ANTARCTIC BOTTOM WATER: MOVEMENTS 113 



in this section, but even this one section narrows the channel indicated by Wiist. The low 

 potential temperature of the bottom water at the Planet St. 59 (Brennecke, 1909) in 47 ° 

 32' S, 26 50' E may be an indication that the station was made in the Antarctic basin, 

 whilst the warmer water at St. 60 in 49 31' S, 29 16' E might belong to the Agulhas basin. 

 The bottom topography of the region is not well known; the difference between 

 the bottom waters at Sts. 849 and 850 in section 8 suggests that there is a well-defined 

 ridge, but the bottom temperatures at Planet Sts. 58-62 indicate that its shape must be 

 irregular. The existence of an S-shaped ridge such as is shown in Plate XLIV would explain 

 the bottom temperature distribution, and it may also explain the increase of bottom 

 temperature from north to south between Sts. 848 and 849, and the existence of cyclonic 

 eddies in the surface, subsurface and deep currents, such as have already been de- 

 scribed (p. 52). The northward movement of the bottom water has been shown by 

 Wiist (1933, p. 74) to be further restricted in passing into the Cape basin, south-west 

 of the Cape of Good Hope (Wiist, pi. viii), and then stopped altogether at the Walfisch 

 ridge. The bottom water found farther north in the eastern Atlantic basin is derived 

 from the western basin through the Romanche Channel, the deep passage through the 

 mid-Atlantic ridge in the neighbourhood of the equator. 



An examination of the sections across the Southern Ocean south of the Indian and 

 Pacific Oceans shows that the temperature (Plate XLIV) and salinity of the bottom 

 water increase continuously towards the east, while its oxygen content decreases, and 

 each of these changes indicates that the current from the Weddell Sea spreads eastwards 

 across both of these oceans without being renewed by any further additions of cold, 

 poorly saline, and highly oxygenated water sinking from the continental shelf. 



East of Enderby Land the coldest bottom water is found near the continental slope, 

 and the temperature chart suggests that there is no longer a movement towards the west 

 near the continent. The properties of the bottom water on either side of the Kerguelen- 

 Gaussberg ridge in section 9 (Plates XVI-XVIII) are such as show that the water is 

 largely derived from an eastward current from the Weddell Sea. The slightly higher 

 temperature and salinity and lower oxygen content of the water at the southern ends 

 of sections 10 and 11 south of Australia (Plates XIX-XXIV) are also evidence of the 

 existence of an eastward current modified by no other influence than that of mixing with 

 the warm deep water in the layer above. The eastward current appears, however, to 

 have some irregularities ; the bending of the isotherms towards the north on the eastern 

 side of the Kerguelen-Gaussberg ridge show that the northward movement is stronger 

 than it is on the west. This bending of the current towards the north is in agreement 

 with Ekman's conclusions (1928) as to the effect of the shallowing of the sea on a deep 

 current, and it must be emphasized that the bottom temperatures found east of the 

 ridge (section 9) are not so low as those found farther south to the west of it. The lower 

 bottom temperature and higher oxygen content at St. 890 in section 11, than at St. 885 

 in the same latitude in section 10, may also be weak indications of an irregularity in 

 the eastward movement. 



At the southern end of section 12 (Plates XXV-XXVII), south of New Zealand, the 



DXV 1 5 



