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| Titel |
Diffusive equilibration of N2, O2 and CO2 mixing ratios in a 1.5-million-years-old ice core |
| VerfasserIn |
B. Bereiter, H. Fischer, J. Schwander, T. F. Stocker |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1994-0416
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| Digitales Dokument |
URL |
| Erschienen |
In: The Cryosphere ; 8, no. 1 ; Nr. 8, no. 1 (2014-02-17), S.245-256 |
| Datensatznummer |
250116020
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| Publikation (Nr.) |
 copernicus.org/tc-8-245-2014.pdf |
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| Zusammenfassung |
| In the framework of the International Partnerships in Ice Core Sciences, one
of the most important targets is to retrieve an Antarctic ice core that
extends over the last 1.5 million years (i.e. an ice core that enters the
climate era when glacial–interglacial cycles followed the obliquity cycles
of the earth). In such an ice core the annual layers of the oldest ice would
be thinned by a factor of about 100 and the climatic information of a
10 000 yr interval would be contained in less than 1 m of ice. The gas record in
such an Antarctic ice core can potentially reveal the role of greenhouse gas
forcing on these 40 000 yr cycles. However, besides the extreme thinning
of the annual layers, also the long residence time of the trapped air in the
ice and the relatively high ice temperatures near the bedrock favour
diffusive exchanges. To investigate the changes in the O2 / N2 ratio, as well
as the trapped CO2 concentrations, we modelled the diffusive exchange of the
trapped gases O2, N2 and CO2 along the vertical axis. However, the boundary
conditions of a potential drilling site are not yet well constrained and the
uncertainties in the permeation coefficients of the air constituents in the
ice are large. In our simulations, we have set the drill site ice thickness
at 2700 m and the bedrock ice temperature at 5–10 K below the ice pressure
melting point. Using these conditions and including all further
uncertainties associated with the drill site and the permeation
coefficients, the results suggest that in the oldest ice the precessional
variations in the O2 / N2 ratio will be damped by 50–100%, whereas
CO2 concentration changes associated with glacial–interglacial variations
will likely be conserved (simulated damping 5%). If the precessional
O2 / N2 signal will have disappeared completely in this future ice core,
orbital tuning of the ice-core age scale will be limited. |
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