Climate / Other
Ancient ocean study links weaker carbon storage to early Eocene warmth
Nitrogen isotopes in marine fossils point to less efficient biological carbon sequestration.
Status: source-checked.
A study published Nov. 6 links high atmospheric carbon dioxide during an ancient warm period to reduced efficiency of the Southern Ocean’s biological carbon pump. The Nature Geoscience paper examines the Early Eocene Climatic Optimum, about 53 million to 49 million years ago, rather than presenting a direct forecast for today’s climate.
Researchers measured nitrogen isotopes bound within foraminifera fossils in four ocean sediment cores. The results indicate higher concentrations of unused surface nitrate in the Southern Ocean during peak warmth. The authors interpret that as evidence that biological processes were storing carbon less efficiently in the ocean interior.
The biological pump normally lowers atmospheric carbon dioxide by helping retain carbon in the ocean. The study argues that weaker storage, together with the early Eocene ocean’s chemistry and a weakened weathering response, could explain at least half the reconstructed increase in atmospheric carbon dioxide during the warm interval.
The authors emphasize that no known ancient analogue matches the rate of ongoing warming. Future high-latitude ocean circulation remains uncertain and can respond differently over different timescales. Their fossil measurements and modeling help explain an earlier climate state, but the size and timing of its carbon changes cannot simply be transferred to the modern world.
What we know / what we don't
What we know
- Nitrogen isotopes in marine fossils point to less efficient biological carbon sequestration.
What we don't know
- Ancient-climate reconstruction and modeling; not a direct numerical forecast of modern warming.
The source record