

Resume. 



HE Hydrographical Conditions in tlie Northern Ocean lue deter- 

 mined by three factors, viz., the Gulf Stream, the Arctic Current 

 andiithe Continent. The influence of each of these factors is subiect 

 annual periods having their maxima and minima. 



"he Gulf Stream reaches its maximum during the summer. 



then attains those dimensions with which we have been made 



''t'ljuamted through the instrumentality of the Norwegian Northern 



cean Expedition. In November it begins to decrease, and by the 



■Winter its thickness, both on the surface and down in the deep, 



nminishes. Whilst it, during summer, covers the greatest portion 



"t the surface of the Northern Ocean, it in winter becomes, reduced 



to a narrow stripe running in the direction SSW to NNE, throughout 



'e central and easterly portions of the Nortliern Ocean. But, 



nevertheless, it forms a liarrier at all times of the year between 



>e East Iceland Arctic current and tlie North European coastal 



*-''^' In the deeps of the Norwegian coast the annual period is 



•-'eii through its being met with, during summer, up to .50 metres 



elow the surface, whilst, during winter, it sinks to a depth of 200 

 to 2 



to 



oO metres. 



In addition to the annual period, the Gulf Stream, according 



our investigations, likewise undergoes changes from one year to ! 



other, but we cann )t, from the materials to hand, determine 



tier tliese variations are connected with a great period or not. i 



ine eastern brancli of the Arctic current (to the eastward 



celand) is iorced liack during the summer, so tliat it but reaches ^ 



soutli eastern point of Iceland. During winter, on the other 

 hand. 



to 

 fr, 



't attains so great dimensions, during March and April, as 



occupy the whole of western ])ortion of the Northern Ocean 



>ni the surface down to a depth of at le;ist 2 to 300 metres. During 



*"s period, as in 1897, it can descend so far in a SSE direction, 



to be separated from the Shetland Islands by but one degree 



a itude. There, however, its course is always checked by the 



oithern In-anch of the Gulf Stream, ])ut probably a great admix- 



"I'e of their waters occurs. 



This current too, is subject to great changes from year to year, 

 and these changes are most closely connected with corresponding 

 changes in the Gulf Stream. 



The Coastal Water, along the entire coast of Norway, under- 

 goes the same annual periodical changes as previously described by 

 Hjobt [9,o]. The most striking phenomenon in this period is the 

 increasing thickness of the coastal water during the autumn and 

 winter, whilst the Gulf Stream is simultaneously forced down to- 

 wards the bottom. From our investigations, this expansion is 

 chiefly caused by the mixing of Atlantic water witli fresh water 

 from the continent, and not by the .addition of water from the 

 Arctic Ocean, i\s is assumed by Pettersson and Ekman. 



The Plankton. In the foregoing pages we have given an account 

 of the various kinds of vegetable Plankton existing on the shores of 

 Norway, and the annual periodicity in the occurrence of the indi- 

 vidual Plankton organisms. 



Of more general interest ai-e our en(]uiries into the causes of 

 this periodicity. It is caused on the one part by the stationary 

 coastal forms' dependence on the physical and chemical conditions 

 necessary to life, as individual species flourish under those specific 

 conditions which favour them, and fall to the bottom in a dormant 

 state so soon as those conditions arc absent. On the other part, 

 the ocean currents convey oceanic organisms from adjacent portions 

 of the North Atlantic. The fate of these organisms is too, both in 

 the ocean and the coast, entirely dependent on hydrographical changes. 

 Their occurence on the coast is thus dependent, partly, on the 

 hydrographical condition of the eastern branch of the Gulf Stream, 

 and partly, on the conditions present on the coast itself. 



As all the inflowing bodies of oceanic water are of an Atlantic 

 kind, the Arctic organisms, which may be met with at certain times, 

 must, in any case, pass through Atlantic water if they really are 

 derived from the Arctic current, but their subsequent appearance, 

 in the colder and fresher water on the coast, is no proof of the 

 coastal water's Arctic origin. 



