Abstract:

In 1960, sound signals traveling from Perth, Australia were recorded at Bermuda. Previous work focused on the path traveled by the sound [Munk , JPO, 1876–1898 (1988)]. Calculation of the horizontal refraction of sound, across the Southern Ocean in particular, gave the perplexing result that Bermuda was in the shadow of Africa. Heaney [J. Acoust. Soc. Am., 2586–2594 (1991)] used low‐resolution atlases for global sound speed and bathymetry to obtain two viable acoustic paths between Perth and Bermuda, both influenced by bathymetry. From a modern perspective, however, the explanation of Heaney is unconvincing [Dushaw, GRL (2008)]. High‐resolution ocean models put the Perth‐to‐Bermuda acoustic problem into a new light. These models suggest that intense, small‐scale features, e.g., Agulhas rings near the Cape of Good Hope, would greatly influence the acoustic paths. The antipodal travel time, 13 382 s, is a measure of the ocean temperature in 1960. If the acoustic propagation issues can be fully understood, data‐assimilating ocean general circulation models might be used to calculate a present‐day travel time. The travel‐time change over the past half‐century, expected to be about 10 s based on nominal estimates of ocean warming, is a measure of ocean climate change.