It has been found that the deep sound channel which is so promi- 

 nent a feature in the waters of the equatorial and subtropical zones 

 shallows to around 80 to 100 meters depth at the Antarctic Convergence 

 and retains approximately this depth into the Antarctic. This also 

 has been found to be true in the Arctic. A recent report (Kutschale, 

 1961) states that in the Arctic Basin the sound channel is from the 

 surface down to about 350 meters. Sound velocity values were about 

 the same order of magnitude as in the Antarctic (4750 feet per second 

 in the sound channel and ranging from about 4690 to 4900 feet per 

 second). In the Arctic, at least, this shallow sound channel is 

 nevertheless effective, Kutschale reporting distances of 700 miles 

 range. 



E. Dissolved Oxygen 



Table 6 presents seasonal variations of dissolved oxygen at depth 

 at the icehole, throughout the period of observation, and these are 

 portrayed graphically in Figure 8. Amounts range from 4.89 to 8.40 

 ml/1. There was little change in oxygen at all levels throughout the 

 winter; a general dropping off of values occurred at all levels as 

 the oxygen was slowly being used up without chance of much replenish- 

 ment except by mass transfer of the water. In the lower levels of 

 the water column, the change was very minor, even during the summer. 

 By mid-December a decided rise in the values for dissolved oxygen 

 above 100 meters depth commenced. Values reached a peak on 10 January, 

 declined throughout the remainder of January and February and then 

 started an increase. Termination of observations did not permit fol- 

 lowing up, unfortunately. The heavy crop of diatoms, which McMurdo 

 Sound is known to have in late November and throughout the summer, is 

 mainly responsible for oxygen increases, although some oxygen is un- 

 doubtedly brought in from other areas by currents. On many occasions 

 when irregularities were noted in the oxygen profile, current measure- 

 ments at these depths, made as soon afterward as possible, showed 

 strong current activity. The depths at which these irregularities 

 occurred were around 50, 100, 300, and 550 meters. The strongest cur- 

 rents observed were close to the bottom or at 550 meters and reach a 

 value of 1.83 knots. 



Figures 3 and 4 show vertical distribution of dissolved oxygen 

 during summer and winter. In the summer curve, dissolved oxygen fol- 

 lows very closely the temperature curve and inversely that of salinity. 

 In winter there is very little vertical variation in dissolved oxygen 

 values. 



Table 7 shows seasonal variation of percentage saturation of dis- 

 solved oxygen at depth at the icehole during the period of observa- 

 tion. At each station, higher percentages occurred near the surface 

 and In the upper layers but at no time was the water completely 



55 



