Although the temperature of the ocean is much more equable than that of
the atmosphere, there is good reason to believe that its waters are susceptible of
climatic changes of a very important nature as regards their effects on the distribution
of life. No doubt these changes are more frequent and less lasting
near the surface, and hence operate more markedly on the creatures that inhabit
the supei-ficial zones ; but it must be borne in mind that the very nature of the
conditions, dependent as they are principally on the reciprocal action of the
atmosphere and water, presupposes a different set of conditions as the depth
increases, and, hence, that a limit is speedily attained, beyond which the sudden
advance of creatures living above or below becomes at once injurious to them.
I t is only when we regard the comparatively insignificant stratum of water to
which animal existence has heretofore been supposed to be circumscribed, that
the capacity of the ocean for the maintenance of life falls short of that which we
are in the habit of ascribing to the atmosphere ; and the moment it is recognized
as a fact that animal life, instead of being confined to the few hundred superficial
fathoms, reaches down into the deeper abysses, it becomes evident that the
vertical limits above and below the sea-level are in reality almost coequal.
Although any attempt to construct a bathymetrical plan of the deeper zoological
zones of the ocean would at present he premature, the data in our possession
are nevertheless sufficient to warrant the inference that, where a few living forms
have been detected, numerous others exist ; and, accordingly, the construction
of such a plan may he regarded merely as a question of time and scientific
research. There may he blank areas on the sea-bed, as there are unquestionably
blank and uninhabitable areas of land ; but, again, assuming that the conditions
are not of a nature to render life impossible, we are warranted in taking for
granted that these areas are no greater in the one case than in the other. “ The
history of our own seas and of all seas,” observes Mr. Godwin-Austen, “ teaches
us that there is a law of proportion in the classes and orders of the living things
that dwell there, and that the presence of one form is safe ground of inference
as to the co-existence of countless others ” *. Higher authority than this we
could not have ; for, although the doctrine thus enunciated bears reference to
the distribution of life apart from that of the deep sea, it must be admitted that
the same general application of the laws of nature, for which Mr. Austen is so
* ‘ Natural History of the European Seas,’ p. 247.
staunch an advocate, is admissible in the present instance the moment the
existence of one living form in the depths of the ocean is incontrovertibly
proved.
Although temperature is the most important element in determining the
climate of a region, its independent influence (that is to say, the temperature of
a locality as due to its geographical position only) is subject to great modification
from collateral causes—namely, the degree of elevation above the sea-level,
the amount of humidity present in the atmosphere, the prevailing winds, and
the surface-configuration. These all act reciprocally on each other, and in
certain cases produce such alterations in the climate within the same area as
would result from a complete change of geographical situation. Thus, at a given
height on the mountain-ranges of equatorial countries we find a region of
perpetual congelation, and in descending from that elevation towards the sea-
level there occurs every variety of temperature, from arctic cold to tropical
heat ; the various zones being distinctly marked by the character of the vegetation
they are adapted to support.
I f we turn to the ocean, we find its climates are dependent, in like manner, on
causes which modify its temperature, namely, the temperature of the superincumbent
air, the prevailing currents, and, to a limited extent, the configuration
of its bed,—the currents, like the winds on land, serving \o equalize the heat and
prevent stagnation ; whilst, in shallow waters, the nature of the bottom serves to
modify the force and direction of the currents, and, both in shallow and in the
deeper portions, it exercises a powerful influence in determining the kind and
the distribution of the creatures that dwell upon it.
It is well known that in every latitude, commencing from the confines of that
portion of the polar area within which the temperature is said never to rise above
freezing-point* and extending to the equator, there exists a belt of atmosphere
of varying thickness, which marks the oscillation of the line of perpetual congelation
dui’ing summer and winter. I t is obrious that the upper boundary of
* I t has been customary to assume that at about the 75th degree of latitude the line of perqietual
congelation is coincident with the sea-level ; but, according to Sir- John Richardson, this does not
accord with observation in the Northern Hemisphere, there being “ no Arctic district to which ttibh
has as yet penetrated in wliich there is a permanent covering of snow thi-ough any wide extent of
low country.”—See ‘ Arctic Searching Expedition,’ by Sir J. Richardson, C.B., F.R.S. London, 1851 :
vol. ii. p. 213.
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