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104
Efter disse Værdier for dh er Kartet over
Tæthedsfladen, Pl. XLII, construeret. Der er optrukket Linier
for ligestore Højder over eller under Niveaufladen
(Grundfladen) for liver Tiendedel Meter, Ved Hjelp af
Observationer fra Ponnnerania-Expeditionen, i den nordlige Del af
Nordsøen, udenfor Skotland, og fra de danske Fyrskibe
Horns Hev og Skagens Rev er Tæthedsfladen forsøgt
o]»construeret over Nordsøen indtil Kartets Sydgrændse.
Kartet viser, at Tæthedsfladen har Fordybninger
nordenfor Færøerne, østenfor Island, østenfor Jan Mayen,
vestenfor Boeren Eiland og i Østhavet. Disse Fordybninger
hidrøre fra saltere Vand og lavere Temperatur. De ligge
ligesom i en Dalsænkning, der strækker sig langs de nævnte
Strøg. Fra dette Strøg af løfter Tæthedsfladen sig mod
Kysterne, hvor det ferskere Vand i Overfladen forhøjer
Vandspejlet, selv henimod Grønlands Østkyst, hvor
Temperaturen er lav. Fra det laveste Punkt, Station No. 48, i
Øst for Island, hvor dh = —0.112Meter, stiger
Tæthedsfladen under Grønlands Kyst til 0.4(1 Meter over
Grundplanet. altsaa ialt henimod 60 Centimeter, under Spidsbergens
Vestkyst til 0.40 Meter, altsaa ialt over 60 em, under det
sydlige Norges Vestkyst og i Skagerak samt ved Jyllands
Vestkyst til 0.55 m og derover, altsaa ialt 66 cm.
Nordenfor Island, mellem denne 0 og Grønland, ligger
en Indsænkniug paa Ordinaten 0. Denne opstaar deraf,
at Vandet, navnlig i Overfladen, er forholdsvis lidet salt
saavel under Grønlands Kyst, som under Islands. Ved
den förste virke smeltende Drivis og Smeltevand fra det
glacierede Land til at forringe Saltholdigheden i de øvre
Vandlag, paa den sidste Islands mægtigste Bræ-Elve, der
alle udmunde paa Nordkysten. Fordelingen i Dybet af
Sova ndets Tæthed under Grønland har jeg opconstrueret
efter Observationerne fra "Gernumia" i 1869—70 fra den
74. 75. Breddegrad og fra "Sofia" i 1883 i Danmarkstrædet.
Tæthedernes Fordeling under Island, hvorfra
Observationer ikke have været mig tilgjamgelige, har jeg
construeret. overensstemmende med den, som vore Observationer
have givet udenfor Norges Vestkyst mellem den 60. og 62.
Breddegrad. Her udmunde ingen synderlig store Elve, saa
at det nok kan hænde, at Tæthedens Tilvæxt med Dybet
nordenfor Island er i Virkeligheden sterkere, end jeg har
antaget. I saa Fald skulde Tæthedsfladen skraane fra
Islands Kyst mod Nord endnu sterkere, end Kartet viser.
Søvaudets Tæthed er betinget af dets Saltholdighed,
dets Temperatur. Nedbør, Isdannelse, Issineltning,
Fordunstning. Den Tæthedsflade, jeg har fremstillet, er den,
som følger af Søvandets virkelige Tæthed, saaledes som
den fremgaar af Iagttagelserne. Idet vi anvende
Tæthedsfladen til Beregningen af Havets gjennemsnitlige
Strømninger, er der altsaa taget Hensyn til de Forandringer i
In acecordance with these values for dh, the Map
of the Surface of Density,’Pl. XLII, has been constructed.
Lines of equal height above or below the surface of level
(the base) are drawn for every tenth of a, metre. By
means of observations taken on the " Ponuneraiiia’’
Expedition in the northern part of the North Sea, oil Scotland,
and at the Danish light-ships Horns Rev and Skagens
Rev, I have sought to construct the surface ol’ density for
the North Sea to the southern extremity of the map.
The map shows that the surface of density has
depressions north of the Færoe Islands, east ol’ Iceland, east of
Jan Mayen, west of Beeren Eiland, and in the Barents
Sea. These depressions arise from salter water and lower
temperature. They extend, as it were, down the
hollow of a valley, stretching along the said tracts. From
this region the surface of density rises in the direction of
the coasts, where the comparatively fresh water at the
surface raises the level of the sea, even towards the east
coast of Greenland, where the temperature is low. From
the lowest point, Station No. 48, east of Iceland, where
dli = —0.112 metre, the surface of density rises ort’ the
coast of Greenland to 0.46 metre above its base, accordingly
in all about 60 centimetres; off the west coast of
Spitzbergen to 0.49 metre, or in all more than 60 cms.;
off the west coast of Southern Norway and in the
Skagerak, as also along the west coast of Jutland, to 0.55
metre and above; therefore in all upwards of 66 cms.
North of Iceland, between that island and Greenland,
lies a depression on the ordinate 0. It arises from the
water, particularly at the surface, being less salt alike off
the coast of Greenland and that of Iceland. In the former
locality, melting drift-ice and water from the glaciated
land tend to diminish the amount of salt in the upper
strata of water; in the latter, the largest of Iceland’s
glacier-rivers, which all disembogue on the north coast. The
distribution in the deep of the density ol’ the sea-water off the coast
of Greenland. I have constructed from observations taken by
the "Germania," 1869—70, on the 74th and 75th parallels
of latitude, and the "Sofia," 1883. in Denmark Strait.
The distribution of density off the coast of Iceland,
a locality whence observations were not obtainable. 1
have constructed in accordance with that given us by
our observations off the West Coast of Norway, between
the 60th and the 62nd parallels of latitude. There, no
rivers of any magnitude empty their water into the
sea, and hence perhaps, north of Iceland, the increase of
density with depth is in reality greater thaii assumed. In
that case, the surface of density should slope, from the
coast of Iceland northwards, at a greater angle than shown
by the map.
The density of sea-water depends on the amount of
salt, on temperature, precipitation, the formation of ice, the
melting of ice, evaporation. The surface of density I have
represented, is that which results from the actual density
of the sea-water as found from observation. Hence, when
applying the surface of density to compute the genera,I
currents of the ocean, regard has been paid to the changes
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