432 DISCOVERY REPORTS 



I therefore conclude that while the circulation of the krill on the Atlantic side is maintained partly 

 by the clockwise movement of the East Wind-Weddell surface stream, as Ruud originally supposed, 

 at the beginning of the life-cycle the northward and eastward spreading of the bottom water, which 

 there is reason to believe (p. loo) is carrying hatching eggs, and the eastward and southward move- 

 ment of the warm deep water (p. ii8) carrying the ascending larvae, are equally involved. In other 

 words, the only southward movement of the population that the hydrological evidence seems to 

 allow possibly occurs when, as Nauplii, Metanauplii and younger First Calyptopes, the young krill 

 are climbing towards the surface, and even then, I believe, only while they are passing through the 

 warm deep layer. 



If, however, as has so often been suggested, there is in fact a southward movement at the surface 

 somewhere near 30° E, and this movement does involve the return of Weddell water to the East Wind 

 zone, then the dynamics of control, on the Atlantic side at least, would appear to be simple enough, and the 

 circulation of the krill in this region would in fact follow the broad lines originally postulated by Ruud.^ 

 Such a movement, too, would help to explain the relative poverty of the krill in the West Wind drift 

 east of 30° E. Model's shallow southward subsurface movement between 18° and 25° E, if real, 

 would also help to explain it, in so far as it might lead here (or in 30° E) to the gradual transference 

 of larval or adult swarms from the Weddell to the East Wind zone, if, as seems possible (pp. 105-18 

 and pp. 268-78), some such swarms undergo a shallow vertical migration by day. If such a trans- 

 ference does in fact take place it would postulate that Model's subsurface current was travelling more 

 quickly than the surface stream and that the migrating swarms, especially the larval swarms, spend 

 more time in it than they do at the surface. We cannot as yet say that they do. The evidence in 

 fact points rather to the contrary (see pp. 105-23, 157-70 and 268-78). 



It may be too, although Deacon's classic survey of Antarctic hydrology (p. 99) does not suggest it, 

 that all round the continent there is small-scale local cascading of shelf water forming, within the 

 East Wind drift itself, miniature cold bottom currents, which, moving away to the north and east, 

 might possibly give rise to a series of local cold bottom-warm deep-surface circulations like that of 

 the major rotary complex we find in the Weddell Sea. In the absence of transport of East Wind water 

 from the Weddell to the Pacific side by way of the Bransfield Strait a series of such complexes, if real, 

 would help to explain the recruitment and continued existence of the west-bound East Wind popula- 

 tion beyond the Atlantic sector. If, moreover, the cyclonic movement (p. 47) claimed to have been 

 discovered by the Russians off Enderby Land is correct then one could conceive the East Wind popula- 

 tion as being in some measure at least, and in some places, static, part of it perhaps not always 

 travelling to the west. As Sverdrup (1933) remarks, although the principal movement in high latitudes 

 bordering the continental land is towards the west several 'whirls of stationary character appear to 

 exist, and these are present partly because of the prevailing winds and partly because of the bathy- 

 metric features'. 



Finally, the East Wind zone, enjoying as it does a certain measure of immunity from the major 

 ravages of whales, seals, penguins and possibly other animals, may be regarded in a sense as a relatively 

 untapped reserve of whale food and as such, whatever the factors contributing to the maintenance of 

 its own population may be, must continually be contributing something to the replenishment of the 

 more heavily suffering krill in the Weddell stream. 



In his recently published Marine Ecology Moore (1958), referring to the Antarctic euphausians as 

 a whole, states that there appears to be ' a regular cycle in which immatures and adults are, in general, 



' Recent observations by the Japanese during; the International Geophysical Year suggest rather strongly that such a 

 movement might in fact exist, there being evidence of particularly strong 'recurvature' in 45° E (Kumagori and Yanagawa, 

 iQS^**)- I would repeat, however, that our Discovery observations provide no evidence of this phenomenon. 



