It’s a little known fact that the sound of calving/cracking/colliding Antarctic icebergs can be recorded on seabed acoustic loggers deployed on the edge of Australia’s continental shelf several thousand kilometres away. If the sound travels that distance, what must their intensity be at source?
Professor Alexander Gavrilov of Curtin University Centre for Marine Science and Technology (CMST) has estimated the source level of these sounds at “220 dB to nearly 250 dB re 1uPa at 1m” (J Hughes, pers. comm. 2013). To get a “feel” for these sounds the interested reader can access playbacks of a variety of Antarctic Ice Sounds recorded at the Alfred Wegener Institute PALAOA listening station.
Listen to the audio and spectral clips entitled “Break-off from the ice shelf” and “Colliding icebergs”. It is remarkable how the former looks and sounds like a series of pulses in a seismic survey.
The sound of colliding icebergs is, of course, very intense but, as we all know, many whale species (we’ve seen them on TV being hunted with icebergs in the vicinity!), including true blue whales, southern right whales and humpback whales feed totally unaffected by sounds in Antarctic waters during the summer months when such noises are at their most intense.
Further evidence of the intense sounds generated by the break-up of ice-bergs and ice-shelves can be found in the recent paper by Robert Dziak et al entitled “Life and death sounds of Iceberg A53a”.
If that iceberg created sounds which “averaged ~ 220 dB-rms re 1 μPa @ 1 m, yielding a total energy flux density of 252 dB μPa2-sec over the ~ 20 minute duration of the entire sequence” one can only imagine what intensity the peaks were! Fig 1C in the paper provides an indication of the intensity of the peaks.
One is left to wonder why, if whales show such tolerance to and are unaffected by intense natural sounds when they are feeding in the Antarctic (which just happen to be at similar frequencies and intensities to seismic survey sounds) they are considered by some to be less tolerant to and adversely affected by similar sounds when they visit Australian waters.