Antarctic krill, the tiny shrimp-like crustaceans that form the foundation of the Southern Ocean food web, play a vastly oversized role in global carbon storage. New research reveals that through their sinking fecal pellets, these small organisms collectively trap millions of tons of carbon in the deep ocean each year, providing an ecosystem service with planetary-scale implications. The findings reposition krill not just as a critical food source, but as major players in the biological carbon pump that helps regulate Earth’s climate.
The scale of this process is immense, rivaling the carbon sequestration capabilities of entire coastal ecosystems. Scientists estimate that Antarctic krill sequester at least 20 million metric tons of carbon annually. This contribution is comparable to the total amount of carbon stored by the world’s seagrass meadows, mangrove forests, and salt marshes combined. This natural process has a profound economic value, estimated to be worth between $4 billion and $46 billion each season, highlighting a previously underappreciated benefit of preserving krill populations.
A Biological Carbon Pump
Krill actively participate in a process known as the biological carbon pump. They feed on carbon-rich phytoplankton in the upper layers of the ocean, consuming vast quantities of microscopic plant life that has absorbed carbon dioxide from the atmosphere through photosynthesis. After digesting this material, the krill excrete dense, carbon-packed fecal pellets. These pellets are significantly larger and sink faster than waste from other, smaller plankton.
This rapid sinking is crucial for effective carbon sequestration. It allows the pellets to descend quickly through the water column, moving the carbon from the surface to the deep ocean before it can be re-released into the atmosphere. The majority of these pellets constitute a significant portion of the sinking carbon particles found in both shallow and deep waters of the Southern Ocean, acting as a conveyor belt that transports atmospheric carbon to the seafloor.
Quantifying a Global Impact
To determine the full extent of this carbon transfer, researchers combined recent data on krill abundance with sophisticated ocean circulation models. Their analysis revealed the 20 million metric ton figure for the carbon moved into the deep sea each year from Austral spring to early autumn. The models showed that once this carbon reaches a mean depth of just 381 meters, it is effectively locked out of the atmosphere for at least 100 years.
The influence of this process extends far beyond Antarctic waters. The ocean circulation models tracked the footprint of the remineralized carbon from the krill pellets, finding that it has a global reach. Currents disperse these nutrients and sequestered carbon to distant parts of the ocean, with some of it eventually reaching as far as the North Pacific. This demonstrates that the health of the Antarctic ecosystem has a tangible connection to the biogeochemical cycles of the entire planet.
An Undervalued Ecosystem Service
For decades, environmental policy has focused on “blue carbon,” a term typically reserved for the carbon captured by coastal vegetated habitats. The new findings argue that open-ocean processes, particularly those driven by organisms like krill, deserve similar recognition and protection. While a mangrove forest may store more carbon per square kilometer, the vast expanse of the Southern Ocean inhabited by krill means their total contribution is of a similar order of magnitude.
Placing a monetary value on this service helps contextualize its importance in a global economic framework. The $4 billion to $46 billion valuation is derived from the social cost of carbon, a metric used to estimate the long-term damage done by emitting one ton of carbon dioxide. This economic perspective provides a powerful argument for the conservation of krill, framing their protection not only as an ecological necessity but as a prudent investment in planetary health.
The Foundational Role of Krill
Antarctic krill, with the scientific name Euphausia superba, have a total biomass greater than the entire human population. They congregate in immense swarms that can be miles wide, forming a critical link in the food web. These crustaceans are the primary food source for a wide array of predators, including penguins, seals, fish, and the largest animal on Earth, the blue whale. Their abundance supports the immense biodiversity of the Antarctic region.
The sheer scale of their population makes their collective biological functions globally significant. Beyond providing food, their daily and seasonal migrations, feeding habits, and life cycles profoundly influence the chemistry and nutrient distribution of the Southern Ocean, which itself is one of the world’s largest carbon sinks.
Compounding Environmental Threats
Despite their importance, Antarctic krill face a precarious future. Their populations are under pressure from multiple environmental stressors, each threatening to diminish their numbers and, consequently, their ability to sequester carbon.
Climate Change Impacts
The polar regions are warming at a faster rate than the rest of the planet. Rising ocean temperatures and the rapid melting of sea ice pose a direct threat to krill. Sea ice provides a crucial habitat for juvenile krill, which feed on the algae that grows on its underside. As the ice disappears, so does this vital nursery, jeopardizing the survival of the next generation.
Commercial Harvesting Pressure
Krill are also targeted by an expanding commercial fishery. They are harvested for aquaculture feed, fish bait, and human nutritional supplements like krill oil. While fishery management bodies have regulations in place, there are growing concerns that current rules do not adequately account for the compounding pressures of climate change or the full value of krill to the carbon cycle. Researchers are calling for management policies to evolve beyond sustainability calculations and consider the broader impacts on ocean chemistry and global climate.
A Call for Broader Conservation
In light of these findings, scientists are urging a reassessment of krill conservation efforts. Protecting krill populations is not only essential for the predators that depend on them but is also a critical mechanism for maintaining a valuable, natural carbon sink. The research provides compelling evidence that krill habitats should be preserved to safeguard the immense carbon sequestration service they provide for the entire planet.
The conclusion is that the management of the Southern Ocean must evolve. It requires integrating the biogeochemical role of krill into conservation policies and fishery limits. By protecting this keystone species, humanity can help preserve both the rich biodiversity of the Antarctic and a powerful, natural ally in the effort to regulate the global climate.
