Source: Global Biogeochemical Cycles
The biological carbon pump moves carbon from near the ocean’s surface to deeper regions, maintaining the upper ocean’s ability to absorb carbon from the atmosphere. One component of this system is driven by eddies, or relatively small-scale circular water currents powered by physical instabilities within the ocean. Previous estimates have suggested the eddy subduction pump may play a large role in moving carbon deep into the ocean, but the absence of global synthesis leaves the question open.
With data from a worldwide network of remote sensors, Keutgen De Greef et al. captured the eddy subduction pump in action around the globe. Their analysis shows that this pump carries less than 5% of the overall organic carbon transported by the biological carbon pump, meaning it’s of secondary importance to understanding ocean carbon flows.
The authors used data spanning 2010 to 2024 from 941 Argo floats drifting autonomously around the globe. They found 1,333 eddy subduction events below 200 meters. Adding up the contribution of a subset of these they identified as carbon subduction events, they estimated the eddy subduction pump exports 0.05 petagram (~50 million metric tons) of carbon per year from the ocean surface. Carbon subduction hot spots exist at mid- to high latitudes in the Southern Ocean and subpolar North Atlantic, both of which also exhibited a strong seasonal peak in spring. The authors also noted a correlation between eddy kinetic energy and physical subduction events (when surface waters sink below the mixed layer), providing insights into the mechanisms driving the eddy subduction pump
The study comes with some limitations, including the sparsity of data in ocean regions including much of the Pacific, the South Atlantic, and the southern Indian Ocean, which could lead to those regions’ contributions being underestimated. The Argo floats measure particulate carbon levels but are unable to effectively measure dissolved organic carbon, meaning some carbon export is being missed. But given the minimal contribution of the eddy subduction pump, these factors may not significantly change estimates of overall biological carbon subduction, the authors suggest. (Global Biogeochemical Cycles, https://doi.org/10.1029/2025GB008912, 2026)
—Nathaniel Scharping (@nathanielscharp), Science Writer
