270 POLAR PROBLEMS 



this equilibrium. Thus arise waves and currents; they strive to 

 reestabhsh this balance, without, however, ever attaining that result. 

 In addition the ocean is affected by the gravitational power of moon 

 and sun, not only on its surface but down to its depths, and thus is 

 involved in a rhythmical to-and-fro movement which we must always 

 bear in mind, although quantitatively it is inferior to the movements 

 induced by warmth and coastal form. At all events the heat of the 

 sun is the main agency by which the movements of the ocean are 

 influenced; and the effect of this agency of course differs most at the 

 two extreme regions, the equator and the poles, so that the strongest 

 equalizing tendency of the oceans occurs between these two regions. 

 As the Arctic, however, is surrounded by connected land masses 

 through which narrow passages exist in Bering Strait and west of 

 Greenland, and somewhat wider ones on both sides of Spitsbergen^ 

 which, however, are again barricaded farther south by the Faroe- 

 Iceland submarine ridge — it is comprehensible that the high north 

 can exert only a slight influence on the oceans and that the aforemen- 

 tioned equalizing tendency is developed most between the Antarctic 

 and the tropics. 



The interchange of water which results from this takes place partly 

 on the surface, partly in the depths. In the warm latitudes the surface 

 water is much warmed from above, and at the edge of the Antarctic 

 Continent it is cooled off; in the former region its temperature rises 

 to 27° C. and more, whereas in the latter it drops to — i .8° and — i .9°, 

 so that there is a temperature difference between the two areas of 

 almost 30°. In the tropics these influences do not go far down, as, 

 for example, can be seen from the rapid downward decrease of the 

 water temperatures there. The effective range of these influences, 

 according to the fundamental plankton researches of H. LohmannS 

 seems to extend to depths of 300 or 400 meters. The cooling influences 

 of the Antarctic Continent are of a somewhat different nature, as 

 they emanate partly from the wall-like termination of the inland ice 

 toward the sea, partly from the surface. Both are jointly effective, 

 but their combined effect is much less powerful than are the warming 

 influences in the tropical zone, inasmuch as these relate to an area 

 ten times as large, if the area of the two regions be estimated accord- 

 ing to Hermann Wagner's values for the distribution of land and water 

 in the different zones.^ The effective lower limit of the cooling in- 

 fluences of the Antarctic may, like that of the warming influences in 

 the tropics, be taken to lie at 300 or 400 meters, as was determined 

 on the Gauss expedition to be the case in the shallow shelf sea off the 



1 H. Lohmann: Die Bevolkerung des Ozeans mit Plankton, nach den Ergebnissen der Zentrifu- 

 genfange wahrend der Ausreise der " Deutschland " 1911, Archiv fiir Biontologie, herausg. von der Gesell. 

 Naticrf. Freimde zu Berlin, Vol. 4, No. 3. Berlin, 1920, especially pp. 255-285 and PI. 13. 



2 Hermann Wagner: Lehrbuch der Geographie (loth edit., Hanover, 1922), Vol. I, Part II, 

 p. 269. 



