Geoscience Reference
In-Depth Information
1 Introduction
The successful simulation of past climate changes is an important indicator of the
ability of climate models to forecast future climate changes. While the climate of
the Holocene has been relatively well investigated with global climate models,
previous interglacials received much less attention.
Within this project, we provided quantitative reconstructions of several inter-
glacials using ice core and terrestrial archives on the one hand and a hierarchy of
Earth System models on the other hand. While components such as peat accu-
mulation and CaCO
3
sedimentation, which are necessary to explain the ice core
data, were previously missing from carbon cycle models, the ice core community
only recently succeeded in measuring carbon isotopic data, which provides
important constraints on the mechanisms of the CO
2
changes observed.
2 Materials and Methods
2.1 CLIMBER2-LPJ
CLIMBER2-LPJ (Kleinen et al.
2010
) is a coupled climate carbon cycle model
consisting of the earth system model of intermediate complexity (EMIC) CLIM-
BER2 coupled to the dynamic global vegetation model (DGVM) LPJ, extended by
a model of peat accumulation and decay (Kleinen et al.
2012
).
2.2 Community Climate System Model Version 3 (CCSM3)
The National Center for Atmospheric Research (NCAR) CCSM3 is a state-of-the-
art coupled climate model (Yeager et al.
2006
). The resolution of the atmosphere is
T31 (3.75
°
transform grid), while the ocean model has a horizontal resolution of 3
°
with a finer resolution around the equator.
13
CO
2
2.3 Ice Core Measurements of Atmospheric
δ
The carbon isotopic composition of atmospheric CO
2
provides important bench-
mark data to test hypotheses on past changes in the global carbon cycle. Previous
δ
13
CO
2
measurements were limited in resolution and precision, requiring large ice
samples. We employed a novel sublimation extraction technique (Schmitt et al.
2011
), cutting down sample size to 30 g of ice, while improving precision by a
factor of up to 2
-
0.06
. This has been applied to ice core samples from the
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