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Is Climate Changing? Secrets Are in the Mud

Professor Stevens sub-sampling the gravity core at the volcanic crater lake, Ia M’ He Lake in Kon Tum, Vietnam.

Professor Stevens sub-sampling the gravity core at the volcanic crater lake, Ia M’ He Lake in Kon Tum, Vietnam.

California recently surfaced from a devastating 5-year drought. Wildfires burned huge swatches of the western US this year. Hurricanes produced flooding not seen in centuries. Given such events, people ask, “Is climate changing?”

If we want to know whether climate is changing, we need to know what climate has been. Most written records of climate are short (100-200 years) and poorly distributed. When we say a flood is a once in a thousand-year event, how do we know? Reconstructing past climates is the domain of the paleoclimatologist. Although paleoclimatologists work in time periods from 2 billion years ago to 10,000 years ago, our goal is the same—documenting how has Earth’s climate evolved.

When people ask what I do for research, my stock reply is “I play with mud.” It’s a cheeky answer but accurate. Granted, I’m not making mud pies, but my work almost exclusively relies on measuring geochemical changes in the mud that collects at the bottom of lakes.

I focus on the last 100,000 years in Iran and Vietnam, which allows me to explore the intersection of climate and humans. To that end, I am most interested in the timing and frequency of extreme events, including droughts and floods. Lakes faithfully record these events, documenting all the changes happening around them by storing clues in the sediment that accumulates in their basins. Collecting these records without disturbing them requires specialized coring equipment and a lot of patience. During one such expedition, I found myself precariously balanced in a saucer-shaped reed boat, coring a coastal lake in Vietnam. When working in the field outside the US, creativity and flexibility are a must.

Dr. Stevens with her graduate research students, Ms. Trang Tran (right) and Ms. Oanh Nguyen (left), at a Central Highlands lake in Vietnam.
Professor Stevens (center) with her Vietnamese Masters students, Nguyen Oanh (left) and Tran Thu Trang (right), at Ia M’ He Lake in Kon Tum, Vietnam.

My colleagues often joke that I could not find more difficult places to work. Realistically I can, but working in Vietnam and Iran does present some challenges. Both require a USDA Foreign Soil permit that regulates how my sediment is shipped, stored and treated. Economic sanctions in Iran require a special waiver from the US Department of Treasury. Accessing research sites in Vietnam may require days of travel and hundreds of pages of stamped permits from every level of the government. Although these hurdles can be daunting, if we really want to understand how climate works, we need a globally distributed set of records.

One of the things I love about my work is the limitless secrets contained in the mud. I have been reconstructing droughts for decades, but recent work with a graduate student led me to coprostanol. Coprostanol is a derivative of cholesterol that forms in the human gut and is expelled in feces. Without modern sanitation, it ends up in sediment where its variations mirror demographic changes. These population changes can be compared to drought events to explore how ancient people responded to extreme climate. I feel privileged to have a job that I look forward to every day, and in which every day, my mud reveals something new about people and the climate in which they live.

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