Global Ocean Warming: An Acoustic Measure?

Abstract

Explosions of 300 lbs of TNT at 1 km depth off Perth, Australia were recorded on Bermuda hydrophones, demonstrating 30 years age the feasibility of global acoustic transmissions. Climate-induced changes in ocean temperature (and hence in sound speed) can be monitored by measuring travel time changes of acoustic signals from remote powerful sources. Warming induced now at the sound axis by CO2 and other greenhouse gases is estimated at 0.005°C per year, too small to be measured locally in the presence of 1°C rms noise from gyre scale and mesoscale fluctuations. The associated rate of decrease in travel time from greenhouse warming (a global measure of temperature rise) is estimated at 0.1 to 0.2 s per year. This climatic signal should be detectable above the gyre and mesoscale noise (less than 1 s rms), given a program of measurements carried out over a decade. An acoustic source at Heard Island in the south Indian Ocean has direct oceanic paths into all five ocean basins?westward to South Georgia, Brazil, South Africa and Bermuda; eastward to Tasmania, New Zealand, Tahiti, Hawaii, San Francisco and Oregon; northward to Indonesia and; southward to Antarctica. A feasibility experiment is planned.