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| Titel |
Impact of brine induced stratification on the glacial carbon cycle |
| VerfasserIn |
N. Bouttes, D. Paillard, D. M. Roche |
| 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 |
250023809
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| Zusammenfassung |
| The link between carbon cycle and climate is at the core of the understanding of the climate
system, and drives many researches. Various mechanisms have been proposed to explain the
variations of atmospheric CO2 and oceanic δ13C measured during the glacial/interglacial
cycles. Still, though the addition of several mechanisms does help, even the most recent
scenarios are neither sufficient to fully explain the low atmospheric CO2 concentration
of approximately 190 ppm observed during the Last Glacial Maximum, about 21
kyrs ago (e.g. Brovkin et al., 2007) nor producing an oceanic δ13C distribution
compatible with what is inferred from sediment cores proxy data (Curry & Oppo,
2005).
In this context, the ocean is believed to play a major role as it can stock huge amounts of
carbon, especially in the abyss, a carbon reservoir that could widen during glacial time. To
create a larger carbon reservoir in the deep ocean, one possible mechanism is to produce very
dense glacial waters thereby stratifying the deep ocean and reducing the carbon exchange
between the deep and surface ocean. The existence of such very dense waters was inferred in
the deep Atlantic during the LGM from sediment cores data, and the deep ocean
stratification has been shown as a possible mechanism to store carbon in the ocean
and ultimately decrease the atmospheric CO2 concentration (Paillard & Parrenin,
2004).
Based on these data we propose a new mechanism that sets up such deep stratification,
relying on the formation and rapid sink of brines, very salty water rejected during sea ice
formation. We investigate the impact of this mechanism on the carbon cycle using the
CLIMBER-2 fully coupled intermediate complexity climate model, well suited for
the long simulations we run. As the model version used explicitly computes the
evolution of the carbon cycle and carbon isotopes (such as δ13C) in every reservoir, it
allows us to directly compare the model output with data from sediment cores. We
show that the brine induced stratification both leads to low glacial CO2 and very
negative deep δ13C values, as observed in the proxy data. In particular, the LGM
drop is quite large as it reaches 47 ppm with the brine induced stratification and
can be further extended to 76 ppm with a simultaneous reduced oceanic vertical
diffusion.
REFERENCES
Brovkin, V., A. Ganopolski, D. Archer, and S. Rahmstorf: Lowering of glacial
atmospheric CO2 in response to changes in oceanic circulation and marine biogeochemistry,
Paleoceanography, 22, PA4202, doi:10.1029/2006PA001380, 2007.
Curry, W. B. and Oppo, D. W.: Glacial water mass geometry and the distribution of
δ13C of ΣCO2 in the western Atlantic Ocean, Paleoceanography, 20, 1017,
doi:10.1029/2004PA001021, 2005.
Paillard, D. and Parrenin, F.: The Antarctic ice sheet and the triggering of deglaciations,
Earth and Planetary Science Letters, 227, 263-271, 2004. |
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