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Discussion papers
https://doi.org/10.5194/essd-2019-235
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/essd-2019-235
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: data description paper 22 Jan 2020

Submitted as: data description paper | 22 Jan 2020

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This preprint is currently under review for the journal ESSD.

Apparent ecosystem carbon turnover time: uncertainties and robust features

Naixin Fan1, Sujan Koirala1, Markus Reichstein1, Martin Thurner3, Valerio Avitabile4, Maurizio Santoro5, Bernhard Ahrens1, Ulrich Weber1, and Nuno Carvalhais1,2 Naixin Fan et al.
  • 1Max Planck Institute for Biogeochemistry, Hans Knöll Strasse 10, 07745 Jena, Germany
  • 2Departamento de Ciências e Engenharia do Ambiente, DCEA, Faculdade de Ciências e Tecnologia, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal
  • 3Biodiversity and Climate Research Centre (BiK-F), Senckenberg Gesellschaft für Naturforschung, Senckenberganlage 25, 60325 Frankfurt am Main, Germany
  • 4European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra, Italy
  • 5Gamma Remote Sensing, 3073 Gümligen, Switzerland

Abstract. The turnover time of terrestrial carbon (τ) controls the global carbon cycle – climate feedback and, yet, is poorly simulated by the current Earth System Models (ESMs). In this study, by assessing apparent carbon turnover time as the ratio between carbon stocks and fluxes, we provide a new, updated ensemble of diagnostic terrestrial carbon turnover times and associated uncertainties on a global scale using multiple, state-of-the-art, observation-based datasets of soil organic carbon stock (Csoil), vegetation biomass (Cveg) and gross primary productivity (GPP). Using this new ensemble, we estimated the global average τ to be 42−5+9 years when the full soil depth is considered, longer than the previous estimates of 23−4+7 years. Only considering the top 1 m (assuming maximum active layer depth is up to 1 meter) of soil carbon in circumpolar regions yields a global τ of 35−4+9 years. Csoil in circumpolar regions account for two thirds of the total uncertainty in global τ estimates, whereas Csoil in non-circumpolar contributes merely 9.38 %. GPP (2.25 %) and Cveg (0.05 %) contribute even less to the total uncertainty. Therefore, the high uncertainty in Csoil is the main factor behind the uncertainty in global τ, as reflected in the larger range of full-depth Csoil (3152–4372 PgC). The uncertainty is especially high in circumpolar regions with a uncertainty of 50 % and the spatial correlations among different datasets are also low compared to other regions. Overall, we argue that current global datasets do not support robust estimates of τ globally, for which we need clarification on variations of Csoil with soil depth and stronger estimates of Csoil in circumpolar regions. Despite the large variation in both magnitude and spatial patterns of τ, we identified robust features in the spatial patterns of τ that emerge regardless of soil depth and differences in data sources of Csoil, Cveg and GPP. Our findings show that the latitudinal gradients of τ are consistent across different datasets and soil depth. Furthermore, there is a strong consensus on the negative correlation between τ and temperature along latitude that is stronger in temperate zones (30º N–60º N) than in subtropical and tropical zones (30º S–30º N). The identified robust patterns can be used to infer the response of τ to climate and for constraining contemporaneous behaviour of ESMs which could contribute to uncertainty reductions in future projections of the carbon cycle – climate feedback. The dataset of the terrestrial turnover time ensemble (DOI: 10.17871/bgitau.201911) is openly available from the data portal: https://doi.org/10.17871/bgitau.201911 (Fan et al., 2019).

Naixin Fan et al.

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Naixin Fan et al.

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Ecosystem turnover times database N. Fan, S. Koirala, M. Reichstein, M. Thurner, V. Avitabile, M. Santoro, B. Ahrens, Ul. Weber, and N. Carvalhais https://doi.org/10.17871/bgitau.201911

Naixin Fan et al.

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Short summary
The turnover time of terrestrial carbon (τ) controls the global carbon cycle – climate feedback. In this study, we provide a new, updated ensemble of diagnostic terrestrial carbon turnover times and associated uncertainties on a global scale. Despite the large variation in both magnitude and spatial patterns of τ, we identified robust features in the spatial patterns of τ which could contribute to uncertainty reductions in future projections of the carbon cycle – climate feedback.
The turnover time of terrestrial carbon (τ) controls the global carbon cycle – climate...
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