of a foreign substance has been demonstrated by the unpub- 

 lished work of E. C. LaFond and of D. E. Root, both of whom 

 have shown that the surface tension of water collected from 

 slicks is less than that of other sea water. Also, surface 

 bubbles produced on slicks tend to persist while those in 

 other water disappear rapidly. 



Artificial slicks produced by ship's oil and other refuse 

 are present in harbors (fig. 38C), where they frequently 

 constitute a fire hazard. They have often been artificially 

 produced on the high seas by ships in distress to damp the 

 roughness of storm waves to keep them from breaking. 

 Artificial slicks can be readily produced by almost any 

 fluid which is nonmiscible and lighter than water. Fluids 

 of low surface tension are especially good slick producers 

 because of their rapid spreading ability. 44 Newly formed 

 artificial slicks commonly display high-order interference 

 colors whereas natural slicks display no color other than 

 possibly a first-order gray, but this difference is obviously 

 related to the relatively large thickness of the newly formed 

 film of an artificial slick. In general, a similar type of 

 origin for natural slicks and for artificial slicks is suggested 

 by their similar appearance. Petroleum released from oil 

 seeps on the sea floor may be responsible for some local 

 slicks, but diatom oil must largely account for the widespread 

 development of slicks in coastal and insular waters. 



DEEP SCATTERING LAYER IN THE PACIFIC AND 

 ANTARCTIC OCEANS* 



Introduction . During Operation HIGHJUMP (U.S. Navy 

 Antarctic Development Project, 1947), the writer frequently 

 noted the presence of a layer of deep scatterers on the fatho- 

 gram of the USS HENDERSON. This layer partially scatters 

 the outgoing sound signal of the recording echo sounder 

 during daylight hours so that a reflection is recorded which 

 shows a false bottom at various depths between 150 and 

 450 fathoms. 



*The writer is indebted to C. Eckart and R. W. Raitt of the 

 University of California Marine Physical Laboratory, to 

 M. W. Johnson of the Scripps Institution of Oceanography, 

 and to R. J. Christensen, E. C. LaFond, and D. W. Pritchard of 

 the U. S. Navy Electronics Laboratory for critically reading 

 this manuscript. The fathograms from which the data are 

 taken were obtained by the personnel of the USS HENDERSON 

 and the USS NEREUS. In connection with obtaining the fatho- 

 grams, the assistance of Captain C. F. Bailey of the USS 

 HENDERSON and of E. C. LaFond, who supervised the ob- 

 taining of the arctic fathograms of the USS NEREUS, is 

 especially appreciated. ____^_ 



