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Dorothy Peteet reconstructing past climate one seed at a time

Dorothy Peteet, a senior researcher at Columbia University's Lamont-Doherty Earth Observatory combines her love of plants and history into her study of paleoclimate. (Photo: Laura Petersen)

There are only about 20 "seed people" in the United States -- paleoecologists who use seeds found in mud cores to reconstruct past climate. Dorothy Peteet is one of them.

"The details, the beauty of the seeds, the aesthetic appeal of them to me is huge because they are such wonderful shapes and colors and textures," said Peteet, a senior researcher at Columbia University's Lamont-Doherty Earth Observatory. "But from that little seed you can gain a lot of climatic information, and it puts a piece in the puzzle that can really help us learn how climate changes, how vegetation changes."

"It all has implications for the future as we go towards a warmer world," the 59-year-old added in her soothing Southern accent.

Peteet has spent more than 30 years plunging metal tubes into marshes and peat bogs, and pulling out ancient records of vegetation and climate stored in the layers of mud. The seeds and pollen mixed in with the peat hint at what the landscape looked like thousands of years ago.

Knowing the conditions required for those plants to flourish or die back, Peteet can extrapolate if the climate was cold or hot, and wet or dry at that time. Pollen blows around, so it provides a broad picture of the ancient landscape. Seeds, on the other hand, don't travel far, and so tell a more precise story of a particular location.

Few paleoecologists use seeds, because unlike pollen, there is not a large inventory of them. Peteet has one of the best seed catalogs, which she inherited from an elderly collector. She keeps the chin-high wooden chest in her office; two doors swing out to reveal a stack of thin draws, each filled with thousands of seeds from around the world.

"This thing is worth its weight in gold," Peteet said.

Seeds have unlocked many questions for Peteet over the years. Notably, she discovered the Younger Dryas, an abrupt cooling period about 10,500 years ago, that occurred on North America. Based on the pollen record, the cold snap was thought to only have been a European phenomenon. However, using the more specific seed record, Peteet found the birches in the New York region were the northernmost type, indicating is was colder there at the time.

Peteet also identified the Younger Dryas in Alaskan peat cores, which revealed the major cold snap involved not only the Atlantic, but the much larger Pacific Ocean.

Peteet returned to Alaska every summer for 20 years, completely enamored with the glacial landscape. "It is so wild and the scale of everything is so different," Peteet said. "You really feel you're a tiny part of the landscape. It's very humbling."

Peteet hasn't been to Alaska for the past 13 years — she's been busy raising a family, teaching at Columbia, working at NASA's Goddard Institute for Space Studies, and studying the Hudson River Valley's paleoclimate.

That is why she is very excited to travel to the Arctic this summer to study how carbon sequestration in peat has changed with the climate. Up to two-thirds of the world's soil carbon is stored in peat, so it will be important to learn how that might change as the climate warms.

"I am very curious to see how the mosses are changing as well as the types of plants over time, and then compare that to the amount of carbon in the landscape," Peteet said, whose research is being funded by a three-year National Science Foundation grant.

Peteet developed a love of nature while growing up during the Civil Rights era in Atlanta, Georgia. The fourth of six children, she chased after her brothers, constantly ripping her dresses while climbing trees. Being the first girl, Peteet quickly learned to stick up for herself.

"I learned to survive in a man's world," Peteet said. "That was important for science."

She watched her father, who was a "rabbit" of a gardener, constantly move plants around the yard of her childhood home. Along with large magnolia and oak trees, he grew figs, raspberries, grapes, azaleas, and Confederation roses. He brought her mother flowers every morning.

During the summer, Peteet's family stayed at a cabin by a lake in the Appalachian Mountains. It was the early pleasure of romping in the woods and learning names of the plants that inspired Peteet to study botany, in addition to literature, at Duke University. She went on to earn a Master's and Doctorate in biology at New York University, with a focus on paleoecology.

"I love history and I love plants, so it's a way to do both," Peteet said.

But despite becoming an expert in plants, Peteet admits she did not inherit her father's green thumb.

"I feel sorry for the weeds," she said.

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Dorothy Peteet, a senior researcher at Columbia University's Lamont-Doherty Earth Observatory combines her love of plants and history into her study of paleoclimate. (Photo: Laura Petersen)
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