Preprints
https://doi.org/10.5194/gmd-2020-205
https://doi.org/10.5194/gmd-2020-205

Submitted as: model description paper 24 Jul 2020

Submitted as: model description paper | 24 Jul 2020

Review status: a revised version of this preprint is currently under review for the journal GMD.

JULES-CN: a coupled terrestrial Carbon-Nitrogen Scheme (JULES vn5.1)

Andrew J. Wiltshire1,2, Eleanor J. Burke1, Sarah E. Chadburn3, Chris D. Jones1, Peter M. Cox3, Taraka Davies-Barnard3, Pierre Friedlingstein3, Anna B. Harper3, Spencer Liddicoat1, Stephen A. Sitch2, and Sonke Zaehle4 Andrew J. Wiltshire et al.
  • 1Met Office Hadley Centre, Exeter, Devon, UK EX1 3PB
  • 2College of Life and Environmental Sciences, University of Exeter, Exeter, EX4 4RJ
  • 3College of Engineering, Mathematics, and Physical Sciences, University of Exeter, Exeter, EX44QE
  • 4Biogeochemical Signals Department, Max Planck Institute for Biogeochemistry, 07745 Jena, Germany

Abstract. Understanding future changes in the terrestrial carbon cycle is important for reliable projections of climate change and impacts on ecosystems. It is known that nitrogen could limit plants' response to increased atmospheric carbon dioxide and is therefore important to include in Earth System Models. Here we present the implementation of the terrestrial nitrogen cycle in the JULES land surface model (JULES-CN). Two versions are discussed – the one implemented within the UK Earth System Model (UKESM1) which has a bulk soil biogeochemical model and a development version which resolves the soil biogeochemistry with depth. The nitrogen cycle is based on the existing carbon cycle in the model. It represents all the key terrestrial nitrogen processes in an efficient way. Biological fixation and nitrogen deposition are external inputs, and loss occurs via leaching and a bulk gas loss parameterisation. Nutrient limitation reduces carbon-use efficiency (CUE – ratio of net to gross primary productivity) and can slow soil decomposition. We show that ecosystem level limitation of net primary productivity by nitrogen is consistent with observational estimates and that simulated carbon and nitrogen pools and fluxes are comparable to the limited available observations. The impact of N limitation is most pronounced in northern mid-latitudes. The introduction of a nitrogen cycle improves the representation of interannual variability of global net ecosystem exchange which was much too pronounced in the carbon cycle only versions of JULES (JULES-C). It also reduces the CUE and alters its response over the twentieth century and limits the CO2-fertilisation effect, such that the simulated current day land carbon sink is reduced by about 0.5 Pg C yr−1. The inclusion of a prognostic land nitrogen scheme marks a step forward in functionality and realism for the JULES and UKESM models.

Andrew J. Wiltshire et al.

 
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Andrew J. Wiltshire et al.

Andrew J. Wiltshire et al.

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Short summary
Limited nitrogen availbility can restrict the growth of plants and their ability to assimilate carbon. It is important to include the impact of this process on the global land carbon cycle. This paper presents a model of the coupled land carbon and nitrogen cycle which is included within the UK Earth System model to improve projections of cliamte change and impacts on ecosystems.