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Ancient volcanism drove global warming that marked the end of the Paleocene

Geological evidence extracted from the floor of the Atlantic Ocean affirms a long-standing theory that greenhouse gas emissions associated with volcanism drove catastrophic climate change 56 million years ago.

A new study by an international team of scientists—including University of Utah geologists—examined hundreds of core samples in search of clues to what drove rapid warming that triggered the deep sea die-off marking the transition from the Paleocene to the Eocene epoch. A paper published this month concludes that large volumes of methane—a potent greenhouse gas—escaped from hydrothermal vents on the ocean floor during a period of intense volcanic activity.

U geologists Sarah Lambart and Dustin Harper, second and third from the right, examine cores extracted from the floor of the North Atlantic in 2021. The Utah scientists were part of a research expedition that has produced fresh insights into the volcanism that is believed to have generated extreme climate change 56 million years ago. Also pictured are Reed Scherer, micropaleontologist, Northern Illinois University, left, and Irina Filina, University of Nebraska, right. Credit: Sandra Herrmann, International Ocean Discovery Program.

Around the time the Americas and Europe started spreading apart to form the North Atlantic, Earth’s temperatures spiked by 5 degree Celsius and ocean chemistry changed during a 200,000-year period known as the Paleocene-Eocene Thermal Maximum, or PETM. This resulted in a major extinction event that wiped out a lot of deep marine life and accelerated evolution among terrestrial creatures, with mammal species becoming more diverse.

Ancient analogue for today’s climate change

“This article provides evidence for hydrothermal venting playing a major role in the global warming event that happened during the PETM by showing vents in the North Atlantic erupted in very shallow water and coincided with the onset of the PETM,” said Sarah Lambart, a U professor of geology and geophysics. “While their origins are different, the PETM presents similarities with global warming today in that the sediments that were heated were very rich in hydrocarbons. So this event can be used as a natural analogue for how the Earth system responds to the rapid burning of fossil fuels.”

She noted that today’s anthropogenic climate change is 100 times faster than what transpired at the end of the Paleocene.

Scientists have long believed the PETM was triggered by rapid and massive releases of carbon dioxide (CO2) and methane (CH4) into the atmosphere from geological sources.

Artist illustration of sill emplacement within organic-rich sediments, with the formation of hydrothermal vents and release of CO2 and CH4 in the atmosphere.

Methane is a far more powerful greenhouse gas than carbon dioxide, although it eventually breaks down in the atmosphere. Over short time frames, methane could have a major impact on the climate, and the scientific team thinks that might be the case with the PETM, which coincided with the volcanic-driven continental breakup that created the Atlantic.

Clues buried under the ocean floor

This is because deposits of organic-rich sediments interacted with horizontal magmatic intrusions called sills, causing the formation of geothermal vents.

“Because those sediments are full of organic matter, they will actually release a ton of methane, that could promote global warming even faster,” Lambart said.

Lambart and U researcher Dustin Harper spent two months aboard a specially equipped research vessel, the JOIDES Resolution, off the coast of Norway two years ago as part of a research effort involving scientists from a dozen nations.

Published Aug. 3 in the journal Nature Geoscience, the resulting study shows the vents were active at shallow depths or even above sea level, which would have allowed much larger amounts of methane to enter the atmosphere than previously estimated.

Lambart and Harper are among the study’s 36 authors who joined the drilling expedition in 2021. Marine geophysicists Christian Berndt of GEOMAR Helmholtz Centre for Ocean Research in Germany and Sverre Planke of the University of Oslo led the drilling campaign, which was organized and funded by the International Ocean Discovery Program (IODP).

Expedition leaders and lead authors of the study Christian Berndt, left, and Sverre Planke. Credit: Morgan Jones

Over a two-month period in late summer, the expedition drilled 21 holes from 10 locations including a transect across an ancient vent on which this new study is based. In total, they collected nearly 2 kilometers of core samples. These cores were pulled up in 30-foot lengths, cut into shorter pieces that were sliced in half lenthgwise.

The U geologists helped examine and characterize the hundreds of 1.5-meter core sections pulled up from several kilometers below the ocean’s surface.

“I’m looking at the minerals that are forming within the sediment associated with this release of carbon and carbonate formation,” Harper said, “to get at past environment reconstruction, what was going on in terms of warming, and other important feedbacks in the carbon cycle like ocean acidification and silica cycling.”

The dinocyst Apectodinium augustum, the biomarker of the PETM, observed under microscope found in sediments extracted from the floor of the Atlantic off Norway. Credit: Henk Brinkhuis

The scientists on the ship were also looking for fossils of a microscopic dinocyst known as Apectodinium augustum in the cores to pinpoint the sediments that were deposited during the PETM.

“If you find it, you know you are in the PETM because it was only alive during that period, 56.0 to 55.8 million years ago,” Harper said. “It’s only a 200,000-year window. That’s why it [Apectodinium augustum] is a very useful biomarker.”

How ocean depths matter

Among the study’s most significant discoveries was evidence that the vents were active in shallow water, such as tree debris and other organic matter.

“That can only be preserved if the craters were filled in very shallow water, a few hundred meters,” Lambart said. “It was the beginning of the rifting so you were shifting from a continent to an ocean. The depths can vary a lot. That was part of what we didn’t know, whether it was deep or shallow. Now we know it was shallow.”

Had the methane been released at the depths seen today in the North Atlantic, it would have oxidized into carbon-dioxide, a less potent greenhouse gas, before reaching the surface, according to Harper.

But there is still much to discover to fully understand the geological dynamics that drove the PETM.

“To say it was 100% because of volcanism is difficult because we know there were a variety of carbon-cycle feedbacks. For instance, when you warm up regions that have permafrost deposits you are going to release greenhouse gasses as well,” Harper said. “Those could be contributors still in terms of the abrupt carbon releases we see. We also know it can’t entirely be methane being released. We must have CO2 being released because we see dramatic shifts in marine carbonate chemistry and ocean acidification during that event.”

Analyses of the cores is ongoing and more papers are in the pipeline.

The study, titled “Shallow-water hydrothermal venting linked to the Palaeocene-Eocene Thermal Maximum, can be found here. The research was funded by the International Ocean Discovery Program.