Why Does the Sea Glow at Night & How Colors Vanish Underwater

This phenomenon is called bioluminescence — the biochemical production and emission of „cold light” by living organisms. Unlike incandescent bulbs that waste 90% of energy as heat, bioluminescence is 98% energy-efficient!

The glow stems from a chemical reaction: the substrate luciferin reacts with oxygen aided by the enzyme luciferase, liberating photons of light. In 99% of marine species, the emitted light is blue-green, the exact wavelength that transmits farthest through water.

White sunlight contains all colors of the rainbow. As light penetrates water, dense water molecules selectively absorb different wavelengths according to their energy levels.

Red light possesses the longest wavelength and lowest photon energy, meaning it is extinguished within the first 5 meters! Orange vanishes by 10 meters, yellow by 20 meters, and green fades by 30–50 meters. Only blue and violet light reach deeper realms.

Without artificial illumination, the underwater world beyond 15 meters appears virtually monochrome. Magnificent red gorgonian seafans and scorpionfish look drab olive or slate gray.

To reveal true hidden colors, underwater photographers employ red optical color-correction filters on lenses or fire powerful strobe flashes that flood the scene with broad-spectrum white light for a fraction of a second.

In air, sound travels at roughly 340 m/s. But in dense, nearly incompressible seawater, acoustic waves propagate at approximately 1,500 m/s — nearly 4.5 times faster!

This extreme velocity confuses human hearing: on land, the brain calculates tiny arrival time differences between left and right ears to triangulate sound direction. In water, sound reaches both ears almost simultaneously, making speedboats sound as if they are right on top of you.

Sound speed decreases with dropping temperature until around 1,000 meters, where rising pressure reverses the trend. This creates a minimum sound-velocity layer called the SOFAR channel (Sound Fixing and Ranging).

Sound waves entering this channel refract back toward its core rather than escaping to the surface or floor. Low-frequency vocalizations from blue and fin whales can travel 3,000 to 5,000 kilometers across entire oceans without degrading!