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.
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Carbon isotope work was supported by NSF Grant 0839078 (E.J.B. and A.C.M.). Oregon State University provided additional support for mass spectrometer purchase and management of the OSU/CEOAS stable isotope laboratory. J.A. was partially supported by a National Research Foundation of Korea (NRF) Grant funded by the Korean Government (MSIP) 2014R1A1A2A16054779. F.J. and R.R. are grateful for financial contributions by the Swiss National Science Foundation, including contributions through the Sinergia Project iTree (grant no. 136295), and by the European Commission through the FP7 project CARBOCHANGE (grant no. 264879) and Past4Future (grant no. 243908). We appreciate the support of the WAIS Divide Science Coordination Office for the collection and distribution of the WAIS Divide ice core (Kendrick Taylor (Desert Research Institute of Reno Nevada), NSF Grants 0230396, 0440817, 0944348 and 0944266—University of New Hampshire). The NSF also funds the Ice Drilling Program Office, Ice Drilling Design and Operations group, which leads coring activities, and The National Ice Core Laboratory, which curates the core and performs core processing. We thank J. Severinghaus for providing δ15N of N2 data, Raytheon Polar Services for logistics support in Antarctica, and the 109th New York Air National Guard for airlift in Antarctica.
The authors declare no competing financial interests.
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Bauska, T., Joos, F., Mix, A. et al. Links between atmospheric carbon dioxide, the land carbon reservoir and climate over the past millennium. Nature Geosci 8, 383–387 (2015). https://doi.org/10.1038/ngeo2422
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