Glacial-interglacial and millennial-scale changes in nitrous oxide emissions pathways and source regions

Menking, J. A., Lee, J. E., Brook, E. J., Schmitt, J., Soussaintjean, L., Fischer, H., Kaiser, J. and Rice, A. (2025) Glacial-interglacial and millennial-scale changes in nitrous oxide emissions pathways and source regions. Global Biogeochemical Cycles, 39 (5). ISSN 0886-6236

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Abstract

During the transition from the Last Glacial Maximum (LGM) to the Holocene, the atmospheric N2O mole fraction increased by 80 nmol mol−1. Using ice core measurements of N2O isotopomer ratios, we show that this increase was driven by increases in both nitrification and denitrification, with the relative partitioning between both production pathways depending on the assumed isotopic end-member source signatures. Similarly, we also attribute a 35 nmol mol−1 N2O mole fraction increase during the Heinrich Stadial 4/Dansgaard Oeschger 8 (HS4/DO8) millennial-scale event to increases in both N2O production pathways. In contrast, the 25 nmol mol−1 N2O mole fraction decrease during the Younger Dryas was driven almost exclusively by a decrease in nitrification. The deglacial and HS4/DO8 increases in N2O production occurred in both marine and terrestrial environments, with the terrestrial source responding faster to warming by about two centuries. Constraints on changes in nitrification and denitrification emissions are robust and consistent with previous studies showing the sensitivity of N2O emissions to abrupt Northern Hemisphere warming. This study demonstrates for the first time the importance of both denitrification and nitrification pathways in driving source changes. Absolute emissions are more uncertain due to uncertainty about source isotopomer signatures. For instance, the contribution of denitrification to emissions at the LGM shifts from (65 ± 10) % to (91 ± 6) % when factoring in isotope enrichment due to partial reduction of N2O to N2 during denitrification. Reducing uncertainty in source signatures will increase the power of ice core N2O isotope records in deducing environmental change.

Item Type:	Article
Additional Information:	Data Availability Statement: Data are publicly available at the United States Antarctic Program data repository Menking and Brook (2025) (USAP-DC, https://www.usap-dc.org/view/project/p0010465). Other data on which this article is based are available in Fischer et al. (2019), Schilt et al. (2014). Acknowledgments: We thank T. Bauska (British Antarctic Survey) and S. Shackleton (Massachusetts Institute of Technology) for diligent sampling at the Taylor Glacier main transect, and we thank S. Toyoda and N. Yoshida (TiTech) and J. Mohn (EMPA) for N2O isotopic calibration gases. The University of Bern gratefully acknowledges financial support by the Swiss National Science Foundation (Award 172506 and 200328). Oregon State University gratefully acknowledges financial support from the National Science Foundation (Award 1903681). Open access publishing facilitated by University of Tasmania, as part of the Wiley - University of Tasmania agreement via the Council of Australian University Librarians.
Uncontrolled Keywords:	4* ,/dk/atira/pure/researchoutput/REFrank/4_
Faculty \ School:	Faculty of Science > School of Environmental Sciences University of East Anglia Research Groups/Centres > Theme - ClimateUEA
UEA Research Groups:	Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences
Related URLs:	https://agupubs.onlinelibrary.wiley.com/...
Depositing User:	LivePure Connector
Date Deposited:	06 May 2025 09:33
Last Modified:	07 May 2025 08:30
URI:	https://ueaeprints.uea.ac.uk/id/eprint/99187
DOI:	10.1029/2024GB008287

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