1

Online Supplementary Information for Holbourn et al.

Site locations and materials

Our study is based on marine sediments recovered at ODP Site 1146 during Leg

184 in Spring 1999 and at ODP 1237 during Leg 202 in April 2002. Site 1146 (19˚

27.40‘N, 116˚ 16.37‘E) is located at 2092 m water depth within a small rift basin on the

mid-continental slope of the northern South China Sea1 (Supplementary Fig. S1).

Tectonic backtracking suggests that middle Miocene paleodepths were not significantly

shallower than in the present day1. A free connection existed between the South China

Sea and the western Pacific during the middle Miocene, as the modern Bashi Strait (sill

depth ~2600 m) only formed between Luzon and Taiwan at ~6.5 Ma, as a result of the

Luzon Arc collision1. Coring with the Extended Core Barrel (XCB) system at Site 1146

recovered a continuous Miocene sequence of carbonate-rich hemipelagic sediments,

which grade from unlithified green nannofossil clay in the lower Miocene to light

brownish gray foraminifers and nannofossil clay in the upper Miocene1. ODP Site 1237

(16°0.421'S, 76°22.685'W) is located at 3212 m water depth on a relatively flat bench

on the easternmost flank of Nazca Ridge, about 140 km off the coast of Peru2

(Supplementary Fig. S1). The tectonic backtrack path moves Site 1237 about 20˚

westward relative to South America over the last 42 myr. In the middle Miocene the site

lay in the oligotrophic subtropical gyre, at slightly shallower water depths than in the

present day2. Middle Miocene sediments recovered with the Advanced Piston Corer

(APC) system at Site 1237 consist of unlithified, pale brown nannofossil ooze with an

average of 95 wt% calcium carbonate2.

2

Sampling strategy

Foraminifers and nannofossil clays were sampled at ~ 10 cm intervals (~ 4 kyr

time resolution, 30cm3 sample size) in Hole 1146A (463.05 – 513.30 meters below

seafloor). One obvious coring gap between Cores 1146A-54X and -55X was bridged

with samples from Hole 1146C, based on the shipboard correlation and the match of our

isotope records. Nannofossil oozes were sampled at ~ 5 cm intervals (~ 4-5 kyr time

resolution, 20 cm3 sample size) from a composite sequence (the so called splice) from

Holes 1237A and C (200.82 - 221.86 meters composite depth). Overlapping XRF

measurements (50-100 cm) were made with 1 cm resolution at correlation points of the

Site 1237 splice to verify its accuracy and ensure the completeness of the record. All

samples were oven dried at 40˚C and weighed, before washing over a 63 µm sieve.

Residues were oven dried at 40˚C on a sheet of filter paper, then weighed and sieved

into 63-150 µm, 150-250 µm, 250–630 µm size fractions.

Chronology

Sites 1146 and 1237

The Site 1146 original age model3 for the interval 11.7-14.7 Ma is constrained by

11 biostratigraphic datums (Supplementary Table S1). We revised the shipboard

foraminiferal datums, based on higher resolution sampling, and integrated the revised

datums with shorebased nannofossil biostratigraphy4, using updated ages from

ATNTS20045. This revised chronology, provided the framework to develop the

orbitally-tuned age model for Site 1146. The Site 1237 original age model for the

interval 12.4-14.9 Ma is based on 8 magnetostratigraphic and 5 biostratigraphic datums

(Supplementary Table S2). We revised the shipboard foraminiferal datums based on

3

higher resolution sampling, and integrated these with datums derived from stacked

shipboard inclination data between 197 and 208 mcd, using updated ages from

ATNTS20045. This revised chronology provided the framework to develop the

orbitally-tuned age model for Site 1237. We subsequently compared ages from

ATNTS20045 with ages derived from the astronomically tuned age models developed

here for Sites 1146 and 1237 (Supplementary Tables S1 and S2). We found a

reasonably good match between datum ages, taking into account uncertainties related to

biogeographic distribution, taxonomic concept, preservation bias, placement of datums

depth within cores, temporal resolution of orbital solution and for datums older than 13

Ma the lack of direct astronomical calibration in ATNTS20045.

New chronologies were generated by initially matching the 400 kyr and 100 kyr

amplitude variations in the δ18O series to the latest astronomical solution6, then fine-

adjusting individual obliquity-scale cycles. As tuning target, we constructed an

eccentricity-tilt composite (ET) with no phase shift and equal weight of eccentricity and

obliquity. We initially experimented with several eccentricity/obliquity mixes, then

selected the target curve, which showed most similarity to our δ18O curves. We tuned

δ18O minima to obliquity maxima, since we assumed (a) that relatively warm summers

during high obliquity would promote ice-sheet melting in Antarctica, whereas cool

summers during low obliquity would favour ice-sheet growth, and (b) that a low

summer insolation gradient between low and high latitudes during high obliquity would

decrease poleward moisture transport, inhibiting ice-sheet buildup7. We did not adjust

our tuning for possible phase lags between δ18O and insolation forcing, since the

response time of a smaller middle Miocene Antarctic ice-sheet is unknown. Age

tiepoints are given in Fig. 1, Supplementary Fig. S2 and Supplementary Tables S3-S4.

The δ18O profiles from Sites 1146 and 1237 are plotted versus depth and time in

Supplementary Fig. S2. The average sedimentation rate in Site 1146 is ~ 0.025 m kyr-1

with a chronologic resolution of ~ 4 kyr. The average sedimentation rate in Site 1237 is

4

~ 0.013 m kyr-1 between 201 and 216 mcd with a chronologic resolution of ~ 4 kyr and

~ 0.010 m kyr-1 between 216 and 222 mcd with a chronologic resolution of ~ 5 kyr. The

change in sedimentation rate at ~ 216 mcd in Site 1237 is supported by XRF Fe and

coarse fraction (> 63 µm) data, indicating increased carbonate dissolution below this

level (Fig. 1).

We applied Gaussian band-pass filters to the 1146 and 1237 δ18O and 1237 Fe

series to extract oscillations associated with the 400, 100 and 41 kyr periods. Gaussian

band-pass filters were centered at 0.0244 kyr-1 (41 kyr period) with 0.005 kyr-1

bandwidth (34.0-51.5 kyr period), 0.01 kyr-1 (100 kyr period) with 0.003 kyr-1

bandwidth (76.9-142.9 kyr period) and 0.0025 kyr-1 (400 kyr period) with 0.0005 kyr-1

bandwidth (333.3-500.0 kyr period). δ18O is phase-locked with obliquity in the 41 kyr

band, and the amplitude modulation of the 41 kyr filtered signals closely follows

obliquity between 14.7 and 13.5 Ma (Fig. 1). The amplitude of the 100 kyr filtered δ18O

and Fe signals increases after 14.1 Ma, exbibiting similar modulation as eccentricity

(Figs. 1 and 2, Supplementary Fig. 2). Spectral analysis of the δ18O, Fe and coarse

residue time series reveal strong power at all Milankovitch frequency bands, except

precession (Supplementary Fig. S4). The spectral peak for short eccentricity shows a

characteristic split into 95 kyr and 125 kyr periods. Spectral power in the short and long

eccentricity periods are enhanced after tuning to obliquity. Orbital tuning, bandpass-

filtering and sedimentation rates calculation were performed with AnalySeries 1.28.

Site 1171

We revised the Site 1171 chronology9-10 for the interval 13.2 to 14.3 Ma by

correlating the benthic δ18O profile in Site 1171 to the benthic δ18O profiles in Sites

1146 and 1237, using tie points shown in Supplementary Fig. S3. The revised age

model is validated by spectral analysis, which in contrast to the original age model,

5

shows Milankovitch periodicities, in particular the 400 and 41 kyr (Supplementary Fig.

S4). The original age model9-10 for the interval 13.2-14.3 Ma was based on a linear

interpolation between magnetostratigraphic, biostratigraphic and isotopic datums, which

were not calibrated to an astronomical timescale. The new 1171 age model indicates

higher sedimentation rates (~ 0.015-0.025 m kyr-1) between 13.7 to 14.3 Ma

(Supplementary Fig. S3) in comparison to the original age model9-10, which assumes a

linear sedimentation rate of 0.0136 m kyr-1 over the interval 13.6 to 17 Ma.

Spectral analysis

Power spectra of benthic foraminiferal δ18O (1146, 1237 and 1171), coarse

fraction (1237) and XRF Fe counts (1237) are given in Supplementary Fig. S4. Spectra

were estimated using REDFIT11 with 2 segments and a Hanning window. Power spectra

show strong response of δ18O at the obliquity (41 kyr) and eccentricity (400 kyr) and to

a lesser extent at the eccentricity (125 kyr, 95 kyr) periods. In contrast, most of the

power is concentrated at the eccentricity bands (400 kyr, 125 kyr, 95 kyr) for carbonate

dissolution proxies (coarse fraction and Fe).

Time frequency analysis

Temporal changes in amplitude of signal components in the Milankovitch band

were estimated using a modified harmonic-filtering algorithm12, which fits sinusoidal

waves to a time series by means of least-squares. This method can process unevenly

spaced time series directly, that is, without the requirement of prior interpolation. To

obtain time-dependent amplitude estimates, the input time series is analyzed within a

6

moving window of width Tw = w × Tf, where w = 3 is a width–factor and Tf denotes the

signal periodicity of interest (e.g. 400 kyr). The window is shifted consecutively by one

data point along the time axis of the input time series. Each “window segment” is

linearly detrended prior to tapering with a Welch-Shape-1 window13. The resulting

amplitude and phase of the best-fit sinusoid are saved vs. the average of the observation

times within the current segment and are used to reconstruct the signal component as

function of time. The result of this procedure is equivalent to band-pass filtering (cf. ref.

14). The selected value of w offers a good compromise between statistical and

systematic errors and results in a half-amplitude bandwidth of approximately 0.5/Tf

cycles/Myr. Note that due to the finite window width, a step-like increase in signal

amplitude appears w × Tf wide. Applying the above filtering algorithm over a

predefined range of frequencies allows us to detect changes in signal components in

time-frequency space15. The dependence of window width, Tw on frequency leads to a

change in temporal resolution with frequency. At low (high) frequencies wide (narrow)

windows result in a low (high) temporal resolution. This scale dependence of the

temporal resolution is similar to that of wavelet analysis. A program for time-frequency

analysis (TIMEFRQ, version 4.3) is available from www.palmod.uni-

bremen.de/~mschulz.

References

1. Wang, P. Prell, W. L. & Blum P. et al. Proc. ODP, Init. Repts. 184 [CD-ROM].

Available from: Ocean Drilling Program, Texas A&M University, College

Station TX 77845-9547, USA (2000).

7

2. Mix, A .C., Tiedemann, R. & Blum P. et al. Proc. ODP, Init. Repts. 202 [CD-

ROM]. Available from: Ocean Drilling Program, Texas A&M University,

College Station TX 77845-9547, USA (2003).

3. Holbourn, A. E. Kuhnt, W. & Schulz, M. in Continent-Ocean Interactions in the

East Asian Marginal Seas (eds Clift, P. Wang, P. Kuhnt, W. Hayes, D.) 309-326

(Geophys. Monog. Ser. 149, AGU, Washington, DC, 2004).

4. Nathan, S.A. & Leckie, R.M. in Proc. ODP, Sci. Results 184 [Online] (eds Prell,

W.L. Wang, P. Blum, P. Rea, D.K. & Clemens, S.C.) Available from World

Wide Web: http://www-odp.tamu.edu/publications/184_SR/219/219.htm. [Cited

2005-06-05].

5. Lourens, L., Hilgen, F., Shackleton, N.J., Laskar, J. & Wilson, D. in A Geologic

Time Scale (eds Gradstein, F., Ogg J., Smith, A.) 409-440 (Cambridge

University Press, 2004).

6. Laskar J. et al. A long term numerical solution for the insolation quantities of the

Earth. Astron. Astrophys. 428, 261-285 (2004).

7. Loutre, M.-F., Paillard, D., Vimeux, F. & Cortijo, E. Does mean annual

insolation have the potential to change the climate? Earth Planet. Sci. Lett. 221,

1-14 (2004).

8. Paillard, D., Labeyrie, L. & Yiou, P. Macintosh program performs time-series

analysis. EOS Trans. AGU 77, 379 (1996).

9. Shevenell, A. E. & Kennett, J. P. in The Cenozoic Southern Ocean: Tectonics,

Sedimentation and Climate Change between Australia and Antarctica (eds

Exon, N., Kennett, J.P. Malone, M.) 235-252 (Geophys. Monog. Ser. 151, AGU,

Washington, DC, 2004).

8

10. Shevenell, A. E., Kennett, J. P. & Lea, D. W. Middle Miocene Southern Ocean

Cooling and Antarctic Cryosphere expansion. Science 305, 1766-1770 (2004).

11. Schulz, M. & Mudelsee, M. REDFIT; estimating red-noise spectra directly from

unevenly spaced paleoclimatic time series. Computers and Geosciences, 28,

421-426 (2002).

12. Ferraz- Mello, S. Estimation of periods from unequally spaced observations,

Astron. J. 86, 619-624 (1981).

13. Welch, P. D. The use of fast Fourier transform for the estimation of power

spectra: A method based on time averaging over short, modified periodograms,

IEEE Trans. Audio and Electroacoustics Au-15, 70-73 (1967).

14. Hinnov, L. A., Schulz, M. & Yiou, P. Interhemispheric space-time attributes of

the Dansgaard-Oeschger oscillations between 100 and 0 ka, Quat. Sci. Rev. 21,

1213-1228 (2002).

15. Schulz, M., Berger, W. H., Sarnthein, M. & Grootes, P. M. Amplitude variations

of 1470-year climate oscillations during the last 100,000 years linked to

fluctuations of continental ice mass, Geophys. Res. Lett. 26, 3385-3388 (1999).

9

Supplementary Figure S1 Location of ODP Site 1146 (19˚ 27.40‘N, 116˚

16.37‘E) drilled at 2092 m water depth in the northern South China Sea, ODP

Site 1237 (16°0.421'S, 76°22.685'W) drilled at 3212 m water depth on the

Nazca Ridge, off Peru and ODP Hole 1171C (48°29.9971´S, 149°6.7051´E)

drilled at 2147.8 m water depth on the southernmost South Tasman Rise.

120°

120

150°

°

180°

180°

-150°

-150°

-120°

-120°

-90°

-90°

-60°

-60°

-60° -60°

-30° -30°

0° 0°

30° 30°

0 2000 km

-70 -70

1146

1237

120

°

150

150

180

180

-150

-150

-120

-120

-90

-90

-60

-60

-60 -60

-30 -30

0 0

30 30

0 2000 km

-70° -70°

1146

1237

Supplementary Figure S1

1171

10

Supplementary Figure S2 Benthic foraminiferal δ18O profiles plotted against

depth (a-b) and against age (c). Age control points (Supplementary Tables S3-

S4) are indicated by crosses (black= both sites, blue=Site 1237, red=Site 1146).

(d) Linear sedimentation rates between age tie points. (e) Comparison of 100

kyr filtered iron contents and eccentricity6. Gaussian band-pass filter centered at

0.01 kyr-1 (100 kyr period) with 0.003 kyr-1 bandwidth (76.9-142.9 kyr period).

Note: Filtered Fe record shows similar phasing and amplitude modulation as

filtered eccentricity. (f) Eccentricity- Tilt tuning target. Age correlation points

marked by crosses.

0.511.522.5

464

468

472

476

480

484

488

492

496

500

504

508

512

11461146

0.511.522.5

202

206

210

214

218

222

1237

δ18O (‰ vs. PDB) δ18O (‰ vs. PDB)

dep

th (m

eter

s b

elo

w s

eaflo

or)

dep

th (m

eter

s co

mp

osi

te d

epth

)

Sedimentation rate (m/kyr)

core break

Ag

e (M

a)

0.511.522.512.7

12.9

13.1

13.3

13.5

13.7

13.9

14.1

14.3

14.5

14.7

1237 1146

0.01 0.03

1237 1146

0.42 0.44 0.46 0.48ET target

1237 Fe (cps) 100kyr filtered

Eccentricity 100kyr filtered

-40 -20

δ18O (‰ vs. PDB)

Supplementary Figure S2

a b c d e f

-0.01 0.010 0.02-0.02

0 20 40

11

Supplementary Figure S3 (a) Comparison of benthic δ18O and δ13C at Sites

1146, 1171 and 1237 (age correlation tie points points are indicated by red

crosses). (b) Linear sedimentation rates between age tie points in Site 1171.

13.2

13.4

13.6

13.8

14.0

14.2

Ag

e (M

a)

2.5 2 1.5 1 0.5 1 1.5 2 2.5

Benthic δ18O (‰ vs. PDB) Benthic δ13C (‰ vs. PDB)

114611711237

Supplementary Figure S3

Sed. Rate (m/kyr)

0.01 0.02 0.03

11711171

13.2

13.4

13.6

13.8

14.0

14.2

Ag

e (M

a)

a b

12

Supplementary Figure S4 Power spectra of (a) δ18O in ODP Site 1237, (b)

δ18O in ODP Site 1146, (c) proportion of coarse fraction in ODP Site 1237, (d)

Fe concentration in ODP Site 1237. (e) δ18O in ODP Site 1171. Spectral power

is given in (units of data)2/f, where f is frequency (cycle/kyr). The 6-dB

bandwidth is ~ 0.0015 cycles/kyr in A to D and 0.002 cycles/kyr in E. Numbers

above peaks indicate associated periods in kyr. The 95% and 80% false-alarm

levels are shown.

a1237 Oδ18

e1171 Oδ18

c1237 Fraction > 63 µm

d1237 Fe

b1146 Oδ18

125

125

125

41

41

41

95

95

95

95

400

400

400

400

400

Supplementary Figure S4

13

Supplementary Figure S5 Chemical element composition from XRF scanning

measurements with 1 cm resolution on archive halves of ODP Site 1237 (12.7-

14.7 Ma). All data are given in counts per second (cps) with a 5-pt moving

average smoothing.

0 50 100 150 200 250 012.7

12.9

13.1

13.3

13.5

13.7

13.9

14.1

14.3

14.5

14.7

Fe (cps)

80 120 160

Mn (cps)

0 5 10

Ti (cps) Cu (cps) Ca (cps)

10000 12000 14000 16000 100 120 140 160

Sr (cps)

40

ice sheet expansion

Supplementary Figure S5

Ag

e (M

a)

12.7

12.9

13.1

13.3

13.5

13.7

13.9

14.1

14.3

14.5

14.7

Ag

e (M

a)

20 40 60

14

Supplementary Table S1 Comparison of ages for 1146 biostratigraphic datums

from ATNTS20045 and this work (all ages given in Ma). The uncertainty in the

placement of datums within cores is 20 cm for planktonic events and 25 cm for

nannofossil events.

Event mbsf ATNTS20045 ages Ages (this work)

FO D. kugleri 447.00 11.86 NA

FO T. rugosus 465.43 NA 12.79

FO F. fohsi robusta 474.53 13.13 13.19

LO C. floridanus 478.22 13.33 13.33

FO F. fohsi s.l. 480.51 13.41 13.45

LO S. heteromorphus 484.58 13.53 13.63

FO F. praefohsi 490.13 13.77 13.85

LO G. archaeomenardii 494.48 13.87 14.04

LO P. circularis 507.85 NA 14.52

FO O. suturalis 515.95 NA 14.78

LO H. ampliapertura 529.18 14.91 15.17

15

Supplementary Table S2 Comparison of ages for 1237 magnetostratigraphic

and biostratigraphic datums from ATNTS20045 and this work (all ages given in

Ma). The uncertainty in the placement of planktonic foraminiferal datums within

cores is 10 cm. The uncertainty in the placement of polarity boundaries is 20-50

cm. We followed the shipboard interpretation for the placement of C5An.2n. We

re-interpreted shipboard inclination data in the interval 200-208 mcd, where a

relatively good correlation exists between Holes 1237B and 1237C.

Event mcd ATNTS20045 ages Ages (this work)

C5An.2n (bottom) 197.70 12.415 12.42

C5Ar1n (top) 200.83 12.730 12.70

C5Ar1n (bottom) 201.65 12.765 12.78

C5Ar2n (top) 202.21 12.820 12.84

C5Ar2n (bottom) 202.71 12.878 12.93

C5AAn (top) 204.57 13.015 13.08

FO F. fohsi robusta 204.48 13.13 13.07

C5AAn (bottom) 206.20 13.183 13.20

C5ABn (top) 207.94 13.369 13.32

FO F. fohsi s.l. 208.78 13.41 13.40

FO F. praefohsi 214.23 13.77 13.81

FO F. peripheroacuta 218.32 14.24 14.25

FO P. circularis 223.98 14.89 NA

16

Supplementary Tables S3 and S4 Age control points between δ18O depth

series and ET target curve used to derive orbitally tuned timescales for interval

12.7–14.7 Ma in ODP Sites 1146 and 1237.

Supplementary Table S3: ODP Site 1146

Depth (mbsf) Age (ka)

466.25 12815

467.24 12848

468.45 12934

469.34 12966

470.24 13016

471.25 13051

473.14 13133

473.60 13168

475.28 13218

475.96 13252

478.45 13334

479.69 13416

481.73 13500

484.32 13620

487.23 13705

490.60 13874

491.15 13908

492.16 13949

492.98 13993

494.20 14025

495.05 14071

496.55 14111

497.39 14146

17

498.25 14189

499.75 14229

501.08 14269

501.45 14310

502.30 14347

503.70 14386

504.65 14430

505.95 14466

507.00 14506

508.58 14547

509.71 14589

513.66 14708

Supplementary Table S4: ODP Site 1237

Depth (mcd) Age (ka)

202.02 12815

202.28 12848

202.73 12934

203.23 12966

203.68 13016

204.26 13051

204.86 13101

205.27 13133

205.72 13168

206.42 13218

206.83 13252

207.68 13297

208.18 13334

208.98 13416

210.32 13500

211.68 13620

212.79 13705

213.93 13791

214.47 13822

18

215.22 13874

215.97 13908

216.22 13949

216.47 13993

216.77 14025

217.02 14071

217.17 14111

217.82 14189

218.12 14229

218.47 14269

218.93 14310

219.36 14347

219.81 14386

220.16 14430

220.51 14466

220.96 14506

221.21 14547

221.61 14589