ACCLIMATE Radiocarbon Time Series

Atmospheric Radiocarbon Signal

Soil Respiration

The radiocarbon signature of soil respiration ∆14CO2 at 10 (gold) and 20cm (blue), and combined 10-20cm (red) depths is declining more quickly than atmospheric ∆14CO2, indicating that there is increased old, permafrost carbon degradation over time within soil respiration CO2

Ecosystem Respiration

The radiocarbon signature of ecosystem respiration ∆14CO2 at CiPHER (pink), DryPEHR (red), and Gradient (blue) is declining more quickly than atmospheric ∆14CO2, indicating that there is increased old, permafrost carbon degradation over time within ecosystem respiration CO2

Summary Points

• What is it: Radiocarbon (Δ¹⁴CO₂) Signatures of Soil and Ecosystem Respiration
• Non-Scientific name: Tracking the Fingerprint of Permafrost Decomposition via CO₂
• Why do we measure it:
  • Radiocarbon (¹⁴C) dating helps us track permafrost carbon in soil and ecosystem respiration over time.
  • We measure Δ¹⁴CO₂ in soil and ecosystem respiration. Soil respiration comes from microbes breaking down soil and from plant roots. Ecosystem respiration includes both plant and microbe respiration.
  • CO₂ samples are a mix of old and young carbon. Instead of determining the exact age, we use radiocarbon to identify the relative age of the mixture and if there is more old or more young carbon present in that mixture.
  • The older the carbon in a sample, the more permafrost has decomposed and been converted to CO₂. Older samples have more negative Δ¹⁴CO₂ values, while younger samples have less negative values.
• How was it measured: We capture CO₂ by trapping this gas either aboveground (for ecosystem respiration) or below the soil (for soil respiration) and then carbon date the carbon in the CO₂ sample in the lab.
• Long term trends:
  • While the radiocarbon signature of both ecosystem and soil respiration were similar to the atmosphere at the start of the timeseries, over time, we started to see an accelerated aging of the mixture, where the Δ¹⁴CO₂ became more negative over time.
  • This indicates that there is more old, permafrost-derived carbon being released into the environment over time.
• What happened in 2025: In 2025…[tbd]
• Where is this science going?: Measuring radiocarbon signature of CO₂ in the permafrost region is important because, as the climate warms, more and more permafrost carbon will be released to the atmosphere, potentially leading to increased climate warming.