164 Thermohaline Features 



A HYPOTHETICAL ANALYSIS OF THE GEOSTROPHIC 

 TRANSPORTS IN THE ATLANTIC OCEAN 



Let us define a function T{z, d), the transport per unit depth across a hydro- 

 graphic section, as a function of depth, z, and of the reference level (level of 

 no motion), z = d. If S{z) is the ratio of the width of the section at depth z 

 to that at the surface, taken as completely determined by bath;yTnetry, then 

 the transport per unit depth, T{z, d), can be expressed in terms of the same 

 function referred to the bottom z = & as the level of no motion in the following 

 manner: rp,j j^s. 



T{z,d) = T{z,h)-^^S{z). (24) 



The total vertically integrated transport across the section, ^{d), is a 

 function of reference level only: 



^{d)= I T{z,d)dz. (25) 



make it difficult to keep track of the deep floats. At Stommel's suggestion, an area 

 off Cape Remain, South Carolina, was chosen. Here the shallow (less than 800 m.) 

 Florida Current flows over the Blake Plateau, while strong pressure gradients are 

 found in the deep water farther offshore. Farther north, towards Cape Hatteras, the 

 violent shallow gradients are superimposed on the deep ones. To the south the deep 

 gradients dwindle away in a maimer not yet understood. On these counts it was 

 decided to place the floats as close as was practicable to the junction of the surface 

 Stream with the deep water. 



'The bulk of the work was carried out in about lat. 33° N., and between long. 

 75° 30' W. and 76° W. Excellent Loran coverage exists in this area. Two ships took 

 part in this work, which was a joint venture of the National Institute of Oceanography 

 and the Woods Hole Oceanographic Institution. The current measurements were made 

 by the R.R.S. DISCOVERY II, whfle the R.V. ATLANTIS occupied hydrographic 

 stations, in which serial observations of temperature and salinity were made in order 

 to provide a nearly synoptic picture of the deep pressure conditions. 



'Nine floats were followed, of which seven were in deep south-going water. The 

 measurements lasted for periods of 1—4 days, with some overlaps when more than one 

 float was being followed. Three floats at 2,500 metres moved in directions between 

 south and south-west with mean velocities between 2-6 and 9*5 cin./sec, and four 

 floats at 2,800 metres depth moved almost due south with velocities of 9*7-17'4 cm./ 

 sec. Additional evidence for a south-going deep current was obtained by A. S. 

 Laughton, who took underwater photographs of the deflexion of a ball suspended on 

 a string, only 50 cm. above the sea floor, in a depth of 3,200 metres. A southward 

 movement of about 5 cm. /sec. was found at that depth. 



'The ATLANTIS hydrographic stations were made at right angles to the drift of 

 each float. The spacing of the stations, eighty-eight in number, did not exceed ten 

 miles in the vicinity of the floats. In one case a rectangular pattern of eight stations 

 not more than three miles apart was laid. There are some irregularities in the slopes 

 of the deep isobars ; but the average conditions suggest that the level of no motion in 

 this area most probably lies between 1,500 and 2,000 metres, if the southerly move- 

 ment of the deep water is to be accounted for by the geostrophic equation.' 



