Extending tree-ring science from forests to oceans at the University of Arizona
Courtesy of Bryan Black
The past isn’t only written in tree rings. It’s etched into the shells of clams and the bones of fish—natural timekeepers that preserve centuries of environmental history.
Dr. Bryan Black, professor and associate director of the University of Arizona’s Laboratory of Tree-Ring Research, has built his career on learning to decode those hidden records.
Trained as a forest ecologist in the Appalachian Mountains, Black once studied the history of forests through tree rings. Near the end of his Ph.D. at Penn State, a job posting on the Oregon coast caught his attention. The Hatfield Marine Science Center was looking for someone to analyze growth increments in long-lived fish.
A diver prepares to head out from a research vessel to collect marine samples.
Courtesy of Bryan Black
“I applied and said, ‘I do tree rings and I’m a forest ecologist, but I think we can use this approach for fish,’” Black recalled. “They were intrigued, they took a chance on me, and I took a chance on them.”
Taking a leap into unknown waters, Black packed up, moved across the country, and took his research underwater.
“It was a completely different field for me, so there was a lot to learn,” he said. “It was certainly a big step to move across the country and be completely immersed in a whole different field, where there were no other forest ecologists in a marine lab.”
In the new role, Black developed precise records of fish and clam growth patterns, mapping them year by year to climate conditions. What began as a two-year postdoc blossomed into nearly a decade of groundbreaking research, producing underwater chronologies that rival the best tree-ring records.
Just like trees, many marine species grow annual rings. The challenge lies in the painstaking work of slicing, polishing, and training the eye to detect subtle patterns.
“In a lot of species, the same techniques apply. Rings are rings,” Black said.
Those rings tell stories other data sources miss. Traditional marine records are expensive and difficult to collect over long periods. But a single century-old fish can carry an unbroken timeline of ocean conditions across generations.
“You can get this hundred-year history of fish growth in one chronology,” Black explained, “something it would take generations of scientists to collect from ships at sea.”
Geoduck clams, some of which can live more than 150 years, preserve centuries of ocean history in their shells.
Courtesy of Bryan Black
The timelines don’t stop at the shoreline. They connect ecosystems across continents and oceans.
“The same atmospheric drivers that control productivity in the oceans also influence precipitation on land,” Black said. “We get this dance between the fish and the trees.” Using centuries-old trees, he and colleagues can extend marine climate records even further back in time.
Black’s work has shed light on key Pacific climate events, including the 2014–2016 marine heatwave known as “the Blob.” With the help of geoduck clams that can live for more than 150 years, he is now piecing together a thousand-year climate history of the North Pacific.
“This is something tree records alone haven’t done well,” he said. “Clams will be a very good tie breaker because their rings are directly shaped by ocean temperature.”
The rings also tell a human story. They show scars of overfishing, with rockfish that once lived 80 years now rarely surviving past 30, though populations are continuing to recover through good fisheries management.
“They don’t even start to mature until they’re 8 to 12 years old,” Black said. “It makes them especially vulnerable.”
A diver collects samples from the seafloor to study long-term ocean climate patterns.
Courtesy of Bryan Black
What continues to amaze him, however, isn’t just the precision of the records but the harmony they reveal.
“We see relationships among birds, fish, trees, and freshwater organisms all dancing to the same tune,” he said. “As climate volatility increases, especially in the western U.S., we see the grip of climate tightening, making everything covary even more strongly than before.”
Looking ahead, Black hopes to expand his research to Arctic systems, where long-lived species and sparse forests offer new windows into Earth’s climate story. His work shows that time leaves its mark in unexpected places—and that by reading those marks, we can glimpse the deep connections that bind life across the planet.
To learn more about Dr. Black and his research, click here.