Placeholder Image

字幕表 動画を再生する

  • This is me.

  • I'm about to go scuba diving

  • for the first time ever.

  • I went in expecting muffled peace and quiet.

  • I mean, one of the earliest documentaries on underwater life was literally calledThe

  • Silent World”.

  • They roamed deep under the Mediterranean, the Red Sea, and the Indian Ocean, in a mysterious

  • realm, a silent world.”

  • But as soon as I got down a few yards, I couldn't help but notice sound all around me.

  • It was hard to tell what direction it was coming from, or how far away it was.

  • It was coming from boats above me.

  • As far as I can tell, the Earth's water is not as quiet as I thought.

  • I've been binging this podcast all about sound, and they've been looking into this too

  • "From DeFacto Sound, you're listening to

  • Twenty Thousand Hertz: The stories behind the world's most recognizable and interesting

  • sounds.

  • I'm Dallas Taylor."

  • So Dallaslife underwater can be pretty loud, right?

  • It can!

  • Just listen to these toadfishthey oscillate their swim bladders to make sounds that are

  • loud enough to keep houseboat residents in Sausalito, California up at night.

  • Or these Barred Grunt fish, that make a grinding sound with the teeth in their gullet.

  • Or these snapping shrimpthey produce a sound by creating

  • tiny popping bubbles with their claws.

  • It's been measured at 200 decibels.

  • That's louder than a gunshot.

  • Light doesn't penetrate very deep in water, so a lot of ocean life has evolved to use

  • sound as its primary sense.

  • Because water particles are more densely packed together than air, sound travels farther and

  • faster in water.

  • That makes it an efficient medium of communication at any depth or time of day.

  • Let's say we had 440, like the middle key of your piano, or whatever.”

  • That's John Hildebrand, he's a professor at the Scripps Institution of Oceanography.

  • He's an expert in the field of underwater sound and how it's used by and how it affects

  • marine mammals.

  • If you looked at the wavelength of that sound in air, that note, the 440 note, would

  • be a little bit less than a meter long.

  • In water, it's more like several meters long.”

  • What that means is that noise travels about four times faster and farther in water than

  • it does in air.

  • In an experiment in 1991, sound emitted from Heard Island was picked up at 16 sites in

  • the Atlantic, Pacific, and Indian Oceans.

  • It turns out that one of the most common noises in the entire ocean that can be picked up

  • almost anywhere these days, sounds like this:

  • It's the sound of boats.

  • Noise from ship traffic has doubled every decade since the 1960s.

  • Basically, anywhere you go, the ambient noise in the ocean is dominated by anthropogenic

  • sound.”

  • Let's say I made a measurement 30 years ago and now if I went to the same place and

  • made the same measurement, it would be 10 dBs or more higher sound level than what I

  • measured when I started my career.

  • That's spooky.”

  • That's a huge problem for animals that use sound as their primary sense.

  • Just listen to this audio of how noise from a passing boat totally drowns out dolphin

  • communication.

  • But arguably the worst culprit of underwater sound pollution is a process that sounds like this:

  • This is seismic surveying.

  • It's a process that allows companies to locate spots on the ocean floor where they

  • can drill for fossil fuels.

  • Boats with about 30-40 airguns that all go off at once will move back and forth over large

  • parts of the ocean.

  • Bubbles from the horns expand and contract typically every 10 seconds, creating a huge

  • amount of acoustic energy that maps geological structures deep in the ocean floor.

  • And it's about as loud as a jet at takeoff.

  • This can go on for weeks at a time.

  • A study of seismic survey noise between 1999 and 2009 found that airgun sounds were recorded

  • almost 2500 miles away from the survey ship itself.

  • At some locations, they were recorded on 80 percent of days for over a year.

  • And that changes how animals behave.

  • A study by the Institute of Marine Science at the University of North Carolina found

  • that reef fish abundance decreased by 78 percent during seismic surveying.

  • This is what the reef looked like before seismic surveying in the area.

  • And this is what it looked like after.

  • Seismic surveying is a constroversial topic at the coast

  • and new research is only adding to the conversation.

  • One of those impacted is local fisherman Jack Cox.

  • He's seen firsthand the impact seismic surveying has on fish.”

  • It does something, thatwe just don't catch fish.

  • For animals like whaleswho rely on complex sound communication systems to socialize,

  • find food, and matethat poses a huge problem.

  • If you watch this heat map from a study of endangered North Atlantic right whales, you

  • can see that shipping paths near Boston squeeze the whales into a tiny space where communication

  • is possibleit's about a third of what it was without the ships.

  • Susan Parks, a biology professor at Syracuse, recorded right whale sounds throughout the

  • early 2000s.

  • And when she compared her audio to some that had been recorded in 1956, she noticed that the

  • older sounds were much deeper than her high-pitched recordings.

  • It turns out that the whales had started calling at higher and higher frequencies in order

  • to hear each other over the hum of ship noise.

  • Apart from habitat displacement and communication changes, there's also evidence that boat

  • noise simply stresses these whales out.

  • After the September 11th attacks, researchers in Canada's Bay of Fundy compared underwater

  • noise levels during a period of reduced ship traffic to the stress-related hormone levels

  • in the right whale population.

  • They discovered a 6 decibel noise decrease in the bay after 9/11, which correlated to

  • lower baseline levels of stress related hormones.

  • Effects like this go all the way down the food chain.

  • A 2017 study found that there were two to three times more dead zooplankton after after

  • a day of blasts from a single airgun.

  • And the larvae of krill, which whales rely on for food, were totally destroyed.

  • In April 2017, Donald Trump signed an executive order to open offshore drilling in the Atlantic.

  • It directed the Interior Department to consider allowing seismic exploration by 5 companies

  • that had been blocked under the Obama administration.

  • It's getting widespread pushback in Congressthere's a bipartisan House bill and

  • Democrat-led Senate bill to ban seismic testingbut if those authorizations go through,

  • companies could be conducting seismic testing in the Atlantic by Fall 2017.

  • Sois there any good news?

  • Yes, there is.

  • In 2014, the International Maritime Organization adopted guidelines for reducing commercial

  • ship noise levels with things like noise-muffling propellers and insulated enginesthough

  • they're not mandatory yet.

  • A year later, the US Navy agreed to limit sonar testingwhich has been linked to

  • whales stranding themselves on beaches in habitats near Southern California and Hawaii

  • following a lawsuit from environmental groups.

  • And in June 2016, the National Oceanic and Atmospheric Administration laid out an Ocean

  • Noise Strategy Roadmap.

  • It's the start of a 10-year plan to assess the human impact on underwater sound and the

  • measures required to reduce it.

  • Seismic surveys can work better, too.

  • Norway has started multi-client surveys, so that seismic data from a particular area is

  • only collected once.

  • US authorities are considering a similar process.

  • The ocean is huge.

  • We've explored less than 5 percent of it so far.

  • So it's easy to forget that what we do on the surface affects everything down below.

  • But like plastic, chemicals, and waste, noise pollutes our oceans.

  • Understanding that is key to doing our part to protect it.

  • Thank you so much for watching, we loved doing this collaboration with Twenty Thousand Hertz.

  • They create super highly produced podcasts that tell stories all about sound.

  • If you enjoyed this video, you should absolutely go check out their podcast on the exact same topic.

  • You can find that and subscribe at applepodcasts.com/20k.

This is me.

字幕と単語

動画の操作 ここで「動画」の調整と「字幕」の表示を設定することができます

B1 中級

Why the ocean is getting louder

  • 4 0
    joey joey に公開 2021 年 05 月 16 日
動画の中の単語