Fluctuations in Arctic climate with biological productivity of the English Channel 2 1 5 



until 60 N Lat. The evidence for these statements is being marshalled and will 

 shortly be published. A great debt is due to the workers on the research ships, Meteor, 

 General Greene, Dana and Heimland. Full acknowledgements will be made later. 



On all sections this piling up of heavy water to the right against the slope is to be 

 seen, but there is much variation in temperature; in some sections there is an abund- 

 ance of water having potential temperature less than T and salinity near to 34-91 "Z,,^ 

 In others there is no water colder than 2-5°, or, in one " Meteor " section, colder than 

 3°. There is always a deep current towards the south-west, but the presence of very 

 cold Denmark Strait water is intermittent. 



Such intermittent bursting of the dynamic dam, due to either process, would result 

 not in a continuous stream of water flowing oil the ridge, but in a series of self- 

 contained, cold, heavy balls or boluses of water. The calving of a large bolus of water 

 from the ridge is likely to be completed in a matter of days or weeks at most, and is 

 likely to occur most often in late winter or early spring. The descent of a bolus from 

 400-500 to 1,500-2,000 metres through much lighter water is likely to need a very 

 short time. It is not surprising, therefore, that no research ship has ever recognized 

 the birth process for what it may be. 



This water does not sink by the shortest route to the bottom of the Atlantic, but is 

 held to the right by the force of the earth's rotation, and so traverses the side of the 

 continental slope for 300 miles to Cape Farewell, and continues in this way around the 

 bottom of the Labrador Sea at least as far as Newfoundland. 



The evidence I have presented gives no idea of the frequency with which these 

 cold water masses or boluses are born or calved in the Denmark Strait. It could be a 

 seasonal event, once a year. It seems more likely that the complex water movements 

 there are constantly meandering, and that the thrust of a cold bolus to the south over 

 the sill may be a rather irregular afl'air. If so, the sinking of boluses along the Greenland 

 coast may also be an irregular affair. 



It is helpful to think of one of these boluses as behaving like a solid but elastic 

 object. As it thrusts forward and downward, it must displace the water already there. 



Moreover, when passing over an irregular slope and bottom, the under surface of 

 such a bolus of water must be expected constantly to adjust and re-adjust itself to the 

 solid topography. Its free surface against the enveloping water must needs also constantly 

 re-adjust itself. The picture one has is of a vigorously writhing interface which should 

 initiate internal waves in the adjacent ocean, even if this is only weakly stratified. 



Shortly after calving, whilst it is sinking rapidly from sill level at about 500 m to 

 1,500 m, the internal wave pattern should be intense but short lived. After a depth 

 of 2,500 m has been reached, a number of such boluses are likely to be present and in 

 some degree to have coalesced. The writhing will be gentler but unceasing. This 

 writhing of boluses in the North Atlantic provides an origin for internal waves down 

 to at least 4,000 m. In the North Pacific no such possible origin for internal waves 

 has been recognized deeper than the bottom of the sub-Arctic water around L5(X) m. 

 Deeper waves might however arrive in the North Pacific from the Antarctic. 



It is commonly believed that the attenuation of such waves in the open ocean is 

 not severe. They may travel great distances. If there is no friclional loss on passage, 

 for a few hundred miles, the energy in a wave propagated in an equipotenlial surface 

 from a point source will be inversely proportional to the distance run. For greater 

 distances such waves, not accompanied by transport of water, should follow great 



