414 APPENDIX V 



precipitation in these regions is constantly decreasing the salinity 

 of the surface water, this vertical circulation must bring about 

 a diminution of salinity in the underlying waters, with which the 

 sinking surface water is mixed into a homogeneous volume of water. 

 The Frithjof section in particular seems to show that the vertical 

 circulation in these regions reaches to a depth of 500 or 600 metres 

 at the close of the winter. If we consider, then, what must happen 

 over a bank in the ocean, where the depth is less than this, it 

 is obvious that the vertical circulation will here be prevented by the 

 bottom from reaching the depth it otherwise would, and there will 

 be a smaller volume of water to take part in this circulation and to 

 be mixed with the cooled and diluted surface water. But as the 

 cooling of the surface and the precipitation are the same there as in 

 the surrounding regions, the consequence must be that the whole 

 of this volume of water over the bank will be colder and less salt 

 than the surrounding waters. And as this bank water, on account 

 of its lower temperature, is heavier than the water of the surround- 

 ing sea, it will have a tendency to spread itself outwards along the 

 bottom, and to sink down along the slopes from the sides of the 

 bank. This obviously contributes to increase the opposition that 

 such banks ofifer to the advance of ocean currents, even when they 

 lie fairly deep. 



These conditions, which in many respects are of great im- 

 portance, are clearly shown in the two Fram sections and the 

 Frithjof section. 



The Northern Fram section went from a point to the north-west 

 of the Rockall Bank (Station 15), across the northern end of this 

 bank (Station 16), and across the northern part of the wide channel 

 (Rockall Channel) between it and Scotland. As might be expected, 

 both temperature and salinity are lower in this section than in the 

 southern one, since in the course of their slow northward movement 

 the waters are cooled, especially by the vertical circulation in 

 winter already mentioned, and are mixed with water containing less 

 salt, especially precipitated water. While in the southern section 



