A vast migration begins each evening
Many copepods and krill travel between depths on a daily cycle. In the most familiar pattern of diel vertical migration, they spend the day in deeper water, rise at dusk and descend around dawn.
A migration that feeds the depths
Phytoplankton fix dissolved inorganic carbon into organic matter through photosynthesis. That carbon passes to the animals that eat them. A migrant that feeds near the surface and then descends can release carbon at depth through respiration or excretion, or transfer it to a predator. Particles also carry carbon down as they sink. How much each process contributes varies, and some of the carbon reaching deeper water can return to the surface.
