News Release | 30-Jul-2026 | Northwestern University

A 113-million-year-old marine mystery has been solved using chemical analysis of microscopic fossils. Northwestern University scientists discovered that ocean acidification triggered one of the largest extinction events in planktic foraminifera history — tiny organisms that build shells and help regulate Earth’s carbon cycle.

The team attributes the acidification to eruptions from the Kerguelen Plateau, a massive volcanic province in the southern Indian Ocean during the Early Cretaceous. These volcanic eruptions released vast quantities of carbon dioxide into the atmosphere. As oceans absorbed the CO2, seawater became more acidic, making it difficult for marine organisms to build and maintain their shells.

By measuring calcium isotopes in fossilized shells, researchers found “a giant increase in calcium isotope ratios right as the extinction unfolded,” according to lead author Jonathan Chen. This indicated that shell calcification rates dramatically slowed during the extinction interval.

The study marks the fifth Northwestern-led investigation linking volcanic eruptions to ocean acidification and extinction. The findings provide insight into how rising CO2 alters ocean chemistry and affects shell-building organisms.

Benthic foraminifera on the seafloor experienced milder effects than surface-dwelling planktic species, suggesting the deeper ocean was less severely acidified. The CO2 entered the atmosphere first and dissolved into surface waters before reaching the ocean depths.

This discovery strengthens understanding of how modern ocean acidification from human-generated CO2 might affect marine ecosystems and the organisms that depend on ocean chemistry.

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Journal: Science
DOI: 10.1126/science.aed9359
Article Title: Calcium isotopes link ocean acidification to Aptian/Albian foraminiferal extinctions
Publication Date: 30-Jul-2026

Source: EurekAlert