A Rutgers-led study finds that “cryptic carbon” in the underground portions of enormous volcanic provinces helped warm the climate at key times in Earth’s past.

An international geoscience team led by a Rutgers University-New Brunswick volcanologist has found that, contrary to current scientific understanding, ancient volcanoes continued to spew carbon dioxide into the atmosphere from deep within the Earth long after their eruption period.

In doing so, the research team solved a long-standing mystery about the causes of prolonged episodes of warming during turning points in Earth’s climate history. Work is detailed in today’s issue of the magazine Geoscience of nature.

“Our findings are important because they identify a hidden source of CO2 in the atmosphere at times in Earth’s past when the climate warmed suddenly and stayed warm much longer than expected,” said Benjamin Black, who led the study and is an associate professor in the Department of Earth and Planetary Sciences in the School of Arts and Sciences. “We think we’ve uncovered an important piece of the puzzle for how Earth’s climate was disrupted and, perhaps just as importantly, how it recovered.”

Today, humans release far more carbon dioxide than all active volcanoes combined, but the new findings could shed light on how the planet’s climate will recover if and when human carbon dioxide emissions decline. “Earth has natural climate control systems — kind of like the thermostat in your house,” Black said. “The question is: Are there thresholds beyond which those climate control systems start to break down, making climate recovery that much more difficult?”

For decades, scientists have been puzzled by climate records showing the failure of Earth’s atmosphere to recover as quickly as expected after what is known as the end-Permian mass extinction in 252 million years ago – the most severe decline in biodiversity known to have occurred on Earth. The mass extinction was linked to huge volcanic eruptions in Siberia. Even after the eruptions stopped, Earth’s climate took nearly 5 million years to stabilize.

“This delayed recovery has long puzzled scientists. Earth’s natural thermostat appears to have gone haywire during and after this event,” Black said. “We noticed that a similar pattern seemed to have occurred at several other times in Earth’s history with massive volcanism, and we set out to understand why.”

Black and an international team of colleagues looked back in time and found evidence for carbon dioxide emissions from this type of volcanic province that could last millions of years after most surface eruptions have ended. They did this by compiling chemical analyzes of the lavas, developing computer models that simulate melting in the Earth’s interior, and comparing the results to records of past climates preserved in sedimentary rocks.

Analyzes have shown that massive ancient volcanic provinces are slowly closing. On the surface, eruptions have stopped, but deep in the crust and mantle, magma is still releasing carbon dioxide, leading to prolonged climate warming.

“We call this CO2 from underground magma ‘cryptic carbon’ because it comes from magmas that are hiding deep in the system,” Black said. “It’s like volcanoes releasing carbon from beyond the grave.”

Black said the findings in the new study are significant because they identify a hidden source of atmospheric carbon dioxide at times when the climate warmed suddenly. If volcanoes continued to “raise the temperature,” it could mean that Earth’s thermostat might be working better than scientists thought.

“If this is true, it could be good news for Earth’s recovery from human-induced climate warming,” Black said. “It means that if we stop turning up the thermostat, over geologic timescales of hundreds of thousands to millions of years, the climate can recover.”

Black pointed out that cryptic carbon from volcanoes cannot explain current climate change. “The type of volcanism we’re investigating is rare, capable of generating enough magma to cover the continental United States half a kilometer deep in lava,” Black said. “This type of volcanism has not occurred for 16 million years. All the volcanism occurring on the planet today releases less than 1% as much carbon dioxide as human activities.”

But scientists still hope to learn from these past eruptions about current and future climate. “These ancient eruptions appear to be some of the only events in Earth’s history that break free carbon on the same scale that humans do today,” Black said. “So by studying these eruptions in the deep past, we can learn more about how Earth’s climate systems respond to the massive release of carbon into the atmosphere.”

These findings are just the beginning of a multi-year effort funded by the National Science Foundation to investigate how cryptic carbon might influence recovery from major disruptions in Earth’s climate. This summer, the team went to North-Eastern Oregonwhere massive volcanism was linked to climate warming 16 million years ago. Scientists focused on the Wallowa Mountains, which are laced with enormous sheets of flat magmatic dikes, created when molten rock flowed into cracks and solidified. Due to erosion, the area known as the “Oregon Alps” exposes these rocks that once constituted magma deep in the Earth.

Team members, including Black and colleagues and graduate students from Rutgers and other universities who are part of the National Science Foundation-funded team, climbed mountains ranging in elevation from 5,000 to 9,000 feet and sampled the material like glass at the edges of the dykes. They were created when magma came into contact with the cooler surrounding rocks. Back in their labs, the researchers look for evidence in the glassy rocks of ancient emissions of carbon dioxide and other gases.