320 DISCOVERY REPORTS 



a measure of the proximity or influence of the cold deep layer at this level or alternatively as a measure 

 of its volume or activity) plotted against the average catch of deep larvae in the 1000-250 m. layer 

 for the 10 years, between 1928 and 1938, in which we have observations in Weddell West and Weddell 

 Middle. The average temperature is calculated from observations covering the period November to 

 April and the average deep catch based on stations, both positive and negative, restricted to the period 

 mid-January to the end of April in Weddell West, and to the period beginning of March to the end of 

 April in Weddell Middle, the restriction in each instance being imposed with the object of excluding 

 from the calculation all stations operated at times when the deep larvae, though doubtless present in 

 both sectors, were too deep to be sampled by our nets. The correlation seems clear enough, especially 

 in the years when the average temperature at 1500 m. was at its lowest and the activity of the cold 

 deep current presumed to be at its strongest. It is true that the stations were not distributed in the 

 same way in the different years, but at least the association of numbers of larvae with cold deep water 

 is of special interest. 



Recently Cooper (1955) has suggested that fluctuations in Arctic climate may be connected with 

 changes in the biological productivity of the English Channel. To explain certain large changes in 

 phosphate distribution and in species and abundance of plankton animals that had been observed 

 there between 1920 and 1955 he has erected two interesting hypotheses, (i) that in cold Arctic winters 

 saline surface water is cooled further and made heavier than in relatively mild ones, and (2) that this 

 leads to a greater recruitment of fresh deep water in the North Atlantic after cold Arctic winters. 



Following this short but necessary digression, the commentary on the May-June distribution of 

 the surface Calyptopes may be resumed with some further remarks on the position in the Weddell 

 drift and the extent of its influence to the east, and concluded with some discussion of the now 

 problematical position in the ice-covered East Wind zone. 



Over the greater part of the Weddell stream it will be seen we have no observations for May and June, 

 such as we have being confined for all practical purposes to Weddell East. We cannot therefore be sure 

 whether the Calyptopes survive in the region west of 0° or not. It seems fairly clear, however, judging 

 from the advanced condition of the majority of the swarms encountered there in April (Fig. 82), 

 that if any do survive they would do so only into May and then only in rapidly declining numbers. 



Turning now to the eastward limit of the influence of the Weddell drift in these latitudes we find 

 from the March-April, and more especially from the May-June distribution of these surface forms, 

 the first indication of a somewhat remarkable point to which attention will frequently be drawn in the 

 distributional charts that have yet to be presented. It is that the young surface swarms borne east- 

 wards in the Weddell stream do not, at any rate as larvae,'^ seem to get carried beyond about 

 meridian 30° E except for a short distance as occasional stragglers. In other words it begins to 

 appear that where the Weddell drift ends there too the purely larval distribution ends, and ends it 

 seems quite abruptly, from which it follows that the larval development in these latitudes, whether 

 in the deep or surface layers, from beginning to end takes place strictly within the confines of the 

 region in which this great surface stream is flowing. The evidence for this inference is perhaps best 

 illustrated in Figs, no, 112, 115 and 117 (pp. 359-69) in which I have plotted the seasonal distribu- 

 tion of the massed surface larvae based on the gatherings of our towed stramin nets. 



The facts of the larval distribution in the East Wind drift are now, as I have said, a matter for 

 inference or conjecture. In view, however, of the lateness of the main spawning and hatching that 

 takes place in these high latitudes (p. 306), and of the slowness of the growth that ensues, there would 

 seem to be good grounds for assuming that throughout May and June, under the ice-sheet that 

 now covers this high southern region of larval abundance, the Calyptopis forms must be surviving in 



^ See, however, p. 376. 



