Fin whale songs can help map the ocean floor

The echoes of fin whale songs can penetrate sediment and volcanic rock on the ocean floor, according to new research.

Why it matters: Fin whale songs could be used to map the Earth's crust when conventional — and in some cases, controversial — methods like firing seismic air guns from ships may not be available.

• “It’s never going to replace air guns,” study co-author Václav Kuna of the Institute of Geophysics in Prague told the NYT.
• “But it is a complement. And it’s free.”

Fin whales are loud — their low-frequency calls can generate more than 185 decibels underwater, on par with a large ship.

• Researchers typically use the endangered whales' low-frequency vocalizations to study the distribution of the species (Balaenoptera physalus) in the oceans.

What they did: Kuna and John Nábelek of Oregon State University analyzed six whale songs, each with 212–593 calls that were 30–40 seconds apart.

• The calls were picked up by a network of seismometers on the ocean floor that monitor for earthquakes off the coast of Oregon. (The researchers suggest machine learning algorithms could be used to locate and analyze calls.)
• Part of the energy in the whales' calls is "transmitted in the ground as a seismic wave. The seismic wave travels through the oceanic crust, where it is reflected and refracted by layers within the crust," the researchers write today in the journal Science.
• They were able to use those signals to map the thickness of sediment and rock on the ocean floor.

Yes, but: It has its limits — for example, the method worked best in relatively flat regions and the resolution of seismic images constructed from the whales' low-frequency signals was lower than the conventional air gun method.

• The broader-frequency calls of sperm whales may produce higher-resolution imaging, the researchers suggest.

The big picture: "Our study demonstrates that animal vocalizations are useful not only for studying the animals themselves but also for investigating the environment that they inhabit," the researchers write.