Thermohaline Features 163 



taking the depth of no motion at 5000 m. In this case the net 'observed' 

 transport is 123 x 10® m.^/sec. (Worthington, 19546). A consistent use of 

 the bottom as the depth of no motion has caused Worthington serious 

 trouble with the conservation of mass, and he has hoped to circumvent this 

 trouble by supposing that there are large-scale nongeostrophic flows in the 

 ocean, particularly between Bermuda and the West Indies. I cannot offer 

 any positive proof to refute Worthington's position on this question, but 

 it is my opinion^ that these difficulties may be mostly resolved in terms of 

 the thermohaline circulation, that the depth of no motion in the western 

 North Atlantic is, roughly, 1600 m. (in agreement with the estimate by 

 Defant, 1941), and that the actual net transport of the Gulf Stream System 

 is much more nearly equal to Munk's theoretical value of 35 x 10® m.^/sec. 

 than previous estimates neglecting the deep countercurrent underneath the 

 Gulf Stream have indicated. A crucial test of this explanation will be to 

 observe by direct means the direction of flow at various depths beneath the 

 Gulf Stream. A deep counterflow is a necessary, but not sufficient, feature 

 to validate this theory. I therefore emphasize the point that this hypothesis 

 of the thermohaline circulation can be struck a mortal blow should direct 

 observation disprove the existence of a deep countercurrent on the western 

 side of the North Atlantic Ocean. ^ 



In order to obtain a rough idea of what the transports in the actual Gulf 

 Stream might be, the following crude analysis is presented. 



^ I have tried to adhere, as much as possible, and perhaps rather slavishly, to the 

 notion that the flow in the deep water is steady and geostrophic, and that the 

 observed data which we have are not much distorted by purely local effects or short- 

 period fluctuations. Recently other students of the subject have begun to doubt 

 both of these assmnptions, but the degree to which they are true is not yet known. 

 Even granting these assumptions, there are other possible interpretations of the data 

 which are quite different from the one I describe here. The conception of the current 

 systems presented here is not a unique solution, nor, indeed, are the schemes proposed 

 by other writers. I think the multiplicity of possible interpretations needs emphasis 

 in order to serve as a warning to the reader. The reason I have used such simple 

 assumptions is that otherwise there are so many degrees of freedom that almost any 

 interpretation becomes possible. 



* As the manuscript for this book was completed in mid- 1955, it has not been 

 possible to include more recent developments in the text; however, in March and 

 early April of 1957 a preliminary set of direct measurements of currents under the 

 Gulf Stream (using Swallow's new neutrally buoyant floats) has been made by J. C. 

 Swallow and L. V. Worthington and reported in a letter to Nature magazine 179 

 (June 8, 1957) : 1183-1184, and since these measvu-ements have an important bearing 

 upon the opinions expressed in the text, I insert an extract from the letter as a footnote 

 added in proof: 



' In choosing the most suitable part of the Gulf Stream system in which to work, 

 various factors were considered. The surface velocities in the Stream off the American 

 continent usually exceed 200 cm./sec, and it was felt that such strong currents would 



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