Nature Reference # 2005-12-14536B
Supplementary Information
Supplementary Figure 1. Age model development for site 1060. Due to the low
concentration of foraminifera at site 1060, it was not practical to develop a continuous
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planktonic 18O record or a 14C chronology. Instead, a timescale was constructed by
correlating variations in the percentage of a group of warm surface-dwelling planktonic
foraminifera to changes in the (a) GRIP ice 18O record on the SS09 sea timescale1
between 64 and 24 ka (ref. 14). b, The sum of the warm surface species (G. ruber, G.
sacculifer, G. aequilateralis, O. universa, G. falconensis, G. digitata, G. rubescens, G.
tenelus, P. obliquiloculata) used to correlate warm intervals at site 1060 to the GRIP
record. Proxy is expressed as a percentage of the total planktonic foraminifera
assemblage (whole tests only). The thin vertical lines mark the position of the points
used to establish the correlations. The pattern of fluctuations in the “warm” group of
species convincingly resembles the Greenland temperature record. The faunal-based age
model for site 1060 is broadly consistent with the 14C-based and the GISP2-tuned age
model developed for nearby core ODP 1059 (31°40.5’N, 75°25.1’W) across the major
transitions between interstadials 12 to 14 (SI Figure 2) (ref. 31). d, Sedimentation rate
resulting from this correlation. The interstadial mean sedimentation rate is 28 cm/ka and
the stadial mean is 53 cm/ka. Figure reproduced from ref. 14.
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-1.0
ODP 1060
G. ruber 18 Oc (‰ V PDB)
-0.8
-0.6
-0.4
-0.2
0.0
0.2
ODP 1059
0.4
0.6
0.8
45
47
49
51
53
55
57
59
Calendar Age (ka BP - tuned to GRIP)
Supplementary Figure 2. Correlation between the G. ruber 18OC records from cores
ODP site 1060 (blue diamonds) (this study) and ODP site 1059 (pink squares) (ref. 31).
The age model for site 1059 has been converted from GISP2-tuned ages to the GRIP
SS09 sea timescale and the site 1059 data points have been smoothed by averaging three
adjacent samples (dashed pink line). The data are in agreement at the initiation of
Interstadial 14 (55.08 ka) and IS 12 (47.36 ka), but the IS 14 termination values show an
age offset because the site 1059 age model assumes linear sedimentation rates between
the IS 12 and IS 14 tie points (ref. 31). The age model used in this study has an
additional tie point for IS 13 (51.6 ka), resulting in increased stadial sedimentation rates
(see SI Figure 1). We suspect that the discrepancy between the two records centered at
57 ka may be due to the fact that the site 1059 tie point for interstadial 15 was selected
incorrectly. The strong correlation between these two records suggests that the majority
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of 18OC change observed in G. ruber at site 1059 is also due to stadial-interstadial shifts
in 18OSW rather than to temperature.
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4.5
Mg/Ca (mmol/mol)
4
3.5
3
2.5
2
1.39
1.41
1.43
1.45
1.47
1.49
1.51
1.53
Sr/Ca (mmol/mol)
Supplementary Figure 3. Mg/Ca – Sr/Ca relationship in G. ruber shell material from
site 1060. Partial dissolution has been shown to reduce both Mg/Ca and Sr/Ca ratios in
planktonic foraminifera32, resulting in a positive covariance between these two metals.
However, regression analysis shows that there is no statistically significant relationship
between Mg and Sr in our 1060 data, suggesting that partial dissolution has not
appreciably affected the primary Mg/Ca record.
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Supplementary Figure 4. Changes in bottom-water masses in the vicinity of site 1060
during MIS 3. Mg/Ca ratios in G. ruber from ODP 1060 and the benthic C. wuellerstorfi
13C records from site 1060 (green triangles) and from nearby cores KNR140-2 JPC-37
(31°41.4’N, 75°28.8’W; ~3000 m water depth; red diamonds) and ODP 1059
(31°40.5’N, 75°25.1’W; ~3000 m water depth; black circles (ref. 31). Although ODP
1060 is ~500 m deeper, all three cores are located on the Blake Outer Ridge. The C.
wuellerstorfi 13C record is interpreted to indicate changes in bottom-water sources in the
western subtropical Atlantic. Negative 13C values indicate the intrusion of more
corrosive Antarctic Bottom Water and more positive 13C values indicate the presence of
North Atlantic Deep Water. The lack of correlation between these two records suggests
that millennial-scale changes in bottom-water masses at site 1060 cannot explain the
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structure of our Mg/Ca-SST reconstruction. Interstadials 12-16 are indicated with the
shaded bars.
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1
13
12
14
16
1.5
2
 O
SW
(д VSMOW)
H5
15
H5a
18
Caribbean
18
 O
2.5
3
SW
+ 0.3‰
Schmidt et al., 2004
46
48
50
52
54
56
Calendar Age (ka BP)
58
60
Supplementary Figure 5. Caribbean and North Atlantic gyre 18OSW values during MIS
3. A previous reconstruction of western Caribbean 18OSW during the last glacial cycle at
ODP site 999A demonstrated that western tropical Atlantic surface salinity was elevated
when North Atlantic Deep Water was reduced on orbital time scales13. However,
millennial-scale 18OSW oscillations were not observed in the Caribbean because of the
lower sedimentation rate (4 cm/ka) and the impact of bioturbation. To compare regional
18OSW change between the Caribbean and site 1060, we add the modern 18OSW
difference between the two sites, 0.3‰ (refs. 19, 33) to Caribbean values to account for
additional evaporation that occurs as waters transit between the tropics and subtropics.
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From 45 to 60 kyr, the average 18OSW values at sites 999A (1.9 ±0.1‰ (n=13)) (white
squares with blue line) and 1060 (2.0 ±0.3‰ (n=93)) (red diamonds with red line) are in
good agreement, suggesting that the glacial salinities reconstructed at site 999A are
consistent with surface waters of the subtropical gyre, reflecting an overall increase in
gyre surface water salinity during cool periods in the North Atlantic. The elevated glacial
salinities at site 999A were interpreted to suggest, in part, a southward shift in the ITCZ
during periods of reduced North Atlantic MOC (ref. 13). The coupling of 18OSW values
between sites 999A and 1060 during MIS 3 suggests that both millennial and orbitalscale changes in the tropical Atlantic hydrologic cycle influenced surface salinities in the
entire North Atlantic subtropical gyre. Numbered interstadials 12-16 and Heinrich Events
(H) 5 and 5a are indicated at the top of the figure.
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12
14
15
16
H5
18
(д VSMOW)
SW
18
 O
 O
b
-50
-70
H5a
0.8
a
-90
IVF-SW
1.2
Sea level below present (m)
-30
13
1.6
2
18
 O
SW
2.4
46
48
50
52
54
56
Calendar Age (ka BP)
58
60
Supplementary Figure 6. Impact of proposed changes in global sea level during MIS 3
on the site 1060 18OSW record. Evaluation of regional salinity change based on 18OSW
change must consider the possible impact of continental ice volume variability on global
18OSW change. a, Green squares with green line represent maximum estimates of sea
level oscillations between interstadials 12 to 16 based on 18O values in planktonic
foraminifera from Red Sea cores, suggesting fluctuations of 26 m (refs. 34,35). b,
Scaling these sea level oscillations using –0.008‰ 18OSW change per meter sea level
lowering34,35 allows us to compensate for the influence of continental ice sheet variability
on global 18OSW change and to compute the regional salinity change due to local
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hydrological system oscillations. The resulting ice volume free 18OSW (18OIVF-SW)
record (red squares with red line) shifts the entire uncorrected 18OSW reconstruction
(black circles with black line) to lower values and accentuates the 18OSW shifts between
stadials and interstadials 15 and 16. More importantly, these millennial-scale sea level
fluctuations cannot explain the rapid stadial-interstadial 18OSW shifts at site 1060.
Numbered interstadials 12-16 and Heinrich Events (H) 5 and 5a are indicated at the top
of the figure.
Supplementary References
31.
Hagen, S. & Keigwin, L. D. Sea-surface temperature variability and deep water
reorganisation in the subtropical North Atlantic during Isotope Stage 2-4. Marine
Geology 189, 145-162 (2002).
32.
Brown, S. & Elderfield, H. Variations in Mg/Ca and Sr/Ca ratios of planktonic
foraminifera caused by postdepositional dissolution - evidence of shallow Mgdependent dissolution. Paleoceanography 11, 543-551 (1996).
33.
Watanabe, T. A., Winter, A. & Oba, T. Seasonal changes in sea surface
temperature and salinity during the Little Ice Age in the Caribbean Sea deduced
from Mg/Ca and 18O/16O ratios in corals. Marine Geology 173, 21-35 (2001).
34.
Siddall, M. et al. Sea-level fluctuations during the last glacial cycle. Nature 423,
853-858 (2003).
35.
Rohling, E. J., Marsh, R., Wells, N. C., Siddall, M. & Edwards, N. R. Similar
meltwater contributions to glacial sea level changes from Antarctic and northern
ice sheets. Nature 430, 1016-1021 (2004).
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