112 



OBSERVATIONS AND RESULTS IN PHYSICAL OCEANOGRAPHY 



of the Carnegie are in close agreement with our general 

 considerations. On both sides of the equator we find 

 westerly currents reaching to considerable depths and 

 there separated by heavy water which is practically at 

 rest. Between the westerly currents the countercurrent 

 is embedded as a swift but shallow current. The heavy 

 water at rest reaches nearest the surface at the northern 

 and southern boundaries of the countercurrent. 



Intermediate Currents 



We have already discussed the origin of the interme- 

 diate water of low salinity in the Southern Hemisphere 

 and have shown that this water probably sinks at the Ant- 

 arctic convergence. When studying the sections we 

 found the axis of the intermediate current at a depth of 

 600 to 700 meters within the areas from which observa- 

 tions are available. These areas are so limited, how- 

 ever, that we cannot follow the flow of the iniar mediate 

 current and our dynamic charts give only some hints as 

 to the character of this current. From the dynamic 

 charts for the levels 500, 700, and 1000 meters it looks 

 as if the circulation of the intermediate current takes 

 place in a clockwise direction, contrary to the tropo- 

 spheric circulation which is counterclockwise. This 

 result needs confirmation, but what seems certain is 

 that the flow of the water takes place principally in an 

 east and west direction and that the north and south com- 

 ponent of the current is very weak in the central part of 

 the South Pacific. The flow of water, which at the 700- 

 meter level is directed away from the coast of South 

 America, perhaps transports back again part of the water 

 which is carried toward the coast by the currents of the 

 troposphere. The westerly current off the coast at a 

 depth of 700 meters should then be regarded as a com- 

 pensation current. 



In the Northern Hemisphere the circulation of the 

 intermediate water takes place in the same direction as 

 the circulation within the troposphere and is in both 

 cases clockwise. We have seen that the intermediate 

 water probably is formed in the eddies which develop off 

 the coast of Japan at the boundary between the warm cur- 

 rent from the southwest and the cold current from the 

 northeast. Water of a salinity between 33.09 and 34.00 

 per mille and of a temperature of about 5°, which is 

 formed in this region, is transported toward the east, 

 turns toward the south when approaching the American 

 coast, and returns toward the west in approximately 

 latitude 20° north. On this journey both the temperature 

 and the salinity of the water increase because of the 

 processes of mixing. The water, therefore, has a higher 

 temperature and a higher salinity when it bends toward 

 the north on the west side of the ocean after having com- 

 pleted one circuit, than it had when beginning the circuit. 

 When carried toward the north it is mixed with water of 

 lower temperature and lower salinity coming from the 

 north, and new water of the typical properties of the 

 intermediate layer is again formed. This new water 

 compensates for the loss which has taken place because 

 of the processes of mixing, and because a transport of 

 intermediate water toward the equator probably exists, 

 as was shown when dealing with the Equatorial Counter- 

 current. 



The intermediate current in the Northern Hemi- 

 sphere is, on the whole, a subsurface current, in con- 

 trast with the corresponding current in the Southern 

 Hemisphere which originates at the surface. The differ- 



ence in the oxygen content of the intermediate water 

 ports this conception (see p. 50). 



sup- 



Velocity of Currents between the Surface and 700 Meters 



Up to this point the discussion of the currents has 

 been based on the topography of the isobaric surfaces, 

 and the currents have been treated qualitatively only. 

 Current charts to 700 meters (figs. 34 to 38) show di- 

 rection and velocity of the currents, as computed from 

 the inclination of the isobaric surfaces, supposing that 

 the conditions are stationary, and that the motion is 

 frictionless and negligible at the 2000-decibar surface. 

 It must again be emphasized that the values in the fig- 

 ures are obtained by combining observations, which in 

 several regions were made at great intervals of time. 

 This combination may lead to apparent irregularities, 

 especially in regions where the currents undergo consid- 

 erable displacement. Also in the vicinity of the equator 

 the computed velocities are uncertain because of the to- 

 pography of the isobaric surfaces and because there the 

 friction may play a greater part than elsewhere. In spite 

 of these reservations, however, it is probable that the 

 charts show the approximate order of magnitude of the 

 currents which are maintained by the distribution of 

 density. 



In the Southern Hemisphere the easterly current of 

 the South Pacific shows velocities which, at the surface, 

 vary from 2 to 9 cm/sec, increase to a depth of 100 me- 

 ters where they reach 12 cm/sec, and decrease rapidly 

 below 100 meters. At 400 meters the eastward velocities 

 are only 3 cm/sec or less, and at 700 meters the direc- 

 tion is reversed, the water flowing toward the west with 

 a velocity of 1 to 2 cm/sec. The Peruvian Current ap- 

 pears to be a very weak current. At the surface the ve- 

 locities range from 2 to 5 cm/sec and decrease down- 

 ward to about 2 cm/sec at 700 meters. 



Within the westerly tropical current of the South Pa- 

 cific we find surface velocities up to 30 cm/sec, 14 nau- 

 tical miles in 24 hours. Still greater velocities are met 

 with at 100 meters, but below this level the velocities 

 decrease rapidly and at 700 meters no distinct motion 

 toward the west is perceptible. The irregular character 

 of the westerly tropical current of the Southern Hemi- 

 sphere is clearly evident from the figures. 



In the northern Hemisphere the westerly tropical 

 current shows the greatest velocities near the surface, 

 where they approach 30 cm/sec. The velocities de- 

 crease with increasing depth, and at the same time the 

 current is being displaced toward the north. At 700 

 meters the velocities are less than 2 cm/sec. 



At the surface, in longitude 140° west, the Equatori- 

 al Countercurrent has a velocity of about 50 cm/sec, or 

 nearly 24 nautical miles in 24 hours. This value is 

 again very probable. At greater depths the countercur- 

 rent disappears, and the crosscurrents, which are shown 

 at 700 meters, probably have no real significance. 



The warm current along the coast of Japan, the Kuro- 

 shio, is not represented in the figures, but the cold 

 Kurile Current (Oyashio) is seen at all levels. The ve- 

 locity of this current decreases from 17 cm/sec at the 

 surface to about 2 cm/sec at 700 meters. The changes 

 in the direction of the current with depth are perhaps 

 associated with the presence of whirls. 



The easterly current in the northern part of the 

 North Pacific can be traced at all levels. The velocities 

 decrease with increasing depth, from 2 to 9 cm/sec at 



