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| Titel |
The carbon cycle during the Mid Pleistocene Transition: the Southern Ocean Decoupling Hypothesis |
| VerfasserIn |
P. Köhler, R. Bintanja |
| 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 ; 4, no. 4 ; Nr. 4, no. 4 (2008-12-02), S.311-332 |
| Datensatznummer |
250001872
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| Publikation (Nr.) |
 copernicus.org/cp-4-311-2008.pdf |
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| Zusammenfassung |
| Various hypotheses were proposed within recent years for the interpretation
of the Mid Pleistocene Transition (MPT), which occurred during past
2 000 000 years (2 Myr). We here add to already existing theories on the
MPT some data and model-based aspects focusing on the dynamics of the carbon
cycle. We find that the average glacial/interglacial (G/IG) amplitudes in
benthic δ13C derived from sediment cores in the deep Pacific ocean increased
across the MPT by ~40%, while similar amplitudes in the global
benthic δ18C stack LR04 increased by a factor of two over the same time
interval. The global carbon cycle box model BICYCLE is used for the
interpretation of these observed changes in the carbon cycle. Our simulation
approach is based on regression analyses of various paleo-climatic proxies
with the LR04 benthic δ18C stack over the last 740 kyr, which are then used
to extrapolate changing climatic boundary conditions over the whole 2 Myr
time window. The observed dynamics in benthic δ13C cannot be explained if
similar relations between LR04 and the individual climate variables are
assumed prior and after the MPT. According to our analysis a model-based
reconstruction of G/IG amplitudes in deep Pacific δ13C before the MPT is
possible if we assume a different response to the applied forcings in the
Southern Ocean prior and after the MPT. This behaviour is what we call the
"Southern Ocean Decoupling Hypothesis". This decoupling might potentially
be caused by a different cryosphere/ocean interaction and thus changes in the
deep and bottom water formation rates in the Southern Ocean before the MPT,
however an understanding from first principles remains elusive. Our
hypothesis is also proposing dynamics in atmospheric pCO2 over the past
2 Myr. Simulated pCO2 is varying between 180 and 260 μatm before the
MPT. The consequence of our Southern Ocean Decoupling Hypothesis is that the
slope in the relationship between Southern Ocean SST and atmospheric pCO2
is different before and after the MPT, something for which first indications
already exist in the 800 kyr CO2 record from the EPICA Dome C ice core. We
finally discuss how our findings are related to other hypotheses on the MPT. |
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