Every night, trillions of tiny animals in the ocean's twilight zone swim up to feed near the surface and then return to deeper water. This daily migration, called diel vertical migration, moves an estimated 6.6 billion tons of carbon into the deep ocean each year. That is more than twice the annual carbon emissions from cars worldwide, according to researchers cited by the BBC. The process works because zooplankton eat carbon-rich organic matter near the surface and then descend, carrying that carbon deeper where it can stay stored for centuries. The twilight zone, 200 to 1,000 meters below the surface, holds about 95% of all fish biomass. Scientists warn that ocean warming and shifting food chains could disrupt this natural carbon pump, which is why some groups are calling for stronger protections for the full water column, not just the seafloor.
