PP43E-02
Glacial-Interglacial and Holocene N2O Stable Isotope Changes Constrain Terrestrial N Cycling
Thursday, 17 December 2015: 13:55
2012 (Moscone West)
Jochen Schmitt1, Renato Spahni1, Michael Bock1, Barbara Seth1, Benjamin David Stocker2, Xu Ri3, Adrian Schilt4, Edward Brook5, Bette L Otto-Bliesner6, Zhengyu Liu7, Iain Colin Prentice8, Hubertus Fischer1 and Fortunat Joos9, (1)University of Bern, Bern, Switzerland, (2)Imperial College London, London, United Kingdom, (3)Key Laboratory of Alpine Ecology and Biodiversity Institute of Tibetan Plateau Research Chinese Academy of Sciences and CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing, China, (4)Oregon State University, Corvallis, OR, United States, (5)Oregon State Univ, Corvallis, OR, United States, (6)National Center for Atmospheric Research, Boulder, CO, United States, (7)Univ Wisconsin Madison, Madison, WI, United States, (8)Northwest A&F University, Yangling, China, (9)Univ Bern, Bern, Switzerland
Abstract:
The land biosphere contributes most to the natural source of the long-lived greenhouse gas nitrous oxide (N2O), with N2O emissions being dependent on the turnover rate of both the terrestrial nitrogen (N) and carbon (C) cycle. The C:N stoichiometry of vegetation and soil organic matter links the cycles intimately. Sustained plant productivity increase must be supported by biological N fixation. Intensified N cycling in turn enhances N loss and thereby N2O emissions. The temporal and spatial dynamics of terrestrial N and C cycles and related terrestrial N2O emissions are poorly constrained over the glacial-interglacial transition and the Holocene. Here we reconstruct increased terrestrial N2O emissions since the Last Glacial Maximum based on N2O concentration and isotope measurements on several ice cores and show that this N2O increase can be explained by N cycle modelling – provided N fixation is allowed to respond dynamically to increasing N demand and turnover. The Ice core reconstructions suggest a deglacial increase of 1.1 ± 0.4 Tg N/yr in terrestrial and 0.6 ± 0.4 Tg/yr in oceanic N2O emissions, but relatively constant terrestrial emissions over the Holocene. Transient simulations with a Dynamic Global Vegetation Model are shown to represent the climate and CO2 induced changes in terrestrial N2O emission, and suggest a deglacial increase in biological N fixation by 20%, independently of its absolute magnitude. Deciphering the response of biological N fixation during climatic changes is an important factor for our understanding of plant growth and the land carbon sink, alongside anthropogenic greenhouse gas emissions.
