2 34 



0. Nordgaard. 



can only in a slight degree be caused by the variations in down- 

 fall from one month to another. The principal cause must be 

 looked for in another direction, and one naturally turns one's atten- 

 tion to the distribution of atmospheric pressure, which, as is well 

 known, determines the motions in the air — atmospheric currents — . 



Dr. Andreas Hansen 1 ) has called attention to the fact that 

 the maximum atmospheric pressure in the spring and the minimum 

 height of the water, and the minimum midwinter barometric altitude 

 and the greatest height of the water are, practically speaking, 

 correspondent. 



Prof. Mohn 2 ) in his meteorology, has given the atmospheric 

 pressure curves at Stykkisholm, in Iceland, and Gjesvser, near the 

 North Cape, and with respect to the course of these curves, he 

 says that, on both sides of the Norwegian Sea, the atmospheric 

 pressure is lowest in the winter and highest in May. 



The lowest atmospheric pressure from January — May, we 

 should expect to find somewhere in the Norwegian Sea, and this 

 is seen to be the case from Mohn's chart (1. c. p. 173) where a 

 minimum is given at the NE of Iceland. This minimum is main- 

 tained, according to Prof. 0. Pettersson, 3 ) by the upper layers 

 of water in the Norwegian Sea giving off heat to the atmosphere. 

 At any rate, it appears to be certain that the distribution of 

 the atmospheric pressure on land and sea during the winter causes 

 such winds as help to sweep the water away from the coasts. 



It is probable that the most important causes of the annual 

 fluctuations in the height of the water on the northern coasts may 

 be found in the different distribution of atmospheric pressure in 

 summer and winter and the winds which are dependent upon this. 



On pi. 21, I have given the down-fall curves for 1899 with 

 crossed lines for the stations at Svolvser, Skomvaer, Tromso and 

 Alten, and have based them upon „Nedb0riagttagelser" (Ob- 

 servations on Downfall) published by the Norwegian Meteorolo- 

 gical Institute. Similarly, the normal curves for the same stations 

 are given in straight lines for a period of observation from 13 to 

 29 years. 



From these curves, it will be seen that, in a single year, there 

 may be great divergence from the normal downfall. 



It is evident that the fluctuations in the amount of downfall 

 exert an influence on the temperature and salinity of the sea. By 

 increasing the height of the water in the fiords, the downfall also 

 has some influence in producing currents. In the chapter dealing 

 with the cod fishery in Lofoten, I will try to prove that there is 

 a correspondence between the fishery results and the variations in 

 the distribution of atmospheric pressure, and will, in so doing, use 

 the height of the downfall as a measure of the influence of the 

 winds. 



c. Biological Notes. 



The problem of the vertical distribution of living beings has 

 occupied many biologists. I will not here treat of it at length, but 

 only mention a few facts. 



As far back as 1835, Michael Saks 4 ) divided our seaweed 

 belt into the following 4 zones: (1) That of the Balanus, 



(2) that of the Patella, (3) of the corals, and (4) that of the La- 

 minaria. The greater depths bad at that time been so little ex- 

 amined, that Sars could not attempt any division of the life found 

 there. Since 1835, however, this subject has occupied the atten- 

 tion of many, and several divisions have been made. But I will 

 only give here the one I prefer. Dr. Stuxberg has, in his book 

 „Evertebratfaunan i Sibiriens Ishaf", accepted the same division 

 for the animals as F. R. Kjellman 5 ) for algae, viz: - 



(1) The littoral tone. 

 That part of the bottom, which is laid bare at low water, 

 and which in Norwegian is called „fjaeren". 



(2) The sublittoral zone. 

 From low water mark to the lower limit for algae. 



(3) The elittoral .com: 

 All that is below the lower limit for algae. 



J ) Skandinaviens Stigning. N<>ru>'< Geol. Unders. Aarb. f. 189(i— 99. 



-I Kristiania 1902. 



3 ) Die hydrographischen Veiliiiltiiisse der oberen Wasserschiciiten des nord- 

 lichen Nordmeeres. Bihang t. K. Svenska Vet. Akad. Handlingar B. 23, afd. II, 

 in-. I 



*) Beskrivelser og Iagttagelser, p. VI. 



5 ) Suxberg refers to Kjellman's treatise: — Ueber die Algenvegetation 

 des Murmanschen Meeres an der Westkiiste von Novaja Senilja und Waigatsch. 

 Nova Acta Reg. Soc. Scient. dps., Sir. Ill, vol. extra ordineni editum. Upsala 

 1877. 



According to P. Boye, 1 ) the dividing line between the sublitto- 

 ral and elittoral zones is fixed by Kjellman at a depth of about 

 4(i in. in Bohuslen, and this figure seems to suit the conditions on 

 the southwest coast of Norway too. „0n the coasts of Nordland 

 and Finmark", says M. Foslie in a letter to me, „algae may ge- 

 nerally be found down to 40— 50 m., but vegetation mostly occurs 

 to a depth of only about 30 m." 



With regard to the vertical distribution of animals, Stuxberg 

 fixes the limit between the sublittoral and elittoral zones in the 

 Siberian polar waters at 30 — 40 fathoms, but I think it is best 

 to keep to the algologists' limit, for a large number of animals is 

 found in the seaweed zone. As far as I know, Norwegian alg- 

 ologists have accepted Kjellman's division, and I would suggest 

 that zoologists also should test its practicability for animals too. 

 If it be necessary to have a finer division, Michael Sars's zones 

 should be given a new trial. 



As algae vegetation only reaches down to a certain depth, the 

 quantity will to some extent depend upon the inclination of the bot- 

 tom. On a rock which forms an angle of 30° with the horizon, 

 there will, other things being equal, be much more algae than if 

 the rock were perpendicular. The space between the shore line 

 and the lower algae limit, which may be called the growing area 

 for algae, has a definite proportion to the angle of inclination. Here 

 again the same remarks as on page 230 are applicable, and the 

 same mathematical explanation stands good. It will be found that 

 the growing areas are in inverse proportion to the sinus of the 

 angles of inclination. 





') Bidrag til Kundskaben urn Algevegetationen ved Norges Vestkyst, p. 3. 

 Berg. AIns. Aarb. 1894—95. No. XVI. 



