2 78 POLAR PROBLEMS 



the bottom water. We may assume that the tropical water at the edge 

 of the continental shelf is cooled through its contact with the polar 

 water — occasionally also through climatic influences — and that there- 

 fore it becomes heavier and sinks to the bottom. Its flowing over the 

 bottom of the oceans is then due to its specific gravity. We may 

 therefore characterize the influence of the Antarctic on the oceans, 

 first, as bringing about the distribution of pure polar water on the 

 surface and later at a depth of looo meters, and, second, as creating 

 the bottom water through the cooling of the tropical water at the edge 

 of the shelf. The warm zones, however, are of greater influence, for 

 they call forth the vast mass of tropical water and drive it as the 

 intermediate layer up to the shelf edge, whence, cooled, it returns along 

 the bottom to the tropics. 



Methods of Investigation to Determine Different 

 Kinds of Water 



These currents may be ascertained directly by current measure- 

 ments in different depths and indirectly by the observation of the phys- 

 ical and biological properties of the different kinds of water and their 

 distribution. Temperature and salinity measurements are the most 

 important. These show that as a rule salinity is the property most 

 generally constant in the different kinds of water, whereas tempera- 

 tures become equalized more readily. Salinity is therefore more 

 important to help trace spatial distribution. Of importance, further- 

 more, are observations on the gas content of the water, especially 

 in oxygen, nitrogen, and carbon dioxide; as, for example, the amount 

 of nitrate plus nitrite nitrogen remains quite constant in spite of the 

 wide distribution of the polar water. Related to the gas content is the 

 bacterial and plankton life ; biological observations thus should supple- 

 ment the physical observations. Not infrequently plankton studies 

 may yield evidence as to the origin of a given type of water, if it cannot 

 be determined by its salinity and temperature.^^ Thus the summer 

 development of plankton in the Gaussberg region showed that the 

 warmth of the tropical water penetrated into the shelf sea in February, 

 although this fact could not be established thermically. It would 

 lead too far, however, to discuss here more fully the methods of 

 investigation. 



Other Problems 



The preceding discussion in no way exhausts the oceanographical 

 problems of the Antarctic, although most of them are connected with 

 the phenomenon of currents, so that the study of currents leads in- 

 directly also to an understanding of other phenomena. Nevertheless 

 a number of other problems may here be touched upon. 



^ Lohmann, oi>. cit., p. 422. 



