Havets Dybde er meget ringe i Forhold til dets 
horizontale Udstrækning. Den største Del af Bevægelsen 
maa derfor foregaa i horizontal Retning, altsaa langs Lige- 
dybde-Linierne (Isobatherne), ligesom Strømmen 1 Overfladen 
langs Kysterne. Hvor Isobarerne gaa langs Isobatherne, 
og ude i det frie Hav, kunne Formlerne faa Anvendelse, 
forudsat at Isobarerne ikke frembyde sterkere Krumninger 
og sterkere Variationer i deres indbyrdes Afstand. I Dyb- 
derne 800 og 500 Favne opfyldes disse Betingelser tildels, 
navnlig i Polarstrømmen. I de større Dybder ligge Isoba- 
rerne jevnlig tvers paa Isobatherne. Dette sidste Tilfælde 
er analogt med Vandets Bevægelse i en Elv, hvor Gra- 
dienten peger i Elvens egen Retning, og Bevægelsens Ha- 
stighed er betinget af Gradientens eller Heldningens og 
Frictionens Størrelse. 
I de større Dybder maa Bevægelsen for en meget 
stor Del foregaa i Retninger, der danne smaa Vinkler 
med Gradienterne. 
systemerne indtil 500 Favnes Dyb vise, Bevægelsen idet- 
heletaget foregaa cyclonisk omkring et Minimum af Tryk, 
der ligger forholdsvis centralt i Havet. I de dybere Lag 
derimod blive de mere radiale Bevægelser fra de Steder, 
hvor Trykket er størst, henimod de Steder, hvor Trykket 
er mindst, de overvejende. Men i Maximumspartierne maa 
Bevægelsen være nedadstigende og i Minimumspartierne opad- 
stigende, og disse verticale Bevægelser befordres i fremtræ- 
dende Grad ved den nævnte radiale Retning af de hori- 
zontale Bevægelser. Som en lhgefrem Folge af Vandets 
Continuitet ville igjen de verticale Bevægelser 1 de dybere 
Lag indvirke paa Bevægelsen i de højere Lag. De ned- 
stigende Bevægelser i Dybet drage de øvre Vandlag efter 
sig, de opstigende ville drive dem til Side. 
Vi have directe Bevis for disse Virkninger af Tryk- 
kets Fordeling i de dybere Lag i Temperaturens og Salthol- 
dighedens Fordeling. Da Stromningerne i vort Nordhav 
hovedsagelig foregaa i meridional Retning, er det Vertical 
snittene for Temperaturen og for den specifiske Vægt langs 
Meridianerne, der lade Aarsagsforbindelsen fremtræde klarest. 
Man sammenstille Snittene XXVIIT Pl. XIV og PI. 
XXXVIII, der gaa langs Greenwich Meridian, med Kartet 
Pl. XLVI og Pl. XLVII. Ved Havbækkenets sydlige 
Rand er der i disse Dybder, 1000 og 1500 Fayne, et 
Samtidig se vi Isothermerne sænke sig 
Der 
er følgelig her en nedstigende Bevægelse af varmere og 
saltere Vand. Denne Bevægelse vedvarer, efter Isother- 
mernes Vidnesbyrd, til 6595 N. Br. 
Maximum af Tryk. 
og Saltholdigheden aftage fra et absolut Maximum. 
I 68° Bredde eller lidt derover have vi et Minimum 
af Tryk. Mod dette Parti løfte Dybets Isothermer sig og 
de have her sine Toppe, medens Saltholdigheden viser et ab- 
solut Minimum, Her have vi altsaa en opstigende Bevægelse 
af koldere og mindre saltholdigt Vand. 
Den norske Nordhavsexpedition. 
I de mindre Dybder kan, som Isobar- 
ILC 
H. Mohn: Nordhavets Dybder, Temperatur og Strømninger. 
The depth of the sea is very trifling compared to 
its horizontal extent. Hence the motion must in greater 
part take a horizontal direction, viz., along the lines of 
equal depth (isobaths), as with the current at the surface 
along the coasts. Where the isobars run parallel to the 
isobaths, and out at sea, the formule can be applied, 
proyided the isobars have no sharp curves or sudden 
their from other. At the 
depths 300 and 500 fathoms these conditions are partially 
variations in distance each 
complied with, in particular throughout the Polar current. 
In greater depths, the isobars lie as a rule straight across 
the isobaths. This last case is analogous with the motion 
of the water in a river, where the gradient points in the 
same direction as the river flows, and the velocity of the 
motion is determined by the steepness of the gradient or 
the inclination, and by the amount of friction. 
In the greater depths, the motion must to a very 
great extent proceed in directions forming but small angles 
with the gradients. In the lesser depths, the motion can, as 
shown by the isobar-systems down to a depth of 500 fathoms, 
proceed on the whole cyclonically, round a minimum of 
pressure, that occupies a comparatively central position in 
the sea. Throughout the deeper strata, on the other hand, 
the more radial motions, from the localities where the pres- 
sure is greatest to those where the pressure is least, will be 
found to prevail. But in the maximum-regions the motion 
must be downward, in the minimum-regions upward; and 
these vertical motions are to a great extent furthered by 
motion. Again, as 
a direct consequence of the water’s continuity, the vertical 
the radial direction of the horizontal 
motions in the deeper strata will act upon the motion in the 
higher strata. The downward motions in the deep must draw 
after them the upper strata; the upward will force them aside. 
We have direct proof of these effects of the distribu- 
deeper strata in the 
The currents in 
tion of pressure throughout the 
distribution of temperature and salinity. 
the North Ocean taking chiefly a meridional direction, it 
is the vertical sections for temperature and specific gravity 
along the meridians that give the clearest insight into the 
causal connection. 
Let us compare the sections XXVIII, Pl. XIV and 
Pl. XXXVIII, extending along the meridian of Green- 
wich, with the maps Pl. XLVI and Pl. XLVII. At the 
southern margin of the sea-basin, we have in these depths, 
1000 and 1500 fathoms, a maximum of pressure. At the 
same time, the isotherms are found to descend, and the 
amount of salt diminishes from an absolute maximum. 
Hence, hereabouts there must be a downward motion of 
warmer and salter water. This motion continues, judging 
from the isotherms, up to lat. 6595 N. 
On the 68th parallel of latitude, or a little higher, 
occurs a minimum of pressure. ‘Towards this part of the 
sea, the isotherms of the deep are found to rise and to have 
here their summits, whereas the amount of salt exhibits 
an absolute minimum. Here, accordingly, we have an 
upward motion of colder water containing a less proportion 
of salt. 
9 
