A New Way To Monitor Ocean Warming Without Harming Whales

Nov 27, 2016

As the Earth’s atmosphere warms because of greenhouse gas emissions, most of the heat gets trapped in the oceans. But measuring the change has proven difficult, especially at greater depths. A researcher at the University of Washington is proposing a new method that has some promise

Measuring the surface temperatures of the world’s oceans is done primarily by satellite. The bigger challenge at this point is monitoring changes in their interior, because it’s expensive to maintain instruments used to take measurements at depth.

A method called acoustic tomography was pioneered in the 1970s. It looked at the travel times of sound waves, which move faster as temperatures rise. But it was discontinued in 2006 because of concern that it was harming whales by interfering with their communication signals.

Now a researcher at the University of Washington has developed a way to instead look at travel times of naturally occurring internal tidal waves.  These originate deep below the surface because of ridges or ‘bumps’ on the ocean floor.  Zhongxiang Zhao is an oceanographer in the UW’s Applied Physics Lab.

“So we measure the travel times of the internal tidal waves from the bottom bump. And then from the travel time change, we can calculate the temperature change inside of the ocean,” Zhao said.  

His method replaces acoustic tomography at much lower cost and without environmental concerns, he says, and allows monitoring the changing temperatures of the ocean over its entire depth.

The paper was recently published in Geophysical Research Letters.