Chapter 5 · Try it yourself
Pressure Dive
At the beach, the air overhead presses on you with 1 atmosphere of pressure. Sink just 10 meters into the sea and the water adds a whole extra atmosphere. Every 10 meters after that adds another. Challenger Deep, the deepest known spot in the ocean, is almost 11 kilometers down. Take the sub there and see what survives the squeeze.
0 m
Arrow keys move a little, Page Up and Page Down move more. Each step gets bigger the deeper you go.
Stop at
The water column
Square-root scale: the top of the ocean is stretched so the busy first few hundred meters fit. Tap the column to jump to a depth.
At the surface
Depth
0 m
0 feet
Pressure
1.0 atm
Water temperature
27 °C
Sunlight zone
The squeeze test
Down here
Why some things crush and others do not
- Air squashes, water barely does. Anything with a pocket of gas inside (lungs, a fish’s swim bladder, a balloon, the tiny bubbles in foam) gets squeezed smaller and smaller as the pressure climbs.
- Animals made mostly of water handle it. With no air spaces, the water inside them pushes back just as hard as the water outside. The hadal snailfish has no swim bladder at all, soft bones and a jelly-like body.
- The squeeze still reaches their proteins. Deep fish load their cells with a molecule called TMAO that helps proteins keep their shape under pressure, and the deeper a fish lives, the more it carries. Somewhere around 8,000–8,500 m fish seem to hit their limit.
- People need a bubble of surface air. A crewed sub keeps its cabin at 1 atmosphere inside a thick sealed sphere that holds the sea out.
Simplified model: pressure = 1 atmosphere of air + 1 atmosphere for every 10 m of seawater. That rule is slightly generous down deep: at Challenger Deep it gives about 1,090 atm, while the measured pressure is about 1,086 bar, or roughly 1,070 atm. Temperatures follow a simplified tropical Pacific profile (real bottom water there is about 1–4 °C). The balloon follows Boyle’s law (volume × pressure stays the same; temperature changes ignored). The foam cup’s shrinking is illustrative, not measured. Challenger Deep: 10,935 m ± 6 m (Greenaway and colleagues, 2021, NOAA). Light zones: NOAA Ocean Service. Sperm whales hunt squid at 1,000–2,000 m (WHOI). Titanic wreck about 3,800 m (12,500 ft). Deepest fish ever filmed: a Pseudoliparis snailfish at 8,336 m in the Izu–Ogasawara Trench off Japan, 2022 (University of Western Australia and Tokyo University of Marine Science and Technology). The amphipod Hirondellea gigas lives on the floor of Challenger Deep. Recreational scuba limit about 40 m (130 ft).