Mesopelagic Zone (Twilight Zone)

node · earth · Global ocean

Conventionally about 200 m to 1,000 m. Sunlight is present but far too dim for photosynthesis to exceed respiration. This is the layer where surface light finally runs out: NOAA states that sunlight does not penetrate below roughly 1,000 m, the top of the permanently dark aphotic realm. The zone hosts the vast vertically-migrating biomass that rises toward the surface at night and sinks by day, and bioluminescence rather than sunlight becomes the dominant light source through most of it.