CLIMATE CHANGE, DOLPHINS, SPACESHIPS AND ANTIMICROBIAL RESISTANCE - THE IMPACT OF BUBBLE ACOUSTICS

Bubbles couple to sound fields to an extraordinary extent, generating and scattering sound, and changing the chemical, physical and biological environments around them when excited to pulsate by an appropriate sound field. This paper accompanies a plenary lecture, opening with the way that the sound emitted by bubbles, when they are injected into the ocean by breaking waves, helps track the >1 billion tonnes of atmospheric carbon that transfers between atmosphere and ocean annually. However, compared to carbon dioxide, atmospheric methane has at least 20 times the ability, per molecule, to generate ‘greenhouse’ warming. Worldwide there is more than twice the amount of carbon trapped in the seabed in the form of methane hydrate than the amount of carbon worldwide in all other known conventional fossil fuels. Acoustics can track the release of bubbles of seabed methane as this hydrate dissociates in response to increasing ocean temperatures, an effect cited by some as a possible climate apocalypse. Continuing the methane theme, this paper discusses the sounds of methane/ethane ‘waterfalls’ on Titan, Saturn’s largest moon, before returning to Earth’s oceans to discuss how whales and dolphins might use the interaction between sound and bubbles when hunting. This in turn suggests possibilities for radar in the search for improvised explosive devices. The paper closes with consideration of another apocalypse, discussing the role that bubbles and acoustics have in mitigating the ‘antibiotic apocalypse’, when in response to the increasing use of antimicrobials (antibiotics to combat bacterial infections; anti-virals for viral infections; anti-fungals for fungal infections; and targeted chemicals to combat parasites) the four classes of microbes all naturally evolve resistance, such that by 2050 Anti-Microbial Resistance will be killing more people than cost the world economy more than the current size of the global economy.