Links between atmospheric carbon dioxide, the land carbon reservoir and climate over the past millennium

Journal name:
Nature Geoscience
Volume:
8,
Pages:
383–387
Year published:
DOI:
doi:10.1038/ngeo2422
Received
Accepted
Published online
Corrected online

The stability of terrestrial carbon reservoirs is thought to be closely linked to variations in climate1, but the magnitude of carbon–climate feedbacks has proved difficult to constrain for both modern2, 3, 4 and millennial5, 6, 7, 8, 9, 10, 11, 12, 13 timescales. Reconstructions of atmospheric CO2 concentrations for the past thousand years have shown fluctuations on multidecadal to centennial timescales5, 6, 7, but the causes of these fluctuations are unclear. Here we report high-resolution carbon isotope measurements of CO2 trapped within the ice of the West Antarctic Ice Sheet Divide ice core for the past 1,000 years. We use a deconvolution approach14 to show that changes in terrestrial organic carbon stores best explain the observed multidecadal variations in the δ13C of CO2 and in CO2 concentrations from 755 to 1850 CE. If significant long-term carbon emissions came from pre-industrial anthropogenic land-use changes over this interval, the emissions must have been offset by a natural terrestrial sink for 13C-depleted carbon, such as peatlands. We find that on multidecadal timescales, carbon cycle changes seem to vary with reconstructed regional climate changes. We conclude that climate variability could be an important control of fluctuations in land carbon storage on these timescales.

At a glance

Figures

  1. Carbon cycle variability of the past millennium.
    Figure 1: Carbon cycle variability of the past millennium.

    CO2 and δ13C-CO2 (red markers, this study) from the WAIS Divide Ice Core with earlier reconstructions from the Law Dome ice core (grey markers)6, 11 and a pristine coral δ13C record16 (purple markers) from the near-surface Caribbean (25 m water depth, 78° 57′ W, 17° 32′ N). Errors bars show the estimated uncertainty at the 1-σ s.d. level. Inset is a cross plot of the WAIS Divide CO2 and δ13C-CO2 data for the pre-industrial (~755—1850 CE; red circles with the mean and 2-σ standard deviation indicated by black error bars and linear fit with a dashed black line) as well as the data covering the industrial period (~1850–1915 CE; yellow triangles).

  2. Double-deconvolution results and anthropogenic emission scenarios.
    Figure 2: Double-deconvolution results and anthropogenic emission scenarios.

    a, Reconstructed changes in organic land carbon with 1-σ standard deviation uncertainty (green shading), modelled anthropogenic land-use change from the KK10 model23 (red) and HYDE-LPX model22 (purple). b, Difference in total organic land carbon change and anthropogenic emissions implying the natural organic land carbon from the KK10 (red shading) and HYDE-LPX (purple shading) scenarios. Dotted lines indicate linear trends from 755–1850 CE.

  3. Multidecadal climate and carbon cycle variability.
    Figure 3: Multidecadal climate and carbon cycle variability.

    Reconstructed change in organic land carbon stocks (green shading) with the MLR model prediction at the 100-year time constant (black markers). Land carbon changes are plotted on a inverted axis to show possible correlations with regional temperature reconstructions25 of the Arctic (red), Asia (blue), N. America (grey), S. America (purple), Europe (yellow), Lake Tanganyika temperature31—as a plausible representation of tropical Africa (thick black with uncertainty in grey)—and a Northern Hemisphere composite (thin black line).

Change history

Corrected online 10 June 2015
In the print and PDF versions of this Letter originally published, the last sentence of the paragraph concerning the double-deconvolution technique should have read: "The data therefore probably rule out a net decrease in organic land carbon stocks between 755 and 1850 CE." In addition, a paper by Schuur et al. was not included in the reference list, and should have been cited as ref. 29 in the following sentence: "Permafrost carbon is also a plausible source of CO2 to the atmosphere during intervals of elevated Arctic temperature29, but would require re-expansion of permafrost into previously active soils during cold intervals to act as a sink for CO2." The remaining references have been renumbered to accommodate this addition. These errors have been corrected in the PDF version.
29. Schuur, E. A. G. et al. Climate change and the permafrost carbon feedback. Nature  520, 171–179 (2015).

References

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Affiliations

  1. College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA

    • Thomas K. Bauska,
    • Alan C. Mix &
    • Edward J. Brook
  2. Climate and Environmental Physics, Physics Institute and Oeschger Center for Climate Change Research, University of Bern, CH-3012 Bern, Switzerland

    • Fortunat Joos &
    • Raphael Roth
  3. School of Earth and Environmental Science, Seoul National University, Seoul 151-742, Korea

    • Jinho Ahn

Contributions

T.K.B., E.J.B. and A.C.M. designed the study with the climate–carbon cycle analysis conceived and performed by T.K.B. and A.C.M. T.K.B. developed the carbon isotope analytical system with E.J.B. and A.C.M. T.K.B. produced the carbon isotope data and J.A. produced the CO2 concentration data. F.J. and R.R. assisted T.K.B. with the deconvolution modelling. T.K.B. wrote the manuscript with input from all authors.

Competing financial interests

The authors declare no competing financial interests.

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