The sound of climate change

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Munk, Walter (2011)

It came as a great shock in the 1960s that the oceans, like the atmosphere, have an active weather (i.e. ocean storms are called eddies). The traditional expedition mode of individual research vessels making independent measurements was no longer adequate. Ocean Acoustic Tomography was developed in direct response to the ‘eddie revolution’. Sound travels faster in warmer water; acoustic waves transmitted from ship to ship give information about the temperature and currents in the intervening waters. The transmission scale has widened over the years from 100 to 1000 to 10 000 km, approaching the antipodal scale of Ewing’s 1960 transmission from Perth (Australia) to Bermuda. In 1991 we successfully transmitted from a source ship on Heard Island in the Indian Ocean to receiver ships in the north and south Atlantic and Pacific Oceans. Brian Dushaw is planning to repeat Ewing’s experiment; he expects a reduction in travel time of approximately 10 s as confirmation of global ocean warming over the last 50 yr. Sea level rose 15 cm in the 20th century. The rate has since doubled; values up to 2 m by 2100 are now being quoted. To make accurate predictions we must understand the melting processes of continental ice sheets. Floating ice sheets from Antarctic and Greenland glaciers cover huge ocean caverns that have not to date been accessible to observation. We propose probing these caverns with sound waves to study the ocean dynamics at the underside of the floating ice sheets: a daring venture.
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