Lam2007b
Vol 452 | 3 April 2008 | doi:10.1038/nature06763
LETTERS
Dust2climate couplings over the past 800,000 years
from the EPICA Dome C ice core
F. Lambert1,2, B. Delmonte3, J. R. Petit4, M. Bigler1,5, P. R. Kaufmann1,2, M. A. Hutterli6, T. F. Stocker1,2, U. Ruth7,
J. P. Steffensen5 & V. Maggi3
Dust can affect the radiative balance of the atmosphere by absorbing or reflecting incoming solar radiation1; it can also be a source
of micronutrients, such as iron, to the ocean2. It has been suggested that production, transport and deposition of dust is influenced by climatic changes on glacial2interglacial timescales3–6.
Here we present a high-resolution record of aeolian dust from
the EPICA Dome C ice core in East Antarctica, which provides
an undisturbed climate sequence over the past eight climatic
cycles7,8. We find that there is a significant correlation between
dust flux and temperature records during glacial periods that is
absent during interglacial periods. Our data suggest that dust flux
is increasingly correlated with Antarctic temperature as the climate becomes colder. We interpret this as progressive coupling of
the climates of Antarctic and lower latitudes. Limited changes in
glacial2interglacial atmospheric transport time4,9,10 suggest that
the sources and lifetime of dust are the main factors controlling
the high glacial dust input. We propose that the observed 25-fold
increase in glacial dust flux over all eight glacial periods can be
attributed to a strengthening of South American dust sources,
together with a longer lifetime for atmospheric dust particles in
the upper troposphere resulting from a reduced hydrological cycle
during the ice ages.
The EPICA (European Project for Ice Coring in Antarctica) ice
core drilled at Dome C (hereafter EDC) in East Antarctica (75u 069 S;
123u 219 E) covers the past 800,000 yr (Fig. 1a). The dust flux record
of Vostok (Fig. 1b) is thus extended over four additional cycles
(Fig. 1c). The glacial–interglacial climate changes are well reflected
in the sequence of high and low dust concentrations with typical
values from 800 to 15 mg kg21 and a ratio of 50 to 1 over most of
the past eight climate cycles. The concentration of insoluble dust in
snow depends on a number of factors such as the primary supply of
small mineral particles from the continents, which is related to climate and environmental conditions in the source region11, the snow
accumulation rate, the long-range transport, and the cleansing of the
atmosphere associated with the hydrological cycle. The strontium
and neodymium isotopic signature of dust12 revealed that southern
South America was the dominant dust source for East Antarctica
during glacial times13, although contributions from other sources
are possible during interglacials14. Because of the low accumulation
rate at Dome C (,3 cm yr21 water equivalent), dry deposition is
dominant and the atmospheric dust load is best represented by the
dust flux15. The total dust flux and the magnitude of the glacial–
interglacial changes are remarkably uniform within the East
Antarctic Plateau, as shown by the similarity between the EDC and
the Vostok records (Fig. 1b, despite some chronological differences
and a 10-times finer resolution at EDC) over the past four climatic
cycles and also depicted by the Dome Fuji dust record16 (not shown).
At EDC, interglacials display dust fluxes similar to that of the
Holocene (,400 mg m22 yr21). However, some differences can be
seen in the record before and after the Mid-Brunhes Event (MBE,
,430 kyr BP) which is considered a transition in the climatic record7,8
from cooler (for example Marine Isotopic Stages, MIS 13, 15, 17) to
warmer (for example MIS 11, 9 and 5.5) interglacials. Before the MBE
there were fewer occurrences of low concentrations, and warm
periods represent ,12% of the time, compared with ,30% after
the MBE. All eight glacial periods appear similar in magnitude and
show an average increase in dust flux by a factor of about 25, with
glacial maxima displaying fluxes of at least 12 mg m22 yr21. The
weakest glacial stages in the EDC ice core are MIS 14 and 16. For
MIS 14 this is consistent with the findings from terrestrial and marine
records6,17,18. In contrast, MIS 16 in those records is the strongest
glacial in the Late Quaternary period.
The extension of the EDC dust record to 800 kyr BP confirms the
increased atmospheric dust load during cold periods of the
Quaternary period with respect to warm stages. The first-order
similarity of EDC dust with the global ice-volume record (Fig. 1e,
r2 5 0.6) confirms that major aeolian deflation in the Southern
Hemisphere was linked to Pleistocene glaciations. Comparison with
the magnetic susceptibility record of loess/palaeosol sequences from
the Chinese Loess Plateau (Fig. 1f) also provides evidence for broad
synchronicity of global changes in atmospheric dust load.
EDC dust has been measured using both a Coulter counter and a
laser sensor (see Methods). Laser measurements are obtained at
higher resolution along the core, but dust size is difficult to calibrate;
therefore only the relative variation of the signal is used. Overall, the
Coulter counter and laser (relative) size records (Fig. 1d) are in good
agreement. The slight discrepancies during MIS 5.5, 6 and 12 are
possibly related to the different sampling resolution, as size data from
the laser and Coulter counter represent a continuous 1.1-m average
and discrete 7-cm subsamples every 0.5–6 m, respectively. From MIS
14 (,2,900 m depth) and downwards in the ice core, the dust size
profile is not available because of the presence of particle aggregates
formed in the ice. This phenomenon, which needs further investigation, has been observed in the EDC core only in very deep glacial
sections, where ice thinning becomes very important and in situ
temperature higher than 28 uC may allow partial melting around
particles. This problem was solved through sonication of the samples,
which allowed us to obtain reliable concentration data (see
Methods). For the upper part of the record, larger (smaller) particles
are generally observed during warm (cold) periods, as reflected by the
1
Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland. 2Oeschger Centre for Climate Change Research, University of Bern,
3012 Bern, Switzerland. 3Environmental Sciences Department, University of Milano Bicocca, Piazza della Scienza 1, 20126 Milano, Italy. 4Laboratoire de Glaciologie et Géophysique de
l’Environment (LGGE), CNRS-University J. Fourier, BP96 38402 Saint-Martin-d’Hères cedex, France. 5Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen,
Juliane Maries Vej 30, 2100 Copenhagen OE, Denmark. 6British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK. 7Alfred Wegener Institute for Polar and
Marine Research, Columbusstrasse, 27568 Bremerhaven, Germany.
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©2008 Nature Publishing Group
LETTERS
–360
–400
–440
0.1
b
1
10
5.5
7.5
9
11
13
15.1
17
19
c
0.1
EDC dust
flux (mg m–2 yr–1)
Vostok dust
flux (mg m–2 yr–1)
a
1
10
EDC dust
FPP (norm.)
Coarse –3
–2
Fine
2
16
14
d
–1
0
Marine δ18O (%0)
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EDC δD (%0)
NATURE | Vol 452 | 3 April 2008
2
f
0
–2
0
200
400
600
800
Age (kyr)
Figure 1 | EDC dust data in comparison with other climatic indicators.
a, Stable isotope (dD) record from the EPICA Dome C (EDC) ice core8 back
to Marine Isotopic Stage 20 (EDC3 timescale) showing Quaternary
temperature variations in Antarctica. b, Vostok dust flux record (Coulter
counter) plotted on its original timescale11. c, EDC dust flux records. Red
and grey lines represent, respectively, Coulter counter (55-cm to 6-m
resolution) and laser-scattering data (55-cm mean). Numbers indicate
Marine Isotopic Stages. Note that the vertical extent of the scales of b and c is
larger than for the other records. d, EDC dust size data expressed as FPP (see
Methods). The orange and grey curves represent measurements by Coulter
counter (2-kyr mean) and laser (1-kyr mean), respectively. e, Marine
sediment d18O stack18, giving the pattern of global ice volume. f, Magnetic
susceptibility stack record for Chinese loess17 (normalized).
variability in the fine particle percentage (FPP)12, which is highest
during the two last glacial periods. The advection of dust to central
Antarctica involves the high levels of the troposphere and the small
changes in dust size may reflect changes in the altitude of transport
and thus transport time12. Higher FPP values in glacial times have
been ultimately attributed to increased isolation of Dome C during
glacials, in terms of reduced dust transport associated with greater
subsidence12 or possibly through baroclinic eddies.
Comparing dust and stable isotope (dD) profiles, there is a significant correlation during glacial periods (Fig. 2), and up to 90% of the
dust variability can be explained by the temperature variations. In
glacial periods, most of the dD events (for example, Antarctic
Isotopic Maxima) have their counterparts in the dust data shown
by a reduction of dust concentrations. In contrast, dust and temperature records are not correlated during interglacial periods (Fig. 2).
Indeed, the (logarithmic) relationship between dust flux and dD can
1.0
0.8
0.6
20
r2
EDC dust flux (mg m–2 yr–1)
25
0.4
15
0.2
0
10
5
0
LGM
0
6
8
10
200
12
400
14
16
600
18
800
Age (kyr)
Figure 2 | EDC correlation between dust and temperature. Linear plot of
dust flux (black) and the coefficient of determination r2 (blue) between the
high-pass filtered values (18-kyr cut-off) of both the dD and the logarithmic
values of dust flux. The correlation was determined using 2-kyr mean values
in both records and a gliding 22-kyr window. Correlations above r2 5 0.27
(dashed line) are significant at a 95% confidence level. Numbers indicate the
marine isotopic glacial stages.
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LETTERS
NATURE | Vol 452 | 3 April 2008
be well fitted by a cubic polynomial (Fig. 3). Over the record, the
geometric standard deviation from the polynomial fit represents a
factor of ,2 in concentrations independent of the climatic period.
Similarly, this relationship does not change before and after the MBE.
The crescent shape of the dust–dD relationship suggests that the dust
fluxes have a higher temperature sensitivity as the climate becomes
colder. For dD values above about –405%, Antarctic temperature
and dust flux are not correlated, whereas there is a clear correlation
for dD values below about –425%. This behaviour may represent the
expression of a progressive coupling between high- and low-latitude
climate as temperatures become colder. During extreme glacial conditions the coupling appears as a direct influence of the Antarctic on
the climate of southern South America19,20. The coupling of Antarctic
and lower-latitude climate is probably coincident with the significantly extended sea ice over the Southern Atlantic and the Southern
Ocean during glacials21 and the consequent meridional (northward)
shift of the atmospheric circulation (that is, the westerlies)19–22.
Questions remain about the main factors influencing the high dust
input into polar areas during glacial periods. So far, general circulation models4,10 have reproduced a glacial dust transport and flux over
tropical and mid-latitude regions which is in good agreement with
global reconstructions3, but they have failed to simulate the 25-fold
increase observed in glacial dust input over Antarctica. This shortcoming is currently attributed to an incomplete representation of the
source strength23. In addition, most of the models suggest modest
changes in atmospheric transport4,9,10, which seems supported by the
relatively small changes in dust size in the EDC ice core, and by the
comparison of the two EPICA ice cores24. Moreover, the suggestion
that the 25-fold dust influx increase is mainly due to changes in
source strength is challenged by evidence from South Atlantic marine
records suggesting a 5- to 10-fold increase in the South American
source strength25,26 during the last glacial period.
On the basis of the new EDC data set, we suggest a new hypothesis
for the glacial–interglacial changes in transport of dust. The indication (Fig. 3) that Antarctica and the southern low latitudes experienced a different coupling during the past 800 kyr is closely linked
with the dust pathway within the high troposphere and the likely
EDC dust flux 0–430 kyr BP
EDC dust flux 430–800 kyr BP
EDC dust flux (mg m–2 yr–1)
10
extended lifetime. With respect to the dust emitted from continents,
the dust arriving in Antarctica, with a mode around 2 mm diameter27,
represents the endmember of the distribution. The small size of dust
particles makes en route gravitational settling inefficient (very long
dry deposition lifetime), allowing mixing and spreading at high altitude within the troposphere. The lifetime of the particles is primarily
constrained by wet deposition23,28 and therefore by water content and
temperature. As an example, along a pathway 4–6 km high and with a
mean temperature of about –40 uC (conditions similar to those
observed over Antarctica), a temperature reduction by 5 uC, associated with a similar change of sea surface temperature over the
Southern Ocean29, reduces the saturation water vapour pressure to
about half. Under such premises, a two-dimensional model28
obtained an increase in dust flux to Antarctica of up to a factor of
5. Thus the roughly 25-fold increase in dust flux over the Antarctic
plateau during glacials could be explained by a progressive coupling
of the climate of Antarctic and lower latitudes with colder temperatures, one influencing the other, and leading to the stronger aeolian
deflation of southern South America and to a significantly increased
dust particle lifetime along their pathway in the high-altitude troposphere over the Southern Ocean. The new EDC data set thus
provides important constraints for models of the dust cycle during
glacial–interglacial cycles.
METHODS SUMMARY
Apparatus. Samples for Coulter Counter Multisizer IIe measurements were
obtained from discrete samples (7 cm long), decontaminated at LGGE through
washing in ultrapure water. We adopted the analytical procedure described in
ref. 12 (and references therein). A total of about 1,100 values have been obtained.
We obtained laser scattering data from the University of Copenhagen device
for the section between 0 and 770 m. The University of Bern device was used
between 770 and 3,200 m. Data from both devices were calibrated by Coulter
counter. Sampling resolution is about 1 cm.
Particle size distribution. Dust size is expressed as FPP. We define FPP according to ref. 12 as the proportion of the mass of particles having diameter between 1
and 2 mm with respect to the total mass of the sample, which typically includes
particles in the size range 1 to 5 mm. This parameter is inversely correlated with
the modal value of the log-normal dust mass (volume) size distribution.
From a depth of 2,900 m and below, some glacial samples show distributions
with an anomalously large mode. This has been attributed to particle aggregate
formation in ice (Supplementary Fig. 1) and prompted us to discard all size
distribution data below that point until this phenomenon is better understood.
To obtain reliable dust mass, samples were submitted to ultrasonic treatment to
break the aggregates apart. Between 3,139-m and 3,190-m depth, 42 samples
with anomalous size distribution were submitted to ultrasonic treatment. For 39
of these we accepted the new dust mass measurement, with 11 samples showing a
significantly different mass value (Supplementary Table 1). Measurement on a
few chosen samples above 3,139-m depth showed normal size distribution and
concentration values. However, additional measurements are scheduled for indepth analysis of the aggregate problem.
Received 14 May 2007; accepted 21 January 2008.
1
1.
2.
3.
4.
0.1
Glacial
Interglacial
5.
–460
–440
–420
–400
–380
–360
δD (%0)
Figure 3 | EDC dust–temperature relationship. Values of dD (ref. 8) are
plotted against dust flux (both at 55-cm resolution). Green and blue dots
represent data from 0–430 kyr BP and 430–800 kyr BP, respectively.
Superposed is a cubic polynomial fit,
log10(f) 5 23.737 3 1026(dD)3 2 4.239 3 1023(dD)2 2 1.607(dD) 2 204,
where f is the dust flux (mg m22 yr21), and dD is in % (r2 5 0.73, N 5 5,164).
6.
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Supplementary Information is linked to the online version of the paper at
www.nature.com/nature.
Acknowledgements We thank H. Fischer, E. Wolff, T. Blunier, R. Gersonde,
B. Stauffer and M. Renold for their comments and suggestions. This work is a
contribution to the European Project for Ice Coring in Antarctica (EPICA), a joint
European Science Foundation/European Commission scientific programme,
funded by the European Commission and by national contributions from Belgium,
Denmark, France, Germany, Italy, the Netherlands, Norway, Sweden, Switzerland
and the United Kingdom. This is EPICA publication no. 193.
Author Information Reprints and permissions information is available at
www.nature.com/reprints. Correspondence and requests for materials should be
addressed to J.R.P. ([email protected]).
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