UC Berkeley scientists find a carbon cycle hiding in desert minerals

PhD candidate Anna Abramova and Professor Ronald Amundson in Hilgard Hall. Photo by Mathew Burciaga.

On the surface, the arid expanses of the Mojave Desert may seem inhospitable and largely removed from the global carbon cycle. But beneath the surface, its mineral-rich soils are running a carbon cycle of their own—one that could account for a surprisingly large share of the planet’s annual carbon exchange.

In a new study published today (September 23) in Science Advances, researchers in UC Berkeley’s Department of Environmental Science, Policy, and Management (ESPM) detail a daily cycle of carbon dioxide (CO₂) adsorption and desorption. At night, as ambient temperatures drop, atmospheric carbon dioxide molecules latch onto minerals and other fine particles in the Mojave soils via a process known as adsorption. When the sun peeks out from over the horizon and temperatures begin to rise, those same molecules detach from the soil and revert to their gaseous state.

Lead author Anna Abramova, an ESPM doctoral candidate, said this newly documented cycle offers an alternative explanation of how soils exchange carbon with the air. Scientists primarily understand this exchange through soil respiration, which begins when plants and other vegetation convert CO₂ into energy and organic carbon via photosynthesis. As plants grow, their roots and associated soil microbes return some of that carbon to the soil. Microorganisms then feed on that organic carbon and convert it back to CO₂ gas that diffuses out of the soil and into the air.

Berkeley researchers in the Mojave. Photo courtesy of Ronald Amundson.

“It's always been assumed that this is entirely driven by a biological process,” explained Ronald Amundson, a professor in ESPM and the study’s senior author. He compares the process to how a “giant, living organism” might breathe. In hot, dry climates like the Mojave, Amundson said this process tends to slow because vegetation and plant life are sparser than in humid hotspots like the tropics.

Since 2017, Amundson’s team has monitored the Mojave using soil sensors that record real-time data. Their long-term monitoring efforts revealed something unexpected. “Instead ofCO₂ coming out of the soil and going back to the atmosphere, we found that carbon was flowing into the soil at night,” said Amundson, who has studied soils across global ecosystems (including Chile’s Atacama Desert, the driest non-polar desert on Earth). “There’s no biological explanation for this.”

Study co-author Jennifer Mills, PhD ’21 ESPM, previously found that at night CO₂ concentration in soil 5 centimeters deep dropped below the concentration at the soil’s surface, resulting in an influx of CO₂. Amundson, who has used vacuum extraction lines in his Hilgard Hall lab to process gases for more than 30 years, knew CO₂ can latch onto solid surfaces when cool. In the Mojave, soil surface temperatures can reach as high as 140°F (60°C) during the day, then drop below 70°F (20°C) at night. He and Mills initially suspected the minerals could hold onto CO₂ as they cool and release it as they warm.

Confirming that took three years of lab work. Researchers collected soil samples from the Mojave and brought them back to Berkeley. Abramova then took them to the Lawrence Berkeley National Laboratory, where she used specialized equipment to measure the amount of CO₂ adsorbed under different temperatures and CO₂ concentrations. Her experimental data showed that it could explain what Mills and Amundson’s Mojave sensors had recorded: carbon dioxide latched into cooling soil. “Once the temperature drops, adsorption capacity increases,” she explained. By repeating the process across temperatures spanning a desert night and a desert afternoon, she found that the soils took up more carbon dioxide as they cooled and released it as they warmed, confirming that the nighttime uptake is driven by adsorption, not biology.

Abramova used liquid nitrogen to cool the soil samples, allowing her to determine the adsorption rates at various temperatures. Photo by Mathew Burciaga.

“We designed these lab experiments to quantify adsorption rates, and compare that to how it occurs in the Mojave,” she said. “It was exciting to see how two completely different, independently obtained data sets are very much aligned.”

When scaled globally, the authors estimate that between one and three gigatons (1-3 GT) of carbon—roughly one-tenth to one-third of annual human emissions—move into and out of desert soils each year. The exact figure could be higher, as the estimate is based solely on Mojave soils. Researchers have observed the same phenomenon in cold deserts, including Antarctica, and Amundson noted it has long been suspected on Mars's surface. Abramova is now studying whether adsorption varies across soils with more organic carbon or minerals with especially high adsorption capacity.

The finding also puts desert dirt in unexpected company. In 2024, former UC Berkeley Chemistry Professor Omar Yaghi (who shared the 2025 Nobel Prize in Chemistry) unveiled a porous crystalline material capable of pulling carbon dioxide from open air. “We're basically showing that natural minerals have essentially the same capabilities,” Amundson said.

The process, Amundson noted, only becomes visible when biological soil respiration rates are relatively low. “This abiotic flow can become comparable in size—and sometimes even bigger than its biological counterpart,” he said. Such a process could add new depth to existing carbon models and inform new, nature-based climate solutions.

UC Berkeley co-authors include Shauna Zahabi, Maedeh Chitsaz, Marco Pfeiffer, and Laura Lammers. Scientists from New Mexico State University and Lawrence Berkeley National Laboratory also contributed to the study. Funding for the project was provided by the California Energy Commission (EPC-15-039) and the U.S. Department of Energy (No. DE-AC02-05CH11231).