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| Titel |
Impact of oceanic processes on the carbon cycle during the last termination |
| VerfasserIn |
N. Bouttes, D. Paillard, D. M. Roche, C. Waelbroeck, M. Kageyama, A. Lourantou, E. Michel, L. Bopp |
| 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 ; 8, no. 1 ; Nr. 8, no. 1 (2012-01-20), S.149-170 |
| Datensatznummer |
250005366
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| Publikation (Nr.) |
 copernicus.org/cp-8-149-2012.pdf |
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| Zusammenfassung |
During the last termination (from ~18 000 years ago to ~9000 years
ago), the climate significantly warmed and the ice sheets melted.
Simultaneously, atmospheric CO2 increased from ~190 ppm to ~260 ppm.
Although this CO2 rise plays an important role in the deglacial
warming, the reasons for its evolution are difficult to explain. Only box
models have been used to run transient simulations of this carbon cycle
transition, but by forcing the model with data constrained scenarios of the
evolution of temperature, sea level, sea ice, NADW formation, Southern Ocean
vertical mixing and biological carbon pump. More complex models (including
GCMs) have investigated some of these mechanisms but they have only been used
to try and explain LGM versus present day steady-state climates.
In this study we use a coupled climate-carbon model of intermediate
complexity to explore the role of three oceanic processes in transient
simulations: the sinking of brines, stratification-dependent diffusion and
iron fertilization. Carbonate compensation is accounted for in these
simulations. We show that neither iron fertilization nor the sinking of
brines alone can account for the evolution of CO2, and that only the
combination of the sinking of brines and interactive diffusion can
simultaneously simulate the increase in deep Southern Ocean δ13C.
The scenario that agrees best with the data takes into account all mechanisms
and favours a rapid cessation of the sinking of brines around 18 000 years
ago, when the Antarctic ice sheet extent was at its maximum. In this
scenario, we make the hypothesis that sea ice formation was then shifted to
the open ocean where the salty water is quickly mixed with fresher water,
which prevents deep sinking of salty water and therefore breaks down the deep
stratification and releases carbon from the abyss. Based on this scenario, it
is possible to simulate both the amplitude and timing of the long-term CO2
increase during the last termination in agreement with ice core data. The
atmospheric δ13C appears to be highly sensitive to changes in the
terrestrial biosphere, underlining the need to better constrain the
vegetation evolution during the termination. |
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