For years, Charlotte Pearson and her colleagues at the University of Arizona Laboratory of Tree-Ring Research have used tree-ring science to travel back in time, hoping that clues from the past will help them better understand the present and perhaps predict the future. 

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Peering into both living and centuries-old trees that were alive long ago, U of A scientists have led the field of tree-ring science since the early 1900s. Tree rings – etched, circular ridges that mark annual growth – can record and reveal what a tree and its environment experienced, including impacts from climate, earthquakes, fires, insect infestations and even bursts of solar particles from the sun. Those particles can eventually help create carbon-14, a radioactive version of carbon that can combine with oxygen to form carbon dioxide that trees breathe in.

“The pattern of tree rings forms a barcode through time that can be matched across regions where a specific climate pattern is in control,” said Pearson, an associate professor of dendrochronology (the study of tree-ring dating). “Much of the work we do is dating and reconstructing climate. We’re constantly pulling out new information.”

And asking new questions. With funding from the Big Idea Challenge, Pearson is leading a new team to study solar hazards and seismic geological hazards. The recently opened $4 million TIME Lab is a key part of the research. The lab employs the latest mass spectrometry technology to analyze radiocarbon in tree-ring samples in finer detail than was possible before.

“The power of tree-ring data to unlock the secrets of the past and help us better prepare society for the solar and seismic events of today exemplifies the innovative and cross-disciplinary nature of the Big Idea Challenge,” said Tomás Díaz de la Rubia, senior vice president for research and partnerships at the U of A. “The program has provided new opportunities for experts in wide-ranging fields, from plant science and geology to space physics, to explore new collaborations aimed at solving complex problems.”

In the first part of the project, researchers are using tree rings to better understand ancient solar storm patterns and perhaps ultimately predict new solar storms.

The sun generates a powerful magnetic field that rises and falls in strength over an 11-year cycle. In solar storms, violent bursts of protons from the sun collide with nitrogen in the atmosphere, resulting in spikes of carbon 14, or radiocarbon. Pearson and her team want to help better prepare for the potential effects such storms might have on satellite infrastructure, power grids and other critical technologies.

“Carbon 14 gets into trees through photosynthesis and is locked away in a series of time capsules of radiocarbon,” Pearson explained. “These tree rings can be dated – we can put a calendar year on a tree ring. This gives us a way to get into the patterns of solar cycles and solar storms over long timescales that can be useful for space-weather research.”

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In analyzing the radiocarbon levels, scientists have found evidence of periodic major solar storms over the last 14,000 years. 

To Pearson, the most exciting part of the work is bringing together different people with different perspectives. One of those people is Joe Giacalone, professor in the Lunar and Planetary Laboratory at the College of Science.

Giacalone’s research into solar physics and space physics includes studying the origin of large solar-energetic particle events, or solar cosmic rays. He has written papers describing the propagation of solar-flare particles from the Sun to the Earth where they are observed by spacecraft.

“Tree-ring science allows us to ask questions about solar storms that we couldn’t otherwise examine by our current observation methods,” Giacalone said. “The tree ring record has information in it that represents a gold mine. The Big Idea Challenge has opened new doors for us to talk to our Tree-Ring Lab colleagues to look for answers.”

Bringing ancient forests back to life

In the second part of the Big Idea Challenge project, Bryan Black, associate director of the Tree-Ring Lab and professor of dendrochronology, will use tree ring radiocarbon dating to uncover new details about ancient seismic activity in the Pacific Northwest. The team is hoping that reconstructing past earthquake patterns in existing fault lines will help them better anticipate new, possibly devastating earthquakes and reduce their impact. 

Black leads a team of researchers who are literally diving into ancient lakes and forests in the Pacific Northwest to trace the past lives of earthquakes and fault lines. They hope to use the information they glean from dead and buried trees, many of which are underwater in lakes, to understand how old earthquakes behaved. Part of the puzzle centers on how interconnected, widespread and active the fault networks are along the Pacific Coast. 

The TIME Lab’s new analysis techniques allow the researchers to refine the use of tree-rings in dating trees in forests buried under earthquake-caused landslides and reconstruct earthquake patterns. 

“The goal is to better understand the interval of time between earthquakes and the behavior of the Cascadian Subduction Zone,” he said. “We want to understand what happened in the past to get a sense of the potential for a similar event to repeat in the present. The new lab lets us address questions that couldn’t be addressed any other way.”

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The Cascadian Subduction Zone is an offshore, underwater fault line stretching from northern California to British Columbia. It’s the longest contiguous fault line in North America. Black’s team already had been studying a more recent earthquake that occurred on the fault in 1700. 

“There are questions about how the earthquake behaved that only trees can answer,” Black said. “Did it rupture all at once in a magnitude 9 earthquake or in segments, in a series of magnitude 8 earthquakes over years in what’s known as the ‘decade of terror’ hypothesis?” 

The team currently is exploring the use of a different dating technique to determine whether trees in California died a year or more earlier than those in Washington State. They are testing whether the southern part of Cascadia ruptured first, followed later by the northern part of the fault.

Using support from the Big Idea Challenge, the team also wants to determine the exact year spruce trees were killed in two earlier Cascadia earthquakes that occurred roughly 1300 and 1600 years ago. The researchers have samples of spruce wood with bark from two different sites for each earthquake. If the trees at the two sites died in the same year, it would suggest the fault ruptured simultaneously at both sites in one large earthquake. If the evidence suggests the trees died in different years, it would indicate there were two separate, smaller earthquakes. 

There aren’t any tree ring chronologies that date back that far in the region, so the TIME Lab team is harnessing the patterns of solar activity in trees. 

“Instead of matching climate barcodes in tree rings, which are limited to a specific region, we are matching patterns from the sun, which are present in any tree, anywhere in the world during the same years,” Pearson said.

The new tree-ring dating approach based on solar cycles – Pearson’s project – is made possible by the TIME Lab and fuels both parts of the Big Idea Challenge project. For the earthquake research, the solar patterns in the trees assist scientists in dating trees – and earthquakes – that cannot be dated by radiocarbon or tree-ring dating alone. The new dating method allows them to measure radiocarbon from solar activity recorded in Cascadia trees in such detail that they can then match their recorded single-year solar activity patterns with trees in other parts of the world.

“No one has done this single-year radiocarbon dating technique before. Now, we can run long series of radiocarbon measurements of every tree ring and pair them to the year-by-year dating of the trees we do have continuous records for,” Black said.

This should provide the exact year the earthquake occurred and the trees died. Both parts of the project have specific real-world applications. 

“Massive solar storms are a threat to our near-earth satellites. We need to understand if what we think we’re seeing in this record really does represent that threat,” Pearson said. “With these patterns of single-year radiocarbon, tree rings can show us the solar cycle and when the sun has a flare or mass ejection, and they can also provide patterns that are the key to pinpointing the timing of massive earthquakes – events that have significant consequences for society.”