Below the light

The sea keeps its light near the top. By two hundred meters, sunlight is a rumor. By a thousand, it’s gone entirely, and whatever glows down there makes its own.

The sunlit zone

Nearly everything you’ve ever seen in the ocean lived here. Red goes first, a few meters down it simply stops existing, then orange, then yellow, until the water is a single blue you can only describe from the inside.

At depth, color isn’t a property of things. It’s a property of distance.

The twilight zone

Between two hundred and a thousand meters, the light is just faint enough to hide in. Every night, lanternfish and krill rise toward the surface to feed and sink back before dawn: the largest migration on Earth, happening in the dark, every single day.

Zone	Depth	Light
Sunlight	0–200 m	enough to grow by
Twilight	200–1,000 m	faint, blue, fading
Midnight	1,000–4,000 m	only what animals make
Abyss	4,000–6,000 m	none
Trenches	6,000 m +	none

Open water, a long way from anywhere.

The midnight zone

Below a thousand meters, most of the animals you meet make their own light.¹ Some use it to hunt, some to hide, some to find each other — and for some, nobody is quite sure why.

The pressure here is a hundred atmospheres and climbing. The water is a few degrees above freezing. And by volume, it’s most of the living space on the planet.

// Pressure grows by about one atmosphere every ten meters.
const atmospheres = (meters) => 1 + meters / 10;
atmospheres(1000); // 101

Notes to self

• Everything interesting is a long way down.
• Light is a budget. Spend it on purpose.
• Bring a flashlight. Make your own.

The surface is where the weather lives. Everything below it is quieter.