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Biogeosciences An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 15 Apr 2019

Submitted as: research article | 15 Apr 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Biogeosciences (BG).

N2O changes from the Last Glacial Maximum to the preindustrial – Part I: Quantitative reconstruction of terrestrial and marine emissions using N2O stable isotopes in ice cores

Hubertus Fischer1, Jochen Schmitt1, Michael Bock1, Barbara Seth1, Fortunat Joos1, Renato Spahni1, Sebastian Lienert1, Gianna Battaglia1, Benjamin D. Stocker1,2, Adrian Schilt1,3, and Edward J. Brook3 Hubertus Fischer et al.
  • 1Climate and Environmental Physics, Physics Institute and Oeschger Centre for Climate Change Research, University of Bern, Bern, CH-3012, Switzerland
  • 2CREAF, E08193 Bellaterra (Cerdanyoladel Vallès), Spain
  • 3College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA

Abstract. Using high precision and centennial resolution ice core information on atmospheric nitrous oxide concentrations and its stable nitrogen and oxygen isotopic composition, we quantitatively reconstruct changes in the terrestrial and marine N2O emissions over the last 21,000 years. We show that N2O emissions from land and ocean increased largely in parallel by 1.7 ± 0.3 TgN yr−1 and 0.7 ± 0.3 TgN yr−1 over the deglaciation, respectively. However, during the abrupt Northern Hemisphere warmings at the onset of the Bølling/Allerød and the end of the Younger Dryas, terrestrial emissions respond more rapidly to the northward shift in the Intertropical Convergence Zone connected to the resumption of the Atlantic Meridional Overturning Circulation. 90 % of these large step increases were realized within maximum two centuries. In contrast, marine emissions start to slowly increase already many centuries before the rapid warmings, possibly connected to a re-equilibration of subsurface oxygen in response to previous changes. Marine emissions decreased, concomitantly with changes in atmospheric CO2 and δ13C(CO2), at the onset of the termination and remained minimal during the early phase of Heinrich Stadial 1. During the early Holocene a slow decline in marine N2O emission of 0.4 TgN yr−1 is reconstructed, suggesting an improvement of subsurface water ventilation in line with slowly increasing Atlantic overturning circulation. In the second half of the Holocene total emissions remain on a relatively constant level, however with significant millennial variability which is currently still difficult to attribute to marine or terrestrial sources. Our N2O emission records provide important quantitative benchmarks for ocean and terrestrial nitrogen cycle models to study the influence of climate on nitrogen turnover on time scales from several decades to glacial/interglacial changes.

Hubertus Fischer et al.
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Status: final response (author comments only)
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Hubertus Fischer et al.
Hubertus Fischer et al.
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Short summary
N2O concentrations were subject to strong variations accompanying glacial/interglacial but also rapid climate changes over the last 21 kyr. The sources of these N2O changes can be identified by measuring the isotopic composition of N2O in ice cores and using the distinct isotopic composition of terrestrial and marine N2O. We show that both marine and terrestrial sources increased from the last glacial to the Holocene but that only terrestrial emissions responded quickly to rapid climate changes.
N2O concentrations were subject to strong variations accompanying glacial/interglacial but also...