Northwestern University Researchers Link Volcanic Eruptions to Ancient Extinction

A 113-million-year-old marine mystery has finally met its solution. Scientists at Northwestern University uncovered chemical evidence proving that ocean acidification drove one of the most severe extinction events in the history of planktic foraminifera, microscopic shell-building organisms vital to Earth’s carbon cycle.

Volcanic Eruptions and the Kerguelen Plateau Connection

The root of the ancient catastrophe traces back to the Kerguelen Plateau, a massive volcanic province located in the southern Indian Ocean. During the Early Cretaceous period, volcanic activity released massive quantities of carbon dioxide into the atmosphere. As ancient oceans absorbed those emissions, seawater turned increasingly acidic, making it exceedingly difficult for marine organisms to build and maintain protective shells.

The study marks the fifth Northwestern-led investigation connecting widespread volcanic activity to ancient ocean acidification and mass extinctions. The findings establish a recurring pattern spanning more than 60 million years of Earth’s history.

Calcium Isotopes Reveal Biocalcification Stress

Scientists previously knew that surface plankton shrank and grew thinner shells during the period, signaling severe biological stress. However, proving that ocean acidification was the primary culprit remained elusive until now.

“By examining fossils, scientists already knew surface plankton were getting smaller and building thinner shells, which suggested they were under stress, but we didn’t know that ocean acidification was responsible. By measuring the fossils’ calcium isotopes, we finally provided that missing evidence. We found a giant increase in calcium isotope ratios right as the extinction unfolded, indicating the organisms’ shells were calcifying at a much slower rate. That was the smoking gun linking ocean acidification to the severe biocalcification stress that ultimately led to their extinction.”

Jonathan Chen, recent graduate and study leader at Northwestern

The research team examined hundreds of fossilized specimens collected from sediment samples originally gathered in the 1980s from a Deep Sea Drilling Project site on the Falkland Plateau in the South Atlantic. Obtained via the Smithsonian Institution, the tiny fossils—each roughly the size of a single grain of sand—required painstaking separation using a fine-tipped brush.

Differential Impacts on Surface and Seafloor Organisms

The Aptian-Albian boundary extinction event devastated surface-dwelling planktic foraminifera, ranking second only to the asteroid-triggered extinction at the end of the Cretaceous period. Yet, remarkably, benthic foraminifera living on the seafloor managed to survive the crisis.

For decades, this dichotomy caused debate among researchers regarding whether acidification could be the main driver, since seafloor dwellers seemingly escaped unhurt. By isolating pristine shell material and analyzing calcium isotope ratios, researchers confirmed the severe carbon-sink disruption.

“They act as a fundamental stabilizing force in the carbon cycle. If we didn’t have this carbon sink anymore, our carbon cycle would be altered in unimaginable ways.”

Jonathan Chen, Northwestern

Modern Climate Parallels in Ancient Data

Beyond resolving a prehistoric puzzle, the research offers a natural experiment for evaluating contemporary environmental pressures. As modern oceans absorb human-generated carbon dioxide, the historical record provides researchers with clear benchmarks for understanding how ongoing acidification impacts shell-building marine species and interconnected ecosystems.