Accelerating rates of Arctic carbon cycling revealed by long-term atmospheric CO measurements.

The contemporary Arctic carbon balance is uncertain, and the potential for a permafrost carbon feedback of anywhere from 50 to 200 petagrams of carbon (Schuur ., 2015) compromises accurate 21st-century global climate system projections. The 42-year record of atmospheric CO measurements at Barrow, Alaska (71.29 N, 156.79 W), reveals significant trends in regional land-surface CO anomalies (ΔCO), indicating long-term changes in seasonal carbon uptake and respiration. Using a carbon balance model constrained by ΔCO, we find a 13.4% decrease in mean carbon residence time (50% confidence range = 9.2 to 17.6%) in North Slope tundra ecosystems during the past four decades, suggesting a transition toward a boreal carbon cycling regime. Temperature dependencies of respiration and carbon uptake suggest that increases in cold season Arctic labile carbon release will likely continue to exceed increases in net growing season carbon uptake under continued warming trends.