How variable were atmospheric CO2 levels during the last deglaciation?
XVI INQUA Congress
July 23-30, 2003
Reno, Nevada, USA
Evidence from stomatal index measurements of a Swedish high-resolution leaf record
Abstract no. 53595
Mats Rundgren and Svante Björck, Quaternary Geology, Lund University, Sweden
CO2 calibration
Stomatal-based reconstruction of past CO2
levels requires species-specific calibration
data sets developed from leaves collected in
the field and from herbaria.
5.6
13
12
Betula nana
(R2 = 0.55)
Stomatal index (%)
6.4
6.5
H
6.7
10
6.8
9
6.9
7
6
Salix polaris
(R2 = 0.54)
7
200
200
100
3
2
A
B
11000
1
12000
Age (calibrated
7000
8000
9000
10000
14
Species-specific CO2 records
A. Reconstructed sample mean
CO2 concentrations (with 95 %
confidence intervals) for Salix
herbacea (red, open circles),
Salix polaris (blue, full circles)
and Betula nana (green
crosses).
B. Smoothed species-specific
CO2 redords (5 point running
mean values).
100
11000
12000
Age (calibrated
14
13000
C yr BP)
11000 12000 13000 14000
Age (calibrated 14C yr BP)
6
Salix herbacea
(R2 = 0.68)
5
4
22
24
26
28
30
32
34
36
38
40
CO partial pressure (Pa)
2
Age model
Vertical and horizontal bars indicate sampled
depth intervals and calibrated (INTCAL98) age
intervals (1 σ) for radiocarbon dated samples.
Calibration data sets
Stomatal indices were measured
on samples covering the period of
rapid atmospheric CO2 rise after
1840 and an altitudinal range of
0-2670 m a.s.l.
Holocene
PBO
(GH-11.2)
YD (GS-1)
400
AL
(GI-1)
Combined CO2 record
The combined record is in many respects similar to previous
stomatal-based reconstructions (Beerling et al., 1995; Wagner et
al., 1999; McElwain et al., 2002).
-20
-22
-24
-26
300
All three
species
combined
-28
-30
-32
Dome C
-34
-36
200
-38
GRIP δ18O
-40
-42
-44
11000
12000
Age (calibrated
14
C yr BP)
13000
The overall deglacial CO2 trend is almost identical to that seen in
the Dome C ice-core record (Monnin et al., 2001), but the amplitude
of change is markedly higher in the stomatal-based record. This
difference may partly be accounted for by the inherent smoothing of
ice-core CO2 records caused by diffusion. A major part of the
difference in amplitude remains, however, unexplained.
The Lake Madtjärn CO2 record shows similarities to the GRIP
oxygen isotope record (Johnsen et al., 2001), e.g. low values during
early YD/GS-1 and PBO/GH-11.2. If correct, the stomatal-based
record therefore suggests that atmospheric CO2 may have played
an important role in climate dynamics during the last deglaciation.
Abbrevations used in figures
What are stomata?
Stomata are pores used by vascular plants to exchange
gases (carbon dioxide, oxygen, water vapour etc.) with the
atmosphere.
Vascular plants respond to CO2 changes by adjusting the
number of stomata as new leaves are developed.
Stomatal index is defined as the number of stomata
proportional to the sum of stomata and epidermal cells
within a unit area.
13000
C yr BP)
100
Stomatal index is insensitive to the influence of
environmental factors other than CO2.
AL
(GI-1)
300
7.0
8
YD (GS-1)
300
5
4
PBO
Holocene (GH-11.2)
AL
(GI-1)
400
YD
AL
YD (GS-1)
400
δ18O (‰)
Close-up of a
Salix herbacea
leaf showing
stomata (arrows)
and epidermal
cells.
6.3
CO 2 concentration (ppmv)
Based on an extensive radiocarbon dating programme in
combination with lithostratigraphic and palaeobotanical
investigations, it was possible to correlate our CO2 record to
the INTIMATE event stratigraphy (Björck et al., 1998;
Walker et al., 1999).
6.2
6.6
11
A stomatal-based CO2 reconstruction
Here we present a Lateglacial and early Holocene CO2
record based on stomatal index data obtained from leaves
preserved in the sediments of a Swedish lake.
6.1
CO2 concentration (ppmv)
Sediment depth (m)
14
Sediment stratigraphy
5.9
Climate stratigraphy
5.8
6.0
By contrast, palaeo-CO2 records based on the inverse
relationship between CO2 partial pressure and stomatal
frequency of terrestrial plant leaves reflect a more dynamic
CO2 evolution (Beerling et al., 1995; McElwain et al., 2002;
Wagner et al., 1999).
Holocene
5.7
CO2 concentration (ppmv)
Background
Data from ice cores suggest that Lateglacial and early
Holocene atmospheric CO2 variations were rather
conservative, the most important change being a gradual
Younger Dryas increase (Monnin et al., 2001).
Investigated site
Lake Madtjärn (c. 4500 m2) is
situated in southwestern Sweden
(58°35'47"N, 12°10'37”E).
Leaf concentration data
Lake Madtjärn sediments are unusually rich in
leaves. Only leaves of Salix herbacea, Salix
polaris and Betula nana were used for CO2
reconstruction.
AL = Allerød interstadial
YD = Younger Dryas stadial
H = Holocene interglacial
PBO = Preboreal oscillation (age according to Björck et al. (1997)).
GI-1 = Greenland Interstadial 1.
GS-1 = Greenland Stadial 1.
GH-11.2 = Greenland Holocene 11.2 event.
GI-1, GS-1 and GH-11.2 are the equivalents to AL, YD and PBO in
the INTIMATE event stratigraphy (Björck et al., 1998; Walker et al.,
1999).
References
Beerling et al., 1995. J. Quat. Sci. 10, 379-384.
Björck et al., 1997. J. Quat. Sci. 12, 455-365.
Björck et al., 1998. J. Quat. Sci. 13, 283-292.
Johnsen et al., 2001. J. Quat. Sci. 16, 299-307.
McElwain et al., 2002. J. Quat. Sci. 17, 21-29.
Monnin et al., 2001. Science 291, 112-114.
Wagner et al., 1999. Science 284, 1971-1973.
Walker et al., 1999. Quat. Sci. Rev. 18, 1143-1150.