By Fern Alling
Medill News Service, Dec. 27, 2024
Yuxin Zhou didn’t set out to be a paleoceanographer. The first undergraduate major he declared was computer science.
“When you’re an international student coming to the United States and you don’t know what to do, you study computer science,” Zhou said, laughing.
Zhou left his hometown of Nanjing, China to earn a degree at the University of Southern California in Los Angeles. He signed up for an oceanography class in his first semester to complete a general education requirement. But Professor William Berelson, a geobiochemist, altered Zhou’s course in one class with a captivating story.
Berelson, a professor of marine systems, told his students about his trip in a submersible to gather data for a project. There wasn’t an ounce of sunlight where he was heading, so Berelson didn’t expect to see much. To his surprise, when he looked out of the window, he saw a bustling community of marine life. He likened it to seeing New York City from an airplane window.
Zhou was sold. He made computer science his minor and switched to a geology major. Now, more than a decade later, he’s still studying geology as a postdoctoral scholar at the University of California, Santa Barbara. Zhou analyzes ancient marine sediments to estimate when the ocean’s temperature, salinity or circulation changed in the past. This field is called paleoceanography: paleo, for the geological past, and oceanography, for the study of the ocean.
“My first impression [of Zhou] was of someone who was very curious and earnest,” said Jerry McManus. McManus, a professor of earth and environmental sciences at Columbia University, first met Zhou at Woods Hole Oceanographic Institution, where McManus is an adjunct scientist. He was visiting Woods Hole for the summer and Zhou was there as an undergraduate intern. They only spoke for 30 minutes, but it was long enough for McManus to tell Zhou’s interest was genuine.
The two met again when Zhou arrived at Columbia for his Ph.D. in earth and environmental sciences. Though Zhou was an oceanographer at the time, he focused on modern climatic shifts. McManus helped spark his interest in paleoceanography and became the thesis advisor for Zhou’s dissertation. The two keep in touch and caught up with each other once again at the annual Comer Climate Conference this fall in southwestern Wisconsin.
The work Zhou highlighted at the conference this year came from a study he conducted with McManus. The research sprang from some strange red material Zhou noticed in a sediment core.
Sediment core samples are mixes of soils, organic matter, and other deposits extracted from dry land or the floor of a body of water. The long tubes that extract the cores keep the materials in chronological order, with the oldest sediments on the bottom and newer layers stacked on top. Scientists can measure change over time by comparing different parts of the sample.
When Zhou received part of a sediment core from the Lamont-Doherty Core Repository to analyze, nothing jumped out at him right away. At first, he just performed some chemical tests and plotted the corresponding data. Nearly everything was as expected. But his results seemed off around a period 125,000 years ago. Zhou didn’t know what to make of it. Nothing else in the data was particularly strange. But when he looked at the core as a whole, he could see a layer of fine red sediment in the section where his data went rogue.
Intrigued, Zhou mentioned his findings to some colleagues. They directed him to a 2012 research paper by University of Cambridge paleoclimate researcher Joseph A. L. Nicholl and several colleagues that proposed the red layer was the result of meltwater released from the Laurentide ice sheet. Ice sheets are large bodies of land ice that can span continents, and the Laurentide ice sheet stretched southward across North America from the Arctic to modern-day St. Louis during the ice ages.
Nicholl and his colleagues argued the water released by the Laurentide was a sign the ice sheet was destabilizing sooner than researchers previously thought. Zhou and McManus expanded on the work Nicholl and others had done in their own study. Their research bolstered the evidence for Nicholl’s theory by outlining how the red sediment’s age, origin, and means of travel serve as further evidence of the Laurentide’s decline. They even invented a snappy name for the phenomenon: LILO, for last interglacial Laurentide outburst. Waving next to the acronym on Zhou’s presentation slides was a smiling picture of the character Lilo from the 1990s Disney animated film “Lilo and Stitch.”
Understanding exactly when the Laurentide collapsed then is vital to unpacking modern ice sheet dynamics. Scientists turn to past ice sheet behavior for insight into how climate change will affect arctic ice in the future. Although the Greenland and Antarctic ice sheets are the only two that remain today, they used to share the globe with others like the Laurentide and Scandinavian ice sheets. Scientists must determine how these long-gone ice sheets influenced the Greenland and Antarctic for the most accurate predictions.
“I may be biased, but I think this is a tremendous study,” said Roger Creel, a postdoctoral scholar at Woods Hole and Comer Conference attendee.
As far as Zhou’s concerned, the big lesson is to examine research materials from all angles.
“It’s very old school, right?” Zhou said. “Looking at a core image – who does that anymore? But in this case, it turned out to be very useful.”
Zhou still remembers what a mentor told him during an undergraduate internship: be kind, or else you won’t make it in paleoceanography. He said that’s how he knew he was in the right place.
“The actual field of science I chose to do has less to do with the science, but more to do with people,” Zhou said. “That led me to stay in paleoceanography to this day.”
Photo at top: Oceanographer Yuxin Zhou at the Comer Climate Conference in fall. (Photo by Fern Alling/Medill News Service)
