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| Titel |
How might the North American ice sheet influence the northwestern Eurasian climate? |
| VerfasserIn |
P. Beghin, S. Charbit, C. Dumas, M. Kageyama, C. Ritz |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 11, no. 10 ; Nr. 11, no. 10 (2015-10-26), S.1467-1490 |
| Datensatznummer |
250117442
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| Publikation (Nr.) |
 copernicus.org/cp-11-1467-2015.pdf |
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| Zusammenfassung |
| It is now widely acknowledged that past Northern Hemisphere ice sheets
covering Canada and northern Europe at the Last Glacial Maximum (LGM) exerted
a strong influence on climate by causing changes in atmospheric and oceanic
circulations. In turn, these changes may have impacted the development of the
ice sheets themselves through a combination of different feedback mechanisms.
The present study is designed to investigate the potential impact of the
North American ice sheet on the surface mass balance (SMB) of the Eurasian
ice sheet driven by simulated changes in the past glacial atmospheric
circulation. Using the LMDZ5 atmospheric circulation model, we carried out 12 experiments under constant LGM conditions for insolation, greenhouse
gases and ocean. In these experiments, the Eurasian ice sheet is removed. The 12 experiments differ in the North American ice-sheet topography, ranging
from a white and flat (present-day topography) ice sheet to a full-size LGM
ice sheet. This experimental design allows the albedo and the topographic
impacts of the North American ice sheet onto the climate to be disentangled.
The results are compared to our baseline experiment where both the North
American and the Eurasian ice sheets have been removed. In summer, the sole
albedo effect of the American ice sheet modifies the pattern of planetary
waves with respect to the no-ice-sheet case, resulting in a cooling of the
northwestern Eurasian region. By contrast, the atmospheric circulation
changes induced by the topography of the North American ice sheet lead to a
strong decrease of this cooling. In winter, the Scandinavian and the
Barents–Kara regions respond differently to the American ice-sheet albedo
effect: in response to atmospheric circulation changes, Scandinavia becomes warmer and
total precipitation is more abundant, whereas the Barents–Kara area becomes cooler
with a decrease of convective processes, causing a decrease of total precipitation.
The gradual increase of the altitude of the American ice sheet leads to less
total precipitation and snowfall and to colder temperatures over both the
Scandinavian and the Barents and Kara sea sectors. We then compute the resulting
annual surface mass balance over the Fennoscandian region from the simulated
temperature and precipitation fields used to force an ice-sheet model. It
clearly appears that the SMB is dominated by the ablation signal. In response
to the summer cooling induced by the American ice-sheet albedo, high positive
SMB values are obtained over the Eurasian region, leading thus to the growth
of an ice sheet. On the contrary, the gradual increase of the American ice-sheet altitude induces more ablation over the Eurasian sector, hence limiting
the growth of Fennoscandia. To test the robustness of our results with respect to the
Eurasian ice sheet state, we carried out two additional LMDZ experiments with
new boundary conditions involving both the American (flat or full LGM) and high Eurasian ice sheets. The most striking result is that the Eurasian ice
sheet is maintained under full-LGM North American ice-sheet conditions, but
loses ~ 10 % of its mass compared to the case in which the North
American ice sheet is flat. These new findings qualitatively confirm the
conclusions from our first series of experiments and suggest that the
development of the Eurasian ice sheet may have been slowed down by the growth
of the American ice sheet, offering thereby a new understanding of the
evolution of Northern Hemisphere ice sheets throughout glacial–interglacial
cycles. |
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