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| Titel |
The carbon cycle during recent interglacials |
| VerfasserIn |
T. Kleinen, V. Brovkin |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250066935
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| Zusammenfassung |
| Climate evolution during recent interglacials, the interglacials of the last 800 ka, shows
similarities and dissimilarities. Especially the evolution of atmospheric carbon dioxide, as
displayed by Antarctic ice cores, requires further investigation in order to explain differences
and similarities between interglacials.
Explaining the difference in carbon cycle dynamics (and hence atmospheric CO2)
between various interglacials is an elusive issue. Several biogeochemical mechanisms of
different origin are involved in interglacial CO2 dynamics, leading to a CO2 release from the
ocean (carbonate compensation, CaCO3 sedimentation) compensated by a land carbon
uptake (biomass and soil carbon buildup, peat accumulation). The balance between these
fluxes of CO2 is delicate and time-dependent, and it is not possible to provide firm
constraints on these fluxes from proxy data. The best framework for quantification of all
these mechanisms is an Earth System model that includes all necessary physical
and biogeochemical components of the atmosphere, ocean, and land. To perform
multi-millennial model integrations through various interglacials, we use an earth system
model of intermediate complexity, CLIMBER-2, coupled to the dynamic global
vegetation model LPJ with a recently implemented module for boreal peatland
dynamics. During glacial-interglacial cycles, the carbon cycle never is in complete
equilibrium due to a number of small but persistent fluxes such as terrestrial weathering.
This complicates setting up interglacial experiments as the usual approach to start
model integrations from an equilibrium state is not valid any more. In order to
circumvent the problem of non-equilibrium initial conditions, the model is initialised
with the oceanic biogeochemistry state taken from a transient simulation through
the last glacial cycle with CLIMBER-2 only. In this simulation, the CLIMBER-2
model was run through the last glacial cycle with carbon cycle in “offline mode” as
interactive components of the physical climate system (atmosphere, ocean, ice
sheets) were driven by concentration of greenhouse gases reconstructed from ice
cores.
Using these initial conditions, we used CLIMBER2-LPJ to perform interactively coupled
climate carbon cycle experiments for the Holocene and the Eemian, as well as Marine Isotope
Stages 11, 13 and 15, driven by orbital forcing and prescribed ice sheets. Contrary
to the results we published previously (Kleinen et al. 2010), peat accumulation
was not prescribed, but rather determined dynamically, making this model setup
applicable to previous interglacials as well. For the Holocene, our results resemble
the carbon cycle dynamics as reconstructed from ice cores quite closely, both for
atmospheric CO2 and δ13CO2. These experiments will be presented, analysing the role
of different forcing mechanisms. The land surface appears to be an overall sink
for CO2, due to carbon accumulation in the soil, as well as peat accumulation,
and oceanic contributions due to temperature and circulation changes are quite
small.
We present results from these simulations, analysing the evolution of the carbon
cycle in these modelled interglacials, and how it compares to results from ice cores. |
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