DEEP CURRENTS: PACIFIC OCEAN 103 



east of New Zealand (see p. 104) shows that the eastward current from the region south 

 of Australia must be joined by warm water from another source — most probably from 

 a southward movement in the upper stratum of the layer, such as that which has been 

 described. The decrease of salinity and oxygen content, which the sections show to 

 accompany the increase in temperature towards the east, also suggests that the current 

 is modified by the addition of less saline and poorly oxygenated deep water from the 

 north. 



The southward movement in the upper stratum of the deep layer in the Antarctic 

 Zone may partly be the cause of the most saline water being confined to such a narrow 

 zone ; although the deeper part of the highly saline current sinks towards the north the 

 upper part appears to have a southward movement, and some of the highly saline water 

 which sinks towards the north is probably carried back with the southward current. 



The intermediate, deep and bottom currents are not separated by any well-marked 

 boundaries. Our observations, made entirely south of 40 S, showed no indication of a 

 temperature inversion such as that found by Wiist to the north of this latitude ; but the 

 relatively small temperature gradient between the 2-25 and 2-5° C. isotherms, with the 

 accompanying sharp salinity gradient, suggests that they mark the boundary region 

 between the intermediate and deep currents. The boundary between the deep and 

 bottom currents is especially vague, and there is probably extensive vertical mixing 

 between them. The oxygen distribution in section 15 (Plate XXXVI) suggests that a 

 large part of the current which flows southwards between 1500 and 2500 m. north of 

 50 S sinks between 50 and 55 S to mix with the bottom water ; this means that a large 

 part of the southward movement does not make the climb to the higher level of the 

 current in the Antarctic Zone but returns directly towards the north with the bottom 

 current. The depression of the isotherms and isohalines in 50-5 5 ° S points to the same 

 conclusion, but it may be caused partly by a difference in the zonal movements. 



Since the water in the southward movement between the intermediate and bottom 

 currents is formed in the Pacific Ocean, and, by analogy with the current systems in 

 the Atlantic and Indian Oceans, it seems that the southward current should be called 

 the Pacific deep current. It must, however, be remembered that the deep current is not 

 more saline than the bottom current, as in the Atlantic and Indian Oceans, but on the 

 contrary less saline. 



A most striking feature of the conditions along section 14 (Plates XXXI-XXXIII) 

 is the low salinity of the deep water between 60 and 65 S, where the data point to 

 the existence of a sharp cyclonic eddy caused by the passage of the eastward deep 

 current over the Cape Adare-Easter Islands ridge. Another point worthy of note is that 

 the observations made farther south suggest that south of 70 S, along the northern side 

 of the Ross Sea, the current flows towards the west ; together with the salinity and 

 temperature charts in Figs. 19, 22, the observations indicate that there is a small 

 cyclonic circulation of the deep water in this region resembling in a slight degree that 

 found in the Atlantic-Antarctic basin. 



The temperature distributions in sections 16-18 (Plates XXXVII-XLII) show that 



