Matsumoto, H., D.R. Bohnenstiehl, J. Tournadre, R.P. Dziak, J.H. Haxel, T.-K.A. Lau, M. Fowler, and S.A. Salo (2014): Antarctic icebergs: A significant natural sound source in the Pacific Ocean. Geochem. Geophys. Geosyst., 15, doi: 10.1002/2014GC005454.
Previous research indicates that low-frequency ocean noise levels have risen 3 to 4 times since the early 1960s in some areas. This rise has been largely attributed to increased global ship traffic. The scientific community has become increasingly concerned about the adverse effects of anthropogenic (human-made) inputs to the marine ecosystem, and in particular to marine animals, which rely on sound to aid in migration, feeding, and breeding.
PMEL’s Acoustics Program has been monitoring the low-frequency acoustic environment in the equatorial Pacific since 1996. In the program’s long-term noise record, a persistent seasonal pattern was found. This pattern, i.e., high during the austral summer and low in winter, was disrupted in 2008, and noise levels stayed relatively high for the following 1.5 years. By examining sound records and satellite images, the authors were able to identify the sound source of two giant tabular icebergs, B15a and C19a, at a distance of ~10,000 km, disintegrating in the Pacific-Antarctic region during the same period.
Examining the iceberg volume derived from satellite altimeter data (provided by IFREMER, France) and hydrophone records in the Indian and the Atlantic oceans (provided by the Comprehensive Nuclear–Test- Ban Treaty Organization, or CTBTO), the authors of this study identify a strong temporal correlation between the long-term noise and iceberg volume and subsequent breakup process in all three oceans. This is the first such study to reveal a correlation between the underwater noise levels observed at low latitudes in the Northern Hemisphere and the seasonal pattern of iceberg volume off Antarctica. The authors conclude that a natural process, the breakup of Antarctic icebergs, is a significant contributor to spatial and temporal variability in underwater background noise levels influencing the entire Southern Hemisphere and even low northern latitudes in all three oceans. Further, the authors show that in order to monitor anthropogenic inputs in the global soundscape, the contribution of iceberg-generated noise must first be understood and quantified.