Every evening, a massive migration takes place in the ocean’s twilight zone, where trillions of microscopic animals ascend toward the surface to feed before sinking back into the depths. This movement, known as diel vertical migration, plays a significant role in transporting carbon from the upper ocean to deeper layers, helping to regulate the planet’s climate system.
The twilight zone, ranging from about 200 to 1,000 meters below the surface, holds roughly 95% of the ocean’s fish biomass and supports an estimated 11 billion tons of living organisms. These creatures feed near the surface on phytoplankton under cover of darkness, then retreat to deeper waters by day to evade predators. This daily journey moves enormous amounts of carbon downward—potentially more than double the annual carbon emissions from all the world’s cars combined.
By carrying organic material to depth inside their bodies, these migrating animals effectively fast-track carbon sequestration. Unlike the slow sinking of organic particles that can be consumed or decomposed on the way down, carbon contained in these animals can remain locked in the deep ocean for centuries or longer. This natural carbon pump supports not only global climate regulation but also sustains marine food webs that underpin important fishery resources.
Scientists warn that warming seas, altered food chains, and changing polar conditions may disrupt this delicate migration pattern, which could affect marine ecosystems and the ocean’s carbon storage capacity. Current ocean protections tend to focus on the seafloor and do not adequately safeguard the entire water column where these migrations occur. Conservation advocates and international bodies have called for a pause on deep-ocean fishing in these sensitive zones to safeguard this crucial process until more is understood.
Regions such as waters near Hawaiʻi, the southwest coast of England, Nova Scotia, and the Azores have marine protected areas, but these efforts rarely cover the full vertical range critical to diel vertical migration. Expanding protections to preserve this natural mechanism is increasingly recognized as essential to maintaining the ocean’s role in mitigating climate change.