow down from the high
latitudes and meet in the equatorial latitudes on the eastern side of
the Pacific, thus cooling the source of the great equatorial current.
But this latter stream, while on its long western passage across
the Pacific and Indian Oceans, beneath a torrid sun, with only
one cold feeder from the south which approaches it along the west
side of Australia, would, on its long tropical journey, be able to
obtain considerable warmth, even during an ice period, to supply the
Mozambique and Agulhas streams, and so greatly assist the Atlantic
waters in bringing about a mild period. Still, the process of subduing
the cold of the southern latitudes would be slow, even with the Cape
Horn channel closed, because of the vast collection of ice burdening
the sea and land.
Yet there were conditions that were naturally brought about to favor
the process of returning warmth; for it appears that, when the southern
ocean was made shallow because of a considerable portion of its waters
having been moved into the northern hemisphere, it will be seen that
the conditions were more favorable for the westerly winds to create
drift currents than would be the case on deeper seas. Therefore,
the high and low sea-levels caused by such winds would be greater
on a shallow ocean than would occur on deeper waters. Thus the low
sea-levels of the shallow southern sea would have strong attraction
for tropical surface waters, and so increase the thickness of its warm
drift currents, and at the same time its lessened depths would have
less capacity for the storage of cold water to reduce the temperature
of the under-waters of the tropical zone.
And, furthermore, when the southern ocean was shallow, New Zealand
acquired a longer extension of land to the north and south.
Consequently, the enlarged low sea-level on its eastern side attracted
more tropical water into the southern latitudes than now.
So, according to the conditions I have pointed out, the ice-sheets
would at length melt away, and a long period of mildness would succeed
on account of the length of time it would require after the ice
disappeared from the earth for the prevailing winds to move the surface
waters of the augmented northern seas into the southern ocean, and
again restore its independent circulation, and so, after a considerable
lapse of time, bring about the geographical and climatic conditions
existing at the present date, which can be seen on map No. 2, which
shows that a cold period has already made considerable advance in the
southern hemisphere, the southern continent and islands being covered
with glaciers, and the prevalence of icebergs as far north as the
latitude of 35° south.
Moreover, when we consider that the independent circulation of the
southern ocean is caused by the westerly winds blowing its surface
waters constantly around the globe through the open Cape Horn channel,
and so largely preventing the tropical currents from entering the
high southern latitudes, and how, in consequence, the cold is slowly
on the increase through the constant accumulation of ice on the lands
and in seas of the southern latitudes, it appears that a frigid age
is slowly progressing in the southern hemisphere. For it seems that
continental ice-sheets should not only be able to retain their freezing
temperature, but also the mean of the low temperature in which they
were formed, for a considerable length of time, and so impart their
extreme coldness in the shape of icebergs into such seas as border on
the glaciated lands.
It has been proved at Point Barrow that strata of ice and gravel can
maintain a wintry temperature through the summer months. Captain
G. B. Borden, keeper of the refuge station in that region, states
that Lieutenant Ray, of the Signal Service, excavated through ice and
gravel to a depth of forty-one feet, and that the lower portion of the
excavation maintains a temperature 15° Fahrenheit above zero the year
around. Therefore, with the probability of southern glaciers obtaining
a temperature of over 15° Fahrenheit below the freezing point, we
can well realize the frigidity imparted to the southern oceans while
melting numerous immense icebergs, and consequently will conclude that
the temperature of the southern latitudes is gradually lowering.
The icebergs of the antarctic seas would not move northward into the
temperature latitudes so readily as they now do, were it not that the
general southward set of the southern ocean currents were interrupted
by the movement of northerly surface currents in the longitudes of
the low sea-levels, caused by the westerly winds drifting the surface
waters of the sea from the eastern coasts of Southern South America and
New Zealand. For it is owing to the low sea-levels thus created, in
connection with the deep under-currents which set northward from the
ice cliffs of the antarctic lands, that many icebergs are enabled to
move into the temperate latitudes, especially to seas north-east of the
Falkland Islands.
On other portions of the southern ocean above the latitude of 55° south
the surface waters, while being drifted eastward by the strong westerly
winds, also set toward the antarctic shores, and so furnish water for
the cold under-currents which set northward from that frigid region.
Thus from such parts of the coast only the largest bergs, which require
a deep sea to float them, are moved by the under-currents into the
temperate latitudes. Therefore, it happens that, while an ice period
progresses, and the antarctic icebergs increase in size, the more
readily the cold, deep under-currents force them into the temperate
zone, in opposition to the winds and surface currents.
The icebergs, after gaining the temperate latitudes, are moved more
or less eastward by the westerly winds and drift currents, and so are
scattered over the southern temperate oceans, where the melting bergs
impart whatever coldness they were able to store up while forming in
the antarctic regions.
The low sea-levels caused by the westerly winds to the leeward of New
Zealand and to the leeward of Argentine, not only cause the ice-bearing
currents to set northward, but they also cause the tropical currents to
make considerable inroads into the high southern latitudes. This is the
reason why the lands are less burdened with ice on the antarctic shores
opposite Cape Horn than on other parts of that glaciated continent.
The tropical currents which turn southward east of New Zealand largely
mingle their waters with the great southern drift current, and so
are carried through the Cape Horn channel. Owing to this cause, the
antarctic lands abreast Cape Horn are less burdened with ice than other
portions of the antarctic shores.
Thus, were it not for this penetration of warm waters southward, the
antarctic coasts south of Cape Horn, because of the great snow-fall of
that region, would obtain heavier glaciers than other portions of the
southern continent. But the time is slowly coming when, with a lower
temperature, the ice-sheets on the lands in the vicinity of the South
Shetlands will attain greater thickness than the glaciers on other
shores of the antarctic continent.
Hence it appears that, when the several agents for producing
and distributing cold in the southern latitudes are taken into
consideration, the immense and continuous storage of ice on the
southern lands, which adds to the wide-spread fleet of icebergs that
float the southern temperate seas, and also the vast movement of
cold antarctic water into the temperate and tropical oceans in deep
under-currents, combined with the increasing coldness of the westerly
winds, are now slowly bringing about in the southern hemisphere a
period of frigidity.