title: Global covariation of carbon turnover times with climate in terrestrial ecosystems.
abstract: The response of the terrestrial carbon cycle to climate change is among the largest uncertainties affecting future climate change projections. The feedback between the terrestrial carbon cycle and climate is partly determined by changes in the turnover time of carbon in land ecosystems, which in turn is an ecosystem property that emerges from the interplay between climate, soil and vegetation type. Here we present a global, spatially explicit and observation-based assessment of whole-ecosystem carbon turnover times that combines new estimates of vegetation and soil organic carbon stocks and fluxes. We find that the overall mean global carbon turnover time is 23(+7)(-4) years (95 per cent confidence interval). On average, carbon resides in the vegetation and soil near the Equator for a shorter time than at latitudes north of 75° north (mean turnover times of 15 and 255 years, respectively). We identify a clear dependence of the turnover time on temperature, as expected from our present understanding of temperature controls on ecosystem dynamics. Surprisingly, our analysis also reveals a similarly strong association between turnover time and precipitation. Moreover, we find that the ecosystem carbon turnover times simulated by state-of-the-art coupled climate/carbon-cycle models vary widely and that numerical simulations, on average, tend to underestimate the global carbon turnover time by 36 per cent. The models show stronger spatial relationships with temperature than do observation-based estimates, but generally do not reproduce the strong relationships with precipitation and predict faster carbon turnover in many semi-arid regions. Our findings suggest that future climate/carbon-cycle feedbacks may depend more strongly on changes in the hydrological cycle than is expected at present and is considered in Earth system models.
authors.affiliation: 1] Max Planck Institute for Biogeochemistry, Hans Knöll Strasse 10, 07745 Jena, Germany [2] Departamento de Ciências e Engenharia do Ambiente, DCEA, Faculdade de Ciências e Tecnologia, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
authors.forename: Nuno
authors.initials: N
authors.lastname: Carvalhais
authors.affiliation: Max Planck Institute for Biogeochemistry, Hans Knöll Strasse 10, 07745 Jena, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Forkel
authors.affiliation: 1] Max Planck Institute for Biogeochemistry, Hans Knöll Strasse 10, 07745 Jena, Germany [2] School of Geography and Earth Sciences, McMaster University, Hamilton, Ontario L8S 4K1, Canada.
authors.forename: Myroslava
authors.initials: M
authors.lastname: Khomik
authors.affiliation: 1] Institute of Biological and Environmental Sciences, School of Biological Sciences, University of Aberdeen, Aberdeen AB24 3UU, UK [2] Lancaster Environment Centre, Lancaster University, Bailrigg, Lancaster LA1 4YQ, UK.
authors.forename: Jessica
authors.initials: J
authors.lastname: Bellarby
authors.affiliation: Max Planck Institute for Biogeochemistry, Hans Knöll Strasse 10, 07745 Jena, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Jung
authors.affiliation: 1] Max Planck Institute for Biogeochemistry, Hans Knöll Strasse 10, 07745 Jena, Germany [2] Remote Sensing of Environmental Dynamics Lab, DISAT, University of Milano-Bicocca, Piazza della Scienza 1, 20126 Milan, Italy.
authors.forename: Mirco
authors.initials: M
authors.lastname: Migliavacca
authors.affiliation: Department of Earth System Science, University of California Irvine, Irvine, California 92697, USA.
authors.forename: Mingquan
authors.initials: M
authors.lastname: Mu
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA.
authors.forename: Sassan
authors.initials: S
authors.lastname: Saatchi
authors.affiliation: Gamma Remote Sensing, Worbstrasse 225, 3073 Gümligen, Switzerland.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Santoro
authors.affiliation: Max Planck Institute for Biogeochemistry, Hans Knöll Strasse 10, 07745 Jena, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Thurner
authors.affiliation: Max Planck Institute for Biogeochemistry, Hans Knöll Strasse 10, 07745 Jena, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Weber
authors.affiliation: Max Planck Institute for Biogeochemistry, Hans Knöll Strasse 10, 07745 Jena, Germany.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Ahrens
authors.affiliation: 1] Max Planck Institute for Biogeochemistry, Hans Knöll Strasse 10, 07745 Jena, Germany [2] Department of Applied Environmental Science and Bolin Centre for Climate Research, Stockholm University, Svante Arrhenius väg 8, 10691 Stockholm, Sweden.
authors.forename: Christian
authors.initials: C
authors.lastname: Beer
authors.affiliation: European Commission, Joint Research Centre, Institute for Environment and Sustainability, Climate Risk Management Unit, Via E. Fermi, 2749, I-21027 Ispra, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Cescatti
authors.affiliation: Department of Earth System Science, University of California Irvine, Irvine, California 92697, USA.
authors.forename: James T
authors.initials: JT
authors.lastname: Randerson
authors.affiliation: Max Planck Institute for Biogeochemistry, Hans Knöll Strasse 10, 07745 Jena, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Reichstein
mesh_terms: D018533:Biomass; D002244:Carbon / Q000378:metabolism*; D057486:Carbon Cycle; D002980:Climate; D017753:Ecosystem; D005246:Feedback; D062070:Hydrology; D008962:Models, Theoretical; D010944:Plants / Q000378:metabolism; D011891:Rain; D012987:Soil / Q000737:chemistry; D013696:Temperature; D013997:Time Factors; D058438:Water Cycle
chemical_list: D012987:Soil; D002244:Carbon