What Happens to Your Body at the Bottom of the Ocean?
The short answer
The water squeezes you. Every 10 meters (33 feet) of seawater adds about one more atmosphere of pressure, the weight of the whole sky above you all over again. At the bottom of the Challenger Deep, about 10,935 m (nearly 7 miles) down, that adds up to more than 1,000 atmospheres: about 8 tons on every square inch.
Your body is mostly water, and water barely squeezes. Air is what loses. The air in your lungs, middle ears and sinuses shrinks as the pressure climbs. At just 10 m, it is already squeezed to half its size.
One more sky every 10 meters
At sea level, the air above you presses on every square inch with 14.7 pounds. That is 1 atmosphere. A column of seawater 10 m (33 ft) tall weighs the same. So each 10 m you go down adds one more atmosphere on top of the air.
Air shrinks as the total climbs. At 10 m the total is 2 atmospheres, so the same air fits in half the space. That is Boyle's law. A pool 2 to 4 m deep adds only 0.2 to 0.4 of an atmosphere, but that is enough to push on your eardrums.
The one breath record in the film is 214 m (702 ft). The total there is about 22 atmospheres, so a fixed amount of air would shrink to about a twenty second of its size. The Challenger Deep is about 51 times deeper than that.
What the foam cup shows
Foam cups are mostly air, held in tiny bubbles. Deep sea scientists decorate cups and send them down on dives. On a 2017 NOAA Okeanos Explorer expedition, cups went to 2,500 m. They come back shrunken, because the pressure squeezes the air bubbles in the foam.
Your body works the other way. Most of it is water, and water barely squeezes, so your body keeps its shape. The air spaces inside you are the parts that would shrink like the cup.
Why fish stop short of the bottom
No fish has been found from about 8,400 m (27,500 ft) down to the bottom, near 11,000 m. In the film, Pressure acts as if it simply wins. The likely limit is chemistry.
Fish rely on a protein protecting chemical called TMAO. That chemistry predicts a depth limit near 8,200 to 8,400 m, just about where fish stop being found.
Key numbers
| What | Number | Source |
|---|---|---|
| Pressure added by seawater | 1 atmosphere (14.7 psi) for every 10 m (33 ft) | NOAA Office of Marine and Aviation Operations |
| Air at 10 m deep | squeezed to half its size (2 atmospheres in total) | NOAA Office of Marine and Aviation Operations |
| Extra pressure at the bottom of a pool 2 to 4 m deep | 0.2 to 0.4 atmosphere | Our arithmetic from NOAA Office of Marine and Aviation Operations |
| Total pressure at 214 m, the record depth in the film | about 22 atmospheres, so air shrinks to about 1/22 of its size | Our arithmetic from NOAA Office of Marine and Aviation Operations |
| Deepest no limits freedive listed by Guinness (Herbert Nitsch, 2012) | 253 m | Guinness World Records |
| Depth of the Challenger Deep, Mariana Trench | about 10,935 m, give or take 6 m (nearly 7 miles) | Greenaway et al. 2021, Deep Sea Research I (NOAA repository) |
| Total pressure at the Challenger Deep | more than 1,000 atmospheres (about 1,087) | Our arithmetic from NOAA Office of Marine and Aviation Operations and Greenaway et al. 2021, Deep Sea Research I (NOAA repository) |
| Weight on each square inch at the bottom of the Mariana Trench | about 16,000 psi, or 8 US tons | NOAA Office of Marine and Aviation Operations |
| Depth foam cups went on a 2017 dive | 2,500 m | NOAA Okeanos Explorer, 2017 |
| Depths where no fish has been found | about 8,400 m (27,500 ft) to 11,000 m | Yancey et al. 2014, PNAS |
| Depth limit predicted by fish's protein protecting chemistry (TMAO) | about 8,200 to 8,400 m | Yancey et al. 2014, PNAS |
What the film simplifies
- The film calls 214 m (702 ft) the official one breath record. That is Herbert Nitsch's 2007 no limits dive, certified by the freediving body AIDA. Guinness World Records lists his 2012 dive to 253 m, which was not an AIDA record.
- "Fifty times deeper" is rounded. The Challenger Deep, at about 10,935 m, is about 51 times deeper than 214 m.
- Real foam cups come back shrunken from dives such as one to 2,500 m. The film's cup goes all the way to the trench floor, and its thimble size there is drawn, not measured.
- Pressure is a cartoon character. Its glowing eye lights nothing. The light on the trench floor is our flashlight, and the snailfish does not glow: outside our beam she is drawn dark.
- Pressure talks as if fish lose a contest of strength. The likely reason no fish has been found below about 8,400 m is body chemistry.
- Pressure's photo of the bottom is black because no sunlight reaches the bottom and Pressure has no flash.
For teachers
Runtime 1 minute 4 seconds · Topics: Water pressure, Deep sea, Human body, Deep sea life · Full script below
Ask your class
At what depth is the air in your lungs squeezed to half its size, and why there?
Answer
At 10 m (33 ft). There the water adds 1 atmosphere to the 1 from the air, so the total doubles and the same air fits in half the space.
A foam cup shrinks on a deep dive. Why would your body mostly keep its shape?
Answer
Foam is mostly air, and air squeezes easily. Your body is mostly water, which barely squeezes, so only its air spaces, like the lungs, ears and sinuses, would shrink.
Using 1 atmosphere for every 10 m of seawater, roughly how much pressure is there at the Challenger Deep, about 10,935 m down?
Answer
About 1,100 atmospheres: about 1,094 from the water plus 1 from the air. A more careful calculation gives about 1,087. Either way it is more than 1,000.
The script
Host: That cup is you. And it's going to the bottom of the ocean.
Pressure: Hi! I'm Pressure. Let's see what's left of you.
Host: You've already felt it: the push in your ears at the bottom of a pool.
Host: Every ten meters down, the water adds the weight of the whole sky.
Host: At ten meters, the air in your lungs is squeezed to half.
Pressure: Anything with air inside? Lungs, balloons, foam cups... I win.
Host: The official record for one breath? Two hundred and fourteen meters down.
Pressure: Cute.
Host: The very bottom is fifty times deeper.
Snailfish: Ooh! Where are you going? Can I come?
Pressure: Nope! Even the deepest fish can't go that deep.
Pressure: Touchdown!
Pressure: Over a thousand skies, stacked on top of you. Undefeated, baby!
Host: So what's left of you?
Pressure: Souvenir!
Host: Scientists really do this. Foam is mostly air, so the cups come back tiny.
Host: You're mostly water, and water barely squeezes. But the air in you would shrink like that cup.
Snailfish: So... what's the bottom like?
Pressure: Got a photo!
Host: Next: Pressure dunks Mount Everest into the ocean. Follow!
Sources
- Every 10 m of seawater adds one atmosphere of pressure. At 10 m deep, a lungful of air shrinks to half.NOAA Office of Marine and Aviation Operations
- The official no limits freedive record is 214 m.Guinness World Records
- The Challenger Deep is about 10,935 m deep.Greenaway et al. 2021, Deep Sea Research I (NOAA repository)
- Foam cups sent 2,500 m down came back shrunken.NOAA Okeanos Explorer, 2017
- Foam is mostly air, so deep sea pressure shrinks foam cups.Live Science
- No fish has been found below about 8,400 m.Yancey et al. 2014, PNAS