Arctic volcano caused ancient global cooling | Polarjournal
The Aniakchak volcano on the Alaska Peninsula (here the caldera) may be responsible for one of the most violent volcanic eruptions in the last 4,000 years. It is located in a region that belongs one of the most active volcanic regions in the world. Image: M.Williams_Alaska_National_Park_Service via Wikicommons

When in 1627 BC a volcanic eruption practically tore apart the ancient island of Thera, people at that time thought that the world was ending. The eruption was followed by a so-called “volcanic winter”, during which the global climate cooled noticeably for a short time. Until now, scientists assumed that the eruption on Thera was responsible. But a new study by an international research team with Swiss participation comes to a different conclusion and locates the cuplrit in Alaska.

The team, led by Charlotte Pearson of the University of Arizona and Michael Sigl of the Oeschger Center for Climate Research at the University of Bern, discovered strong evidence in tree rings and in ice cores from Greenland and Antarctica that the former Aniakchak volcano on the Alaska Peninsula had erupted around the same time period. The eruption, which experts count among the strongest in the Northern Hemisphere in the past 11,700 (Holocene) years, must have been so massive that more than 100 megatons of sulfur dioxide were ejected into the atmosphere, causing a rapid cooling of the global climate.

Using analysis of tree rings from the Great Basin bristlecone pine Pinus longaeva (the dark band is the frost of volcanic winter) from California and sulfuric acid droplets in ice cores from Greenland and Antarctica, the team was able to show that the eruption of Aniakchak was strong enough to affect global climate. Images: Crater: Google Earth / NASA, Methods: Charlotte Pearson / Michael Sigl

Until now, the global cooling in 1627 BC was attributed to the eruption of Thera. This has proven to be wrong.

Professor Dr. Michael Sigl, Oeschger Center for Climate Research, University of Bern

Climate and environmental physicist Professor Michael Sigl, together with scientists from the U.S., the U.K., Italy and Switzerland, analyzed inclusions of sulfuric acid droplets in ice cores originating from Greenland and Antarctica as part of research on volcanic eruptions from the past and their influence on global climate. Through geochemical analysis of the inclusions and a comparison of data with tree rings from samples of the Great Basin bristlecone pine (Pinus longaeva), considered the oldest life form in the world at more than 4,000 years old, the team was able to show that the sulfur inclusions are not consistent with the Mediterranean outbreak. Rather, were associated with an eruption of Aniakchak, a volcano on the Alaska Peninsula and part of the Pacific Ring of Fire. “Until now, global cooling in 1627 B.C. had been attributed to the eruption of Thera,” says Professor Sigl. “That turned out to be wrong. We were able to show that a colossal eruption of Aniakchak was responsible.”

Although the two volcanic craters Aniakchak (left) and Thera (right) both have similar dimensions and the one in the Mediterranean must have been devastating as well. But geochemical analyses assign responsibility for global cooling to the volcano in Alaska. Images: left Google Earth / right: NASA /EOS

The timing of the eruption of the volcano on the island of Thera, also known as the “Minoan eruption,” and its impact on the subsequent cooling of the Earth has long been worked on, including by Charlotte Pearson, the lead author of the study. With their findings, the research team believes, the debate over who caused the cooling, which also brought widespread social upheaval to the Mediterranean region, should now be resolved. Because, although the eruption on Thera was massive, only the eruption of Aniakchak managed to throw so much sulfur dioxide about 40 kilometers high into the atmosphere that it could be transported from there around the globe. The eruption, experts are convinced, is likely to be one of the most violent in the past 4,000 years or even 11,700 years and left behind a blast crater more than 10 kilometers in diameter.

The volcano Aniakchak is located on the Alaska Peninsula and was probably still active after the eruption in 1628 BC. Michael Sigl and other researchers were able to document eruptions in ice cores from Greenland even more than 1,600 years later. Image: Michael Wenger via Google Earth

Professor Michael Sigl is no stranger to the Aniakchak volcano. Already last year, the researcher published a paper in which he was able to show how explosive the mountain in Alaska must have been. He was able to prove that deposits in Greenland ice cores, often used for dating, must be attributed to a violent eruption of Aniakchak rather than the famous Vesuvius eruption. This shows that the volcano in Alaska, which is now a national monument, has not only an explosive history, but also a far-reaching one.

Dr Michael Wenger, PolarJournal

Study link: Pearson et al (2022) PNAS Nexus pgac048 Geochemical ice-core constraints on the timing and climatic impact of Aniakchak II (1628 BCE) and Thera (Minoan) volcanic eruptions;

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