Taking the Ocean’s Temperature

About 90 percent of the heat trapped by greenhouse gases is absorbed by the oceans. Now scientists have found a creative (and maybe more effective) way to monitor changes in ocean temperature using a unique source of sound – earthquakes. Current methods employ ship-based or flotilla-based temperature sensors that can drop down to depths of about 6,500 feet, but they are limited in number and only provide a snapshot in time. Satellite imaging covers a broader area, but it cannot penetrate deep beyond the surface.

In recent years, researchers determined that sound travels more quickly in warmer water than in cold and are now using that speed differential to reveal temperature changes over time. Although they initially considered deploying acoustic emitters, the cost was prohibitive and there was also concern about the effect on marine life.

Instead, they decided to use the low-frequency waves that earthquakes create. Using acoustic data from more than 4,700 magnitude-3 or lower quakes, they compared sound wave speeds originating from the same location over a period from 2004 to 2016. The data indicated a definite warming trend of about 0.08 degree per decade, and while that doesn’t sound like a lot, it takes a tremendous amount of heat to warm the eastern Indian Ocean. When used in conjunction with other methods, this technology could fill significant gaps in climate change data.