Resume, 



I HE Hydrographical Conditions in the Northern Ocean are deter- 

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

 and the Continent. The influence of each of these factors is subject 

 to annual periods having their maxima and minima. 



The Gulf Stream reaches its maximum during the summer. 

 It then attains those dimensions with which we have been made 

 acquainted through the instrumentality of the Norwegian Northern 

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

 winter its thickness, both on the surface and down in the deep, 

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

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

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

 the central and easterly' portions of the Northern Ocean. But, 

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

 the East Iceland Arctic current and the North European coastal 

 sea. In the deeps of the Norwegian coast the annual period is 

 seen through its being met with, during summer, up to 50 metres 

 below the surface, whilst, during winter, it sinks to a depth of 2<>0 

 to 250 metres. 



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

 to our investigations, likewise undergoes changes from one year to 

 another, but we cannot, from the materials to hand, determine 

 whether these variations are connected with a great period or not. 



The eastern branch of the Arctic current (to the eastward 

 of Iceland) is forced back during the summer, so that it but reaches 

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

 hand, it attains so great dimensions, during March and April, as 

 to occupy the whole of western portion of the Northern Ocean 

 from the surface down to a depth of at least 2 to 300 metres. During 

 this period, as in 1897, it can descend so far in a SSE direction, 

 as to be separated from the Shetland Islands by but one degree 

 of latitude. There, however, its course is always checked by the 

 northern branch of the Gulf Stream, but probably a great admix- 

 ture 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 [95]. 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 with fresh water 

 from the continent, and not by the Addition of water from the 

 Arctic Ocean. HS is assumed by PETTEESSON 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 are our enquiries 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 are 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. 



