222 L. H. N. Cooper 



confined to depths between about 300 m and the sill depth of about 550 m. Local 

 surface waters seem not to be overmuch concerned. 



(6) That the cold heavy water flows away from the sills of the two ridges not as a 

 smooth continuous current, but intermittently as discrete large boluses. 



(7) That due to the effect of the earth's rotation these boluses are held strongly to the 

 right against the eastern slope of the Reykjanes Ridge, and against the eastern con- 

 tinental (or insular) slope of Greenland. 



(8) That where the boluses are constrained by restricted topography, they move fast 

 horizontally and sink slowly. 



(9) That where narrow straits open out to oceanic dimensions and constraints are 

 removed, then horizontal velocity decreases and the boluses sink rapidly. 



(10) That where boluses of heavy water pass over a dissected bottom or slope, they 

 mould themselves to the rock configuration, and that in consequence the free interface 

 against the enveloping water writhes vigorously. 



(11) That such a writhing interface, at what is effectively a strongly developed dis- 

 continuity layer, initiates strongly developed internal waves which may travel great 

 distances through the open ocean with little attenuation. 



(12) That when such waves meet a continental slope vertical mixing should result, 

 and that when they meet a highly dissected continental slope at a glancing angle, 

 the mixing should be very vigorous indeed. Homogenization of all properties would 

 be much favoured, i.e. shallower layers would be enriched with nutrients at the 

 expense of the deeper and, conversely, deeper layers would, in most places, be warmed 

 at the expense of the shallower. 



(13) That the nutrients are finally brought to the surface by thermal and wind-driven 

 mixing processes, and by upwelling processes which may be always operative. It 

 is suggested that these processes are much more effective in producing surface enrich- 

 ment when a series of cold Arctic winters has produced a situation in the deep Atlantic 

 which favours upward displacement and homogenization of nutrients, especially 

 against continental slopes. 



(14) That in the North Pacific there is no exact parallel to events in the North Atlantic. 

 The only comparable process would seem to be unable to affect the North Pacific 

 waters deeper than about 2,000 m at most. Consequently the nutrient resources of 

 the deep North Pacific seem to be much less effectively used than are those of the 

 deep North Atlantic. 



Some evidence for hypotheses 1-9 has been presented elsewhere (Cooper, 1955). 

 Further evidence for hypotheses 1-9, applying to the Denmark Strait and East Green- 

 land, is being marshalled for publication. 



Hypotheses 10 and 11 are intuitive and no supporting evidence is known to the 

 writer. 



Direct observations in support of hypotheses 12 and 13 are now being sought in the 

 Atlantic near Plymouth. Further evidence in support of hypothesis 14 is still being 

 sought. 



