Ancient oceans began suffocating millions of years before Triassic mass extinction

One of the most devastating extinctions in Earth’s history is best known for what didn’t die — dinosaurs.

But the end-Triassic extinction 201 million years ago wiped out roughly 60 percent of Earth’s species, and scientists are still piecing together how it unfolded.

New evidence from Virginia Tech geologists shows that the volcanic eruptions that ripped apart the land and acidified the oceans also stripped the oxygen out of their waters.

And, in an unexpected finding, the research team discovered that oxygen starvation began nearly 8 million years before the mass extinction.

Their study was published May 26 in Nature Communications Earth & Environment.

Hot planet, cold case

Scientists have long linked the end-Triassic extinction to massive volcanic eruptions that warmed the planet and set off cascading environmental changes.

In a warmer climate, rocks break down faster and release nutrients that increase ocean acidity. Warmer seawater also holds less oxygen, creating dead zones.

More acid and less oxygen is “kind of like a one-two punch,” said geochemist Ben Gill. “It wouldn't have been a very happy place to be.”

Until now, evidence for widespread marine deoxygenation came from a limited geographic area, leaving questions about when and where it began. Plus, there was something of a mystery associated with recent studies suggesting that environmental deterioration might have started a lot earlier than previously believed.

“It's a 200-million-year-old cold case,” said Kayla McCabe, a former geosciences graduate student and first author of the study.

Consulting the ancient ocean

To answer those questions, the Virginia Tech team members turned to the rock record.

In 2017, 2019, and 2022, they traveled to Grotto Creek in Alaska’s Wrangell–St. Elias National Park, a remote site accessible only by small aircraft.

There, they compared sedimentary rock layers deposited before, during, and after the extinction.

The rock layers preserve a record of past ocean conditions, like pages in a book. Flipping back through time revealed that oxygen levels in shallow oceans began to decline about 8 million years before the end-Triassic mass extinction.

That early loss of oxygen likely stressed marine ecosystems long before the main extinction event.

It got worse later. Geochemical analyses show that oxygen loss intensified during the extinction itself and became a major driver of species loss.

But what caused the apocalyptic opening act?

“There's evidence of another volcanic province that roughly lines up with this time interval,” Gill said. “But we're in the very beginning of trying to understand what happened.”

Scientists may not yet know the cause, but they know how it played out. Which means we have a rough guide for the future, as our oceans are again undergoing acidification and deoxygenation — including in the Chesapeake Bay. 

“Earth has run this experiment in the past. We have evidence that the climate gets warmer, and then all these other knock-on effects come afterwards,” Gill said. “It gives us some sense of what we can expect to happen.”

Study collaborators included:

• Selva M. Marroquín, former graduate student, now faculty at University of Wisconsin-Madison
• Rachel E. B. Reid, research assistant professor, Department of Geoscience, Global Change Center

This research was supported with funding from:

• National Science Foundation
• National Geographic Society
• Alaska Geological Society
• Virginia Tech Department of Geosciences
• Virginia Tech College of Science Dean’s Discovery Fund

Original study DOI 10.1038/s43247-026-03362-w

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