APPENDIX
I.
The TALDICE-1 age scale
For the TALDICE ice core, we use the TALDICE-1 age scale built by Buiron et al.,
(2011). Between 20 and 50 ky BP, it relies on the synchronization of the TALDICE methane
profile (Buiron et al., 2011), with the Greenland composite one of Blunier et al. (2007) itself
on the absolute GICC05 age scale (Svensson et al., 2008). 18 age markers have been defined
by wiggle-matching, chosen at the CH4 mid-slope or maximum or minimum depending on the
signal shape, with an associated age uncertainty of ± 200 yr for sharp transitions of major DO
events.
A new inverse dating method has been used (Buiron et al., 2011; Lemieux-Dudon et
al., 2009) to calculate the best compromise between the CH4 age markers and a background
dating scenario provided by an 1D ice flow model (Parrenin et al., 2007). The model
optimises three glaciological entities: the accumulation rate scenario, the thinning function,
and the evolution of the Close-Off-Depth expressed in Ice-Equivalent (CODIE), the latter
corresponding to the depth where air bubbles are definitively trapped in the surrounding ice.
Different a posteriori evaluations of the resulting chronology have been performed.
The inverse model provides a confidence interval on the chronology through
probabilistic combinations of uncertainties from the model and observations. The largest ice
age uncertainty (± 1500 yr) corresponds to the time interval ranging between 20 and 25 ky BP
where CH4 variations are too small to allow firm definition of tie points (Figure S1). It then
improves and typically lies between 450 and 650 yr during MIS 3. In other words the
chronological uncertainty remains smaller than the duration of AIM events, thus enabling to
properly study the timing and duration of each single event.
II.
Calculation of AIM 8 and 12 warming duration
1.
Method used for TALDICE, EDML and EDC ice cores
For these three ice cores we calculate the first derivative of the isotopic profile after it
has been smoothed and resampled at 200 yr (for AIM12 at EDC, resampling is done at 300
yr). The onset and end of each warming phase is determined where the sign of the first
derivative changes (Figure S2). The associated age uncertainty is estimated to be ± 300 yr.
Results are summarized in Table S1.
2. Quantification of the warming phase in the four other ice cores
For the Dome F, Vostok, Siple Dome and Byrd remaining ice cores, our estimate is only
indicative because their chronologies are less accurate and in particular not common with the
one of EDC, EDML, and TALDICE. The duration of each warming phase has thus been
visually defined between the minimum and maximum isotopic data (Figure S3).
III.
Further climatic simulations
To further analyze the atmospheric teleconnections between the tropics and the southern
Pacific in our experiments, we have run LGM atmosphere-only GCM simulations in which
we have imposed different surface ocean conditions. Figure S4c presents the result of
simulations where we use the reference surface ocean conditions for the LGM (LGM-ref)
everywhere but in the tropical Atlantic. In this region, the SST of LGM conditions with
freshwater were imposed (LGM-fw). Figure S4d shows the result of the symmetric
experiment, in which the SST of LGM conditions with freshwater (LGM-fw) were applied
everywhere but in the tropical Atlantic. In this region, the reference surface ocean conditions
for the LGM (LGM-ref) were imposed. The aim of these 2 experiments is to disentangle the
part of the atmospheric response related to surface changes in the tropical Atlantic and the
part related to surface changes outside this region. Comparison of figures S4c and S4d shows
that the two northernmost centers of action located over the southeast Pacific are a constant
feature in both simulations, but with a strongest expression when freshwater SST conditions
are not applied on the tropical Atlantic. This suggests that the tropical Atlantic ITCZ and SST
changes are able to generate a stationary wave reaching the southeast Pacific, which can be
amplified by local interactions with the surface ocean.
Bibliography
Blunier, T., Spahni, R., Barnola, J.M., Chappellaz, J., Loulergue, L., Schwander, J., 2007.
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Buiron, D., Chappellaz, J., Stenni, B., Frezzotti, M., Baumgartner, M., Capron, E., Landais,
A., Lemieux-Dudon, B., Masson-Delmotte, V., Montagnat, M., Parrenin, F., Schilt, A., 2011.
TALDICE-1 age scale of the Talos Dome deep ice core, East Antarctica. Climate of the Past
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Lemieux-Dudon, B., Parrenin, F. and Blayo, E., 2009. A probabilistic method to construct a
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Parrenin, F., Dreyfus, G., Durand, G., Fujita, S., Gagliardini, O., Gillet, F., Jouzel, J.,
Kawamura, K., Lhomme, N., Masson-Delmotte, V., 2007. 1-D-ice flow modelling at EPICA
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Svensson, A., Andersen, K. K., Bigler, M., Clausen, H. B., Dahl-Jensen, D., Davies, S. M.,
Johnsen, S. J., Muscheler, R., Parrenin, F., Rasmussen, S.O., 2008. A 60 000 year Greenland
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Figure S1: TALDICE-1 age scale between 20 and 50ky BP. Upper two curves: methane profiles of the
Greenland Composite (black line) and TALDICE (blue line), on the GICC05 age scale. Black diamonds
indicate the tie points. Middle curve: TALDICE-1 ice age uncertainty estimated with the inverse model of
Lemieux-Dudon et al. (2009). Lower two curves: age/depth relationship for the ice (purple line) and for
the gas (blue line), including the CH4 markers (black diamonds).
Figure S2: From top to bottom and from left to right: TALDICE, EDML and EDC AIM 8 and 12. In each
graph, the upper record corresponds to the isotopic signal (black line), with running average (blue line)
followed by regular resampling (pink line). The black line below is the first derivative of the resampled
isotopic data. Purple shading highlights the warming periods. The warming phase duration is written.
Orange and blue shadings correspond to warming and cooling phases respectively. Note that the
smoothing process looses part of the real amplitude.
Figure S3: Determination of the warming phase duration for both AIM 8 and 12 according to the isotopic
signal of each Antarctic ice cores for. The records are represented on relative age scales based on official
chronologies of each ice core, where the origin corresponds to the isotopic maximum (dashed line). Black
arrows point the beginning of the southern warming observed in each signal.
Figure S4: Teleconnection from the tropical Atlantic to the South East Pacific and Antarctica. Results
from the Atmosphere-only GCM, using different surface ocean forcing. All fields are shown for JuneJuly-August. 4a: reference run LGM-refatm, using surface ocean conditions from LGM-ref: SAT (°C,
shading) and 200 hPa stream function (106 m2/s, contours). Other panels: anomalies in SAT (°C, shading)
and stream function (106 m2/s, contours, dashed for zero line, dotted for negative values) for the FWglobal SST experiment (4b), the FW-TA-SST experiment (4c) and the FW-out-TA-SSTexperiment (4d).
Table S1: Ages of onset and end of both AIM 8 and 12 warming in TALDICE, EDC, and EDML ice cores.
Table S1: Ages of onset and end of both AIM 8 and 12 warming in TALDICE, EDC, and EDML ice cores.
AIM 8
Warming onset (yr BP)
Warming end (yr BP)
Total duration (yr)
TALDICE
39 850
38 200
1 650
EDC
39 750
38 150
1 600
EDML
39 900
39 050
850
AIM 12
Warming onset (yr BP)
Warming end (yr BP)
Total duration (yr)
TALDICE
48 650
46 850
1 800
EDC
48 250
46 670
1 600
EDML
48 470
47 500
970