Carbon-nitrogen interactions in idealized simulations with JSBACH
Daniel S. Goll1,2, Alexander J. Winkler3,4, Thomas Raddatz3, Ning Dong5,6, Ian Colin Prentice5,7, Philippe Ciais1, and Victor Brovkin31Le Laboratoire des Sciences du Climat et de l'Environnement, IPSL-LSCE CEA/CNRS/UVSQ Saclay, Gif sur Yvette, France 2also guest scientist at Max Planck Institute for Meteorology, Hamburg, Germany 3Max Planck Institute for Meteorology, Hamburg, Germany 4International Max Planck Research School on Earth System Modelling, Hamburg, Germany 5Department of Biological Sciences, Macquarie University, North Ryde, NSW 2109, Australia 6Faculty of Agriculture and Environment, Department of Environmental Sciences, University of Sydney, NSW 2006, Australia 7AXA Chair in Biosphere and Climate Impacts, Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot SL5 7PY, UK
Received: 17 Dec 2016 – Accepted for review: 05 Jan 2017 – Discussion started: 09 Jan 2017
Abstract. Recent advances in the representation of soil carbon decomposition (Goll et al., 2015) and carbon-nitrogen interactions (Parida, 2011; Goll et al., 2012) implemented previously into separate versions of the land surface scheme JSBACH are here combined in a single version which is set to be used in the upcoming 6th phase of coupled model intercomparison project (CMIP6) (Eyring et al., 2016).
Here we demonstrate that the new version of JSBACH is able to reproduce the spatial variability in the reactive nitrogen loss pathways as derived from a compilation of δ15N data (r=.63, RMSE=.26, Taylor score=.81). The inclusion of carbon-nitrogen interactions leads to a moderate reduction (−10 %) of the carbon-concentration feedback (βL) and has a negligible effect on the sensitivity of the land carbon cycle to warming (γL) compared to the same version of the model without carbon-nitrogen interactions in idealized simulations (1 % increase in atmospheric carbon dioxide per yr). In line with evidence from elevated carbon dioxide manipulation experiments (Shi et al., 2015; Liang et al., 2016), pronounced nitrogen scarcity is alleviated by (1) the accumulation of nitrogen due to enhanced nitrogen inputs by biological nitrogen fixation and reduced losses by leaching and volatilization as well as the (2) enhanced turnover of organic nitrogen.
The strengths of the land carbon feedbacks of the recent version of JSBACH, with βL=0.61 Pg ppm−1 and γL=−27.5 Pg °C−1, are 34 % and 53 % less than the averages of CMIP5 models (Arora et al., 2013), although the CMIP5 version of JSBACH simulated βL and γL which are 59 % and 42 % higher than multi-model average. These changes are primarily due to the new decomposition model, stressing the importance of getting the basics right (here: the decomposition of soil carbon) before increasing the complexity of the model (here: carbon-nitrogen interactions).
Goll, D. S., Winkler, A. J., Raddatz, T., Dong, N., Prentice, I. C., Ciais, P., and Brovkin, V.: Carbon-nitrogen interactions in idealized simulations with JSBACH
(version 3.10), Geosci. Model Dev. Discuss., doi:10.5194/gmd-2016-304, in review, 2017.