TY - JOUR
T1 - Constraints on N2O budget changes since pre-industrial time from new firn air and ice core isotope measurements
AU - Bernard, S.
AU - Röckmann, T.
AU - Kaiser, J.
AU - Barnola, j.m.
AU - Fischer, H
AU - Blunier, T.
AU - Chappellaz, J.
PY - 2006
Y1 - 2006
N2 - A historical record of changes in the N2O isotope
composition is important for a better understanding of
the global N2O 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 18O and position dependent 15N isotopic
composition of N2O. By comparing these data to simulations
carried out with a firn air diffusion model, we have
reconstructed the temporal evolution of the N2O 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 15N,
1 15N, 2 15N and 18O, respectively, since 1700AD. Firn air
data imply a decrease of about −1.1‰, −1.2‰, −1.0‰ and
−0.6‰ for 15N, 1 15N, 2 15N and 18O, respectively, since
1970 AD. These results imply consistent trends from firn
and ice measurements for 15N and 18O. The trends for the
intramolecular distribution of 15N are less well constrained
than the bulk 15N trends because of the larger experimental
error for the position dependent 15N measurements. The decrease
in the heavy isotope content of atmospheric N2O can
be explained by the increasing importance of agriculture for
the present atmospheric N2O budget.
AB - A historical record of changes in the N2O isotope
composition is important for a better understanding of
the global N2O 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 18O and position dependent 15N isotopic
composition of N2O. By comparing these data to simulations
carried out with a firn air diffusion model, we have
reconstructed the temporal evolution of the N2O 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 15N,
1 15N, 2 15N and 18O, respectively, since 1700AD. Firn air
data imply a decrease of about −1.1‰, −1.2‰, −1.0‰ and
−0.6‰ for 15N, 1 15N, 2 15N and 18O, respectively, since
1970 AD. These results imply consistent trends from firn
and ice measurements for 15N and 18O. The trends for the
intramolecular distribution of 15N are less well constrained
than the bulk 15N trends because of the larger experimental
error for the position dependent 15N measurements. The decrease
in the heavy isotope content of atmospheric N2O can
be explained by the increasing importance of agriculture for
the present atmospheric N2O budget.
M3 - Article
SN - 1680-7316
VL - 6
SP - 493
EP - 503
JO - Atmospheric chemistry and physics
JF - Atmospheric chemistry and physics
IS - 2
ER -