i68 DISCOVERY REPORTS 



of the vertical component will then be only 0-0027 cm./sec, and a water particle needs 

 80 days in order to cover a vertical distance of 200 m. The total time used for a complete 

 circuit in the region to the east of Drake Passage is, therefore, at least one year. 



The transversal circulation is no doubt more rapid within the Drake Passage and the 

 Scotia Sea than in any other region because the Antarctic water is there pressed to- 

 gether. Comparisons of the sections in the Drake Passage with those in the Pacific and 

 the Atlantic show this clearly. This feature is perhaps of considerable importance to 

 several of the biological problems of the South Atlantic. It is possible that the surface 

 water to the east of South Georgia left the surface in the Drake Passage or the Scotia 

 Sea in the preceding year, while water masses which are drawn to the surface in the 

 Pacific Antarctic Ocean have spent years at intermediate depths after they left the sur- 

 face. This difference in the history of the water masses may in part explain the difference 

 in the development of plant and animal life in the two regions. 



Until now we have disregarded the circulation which, within wide areas, takes place 

 to the south of the Antarctic current, along the Antarctic Continent. Near the Continent 

 the wind direction is easterly, and in agreement with this direction we find currents to- 

 wards the west in high southerly latitudes. Several whirls of stationary character appear 

 to exist, and these are present partly because of the prevailing winds and partly because 

 of the bathymetric features. 



Within the westerly currents along the Continent we must also find a vertical circula- 

 tion which is similar to the vertical circulation within the Antarctic easterly current. 

 The surface layers are transported to the south by the pure drift current which is upheld 

 bv the prevailing easterly winds, and as compensation the water must flow north at some 

 lower depth. We know that the bottom water flows towards the north, and within the 

 Weddell Sea the water at a depth of about 500 m. also appears to have a component to 

 the north. The latter current represents, however, not a direct return of surface water 

 because it has a higher temperature than any other water mass in high latitudes. It must 

 have been drawn south at an intermediate depth within some of the whirls. 



In this connection it is of interest to draw attention to the following feature : The light 

 water which is carried by the wind towards the shelf of the Antarctic Continent is 

 effectively cooled on the shelf. The tendency of the wind is to accumulate light water 

 along the coast and thus build up a stronger and stronger solenoid field, but this 

 tendency is effectively counteracted by the cooling of the water. Here we thus have an 

 example showing how factors which influence the density of the water prevent the de- 

 velopment of a strong solenoid field under the action of the wind. 



In the preceding part of this paper it has been attempted to give a picture of the 

 vertical circulations within the Antarctic circumpolar current, starting out from general 

 considerations as to the eftect of the wind. The observations of the Discovery Expedi- 

 tions indicate that circulations of the supposed character are present, but many questions 

 still remain open and in conclusion some of these will be pointed out. The existence of the 

 Antarctic Convergence and the character of the movement of the water near the con- 

 vergence must be explained. In connection with the latter question one difficulty will 



