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| Titel |
Retrieving the paleoclimatic signal from the deeper part of the EPICA Dome C ice core |
| VerfasserIn |
J.-L. Tison, M. De Angelis, G. Littot, E. Wolff, H. Fischer, M. Hansson, M. Bigler, R. Udisti, A. Wegner, J. Jouzel, B. Stenni, S. Johnsen, V. Masson-Delmotte, A. Landais, V. Lipenkov, L. Loulergue, J.-M. Barnola, J.-R. Petit, B. Delmonte, G. Dreyfus, D. Dahl-Jensen, G. Durand, B. Bereiter, A. Schilt, R. Spahni, K. Pol, R. Lorrain, R. Souchez, D. Samyn |
| 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 ; 9, no. 4 ; Nr. 9, no. 4 (2015-08-20), S.1633-1648 |
| Datensatznummer |
250116838
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| Publikation (Nr.) |
 copernicus.org/tc-9-1633-2015.pdf |
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| Zusammenfassung |
| An important share of paleoclimatic information is buried within the
lowermost layers of deep ice cores. Because improving our records further
back in time is one of the main challenges in the near future, it is
essential to judge how deep these records remain unaltered, since the
proximity of the bedrock is likely to interfere both with the recorded
temporal sequence and the ice properties. In this paper, we present a
multiparametric study (δD-δ18Oice, δ18Oatm, total air content, CO2, CH4, N2O, dust,
high-resolution chemistry, ice texture) of the bottom 60 m of the EPICA (European Project for Ice Coring in Antarctica) Dome
C ice core from central Antarctica. These bottom layers were subdivided into two distinct facies: the lower 12 m showing visible solid inclusions (basal
dispersed ice facies) and the upper 48 m, which we will refer to as the
"basal clean ice facies". Some of the data are consistent with a pristine
paleoclimatic signal, others show clear anomalies. It is demonstrated that
neither large-scale bottom refreezing of subglacial water, nor mixing (be it
internal or with a local basal end term from a previous/initial ice sheet
configuration) can explain the observed bottom-ice properties. We focus on
the high-resolution chemical profiles and on the available remote sensing
data on the subglacial topography of the site to propose a mechanism by which
relative stretching of the bottom-ice sheet layers is made possible, due to
the progressively confining effect of subglacial valley sides. This stress
field change, combined with bottom-ice temperature close to the pressure
melting point, induces accelerated migration recrystallization, which results
in spatial chemical sorting of the impurities, depending on their state
(dissolved vs. solid) and if they are involved or not in salt formation. This
chemical sorting effect is responsible for the progressive build-up of the
visible solid aggregates that therefore mainly originate "from within", and
not from incorporation processes of debris from the ice sheet's substrate. We
further discuss how the proposed mechanism is compatible with the other ice
properties described. We conclude that the paleoclimatic signal is only
marginally affected in terms of global ice properties at the bottom of EPICA
Dome C, but that the timescale was considerably distorted by mechanical
stretching of MIS20 due to the increasing influence of the subglacial
topography, a process that might have started well above the bottom ice. A
clear paleoclimatic signal can therefore not be inferred from the deeper part
of the EPICA Dome C ice core. Our work suggests that the existence of a flat
monotonic ice–bedrock interface, extending for several times the ice
thickness, would be a crucial factor in choosing a future "oldest ice"
drilling location in Antarctica. |
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