where faint lights flicker and toothy grins flash.

You are now entering... the Twilight Zone.

Your mission is to survive these depths

and journey to the surface after sundown to feed.

You may now pick your player.

Just kidding— you don't have a choice.

You're a hatchetfish.

And almost everything else is trying to eat you.

The tools at your disposal are a uniquely shaped body,

shiny scales, and glowing spots on your belly.

You're going to need a lot of skill and a little luck.

Your first challenge is to begin your upwards trek.

Your swim bladder allows you to precisely control your buoyancy.

Come nightfall, you slowly fill it up,

becoming less dense and rising towards the surface.

You can't swim fast, but your narrow build makes you maneuverable.

This is especially important since predators could spring out of the darkness

at any moment.

In fact, a fangtooth is gliding beneath you.

It has the ocean's biggest tooth-to-body size ratio.

Food is hard to come by in the Twilight Zone,

so predators have fearsome adaptations to make every attack count.

The fangtooth's skin is ultra-black:

it reflects less than 0.5% of the light that hits it,

making this fish particularly hard to spot.

Fortunately, the bioluminescent organs lining your belly are regulated

to match the intensity and pattern of the faint light from the ocean's surface.

This counter-illumination disguises your silhouette.

So when the fangtooth gazes upwards, you're almost invisible.

A bright spot appears in the distance.

You go to check it out, but something's looming in the darkness.

The light is a bioluminescent lure belonging to an anglerfish.

You dart away before it quickly opens its jaws,

sucking in a hapless fish that got too close.

Another narrow escape, but you're nearly there.

Although more than 90% of deep-sea creatures are bioluminescent,

only one group produces the color red: dragonfishes.

One of them is near.

Because red light is quickly absorbed by seawater,

most deep-sea inhabitants can't see it.

The dragonfish emits red light from organs by its eyes,

using an invisible headlight to locate unsuspecting prey

that its scoops into its cavernous jaw.

You can't see your enemy,

but your silvery, mirror-like scales scatter and soften direct light,

keeping you hidden.

After three close calls, you reach... the Photic Zone.

You've just participated in the world's largest migration.

It takes place every night as trillions of organisms rise from the ocean's depths

to enjoy the surface's rich resources under the cover of darkness.

The payoff is huge.

Here, your light-sensitive eyes take in a buffet of small crustaceans

and gelatinous zooplankton.

During the day, phytoplankton use sunlight to turn dissolved carbon dioxide

into energy and build their own cells.

They become food for small grazers, forming the base of the food web,

which extends back down to the Twilight Zone— and beyond.

Organic matter generated up here— like bits of skin, poop, and dead animals—

eventually sinks or is transported in the stomachs of animals

returning from their nightly migrations.

These materials then feed the creatures below that don't migrate.

This ensures that some of the carbon from the atmosphere

is locked away in the ocean for hundreds of years to come.

That's why this process is known as the biological carbon pump.

Without it, there'd be much more carbon dioxide in the atmosphere,

where it contributes to climate change.

Your avatar, the hatchetfish, is part of this crucial process.

Your first quest is complete,

but you must repeat this journey every night for the rest of your life.

As the sun rises, the surface becomes dangerous,

and you descend back into the shadows of the Twilight Zone.