1906. No. 3: AMUNDSEN’S OCEANOGRAPHIC OBSERVATIONS IN 1901. 75 
from the surface, will not be able to reach very deep, and break through 
the upper water-strata, where the salinities and densities increase too 
rapidly downwards. The writer found that in the North Polar Basin 
the vertical circulation during winter, did not reach much more than 30 
metres below the water-surface. Besides the water of the upper temperature- 
minimum is near its freezing point and cannot become much heavier by 
cooling. There cannot, therefore, be any considerable vertical circula- 
tion at any time of the year. The underlying warm water-stratum can 
thus be cooled only by conduction of heat, which is extremely slow in 
water, and by intermixture with the colder overlying layers, which is 
also slow where the densities so rapidly decrease upwards, and where 
the surface is covered by ice, so that the wind cannot stir the water 
much. 
The intermediate warm layer may thus exist for a very long time, 
without being much cooled, and it may, therefore, be expected every- 
where under the polar current, because the density of this warmer water 
is between that of the light Polar water, and that of the’ bottom-water ; 
it will thus easily find its way in between these two waters}. 
At most of Amundsen’s stations east of Greenland there is hardly 
any similarity to the polar conditions. At some of the western stations, 
(especially Stats. 17, see also Stats. 18, 19, 23), there are indications of 
an upper temperature-minimum at about 40 or 50 metres with an under- 
lying, somewat warmer layer; but the salinities are on the whole so high 
that an active vertical circulation may be produced by cooling during 
the winter. If, for instance, at Stat. 17, the water at 50 metres be 
slightly cooled, it will become heavier than the underlying warmer water 
at 60 metres. 
The temperature-maximum at these stations, is at about 60 to 100 
metres below the water-surface?. Farther west, under the Polar Current, 
this intermediate warmer layer increases much in thickness towards the 
Greenland coast, while its temperature rises; — and the further west the 
deeper its upper boundary. The isopycnals also slope fairly steeply 
towards the Greenland coast (see Sections V and VI). This very cha- 
racteristic feature indicates that the overlying cold Polar water-layer as 
well as the underlying warmer layer is in movement southwards along 
1 It is, for instance, noteworthy that in Section IV—VI, the underlying warmer water 
with temperature above zero, has very nearly the same extension eastward as the 
overlying cold water with temperature below —r1° C. 
2 At Nathorst’s Station VI (N VI) Akerblom observed a maximum of o'19° C. at 100 
metres (see Section VI, Pl. VII). 
