A chemical analysis of sediment cores from the North Pacific Ocean show a consistent pairing of volcanic ash and hypoxia, a low ocean oxygen interval spanning thousands of years, during times of rapid climate warming at the end of the last ice age, new research shows.
Understanding the relationship between volcanic activity, hypoxia and ice melt due to warming temperatures during the last ice age, which ended about 18,000 years ago, raises important questions about what might occur as the planet warms today.
“It is unknown right now whether volcanic eruptions will increase as the climate warms,” said the study’s lead author, Jianghui Du of ETH Zurich in Switzerland, who conducted the research as a doctoral student at Oregon State University’s College of Earth, Ocean, and Atmospheric Sciences. “But we know that the remaining glaciers on volcanoes in the Pacific Ocean ring of fire are melting fast, and it will be important to include this ice loss in predictions of future eruptions, which would be risky for populated regions and could also make emerging hypoxic dead zones in the North Pacific worse.”
The volcanic region in the Pacific Ocean is known as the ring of fire in part because it is one of the most active tectonic and volcanic regions of the world. The timing of volcanic events in relation to the retreat of the Cordilleran Ice Sheet, which once covered large portions of western North America, suggests that the rapid melting of ice covering volcanoes in the region induced increased volcanic activity, according to Alan Mix, an oceanographer and paleo- climatologist at Oregon State and a co-author of the paper. “Ice cover to volcanoes is like a cork in a champagne bottle. Remove the icy cork and boom, the eruptions begin,” he said.
Past research had shown a few ash layers in sediment in the region, but Du’s chemical study, using deep-sea sediment cores from the Gulf of Alaska, revealed more traces of ash that were not visible to the eye. Du catalogued and compared volcanic eruptions from areas that were covered in ice against those areas that were not ice-covered during the last ice age. The chemical fingerprints also showed a consistent pairing of volcanic ash and hypoxic events. The increase in volcanic ash likely fueled ocean productivity that ultimately created low-oxygen conditions.
