Constraints on N 2 O budget changes since pre-industrial time from new firn air and ice core isotope measurements

• Main Authors: S. Bernard, T. Röckmann, J. Kaiser, J.-M. Barnola, H. Fischer, T. Blunier, J. Chappellaz
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2006
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Arctic; Antarctic; Greenland; Berkner Island; Antarc*; Greenland ice core; Greenland Ice core Project; ice core; NGRIP; North Greenland; North Greenland Ice Core Project
• Online Access: https://doaj.org/article/856901d29228420e936032f9f765e470

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.