2]4 L. H. N. Cooper 



at a greater depth, perhaps at the very bottom of the Atlantic, had to arrive from 

 somewhere else. Such deep water is always cold and has sunk from the surface in 

 polar regions. 



Two events are necessary for the production of deep, bottom water in polar regions: 

 one is that there must be present water of sufficiently high salinity, the other is that 

 air temperatures must be low enough to cool this saline water sufficiently for it to 

 become very heavy and so able to sink deep in the ocean. 



Deacon (1937) has shown that this happens in the Weddell Sea and around the 

 South Orkney Islands. Taking the world as a whole, this part of the Antarctic is by 

 far the most important centre for creation of oceanic bottom water. As this water 

 moves away from the Antarctic it may become much modified by mixing processes, 

 particularly over the deep submarine ridges which separate the deep oceanic basins. 



In the North Atlantic there are two areas of sinking of cold saline water. One is 

 over the ridge which joins Faeroe to Iceland (Cooper, 1955) and the other is in the 

 Denmark Strait and around East Greenland. In neither case can it be said with 

 strict truth that the cold, heavy water which sinks deep in the Atlantic is formed in a 

 localized area. Rather are we concerned with a continuous process which takes place 

 all the way from Jan Mayen to the Southern tip of Greenland, It so happens, however, 

 that events which happen between 300 metres depth and the sill of the two ridges 

 connecting Iceland with Faeroe and Greenland stand out in high relief, 



in the development for the Faeroe-Iceland area (Cooper, 1955) it was suggested 

 that the density distribution associated with the Iceland-Faeroe current acts as a 

 dynamic dam, parting the waters of the Atlantic from those of the Norwegian Sea. 

 Whilst it runs steadily, little water need flow over the ridge. Our increasing knowledge 

 of such currents (cf, Fuglister and Worthington, 1951) suggests that they rarely 

 run steadily for very long and tend to meander all over the place. A meander to the 

 south will carry cold Norwegian Sea water to the Atlantic, where it will lie above much 

 lighter water through which it must sink. Again, if the current weakens, the isopycnals 

 will flatten out. Saline surface Atlantic water will flow into the Norwegian Sea, and 

 in compensation Norwegian Sea water below about 250 m will spill over into the 

 Atlantic. In the neighbourhood of 62' N, 13° W, this cascading water sometimes has 

 a salinity exceeding 35-07oo '^^^ ^ temperature of less than 2° C. It is responsible for 

 the salinity maximum which can be followed south-west for many hundreds of miles 

 along the Reykjanes Ridge (Cooper, 1955) and round into the Western Basin. 



A similar process in the Denmark Strait may differ in detail. The cold but brackish 

 East Greenland current flows south along the coast, whereas the warm saline Trminger 

 current flows from the south of Iceland round by the west to the north coast of 

 Iceland. These two currents throw off" spurs which coalesce with their opposite 

 numbers, but in the centre there is a region where the two main currents must be 

 moving more or less side by side and in opposite directions. This is an unstable 

 situation, and must lead to a lot of eddying, swinging about of the main water masses, 

 and mixing. The sill depth of the Denmark Strait is rather more than 500 m. At 

 depths shallower than this north of the Strait there is much water heavier than 27-9 

 or 28-0 sigma-/ and able, if it can escape, to sink into the Atlantic. It comes through 

 the strait banked against the west side. South of the sill it does not fall straight into 

 the trough, but is held against the terrace at depths less than 600 m. It travels south 

 banked against the continental slope of Greenland, and does not reach the bottom 



