3.6 Straits of Sicily 



The Straits of Sicily site, 36°-38°N, 1 r-13°E, is located on the chart (Refer- 

 ence 12) in Figure 3.1 1. The straits separate Sicily from Africa and divide the Mediterranean 

 Sea into two basins. The bathymetry is complicated in the central part but simple on the 

 continental shelves along the Sicilian and African coasts. The sea floor of the shelf area is 

 very flat except for a few very shallow banks. In the middle of the straits there is a region 

 of depths greater than 900 m. In the complicated zone between, the depths very between 

 200 and 900 m. 



The data sample from this area contains sound speed profiles to 700 m in depth with 

 about one-third of the sample profiles deeper than 200 m. The representative winter and 

 summer profiles are shown in Figure 3.12. Two bottom depths are considered in our model, 

 165 m and 500 m. The characteristic deep profiles (500 m) were found to be extensions of 

 the shallower sound speed profiles (150-200 m). 



Table 3.11 gives a summary of the sound speed profiles. Although the samphng for 

 fall and winter is not robust, the 98 percent positive gradient profiles found are most likely 

 a true value. The percentage found in spring and summer (10.3) is the average of the two 

 seasons. 



The geoacoustic models of the sediments in the Straits of Sicily were taken from 

 Reference 13 and are given in Tables 3.12 and 3.13. The model in Table 3.12 is applicable 

 to water depths shoal of 300 m while the second model (Table 3.13) is apphcable in the 

 deeper waters of the straits. Both have an acoustic basement of hmestone and chalk 

 although at different depths. The compressional wave attenuation is an order of magnitude 

 greater in the shallow model while the densities differ only slightly. 







Positive 



Positive 



Season 



Total 



Gradient, # 



Gradient, % 



FaU 



21 



20 



95.2 



Winter 



28 



28 



100.0 



Totals 



49 



48 



98.0 



Spring 



71 



4 



5.6 



Summer 



40 



6 



15.0 



Totals 



111 



10 



(10.3) 



Table 3.11. Straits of Sicily sound speed profiles. 



12. 



13. 



Oceanography of the Straits of Sicily, Thomas D. Allen, Tuncay Akal and Robert Molcard, Pro- 

 ceedings of a conference held at SACLANTCEN on 1 1-12 April 1972, SACLANT ASW Research 

 Centre, 15 September 1972. 



Geoacoustic Models for the Straits of Sicily and Sardinia-Tunisia, J. E. Matthews, Ocean Science 

 and Technology Laboratory, Naval Ocean Research and Development Activity (unpublished 

 manuscript). 



33 



