Brittle star (Class Ophiuroidea, probably Ophiura sp., 

 possibly Ophivira sarsi , plus others) 



Sea urchin (Class Echiuroidea, probably Strongy-locentrotu^ 

 droebachiensis ) 



Sea cucumber (Class Holothuroidea, burrowing type with re- 

 versible respiratory tree (gills) extended above mud) 



Sea lily (Class Crinoidea, probably Helimoctra glacialis ) 



Phylum Mollusca 



Ifaeoma calcarea, white shells on mud (Class Lamellibranchiata) 

 Pecten sp., possibly p. islandicus (Class Lamellibranchiata) 



Through-Ice Echo Sounding 



The through-ice echo sounding experiment demonstrated that it 

 is possible to 12 kilocycle echo so^Ind through a it— foot thick first- 

 year plate -ice cover in a shallow water area. A photograph of an 

 annotated section of echo sounding record is presented as Figure 19. 

 A crisp echo from the sea floor is present on the record and indi- 

 cates a depth of khO feet. (Note: full sweep is 2kO feet, and the 

 sea floor echo is arriving dviring the second sweep.) A diffuse long- 

 drawn-out echo return is present on the left hand side of the record. 

 This is reverberation caused by the out-going ping passing through 

 the ice cover. The reverberation appears on the first recording 

 sweep only and can be phased out by not recording on the sweep as- 

 sociated with the out -going ping. This has been done on the top- 

 most section of the record in Figure 19. 



Ice Thickness Measurements 



The thickness of the ice was measured at 50 random locations 

 throughout the study area. Ice thickness ranged from a minimvmi of 

 20 inches to a maximimi of k6 inches. A representative areal distri- 

 bution of the ice thiclaiess during the beginning of the survey is 

 shown in Figure 20. Additional measurements were made at Sites 1 

 and 2 to determine the homogeneity of the ice thickness over a small 

 area. The thickness measxxrements were made systematically at 10 and 

 20 foot spacings along two intersecting lines, each 100 feet long. 

 The results of the meastorements at Site 1 indicated a mean thickness 

 of 52 inches, a maximum of 37 inches, and a minim\jm of 29 inches. 

 Jfeasurements at Site 2 indicated a mean thickness of 42 inches, a 

 maximum of kh inches, and a minimum of 39 inches. These measure- 

 ments indicate a relatively uniform ice thickness over the small 

 areas sampled. 



326 



