This recording was made and posted by German composer Andreas Bick at a frozen lake in the Berlin area over the winter of 2005/2006. He explains:
Underwater microphones proved especially well-suited for these recordings: in a small hole drilled close beneath the surface of the water, the sounds emitted by the body of ice carry particularly well. The most striking thing about these recordings is the synthetic-sounding descending tones caused by the phenomenon of the dispersion of sound waves. The high frequencies of the popping and cracking noises are transmitted faster by the ice than the deeper frequencies, which reach the listener with a time lag as glissandi sinking to almost bottomless depths.
[via Boing Boing]