AYESHA RASCOE, HOST:
Through the power of radio, we're about to take you deeper into the ocean than most scuba divers ever go.
(SOUNDBITE OF BUBBLES POPPING)
RASCOE: We're taking you to the twilight zone, 200 to 1,000 meters down or around 650 feet to nearly 3,300 feet. That's where Noelle Bowlin, a marine biologist at the National Oceanic and Atmospheric Administration - or NOAA - says the light is very dim.
NOELLE BOWLIN: There's great amounts of pressure. There's not a lot of oxygen, and it's deep.
RASCOE: But this great depth is teeming with life. NPR's Short Wave host Emily Kwong takes us there.
EMILY KWONG, BYLINE: "The Twilight Zone" is more than a TV show. It is a real place, mysterious and disorienting, in the ocean. And during World War II, while militaries were using sonar to look for enemy submarines, people surveying the zone found something odd.
BOWLIN: The signal coming back was so - it was as if they had - were bouncing the sound off the bottom of the ocean.
KWONG: But that didn't make any sense because the bottom of the ocean should've been much further away. And even weirder...
BOWLIN: It seemed like the bottom was moving up.
KWONG: Scientists would eventually learn that the sonar was bouncing off a giant mass of sea creatures, the largest synchronous migration on Earth. It happens every night. Countless fish, crustaceans and other organisms rise up from the deep and travel to the shallows to feed under the cover of darkness. It's a dinnertime commute that is tremendously far. Bowlin said, think of it this way.
BOWLIN: That's like saying, oh, Emily, you know, I'm really hungry. We're in San Diego right now. What are we going to do for dinner? I know. The sun is going down. Let's start walking to Los Angeles for dinner, and we need to walk back before the sun comes up. It's that kind of distance.
KWONG: This mass movement is called diel vertical migration, and these migrating organisms perform an essential service for the entire Earth. Here's how. So in the upper layer of the atmosphere, you have phytoplankton - these microscopic plant-like organisms that photosynthesize. They convert sunlight to energy and pull carbon out of the atmosphere. And during that diel vertical migration at night, when all these jellies and mollusks and small fish come up from the deep, they eat the phytoplankton. (Imitating eating food). And once they've had their fill, they return to the twilight zone, effectively bringing that carbon down with them as food in their bellies.
BOWLIN: Then they expel waste that isn't going back up to the surface. It's falling...
KWONG: Oh.
BOWLIN: ...Down...
KWONG: As poo.
BOWLIN: ...As poo and snow...
KWONG: Or in...
BOWLIN: ...And...
KWONG: ...Snow as we call it in (laughter)...
BOWLIN: Yeah, right. Or they'd be eaten at the surface, and eventually they die. Maybe they die at depth.
KWONG: And as a result, carbon from the atmosphere gets brought down by ocean organisms eating and dying and pooping. This is what scientists mean when they say that the ocean sequesters carbon, that the ocean is the largest carbon sink on Earth. So I had to ask Bowlin, how is climate change impacting the twilight zone? - because that's where so many of the organisms that power carbon sequestration live. And she gave me this example.
BOWLIN: As the water warms, there's less oxygen available, and so you get lower oxygen concentrations, and that makes a hostile living environment for a lot of organisms. And these low-oxygen areas in the twilight zone are expanding, and that's a bad thing for the organisms that cannot inhabit those regions.
KWONG: But Bowlin says it is not too late to protect these organisms if humans act to curb climate change.
BOWLIN: I believe there's room for all of us. We just have to change the way we do some things.
KWONG: And considering that the ocean produces 50% of the oxygen on Earth, our lives depend on it.
Emily Kwong, NPR News. Transcript provided by NPR, Copyright NPR.
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