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| Titel |
Gas transport in firn: multiple-tracer characterisation and model intercomparison for NEEM, Northern Greenland |
| VerfasserIn |
C. Buizert, P. Martinerie, V. V. Petrenko, J. P. Severinghaus, C. M. Trudinger, E. Witrant, J. L. Rosen, A. J. Orsi, M. Rubino, D. M. Etheridge, L. P. Steele, C. Hogan, J. C. Laube, W. T. Sturges, V. A. Levchenko, A. M. Smith, I. Levin, T. J. Conway, E. J. Dlugokencky, P. M. Lang, K. Kawamura, T. M. Jenk, J. W. C. White, T. Sowers, J. Schwander, T. Blunier |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 12, no. 9 ; Nr. 12, no. 9 (2012-05-14), S.4259-4277 |
| Datensatznummer |
250011133
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| Publikation (Nr.) |
 copernicus.org/acp-12-4259-2012.pdf |
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| Zusammenfassung |
| Air was sampled from the porous firn layer at the NEEM site in Northern
Greenland. We use an ensemble of ten reference tracers of known atmospheric
history to characterise the transport properties of the site. By analysing
uncertainties in both data and the reference gas atmospheric histories, we
can objectively assign weights to each of the gases used for the
depth-diffusivity reconstruction. We define an objective root mean square
criterion that is minimised in the model tuning procedure. Each tracer
constrains the firn profile differently through its unique atmospheric
history and free air diffusivity, making our multiple-tracer characterisation
method a clear improvement over the commonly used single-tracer tuning. Six
firn air transport models are tuned to the NEEM site; all models successfully
reproduce the data within a 1σ Gaussian distribution. A comparison
between two replicate boreholes drilled 64 m apart shows differences in
measured mixing ratio profiles that exceed the experimental error. We find
evidence that diffusivity does not vanish completely in the lock-in zone, as
is commonly assumed. The ice age- gas age difference (Δage) at the
firn-ice transition is calculated to be 182+3−9 yr. We further
present the first intercomparison study of firn air models, where we
introduce diagnostic scenarios designed to probe specific aspects of the
model physics. Our results show that there are major differences in the way
the models handle advective transport. Furthermore, diffusive fractionation of
isotopes in the firn is poorly constrained by the models, which has
consequences for attempts to reconstruct the isotopic composition of trace
gases back in time using firn air and ice core records. |
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