does not show good correlation, Mich more extensive and detailed ob- 

 servational data in the same geographical area may be required before 

 such correlations can be made. 



The daytime layer trace was frequently masked by a dark or elon- 

 gated outgoing signal trace, caused either by a high gain setting or 

 reverberation daring high seas* This situation made it difficult and 

 often impossible to ascertain the depth, time of descent and ascent, 

 or even the exisxence of the layer. In figure 19, whenever masking of 

 the daytime xayer trace was almost complete, the layer is recorded as 

 present if some evidence of the layer appeared during the day and if 

 the layer were present on the preceding and following days. 



Comparison of the characteristics of the layer as recorded by the 

 ATKA in V^Sh-SS, the USS HENDERSON in 19\x6-hl (Operation HIGHJTJMP), 

 and the French Ship COMMANDANT CRIRCOT in 19U8-l!9, may be made. A 

 distinct double layer was recorded on only one occasion by the ATKA, 

 whereas numerous double layers and even triple layers were observed 

 aboard the HENDERSON and COMllANDAIMT CffiRCOT. The possible existence 

 of a double layer, of v/hich the lovrer layer persisted at an unchanged 

 level throughout the night, was noted on the ATKA's fathogrsjn. Such 

 an occurrence was also noted on the HENDERSON. The HENDERSON recorded 

 no DSL for 2 d?ys and a poor development of the layer on 1 day between 

 IQO and 20° S., and lliOO and 150° W, in the vicinity of the Maixjuises 

 Islands and the Tuamotu Archipelago, where the water was deep enough 

 for development of the layer. It is interesting to note a sim;Llar 

 poor development and ultimate disappearance of the layer trace on the 

 ATKA fathogram in the same general mid-Pacific area, although it began 

 about 10° farther south and extended over a longer distance. 



The absence of the layer in Ant^arctic waters as noted on the ATKA 

 fathograms compares well with the results reported from the COMMANDANT 

 CHARCOT, but poorly with those from the HENDERSON, The COMMANDANT 

 'CHARCOT did not record the layer at any time south of 62° S, The 

 HENDERSON, hovrever, recorded observations of the layer on a number 

 of days while navigating in Antarctic waters between 61° and 67° S. 

 Generally, the layer was recorded indistinctly and sporadically, but 

 on 2 days it was as well developed as in tropical Pacific waters. 



Discrepancies exist among the reported latitudes at which the 

 layer disappeared in Pacific Antarctic waters on each of the three 

 ejqjeditions. Termination of the layer at about 56° S, or about 7° to 

 the north of the Antarctic Convergence was recorded aboard the ATKA, 

 The HENDERSON recorded the temporary termination of DSL x^hcn crossing 

 the Antarctic Convergence at about 62° S,, whereas en the COMIIANDANT 

 CHARCOT the layer was observed tmtil the limit of drifting icepacks 

 was reached at about 6U° S. or almost 10° to the south of the con- 

 vergence at that time. 



60 



