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| Titel |
Paleotemperatures derived from the EPICA Dome-C core based on isotopic diffusion in the firn pack. |
| VerfasserIn |
V. Gkinis, S. J. Johnsen, B. Vinther, S. Sheldon, C. Ritz, V. Masson-Delmotte |
| 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 |
250027928
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| Zusammenfassung |
| Water isotope ratios as measured from ice core samples have been used as a proxy for past
temperatures. Based i.a. on a Rayleigh fractionation process they record the cloud
temperature during snow formation. However, changes in the temperature and humidity of the
vapor source can also affect the isotopic signal of the polar precipitation, thus inducing
isotopic artifacts. Furthermore, for the case of the Antarctic ice cap, temperature
inversions frequently occur during snow formation. As a result, the cloud temperature as
recorded by the water isotopes can differ significantly from the temperature at the
surface.
After the deposition of snow and until pore close off, a diffusive process occurs in the
pore space of the firn pack, mixing water vapor from different layers and smoothing the
isotopic profiles. The smoothing depends only on the resulting diffusion length. This process
is temperature dependent and it presents a slightly different rate between the two
isotopic species of water, H218O and HD16O. This is because the fractionation
factors as defined for these two isotopic species have a different dependence on
temperature.
In this study we present a temperature reconstruction based on the different diffusion rates
of H218O and HD16O water molecules in firn. The advantage of such an approach is that the
temperatures estimated represent the actual conditions in the firn stack. As a result, we can
surpass the artifacts that can possibly disrupt the use of the classical technique. We will
present temperature estimations as extracted from two high resolution (2.5 cm) data sets,
from the EPICA Dome C deep core focused on the Holoene Climatic Optimum and the Last
Glacial Maximum and compare them with results obtained with the classical slope method as
well as constrains imposed by the measured temperature profile. We will also address
the problems of spectral power estimation for determining the diffusion lengths. |
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