CAUSES OF PATCHINESS 217 



peripheral region of the cyclone, thus forming a "clearing" in the diatom bloom', in which, he 

 continues, the rising euphausians, ' the later Furcilia larvae and young adolescent krill ', assisted by the 

 upwelling water, accumulate from below to gather in a plantless zone. An interesting hypothesis, 

 but can it after all be reconciled (pp. 157-70) with the general subsurface scarcity of older animals, 

 more particularly of late Furcilias and early adolescent forms, we so repeatedly record, especially in 

 the deep intermediate layer from which (p. 47) Beklemishev distinctly suggests this rising popu- 

 lation may be coming? 



Beklemishev (1959) has recently invoked this hypothesis to explain gross irregularities in the 

 distribution of the euphausian population as a whole. He starts with the assumption that the krill 

 live deep in the warm intermediate layer, but get carried to the surface by local upwellings in the 

 centres of isolated cyclonic movements along the East Wind- West Wind boundary zone. Thus, since 

 it has been suggested (Ivanov and Tareev, 1959) that such upwellings are in turn generated by atmo- 

 spheric cyclones centred over them, he concludes that the grosser irregularities of the distribution of 

 this species spring ultimately from atmospheric phenomena. This again is an interesting hypothesis 

 but it does not fit the facts, {a) because the krill it is now clear do not live deep in the warm inter- 

 mediate layer, and {b) because our net-hauls in aggregate do not reveal any discrete accumulations of 

 the population along the East Wind- West Wind boundary zone, but suggest that the swarms, larval, 

 adolescent and adult, without any gross irregularity or conspicuous discontinuity, are spread more 

 or less uniformly throughout the East Wind surface stream (p. 60, Fig. 5 a) and that their principal 

 locus of abundance (outside the Weddell current) lies (Fig. 56) to the south of the divergence zone. 



As Nansen did (p. 72) so many years before him, Bogorov (1938) attributes the intense spring 

 flowering on the fringes of the Arctic basin to the great build-up of nutrients that takes place below 

 the solid pack in winter. Various factors he observes contribute to this massive accumulation, the 

 decay of plankton, the enriching of the surface waters by nutritive material carried up from the bottom, 

 the rich salt load brought down by the great Arctic rivers and above all because, since there is no, or 

 virtually no, phytoplankton below the ice to consume them, the accumulating salts can go on accumu- 

 lating. During this period of ' biological winter', as he has called it, 'when darkness and ice dominate 

 over the sea ', the plankton as a whole is poor, the quantity of zooplankton, however, prevailing a 

 little over that of plant plankton. With the spring break-up and melting of the sea ice and the exposure 

 of the surface to sunlight, the phytoplankton, feeding without stint on the wealth of nutrients 

 accumulated in winter, begins to multiply, rapidly reaching a massive maximum. This intense 

 flowering, or 'biological spring', occurs principally along the ice-edge, in recently opened spaces 

 among the floes and in 'water breaches' in the fast ice, and while it lasts he finds the plant plankton 

 may increase until it outweighs the zooplankton sometimes 120-fold. Soon, however, the position 

 is reversed. The plants, having quickly consumed the salts, begin to die oflF and develop at a slower 

 rate, their decline being accelerated by the massive assault of the rapidly accumulating herbivores 

 feeding on them. Thus, by the time large areas of open water appear ('biological summer'), the 

 zooplankton has become established as dominant. As Bogorov points out, the spring break-up of the 

 Arctic pack does not occur simultaneously all over the polar basin. It may be late in one area and 

 early in another and thus biological spring, possibly even in areas adjoining one another, could be 

 correspondingly late or early. In the area of late break-up phytoplankton would dominate, in the 

 area of early break-up the dominant plankton would be animal. Thus, he concludes, the wide- 

 spread inverse correlation between relative abundance of plant and animal plankton observed in the 

 Arctic seas has its roots primarily in the seasonal and regional history of the polar pack. In other 

 words it seems, if I follow him correctly, the vagaries of the ice-cover could be producing biological 

 winter in areas adjoining others already in a condition of biological spring or even in the sununer state. 



24 DM 



