Accelerating rates of Arctic carbon cycling revealed by long-term atmospheric CO2 measurements

S. Jeong, A.A. Bloom, D. Schimel, C. Sweeney, N.C. Parazoo, D. Medvigy, G. Schaepman-Strub, C. Zheng, C.R. Schwalm, D.N. Huntzinger, A.M. Michalak and C.E. Miller


SUMMARY

Warming resulting from global climate change is strongest near the poles. As a result, the arctic is one of the regions where the largest changes might be expected in terms of carbon cycle dynamics. In this study, we show that the cycling of carbon is accelerating in the arctic, as demonstrated by the fact that the mean residence time of carbon in the ecosystem is getting shorter. A decrease in high-latitude residence time indicates an increased sensitivity of Arctic carbon cycling to warming and, therefore, an enhanced role of Arctic ecosystems in the variability of atmospheric CO2.

Figure: Retrieved changes in carbon residence time based on the difference between 1979-1988 and 2004-2013 10-year periods. The vertical red line indicates the average of retrieved changes in carbon residence time. The blue line indicates mean (solid line) and range (shading) in the equivalent residence time change estimates from the MsTMIP model ensemble.


ABSTRACT

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 et al., 2015) compromises accurate 21st-century global climate system projections. The 42-year record of atmospheric CO2 measurements at Barrow, Alaska (71.29 N, 156.79 W), reveals significant trends in regional land-surface CO2 anomalies (ΔCO2), indicating long-term changes in seasonal carbon uptake and respiration. Using a carbon balance model constrained by ΔCO2, 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.

Jeong, S, A.A. Bloom, D. Schimel, C. Sweeney, N.C. Parazoo, D. Medvigy, G. Schaepman-Strub, C. Zheng, C.R. Schwalm, D.N. Huntzinger, A.M. Michalak, C.E. Miller (2018) "Accelerating rates of Arctic carbon cycling revealed by long-term atmospheric CO2measurements," Science Advances, 4 (7), doi:10.1126/sciadv.aao1167.