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Richard Aster
Department of Earth and Environmental Science
New Mexico Institute of Mining and Technology
Socorro, NM

Seismometers sited on the great ice sheets and icebergs of Antarctica are also revealing signals due to waves from extreme ocean storms and from regional iceberg calving. Hours-long collisions between Earth's largest icebergs as they gyrate under the influence of coastal currents also cause the icebergs to "sing" with a newly discovered type of seismic and ocean acoustic tremor. Extreme storms occurring during the Arctic winter produce waves that propagate to Antarctica. One resulting hypothesis arising from seismic studies conducted atop giant icebergs is anecdotally supported by the breakup of Earth's largest iceberg in late 2005. It seems that these waves can influence iceberg behavior in the Antarctic because they arrive during what is summer in the southern hemisphere, when large tabular icebergs and ice shelves are largely unprotected by sea ice and are thus susceptible to calving and breakup.

The worldwide network of seismographs designed to detect earthquakes is also recording aspects of Earth's climate. Buried in the background of these continuous seismic recordings, even in the deep interiors of continents, are "microseisms" -- seismic waves created by ocean waves pounding the coast and interacting with the sea floor. From over 35 years of high-quality continuous global seismic recordings, my colleagues and I have been able to reconstruct a unique record reflecting past patterns of ocean-storm intensity. This work includes evidence suggesting that violent ocean storms across planet, and associated ocean waves, may be increasing in their frequency of occurrence across the past three decades.

MacAyeal, D. R., Okal, E., Aster, R., Bassis, J., Seismic and hydroacoustic tremor generated by colliding icebergs, J. Geophys. Res ., 113, F03011, doi:10.1029/2008JF001005 , 2008.

Aster, R.C., McNamara, D.E., Bromirski, P.D., Global trends in extremal microseism intensity, Geophys. Res. Lett. , 37 , L14303, doi:10.1029/2010GL043472 , 2010.

Host Greg Waite