Discovery reports (1953) Discovery reports discoveryreports25inst Year: 1953 52 DISCOVERY REPORTS producing an excessive angle between the ocean floor and the face of the hydrophone tank, made the incoming echo less audible. The former explanation seems the more probable, for heavy rolling may take place anywhere in the Southern Ocean, and it was certainly not the cause of the faint echoes found by the 'Discovery II' near the Convergence, for, as mentioned above, the rolling could always be remedied by manoeuvring the ship to suit the weather. Another local area in which only weak echoes wer
Discovery reports (1953) Discovery reports discoveryreports25inst Year: 1953 52 DISCOVERY REPORTS producing an excessive angle between the ocean floor and the face of the hydrophone tank, made the incoming echo less audible. The former explanation seems the more probable, for heavy rolling may take place anywhere in the Southern Ocean, and it was certainly not the cause of the faint echoes found by the 'Discovery II' near the Convergence, for, as mentioned above, the rolling could always be remedied by manoeuvring the ship to suit the weather. Another local area in which only weak echoes were received was found by the 'Discovery II' on the Greenwich meridian, south of the region of diatom ooze. It lay roughly between 54° S and 60° S and from the number of soundings which we eventually obtained during a series of repeated cruises in that area it seems likely that an extremely irregular bottom was the cause of our weak echoes. Rapid changes in depth were experienced and on one occasion the depth shoaled by nearly 2000 m. (1094 fm.) in 30 min., with the ship proceeding at normal speed. Changes of depth nearly of this magnitude were by no means uncommon, and attempts to take a record of some of the slopes with the ' Acadia' recorder were not very successful. On some occasions, indeed, the depth altered so rapidly that it was impossible to get an accurate reading even on the old ' listening' receiver. This problem of echoes from steep slopes will be considered in more detail in the next section of this report; but it may be stated here that owing to the extreme irregularity of the bottom now known to exist in many areas of the Southern Ocean, it seems probable that the weakness of echo strength reported often from south of the Antarctic Convergence-ooze area is more than likely to be due to this cause. SLOPE CORRECTION AND THE CONDITION OF THE OCEAN FLOOR In general it appears to have been accepted that the soundwaves transmitted by sonic echo-sounding apparatus are
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