In a laboratory located on the campus of Shanghai Jiao Tong University, Hu Huanting is engaged in a delicate dance with time itself.

The 35-year-old oceanographer carefully picks up a small block of ice about the size of a sugar cube and places it into a container filled with a chemical reagent kept at a frigid negative 30 degrees Celsius.

Hu isn’t interested in the ice, which formed tens of thousands of years ago, but in the secrets locked within. A closer look at the cube reveals countless tiny bubbles trapped under the surface, frozen pockets of air that document millennia of volcanic eruptions, dust storms, and climactic shifts.

After verifying the container is sealed and uncontaminated, Hu transfers it gently into a vessel filled with warm water. As the ice cube begins to melt, the bubbles disperse, filling the vacuum with air — the breath of an ancient and long-forgotten earth.

Hu is part of a small but growing community of researchers in China studying ice cores: long, narrow samples of ice drawn from Antarctica, Greenland, and high-altitude glaciers.

In these frigid corners of the Earth, where temperatures remain at or below freezing year-round, air and other particles become trapped in gaps between snowflakes. As the snow accumulates, it compacts and slowly transforms into impermeable glacial layers, leaving these molecules ensconced within the ice.

Since the mid-20th century, scientists have plunged their drills into the ice sheets, retrieving cores that are essentially time capsules of our planet’s past. Each layer is an epoch, each bubble an archive. The Vostok ice core, named after the base in eastern Antarctica where it was retrieved, spans an impressive 420,000 years and four ice age cycles. An ice core retrieved from Dome C — one of the continent’s inland summits — goes back even further, to nearly 800,000 years before the present day, and covers eight glacial cycles.

The researchers studying these cores are as varied as the secrets they hold. Particles within the cores hold clues for geologists about volcanic activity, dust storms, and climate change. Traces of heavy metals allow scientists to track pollution from human-made emissions, while the deepest ice preserves bacteria, viruses, algae, and fungi that have otherwise disappeared from the world.

Hu’s research is focused on what the cores can tell us about past variations in the Earth’s climate. “The beauty of ice cores is their purity,” Hu says. “They’re almost our only source of prehistoric air.”

“Even better, this air is not localized to the region where the glacier is located, but it represents the air of the entire globe at a certain time,” she adds.

Hu brings an impressive pedigree to her research. After receiving her undergraduate degree in geochemistry at the prestigious University of Science and Technology of China, she undertook her Ph.D. in stable isotope geochemistry at Johns Hopkins University. By the time she joined Rice University as a postdoctoral researcher in 2016, she seemed on track for a career at one of the world’s top research labs.

But while Hu felt comfortable she could secure a position at a university or research institute in the United States, she was beginning to feel homesick. She wanted to return to China, reunite with her boyfriend, and start a family.

There was just one problem: There were very few labs in the country specializing in the kind of work she was trained to do.

A new approach

On a snowy day in February 2014, Zhou Meng, an oceanographer based at Jiao Tong University, made his way to the home of Michael Bender in Princeton, New Jersey. He was there to extend an invitation to Bender — a professor of geosciences at Princeton University since 1997 — to join Jiao Tong’s newly established Oceanographic Research Institute.

Zhou himself was a recent addition to Shanghai Jiao Tong’s faculty; he had spent most of the previous two decades in the United States, at institutions such as the State University of New York, the Scripps Institution of Oceanography, and the University of Massachusetts. In 2013, he had been on the verge of a move to southern France when Su Jilan, a member of the Chinese Academy of Sciences, persuaded him to return to his hometown to establish a program in marine science at Jiao Tong.

At the time, China was in the midst of a massive academic hiring spree, part of a broader plan to speed the construction of “world-class universities” in the country. Zhou believed the proposed Oceanographic Research Institute at Jiao Tong — known for its engineering and scientific research programs — had potential, but it would require a major recruitment drive targeting top researchers based around the world.

The first person who came to Zhou’s mind was Bender, a longtime friend and specialist in the field of climate change. The offer was extended and accepted, and Bender was officially added to the faculty in 2015.

In his new role, Bender set about laying the foundations for a polar and climate change laboratory at the school. One of his first hires was Hu, who heard about the lab shortly after joining Rice.

Zhou was thrilled: He saw in the pair the ideal kind of collaboration between veteran scholar and early-career researcher — international and Chinese — that he wanted to build his new institute around.

With Bender’s support, Hu became a cornerstone of the polar laboratory, helping oversee the meticulous process of extracting, purifying, and measuring gasses trapped in the ice.

Tracking climactic changes through oxygen values is tricky. Atmospheric values of oxygen-18, an isotope commonly used to measure temperature shifts over time, have only moved about two parts per thousand over the past 800,000 years.

“Our measurement precision needs to be extremely high to decipher these changes,” Hu says. “Currently, our laboratory’s measurement precision has reached 0.04 parts per thousand.”

Indeed, the biggest challenge currently facing the lab isn’t precision but a lack of samples.

Blue ice

The Earth’s polar ice caps jealously guard their secrets, and extracting ice cores poses an immense scientific challenge. Consider the illustrious Vostok ice core, for instance, which took engineers over 40 years to drill, beginning in 1958.

The value of ice cores has only risen as more labs turn their attention to climate change. With global warming posing a threat to life everywhere on the planet, scientists see ice as a way to reconstruct Earth’s past climate change patterns — and thereby develop more accurate models of the future.

China is a relative latecomer to the field, only sending its first team to the continent in 1984. However, the country has rapidly expanded its presence in Antarctica, especially over the past 23 years. In 2004, the 21st Chinese Antarctic Research Expedition team successfully drilled a 109.91-meter ice core in the Dome A region, believed to be the coldest place on Earth. In 2017, the Chinese Antarctic Scientific Expedition surpassed the 800-meter milestone in the same region.

These arduously obtained polar ice cores, akin to lunar soil samples, are coveted by research teams globally. While Jiao Tong’s lab possesses some ice cores from Antarctica — a side benefit of its collaboration with Bender — they are limited and difficult to replace.

Fortunately, valuable ice cores aren’t solely sourced from the most remote parts of Antarctica.

In theory, the age of ice layers in polar glaciers increases with depth: The deeper scientists drill, the older the ice. Each meter represents a potential new breakthrough, but progress is slow, and costs are high.

Bender believes there’s a better way: tapping Antarctica’s “blue ice.”

Blue ice forms when mountainous terrain obstructs glacier movement, pushing the hard bottom layers of ice up to ground level. The history recorded in these blue ice areas is remarkably ancient; for example, one of Bender’s teams discovered blue ice dating back an estimated 2.7 million years. Armed with this information, scientists can potentially track climate variations on a far grander time scale than ever before.

With ice core supplies scarce, Chinese scholars have embraced the blue ice approach. Last October, one of Hu’s colleagues, Shi Guitao, a scholar at East China Normal University, led a team to Antarctica on a monthslong mission to obtain new blue ice samples.

Hu hopes to make her own trip one day. “I might not be of much help on the ice, but I still hope to go there, to stand upon those ancient ice fields and see these archives of nature with my own eyes, even if just for a second,” she says. “I think of it as a pilgrimage.”

(Header image: D.A. Peel/Science Photo Library/VCG)