Carbon ‘burps’ from Earth’s past warn of ocean trouble ahead

Roughly 300 million years ago, long before dinosaurs roamed the land, Earth’s atmosphere underwent a series of sudden carbon dioxide surges. Each burst – dubbed a “carbon burp” by geoscientists – was followed by an ominous drop in ocean oxygen.

In a new study, researchers from the University of California, Davis, the Chinese Academy of Sciences, and Texas A&M University show that these episodes cut global ocean oxygen by as much as 12 percent, enough to stall marine biodiversity for hundreds of thousands of years at a stretch.

“This is our only analog for big changes in carbon dioxide at levels comparable to what we’re living in today, where we see doublings and triplings of the levels,” said senior author Isabel Montañez, a professor of Earth and planetary sciences at UC Davis.

Signs of past ocean loss

The team drilled into a famous geological archive known as the Naqing succession in South China. Layer by layer, the cores preserve chemical snapshots of a 20-million-year window between 310 and 290 million years ago.

By measuring uranium isotopes locked inside carbonates, the scientists reconstructed how much of the global ocean became breathless – what researchers call “anoxic” – during each CO2 surge.

“Through that analysis, we see these ‘burps’ not just in carbon dioxide but in the ocean’s uranium isotope signature too,” Montañez explained. “They’re totally aligned, and the size of those uranium spikes tell us about the magnitude of the ocean anoxia.”

Five distinct events emerged from the data. Each one coincided with atmospheric CO2 increases large enough to force a four-to-twelve-percent drop in dissolved oxygen, conditions severe enough to stress marine life even in an era when atmospheric oxygen was far higher than today’s.

Supercomputers model CO2 spikes

To translate those chemical fingerprints into a planet-wide narrative, co-author and climate-model specialist Chen-Xiao integrated the proxy data into a suite of advanced simulations.

“It’s a mathematical framework in which we put in all our proxy information and we run it hundreds of thousands of times on a supercomputer,” Montañez said.

The exercise confirmed that each carbon pulse likely lasted 100,000 to 200,000 years, long enough to halt evolutionary diversification in the marine fossil record.

“We do see these pauses in biodiversity each time these burps happen,” she noted, adding that although no mass extinction aligns perfectly with the events, the stops and starts echo through Paleozoic reef communities and other marine ecosystems.

Natural vs. human burps

Back then, the main culprit behind sudden CO2 spikes was rampant volcanism tied to the assembly of the supercontinent Pangea.

Today the trigger is very different: fossil fuels, cement production, deforestation, and other human activities pushing atmospheric carbon upward at a speed the geological record rarely, if ever, matches.

“We’re creating a burp now and at a rate two, maybe three, orders of magnitude faster than in the past,” Montañez said.

Put another way, the modern ocean could experience oxygen losses comparable to those ancient downturns – but compressed into mere centuries rather than millennia.

Today’s oceans at risk

If a four-to-twelve-percent global drop in ocean oxygen unfolded today, the first casualties would be coastal food webs that sustain major fisheries from the Gulf of Mexico to the Bay of Bengal.

Low-oxygen zones already appear more frequently in warming seas, squeezing habitats for species such as cod, anchovy, and squid.

The study suggests these dead zones could grow far larger if humanity continues to pump carbon into the sky unchecked.

“This is a huge discovery because how do you take an ocean sitting under an atmosphere with much more oxygen than today and permit this?” Montañez said.

In other words, high atmospheric oxygen couldn’t prevent ancient anoxia, and it won’t save modern oceans from the same fate.

Ocean change tied to carbon

The Paleozoic record offers no neat rescue plan, only a warning that Earth’s systems can respond dramatically to carbon overload.

“The message for us is, ‘Don’t be so sure that we can’t do this again with our current human-driven release of carbon dioxide,’” Montañez said.

The study’s blend of uranium isotope chemistry and high-resolution modeling now provides a template for tracking ancient ocean oxygen with far greater precision.

Armed with that deep-time perspective, scientists and policymakers can better judge how today’s emissions trajectory might play out beneath the waves.

Whether humanity heeds the ancient alarm – or repeats history on fast-forward – remains an open question.

The study is published in the journal Proceedings of the National Academy of Sciences.

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