FOREWORD 



Owing to various circumstances not altogether within my own 

 control, the completion of this paper has been delayed to an extent 

 which I greatly regret, particularly as this has inconvenienced the 

 authors of other parts of the scientific report on the "Michael Sars" 

 Expedition. 



Shortly after the termination of the cruise preliminary reports were 

 published on its results, including the researches in physical oceano- 

 graphy. Subsequently communications on certain special geophysical 

 problems were issued from time to time, either in publications or in 

 the form of lectures. A good deal that is contained in this paper may 

 therefore be already known to the reader. In the interval that has elaps- 

 ed, however, new investigations have furnished us with observations 

 which supplement the "Michael Sars" material, and other progress has 

 been made which has been of value for the final working-up of the 

 results. I have endeavoured to present the subject in a form adapted 

 for biologists as well as geophysicists. 



I desire to express my cordial thanks to my friends and colleagues 

 Dr. V. Walfrid Ekman and Dr. H. U. Svkrdrup for the help they have 

 rendered me by subjecting parts of the manuscript to critical revision; 

 and also to my assistants for their unremitting and faithful aid. 



Bjorn Helland-Hansen. 



