E, Deep Scattering Layer 



The Deep Scattering Layer (DSL) causes a premature and partial 

 reflection of the intermittent sound signals emitted by an echo-so-under. 

 This results in a trace at shallower depths on the echograms in addition 

 to the normal bottom trace. The exact cause of this "phanc.ora bottom" 

 has not been fully determined, but as it migrates toward the surface 

 during darkness, and away from the surface during brightness, a biolog- 

 ical origin is implied„ 



Echograms from an AN/UQN-1 series echo-sounder were obtained aboard 

 the USS GLACIER during Operation DEEP FREEZE II. Notes on the daily 

 occurrence of the DSL were taken by the Hydrographic Office Representa- 

 tive aboard the GLACIER, and the data obtained from the Pacific and 

 Antarctic areas were subsequently analyzed in the U. S. Navy Hydrographic 

 Office, 



Dxiring the 63 days of steaming, definite evidence of a daytime 

 development of the DSL appeared on the echograms south of about 64°30'S. 

 The layer was observed only as an audible signal on at least 12 other 

 days, and was heard along one track as far south as about 65°30'S. 

 The layer traces usually exhibited typical negative phototaxis movement, 

 i.e., movement away from light. Variations in this cycle have been 

 described and discussed in the DEEP FREEZE I Report. Prevailing daytime 

 depth of the layer, both on the echograms and by audible signal, the 

 occurrence of double layers, and other pertinent notes are shown in 

 Figure 28. 



The Antarctic Convergence was crossed once in October, by the 

 GLACIER while the DSL was being recorded, and no change in depth was 

 evident. In February, south of Tasmania, rough weather during the 

 crossing of the convergence interfered with the recording. However, 

 south of the convergence the DSL was recorded at a depth of 200 fathoms, 

 and 250 fathoms to the north for a period of two ho\irs. 



Data on the positions of disappearance and reappearance of the 

 layer as recorded on the echograms of the GLACIER are shown below: 



Position of Disappearance and Reappearance of DSL 



Approximate Approximate 



Location of Location of 



Antarctic Antarctic 



Disappearance Convergence Reappearance Convergence 



Date 



13 Oct 56 



14 Nov 56 

 U Dec 56 

 20 Feb 57 



62°21'S 

 6l°20'S 



2° 21' to north 

 1°10' to south 



58°30'S 

 6l°20«S 



3°30' to south 

 6°20» to north 



61 



