Findings by Berkeley Lab researchers mean the Arctic may be even less of a carbon sink than previously thought

Scientists confirmed carbon dioxide pulses in spring thaw using Eddy Correlation (ECOR) Flux Measurement System data from the ARM Climate Research Facility Barrow observatory. Pulses of greenhouse gases, namely, carbon dioxide and methane, are released by soil when the frozen Arctic tundra starts to thaw around June of each year. Little is known about these releases, until now.

In collaboration with a team taking measurements both in the field and in the lab, scientists at the U.S. Department of Energy’s (DOE) Lawrence Berkeley National Laboratory have quantified the scale of such releases and explained the underlying mechanisms for the phenomenon. Their study was based on a spring pulse in northern Alaska that they documented in 2014 that included carbon dioxide (CO₂) emissions equivalent to 46 percent of the net carbon dioxide that is absorbed in the summer months and methane emissions that added 6 percent to summer fluxes. What’s more, recent climate trends may make such emissions more frequent, the scientists conclude.

“We can see the effects of climate change happening more rapidly in the Arctic than in any other part of world,” said Berkeley Lab scientist Naama Raz-Yaseef. “So we need to understand the processes that are occurring and what to expect in the future. The amount of CO₂ and methane (CH­­₄) in the atmosphere determines the greenhouse effect—so we need to know more about these sources.”

Their study was recently published in Geophysical Research Letters in a paper titled, “Large CO₂ and CH­­₄ Emissions from Polygonal Tundra During Spring Thaw in Northern Alaska.” Raz-Yaseef, an ecohydrologist, was the lead author. Co-authors were Berkeley Lab researchers Margaret Torn, Yuxin Wu, and Tim Kneafsey; Dave Billesbach of the University of Nebraska; Anna Liljedahl and Vladimir Romanovsky of the University of Alaska; David Cook of Argonne National Laboratory; and Stan Wullschleger of Oak Ridge National Laboratory.

The study was a project of DOE’s Next-Generation Ecosystem Experiment (NGEE-Arctic), which seeks to gain a predictive understanding of the Arctic terrestrial ecosystem’s feedback to climate. The team used two towers 4 meters high to collect gas flux readings. The towers are located about 5 kilometers apart near Barrow, Alaska, the northernmost town in the U.S., one tower operated by NGEE and the other by DOE’s Atmospheric Radiation Measurement (ARM) Climate Research Facility.

“Typically we just measure what happens during summer,” Raz-Yaseef said. “We assume nothing happens during winter because it’s frozen, so there’s no biological activity. But in 2014 we measured a big flux of carbon and methane emitted from the ground, at the very beginning of thaw and snowmelt. At first we didn’t know if it was real or a measurement error. Then we confirmed it with another tower 5 km away (the ARM tower), which measured a very similar flux of the same size during the same period.”

That spring they measured a total of three pulses, the longest lasting five days. These findings are important in understanding the carbon balance of ecosystems in the Arctic. So far, the Arctic is considered a carbon sink, meaning it absorbs more carbon dioxide than it emits on an annual basis, thanks mainly to the vegetation that grows in the summer. (Oceans and forests are bigger carbon sinks.)

“Given our findings, the Arctic is an even smaller carbon sink than we thought since during some years nearly half of the summer uptake of CO₂ is offset with these spring emissions,” Raz-Yaseef said.

To read the rest of the story, see the Berkeley Lab press release or read the journal article.

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The ARM Climate Research Facility is a national scientific user facility funded through the U.S. Department of Energy’s Office of Science. The ARM Facility is operated by nine Department of Energy national laboratories, including Lawrence Berkeley National Laboratory.