Your work involves both geochemistry and microbiology. How would you describe yourself? A microbiologist? A geochemist? Something else?
I would describe myself as a biogeochemist. And that means I use the methods and understandings from all three fields to study life and how it interacts with its environment.
Much of your work has focused on “climate proxy development.” Can you explain what that means?
Climate proxies are preserved geochemical signals that carry information about past climates. A couple of examples are tree rings, which help us track drought in the past, and oxygen isotopes in carbonate shells, which tell us about ancient sea temperatures. Another example is the abundance ratios of membrane lipids from algae that vary in proportion with sea surface temperatures. I have worked with carbon isotopes in lipids from unicellular algae that record local growth conditions. We measure isotope abundances in alkenones, which come from haptophyte algae, and we use these values carefully to track large scale changes in atmospheric carbon dioxide over geological time.
You’ve studied the ancient climate and tracked atmospheric carbon dioxide levels over millions of years. Does your work speak to modern trends in climate?
Yes – I think the past is our future. The proxy records go back about 45 million years now. The current levels of carbon dioxide are rapidly approaching 400 ppm, which was last experienced on earth more than 5 million years ago. We’re on a trajectory to reach carbon dioxide levels that haven’t been experienced in earth’s biosphere in the last 45 million years.
Think about that: we’re approaching an environment that hasn’t been experienced by life in a long, long time. So can the past help us anticipate the biological impacts of this change?
In my current work I’m focused on land—that is, the linkages between global climate, local vegetation, and the water cycle. We’re using plant biomarkers and both carbon and hydrogen isotope measurements. We’re studying modern environments to understand relationships in modern plants and we’re also looking at plants in the past. These include the rise of grasslands in North America in the Late Miocene (12 to 5 million years ago). We are interested in how climate might have fostered the change over from forested lands to grassland – and the implications for vegetation’s influence on the water cycle through transpiration. Another example is in the early Eocene (55.8 million years ago), when the climate warmed sharply. It may be the closest analogy we have to today’s rapidly changing climate. We are trying to find new ways to understand the influence of both rapid warming and rising CO2 on the dynamics between plants and water.
Where do you see your field in 10 years?
I can think of two directions. One is that there’s been big technological advances that allow modern ecologists to put out sensors and detectors in the field that provide datasets. The influx of new data will help us frame interpretations of ancient signals. The second direction I see is a change in geochemistry, which has a very basic science-oriented culture. The field continues to be tied to basic science questions, but I now see a shift toward addressing larger societal challenges related to energy, water, waste, and sustainability.
If you had to change careers today and you could do anything, what would you do?
I love what I do and it’s a privilege to be paid to learn and to teach. Being a biogeochemist allows me to explore wide intellectual territory. I love it. I wouldn’t change it. There’s always something new to learn. However, as an untenured faculty member, I did have a backup plan to own a bookstore, because I love to read. But that probably would have been a disaster because I would have been too busy reading books and not selling them.
What’s your favorite science book?
The Curve of Binding Energy: A Journey into the Awesome and Alarming World of Theodore B. Taylor by John McPhee. It’s about isotopes, and McPhee’s writing is beautiful.
What is something about you that most people don’t know?
I actually didn’t decide to study science until relatively late. I was a sophomore in college before I figured out I wanted to pursue studies in science. I took a geology class and I was hooked.