12 



ASTRID CLEVE-EULER, QUANTITATIVE PLANKTON RESEARCHES IN THE SKAGER RAK. 



Among the Ceratia, imported by thc North Sea- water, C. longipes is the dominating 

 species, just the form lacking in the Kattegat-water of Extra II, whose leading Ceratium, 

 the C. furca, is in return scarce here. Then eome C. macroceras and C. tripos, whereas 

 ( '. bucephalum is, as usually, rare. In the surface, Ceratium tripos is again the least scarce 

 species, being evidently drifted hither from the coasts. 



The infusiorians have also a remarkably homogeneous vertical distribution with 

 only a slight increase upwards, this water far off from land being little favourable to their 

 development. 



Table 9. S. Skag. 8. 58° 10' N., \f 18' E. 



VIII. 1012. 



Depth 



CB o 



£ £ 



o 



o 



>> 

 fl 



"3 



t/3 



n" 

 >> 

 "w 



a 



CD 



O 



Paralia 

 sulcata 



Guinardia 

 flaccida 



Rhizosolenia 



alata f. 



gracillima 



Thalassio- 



thrix nitz- 



schioides 



Diatoms 



total 

 numbers 



Ceratia 



Peridiniales 



total 



numbers 



Laboefe 



Cyttarocylis 

 elegan3 



Infusorians 



total 



numbers 







16,66 



26,65 



19,22 







20 





80 



120 



320 



80 





140 



Kl 



15,14 



29,56 



21,80 













480 



740 



20 



90 



130 



20 



7,18 



34,58 



27,07 













380 



590 





170 



200 



30 



6,41 



34,78 



27,35 



— 



— 

















t 



40 



5,99 



34,78 



27,40 







20 



920 



2,810 



100 



450 





240 



360 



50 



5,90 



34,87 



27,48 







5 



430 



575 



10 



90 



20 



50 



110 



60 



5,89 



34,94 



27,54 







10 



40 



50 





110 



10 



30 



70 



80 



5,86 



34,97 



27,57 



70 





10 





110 





10 



10 





10 



100 



6,07 



35,01 



27,58 











10 



10 



60 



10 



10 



20 



150 



5,90 



35,03 



27,61 





















20 



200 



5,86 



35,05 



27,62 















20 









300 



6,03 



35 — 



27 — 















30 









The great inflow of temperate North Sea-water, so marked in Central Skager Rak, 

 does not reach this deep-water station, that is filled from the bottom up to less than 20 

 m with a cold (7°,2 — 5°,9) *and salt (34,6 — 35 %o) Atlantic water, overlayered by a rela- 

 tivcly thin couch of warm and diluted coast-water. In this uppermost part, diatoms 

 are almost absent and Ceratia not numerous, giving a scanty Tripos-plankton. Then 

 there is a biological limit somewhere between 20 and 40 m; as the water-sample from 

 30 m was löst, a more exact information cannot be given. Even if this limit comes little 

 beneath 20 m, as is most probable, it runs several metres beneath the hyrographical 

 limit, spöken of above. An abrupt increase of the diatom-numbers is brought by the 

 change of water and is chiefly owing to the presence of a needle-shaped Nitzschia, deter- 

 mined to N. pungens v. atlantica Cl. (see part II), together with some common winter- 

 forms of the Sira-plankton. But these remnants of the arctic flora cease rapidly down- 

 wards (beneath 100 m, the water is almost empty ). Cyttarocylis elegans is the only Tintinnid 

 of importance. 



The Ceratia do not present any irregularity in their vertical distribution, 

 which is no doubt due to their belonging only to the surface-water, from where they sink 



1 The sample from 30 m was broken tluring the transport. 



