Using fin whale songs to find out what's below the sea floor
Adam Murphy’s been looking into how whales singing as they travel through the water may hold the key to a more environmentally-sensitive way to search for oil and gas and see what’s happening under the ground, as he heard from researcher Vaclav Kuna...
Adam - Finding out what is under the ocean floor is serious business. It can tell us more about our planet, sure, but it also helps us find deposits of gas and oil. One of the best ways to do that is using sound, like sonar. Sound travels at different speeds through different materials. And at the boundary between two materials it can change direction, or even reflect off of it. So the sound from one source can reach its destination through a load of different ways. And by mapping out all those different ways as they come in, you can start to get a picture of what's going on under the surface. But it's not easy, and the way to generate that sound is somewhat dramatic. Right now we use air guns - big underwater explosions - to give us the noise we need. And it disturbs sea life and has been linked to a whole host of negative effects. But what if there was a way to work with that sea life instead of against it? Well, Vaclav Kuna from the Institute of Geophysics in Prague may have spotted a solution.
Vaclav - When I saw those whale calls and I saw the characteristics of the whale calls, I noticed that there are some signals that I couldn't really explain - those echoes. And it came to my mind that those may be actually those subsurface signals, and then t was quite easy for me then to say, "Hey, maybe we can test out this seismic imaging method on this"
Adam - Fin whales are relatives of blue whales and they sing as they travel, like this song which has been sped up by 10 times.
And they're loud, loud enough that you might be able to map under the ocean floor as they're travelling along.
Vaclav - So the highest energy wave, the call comes straight from the whale to the station. Then there are other kinds of waves or reflections of the direct wave. It's a wave that goes from the whale down to the ocean bottom, and then it bounces off, travels to the ocean surface and bounces again and travels to the station. And then there are other waves - phases as we call them - that goes down to the ocean bottom. And when it meets the ocean floor, it actually penetrates through the floor. It goes in the sediment layer and then it either bounces off or sometimes it even penetrates that and goes even deeper. And those waves, eventually they either bounce off or kind of like turn slowly back up and we can record them on the ocean bottom seismic station.
Adam - And although the whale calls don't have the same resolution as the airgun approach, doing it this way has its advantages.
Vaclav - There is a few reasons. First of all, they are for free and they are pretty much globally spread. So it's kind of a win-win that we have some signals already recorded somewhere and we don't need to pay for them. And also there's a very long on-going debate about the traditional seismic surveys that may be harming ocean mammals because they produce very loud sounds. So yeah, we don't really want to add more noise in the ocean if we don't have to.