UAN X IWO 



I. The Hydrograpliical Conditions of the Northern Ocean. 



HE greatest part of the Northern Ocean is a deep-\yater sea. 

 The 1000 metre curve, in many places approaches nigh to the 

 Norwegian coast (as for instance at Storeggen olT Kristianssund, 

 and at Vesteraalseggen). From these points, and across to Ice- 

 land, Jan Mayen and Greenland, tlie depth exceeds 1000 fathoms. 

 Throughout this deep-water sea, the physical conditions at the 

 bottom are very uniform, and of an Arctic character. 



If one follows the 400 metre curve on the Chart of Depths, 

 ^^- ^ °"e ^^'Jll finf^ the boundary of the Norwegian "coastal banks". 

 It will be perceived that tlie sea-bottom beyond them descends almost 

 perpendicularly downwards, so that the banks themselves form a 

 sort of barrier or breast ,vork to the Norwegian coast. It will 

 furthermore be seen that this barrier extends from off the Sogne 

 Fjord to the shores of Scotland, and that the whole of the North 

 Sea IS thus of a depth, and similar physical conditions to the banks. 

 In order to understand the physical conditions of these banks 

 — our especial subject — , one must, above all, remember, that the 

 latter are quite isolated from the cold polar water of the deeper 

 sea. The water which covers our coastal banks comes from the 

 southward, and is carried on to our shores by the well known 

 Atlantic current ~ the Gulf Stream — which, in the area 

 comprised within a line from Scotland to Iceland and Finmarken, 

 covers the central portion of the surface of the Northern Ocean, 

 and, down in the deep, spreads itself over the banks, the North 

 Sea, the Skagerak, and up to the Swedish Coast and mouth of the 

 Christiania Fjord. 



From PL 2. it will be seen that the greatest portion of the 

 surface of the Northern Ocean is occupied in summer by water 

 containing over 35 "/'oo of salt. 



In like manner the bottom from -'Eggen'" in to the coast is 

 covered with water, the salinity of whicli is 35 »/oo, of a temperature 

 ranging from 6" to 7« Celsius. Only Ijelow "Eggen" will a lower 

 temperature be found, down to — 1° at a depth of 900 metres, 

 where the salinity is also less, as the water is mixed with that 

 from the polar ice. In on the coast the salinity, too, decreases, 

 as will be seen from the plate, and therefore one can lay down 3 

 deep regions according to the physical conditions: — 



1. The Arctic Sea Region at the greatest depth. 



2. The warm Atlantic Ocean Eegion. 



3. The Coastal Water Region. 



A general view of the layers of water to be met with on, and 

 off our Northern Ocean seaboard, -will be best seen from the hydro- 

 graphic section which was obtained, through the kindness of the 

 Geografiske Opmaaling (Geographical Survey), off Hustadviken, where 

 the declivity towards the great depths, Storeggen, is comparatively 

 near land. The section is given on PI. 5, Fig. 2. 



The same layers of water which are met with, the one below 

 the other along the coast, appear on the surface of the sea when 

 far off the land. The hydrographic profile from the Sogne Fjord 

 to the Arctic Ocean, PI. 4, Fig. 1, thus shews that the salt Atlantic 

 water fills the entire central portion of the Northern Ocean from 

 the surface downwards to a deptli of at least 300 metres (during 

 this expedition deeper investigations were not instituted). The Arctic 

 water, with its lesser salinity, shoves itself like a cold wedge across 

 the Gulf Stream, and in the Arctic Ocean is met with from the 

 surface to the greatest depths. 



The thickness of the coastal water varies greatly with the 

 seasons. In the winter it can form a layer up to 250 metres in 

 thickness, whilst in summer the Atlantic water may be mot with, 

 close in to land, at a depth of 40 to 50 metres. 



On PI. 5, Figs. 3 and 4, will be found a representation of the 

 annual variations of temperature and salinity off the west coast of 

 Norway. 



The method of representation has been devised by Mr. Aksel 

 Steen. 



The drawings have been made from investigations already 

 published by H.jokt [95]*). 



In summer the layers in tlie surface water have been found 

 to be excessively warm, but containing little salt, whilst the Atlantic 

 water forces its way up from beneath. Subsequently the high tem- 

 perature descends, so that at a depth of 250 metres the greatest 

 warmth (8") is met with in December. 



The periodical changes thus vary to a depth of 250 metres, 

 on the west coast of Norway. Up to the present time no inve- 

 stigations have been carried out during the whole year off the 

 seaboard of the Northern Ocean, but there is good ground for 

 believing that the conditions there are not very different to those 

 on the west coast. 



*) [ ]. This form of brackets, with figures Inside, indicates the date of 

 literary publications. 



