OCEANOGRAPHIC INVESTIGATIONS 361 



cause near-bottom particle movement of the amplitude needed for adequate accuracy. At the 

 depth of Sealab II, wave-induced bottom motion was observed only for waves with periods longer 

 than 10 sec. On the several days that wave- induced motion was observable at all at Sealab, 

 measurements showed that the period was 11 to 13 sec, and horizontal amplitude of particle 

 motion never exceeded 5 cm (2 in.). It is concluded that in general this type of experiment 

 will be successful only in shallower water, and hence does not lend itself to future Sealab efforts. 



MEDIUM SCALE TURBULENT DIFFUSION OF BOTTOM TRAILERS 



It was planned to track quantitatively several types of bottom drifting objects undergoing 

 turbulent diffusion in the range of turbulence scale sizes 1 to 100 ft. Such data from the sea 

 floor are potentially useful in developing theories to understand and predict the spread of 

 almost neutrally buoyant objects from marine disasters. The technique for performing this 

 experiment was to have been as follows. After releasing five to ten nearly neutrally buoyant 

 objects at a preselected spot, special small marker buoys would be dropped periodically near 

 each one (as it disperses) to mark its position at known times. Thus, after these objects have 

 dispersed approximately 100 ft from their origin, their paths have been essentially recorded on 

 the bottom. Then, by use of the compass roses and surveyor's tapes (previously described in 

 "Underwater Surveying and Mapping"), the location of each marker would be determined and 

 a map made which is essentially a Lagrangian plot of each object's movement. These data 

 may then be applied to theories of turbulent diffusion. It is obvious from the above discussion, 

 that a large amount of diving time (namely, three to five hours) would be required for each 

 trial of this experiment; prior to entering Sealab it was hoped that such times would be avail- 

 able. As has been pointed out already, of course, such diving times were not available; hence 

 this study was not successfully completed. However, this experiment was carried out in a 

 qualitative manner by releasing standard plastic Woods Hole Oceanographic Institute bottom 

 trailers on a daily basis and observing their general behavior pattern. These bottom trailers 

 are numbered, addressed, and have a reward statement affixed so that if one is found by a 

 trawler, diver, fisherman, or beach comber, its location will be forwarded to Woods Hole, 

 thus providing information about bottom currents. Their design is such that a current of a 

 few hundredths of a knot will move them. In all, about 200 of these bottom trailers were re- 

 leased. 



Observation of these bottom trailers indicates that their diffusion rate was typically very 

 slow; on several occasions those released on a previous day were observed a day later within 

 10 ft of the release point. On Sept. 22 trailers were found in the release area which had been 

 released 1,2, and 6 days earlier. This slow rate of diffusion was another reason that the 

 quantitative aspects of this experiment were not successful. 



The main sources of movement for the bottom trailers were the quasisteady bottom cur- 

 rents (associated with tides or seiches) which, although weak, were sufficient to transport 

 them. Thus, if movement due to such currents is neglected, it appears that an approximate 

 upper limit on the diffusion transport rate by medium- scale turbulence is of the order of a few 

 tens of feet per day. It is expected that current-meter records will yield data about current 

 fluctuations which can be analyzed from the point of view of the turbulent components of the 

 current, and hopefully, correlated with bottom-trailer observations. 



FISH-BEHAVIOR STUDIES 



Sealab offered the opportunity of making long-term, detailed studies of the behavior, and/ 

 or reactions of various marine organisms to manmade objects placed in their natural environ- 

 ment. To take advantage of this opportunity, the writers had planned a number of observational 

 studies. As it turned out, it was not possible to complete any of these investigations, success- 

 fully, all of which had a fairly low priority in terms of the overall planned program and naval 

 applications. Data provided by these studies, however, do have direct application in fisheries 

 research and in the utilization of the products of the sea, and these studies should be considered 

 for future Sealab efforts. The primary reason for not attempting these research tasks as 

 planned was that the available bottom time was far less tha,. had been expected; other reasons 

 are described below, along with a description of the proposed effort and the expected results. 



