Volcanic activity and episodes of low ocean oxygen linked to global warming and rapid ice melt during the last ice age

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A chemical analysis of sediment cores from the North Pacific Ocean shows a consistent pairing of volcanic ash and hypoxia, a low ocean oxygen condition spanning thousands of years, during periods of rapid global warming at the end of the last ice age, new research published today in Nature shows.

Understanding the relationship between volcanic activity, hypoxia and melting ice due to warming temperatures during the last ice age, which ended around 18,000 years ago, raises important questions about what that could happen when the planet warms up today.

“It is currently unclear whether volcanic eruptions will increase as the climate warms,” said study lead author Jianghui Du of ETH Zurich in Switzerland, who led the research. as a doctoral student at the College of Earth, Ocean, and and at Oregon State University. Atmospheric sciences.

“But we do know that the remaining glaciers on volcanoes in the Pacific Ocean’s Ring of Fire are rapidly melting, and it will be important to include this ice loss in forecasts of future eruptions, which would be risky for scientists. populated regions and could also make hypoxic dead zones in the North Pacific worse.”

The results indicate a systematic relationship between climate, glacier retreat, volcanic activity, biological productivity and ocean deoxygenation, said Alan Mix, an oceanographer and paleoclimatologist at Oregon State and co-author of the ‘article.

“These surprising connections between parts of the Earth that we usually consider distinct show how interconnected the whole system really is,” he said. “Solving environmental problems, such as those we face in the current climate crisis, requires that we look with an open mind at the whole linked system and not just isolated parts.”

The volcanic region of the Pacific Ocean is known as the Ring of Fire in part because it is one of the most active tectonic and volcanic regions in the world.

The timing of volcanic events relative to the retreat of the Cordilleran Ice Sheet, which once covered large parts of western North America, suggests that the rapid melting of ice covering volcanoes in the region induced increased volcanic activity, Mix said.

“The ice cover of volcanoes is like a cork in a bottle of champagne. Pull out the icy cork and boom, the eruptions begin,” he said.

Previous research had shown a few layers of ash in the sediments of the area, but Du’s chemical study, using deep-water sediment cores from the Gulf of Alaska, revealed more traces of ash that were not visible to the naked eye.

Du cataloged and compared volcanic eruptions from ice-covered areas with those from areas that were not ice-covered during the last Ice Age.

“We found a distinct pattern of many eruptions during ice warming and retreat in areas where glaciers were present, and much less change in eruption frequency outside the ice-covered zone, particularly in the ice-covered area. western North America,” Du said. “This provides strong evidence for volcanic response to warming and retreating ice.”

Chemical fingerprints also showed a consistent pairing of volcanic ash and hypoxic events. Increased volcanic ash likely fueled ocean productivity, which ultimately created low oxygen conditions.

Texas A&M University co-authors Christina Belanger and Sharon (who only use one name) examined a species of seafloor organisms called foraminifera and found that they closely track the intake of volcanic ash from the Gulf of Alaska. These organisms thrive in highly productive waters and can tolerate low oxygen conditions.

“Volcanic ash contains important trace minerals for plankton, especially iron,” said co-author Brian Haley, a research professor at Oregon State.

“When the ash reaches the ocean, plant plankton engulf this iron and bloom. This fertilization effect points to a practical application of our work. Some have proposed fertilizing the North Pacific with iron to capture excess carbon dioxide of the atmosphere,” he said. .

“We show that the real world has indeed conducted this experiment in the past with volcanic iron, and that the fertilization effect works and exports carbon to the deep sea. This is good news. But there are consequences dangerous because when this excess organic matter decomposes into it falls to the depths of the ocean, it consumes oxygen and creates dead zones.”

More information:
Jianghui Du, volcanic trigger for ocean deoxygenation during Cordilleran ice sheet retreat, Nature (2022). DOI: 10.1038/s41586-022-05267-y.

Provided by Oregon State University

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