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Plenary Session Shrimp, Snap, Bubble, and Pop Michel Versluis, University of Twente, Enschede, The Netherlands The oceans may be deep, but they are not at all quiet. Sounds in the ocean include those of waves, produced by tides, winds and thunderstorms, and those of falling rain, hail and snow. In addition, one can hear biological sounds of fish, dolphins, whales and snapping shrimp. The latter, in particular, produce the dominant level of ambient noise in (sub)tropical shallow waters throughout the world. These shrimp live in colonies in such large numbers that there is continuous snapping, providing a permanent crackling background noise. Photograph of a snapping shrimp. Listen to a snapping shrimp (audio file). The snapping sound can be heard day and night, with source levels as high as 200 dB which severely limits the use of underwater acoustics for active and passive sonar, both in scientific and naval applications. The frequency spectrum of a snap is extremely broad, ranging from tens of hertz to beyond 200 kHz. The snapping shrimp produces the impulsive click by an extremely rapid closure of its so-called snapper claw. It was commonly believed that the sound is generated when the two claw halves hit each other. Animation of claw closure. In this talk we will in fact see that the sound of snapping shrimp originates solely from the collapse of a cavitation bubble that is generated by the fast water jet resulting from the rapid claw closure. The water jet velocity is so high that the corresponding pressure drops below the vapor pressure of water and a cavitation bubble is generated which will initially grow in size, then it collapses violently when the pressure rises again. High-speed recording of bubble growth and collapse. In the course of our experiments on snapping shrimp sound we also discovered a short intense flash of light emitted at bubble collapse. The light emission reveals the extreme pressures and temperatures of at least 5000 K in the bubble interior at bubble collapse. In light of the apparent similarity with sonoluminescence, the light emission of a bubble periodically driven by ultrasound, we have termed this phenomenon shrimpoluminescence. Animated artist's impression of shrimpoluminescence.

For more information contact Jim Greenleaf and Bill O'Brien IEEE International Ultrasonics Symposium October 5-8, 2003