SURFACE WATERS OF THE NORTH ATLANTIC OCEAN. 
107 
limited area, mixing little with the waters on which it lies, and being gradually 
warmed by the direct rays of the sun. Between Iceland and Jan Mayen, and in the 
Spitsbergen area, the quantity of water coming from the south is greater, the melting 
of the ice takes place more rapidly, and there is therefore a greater return of Polar 
water on the surface, forming streams which may cover over large portions of the 
northerly current, and penetrate southward into the Faeroe Channel and along the 
coasts of the British Isles. 
This circulation reaches its greatest development in August or early in September, 
when the easterly movement again becomes marked in the higher latitudes—50° to 
60° N.—and wmakens in the lower. The northward discharge by a stream current in 
the eastern area accordingly diminishes, but the increased drift is shown Ijy the 
spreading eastward of the Polar water from south-east of Greenland and from the 
Labrador coast. This can be distinctly traced in October and November, and it is 
followed by a transition into the partial cyclonic circulation first described, the drift 
nature of the circulation being characterised by the gradual lessening of gradients, 
both of temperature and salinity. 
If it be admitted that the surface circulation undergoes the periodic changes 
described, it appears that they follow directly from the seasonal changes in the 
circulation of the atmosphere at the surface, modified by the position and form of 
the land. 
During winter the prevailing winds on the east coast of Canada are north-westerly. 
Large cyclones make their way in continuous succession north-eastward across the 
Atlantic, the region of lowest average })ressure forming a Ijelt from the south-east of 
Greenland, round Iceland, and thence in a north-easterly direction; so that the 
prevailing winds to the right of that belt are west in the central area, south-west 
nearer Europe. Pressure is high, Avith anticyclonic circulation, over the Eurasian 
continent. The Atlantic anticyclone is during the winter months at its smallest and 
weakest, and the AAfiiole ai'ea doAvn to 40° N. is therefore practically under the control 
of the equatorial side of the cyclonic circulation. Under the influence of the strong 
Avinds, Avhich noAvhere form a large angle AAuth tiie coast-line, an immense system of 
surface drifts is developed, the AAarter moving northAvard in the eastern half of the 
basin, and soutliAA^ard in the AA^estern half, AA'hile the main area of purely easterly drift 
is confined to the centre and to loAver latitudes (44). 
The characteristic feature of the Avinter circulation is therefore the purely drift 
nature of the surface currents : it is specially important to notice this in relation to 
the north-eastern part of the area, for the Avater moving nortliAvard betAveen Scotland 
and Iceland is then a Avide surface stream of small depth, consisting of mixed Avaters 
brought from different sources into the central Atlantic area during the preceding 
autumn. 
The transition from AAfinter to summer conditions in the atmospheric circulation 
consists of a gradual increase in size and strength of the Atlantic anticyclone, and 
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