Hydroacoustic Signals from Huge Icebergs in the Ross Sea

Hydroacoustic signals detected in Late 2000 by seismic stations of the Polynesian network are shown to originate from huge icebergs which at the time were drifting in the Ross Sea after calving off the Ross Ice shelf. The signals present a broad variety of spectral characteristics, most of them featuring prominent eigenfrequencies in the 4-to-7 Hz range, often complemented by overtones. They can last as little as a few mn or as long as 3 hours. Most epicenters, obtained by combining observations of distant hydroacoustic and regional seismic records, follow the spatio-temporal evolution of the drift of iceberg B15-B. Most of the signals are generated during a 36-day time window when it is speculated that B15-B collided with smaller icebergs or was scraping the ocean floor on the shallow continental shelf. We speculate on the possible physical nature of the resonator generating the signals, which could correspond to an elastic mode of the iceberg, or to the oscillation of the fluid-filled crack in the ice.