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Bruce Vaughn gives local middle schoolers a primer on ice core science in the Stable Isotope Lab's walk-in freezer in 2025. (Gabe Allen)

“This would be a warm day in Greenland,” Bruce Vaughn tells us as we crowd into the walk-in freezer at the back of the Stable Isotope Laboratory. Some of the students have heeded warnings to dress warmly. A few brave souls arrived in shorts. All of us discover that -25°C (-13°F) gets cold fast.

Vaughn, one of the lab’s founders, holds a thick cylinder of ice up to the light. It’s about the size of a Nalgene bottle and perfectly clear. Such cores come from deep in the permanent ice sheets of Greenland and Antarctica, where trapped air bubbles are locked in the ice for hundreds of thousands of years. If you popped a chunk in your mouth, the air bubbles would fizz on your tongue as they escaped. You might be breathing the same air as a woolly mammoth or saber-tooth tiger.

Since 1989, the Stable Isotope Laboratory (SIL) has been one of the flagship laboratories for CU’s Institute of Arctic and Alpine Research (INSTAAR), which is celebrating its 75th anniversary this year. The lab supports cutting-edge climate research using custom-made technology, but don’t let its technical-sounding name fool you, the team has a blast doing it. Vaughn’s motto? “No one said it couldn't be fun.”

The chemistry of stable isotopes offers a powerful tool for learning about our world. Carbon dating — used to determine the age of the ancient Dead Sea Scrolls — is probably the most well-known example of isotopes at work. But isotope ratios can record everything from ocean and air temperatures to the sources of greenhouse gases in our atmosphere. Forensic technicians use isotopes, too: isotope ratios can tell them whether olive oil is really from Italy, whether the steroids in an athlete’s blood are natural or synthetic, and even where a person has spent the last three months of their life.

At the SIL, isotopic ratios are used primarily to study two things: ice cores and greenhouse gases. Ice cores tell us about the past atmosphere, while the greenhouse gas research can help establish the sources of warming in our world today. The SIL’s ability to investigate these variables at high levels of precision has made the lab a powerhouse in climate science. “Water and air,” says Vaughn — these are the lab’s bread and butter.

Tracing Water

How do isotopes work? Let’s take a trip back to high school chemistry class. Every element in the universe has a unique number of positively charged protons in its atomic nucleus. However, the number of neutrons can vary. An oxygen atom, for instance, will always have 8 protons, but may have 8 or 10 neutrons. The resulting atoms are the same in all ways but one: the oxygen-16 isotope will weigh slightly less than the oxygen-18 isotope.

Those extra neutrons might seem unimportant. After all, how heavy is an atom, really? But many natural processes filter molecules by their weights. Imagine you’re a “light” oxygen isotope within a drop of seawater in Monterrey Bay, California. It’s a hot day, so you evaporate and become part of a cloud. As you move northwest on jet stream winds, the air gets colder and rain droplets form around you. The heavier isotopes — water whose hydrogen or oxygen atoms have more neutrons — fall to earth first, while you are left in the cloud.

As your cloud hits the Rocky Mountains, even more heavy companions fall away (heavier isotopes have a harder time staying gaseous at higher elevations). By the time you reach Boulder, the population of water molecules in your cloud has undergone a noticeable shift toward lighter isotopes.

When you finally precipitate down to Earth as rain or snow, researchers can use the ratio of O-16 to O-18 isotopes to reconstruct your voyage, all the way back to the temperature of Monterrey Bay when you evaporated.

Valerie Morris loads an ice core sample into a carousel in the stable isotope lab at INSTAAR. The carousel is the front end of a continuous flow analysis system developed by Morris and Bruce Vaughn, which continuously measures isotopic ratios for hydrogen and oxygen as the ice core melts. (Gabe Allen)

Ice cores tell us about the travels of water vapor — like our drop from Monterrey Bay — going back hundreds of thousands of years. As snow falls in Greenland or Antarctica, it presses down older snow beneath it. That pressure creates ice, which becomes denser as more snow and ice pile on top of it. These polar regions have remained frozen for a long time, so their ice preserves a continuous chronological record of ancient snow, and the isotopic ratios within reveal past ocean and air temperatures.

To get the information, though, scientists must melt the ice, destroying a slice of the ice core. It takes several years and millions of dollars to drill these cores — the stakes are high.

To make the most of the ice cores examined at the SIL, Vaughn and his longtime colleague Valerie Morris developed a sophisticated system that transformed the way ice is studied. Back in the 1990s, Vaughn explains, researchers looking for oxygen and hydrogen isotopes could only get a single data point every 3-5 centimeters, which might represent hundreds, or even thousands, of years. “You were looking at a blurry vision of the past,” Vaughn says.

When an ice core came back from West Antarctica around 2011, Vaughn and Morris decided to try something new. Working with a Danish team, they overhauled an ice core analysis protocol that was previously considered state-of-the-art. “We took each component in that system, and we were like: How do we optimize this? How do we optimize this? How do we optimize this?” Morris explains.

The new system took several years of trial-and-error, elbow grease, and ingenuity — including finding creative solutions in surprising places, such as “adult” stores. The result was revolutionary. Rather than melting 5-centimeter chunks at a time, Vaughn and Morris’ “continuous flow” system melts the ice slowly, gathering data millimeter by millimeter. With this technological leap, the SIL went from a couple dozen data points per meter to over 2000. The resolution is high enough to see annual summer and winter changes going back thousands of years. “That,” says Vaughn, “was the game changer.”

The “continuous flow” system is such an improvement that the SIL recently secured funding to re-examine an ice core they first studied in the 1990s. According to Brad Markle, a principal investigator at the SIL, the updated technology can enable much finer-grained investigations of temperature and weather patterns over the course of human history. By looking at both oxygen and hydrogen isotope ratios in a core simultaneously, Brad and his colleagues can observe not just overall air temperature, but also temperature differences between the tropics and the poles. Those relationships illuminate how weather patterns change as the planet warms or cools — which can in turn help scientists develop predictive models of global warming.

Counting emissions

Rachel Edie changes gas flasks out on Spock, a mass spectrometer that measures stable isotopes of carbon and oxygen in atmospheric CO2, primarily from the NOAA CMDL Cooperative Air Sampling Network. (Ethan Welty)

A second key to predicting the future of our planet’s climate comes from understanding greenhouse gases. There, too, SIL is a global leader. Since its founding, the SIL has been a go-to lab for one of the largest environmental monitoring programs in the world today: the Global Monitoring Laboratory run by the National Oceanic and Atmospheric Administration (NOAA). Every week, SIL receives air samples collected from over 50 locations on all seven continents. The SIL measures carbon and methane isotope ratios in these samples and provides publicly accessible data to labs around the world — all while making important discoveries of their own.

“We need to understand where these gasses are coming from,” says Sylvia Michel, the SIL’s Laboratory Manager. “Stable isotopes act like a fingerprint.”

In one recent paper, Michel used isotopic ratios to measure the respective contributions of wildfires, fossil fuels, and microbial activity to global methane emissions. As it turns out, the microbes are big contributors.

“The metabolism of these little critters is such that they will take the carbon and spit out methane,” Michel said. Methane traps heat 80 times more efficiently than carbon dioxide over a 20 year period.

As the world warms, microbial activity has been heating up, too. Methane-producing microbes are hard to measure because they’re, well, microscopic. They live wherever oxygen is absent — from melting permafrost to jungles to the intestines of cattle. Supported by the SIL’s data, though, researchers around the world are recognizing microbes’ key role in increasing atmospheric methane concentrations. It’s a new consensus which would not exist without the isotopes.

A few other labs are set up to measure isotope ratios, but, thanks to the NOAA collaboration, the SIL stands out.

“There are probably five labs in the world that measure isotopes of methane,” Michel said. “And we measure by far the most samples.”

The partnership with NOAA also brings stability, which allows the lab to build and retain an impressive roster of researchers with overlapping interests. When people stick around a lab for decades, says postdoctoral fellow Kevin Rozmiarek, “suddenly big things are really possible.”

It helps, adds Markle, that the researchers have “different but related goals.” Ice cores and greenhouse gases can feel distinct, but researchers in both fields benefit from each other’s insight and collaboration. The lab’s founder, Jim White, was passionate about both, and, more than three decades later, the lab still fosters a vibrant and diverse intellectual community.

“I love that about INSTAAR,” Markle said. “Because the point is to bring together people with lots of different interests. [The SIL] is a cool microcosm of what the institute itself is trying to do.”

Alex Rudick, an undergraduate in Aerospace Engineering who traveled to Alaska with the lab, agrees. He joined the team to design and build drone-compatible instruments capable of tracking how water vapor travels over ice sheets.

“The people at SIL are genuinely so passionate about what they do,” he said. “They are people I’d want to be like in the future.”