300 VOLKMANN [CHAP. 13 



and will provide us with new concepts of deep currents. These measurements 

 have not yet appeared in the literature and, indeed, have not yet been fully 

 analyzed. It has become fashionable in this, the day of rapid scientific advance- 

 ment, to assure the reader that our ideas are in a state of flux, and that is the 

 case with deep circulation in the oceans. 



The first measurements (Swallow, 1955) were made off Spain in June, 1955, 

 when two floats were followed successfully. A lunar semidiurnal tidal oscillation 

 was detected in the movement of the floats. It was at a depth of 600 + 200 m in 

 a water depth of 5330 m. 



In 1957, Swallow reports two more sets of measurements, one group again 

 off Spain, the other in the Faroe-Shetland Channel and Norwegian Sea. One 

 of the floats off Spain was very near the core of the Mediterranean outflow but 

 showed a northerly drift. The others in this area were quite variable, apparently 

 the result of the nearby bottom topography. In the Norwegian Sea an attempt 

 was made to correlate the measured drift with gradient currents computed 

 from a hydrographic section made at the same time. While the currents agreed 

 in direction, subsequent measurements made further north in the Norwegian 

 Sea were quite variable and the lack of agreement between the measured and 

 computed velocities in the channel was not surprising. 



Swallow and Hamon (1960) report another series of measurements off Spain, 

 this time over the flat abyssal plain. They found that the currents did not 

 decrease uniformly with depth although there was moderately good agreement 

 between pingers at different depths and geostrophic shear in at least one 

 instance. They also report considerable variability in the measurements with 

 one float of particular interest which was followed for 48 days. It both speeded 

 up and changed direction markedly during its trajectory. 



In the Pacific, Knauss has reported measurements with pingers in both the 

 Equatorial Countercurrent (Knauss and Pepin, 1959) and the Cromwell Current 

 (Knauss, 1960). In both cases, propeller-type current meters were used for the 

 near-surface measurements while pingers were used at the deeper depths. In 

 the case where the two measurements overlapped in depth the agreement was 

 good. 



On the basis of theoretical consideration of thermohaline circulations, H. 

 Stommel suggested that a southward-flowing deep current existed along the 

 western boundaries of the oceans. [These suggestions were reported later by 

 Stommel (1958) and stated more formally by Stommel and Arons (1960, 

 1960a).] In 1957 a joint cruise was undertaken by the National Institute of 

 Oceanography with Discovery II and by Woods Hole Oceanographic Institution 

 with Atlantis to an area off Charleston along the coast of the United States. 

 Swallow aboard the Discovery II made the measurements at places determined 

 from the deep temperature field as measured by Worthington aboard Atlantis 

 (Swallow and Worthington, 1961). The current at the deep depths was indeed 

 flowing south and, by using the measured velocities to adjust the reference 

 level, a net transport to the south was computed for the region below about 

 1500 m. As Swallow and Worthington point out, such a transport can greatly 



