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178
Under 70° til 71° Bredde have vi et Maximum af
Tryk. Her se vi Dybets Isothermer bøje sig nedad, og
fremkalde et Teniperaturmaximum ved Bunden, paa samme
Tid som Saltholdigheden ogsaa viser et Maximum. Yi
have med andre Ord en nedstigende Bevægelse af varmere
og saltere Vand.
Under 73° til 74° Bredde have vi, paa Nordsiden
af Tverryggen, i Svenskedybet, et Minimum af Tryk i de
dybere Lag. Samtidig stige Isothermerne her opad og
Isothermen for —1°.(> naar sin største Højde under 74°
Bredde, medens Saltholdigheden synker til et Minimum.
Det er en opstigende Bevægelse af koldt og saltfattigere Vand.
Under 7(>".5 Bredde have vi et Maximum af Tryk.
Isothermerne have her et Minimum af Højde.
Saltholdigheden har et Maximum. Der er en nedstigende Bevægelse
af varmere og saltere Vand.
Vende vi nu vor Opmerksomhed paa Snittet XXIX
efter Meridianen 10° E, Pl. XV, og sammenligne det med
Karterne PI. XLVI og XLVII.
Under 70° Bredde have vi Maximum af Tryk.
Isothermerne sænke sig sterkt mod Dybet.
Under 72° til 73° Bredde er et Minimum af Tryk.
Dybets Isothermer ere løftede til en Top.
Sammenligne vi Snittet XXX. Pl. XV, med
Isobar-karterne, saa linde vi, i Meridianen 10°W, Jan Mayen Ilendens
Sydside optaget af temmelig koldt Vand, medens dens
Nordside, under Indflydelse af Trykmaximct under 70°, har
varmere, nedstigende Vand. Nordenfor Jan Mayen kommer
man paa et Minimum af Tryk. Her løfte Dybets
Isothermer sig op.
Trykkets Maxima ere saaledes gjennemgaaende
ledsagede af nedstigende Bevægelser af varmere og saltere Vand,
Trykkets Minima af opstigende Bevægelser af koldere og
saltfattigere Vand. Dette er i Overensstemmelse med, at
Temperaturen i Havet er hojest i de øvre Lag og lavest
i de dybere. 1 Atmosfæren er det omvendte Tilfældet.
Her ere derfor de barometriske Minima ledsagede af
opstigende Strømme af varmere og fugtigere Luft og de
barometriske Maxima af nedstigende Strømme af koldere og
tørrere Luft. Fra Jordens af Solen opvarmede Overflade
udgaa de varmere Strømninger saavel i Atmosfæren som
i Havet.
Af Meridiansnittene XXVIII. XXIX og XXX ser
man, at Isothermerne i de øvre Lag, saavel i 500 Favne
som i 3U0 Favne, følge som Hegel do Bøjninger, som disse
Linier have i de beskrevne dybere Lag. Navnlig er
Iso-thermernes Bøjning nedad i 70° til 71° Bredde, opad i
73° til 75° Bredde og nedad i 7(>° til 77° Bredde udpræget,
især i Snittet efter Greenwich Meridian. Saltholdigheden
(Pl. XXXVIII) viser tilsvarende Forhold. De sterkere
vcrticale Bevægelser i Dybet foraarsages altsaa tilsvarende
verticale Bevægelser i de øvre Lag.
From the 7()th to the 7lst parallel of latitude, we
have a maximum of pressure. Here, the isotherms of the
deep are seen bending downwards, and thus produce a
maximum of temperature at the bottom, the amount of
salt also showing a maximum. In other words, we have a.
downward motion of warmer and salter water.
From the 73rd to the 74th parallel of latitude, we
have, on the north side of the Transverse Ridge, in the
Swedish Deep, a minimum of pressure throughout the
deeper strata. At the same time, the isotherms here rise
upwards; and the isotherm for —1°.6 reaches its greatest
height on the 74th parallel of latitude, whereas the amount
of salt sinks to a minimum. It is an upward motion of
cold water containing a comparatively small proportion
of salt.
In latitude 7(5°.5, we have a maximum of pressure.
The isotherms have here a minimum of height; the amount
of salt exhibits a maximum. ■ There is a downward motion
of warmer and salter water.
Let us now turn our attention to section XXIX,
extending along the meridian long. 10° E, PI. W’, and
compare it with the maps PI. XLVI and Pl. XLVII.
On the 70th parallel of latitude, we meet with a
maximum of pressure. The isotherms dip down towards
the deep.
In latitude 72° to 73°, we have a minimum ol’
pressure. The isotherms of the deep rise to a summit.
Let us compare section XXX, Pl. XV". with the
isobar-maps. We shall find, on the meridian 10" W, the
south side of the Jan-Mayen Channel filled with
comparatively cold water, whereas the north side, under the
influence of the pressure-maximum in lat. 70° N, has warmer
water, with a downward motion. North of «Tan Mayen
occurs a minimum of pressure. Here, the isotherms of
the deep rise upwards.
Hence the maxima of pressure are always
accompanied by downward motions of warmer and salter water,
the minima ol’ pressure by upward motions of colder water,
having a less amount of salt. This accords with the fact,
that the temperature of the sea is highest in the upper
strata and lowest in the deeper. In the atmosphere the
reverse is the case. There, accordingly, the barometric
minima are accompanied by ascending currents of warmer
and moister air. the barometric maxima by descending
currents of colder and drier air. From the surface of
the earth, heated as it is by the rays of the sun, the warm
currents issue alike in the atmosphere and in flit* sea.
The meridional sections XXVIII, XXIX. and XXX
show us that the isotherms in the upper strata, both those
at 500 and those at 300 fathoms, as a rule follow the
bends which these lines are found to make in the deeper
strata. Note particularly the downward bend of the
isotherms from the 70th to the 71st parallel of latitude, the
upward bend from the 73rd to the 75th parallel, and
the downward bend from parallel 7G to parallel 77. especially
throughout the section extending along the meridian of
Greenwich. The amount of salt (Pl. XXXVIII) exhib-
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