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| Titel |
Surface temperatures from the North-GRIP core during the last deglaciation based on isotopic diffusion of water molecules in the firn. |
| VerfasserIn |
S. B. Simonsen, S. J. Johnsen, T. J. Popp, B. Vinther, H. C. Steen-Larsen, V. Gkinis, Á. E. Sveinbjörnsdóttir, V. Mason-Delmotte, J. White |
| 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 |
250028759
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| Zusammenfassung |
| In the North-GRIP ice core a section of 124.7 m has been measured for the isotopic content
of both 18O and deuterium in 5 cm sample resolution. Based on the GICC05 time scale this
section covers the period from 14830-11547 year b2k. This record of 2494 samples from
the last deglaciation is ideal for estimating past surface temperatures based on the
difference in smoothing of the stable water molecule profiles δ18O and δD in the
firn.
The diffusion of the isotopic signal is shown to be dependent on the temperature in the firn
column above the pore close-off, which is directly linked to the surface temperature of the
site. In the firn the two isotopic species have different fractionation constants, which results in
a slightly longer diffusion length for δ18O than for δD. Below the pore close-off
further diffusion is caused by the slow single crystal self-diffusion, thereby the
differential diffusion length is only affected by the temperature dependent diffusion in
the firn column and the general layer thinning. For a given accumulation rate and
temperature the differential diffusion length can be modeled down through the firn
column.
Power spectral methods are applied on the isotopic profiles of an ice core section in order to
estimate the differential diffusion length. The estimated diffusion lengths need to
be corrected for the total layer thinning, to give the diffusion lengths at the pore
close-off.
In the NorthGRIP ice core, the past accumulation rate has been determined by annual layer
counting back to 60 kyr b2k. This data combined with the corrected diffusion lengths gives
the surface temperature record covering the last deglaciation.
This study shows a remarkable correlation with the temperature reconstructions done by
combining borehole thermometry methods and the δ18O record, which supports the
feasibility of temperature reconstruction from high resolution records of δ18O and δD
measured in ice cores. |
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