Yearly, billions of microscopic ocean drifters—copepods, krill, and different zooplankton—carry out a wide ranging migration within the Southern Ocean, diving tons of of meters into the deep.
As they descend to hibernate for the winter, they carry carbon from the floor with them and, by way of respiration and mortality, lock it away beneath 500 meters. This newly quantified “seasonal migrant pump” strikes round 65 million tonnes of carbon yearly, a hidden pure course of that performs an enormous function in regulating Earth’s local weather.
Zooplankton’s Hidden Position in Carbon Storage
A significant worldwide examine has uncovered that among the ocean’s smallest inhabitants, zooplankton similar to copepods, krill, and salps, play a a lot greater function in storing carbon within the Southern Ocean than beforehand understood.
Revealed in Limnology and Oceanography, the analysis supplies the primary detailed measurement of how these tiny creatures assist entice carbon by way of their seasonal vertical migrations. Scientists have lengthy recognized that the Southern Ocean is likely one of the planet’s most essential areas for locking away carbon, however till now, it was broadly believed that almost all of this course of trusted the sinking of natural detritus created by bigger zooplankton like krill.
The “Seasonal Migrant Pump” Defined
The examine highlights a much less acquainted however extremely important course of often known as the “seasonal migrant pump.” Every year, numerous zooplankton journey from floor waters to depths higher than 500 meters to outlive the winter months. Throughout this deep hibernation interval, they launch carbon by way of respiration and mortality, successfully transferring it into the deep ocean the place it may well stay saved for hundreds of years or longer.
Historically, scientists thought carbon reached these depths primarily when zooplankton consumed phytoplankton close to the floor and their waste, often known as particulate natural carbon (POC), passively sank. The brand new findings reveal that the seasonal migrant pump provides one other highly effective pathway. By descending to deep waters every autumn, zooplankton straight inject an estimated 65 million tonnes of carbon into the ocean’s depths yearly, making them way more influential in world carbon storage than beforehand acknowledged.
Constructing a Century of Zooplankton Information
The crew first constructed an enormous database of zooplankton collected in hundreds of web hauls from across the Southern Ocean, courting from the Twenties to the current day. From these, they quantified the extent of the zooplankton’s annual descent to overwinter at nice depths, the place they respire CO2 — straight and effectively injecting carbon into the deep ocean.
Key Findings:
- 65 Million Tonnes of Carbon Saved Yearly: The seasonal, vertical migration of zooplankton transports roughly 65 million tonnes of carbon to depths beneath 500 meters.
- Copepods Dominate the ‘Seasonal Migrant Pump’: Mesozooplankton (primarily small crustaceans known as copepods) account for 80% of this carbon flux, whereas krill and salps contribute 14% and 6%, respectively.
- Local weather Implications: The Southern Ocean is a important carbon sink, however present Earth System Fashions overlook this zooplankton-driven course of. As warming shifts species distributions (e.g., declining krill, increasing copepods, changing food sources), the carbon storage dynamics may change dramatically.
Why does the ‘Seasonal Migrant Pump’ matter:
The Southern Ocean absorbs approximately 40% of all human-made CO2 taken up by oceans, yet the role of zooplankton has been underestimated. Unlike sinking detritus, which removes both carbon and essential nutrients like iron, migrating zooplankton efficiently inject carbon into the deep ocean while recycling nutrients near the surface. This ‘Seasonal Migrant Pump’ could become even more important as marine ecosystems respond to climate change.
Dr. Guang Yang, first author and Marine Ecologist from Institute of Oceanology, Chinese Academy of Sciences, said: “Our work shows that zooplankton are unsung heroes of carbon sequestration. Their seasonal migrations create a massive, previously unquantified carbon flux—one that models must now incorporate.”
Prof. Angus Atkinson MBE, co-author and Senior Marine Ecologist at Plymouth Marine Laboratory, added: “This study is the first to estimate the total magnitude of this carbon storage mechanism. It shows the value of large data compilations to unlock new insights and to get an overview of the relative importance of carbon storage mechanisms.”
Dr. Katrin Schmidt, co-author and Marine Ecologist at the University of Plymouth, said: “The study shows the ‘seasonal migrant pump’ as an important pathway of natural carbon sequestration in polar regions. Protecting these migrants and their habitats will help to mitigate climate change.”
Dr. Jen Freer, co-author and Ecological Modeller at the British Antarctic Survey (BAS), added: “Krill are famous for their role in the Antarctic food web, but we find that copepods significantly dominate carbon storage overwinter. This has big implications as the ocean warms and their habitats may shift.”
This research stresses the urgent need for updates to climate models to include zooplankton-driven carbon fluxes. It also highlights the necessity to manage and protect Southern Ocean ecosystems, where industrial fishing and warming threaten krill populations – a key species that supports both carbon export and Antarctica’s unique biodiversity.
Reference: “Seasonally migrating zooplankton strongly enhance Southern Ocean carbon sequestration” by Guang Yang, Angus Atkinson, Evgeny A. Pakhomov, Katrin Schmidt, Weilei Wang, Jennifer J. Freer and Geraint A. Tarling, 23 June 2025, Limnology and Oceanography.
DOI: 10.1002/lno.70120
This international study was a collaboration among scientists from China, UK, and Canada, and leverages a century’s worth of data on zooplankton biomass, distribution, respiration and mortality across the Southern Ocean.
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