SECT. 3] DEEP-CUKRENT MEASUREMENTS 301 



change the total volume transport of the Gulf Stream by moving the reference 

 level to mid-depths. Another important discovery during this cruise was that 

 the velocity can increase with depth in the deep water and that water as deep 

 as 2800 m could be moving at a velocity as high as 18 cm /sec. 



Subsequent measurements made by Volkmann (in press) in the summer of 

 1959 in the area south of Woods Hole but north of the Gulf Stream showed a 

 similar current (moving westward here) although it was much more widespread. 

 In fact all the water below 1500 m across the 200 km section was moving in the 

 same direction at 10 to 20 cm/sec and the transport was much larger than the 

 transport reported by Swallow and Worthington off Charleston. 



The following year separate measurements made by Barrett (in litt.) and by 

 the author showed that all the deep water offshore was moving in the opposite 

 direction, toward the east at velocities comparable to the westward velocities 

 of the previous year. These opposing water motions occurred in the same 

 area in the same water-mass and in the presence of similar slopes of the iso- 

 therms. 



A long series of pinger measurements in the vicinity of Bermuda has just 

 been completed by J. C. Swallow (in litt.). These also show an extreme variability 

 of current speed and direction on a time scale of as little as two weeks and over 

 a separation of as little as 20 km. While analysis is far from complete, it seems 

 probable that a statistical analysis will show the significant features of the 

 deep-water offshore circulation. The measured velocities were seldom less than 

 3 cm/sec and ranged up to 16-18 cm/sec and occasionally even higher. 1 



It would appear from these measurements that the deep circulation consists 

 of a wide spectrum of motions containing some components with velocities at 

 least an order of magnitude higher than the mean velocities. The significance 

 of a single measurement in relation to the general circulation is now difficult 

 to assess, although shorter series can be useful in specific problems and can. 

 as they have in the Atlantic, serve as pilot studies. For the more general 

 studies of oceanic circulation, it would seem that long-term continuous 

 measurements are required. 



References 



Knauss, J. A., 1960. Measurements of the Cromwell Current. Deep-Sea Res., 6, 265-286. 



Knauss, J. A. and R. O. Pepin, 1959. Measurements of the Pacific Equatorial Counter- 

 current. Nature, 183, 380. 



Stommel, H., 1958. The abyssal circulation. Deep-Sea Res., 5, 80-82. 



Stommel, H. and A. B. Arons, 1960. On the abyssal circulation of the world ocean — I. 

 Stationary planetary flow patterns on a sphere. Deep-Sea Res., 6, 140-154. 



Stommel, H. and A. B. Arons, 1960a. On the abyssal circulation of the world ocean — -II. 

 An idealized model of the circulation pattern and amplitude in oceanic basins. 

 Deep-Sea Res., 6, 217-233. 



Swallow, J. C, 1955. A neutral -buoyancy float for measuring deep currents. Deep-Sea 

 Res., 3, 74-81. 



1 One 4000-m pinger travelled 60 km in 40 hours- — a velocity of 42 cm/sec. 



