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Quaternary Science Reviews 25 (2006) 3391–3403

Interhemispheric anti-phasing of rainfall during the last glacial period

Xianfeng Wanga,�, Augusto S. Aulerb, R. Lawrence Edwardsa, Hai Chenga,Emi Itoa, Maniko Solheida

aDepartment of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, USAbCPMTC, Instituto de Geociencias, Universidade Federal de Minas Gerais, Av. Antonio Carlos 6627, Belo Horizonte, Minas Gerais 31270-901, Brazil

Received 3 October 2005; accepted 12 February 2006

Abstract

We have obtained a high-resolution oxygen isotopic record of cave calcite from Caverna Botuvera (271130S, 491090W), southern Brazil,

which covers most of the last 36 thousand years (ka), with an average resolution of a few to several decades. The chronology was

determined with 46U/Th ages from two stalagmites. Tests for equilibrium conditions show that oxygen isotopic variations are primarily

caused by climate change. We interpret our record in terms of meteoric precipitation changes, hence the variability of South American

Monsoon (SAM) intensity. The oxygen isotopic profile broadly follows local insolation changes and shows clear millennial-scale

variations during the last glacial period with amplitudes as large as 3% but with smaller centennial-scale shifts ðo1%Þ during the

Holocene. The overall record is strikingly similar to, but strongly anti-correlated with, a number of records from the Northern

Hemisphere.

We compared our record to other precisely dated contemporaneous records from Hulu Cave eastern China. Minima in d18O (wet

periods, intense SAM) at our site are synchronous with maxima in d18O (dry periods, weak East Asian Monsoon, EAM) in eastern China

(within precise dating errors) and vice versa. This anti-phased precipitation relationship between two low-latitude locations may be

interhemispheric in extent, based on comparison with records from other sites. Precipitation anti-phasing may be related to north–south

shifts in the mean position of the intertropical convergence zone (ITCZ) and asymmetry in Hadley circulation in two hemispheres,

associated not with seasonal changes as observed today, but with millennial-scale climate shifts. The millennial-scale atmospheric see-saw

patterns that we observe could have important controls and feedbacks on climate within hemispheres because of water vapor’s

greenhouse properties.

r 2006 Elsevier Ltd. All rights reserved.

1. Introduction

More than a decade ago, ice cores retrieved fromGreenland revealed that the last glacial period climate ofthe North Atlantic region was characterized by largeabrupt warming events that lasted several hundred years orlonger before a return to cold temperatures, commonlyknown as Dansgaard–Oeschger (D–O) oscillations (e.g.Dansgaard et al., 1993; Grootes et al., 1993). Since thisdiscovery, similar millennial-scale climate events have beenidentified at many localities outside of the North Atlantic(Leuschner and Sirocko, 2000; Voelker and workshopparticipants, 2002). However, questions remain as to what

e front matter r 2006 Elsevier Ltd. All rights reserved.

ascirev.2006.02.009

ing author. Tel.: +1612 624 9598; fax: +1 612 625 3819.

ess: wang0452@umn.edu (X. Wang).

degree such events are in phase, out of phase, or completelyunrelated (see Broecker and Hemming, 2001; Lynch-Stieglitz, 2004). If resolved, this will lead to a significantlyimproved understanding of the fundamental nature andcauses of millennial-scale events. In the few cases whererecords are sufficiently robust to resolve phasing, themillennial-scale events as recorded at different NorthernHemisphere sites are ‘‘in phase’’. For instance, a marinerecord recovered off southern Portugal margin shows thatthe oxygen isotope variability in planktonic foraminiferaclosely matches the temperature change over Greenland(Shackleton et al., 2000). Another sediment core recordfrom the Cariaco Basin reveals that the tropical Atlanticexperienced significant hydrological changes during the lastglacial period, and that such changes are associated withNorth Atlantic temperature swings (Peterson et al., 2000).

ARTICLE IN PRESSX. Wang et al. / Quaternary Science Reviews 25 (2006) 3391–34033392

Synchronous climate oscillations are documented in con-tinental regions as well. Speleothems from Hulu Cave,eastern China, record EAM intensity changes that co-varywith northern high-latitude climate (Wang et al., 2001). Inaddition, the precise chronology of the Hulu recordprovides a benchmark for correlating and calibratingclimate variability (Shackleton et al., 2004).

For interhemispheric comparisons of millennial-scaleclimate events, the best indication of their relationshipcomes from correlations between Greenland and Antarcticice cores. Using an ingenious tool, the record of atmo-spheric methane as measured in both Greenland andAntarctic ice, Blunier and Brook (2001) were able tocorrelate Greenland and Antarctic ice and thereby demon-strated that Greenland and Antarctic climate wereasynchronous during the last glacial period. Whereasasynchroneity between climate at the high northern andhigh southern latitudes was established, a full under-standing of the causes of these events requires someknowledge of how they relate to climate at lower latitudes.As long ice cores are not present at low latitude, theextension of the methane correlation technique to lowerlatitudes is not possible. Further information from lowlatitudes is critical for understanding the causes andramifications of these abrupt events.

A major hindrance for correlating climate events hasbeen the inability to precisely and accurately date materialsthat record climate history. In recent years, studies havedemonstrated that the oxygen isotopic composition (d18O)of cave calcite can reflect the variations of meteoric rainfallat a cave site at the time of calcite precipitation, includingrainfall volume change (Burns et al., 1998; Bar-Matthewset al., 2003; Yuan et al., 2004) or a seasonal rainfall sourceshift (Wang et al., 2001; Cruz et al., 2005). As well-chosenspeleothems can be dated accurately and precisely using230Th dating methods (Richard and Dorale, 2003), recordsof cave calcite d18O can, in principle, be used to determinethe phasing of these events as recorded at differentlocalities around the world. Here, we use speleothemd18O values to reconstruct a precipitation history of theLateglacial period at Caverna Botuvera, southern Brazil(271130S; 491090W, 200m above sea level), and directlycompare this to contemporaneous records from HuluCave, (321300N; 1191100E, Wang et al., 2001) and DonggeCave (251170N; 1081050E, Yuan et al., 2004; Dykoski et al.,2005; Wang et al., 2005), eastern China. As all the recordsare precisely dated using the uranium series methods, wecan directly observe the relationships between the lastglacial period climate changes at these sites in bothhemispheres.

2. Study site and local climate

Caverna Botuvera is located in Santa Catarina state,southern Brazil (Fig. 1). The host rock is Precambrianlimestone of the Brusque group, and the vegetation in thisarea comprises the Atlantic rainforest. Modern climate is

humid, with an average annual rainfall of �1400mm andslightly higher rainfall during the austral summer. Averageyearly temperature is 22 1C, with a large daily range from0 to 35 1C.Climate of southern Brazil is largely affected by the

SAM, a large-scale atmospheric circulation system overmost of the tropical and subtropical South Americancontinent (Zhou and Lau, 1998; Fig. 1). When the SAMdominates during the austral summer season, equatorialtrade winds transport moisture from the tropical Atlantictoward the Amazon basin and east of the Andes. Due tothe blocking effect of the mountains, warm and humid airis forced to veer to southeast and develops deep convectionover central and southern Brazil. This circulation is weakerduring the austral winter. Instead, the western part of thesubtropical South Atlantic High carries water vapor fromthe South Atlantic Ocean directly into subtropical SouthAmerica. Modern rainfall in southern Brazil, therefore, hastwo distinct sources (Rao et al., 1996; Vera et al., 2002;Cruz et al., 2005). A large amount of moisture is derivedfrom the Amazon basin during the austral summer, whilelocal dynamic precipitation is created in winter with airmasses from the nearby ocean, occasionally accompaniedby polar cold fronts. Therefore, our study area is ideal forstudying low-latitude climate, involving both maritimeatmospheric circulation and continental convection. More-over, southern Brazil is heavily populated and the economyis dependent on agriculture and the use of hydroelectricpower. Thus, an improved understanding of the climatol-ogy in this region is of academic interest and also haspractical benefits for local society.

3. Materials and methods

The 1.2 km long Caverna Botuvera is rich in cave calcitedeposits, such as stalagmite, stalactite, and flowstone.Because of conservation ethics, only broken stalagmites,mostly cylindrical in shape, were collected from the cave inAugust 2002. Samples were cut along the growth axis andpolished to clearly expose the growth lamina. All arecomposed of calcite, but some were strongly affected byredissolution. In this study, we focus on two stalagmites,BTV4A and BTV4C, which are about 24.0 and 47.0 cmlong, respectively.Forty-six speleothem subsamples were dated with

U-series methods (Table 1). About 0.1–0.3 g of powderwas extracted by milling from flat polished surfaces using ahand-held carbide dental drill. Procedures for chemicalseparation and purification of uranium and thorium aresimilar to those described in Edwards et al. (1986/87) andCheng et al. (2000). Measurements were performed on aFinnigan ELEMENT inductively coupled plasma massspectrometer (ICP-MS) which is equipped with a double-focusing sector magnet and energy filter in reversedNier–Johnson geometry and a single MasCom multiplier,following procedures modified from Shen et al. (2002) andWang et al. (2004a). All dates are in stratigraphic order,

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90° 80° 70° 60° 50° 40°W

10°

0°

10°

20°

30°

50°

40°

500 kmswind direction

BR AZIL

Pacific Ocean

Atlantic Ocean

Polar Advections

Trade Winds

Trade Winds

Botuverá

São Paulo

Brasilia

SACZ

ITCZ

LLJ

S

Fig. 1. Location of Botuvera Cave (271130S; 491090W) and the current regional climate patterns. Also shown are major components of the South America

monsoon (SAM), including the intertropical convergence zone (ITCZ), South Atlantic convergence zone (SACZ) and low-level jet (LLJ) (after Mechoso,

2000). The SAM is a typical climate feature during austral summer, but is much weaker or even absent during winter, while the cold polar front can

penetrate northward as far as southeastern Brazil and Amazonia (Zhou and Lau, 1998).

X. Wang et al. / Quaternary Science Reviews 25 (2006) 3391–3403 3393

with a typical relative 2s error of about 0.5%. Becausemost subsamples have low concentrations of detritalthorium (on the order of 101–102 ppt, parts per trillion),sample-specific 230Th/232Th ratios are not necessary for usein correcting for initial 230Th and a generic bulk earth ratioð4:4� 2:2� 10�6Þ is used. In particular, subsamples ofstalagmite BTV4C have unusually high measured230Th/232Th atomic ratios ð41000 ppmÞ. In such cases,corrections for initial 230Th amount to less than 5 yr, muchsmaller than other dating errors.

Approximately 700 oxygen and carbon isotopic analyseswere measured on the two stalagmites (SupplementalTable 1). About 100 mg of calcite powder was milled everymillimeter along the central axis using drill burrs ranging insize from 0.3 to 0.5mm. In addition, we selected fiveindividual growth layers on BTV4C and sampled from thecenter toward the two edges to check for isotopicequilibrium conditions during calcite precipitation, theso-called ‘‘Hendy Test’’ (Hendy, 1971). The analyses wereperformed in the Minnesota Isotope Laboratory on aFinnigan MAT 252 mass spectrometer equipped with aKiel II Carbonate Device. Standards and sample duplicateswere run every 10 and 20 samples, respectively, to check for

homogeneity and reproducibility. All oxygen isotopicvalues were calibrated against the international standardsNBS-18 and NBS-19 and are reported in d notation,the per mil deviation relative to the Vienna Pee DeeBelemnite (VPDB) standard ðd18O ¼ ½ðð18O=16OÞsample=ð18O=16OÞVPDBÞ � 1� � 1000Þ. The 1s analytical error iso0:10%.

4. Results

4.1. The speleothem oxygen variation

BTV4A continuously grew through the last 10 ka.BTV4C covers the last 36 ka, but with three hiatusesbetween 17.4 and 14.4 ka before the present (BP), 14.0 and10.9 ka BP, and 8.1 and 6.4 ka BP, respectively (Fig. 2). Weinterpolated linearly between dated intervals to establishages for each d18O analysis (Fig. 3). The stable isotopicmeasurements gave a temporal resolution correspondingto �40 yr, with contemporaneous sample growth over thelast 10 ka.The speleothem d18O ratios fluctuate significantly

throughout the whole profile, with amplitudes as large as

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Table 1

Uranium and thorium isotopic compositions and 230Th ages for Caverna Botuvera speleothems by ICP-MS

Sample Weight 238U 232Th d234U [230Th/238U] Age (ka BP) Age (ka BP) d234Uinitial

ID (g) (ppb) (ppt) measureda activityb uncorrected correctedb,c corrected

BTV4A

BTV4A-3mm 0.2460 61.470.1 691719 49575 0.009070.0008 0.6670.06 0.4470.12 49675

BTV4A-19mm 0.2114 74.170.2 253722 49776 0.009870.0008 0.7270.06 0.6570.07 49876

BTV4A-45mm 0.2149 63.270.2 109722 50576 0.022670.0010 1.6570.08 1.6270.08 50776

BTV4A-61mm 0.1986 72.570.2 624723 50676 0.034070.0011 2.4970.09 2.3270.12 50976

BTV4A-100mm 0.2706 82.470.2 238717 50075 0.053670.0010 3.9770.08 3.9170.08 50575

BTV4A-124mm 0.3157 72.270.2 777715 50375 0.072770.0012 5.4070.09 5.2070.14 51075

BTV4A-146mm 0.2200 83.070.2 114721 49175 0.072970.0014 5.4670.11 5.4370.11 49975

BTV4A-185mm 0.2270 86.870.3 1702721 48475 0.100370.0016 7.6170.13 7.2370.23 49475

BTV4A-194mm 0.1854 70.870.2 870725 48476 0.102970.0018 7.8270.15 7.5870.19 49476

BTV4A-199mm 0.2286 71.570.2 2517721 49175 0.119570.0017 9.0970.14 8.4070.37 50275

BTV4A-225mm 0.1902 84.070.2 513724 48376 0.117270.0020 8.9570.16 8.8370.17 49576

BTV4A-236mm 0.2503 72.170.1 938719 47774 0.131170.0016 10.1170.13 9.8570.18 49074

BTV4C

BTV4C-2.0mm 0.1663 260.670.5 282728 165975 0.020070.0004 0.8270.02 0.8170.02 166275

BTV4C-5.5mm 0.2075 256.970.4 1024722 166575 0.069170.0007 2.8670.03 2.8270.04 167875

BTV4C-14.5mm 0.2292 291.770.4 541720 159373 0.085170.0006 3.6370.03 3.6170.03 160973

BTV4C-28.0mm 0.2334 314.670.4 365720 151773 0.089770.0006 3.9570.03 3.9470.03 153473

BTV4C-40.5mm 0.2038 271.070.4 153723 161374 0.109170.0007 4.6470.03 4.6370.03 163474

BTV4C-48.0mm 0.1681 217.970.5 97728 174375 0.114970.0013 4.6570.06 4.6570.06 176675

BTV4C-68.0mm 0.1962 274.870.6 157724 173374 0.128670.0012 5.2470.05 5.2370.05 175974

BTV4C-75.5mm 0.2000 383.970.6 167723 174074 0.135670.0008 5.5170.03 5.5170.03 176874

BTV4C-77.0mm 0.2835 297.370.6 103716 173874 0.138970.0008 5.6670.04 5.6570.04 176674

BTV4C-89.0mm 0.1764 337.170.8 10726 173975 0.141370.0013 5.7570.05 5.7570.05 176875

BTV4C-95.5mm 0.2000 368.870.6 413723 168574 0.147670.0008 6.1470.04 6.1370.04 171474

BTV4C-97.0mm 0.2734 325.070.9 1155717 167876 0.152170.0008 6.3570.04 6.3170.04 170876

hiatus

BTV4C-101.5mm 0.2216 294.970.7 27721 170976 0.198170.0010 8.2370.05 8.2370.05 174976

BTV4C-109.5mm 0.1942 304.070.6 40724 167174 0.205870.0012 8.6970.05 8.6870.05 171374

BTV4C-141.0mm 0.3244 422.870.5 65714 171272 0.257170.0011 10.7770.05 10.7770.05 176573

BTV4C-154.5mm 0.2237 412.771.2 17721 171975 0.260370.0013 10.8870.06 10.8870.06 177375

hiatus

BTV4C-159.0mm 0.2040 318.470.8 0723 165675 0.325370.0015 14.0870.07 14.0870.07 172376

BTV4C-164.0mm 0.2531 406.670.5 16718 166473 0.332970.0013 14.3970.06 14.3970.06 173373

hiatus

BTV4C-167.5mm 0.3091 167.870.3 68715 178574 0.419070.0019 17.5170.09 17.5070.09 187574

BTV4C-178.0mm 0.2993 171.970.3 139716 183873 0.448170.0018 18.4370.08 18.4370.08 193674

BTV4C-202.5mm 0.2459 117.170.2 73719 175074 0.499170.0023 21.4270.11 21.4270.11 185974

BTV4C-222.5mm 0.2424 276.370.4 35719 163173 0.532170.0020 24.1170.10 24.1170.10 174673

BTV4C-251.5mm 0.2329 313.370.7 0720 163575 0.561370.0022 25.5370.12 25.5370.12 175775

BTV4C-257.0mm 0.2878 319.670.7 20716 161075 0.559070.0020 25.6870.11 25.6870.11 173275

BTV4C-285.5mm 0.2293 354.170.5 30720 164973 0.587970.0019 26.7070.10 26.7070.10 177873

BTV4C-302.5mm 0.2329 246.770.3 38720 183273 0.650670.0023 27.7270.11 27.7170.11 198173

BTV4C-320.0mm 0.1865 242.770.4 16725 163674 0.636470.0025 29.3170.14 29.3170.14 177875

BTV4C-346.5mm 0.2440 307.570.4 30719 157373 0.632370.0020 29.9270.11 29.9270.11 171273

BTV4C-368.0mm 0.2401 267.470.3 24719 165973 0.668470.0021 30.6870.12 30.6870.12 180973

BTV4C-389.5mm 0.2794 320.670.4 48717 159073 0.679970.0021 32.2170.12 32.2170.12 174273

BTV4C-409.5mm 0.2253 256.170.4 0721 155874 0.695970.0025 33.5570.15 33.5570.15 171374

BTV4C-430.0mm 0.2452 279.470.4 18719 160573 0.731570.0022 34.7870.13 34.7870.13 177073

BTV4C-454.0mm 0.2164 294.670.4 37721 154973 0.727170.0028 35.4370.16 35.4270.16 171273

BTV4C-470.0mm 0.2501 394.070.7 3719 157974 0.745670.0025 35.9570.15 35.9570.15 174874

Sample ID is given as a combination of sample name and depth. Analytical errors are 2s of the mean.ad234U ¼ ð½234U=238U�activity � 1Þ � 1000. d234Uinitial corrected is calculated based on 230Th age (T), i.e. d234Uinitial ¼ d234UmeasuredXel234�T , and T is

corrected age.b½230Th=238U�activity ¼ 1� e�l230�T þ ðd234Umeasured=1000Þ � ½l230=ðl230 � l234Þ� � ð1� e�ðl230�l234Þ�T Þ, where T is the age (Kaufman and Broecker, 1965).

Decay constants are 9:1577� 10�6 yr�1 for 230Th, 2:8263� 10�6 yr�1 for 234U (Cheng et al., 2000), and 1:55125� 10�11 yr�1 for 238U (Jaffey et al., 1971).cAge corrections are calculated using an average crustal 230Th/232Th atomic ratio of 4:4� 10�6 � 2:2� 10�6. These are the values for a material at

secular equilibrium, with the crustal 232Th/238U value of 3.8. The errors are arbitrarily assumed to be 50%.

X. Wang et al. / Quaternary Science Reviews 25 (2006) 3391–34033394

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0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

0 100 200 300 400 500

Depth (mm)

Ag

e (

ka B

.P.)

BTV4C

BTV4A

Fig. 2. Plots of age versus depth for Botuvera stalagmites BTV4A and

BTV4C. Age error bars indicate 2s error. Most dating errors are smaller

than the dot sizes. Ages are reported as years before the present

(1950 AD), BP.

X. Wang et al. / Quaternary Science Reviews 25 (2006) 3391–3403 3395

4% (Fig. 3). BTV4C d18O is relatively low during the lastglacial period and has noticeable millennial-scale varia-tions. Minimum values ð� � 5%Þ are observed at 36.0,29.9, 25.8 and 18.4 ka BP. Relatively high values (��3% to�2%) occur around 22.7, 27.9, 29.2, 32.6, 33.5 and 34.6 kaBP, which correspond within error to Greenland Inter-stadials 2, 3, 4, 5, 6 and 7 (Dansgaard et al., 1993; Wanget al., 2001), respectively. Such high d18O values during thelast glacial period also coincide with fairly slow growthrates (�15mm/ka) in the sample (Fig. 4).

As observed in BTV4C, d18O values, in general, increaseduring the last deglaciation and reach a maximum of��1.5% at 10.1 ka BP d18O then maintains peak values(�1.3% to �2.0%) during the early Holocene until 8.7 ka

BP. Through the entire Holocene, d18O values are relativelyhigh and broadly decrease from �1.3% toward �4.1%near present, while the amplitude of centennial-scalevariation is quite small, only �0.5%. This gradualdecreasing trend is interrupted by at least one abruptexcursion. A sharp drop (�1.5%) around 8.2 ka BP isobserved in stalagmite BTV4C. A similar event is observedin the BTV4A record. However, BTV4A has a relativelyhigh content of 232Th in this time range, leading toincreased age uncertainty. BTV4C has a hiatus between8.1 and 6.4 ka BP, also leading to age uncertainty. Thus,there is still substantial uncertainty in a plausible linkbetween the event observed here and the so-called �8200 yrevent, a widespread cooling event in the North Atlantic(Alley et al., 1997). We will pursue this question further infuture work.

4.2. Isotopic equilibrium tests

It is critical to understand what the calcite stable isotoperesults represent. Many processes other than climate, suchas water–rock interactions in the vadose zone and kineticfractionation, may contribute to the d18O signal observedin speleothems. Equilibrium conditions of calcite precipita-tion thus need to be confirmed before we interpretstalagmite d18O values solely in terms of a climate proxyat the time of calcite deposition.d18O and d13C values have a low correlation coefficient

(R2 ¼ 0:011, Fig. 5a) throughout the entire data set forsubsamples measured along the BTV4C growth axis.Moreover, the ‘‘Hendy Test’’ (Hendy, 1971), performedon five individual growth laminae with different growthrates, indicates that d18O variations along the same layerare as small as 0.2%, much less than the 43% changesthroughout the growth axis (Fig. 5b). In addition, nosystematic isotope value increase was found toward theedges of the sample.Another test for isotopic equilibrium conditions is the

replication test, made by comparing contemporaneousportions of d18O records of stalagmites from the same cave(Dorale et al., 1998; Wang et al., 2001). If the d18O profilesreplicate, additional hydrological processes must not havehad differential effects on calcite d18O. Our two Botuverasamples grew contemporaneously for the last 10 ka andthey share similar d18O profiles (Wang et al., 2004b; Fig. 3).Considering that the two samples have different color,growth rate, and calcite structure, it is very unlikely thatthe combination of hydrological conditions experienced byeach set of drips was identical in each case.The above independent lines of evidence suggest that

negligible kinetic fractionation took place during calciteprecipitation. Therefore, we interpret the variations incalcite oxygen isotopic ratios as variations in climate:changes in the oxygen isotopic composition of meteoricprecipitation and cave temperature at the time of calciteprecipitation.

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WARM

WARM

WET

DRY

460

500

0 5 10 15 20 25 30 35 40

-7

-6

-5

-4

-3

-2

-1

0 5 10 15 20 25 30 35 40

-44

-42

-40

-38

-36

-34

-32

-44

-42

-40

-38

-36

-34

-32

-10

-9

-8

-7

-6

-5

-4

δ18O

(‰

, VP

DB

)

Age (ka B.P.)

Hulu

δ18O

(‰

, VP

DB

)δ18

O (

‰, V

SM

OW

)

δ18O

(‰

, VS

MO

W)

Age (ka B.P.)

Byrd

GISP2

BTV4C

HIA

TU

S

HIA

TU

S

Inso

lati

on

(W

/m2 )

(a)

(b)

(c)

(e)

(f)

(d)30οS DJF

Insolation

BTV4A

Botuverá

Botuverá

Dongge

Fig. 3. (a) Oxygen isotopic record from the GISP2 ice core, Greenland, over the last 40 ka (Grootes and Stuiver, 2001). (b) d18O record from the Byrd ice

core, Antarctica (Blunier and Brook, 2001). (c) d18O profiles of stalagmites from Hulu (red) and Dongge (dark red) Caves (Wang et al., 2001; Yuan et al.,

2004; Wang et al., 2005). The d18O scales are reversed for Hulu and Dongge (increasing down) as compared with Greenland and Antarctica (increasing

up). (d) d18O record of Botuvera stalagmites BTV4A (dark green) and BTV4C (blue). The profile shows clear millennial-scale variations during the last

glacial period with amplitudes as large as 3% but with much smaller shifts (o1%) during the Holocene. Yellow bands indicate the durations of hiatuses in

Botuvera samples, which coincide with Heinrich event 1 and the Younger Dryas. (e) Insolation at 301S averaged over the months of December, January

and February for the last 40 ka, with a reversed scale (Berger, 1978). (f) Age error bars indicate 2s error and are color-coded by stalagmite. Oxygen isotope

ratios are expressed in d notation. d18O values are reported relative to the standards. VPDB, Vienna Pee Dee Belemnite, or VSMOW, Vienna Standard

Mean Ocean Water.

X. Wang et al. / Quaternary Science Reviews 25 (2006) 3391–34033396

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Botuverá Cave

BTV4C

Age (ka B.P.)

15 20 25 30 35 40

15 20 25 30 35 40

-6

-5

-4

-3

-2

δ18O

(‰

, VP

DB

)

0

10

20

30

40

50

Gro

wth

Rat

e (m

m/k

a)

Age (ka B.P.)

Fig. 4. Comparison of calcite stalagmite BTV4C d18O (dark curve) and growth rate (gray curve) variations, with lower d18O values corresponding to

higher growth rates.

X. Wang et al. / Quaternary Science Reviews 25 (2006) 3391–3403 3397

4.3. Climatic interpretation of calcite d18O

Whereas the temperature dependence of the calcite/wateroxygen isotopic fractionation is �0.23%/1C (Friedman andO’Neil, 1977), the amplitude of the calcite d18O values inour record is quite large (glacial/interglacial transition�4%). So, the cave temperature effect on the observedd18O variation is likely small. Otherwise, the requiredtemperature change would be too large. Lower tempera-ture during the last glacial maximum (LGM), suggested bylow-latitude continental observations (Stute et al., 1995;Colinvaux et al., 1996), may even result in d18O increases,opposite to the depleted values we observe. Thus, d18Ochange in meteoric precipitation is the primary contributorto the d18O signal recorded in this speleothem.

In low-latitude regions, low d18O of meteoric precipita-tion is mainly related to increased rainfall amount(Dansgaard, 1964; Rozanski et al., 1993). Seasonal shiftsof moisture source can lead to additional variation ofrainfall d18O (Cole et al., 1999; Vuille et al., 2003). Basedon the Rayleigh fractionation model (Dansgaard, 1964),these precipitation d18O variations can be viewed simply asa measure of the percentage of water vapor removed fromoriginal air masses, an integration from the source regionto the location of the measurement. As moisture movesaway from the source region, progressive removal of watervapor from air masses basically results in decreasing watervapor and precipitation d18O.

In southern Brazil, d18O of precipitation has a significantnegative correlation with the intensity of the SAM,indicated by both the instrumental data and AtmosphericGeneral Circulation Model (AGCM) simulations (Vuilleand Werner, 2005). When the SAM is initiated, deepconvection develops in the Amazon basin. Blocked by thevery high mountains to the west, moisture is thentransported southeastward in the form of the low-level jet(LLJ). Such vapor has characteristically low d18O valuebecause of recycling in the source region and the longtransportation route (Hoffmann, 2003). During an intensi-fied SAM, a greater portion of upstream vapor loss leads toeven lower d18O of rainfall when it finally reaches southernBrazil. In a parallel study (longer term, but lowerresolution) of a stalagmite from Botuvera cave, Cruz etal. (2005) found that calcite d18O variation represents theratio change between this low d18O moisture and the watervapor from nearby Atlantic source, which has distinctlyhigher d18O. Moreover, an enhanced SAM is associatedwith a stronger LLJ, hence, transporting more moistureinto downstream southern Brazil (Mechoso, 2000; Lieb-mann et al., 2004). Abundant Amazon moisture trans-ported into southern Brazil contributes to the low d18O ofprecipitation. At Botuvera, speleothem d18O may capturethis rainfall amount signal, in addition to seasonal sourceshifts suggested by Cruz et al. (2005). This is furtherconfirmed by the observations that lower d18O valuecorresponds to higher sample growth rate in our record

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(a)

y = 0.080x - 3.039R2 = 0.011

-6.0

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atio

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Fig. 5. (a) d18O versus d13C from stalagmite BTV4C. The low correlation ðR2 ¼ 0:011Þ of the plotted results indicates that carbon and oxygen are not

highly correlated as would be expected with kinetic fractionation. (b) The ‘‘Hendy Test’’ (Hendy, 1971) on five different growth laminae suggests that the

speleothems most likely grew under isotopic equilibrium conditions. d18O variations are �0.2% along the same layers but 43% along the growth axis.

X. Wang et al. / Quaternary Science Reviews 25 (2006) 3391–34033398

(Fig. 4), which probably is linked to drip water supply(Baker et al., 1998). Furthermore, it is unlikely thatthe nearby subtropical Atlantic source could have amajor contribution on meteoric precipitation at Botuveraduring the glacial periods. Otherwise, this wouldcause isotopically enriched rain in part due to the oceanreservoir effect (Schrag et al., 1996), in contrast to ourobservations. Overall, Botuvera calcite d18O valuesmay represent the strength of LLJ along the moisturetrajectory from the central Amazon Basin to southernBrazil, i.e. the intensity of the SAM. Thus, low (high)calcite d18O in our record suggests a higher (lower)Amazon moisture contribution and an intensified(weakened) SAM.

5. Climate discussions

5.1. Orbital- and millennial-scale SAM intensity change

Similar to observations in the northern low latitudes(Wang et al., 2001; Yuan et al., 2004), our record broadlyfollows orbital-induced summer insolation variations. Lowcalcite d18O values appear to have occurred in phase withlocal summer insolation maxima produced by the Earth’sprecession cycle (Wang et al., 2004b; Fig. 3). Recent workon another stalagmite from the same cave also showsstrong Milankovitch forcing over the last 110 ka (Cruzet al., 2005). Lake sediment records from both the Andesand Amazon Basin also indicate that lake levels have a

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strong response to precession cycles (Baker et al., 2001a;Bush et al., 2002). Increased summer insolation in the tropicstends to enhance continental convection and SAM intensity,which eventually brings more d18O-depleted rainfall intosouthern Brazil. The orbital-controlled signal in our record isparticularly robust during the Holocene, with the calcited18O linearly tracking local summer insolation. Persistentescalation of SAM intensity, indicated by the decreasingcalcite d18O values through the Holocene, is in a goodagreement with the expansion of Araucaria forest in southernBrazil (Behling et al., 2004) and increasing terrigenoussediments off the coast (Heil et al., 2004).

During the last glacial period, superimposed upon thefirst-order insolation-driven relationship, our calcite d18Orecord is punctuated by numerous millennial-scale events,with amplitudes up to 3%, similar to the NorthernHemisphere events such as those recorded in the Hulucave speleothems (Wang et al., 2001) and the Greenland icecore records (Grootes and Stuiver, 1997; Fig. 3). However,the events observed here are, within precise dating errors,anti-phased with their northern counterparts. The Botu-vera millennial-scale variations are also larger in amplitudethan their Holocene centennial-scale counterparts, prob-ably due in some fashion to glacial boundary conditions.The presence of large ice sheets may amplify the millennial-scale climate oscillations (Broecker et al., 1990; Clark et al.,1999). However such variations are weak, even notidentifiable, in the speleothem record from the same cavereported by Cruz et al. (2005). We suspect, we are able tosee these remarkable millennial-scale changes because oursamples have higher growth rates (Fig. 2), which enablemore precise dating and higher resolution stable isotopicdata. Our record shows that the intensity of the SAM hasendured significantly abrupt changes during the last glacialperiod.

5.2. Regional and global correlations of millennial-scale

climate events

The Botuvera record shares some similar features withice core d18O records from Greenland (Grootes andStuiver, 1997), particularly during the last glacial period(Fig. 3). Increasing calcite d18O (drying) corresponds torising d18O in the ice core (warming), and vice versa, whichindicates a possible common forcing between SAMprecipitation in southern Brazil and temperature over theNorth Atlantic. However during the Holocene, SAMintensity tends to follow local insolation change whilehigh-latitude temperature only has minor variations. Incontrast, the Botuvera d18O shows remarkable similarity,but of opposite sign, to the calcite d18O from Hulu andDongge Caves in eastern China, throughout the durationof growth. Here, we plot the Hulu and Dongge Caveprofiles together because both represent EAM intensityand the absolute d18O values from their contemporaneoussamples are essentially identical (Yuan et al., 2004;Dykoski et al., 2005; Fig. 3).

The most striking feature of our record is its robust anti-correlation with the calcite d18O variation in the Hulurecord during the last glacial period (Fig. 6). Note that wehave used inverse scales for the two records. The fact thatthe resulting two records essentially plot on top of eachother, i.e. a mirror image of each other, indicates astrong anti-correlation. Thus, low d18O values in theBotuvera record coincide precisely with high d18O valuesin Hulu, and vice versa. As both records are dated with aprecision (typical relative 2s errors in age of �0.4% and0.8% for Botuvera and Hulu speleothems, respectively)that is much better than the length of any of the millennial-scale events, the two records can be compared directly andthe phasing of the events can be determined. The Hulu andDongge calcite d18O is recognized as a proxy of theintensity of the EAM (Wang et al., 2001; Yuan et al., 2004;Wang et al., 2005). If the intensity of the SAM is indeeddocumented by the Botuvera d18O (Fig. 1), our observationindicates that strong SAM correlates to weak EAM, andvice versa, on a millennial-time scales as well as orbital-time scales.A number of northern low-latitude locations, such as

Israel (Bar-Matthews et al., 2003), Oman (Burns et al.,1998), Socotra Island (Burns et al., 2003) and northernSouth America (Gomez et al., 2003) also show precipita-tion histories similar to the Hulu (Wang et al., 2001) andDongge (Yuan et al., 2004; Dykoski et al., 2005; Wanget al., 2005) sites in China, although their modernmeteorological conditions are very different (Fig. 7). Inthe Southern Hemisphere, our Botuvera precipitationrecord is broadly similar to previous observations fromanother southern low-latitude site, in northeastern Brazil(Wang et al., 2004a). Wet intervals in currently semi-aridNordeste region are synchronous with the timing of weakEAM and cold periods in the North Atlantic. Peat and lakesediment in northeastern Australia also show millennial-scale wet phases that relate to D–O cold events (Turneyet al., 2003). A strong SAM during the LGM, suggested bythe Botuvera low d18O, is consistent with high snowaccumulation on Sajama mountain (Thompson et al.,1998) and rising lake levels over the Altiplano (Baker et al.,2001b). Relatively low calcite d18O during the LGM isfurther identified in stalagmites from South Africa(Holmgren et al., 2003). Thus, the observed anti-phasingbetween the Botuvera and Hulu sites may be part of ageographically widespread millennial-scale anti-phasing oflow-latitude precipitation between hemispheres. In general,wet northern low latitudes with a strong EAM and IndianMonsoon correlate to dry southern low latitudes, includinga relatively weak SAM, and vice versa: a low-latitudeinterhemispheric climate see-saw.

5.3. Mechanisms of millennial-scale climate events

Currently, summer rainfall in southern Brazil is highlycorrelated with sea surface temperature (SST) over thewestern subtropical South Atlantic (WSSA) (Barros et al.,

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Fig. 6. Comparison of speleothem d18O records from Botuvera Cave, southern Brazil (blue curve), and Hulu Cave, eastern China (red curve, Wang et al.,

2001). Note that we have used inverse scales for two records. Wet periods at the Hulu site are correlated to dry periods at Botuvera, and vice versa,

indicating a low-latitude atmospheric precipitation see-saw. Numbers for the last glacial interstadials and Heinrich events are also shown here based on the

correlation between the Hulu Cave and Greenland ice core records (Wang et al. 2001).

austral summer ITCZ 2

1

boreal summer ITCZ3

45

6

7

89

10

11

14

12

13

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17

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Fig. 7. Spatial patterns of millennial-scale climate change events (see discussions in the text). Speleothem records (green dots) from low-latitude regions

indicate the variation of precipitation: 1. Caverna Botuvera, southern Brazil; 2. Caves in northeastern Brazil (Wang et al., 2004a); 3. Cueva Zarraga,

Venezuela (Gomez et al., 2003); 4. Hulu Cave, eastern China (Wang et al., 2001); 5. Dongge Cave, eastern China (Yuan et al., 2004; Dykoski et al., 2005;

Wang et al., 2005); 6. Qunf Cave, Oman (Fleitmann et al., 2003); 7. Moomi Cave, Socotra Island (Burns et al., 2003); 8. Peqiin Cave, Israel (Bar-Matthews

et al., 2003); 9. Soreq Cave, Israel (Bar-Matthews et al., 2003); 10. Cold Air Cave, South Africa (Holmgren et al., 2003), and other sites discussed in the

text, from the tropics (green squares): 11. Cariaco Basin (Peterson et al., 2000); 12. Lake Titicaca (Baker et al., 2001b); 13. Sajama ice core (Thompson et

al., 1998); 14. Lynch’s crater (Turney et al., 2003), and from mid-to-high latitudes (blue squares): 15. GRIP ice core (Dansgaard et al., 1993); 16. GISP2 ice

core (Grootes and Stuiver, 1997); 17. MD 95-2042 deep sea core off Portugal (Shackleton et al., 2000); 18. Vostok ice core (Petit et al., 1999) and 19. Byrd

ice core (Blunier and Brook, 2001). During the last glacial period, the displacement of the mean annual position of the ITCZ and associated

atmosphere–ocean system changes would contribute to the meridional asymmetry of the Hadley circulation causing, therefore, a see-saw pattern of rainfall

distribution observed between the northern and southern low latitudes.

X. Wang et al. / Quaternary Science Reviews 25 (2006) 3391–34033400

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2000; Liebmann et al., 2004). A positive (negative) SSTanomaly in the WSSA region tends to accompany aweakened (strengthened) and southward (northward)shifted South Atlantic convergence zone (SACZ), whichis convective activity oriented from northwest to southeastand on average located over southeastern Brazil. Feedbackbetween a positive (negative) SST anomaly and a weak(intense) SACZ may enhance (decrease) the LLJ, whichincreases (reduces) basin moisture contribution into south-ern Brazil (Doyle and Barros, 2002). Liebmann et al. (2004)show a positive association between SAM activity and SSTin the WSSA. Confirmed by instrumental evidence, riverdischarges in this region also appear to coincide with theSST anomaly on interannual and decadal time scales(Robertson and Mechoso, 2000). We propose that thisassociation exists in the geological past as well. Onmillennial and even orbital-time scales, the SST anomalyin WSSA may influence rainfall in southern Brazil andSAM activity.

During the last glacial period, millennial-scale changes inocean heat circulation related to the bipolar see-sawmechanism may have changed meridional Atlantic SSTgradients (Broecker, 1998). Modeling efforts indicate thatweak ocean circulation may result in a positive SSTanomaly in the South Atlantic (e.g. Crowley, 1992) and thepredictions are confirmed by studies of ocean sedimentcores (e.g. Arz et al., 1998; Ruhlemann et al., 1999). Awarm SST anomaly in the WSSA may stimulate apersistent intense SAM and strong LLJ, which conse-quently supplies plenty of isotopically depleted precipita-tion into southern Brazil.

The mechanisms discussed above may explain aspects ofour observed millennial-scale interhemispheric rainfall see-saw as well. Weak ocean circulation in the northernAtlantic and more ice coverage in the Northern Hemi-sphere result in a southward shift of the ITCZ (Chiang etal., 2003; Chiang and Bitz, 2005). The southward ITCZdisplacement would generate a warm anomaly in thesouthern Atlantic and a strong SAM, while the EAM andIndian Monsoon would weaken. Moreover, analogous tomodern seasonal observations in boreal winters (Lindzenand Hou, 1988), southward ITCZ migration duringmillennial-scale stadial events may have caused meridionalasymmetry in Hadley circulation. This anomalous Hadleycell is probably further enhanced because weakened oceancirculation induces substantial cooling in the northern highlatitudes. An intensified northern branch of the Hadleycirculation will drive atmospheric heat transport north-ward to compensate for northern cooling (Clement et al.,2004). A southward shift of the zonal-mean Hadley cellwould change meridional moisture transport throughintense ascending air masses in the southern low latitudesand increased subsidence in the northern tropics andsubtropics. Broadly, the northern low latitudes would bedrier and the southern low-latitudes wetter, which has beenconfirmed by recent model results (e.g. Clement et al., 2004;Chiang and Bitz, 2005; Zhang and Delworth, 2005). The

opposite scenario would have been true during glacialinterstadial periods.

6. Conclusions

With precise uranium series dating, we have obtained ahigh-resolution oxygen isotopic record of cave calcite fromCaverna Botuvera, southern Brazil. The d18O profilebroadly follows local summer insolation changes andadditionally shows noticeable millennial-scale variationsduring the last glacial period. We ascribe variability ofSAM intensity as the cause of these d18O variations. SAMintensity influences the amount of rainfall transported fromthe Amazon Basin into southern Brazil, which has asignature of low d18O. Variation of SAM intensity haslikely affected precipitation in the Amazon Basin as well(Zhou and Lau, 1998). Our work suggests that at least inpart of the Basin, the climate may have suffered dramaticchanges in the past. This would have significant con-sequences for tropical plant communities.Comparison of the calcite d18O records from southern

Brazil and eastern China reveals, for the first time, aremarkable anti-correlation of precipitation at two low-latitude locations. This correlation may be interhemi-spheric in extent, based on comparison with records fromother sites in both low latitudes. Precipitation anti-phasingmay be related to changes in the mean position of the ITCZand associated asymmetry in Hadley circulation in the twohemispheres. Such a low-latitude interhemispheric precipi-tation see-saw may have had a significant impact ontropical and extratropical temperatures on millennial timescales because it would have changed the distribution ofwater vapor, the atmosphere’s primary greenhouse gas,between hemispheres (Pierrehumbert, 1999).

Acknowledgements

We would like to dedicate this paper to Nick Shackleton,who was so enthusiastic about this type of research. R.L.E.would like to thank Nick, wherever he may be, for hissupport and encouragement over the years.We thank W.S. Broecker and G. Comer for their

generous support of our work. Cave sampling wasperformed with permission from IBAMA/CECAV. Wethank the friendly collaboration of land owners and localpeople. This work was supported by NSF GrantsESH0214041, ESH0502535 and MRI0116395 (to R.L.E.),a Gary Comer Science and Education Foundation GrantCC8 (to R.L.E.), a CNPq Grant 540064/01-7 of Brazil (toA.S.A.), and GSA research Grants 7830-04 and 8163-05 (toX.F.W.).

Appendix A. Supplementary data

Supplementary data associated with this article can befound in the online version at 10.1016/j.quascirev.2006.02.009.

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