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190
dot hovedsagelig Polarvand, dor stiger nod og op ; kun ved
Spidsborgen stiger atlantisk Vand ned.
Strømningerne i de forskjellige Retninger maa
gjensidig compensere hverandre, naar Havets Vandmængde eller
dets Niveau skal holde sig uforandret. Do opstigende
Strømmes Vandmasse maa være lige stor som do
nedsti-gendes. At saa er Tilfældet, synes vel ovorenssteniniende
mod de beskrevne verticalø Bevægelser, navnlig naar vi
tage Hensyn til den Opstigning, som finder Sted langs
Bankernes dybere. Skraaninger. I de højere Lag, hvor
Bevægelsen foregaar vod horisontale Strømninger, kunne vi
nærmere godtgjøre, at Compensation finder Sted. Fra 300
Favnes Dyb af or Nordhavet udestængt fra Atlanterhavet.
1 denne Dybde se vi , PI. XLIV) Vandet komme ind
mollem Grønland og Spidsbergen og strømme ud mellem
Grønland og Island. Afstanden mellem Isobarerne betegner de
enkelte Strønitraades Tversnit. Mellom de samme to
Isobarer strømmer hele Vejen, naar Bevægelsen følger dem,
den samme Vandmasse. Knibe Isobarerne sig sammen,
øges Hastigheden i samme Forhold og omvendt, naar do
fjerne sig fra hverandre. Se vi nu paa Kartet, finde vi,
at Indstrømningen ved Spidsborgen sker gjennem 3
iso-bare Mellemrum, og i Danmarkstrædet sker
Udstrømningen mellem de samme Isobarer. Der strømnier ligemeget
Vand ud af Nordhavet i dette Niveau, som der
strømmer ind.
Udføres den samme Undersøgelse for Overfladens
Vedkommende efter PI. XLIII, saa finder man følgende
Antal af Mellemrum mellem to Isobarer ved Ind- og
Udstrøm-ningsaabniugerne.
I n d s trø m n i n g. U d s t røm n i n g.
Nordenfor Island 1 Mellemr. Danmarkstrædet 6 Mellemr.
Færøerne til Skotland (i — Söndenfor Island 2 —
Grønlandshavet 8 — Spidsbergen 2 —
Novaja Seinlja 5 —
Tilsammen 15 Mellemr. Tilsammen 15 Mellemr.
Der strømmer altsaa i Overfladen ligesaa meget Vand
ud af Nordhavet, som der strømmer incl i det. Dette er
en interessant Verification af Strømkartet. Hvad Havets
Overflade taber ved Fordunstning, faar det igjen ved
Nedbør, Elvevand og Isbræer. Muligens condenseres en Del
af det i Nordhavet fordunstede Vand først i det indre
Polarhav, men dels kommer dette igjen ind i Nordhavet
med Polarstrømmen, dels erstattes det ved Elvevand
hidrørende fra Dampe, der ere optagne paa Atlanterhavet.
Den Tilførsel, som Nordhavets Dyb erholder af
atlantisk Vand. godtgjøres ikke alene af dettes Temperatur,
men ogsaa, som Tornøe har vist, af dets Saltholdighed og
dets Luft- eller Kvadstof holdighed. Som ovenfor paapeget,
er det især det søndre Bækken, det norske Hav, hvis Vand
i Dybet for en stor Del er af atlantisk Oprindelse, om det
end paa Grund af Berøring og Blanding med Polarvand
ticular is found to sink. Throughout the northern basin,
it is chiefly Polar water that descends and rises;
oil’Spitzbergen only, Atlantic water is found to descend.
The currents setting in different directions must
compensate one another, provided the amount of water in
tin-sea or its level shall keep unchanged. The discharge of water
by the ascending currents must be equal to that by the
descending. And that such is the case would seem to be
in accordance with the vertical motions described, more
particularly if we have regard to the ascent prevailing
along the deeper declivities of the banks. In the higher
strata, where the motion proceeds by horizontal currents, we
are better able to prove that compensation actually occurs.
From a depth of 300 fathoms, the North Ocean is shut out
from the Atlantic. At this depth, we observe (PI. XLIV)
the water passing in between Greenland and Spitzbergen,
and flowing out between Greenland and Iceland. The
distance between the several isobars indicates the transverse
sections of the different stream-threads. Between any two
isobars flows, throughout the whole course, provided the
motion proceed along them, the same quantity of water.
Where the isobars converge, the velocity will increase,
and the reverse take place where they diverge. Now. if we
regard the map, we shall observe that the influx at
Spitzbergen finds its way through 3 isobaric interspaces, and
that the efflux passes through Denmark Strait between the
same isobars. As much water flows out ol’ the North
Ocean at this level as flows into it.
Supposing the same investigation, as regards the
surface, to be carried out according to Pl. XLIII, we shall
find the following number ol’ interspaces between two
isobars at the inlet and outlet.
Influx. Efflux.
North of Iceland 1 Interspace. Denmark Stra it G Tntorsp.
Færoes to Scotland 6 Interspaces. South of Iceland 2
Greenland Sea 8 — Spitzbergen 2
Novaja Semlja 5 —
Total . . . 15 Interspaces. Total . . 15Intersp.
Hence, an equal quantity of water flows at the
surface out of the North Ocean as flows into it. This is
an interesting verification of the Current-Mai). Whatever
loss the surface of the sea may sustain by evaporation, is made
good by precipitation, river-water, and glaciers. Possibly,
some part of the water evaporated in the North Ocean may
not be condensed before it reaches the inner tracts of the Polar
Sea; but if so, this water will again be partly brought
into the North Ocean with the Polar current, or be
compensated by river-water originating in vapour from the
Atlantic.
The discharge of Atlantic water into the deep of
the North Ocean, is not only proved by the temperature
of the water, but also, as Tornøe has shown, by its
salinity and content of air, or proportion of nitrogen.
As pointed out above, it is more especially the
southern basin, or Norwegian Sea, the water of which in great
part is of Atlantic origin throughout the deep, though
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