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| Titel |
Measurements of the diffusion rate of stable isotopes in firn in a controlled laboratory experiment. |
| VerfasserIn |
L. G. van der Wel, V. Gkinis, V. A. Pohjola, H. A. J. Meijer |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250027899
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| Zusammenfassung |
| The stable water isotope signal in ice core records is known to be a proxy for past climatic
conditions. The 1H16O2H and 1H18O1H isotope ratios in precipitation water depend on cloud
temperature during snow formation. However, before the isotope signal is frozen into the ice
it is altered as a result of firn diffusion. Firn diffusion is caused by random movement of
water vapor in the pores of the snow. As a consequence the measured isotope signal in an ice
core is a smoothed version of the original precipitation signal. Therefore, before
we can use the measured signal as a climate proxy it has to be back-corrected for
diffusion.
In order to obtain a higher quantitative understanding of the diffusion process we have set
up two laboratory experiments in which we measure the diffusion rate. In both experiments
snow made from isotopically enriched water was interlayered with snow made from natural
water, where the layers were of varying thicknesses. At given intervals samples were taken
from the firn stack and measured for their isotopic concentration. The measurements are
compared to a model based on an existing theory for firn diffusion (see for example Johnsen
et al [1]) and to a previous laboratory experiment [2]. The outcome of this experiment will
help the understanding of the diffusion process and therefore make the back-correction more
accurate.
[1] Johnsen S.J. et al., Diffusion of stable isotopes in polar firn and ice: the isotope effect
in firn diffusion, in Physics of ice core records, edited by T. Hondoh, Hokkaido University
Press, Sapporo, 121-140, 2000.
[2] Pohjola V.A. et al., Controlled experiments on the diffusion rate of stable
isotopes of water in artificial firn, Journal of Glaciology, Vol 53, 537-546, 2007. |
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