High-resolution atmospheric CO2 data for
the Eemian interglacial based on stomatal
indices
Mats Rundgren, Svante Björck and Dan Hammarlund
GeoBiosphere Science Centre, Quaternary Sciences, Lund University, Sweden
Introduction
Data from the Antarctic Vostok ice core have
revealed that atmospheric CO2 plays an
important role as an amplifier of climatic changes
over glacial-interglacial timescales (Petit et al.,
1999). CO2 is likely also to be important for
interglacial climate dynamics, but the possibility
of early human influence on CO2 levels makes
the Holocene unsuitable for investigating the role
of CO2 in (natural) interglacial climate evolution.
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Time after the Emian onset (years)
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CO2 concentration (ppmv)
Reconstructed CO2 concentrations
with 95 % confidence intervals. Blue line
= 5 point running mean values. Red
circles = Betula pendula. Green circles =
Quercus robur/Quercus petraea.
Hollerup age relative to start of sedimentation (years)
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interglacial
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CO peak
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sedimentation
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at Hollerup
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Vostok gas age (yr BP)
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Tentative matching of the Vostok and
Hollerup CO2 records based on a 6-7 kyr
lag of peak sea levels relative to the early
interglacial Vostok CO2 peak (Sowers et
al.,1991) and a 3-4 kyr delayed attainment
of peak interglacial sea levels relative to
the onset of the Eemian in NW Europe
(Zagwijn, 1996).
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Pollen and leaf/needle stratigraphies of the Hollerup sequence. Pollen data (percentages) and pollen
zones are based on Andersen’s (1965) analysis. Only the most common taxa and those typical of the Eemian
are shown. Leaf and needle data are concentrations (fragments in 100 cm3 of sediment). Age estimates are
according to Björck et al. (2000) and based on pollen stratigraphic correlation to partly annually laminated lake
sediments in northern Germany (Müller, 1974).
Results and discussion
The first c. 3000 years of the reconstruction are characterised
by centennial to millennial CO2 variations in the range of 250290 ppmv, while CO2 concentrations during the following 30004000 years are more stable and slightly higher (290-300 ppmv)
(see figure to the left). Rapid CO2 oscillations are reconstructed
for a period of c. 300 years immediately before stable conditions
are established.
The transition to more stable CO2 conditions coincides with the
end of the early Eemian climate optimum in northern, central
and western Europe (Zagwijn, 1996; Aalbersberg & Litt, 1998;
Rioual, 2001). Pollen records from these regions indicate that
early Eemian CO2 instability may be linked to vegetation
succession following deglaciation in Europe, but vegetation
dynamics on other northern continents are also likely to be
important.
In addition, CO2 instability during the first 3000 years may reflect
a relatively unstable early Eemian climate as indicated by proxy
data from Hollerup (see figure to the right) and other European
sites (Cheddadi et al., 1998; Rioual, 2001). Comparison with
foraminiferal data from the NE Atlantic and Nordic seas
(Rasmussen et al., 2003) indicates that oceanic processes also
may have contributed to the reconstructed CO2 evolution through
the influence of sea surface temperature on CO2 solubility.
The rapid CO2 oscillations c. 2700-3000 years into the Eemian
are synchronous with a dry and cool event previously inferred
from Hollerup proxy data (see figure to the right), suggesting that
this was a climatic event of regional or global significance. This
event may correspond to one of a series of brief cooling
episodes in the easternmost North Sea (Seidenkrantz &
Knudsen, 1997) and Nordic seas (Fronval et al., 1998), but
the high frequency of the CO2 oscillations is not consistent with
a dominant oceanic origin.
Time after the Eemian onset (years)
Our CO2 reconstruction may be directly
compared with palaeoclimatic records from the
same site (Björck et al., 2000), and pollen
stratigraphic correlation also allows comparison
with climate records from other European sites.
In addition, pollen based correlation suggests
that our CO2 record spans the first c. 7400 years
of the Eemian as defined in NW Europe.
Pollen percentages
Leaf and needle concentrations
Be
tu
We present a CO2 reconstruction based on
stomatal index data obtained from Betula and
Quercus leaves extracted from a lake sediment
sequence at Hollerup, Denmark. This method
rests on the inverse relationship between
stomatal frequency of terrestrial plant leaves and
CO2 partial pressure (Royer, 2001).
Hollerup
Depth (m) in section studied by Björck et al. (2000)
The last interglacial (c. 130-116 ka) offers
climate records from a wide array of archives
and regions at relatively high resolution.
However, because of its relatively low resolution
and high dating uncertainty, it is difficult to
directly relate the Vostok CO2 record to
palaeoclimatic data from distant regions.
Map showing the position of the Hollerup site.
The interglacial lake sequence is exposed in a
disused diatomaceous earth pit (see photo) and
has earlier been studied by Hartz & Østrup
(1899), Jessen & Milthers (1928) and Andersen
(1965). Recently, Björck et al. (2000) presented
a reconstruction of lake development and
hydrologic and climatic conditions based on a
detailed multi-proxy study of the site. (Map and
photo from Björck et al., 2000.)
Fr
a
Co xin
ry us
lu
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Bjerknes Centenary
2004, Bergen,
September 1-3
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Organic
matter
(%)
Carb.
(%)
Mineral δ13Corg
matter
(‰)
(%)
δ13Ccarb
(‰)
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δ18Ocarb Plankt. Inferred CO2
(‰) diatoms relative conc.
(%) lake level (ppmv)
Palaeohydrologic, palaeoclimatic and CO2
data from Hollerup. All proxy records (except
CO2), lithologic units and inferred relative lake
levels are from Björck et al. (2000).
References
Aalbersberg & Litt, 1998. J. Quat. Sci. 13, 367-390.
Andersen, 1965. Medd. Dansk Geol. Foren. 15, 486-504.
Björck et al., 2000. Quat. Sci. Rev. 19, 509-536.
Cheddadi et al., 1998. Pal. Pal. Pal. 143, 73-85.
Fronval et al., 1998. Quat. Sci. Rev. 17, 963-985.
Hartz & Østrup, 1899. Danm. Geol. Unders. II 9, 1-80.
Jessen & Milthers, 1928. Danm. Geol. Unders. II 48, 1-379.
Müller, 1974. Geol. Jahrb. A 21, 149-169.
Petit et al., 1999. Nature 399, 429-436.
Rasmussen et al., 2003. Quat. Sci. Rev. 22, 809-821.
Rioual et al., 2001. Nature 413, 293-296.
Royer, 2001. Rev. Pal. Pal. 114, 1-28.
Seidenkrantz & Knudsen, 1997. Quat. Res. 47, 218-234.
Sowers et al., 1991. Paleoceanography 6, 679-696.
Zagwijn, 1996. Quat. Sci. Rev. 15, 451-469.