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191
har on Temperatur under 0°. Tornøe har vist, at Vandet
i de dybeste Lag indeholder omtrent den samme
Luftmængde som ved Overfladen, og at det er her, at
Havvandet optager sin Luft. Med de nedstigende Strømme,
som vi have paavist, fores Luften ned til Dybene; Havet
er saaledes fuldstændig ventileret, og denne Betingelse for
det organiske Livs Trivsel i alle Dybder og paa
Havbunden er tilvejebragt ved Strømningernes Mekanisme.
Vi have seet, hvorledes Strømningernes Hastighed
aftager mod Dybet, og at den i de store Dyb rimeligvis er
temmelig ringe, men dog tilstrækkelig til at holde Vandets
Circulation vedlige. De Aflagringer, der findes paa
Havbunden, ere af en mere grovkornet Art ved Kysterne, hvor
Strømmen er sterkest, og Landjorden, hvorfra Materialet
tages, er nærmest, medens de finere Partikler findes i de
store Dybder, hvor Vandet er roligere og Afstanden fra Land
større. Her dækkes Bunden af Biloculinleret, hvis
Hovedbestanddel er Skaller af Foraminiferer, især Globigeriner,
og soin i chemisk Henseende indeholder kulsur Kalk som
Hovedbestanddel1. Om dette Ler siger J. Murray2:
"Den kulsure Kalk i det norske Hav bestaar
hovedsagelig af Skaller af Globigeriner, der ere sunkne ned fra
Overfladen, og nogle andre Arter Foraminiferer (mest
Bi-loculiner), der leve ved Bunden. Paa nogle Steder nænner
denne Aflejring sig i sin Charakter til Atlanterhavets
Globi-gerina-Ler eller Mudder, men er meget fattig paa
pelagiske Skaller i Sammenligning meel Aflejringerne under
lavere Bredder. De pelagiske Foraminiferer og
Pteropo-der, der ere saa talrige i de tropiske Dele af
Golfstrømmen, dø og falde tilbunds, idet de føres ind i
Nordatlanterhavets koldere Strøg".
Efter disse Udtalelser af Mr. Murray er det at vente,
at di’ varme nedstigende Strømninger i Nordhavet skulde
medføre en større Rigdom paa kulsur Kalk paa
Havbunden ond de kolde opstigende. Et opmerksomt Studium af
S c li m ei eks Afhandling og navnlig af hans Kart over
Mængden af kulsur Kalk i Biloculinleret vil ogsaa i det
hele taget stadfæste dette. Hele det søndre Bækken er rigt
paa kulsiir Kalk, medens det nordre Badeken er yderst
fattigt, undtagen — og det er meget interessant — langs
Spidsbergbanken og der, hvor vi under Greenwichs
Meridian i 77° til 78° Brodde have et Trykmaximum, begge
Steder med nedstigende Bevægelse af oprindelig atlantisk
Vand. Den hos Schmelck antydede store Mængde af
kulsur Kalk i Jan Mayen Renden svarer ogsaa til de
sammesteds ovenfor omtalte nedadgaaende Strømninger. Imellem
Island og Norge findes et Par Steder over 40 Procent kulsur
Kalle, i Station No. 52 (Temperaturmaximum) over 45 Procent.
Den yderst ringe Kalkinængde i Strøget Nordost for Jan
1 Den norske Nordhavé-Expedition. Chemi. Al’ 0. Schmelck.
1 Encyclopedia Britannica. Norwegian Sea.
by contact and intermixture with Polar water it has a
temperature of under 0°. Tornøe has shown that the
water in the deepest strata contains about the same
amount of air as at the surface, and that here it is
sea-water absorbs its air. As we have pointed out. the
air is carried, with the descending currents, down into the
deep; thus the sea becomes thoroughly ventilated, and this
condition for the existence of organic life at all depths and
on the sea-bed, is brought about by the mechanism of
the currents.
We have already seen how the velocity of the currents
diminishes with depth, and that probably in the great deeps
it is but trifling, though amply sufficient to keep up
the circulation of the water. The deposits met with on
the sea-bed are coarsely granulous in character off the
coasts, where the current is strongest and the
detritus-yielding land nearest, whereas the finer particles of matter
occur in the great depths, where the water is calmer and
the land more distant. Here the bottom is covered with
Biloculina clay, the chief constituents of which are the
shells of Foraminifera, more especially Globigerina. and
which, regarded chemically, contain as their principal
constituent carbonate of lime.1 Respecting this subject, J.
Murray states.2
"The carbonate of lime (in the Norwegian Sea)
consists chiefly of the shells of Globigerina, which have fallen
from the surface, and some other species of Foraminifera
(the most frequent of which is Biloculina) which live on
the bottom. In some places this deposit approaches in
character the Globigerina ooze or mud of the Atlantic, but
is very poor in pelagic shells when compared with the
deposits in lower latitudes. The pelagic Foraminifera and
Pteropod shells so abundant in tropical parts of the Gulf
Stream are killed oft" and fall to the bottom as they are
carried into the colder areas of the North Atlantic."
From these statements by Mr. Murray, there was reason
to expect that the warm descending currents in the North
Ocean would be attended with a greater amount of
carbonate of lime on the sea-bed than the cold ascending
ones. An attentive study of Schmelck’s Memoir, and more
especially of his map showing the amount of carbonate of
lime in the Biloculina clay, will also in the main confirm
this result. The whole of the southern basin is rich in
carbonate of lime, whereas the northern basin is exceedingly
poor, except — and this fact is very interesting — along
the Spitzbergen Bank, and where, on the meridian of
Greenwich, in lat. 77° to 78° N. we have a
pressure-maximuni, in both places with a descending motion of
originally Atlantic water. The large amount of carbonate
of lime found by Schmelck, in the Jan-Mayen Channel,
corresponds to the above-mentioned descending currents in
the same locality. Between Iceland and Norway,
carbonate of lime, in a proportion of more than 40 per cent, is
1 The Norwegian North-Atlantic Expedition. Chemistry. By
L. Schmelck.
2 Encyclopedia Britannica. Norwegian Sea.
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