Tree rings provide evidence of ancient solar storms, helping scientists predict and prepare for future events that could disrupt satellites and technology. Harsh space weather can leave scars in tree rings, a West Virginia University researcher suggests, providing valuable evidence that could help us prepare for future catastrophic events that could endanger communications satellites and astronauts.

There are many types of unpredictable space weather, including geomagnetic storms that cause auroras near the poles, and ancient tree rings are evidence of some rare and extreme events, says Amy Hessl, a professor of geography at the University of Virginia’s Eberly College of Arts and Sciences. in the distant past.

“If one of these events were to happen today and you were on a high-latitude flight to Norway, you would probably be exposed to a lifetime dose of radiation on board,” Hessl says. “And if you were in space, it could kill you.” Hessl recently received more than $202,000 from the National Science Foundation to study this topic more deeply.

Radiocarbon in tree rings and the Miyake phenomenon

Some events produce solar-energetic particles that form radioactive carbon through a series of reactions in the atmosphere. Hessl says annual tree rings record a history of past solar activity as trees use carbon from the air to make wood. Long tree-ring records going back centuries have revealed evidence of extremely intense storms characterized by rapid increases in the amount of radioactive carbon in the atmosphere, known as the Miyake phenomenon. The first Miyake events, which occurred between 774 AD and 993 AD, were discovered 12 years ago. Since then, the research community has identified seven more events in the last 14,000 years.

“Some of these events were really extreme and could be incredibly disruptive to our telecommunications system right now,” Hessl said. “This is a very rare event but it is not being ignored. We depend on satellites and if this were to happen again most of our telecommunications systems would probably be destroyed and it would take 15 years to restore. It is that powerful.”

Solar flares cause most energetic particle events hitting Earth, but particles can also come from galactic cosmic rays outside the Solar System, often initiated by explosions such as supernovae. While most evidence points to the Sun as the source of Miyake events, Hessl hopes that tree ring records from around the world will help the scientific community determine the causes of the events and determine how severe the events were.

Difficulties in interpreting tree ring data

The problem is that the data recorded in tree rings may not be as simple as researchers previously thought.

“Until recently, scientists thought that trees absorbed radiocarbon equally,” says Hessl. “We treated the trees as if they were scientific instruments. But it is not like that. They are potentially very biased in how they absorb radiocarbon. So we investigated why different tree species or trees in different locations absorb radioactive carbon in different ways. “When you look at the data later, you better understand how reliable this recorder is.”

Evidence from Miyake events also suggests that some trees store carbon that they later release, making them less reliable recorders of atmospheric chemistry. To understand why, Hessl and her colleagues (Maria Carbone of Northern Arizona University and Rachel Filvett of Montana State) examined how consistently different trees recorded atmospheric radiocarbon on an annual scale. They found three sites in the United States where wood dates back to at least one of the last three major Miyake events and where they could study the physiology of the same species in living trees.

Examination of different tree species

“We are studying three species with very different physiological strategies for wood production,” says Hessl. “The bristlecone pine, an evergreen conifer native to Utah, is the longest-lived tree species in the world. They live for several thousand years and form the basis of what we know about the past content of radiocarbon in the atmosphere. We know what its past level was because of them, and they are the most studied.”

The team will be able to compare Utah’s bristlecone pines to North Carolina’s deciduous bald cypresses and protected oaks in Missouri riverbeds. After taking a pencil-sized core sample (or a cross-section if the tree is dead), they will date each ring by year using cross-dating, an independent dating method that allows scientists to verify the year each ring formed. Any tree that was alive during one of Miyake’s events would have recorded those events according to its ring chemistry. But Hessl says he expects not all trees do this the same way.

“We are trying to determine how extreme these events are,” Hessl said. “Exactly when did they happen? How much radioactive carbon remained in the atmosphere? We need to make sure we use reliable recording companies, and that’s exactly what we’re trying to find out. How reliably do these trees record the level of radiocarbon in the atmosphere?”

By examining how different trees record past events and how they absorb radioactive carbon today, Hessl hopes to better understand how to prepare for future events, including ones intense enough to threaten technological infrastructure. Although the Miyake incident is extreme and unlikely, the important thing is to prepare in advance, he said.

“Some things are a bit exaggerated, but we saw what happened during the pandemic in terms of the initial panic. So it would be very smart to try to figure out what the upper limit of these things is and then communicate that to the IT community so we can ensure that our technology is protected.”

The research was funded by the US National Science Foundation.