I. INTRODUCTION. 



1. The North Atlantic Ocean. 



The North Atlantic proper is that part of the Atlantic 

 Ocean which extends from the Equator northwards to the 

 submarine ridge (with islands) between Greenland and Scot- 

 land. The Norwegian Sea to the north of this ridge has often 

 been classed as a part of the North Atlantic, but it is now 

 generally admitted that the Norwegian Sea topographically 

 and oceanographically forms a so well defined area that it 

 must be kept distinct from the Atlantic much in the same 

 manner as the North Sea or Baffin's Bay generally are. 

 This distinction will always be maintained in the present 

 paper. 



The essential topographic features of the North Atlantic 

 are well known : the central ridge extending as a comparatively 

 narrow, continuous bar from Iceland to the Equator, and 

 thus clearly dividing the ocean into an eastern and a 

 western part: — a series of deeps on both sides of the 

 ridge; — a very irregular bottom configuration in many 

 places, especially conspicuous in the northern part of the 

 ocean between western and southern Europe and the 

 Newfoundland Banks, the area where most soundings 

 have been made. The details will be seen from the 

 chart on p. 63*; it is based upon the thorough mapping 

 by Dr. Groll. Even the details are of great importance 

 for studying the currents, as will be shown later on. 



The basin of the North Atlantic Ocean contains very 

 different kinds of water. The greater part of the water- 

 masses consists of the so-called bottom-water or deep 

 water, filling nearly all the basin below some 2000 metres. 

 The average depth of the North Atlantic is almost 4000 

 metres. In the upper strata there are great variations 

 from equatorial (or tropical) waters in the south to polar 

 (or arctic) waters in the north, and at intermediate depths 

 the characteristic water from the Mediterranean is traced 

 over great areas in the eastern part of the ocean. The 

 different waters mi,\ and thus form what may be called 

 "Atlantic water". It is subject to variations through 

 different agencies acting upon the sea-surface but may on 

 the whole be characterized by the correlation between 

 temperature and salinity (section 18). 



The general circulation in the North Atlantic Ocean 



— though well known — must, for the sake of clearness, 

 be shortly mentioned here: The North Equatorial Current 

 is joined by a considerable part of the South Equatorial 

 Current N. of Brazil. The water passes partly N. of the 

 Antilles and partly through the Caribbean Sea a-id the 

 Gulf of Mexico. The excess water from the Gulf passes 

 the Strait of Florida and joins the Antille Current, 

 the whole mass of water flowing (under the name 

 of "The Gulf Stream") along the American coast as 

 far as the southern slope of the Newfoundland Bank. 

 Then it crosses the ocean towards Europe. Part of it 

 branches off towards the north, flowing either towards 

 Iceland or through the Faeroe-Shetland Channel into the 

 Norwegian Sea. The other part of the "Gulf Stream" 

 flows southwards, contributing to the formation of the 

 Canarian Current, which continues into the North Equatorial 

 Current. A great anticyclonic circulation is thus established 

 in the Southern and central part of the North Atlantic. — 

 Polar water flows southwards along the east coast of 

 Greenland, makes at Cape Farewell a turn northwards 

 and — after mixing with polar water from Baffin's Bay 



— ultimately runs southwards along the coasts of Labrador 

 and Newfoundland as "The Labrador Current". The waters 

 of this surface-current disappear by mixing with the "Gulf 

 Stream", but traces of them may be recognized pretty 

 far to the south along the coast of U.S.A. 



2. The Cruise of the "Michael Sars" and the 

 Geophysical Work on Board, 



The chief aim of the "Michael Sars" Expedition was 

 to make a general biological survey of the North Atlantic 

 Ocean by means of modern methods and based upon 

 the experience gained by the Norwegian Fisheries' Research. 

 The geophysical investigations could only form a minor 

 part of the programme, and had to take the second 

 place. As much time as the other work permitted was, 

 however, devoted to them. 



When plainiing the work it was decided that the 

 geophysical investigations should embrace a survey of the 



