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Mayen turde ogsaa hidrøre, foruden fra den hengere
gjennem-løbne Vej fra Atlanterhavet af, tildels fra. at
Foramini-ferskallerne her synke i en opstigende Strøm og saaledes
i hengere Tid ere udsatte for Søvandets tærende Virkning.
Efter Alt synes der saaledes at være god Overensstemmelse
mellem de organiske Aflejringer paa Bunden og vort
Strømsystem.
Efter Zöppritz1 fremgaar det nu existerende
Strømsystem som Resultatet af Vindenes Arbejde i seculære
Tidsrum. Som jeg har søgt at vise, udføres dette Arbejde
derigjennem, at der dannes en Overflade, som afviger fra
Niveaufladen, dels ved Vindenes directe Virkning og
Jordens Rotation, dels ved de af Vindstrømningerne og
Elve-vandet vedligeholdte Uligheder i Søvandets Tæthed. Hvad
de normale Vinde, Fordunstning og Nedbør udrette^ efterat
Strømsystemet er blevet constant, er at vedligeholde
Strømfladen og med den Strømsystemet. De normale Vinde ere
Resultatet af det normale Lufttryks Fordeling, hvilken igjen
beror paa Temperaturens Fordeling. Men denne er
afhængig i høj Grad af Havets Temperatur og af
Fordelingen af Land og Vand. Vi komme saaledes til Solens
Varme, Fordelingen af fast Land og Hav og Jordens
Rotation som Hovedfactorer for Klima, Lufttryk, Temperatur,
Fordunstning, Nedbør, Vinde og Havstrømme.
Forandringer i disse Grundbetingelser ville medføre
Forandringer i Havets Strømninger, der kunne blive af stor
Betydning for Kli matet. Seculære Forandringer af den
relative Havstand ved Kysterne synes ikke at kunne
forklares paa saadan Maade, da Strømfladens største Højde
over Niveaufladen gjennem Havoverfladens [dybeste jPunkt
kun gaar op til halvanden Meter.
En aarlig periodisk Variation i Havstrømmenes
Bevægelse finder rimeligvis Sted i cle øverste Lag. De
dybere Lag ere ikke underkastede nogen saadan, ifølge
Zöppritz’ Undersøgelser2. Vindenes [Styrke er i Nordhavet
betydelig større 0111 Vinteren end om Sommeren, og
Lufttrykkets Minimum befinder sig altid ude over Havet3.
Derimod er den fra Elvevandet og Sne- eller Issmeltning
hidrørende Forhøjelse af Havniveauet under Kysterne
betydelig større om Sommeren end 0111 Vinteren. I hvilken
Udstrækning disse Aarsager opveje hverandre, faa]
kommende Undersøgelser afgjøre.
Havstrømmenes Virkning paa de Landes Klima, , som
de berøre, er en anerkjendt Kjendsgjerning. Her kun en
1 Wiedemann« Annalen, III. 4. S. .r>82.
2 L. c. S. (101.
3 Zeitsclirift der üsterreichischen Gesellschaft für Meteorologie,
1884, April, m. ICart.
176
met with in a few places, nay at Station 52 (max. of temp.) it
exceeds 45 per cent. The very trifling amount of lime met
with in the tract north-east of Jan Mayen, may come, not only
of the great distance traversed from the Atlantic, but
in part also of the Foraminifera shells sinking here in an
ascending current, and being thus exposed for a considerable
time to the dissolving action of the sea-water. After
all, there would accordingly appear to be fair agreement
between the organic deposits on the sea-bed and our
current-system.
According to Zöppritz,1 the current-system as now
existing is the work of the winds during a period of
secular extent. As I have sought to show, this
work-is brought about by the formation of a surface
deviating from the surface of level, partly by the direct action
of the winds and the rotation of the earth, partly
by the differences in the density of the sea-water, as
maintained by the wind-currents and the river-water. As
regards the effect of tilt; normal winds, evaporation, and
precipitation after the current-system has become
constant, this consists in maintaining the current-surface, and
along with it the current-system. The normal winds are
the result of the normal distribution of atmospheric
pressure, which in turn depends on the distribution of
temperature. But this is dependent to a very great extent
on the temperature of the sea and the distribution of land
and water. Thus we come to the heat of the snil. the
conformation of land and sea, and the rotation of the earth
as principal factors in determining climate, atmospheric
pressure, temperature, evaporation, precipitation, winds, and
ocean-currents.
Any changes in these fundamental conditions will
involve changes in the currents of the ocean, which may
exert a great influence on climate. Secular changes in the
relative sea-level at the coasts, cannot be explained, it would
seem, in this way, since the greatest height of the
current-surface above the surface of level through the deepest point
of the sea-surface reaches only a metre and a half.
An annual periodic variation in the motion of
ocean-currents takes place in all probability throughout the
uppermost strata. The deeper strata are not subjected to such
variation, according to Zöppritz’ investigations.2 The force
of the winds in the North Ocean is considerably greater
in winter than in summer, and the minimum of atmospheric
pressure lies invariably out at sea.3 On the other hand,
the rise of the sea-level in immediate proximity to the
coasts, occasioned by river-water and the melting of snow
or ice, is much greater in summer than in winter. To what
extent these causes counteract each other, it must rest with
future investigations to determine.
The influence of ocean-currents on the climate of
countries with which they come in contact, is a well-known
1 AViedemanns Annalen, 111, 4, p. .">8"2.
1 Ibid. p. 601.
8 Zeitsclirift der österreichischen Gesellschaft fiir Meteorologie,
1884, April, with Chart.
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