Constraints on N2O budget changes since pre-industrial time from new firn air and ice core isotope measurements

A historical record of changes in the N 2 O isotope composition is important for a better understanding of the global N 2 O atmospheric budget. Here we have combined measurements of trapped gases in the firn and in ice cores of one Arctic site (North GReenland Ice core Project - NGRIP) and one Antar...

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Bibliographic Details
Published in:Atmospheric Chemistry and Physics
Main Authors: Bernard, S., Röckmann, T., Kaiser, J., Barnola, J.-M., Fischer, H., Blunier, T., Chappellaz, J.
Format: Text
Language:English
Published: 2018
Subjects:
Antarctic
Arctic
Berkner Island
Greenland
Antarc*
Greenland ice core
Greenland Ice core Project
ice core
NGRIP
North Greenland
North Greenland Ice Core Project
Online Access:https://doi.org/10.5194/acp-6-493-2006
https://www.atmos-chem-phys.net/6/493/2006/
Description
Summary:A historical record of changes in the N 2 O isotope composition is important for a better understanding of the global N 2 O atmospheric budget. Here we have combined measurements of trapped gases in the firn and in ice cores of one Arctic site (North GReenland Ice core Project - NGRIP) and one Antarctic site (Berkner Island). We have performed measurements of the 18 O and position dependent 15 N isotopic composition of N 2 O. By comparing these data to simulations carried out with a firn air diffusion model, we have reconstructed the temporal evolution of the N 2 O isotope signatures since pre-industrial times. The decrease observed for all signatures is consistent from one pole to the other. Results obtained from the air occluded in the ice suggest a decrease of about -2.8, -2.4, -3.2 and -1.6 for δ 15 N, 1 δ 15 N, 2 δ 15 N and δ 18 O, respectively, since 1700 AD. Firn air data imply a decrease of about -1.1, -1.2, -1.0 and -0.6 for δ 15 N, 1 δ 15 N, 2 δ 15 N and δ 18 O, respectively, since 1970 AD. These results imply consistent trends from firn and ice measurements for δ 15 N and δ 18 O. The trends for the intramolecular distribution of 15 N are less well constrained than the bulk 15 N trends because of the larger experimental error for the position dependent 15 N measurements. The decrease in the heavy isotope content of atmospheric N 2 O can be explained by the increasing importance of agriculture for the present atmospheric N 2 O budget.

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