Controls of Caribbean surface hydrology during the mid- to

Clim. Past, 9, 841–858, 2013www.clim-past.net/9/841/2013/doi:10.5194/cp-9-841-2013© Author(s) 2013. CC Attribution 3.0 License.

EGU Journal Logos (RGB)

Advances in Geosciences

Open A

ccess

Natural Hazards and Earth System

Sciences

Open A

ccess

Annales Geophysicae

Open A

ccess

Nonlinear Processes in Geophysics

Open A

ccess

Atmospheric Chemistry

and Physics

Open A

ccess

Atmospheric Chemistry

and PhysicsO

pen Access

Discussions

Atmospheric Measurement

Techniques

Open A

ccess

Atmospheric Measurement

Techniques

Open A

ccess

Discussions

Biogeosciences

Open A

ccess

Open A

ccess

BiogeosciencesDiscussions

Climate of the Past

Open A

ccess

Open A

ccess

Climate of the Past

Discussions

Earth System Dynamics

Open A

ccess

Open A

ccess

Earth System Dynamics

Discussions

GeoscientificInstrumentation

Methods andData Systems

Open A

ccess

GeoscientificInstrumentation

Methods andData Systems

Open A

ccess

Discussions

GeoscientificModel Development

Open A

ccess

Open A

ccess

GeoscientificModel Development

Discussions

Hydrology and Earth System

Sciences

Open A

ccess

Hydrology and Earth System

Sciences

Open A

ccess

Discussions

Ocean Science

Open A

ccess

Open A

ccess

Ocean ScienceDiscussions

Solid Earth

Open A

ccess

Open A

ccess

Solid EarthDiscussions

The Cryosphere

Open A

ccess

Open A

ccess

The CryosphereDiscussions

Natural Hazards and Earth System

Sciences

Open A

ccess

Discussions

Controls of Caribbean surface hydrology during the mid- to lateHolocene: insights from monthly resolved coral records

C. Giry 1, T. Felis1, M. K olling1, W. Wei2, G. Lohmann2, and S. Scheffers3

1MARUM – Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany2Alfred Wegener Institute for Polar and Marine Research, 27570 Bremerhaven, Germany3Marine Ecology Research Centre, Southern Cross University, Lismore, NSW 2480, Australia

Correspondence to:C. Giry ([email protected])

Received: 29 July 2012 – Published in Clim. Past Discuss.: 21 August 2012Revised: 14 January 2013 – Accepted: 26 February 2013 – Published: 22 March 2013

Abstract. Several proxy-based and modeling studies haveinvestigated long-term changes in Caribbean climate dur-ing the Holocene, however, very little is known on its vari-ability on short timescales. Here we reconstruct seasonal-ity and interannual to multidecadal variability of sea sur-face hydrology of the southern Caribbean Sea by applyingpaired coral Sr/Ca andδ18O measurements on fossil annuallybandedDiploria strigosacorals from Bonaire. This allowsfor better understanding of seasonal to multidecadal variabil-ity of the Caribbean hydrological cycle during the mid- tolate Holocene. The monthly resolved coral1δ18O recordsare used as a proxy for the oxygen isotopic composition ofseawater (δ18Osw) of the southern Caribbean Sea. Consis-tent with modern day conditions, annualδ18Osw cycles re-constructed from three modern corals reveal that freshwaterbudget at the study site is influenced by both net precipitationand advection of tropical freshwater brought by wind-drivensurface currents. In contrast, the annualδ18Osw cycle recon-structed from a mid-Holocene coral indicates a sharp peaktowards more negative values in summer, suggesting intensesummer precipitation at 6 ka BP (before present). In line withthis, our model simulations indicate that increased seasonal-ity of the hydrological cycle at 6 ka BP results from enhancedprecipitation in summertime. On interannual to multidecadaltimescales, the systematic positive correlation observed be-tween reconstructed sea surface temperature and salinity sug-gests that freshwater discharged from the Orinoco and Ama-zon rivers and transported into the Caribbean by wind-drivensurface currents is a critical component influencing sea sur-face hydrology on these timescales.

1 Introduction

Proxy records and model simulations indicate that hydro-logical conditions in the Caribbean have experienced sig-nificant changes on glacial/interglacial timescales. Changesin the tropical hydrological cycle on these timescales havebeen associated with both the mean latitudinal position ofthe Intertropical Convergence Zone (ITCZ) and strength ofthe Atlantic Meridional Overturning Circulation (AMOC)(Lohmann, 2003; Zhang and Delworth, 2005; Carlson et al.,2008; Wan et al., 2010; Leduc et al., 2007; Schmidt andSpero, 2011; Schmidt et al., 2004; Sepulcre et al., 2011).Moreover, changes in Caribbean freshwater budget have aprofound effect on the strength of the AMOC, which pointsto the critical role of the tropical Atlantic in mediating globalclimate changes (Leduc et al., 2007; Jaeschke et al., 2007).

Low-latitude climate reconstructions have designated thenet precipitation (P − E, precipitation minus evaporation)associated with latitudinal movement of the ITCZ asthe main driver of the Caribbean freshwater budget onglacial/interglacial timescales (Leduc et al., 2007; Schmidtet al., 2004; Sepulcre et al., 2011). For example, during theearly and mid-Holocene, there are indications for a morenorthward position of the ITCZ, which intensified precipi-tation over the northern tropical Atlantic and the Caribbean(Haug et al., 2001; Hodell et al., 1991), whereas today, withthe position of the Atlantic ITCZ in a more southerly posi-tion, net evaporation due to enhanced subsidence contributesto the negative freshwater budget of the Caribbean (Etter etal., 1987 and references therein). However, due to the lackof suitable high-resolution proxy data that clearly resolve the

Published by Copernicus Publications on behalf of the European Geosciences Union.

842 C. Giry et al.: Controls of Caribbean surface hydrology during the mid- to late Holocene

annual cycle, the seasonal dynamics of the Atlantic ITCZ un-der different climate background states are not well known.

In order to investigate seasonal to multidecadal variabil-ity patterns of surface hydrology in the Caribbean Sea duringthe mid- to late Holocene, we use decades-long monthly re-solved paired Sr/Ca andδ18O records of fossil corals fromBonaire (southern Caribbean Sea) to assess changes in theoxygen isotopic composition of seawater (δ18Osw) over thelast 6 ka. The Sr/Ca ratio in coral skeletons is a proxy forsea surface temperature (SST) (Beck et al., 1992; Smith etal., 1979), whereas the coralδ18O reflects changes of bothtemperature and seawaterδ18O (δ18Osw), which is linearlyrelated to sea surface salinity (SSS) (Carriquiry et al., 1994;Urey, 1947; Watanabe et al., 2001; Wellington et al., 1996).Therefore, paired measurements ofδ18O and Sr/Ca in coralskeletons provide a unique opportunity to reconstruct SSTand SSS changes at subseasonal to interannual resolution(Felis et al., 2009; Gagan et al., 1998; Hendy et al., 2002;Linsley et al., 2006; McCulloch et al., 1994). Our study aimsat better understanding the natural range of surface hydrol-ogy variability in the Caribbean on seasonal to multidecadaltimescales during the Holocene, by using sub-seasonally re-solved coral records and climate model simulations. Such acombined approach is still rare. Exceptions include Felis etal. (2004), Abram et al. (2007), and Yokoyama et al. (2011).

2 Regional setting and hydrography of the study area

Coral colonies used in this study were collected on Bonaire(Giry et al., 2012), an open-ocean island in the south-ern Caribbean Sea, located∼ 100 km north of Venezuela(∼ 12◦10′ N, 68◦18′ W). Caribbean climate is primarilyforced by a co-varying pattern of SST and trade winds asso-ciated with the seasonal migration of the ITCZ (Hastenrath,1984). Bonaire has a tropical-arid climate characterised bylow annual mean rainfall (∼ 500 mm yr−1) and high evapo-ration rate. In contrast to other less arid Caribbean Islandswhich receive most of their yearly rain in summer (Gianniniet al., 2000), Bonaire’s main rainy season lasts from Octo-ber through January and is followed by a dry season betweenFebruary to May with a transition period called “small rains”season (Martis et al., 2002) from June to September. The sea-sonal displacement of the ITCZ affects the strength of thenortheast trade winds blowing over the western tropical At-lantic and the Caribbean. Trade winds weaken in boreal sum-mer and strengthen in boreal winter and thus affect the pat-terns of ocean circulation and precipitation in the Caribbean.

Freshwater budget in the Caribbean suggests the influ-ence of two major processes: (1) the local freshwater fluxthrough evaporation (E) and precipitation (P ) (Etter et al.,1987) over the basin and (2) freshwater input from the Ama-zon and Orinoco rivers by advection of low salinity watermasses by surface currents (Hellweger and Gordon, 2002).Net water loss due to yearlong easterly trade winds results in

Se

a S

urf

ac

e S

ali

nit

y (

ps

u)

38

37

36

35

34

33

32Ocean

Data

Vie

w

GC

NECCC

GS

FC

NBC

Fig. 1. Modern oceanographic setting of the Caribbean and west-ern North Atlantic. Schematic of major surface currents constitut-ing the upper branch of the Atlantic meridional overturning circula-tion (AMOC) are superimposed on annual mean sea surface salin-ity (Antonov et al., 2006). Major surface currents: North Brazil-ian Current (NBC), Guyana Current (GC), Caribbean Current (CC),Florida Current (FC), Gulf Stream (GS) and North Equatorial Cur-rent (NEC). White circle indicates the study site (Bonaire).

excessiveE overP , which is strongest over the basin in win-tertime (Etter et al., 1987; Giannini et al., 2000; Hastenrathand Lamb, 1978). Caribbean freshwater budget indicates thatriver discharge in the western Caribbean (west of 70◦ W)does not compensate for net water loss due to net evaporation(Etter et al., 1987), whereas it does in the western tropical At-lantic and eastern Caribbean (Hellweger and Gordon, 2002).Hence, the freshwater budget in the eastern Caribbean and atthe study site might reflect both the local freshwater flux andfreshwater supply from tropical rivers.

Caribbean hydrography is characterised by a stratifiedupper 500 m of the water column due to the presence oftwo dominant water masses with contrasting physical prop-erties (Wust, 1964). The North Atlantic Subtropical Un-der Water (SUW), formed in the subtropical north AtlanticwhereE exceedsP , is characterised by a salinity maximum(> 36.5) that sinks below fresher surface water referred to asCaribbean Surface Water (CSW) at about 120 m depth (Wust,1964). The latter water mass is thought to be a mixture ofNorth Atlantic surface water and freshwater from the Ama-zon and Orinoco rivers, as well as from other South Ameri-can rivers that is transported north-westward by the Guyanaand Caribbean Currents (Fig. 1). As the CSW is transportedwestward by the Caribbean Current, freshwater masses areevaporated and mixed with the more saline SUW (Gordon,1967).

At interannual timescales the tropical Atlantic is linkedto the competing influence of local and remote forcingemanating from tropical and subtropical oceans. On thesetimescales, El Nino–Southern Oscillation (ENSO)-relatedanomalous atmospheric circulation is one of the dominantfactors suppressing rainfall over the Caribbean. Chiang etal. (2002) suggested that the teleconnection of ENSO warmevents to the tropical Atlantic results in an anomalous

Clim. Past, 9, 841–858, 2013 www.clim-past.net/9/841/2013/

C. Giry et al.: Controls of Caribbean surface hydrology during the mid- to late Holocene 843

warm north/cool south SST gradient that would shift theITCZ anomalously north; warm ENSO also induces a stronganomalous Walker circulation that suppresses precipitationover the western tropical Atlantic and Caribbean by strength-ening subsidence. Such a pattern of ENSO teleconnec-tion to the tropical Atlantic is consistent with other studies(Alexander and Scott, 2002; Giannini et al., 2001). At inter-to multidecadal timescales, the Atlantic Multidecadal Oscil-lation (AMO) plays a critical role in controlling both SST andrainfall in the Caribbean (Sutton and Hodson, 2005). Forcingmechanisms responsible for the leading large-scale pattern ofmultidecadal climate variability are partially related to vari-ability in the oceanic thermohaline circulation (Delworth andMann, 2000; Dima and Lohmann, 2007; Knight et al., 2005)as recently identified along the north-eastern coast of Brazilin the surface return flow of the AMOC (Zhang et al., 2011).

3 Material and methods

U-series dating, screening for diagenesis, and Sr/Ca analy-ses were performed on fossilDiploria strigosacorals fromBonaire as recently described (Giry et al., 2012). Based onthe annual density bands inferred from X-radiographs, a sam-pling resolution of∼ 12 samples per year was targeted alongthe growth axis of pristine coral skeletons. For each sample,skeletal powder was carefully drilled using a 0.6 mm diame-ter drill bit along the centre of the dense thecal walls, whichis the skeletal element that provides the best environmentalseasonal signal (Giry et al., 2010a). Each powdered samplewas split for both stable oxygen isotope (δ18O) and Sr/Caanalyses performed at MARUM and the Department of Geo-sciences of the University of Bremen, respectively. Furtherdetails on stable isotope and Sr/Ca analyses have been de-scribed (Giry et al., 2010a, 2012; Felis et al., 2012).

The internal chronology of individual coral records isbased on annual density-banding patterns inferred from bothX-radiographs and annual Sr/Ca cycles. Maximum and min-imum Sr/Ca values in any given year were assigned to theon average coldest (February/March) and warmest months(September/October) of present-day SST, respectively (Giryet al., 2012). This method introduces a non-cumulative errorof ±1 month in any given year. The same anchor points as forSr/Ca were used for the age model construction of the corre-spondingδ18O record. To obtain monthly time series, coralSr/Ca andδ18O records were linearly interpolated to monthlyresolution following established procedures (e.g. Felis et al.,2004, 2009; Giry et al., 2010b). As both Sr/Ca andδ18O weremeasured on the same powder samples, the variation of Sr/Carelative to that ofδ18O has no age uncertainty.

Subseasonal reconstruction of seawaterδ18O (δ18Osw)variations is achieved by paired coral Sr/Ca andδ18O mea-surements. The most commonly used method to calculateδ18Osw exploits proxy-SST regressions to convertδ18O andSr/Ca to temperature (Gagan et al., 1998; McCulloch et al.,

1994). However, the regressions have generally different in-tercepts due to different mean values between different coralcolonies (e.g. Abram et al., 2009; Felis et al., 2003, 2004).Therefore, omitting the intercept values in order to assess in-stantaneous changes ofδ18Osw is critical (Ren et al., 2003).To do so, the centering method and the combined analyticalerror are used (Cahyarini et al., 2008). Multitaper Method(MTM) spectral analysis (Ghil et al., 2002), with signifi-cance relative to a red noise null hypothesis determined withthe robust method of noise background estimation (Mannand Lees, 1996), is applied to the detrended and normalisedδ18Osw and instrumental records with the mean annual cycleremoved. In correspondence with previous work (Felis et al.,2009; Gagan et al., 1998; Hendy et al., 2002), we term theδ18Osw variations reconstructed from paired coral Sr/Ca andδ18O measurements coral1δ18O.

The numerical experiments were performed with the cou-pled general circulation model COSMOS consisting of theatmospheric model ECHAM5 (Roeckner et al., 2003), oceanmodel MPIOM (Marsland et al., 2003), and dynamical veg-etation model JSBACH (Raddatz et al., 2007). The atmo-spheric model has a resolution of T31 (3.75◦

× 3.75◦) inhorizontal and 19 vertical hybrid sigma pressure levels. Theocean model has a 3◦

× 1.8◦ averaged horizontal grid with40 unevenly spaced vertical levels with higher resolutionaround Greenland and Antarctica (Marsland et al., 2003). Wecarried out two experiments: a pre-industrial (CTL) experi-ment and a mid-Holocene one (6 ka), by prescribing the ap-propriate orbital parameters and greenhouse gases. Details ofthe model experiments are described in Wei et al. (2012) andWei and Lohmann (2012).

4 Results

4.1 Modern coral δ18O–SST relationship

The coralδ18O–SST relationship of theD. strigosacolonycollected live in Bonaire (BON-0-A) was assessed for theperiod 1993–2009. The regression equation in reference togridded monthly SST data (Smith et al., 2008) is

δ18O(‰) = −0.106(±0.010) × SST− 1.432(±0.259)(r2

= 0.41, p < 0.01, N = 188).

Moreover, coralδ18O is investigated in reference to localSST data from a nearby island, Curacao (distance∼ 80 km),for a period of 18 months spanning April 1999 to Septem-ber 2000 (M. J. A. Vermeij, personal communication, 2009).The linear regression for this data is

δ18O(‰) = −0.124(±0.016) × SST− 0.951(±0.437)(r2

= 0.79, p < 0.0001, N = 18).

www.clim-past.net/9/841/2013/ Clim. Past, 9, 841–858, 2013


Internal chronology (a)

Fig. 2.Monthly resolved coral Sr/Ca (red) (Giry et al., 2012), coralδ18O (blue) records and derived coral1δ18O (black) records of modern(yellow shading) and fossil (grey shading)Diploria strigosacorals from Bonaire and corresponding 5-yr running mean. Coral1δ18O recordswere calculated using the centering method (Cahyarini et al., 2008) and Sr/Ca-SST andδ18O–SST slopes of−0.061 mmol mol−1 ◦C−1 and−0.180 ‰◦C−1 (Correge, 2006; Gagan et al., 1998), respectively. The U-series ages of the individual coral colonies (Giry et al., 2012) areindicated.

We note that the coralδ18O–SST regression slopes are lowerthan the published values forD. strigosafrom Guadeloupein the eastern Caribbean (Hetzinger et al., 2006). This dis-crepancy might arise from distinct annual temperature andhydrological cycles between Bonaire and Guadeloupe that inturn affect the amplitude of the oxygen isotopic ratio of coralskeleton at both sites. For instance, Hetzinger et al. (2010)showed that the annual salinity cycle at Guadeloupe de-creases when temperature increases. However, at Bonairesuch correlation between salinity and temperature is not sostraightforward (cf. Sect. 5.2 and Fig. 10), Therefore the re-gression existing for Bonaire coralδ18O–SST will be differ-ent from that of Guadeloupe. Consequently, in order to cir-cumvent uncertainties associated with calibrating proxy data,the reconstructedδ18Osw is derived from a range of proxy-SST calibrations rather than from fixed calibration values.

4.2 Surface hydrology changes during the mid- to lateHolocene

Monthly resolved coral Sr/Ca and coralδ18O of three modernand six fossil corals are shown in Fig. 2. Each coral recordshows clear annual cycles in both Sr/Ca andδ18O, which cor-relate with the corresponding annual-density bands. There-fore, robust coral internal chronologies could be established,enabling accurate assessment of seasonal to multidecadalvariability of coral proxies for well-distributed time windowsthroughout the mid- to late Holocene.

Mean coral1δ18O values for individual colonies werecalculated by averaging data of each year and subsequentlyaveraging the resulting annual means of all years consti-tuting the coral record. The mean1δ18O values for indi-vidual Bonaire corals are shown in Fig. 3. This has beencalculated using the coral Sr/Ca-SST andδ18O–SST rela-tionships of−0.061 mmol mol−1 ◦C−1 (Correge, 2006) and−0.180 ‰◦C−1 (Gagan et al., 1998), respectively, follow-ing established procedures (Cahyarini et al., 2008). Thethree modern corals exhibit between colony offsets in mean1δ18O. The standard deviation of such intercolony variabil-ity is 0.161 ‰ (1σ ). The mean1δ18O values of all coralssuggest a trend towards more positive values over the last6.2 ka (Fig. 3). This tendency in the coral data does notchange when a range of proxy-SST relationships is used(Table S1 in the Supplement). Since modern intercolonyvariability in mean coral1δ18O is large, and equivalentto ∼ 1.6 psu (2σ ) using theδ18Osw-salinity relationship ofWatanabe et al. (2001) for modern Caribbean surface waters,quantification of mean1δ18O in terms of SSS for past timeintervals is not further considered.

4.3 Seasonal changes in coral1δ18O

4.3.1 Insights from raw data

The seasonality is defined as the difference between maxi-mum and minimum monthly values of a given year that isthen averaged for all years constituting the record. The coral



0 1 2 3 4 5 6

Age ka BP

0.4

0.2

0.0

-0.2

-0.4

An

nu

alm

ean

Dd1

8O

(‰)

0.0

0.1

0.2

0.3

0.4

Tit

an

ium

(%)

Coral Dd18O

Less saline

More saline

Wet

Dry

Ti content (%), Haug et al., (2001)

Co

ral

Fig. 3. Comparison between mean coral1δ18O and Cariaco Basin Ti record (Haug et al., 2001). Coral1δ18O has been calculated forindividual records using established procedures (Cahyarini et al., 2008; Correge, 2006; Gagan et al., 1998). Error bars are the combinederror (root of the sum of the squares) of the standard deviation (2σ ) from mean coral1δ18O of three modernDiploria strigosaand thestandard error (2 SE) of the mean coral1δ18O value for individual corals, following established procedure (Abram et al., 2009) but appliedto reconstructed coral1δ18O. Note that coral1δ18O records indicate a trend toward more saline conditions during the mid- to late Holocenethat might be linked to more precipitation at 6 ka.

δ18O records of three modern corals indicate a meanδ18Oseasonality of 0.440± 0.047 ‰ (1σ ) ranging from 0.400 to0.491 ‰ (Fig. 4). It is assumed that the between-colony dif-ferences in coralδ18O seasonality do not result from chang-ing environmental conditions over the last century, but ratherreflect coral growth processes (e.g. Gagan et al., 1998).Therefore, the combined error (Abram et al., 2009) that takesinto account modern between-colony offsets in coralδ18Oseasonality (Giry et al., 2012) is considered for our estimatesof Holocene coralδ18O seasonality. Considering this uncer-tainty, most of the fossil coral records showδ18O seasonal-ity that is not significantly different from that given by threemodern corals. However, significantly increasedδ18O sea-sonality (0.622± 0.098 ‰) is observed in the 6.22 ka coral(Fig. 4).

Composite annual Sr/Ca andδ18O cycles derived frommonthly resolved records of individual corals reveal clearannual cycles for both modern and fossil colonies (Fig. 5a).Therefore, changes in the timing between both proxies are as-sessed for the annual cycle (Fig. 5b). Cross-spectral analysesbetween measured coral proxies reveal that coralδ18O an-nual cycles lead corresponding coral Sr/Ca cycles by about amonth in modern colonies. The phase angle for modern coralrecords indicates very similar values, showing good repro-ducibility among modern colonies. Annual Sr/Ca andδ18Ocycles from fossil corals indicate different patterns in thepast. For instance, most of the fossil corals reveal that coralSr/Ca either leads or is in phase with coralδ18O (Fig. 5b).However, the 6.22 ka coral indicates thatδ18O leads Sr/Cachanges, by 0.3 month (Fig. 5b), all of which provide evi-dence for changes in the seasonality of the hydrological cyclethroughout the mid- to late Holocene.

0

0.2

0.4

0.6

0.8

Co

rald1

8O

se

aso

na

lity

(‰)

Modern6.2

2 k

a

4.2

7 k

a

3.8

3 k

a

3.7

9 k

a

2.3

5 k

a

1.8

4 k

a

1912 A

D

1957 A

D

2009 A

D

Fig. 4. Coral δ18O seasonality calculated for individual Bonairecoral records. Dashed line represents the mean modernδ18O sea-sonality (0.440 ‰) calculated from the mean seasonality of the threemodern corals. Error bars for fossil corals are the combined error(root of the sum of the squares) of the standard deviation (2σ ) frommeanδ18O seasonality of three modernDiploria strigosaand thestandard error (2 SE) of the averagedδ18O seasonality measure-ments for individual coral records, following established procedures(Abram et al., 2009) but applied to reconstructed seasonality. Errorbars for modern corals are 2 SE. Note that the 6.22 ka coral showssignificantly increasedδ18O seasonality compared to that given bythree modern corals.

4.3.2 Insights from calculated coral1δ18O

Composite annual coral1δ18O cycles were calculated forindividual coral records using a range of proxy-SST cali-brations. This is used in order to test the impact of vary-ing calibrations on the reconstructed1δ18O (Fig. S1 in theSupplement). Annual1δ18O cycles calculated using calibra-tions from Hetzinger et al. (2006) are very different in ampli-tude and timing from that given by a set of four other cali-brations, including local calibrations (Giry et al., 2012, this



DJF

MAM

JJA

SON

6.22 ka 4.27 ka 3.83 ka 3.79 ka 2.35 ka 1.84 ka 1912 AD 1957 AD 2009 AD

J MM J S N J MM J S N J MM J S N J MM J S N J MM J S N J MM J S N J MM J S NJ MM J S N J MM J S N

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Co

mp

os

ite

an

nu

al

cy

cle

Pro

xy

-de

riv

ed

SS

T(°

C)

Coral Sr/Ca

Coral d18O

Warm

Cold

Less saline

More saline

Months

a)

Age ka6 5 4 3 2 1 0

-1.0

-0.5

0

0.5

1.0

Ph

as

ea

ng

le(m

on

ths

)

18Coral d O leads

leadsCoral Sr/Ca

b)

Fig. 5. (a)Composite annual cycles of coral Sr/Ca andδ18O for each coral record used in this study converted in degree Celsius by usingSr/Ca-SST andδ18O–SST relationships of−0.061 mmol mol−1 ◦C−1 and−0.180 ‰◦C−1 (Correge, 2006; Gagan et al., 1998). Error barsindicate the standard error of the mean calculated for individual months.(b) Phase angles of the annual cycles estimated by cross-spectralanalyses between monthly coral Sr/Ca and coralδ18O time series. Error bars indicate the 80 % confidence interval.

study). Since the amplitude of the annual1δ18O cycle givenby our local calibrations provide reasonably good estimatesof the real Caribbean annualδ18Osw cycle (Watanabe et al.,2001), we rely on well-established coral proxy-SST calibra-tions (Correge, 2006; Gagan et al., 1998) for the interpreta-tion of our fossil coral records. The combined analytical un-certainties for reconstructing1δ18O using the Sr/Ca-SST re-lationship of−0.061 mmol mol−1 ◦C−1 (Correge, 2006) andthe δ18O–SST relationship of−0.18 ‰◦C−1 (Gagan et al.,1998) is±0.077 ‰ (1σ ). Consequently, coral1δ18O vari-ability with amplitude greater than 0.154 ‰ were consideredsignificant with respect to analytical uncertainty (Cahyariniet al., 2008). Assuming that the above calibrations (Correge,2006; Gagan et al., 1998) are the most representative, thecomposite annualδ18Osw cycles from three modern coralsindicate lower values in spring and summer and higher valuesin fall and winter with average amplitude of 0.157 ‰ (Fig. 6).Since the composite annual cycles are derived from multi-ple years constituting the record, their timing is reliable, al-though the reconstructed amplitude appears insignificant insome records. The reconstructions of coral1δ18O indicatea similar seasonal hydrological regime (e.g. low/high coral1δ18Osw values in summer/winter) at 6.22, 4.27 and 3.79 ka,whereas distinct regimes are observed at 3.83, 2.35 and1.84 ka. The 6.22 ka coral record reveals increased coral1δ18O seasonality with amplitude of 0.193 ‰ that is 23 %greater than the amplitude of the modern annual1δ18O cy-cle given by three modern corals. Moreover, a period ofreversed seasonality of the hydrological cycle is detectedat 2.35 ka BP. This record indicates more positive values in

summer and more negative values in winter. The deviationfrom the mean1δ18O value is investigated for individualmonths in each coral record (Fig. 6). It is found that great-est deviation from the mean occurs in fall and winter in thethree modern corals. Although this pattern is fuzzy in theHolocene corals, the 6.22 ka coral record indicates that thegreatest negative and positive deviation from the mean valueoccurs during both summer and winter seasons, respectively.

4.4 Interannual to multidecadal coral1δ18O variability

The MTM spectral analysis of monthly coral1δ18O recordsindicates significant quasi-biennial and interannual variabil-ity that is often superimposed on inter- to multidecadal scalevariability (Fig. 7). Significant spectral peaks in the quasi-biennial band (defined here as< 2.3 yr) are detected in mostcoral records. Interannual (2.3 to 7 yr), near-decadal (7 to15 yr) as well as inter- to multidecadal (15 to 40 yr) variabil-ity of coral1δ18O are identified in most of the coral records.Instrumental rainfall data (Hulme et al., 1998) reveal thatprecipitation over Bonaire is also characterised by signifi-cant quasi-biennial and interannual spectral peaks (Fig. 7),whereas inter- to multidecadal variability of Bonaire pre-cipitation is not significant over the period 1930–1999. Fur-thermore, while interannual variability seems to be a promi-nent feature of the coral1δ18O records, the coral record at2.35 ka indicates enhanced spectral power at interannual pe-riodicities centred at 6.1 yr and the 6.22 ka coral reveals pro-nounced variability at 7.8 yr. Moreover, inter- to multidecadalvariability seems to be a prominent feature in the Holocene



0.15

0.10

0.05

0.00

-0.05

-0.10

-0.15

Co

mp

os

ite

an

nu

al

cy

cle

Dd1

8O

(‰)

J A JO J A J A JO J A J A JO J A J A JO J A J A JO J A

Months

J A J O J A

±0.077‰ (1s)

18Dd O auncertainty

nalytical

J A JO J A

0.15

0.10

0.05

0.00

-0.05

-0.10

-0.15

Co

mp

os

ite

an

nu

al

cy

cle

Dd1

8O

(‰)

J A J O J A J A JO J A

Months

0.1

62‰

0.1

62‰

DJF

MAM

JJASON

0.1

47‰

1912 AD 1957 AD 2009 AD

6.22 ka 4.27 ka 3.83 ka 3.79 ka 2.35 ka 1.84 ka

0.1

93‰

Fig. 6.Composite annual coral1δ18O cycles for three modern (top panel) and six fossil (bottom panel) corals calculated using the centeringmethod (Cahyarini et al., 2008) and Sr/Ca-SST andδ18O–SST relationships of−0.061 mmol mol−1 ◦C−1 and−0.180 ‰◦C−1 (Correge,2006; Gagan et al., 1998). Combined analytical uncertainty is 0.154 ‰ (2σ ). Composite annual cycles represented in black (gray) arecharacterised by an amplitude of the annual1δ18O cycle higher (lower) than 2σ . Vertical gray shading indicates seasons: winter (December–February, DJF), spring (March–May, MAM), summer (June–August, JJA) and fall (September–November, SON). Negative and positivedeviations from the mean value greater than 0.4 ‰ are indicated by blue and red colours, respectively.

coral1δ18O records. These periodicities are, however, at thelimit of detection with respect to the length of the consid-ered time series, where oscillatory behaviour becomes indis-tinguishable from a secular trend. Nevertheless, the 6.22 kacoral record indicates enhanced spectral power in this bandthat is unprecedented in any other coral records.

The magnitude of1δ18O changes throughout the mid- tolate Holocene is further investigated for different timescales.Individual coral 1δ18O records have been filtered with aGaussian bandpass filter (Paillard et al., 1996) to isolatequasi-biennial (< 2.3 yr), interannual (2.3 to 7 yr), near-decadal (7 to 15 yr) and inter- to multidecadal (15 to 40 yr)components of variability (Fig. 8). The amplitude of thequasi-biennial, interannual, and near-decadal coral1δ18Ovariability has not notably changed throughout the mid- tolate Holocene compared to that of the inter- to multidecadalband. Interestingly, the standard deviation of the 15 to 40 yrbandpass-filtered time series of the 6.22 ka coral1δ18Orecord is twice as large as the average variance given by allcoral records (Fig. 8).

4.5 Correlation between coral1δ18O and Sr/Ca-SST

The correlation between Sr/Ca-derived SST and1δ18O-related salinity is investigated for quasi-biennial, interannual,

near-decadal, and inter- to multidecadal timescales (Fig. 9)by using the corresponding filtered time series. Coral dataindicate that warmer than average SSTs are characterised bymore saline conditions and vice versa. The correlation co-efficient is positive for all investigated timescales. The cor-relation coefficients between filtered time series are greaterthan 0.5 in most of the records, suggesting that the observedrelationship between SST and1δ18O was prominent in thesouthern Caribbean Sea over the last 6.2 ka. To investigatethe effect of different calibration values on the sign of the cor-relation,1δ18O records derived from a range of proxy-SSTcalibrations (i.e. Hetzinger et al., 2006) were used. However,different calibration values do not affect the sign of the corre-lation between Sr/Ca-derived SST and1δ18O-related salin-ity (not shown).

5 Discussion

5.1 Meanδ18Osw changes over the last 6.2 ka

During the early and mid-Holocene, mid-latitudes of thenorthern Hemisphere were characterized by greater insola-tion in summer compared to today, and proxy reconstruc-tions showed that the ITCZ was located further to the northat that time, thus enhancing precipitation in more northern



1.9

7.8

1.8

12*

3.9 1.9

34* 6.12.5

1.9

a) b)

1.0

0.5

0.0

-0.5

-1.0

Co

ralDd

18O

(‰)

1.0

0.5

0.0

-0.5

-1.0

Co

ralDd1

8O

(‰)

1.0

0.5

0.0

-0.5

-1.0

Co

ralDd1

8O

(‰)

1.0

0.5

0.0

-0.5

-1.0

Co

ralDd1

8O

(‰)

1912 ± 8 AD

1.0

0.5

0.0

-0.5

-1.0

Co

ralDd1

8O

(‰)

1.0

0.5

0.0

-0.5

-1.0

Co

ralDd1

8O

(‰)

1957 ± 5 AD 2009 AD

2347 ± 49 a BP

3793 ± 29 a BP

3831 ± 34 a BP

4268 ± 25 a BP

6218 ± 46 a BP

0.1

1

10

100

Re

lati

ve

va

ria

nc

e

0.1

1

10

100

Re

lati

ve

va

ria

nc

e

0.1

1

10

100

Re

lati

ve

va

ria

nc

e

0.1

1

10

100

Re

lati

ve

va

ria

nc

e

0 0.2 0.4 0.6

Frequency (cycles yr-1)

0.1

1

10

100

Re

lati

ve

va

ria

nc

e

3.83 ka BP

6.22 ka BP

4.27 ka BP

3.79 ka BP

2.35 ka BP

99 %95 %90 %

99 %95 %90 %

99 %95 %90 %

99 %95 %90 %

10 yearsGrowth direction

99 %95 %90 %

1.5

1.5

19*

2.8

16*

1.52.8

34*

1930 1940 1950 1960 1970 1980 1990 2000

Years AD

0

100

200

300

400P

rec

ipit

ati

on

(mm

/mo

nth

)Bonaire rainfall

0.1

1

10

100

Re

lati

ve

va

ria

nc

e

UEA CRU 1930-1999

99 %95 %90 %

1.53.6

5.3

1837 ± 18 a BP

0 0.2 0.4 0.6

Frequency (cycles yr-1)

Fig. 7. (a) Monthly rainfall record from gridbox centred on Bonaire (12.5◦ N; 67.5◦ W) (top panel) (Hulme et al., 1998) and monthlyreconstructed coral1δ18O records from Bonaire corals calculated using the centering method (Cahyarini et al., 2008). Thick blue linesrepresent the 5-yr running average. Sr/Ca-SST andδ18O–SST regression coefficients used are−0.061 and−0.180 mmol mol−1 ◦C−1,respectively. U-series ages of fossil corals (Giry et al., 2012) are indicated.(b) Multitaper method (MTM) spectral analysis (significancerelative to a red noise null hypothesis determined with the robust method of noise background estimation; Ghil et al., 2002; Mann and Lees,1996; number of tapers 3; bandwidth parameter 2) of detrended and normalised monthly precipitation and coral1δ18O records with length> 20 yr where the mean annual cycle has been removed. Ninety (90), 95, and 99 % confidence levels are indicated. Significant spectral peaksare labelled. Asterisks indicate periodicities at the limit of detection with respect to the length of the time series, where oscillatory behaviourbecomes indistinguishable from a secular trend.



0.00

0.05

0.10

0.15

ST

D(‰

Dd

18O

)

0.00

0.05

0.10

0.15

ST

D(‰

Dd1

8O

)

0.00

0.05

0.10

0.15

ST

D(‰

Dd1

8O

)

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

Dd1

8O

(‰)

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

Dd1

8O

(‰)

Near-decadal(7- to 15-year)

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3Interannual(2.3- to 7-year)

Quasi-biennial(<2.3-year)

6.22 ka 4.27 ka 3.83 ka 3.79 ka 2.35 ka

Multidecadal(15- to 40-yr)

Near-decadal(7- to 15-yr)

Interannual(2.3- to 7-yr)

Quasi-biennial(<2.3-yr)

6.2

2 k

a

4.2

7 k

a

3.8

3 k

a

3.7

9 k

a

2.3

5 k

a

6.2

2 k

a

4.2

7 k

a

3.8

3 k

a

3.7

9 k

a

2.3

5 k

a

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

Dd1

8O

(‰)

Multidecadal(15- to 40-year)

10 years

0.00

0.05

0.10

0.15

ST

D(‰

Dd1

8O

)

Dd1

8O

(‰)

Fig. 8.Quasi-biennial, interannual, near-decadal and multidecadal Gaussian bandpass-filtered time series for individual coral1δ18O records(from Fig. 7) with length> 20 yr (left panel) and the corresponding standard deviations of filtered time series (right panels). Horizontaldashed lines and grey areas indicate the mean standard deviations (STD) of the filtered time series and the corresponding 2σ , respectively.Black arrows indicate that the variance of the multidecadal bandpass-filtered time series of the 6.2 ka coral1δ18O record is twice as large asgiven by the corresponding mean standard deviation of all coral records.

-1.0

-0.5

0.0

0.5

1.0

Sr/

Ca

-SS

Ta

no

maly

(°C

)

-0.2 -0.1 0.0 0.1 0.2

Dd18O anomaly (‰)

-1.0

-0.5

0.0

0.5

1.0

Sr/

Ca

-SS

Ta

no

maly

(°C

)

-0.2 -0.1 0.0 0.1 0.2

Dd18O anomaly (‰)

Multidecadal(15- to 40-year)

Near-decadal(7- to 15-year)

Interannual(2.3- to 7-year)

Quasi-biennial(<2.3-year)

SS

T +

Salinity +

Fig. 9.Linear regressions between Gaussian bandpass-filtered coral1δ18O and Sr/Ca-SST time series for Bonaire coral records withlength > 20 yr as calculated after Correge (2006) and Gagan etal. (1998). Note that for all investigated timescales, most coralrecords indicate positive correlation coefficients which suggest thatperiods of warmer than average sea surface temperatures (SST) arecharacterised by more saline conditions and vice versa.

latitudes of the tropical Atlantic (Fleitmann et al., 2003;Haug et al., 2001; Hodell et al., 1991). In line with this,our coral1δ18O records indicate a trend from the mid- to-ward the late Holocene (Fig. 3), suggesting that the hydro-logical balance of the Southern Caribbean shifted from lesssaline in the mid-Holocene towards more saline conditionstoday. However, this trend is not significant, possibly due tothe combined effect of different vital effects between coralcolonies (Giry et al., 2012) and rapid shifts of the regionalhydrological conditions (Haug et al., 2001). Although accu-rate quantification of changes in meanδ18Osw is difficult toinfer from our coral records, the increase ofδ18Osw over thelast 6.2 ka did not exceed 0.322 ‰ (2σ given by three mod-ern corals) which would correspond to a salinity increase of< 1.6 psu according to Watanabe et al. (2001). In line withthis, numerical simulations integrating an isotopic module(Oppo et al., 2007) indicated lighter Caribbeanδ18Osw dur-ing the mid-Holocene that is linked to a reduced Atlantic toPacific water transport.

5.2 Today’s hydrological cycle and advection of freshwater

The composite annual1δ18O cycles derived from moderncorals revealed lower values in spring and summer and highervalues in fall and winter (Figs. 6 and 10). Climatologicaldata from the World Ocean Atlas 09 (Antonov et al., 2010)indicate SSS seasonality near Bonaire of∼ 1.2 psu withmaximum and minimum SSS values occurring in May and



J F M A M J J A S O N D

M th

36.4

36.0

35.6

35.2

34.8

SS

S(p

su

)

0

20

40

60

80

100

Ra

infa

ll(m

m/m

on

th)

25.5

26.0

26.5

27.0

27.5

28.0

28.5

SS

T(°

C)

SODA, SSSWOA09, SSS

ERSST, SSTRainfall

Warm

Cold

Wet

Dry

a)

b)

J F M A M J J A S O N D

0.15

0.10

0.05

0.00

-0.05

-0.10

Co

mp

os

ite

an

nu

alc

yc

leC

ora

lDd1

8O

(‰)

on s

ModelLarsen (1992)

Schott et al., (1988)

Molinari et al., (1990)

35

30

25

Tra

ns

po

rt (

Sv

)

18Modern Coral Dd O

Months

Strong

Weak

18d Osw

More negative

More positive

Caribbeanwater transport

c)

d)

LEGOS, SSS

Fig. 10. Left panel: monthly mean climatology of environmental parameters at the study site, Bonaire.(a) Composite annual sea surfacesalinity (SSS) cycles from World Ocean Atlas 09 (Antonov et al., 2010) in a 1◦

× 1◦ gridbox (blue), from CARTON-GIESE SODA v2p0p2-4 (Carton and Giese, 2008) in a 0.5◦

× 0.5◦ gridbox (black) and from Sea Surface Salinity Observation Service (Reverdin et al., 2007) ina 1°x1°gridbox (orange);(b) sea surface temperature (SST) monthly climatology for 1970–2000 from ERSSTv3b (Smith et al., 2008) ina 2◦ × 2◦ gridbox (red line) and climatology of monthly mean precipitation for the same period from UEA CRU Hulme Global prcp in agridbox centred at 67.5 and 12.5◦ (Hulme et al., 1998) (vertical bars). Right panels:(c) composite annual coral1δ18O cycle of three moderncorals, 1912 AD (dashed line), 1957 AD (dotted line) and 2009 AD (solid line) calculated as previously described (cf. Fig. 6);(d) modelled(black dashed line) and observed annual cycle of the Florida Current (modified from Johns et al., 2002).

September, respectively. However, according to SODA salin-ity (Simple Ocean Data Assimilation Reanalysis) (Cartonand Giese, 2008), the seasonal cycle for Bonaire is∼ 0.6 psuin amplitude with maximum and minimum SSS values oc-curring in April and November, respectively (Fig. 10). More-over, together with a lack of local salinity data, these datasetsand others (Reverdin et al., 2007) indicate that there is noconsensus on the real amplitude and timing of the annualsalinity cycle around Bonaire. Since Bonaire’s climate ischaracterized by high evaporation rate and low annual rain-fall with the rainy season lagging maximum SST by a month,local rainfall cannot explain the phase lag between coralδ18Oand Sr/Ca as inferred from the modern corals (Fig. 6). Con-sequently, alternate mechanisms are proposed for explainingthe modern freshwater budget of the region as documentedin Bonaire corals.

The freshwater budget in the Caribbean is influenced byboth the evaporation and precipitation over the basin (Etteret al., 1987) and freshwater transported from the Amazonand Orinoco rivers by surface currents to the Caribbean(Hellweger and Gordon, 2002). The period of strongest evap-oration occurs in wintertime (Etter et al., 1987; Giannini etal., 2000; Hastenrath and Lamb, 1978) and the lowest insummertime. Therefore, the annual1δ18O cycle inferredfrom modern corals could be partially explained by sea-sonal changes in the local freshwater flux over the Caribbean.The Caribbean Current (CC) is the dominant surface currentin the Caribbean, transporting warm and fresh surface wa-ter northwestward from the southeastern part of the basinto the Gulf of Mexico (Wust, 1964) (Fig. 1). The outflow

of this warm water mass concentrates in the Florida Strait,contributing to the Gulf Stream and the Western BoundaryCurrent. The highest surface velocity of the CC (exceed-ing 100 cm s−1) occurs near the southern boundary along thecoast of Venezuela and the Netherlands Antilles (Fratantoni,2001; Hernandez et al., 2000) suggesting that Bonaire ishighly sensitive to changes in surface water transport bythe CC. Water masses transported through the Caribbeanoriginate from the North Brazilian Current (NBC) and theGuyana Current (GC), which transport South Atlantic wa-ters and fresh, isotopically light waters discharged from theAmazon River into the Caribbean (Cherubin and Richard-son, 2007; LeGrande and Schmidt, 2006; Hellweger andGordon, 2002) (Fig. 1). The flow through the Caribbean dis-plays a seasonal cycle that is strongest in the far southeasternCaribbean through the Windward Islands passages (Johns etal., 2002). Moreover, this inflow is intimately linked to theoutflow through the Florida Current (Johns et al., 2002). TheFlorida Current indicates strong seasonality in surface wa-ter transport through the Florida Strait (Johns et al., 2002;Larsen, 1992; Molinari et al., 1990; Schott et al., 1988)(Fig. 10). The outflow from the Caribbean shows maximumtransport in spring and summer and minimum in fall. Fromspring to summer, maximum transport appears to result froma strengthened NBC and GC primarily driven by changesin seasonal winds (Johns et al., 2002; Muller-Karger et al.,1989). The reduction of Atlantic inflow into the Caribbean inthe second half of the year is thought to be linked to a weak-ened NBC and GC that redirect fresher tropical Atlantic wa-ter eastward at this time (Johns et al., 2002). Consequently,



the annual1δ18O cycle of our modern Bonaire corals canalso reflect the annual cycle of fresher and isotopically lightwater transported by the western boundary flow into theCaribbean.

5.3 Mid-Holocene: enhanced precipitation in summer

The mid-Holocene coral indicates significantly increasedseasonality of the hydrological cycle at 6.2 ka as inferredfrom both the measured coralδ18O (Figs. 4 and 5) and the re-constructed coral1δ18O records (Fig. 6). The composite an-nual1δ18O cycle of the mid-Holocene coral indicates lowestand highest values in August and January, respectively. Thelarge uncertainties for estimating mean1δ18O conditions(cf. Sect. 4.2) along with differences in the offset betweenmean coral Sr/Ca andδ18O among individual colonies donot allow us to conclude whether this increased seasonalityis due to enhanced precipitation in summer and/or increasedevaporation in winter. Nevertheless, the magnitude and tim-ing of this annual1δ18O cycle are further investigated. Pe-riods of the year characterised by deviation from the meangreater than 0.4 ‰ (standard choice) are displayed in Fig. 6.The annual1δ18O cycle documented in the mid-Holocenecoral indicates that significant deviations occur during bothsummer and winter seasons. However, the negative deviationfrom the mean during summer months is unprecedented inthis record. The sharp transition from more positive to morenegative values seems to occur within less than two months.This sharp summer peak occurring in June–July is typical fora transition from more to less saline conditions that could belinked to enhanced convective activity at that time.

Our sub-seasonally resolved 6.22 ka coral record indicatesthat the large deviation towards more negativeδ18Osw val-ues documented in summer provides strong support for in-tense summer precipitation in the southern Caribbean Sea,which is possibly brought by a more northern position of theITCZ. This interpretation is consistent with other reconstruc-tions of hydrological conditions in the Caribbean region thatshowed that the ITCZ was located further to the north duringthe mid-Holocene (Haug et al., 2001; Hodell et al., 1991).In line with this, our simulations using the coupled generalcirculation model COSMOS (Wei et al., 2012) indicate morehumid conditions in the Caribbean during the mid-Holocenedue to more precipitation (Fig. 11b, blue colour). The an-nual hydrological cycle inferred from the model simulationsuggests that more summer precipitation contributed to theincreased annual hydrological cycle over the Caribbean at6 ka BP (Fig. 11a).

The regional SSS in the Caribbean is affected by both theocean currents and localP − E. The ocean currents trans-port relatively fresh water from southward locations whichare under the influence of the Amazon and Orinoco rivers. Inthe area off the coast of northern South America, the modelis not suitable to resolve all regional details. However, wecan detect two main features. Along the coast where the

a)

b)

Fig. 11. Precipitation minus Evaporation (P − E) anomaly(mm day−1) at 6 ka BP inferred from numerical simulations withthe coupled general circulation model COSMOS.(a) Normalisedannual cycle ofP − E (mm day−1) for Pre-Industrial (PI) times(black), 6 ka (red) and their difference (blue dotted) averaged overthe area of 65–83◦ W, 10–20◦ N. (b) Annual meanP − E for PI(contour) and for 6 ka anomalies relative to PI (shaded).

freshwater from Columbian and Venezuelan rivers (includ-ing the Orinoco) enters the sea (Fig. 12), SSS is reduced for6 ka, whereas offshore SSS is increased, mainly for the borealspring season (not shown). The model simulation indicatesthat easterlies get weakened at 6 ka by about 10 %, resultingin slower ocean currents and less import of freshwater fromthe south, especially from the Amazon, into the Caribbean.Consequently, the Caribbean offshore waters were more un-der the influence of surface water masses from subtropicalregions with negativeP − E.

In summary, the model simulations indicate that increasedprecipitation during summer is the prevailing factor control-ling the increased seasonality of the hydrological cycle inthe southern Caribbean during the mid-Holocene (Fig. 11)as reconstructed from our monthly resolved coralδ18Oswrecords (Fig. 6). Moreover, the decrease in meanδ18Oswreconstructed from those records for the mid Holocene is



Fig. 12. Annual mean sea surface salinity anomaly (psu) at 6 karelative to pre-industrial, inferred from numerical simulations fromthe coupled general circulation model COSMOS.

consistent with the increased mean precipitation at that timeas inferred from the model simulation (Figs. 3 and 11).

5.4 Mid- to late Holocene transition

The 6.22 ka coral suggests a dominant effect through en-hanced summer rainfall relative to advection of freshwater,whereas the three modern corals indicate lessP − E, rela-tive to the advection of freshwater as the prevailing factorcontrolling the annual cycle of sea surface hydrology. Thesedifferences suggest a transition since the mid-Holocene. The4.27 and 3.79 ka corals show highδ18O seasonality, havingno phase lag with the corresponding Sr/Ca record and sug-gesting that more negative (positive)δ18O values occurredin phase with warmer (colder) SST. This suggests wet sum-mers and/or dry winters. As for the 6.22 ka coral, “sharp”δ18Osw summer peaks towards more negative values are ob-served in the composite annual cycle, suggesting that wetsummers were potentially characteristic during these timeintervals. However, this “sharp” peak is less pronounced inmore recent and especially in the modern coral records, sug-gesting that either loss of summer precipitation or reducedadvection of fresher water through the Caribbean Current insummer occurred throughout the mid- to late Holocene, thusdamping this “sharp” summer peak in the more recent coralrecords (Fig. 6). Moreover, the 3.83 and 1.84 ka records indi-cate that the annual cycle of coral Sr/Ca leads the correspond-ing annual cycle ofδ18O by about half a month, suggestingthat less (more) saline conditions occurred after maximum(minimum) SST values. One can infer from the measuredcoral Sr/Ca andδ18O data that changes in the timing be-tween annual SST andδ18Osw cycles occurred in the south-ern Caribbean Sea throughout the mid- to late Holocene. Thisgives rise to the possible competing influence of both the hy-drological cycle and oceanic advection of freshwater on theannual hydrology.

An exceptionally large increased SST seasonality com-pared to both today and the mid-Holocene is indicated bythe 2.35 ka coral Sr/Ca record (Giry et al., 2010b, 2012).This is accompanied by a dampening of coralδ18O sea-sonality, resulting in a reversal of the reconstructedδ18Oswannual cycle, with more negative (positive)δ18Osw valuesin winter (summer). Considering local rainfall as the maindriver of seasonalδ18Osw variations, enhanced precipita-tion/reduced evaporation during winter and/or reduced pre-cipitation/enhanced evaporation during summer/fall relativeto today could explain the annual1δ18O cycle at 2.35 ka.However, reduced advection of freshwater during the warmseason and/or enhanced advection during the cold seasoncould be an alternate mechanism. With respect to the latter,surface winds would modulate both temperature (i.e. wind-induced heat loss) and hydrological conditions (i.e. wind-induced oceanic advection of freshwater from the south) atthe sea surface. In this sense, weakened (strengthened) sur-face winds in summer (winter) could generate positive (neg-ative) SST anomalies and reduced (intensified) transport offresher water to the study site, thus explaining the increasedSST seasonality and reversal of the annual hydrological cycleat 2.35 ka.

To summarise, summer precipitation dominated the an-nual hydrological cycle in the mid-Holocene. In contrast, en-hanced evaporation in winter and oceanic advection of fresh-water discharged from the Orinoco and the Amazon Riversby wind-driven surface currents dominate the annualδ18Oswcycle at Bonaire today. This is consistent with the strength-ening of easterly trade-winds associated with the southwardmigration of the ITCZ throughout the Holocene.

5.5 Control of surface winds on surface temperatureand hydrology

From December through May, the Ekman transport inducedby easterly trade winds causes upwelling at Cariaco Basin(Taylor et al., 2012). The source of the upwelled water isthe more saline and colder Subtropical Underwater (Wust,1964). Consequently, if upwelling were the prevailing fac-tor influencing sea surface hydrology at Bonaire, one wouldexpect colder conditions to be accompanied by more salineconditions. However, as presented in Sect. 4.5 (cf. Fig. 9),the coral data show the opposite pattern (colder-less saline)throughout the mid- to late Holocene. Furthermore, the Cari-aco upwelling occurs more than 300 km to the south eastof Bonaire and the nutrient rich waters must be transportedlong enough to directly influence sea surface hydrology atBonaire. Although there is evidence for short-lived upwellingevents (filaments) that would bring cold and salty water toBonaire at timescales of a day up to a week (cf. Andrade andBarton, 2005), these synoptic events are not long enough tobe recorded in our monthly resolved coral records. Moreover,there is evidence for an eastward flow between Bonaire andthe northern coast of Venezuela (cf. Fig. 5a from Andrade



et al., 2003), whereas the typical westward flow of theCaribbean Current occurs north of the island. Consequently,while there might be a synoptic influence of the upwellingfilaments at Bonaire, the dominant oceanographic features atthis open-ocean location disable upwelled waters from Cari-aco to be transported directly to Bonaire.

The coral Sr/Ca-SST and1δ18O records reveal thatwarmer (colder) than average SST around Bonaire werecharacterised by more (less) saline conditions through-out the mid- to late Holocene (Fig. 2). This is true forquasi-biennial, interannual, near-decadal and multidecadaltimescales (Fig. 9). On quasi-biennial timescales, the oscil-lation of zonal winds in the tropical troposphere is associ-ated with sea level pressure anomalies and hurricane activ-ity in the Atlantic (Gray, 1984). On interannual timescales,ENSO is known to be a major player in controlling bothtropical Atlantic SST and precipitation (Alexander and Scott,2002; Chiang et al., 2002; Giannini et al., 2000). El Nino re-sults in an anomalously warm tropical North Atlantic, mainlythrough a warming of the tropical troposphere (Chiang etal., 2002). In addition, warming of the troposphere reducesconvection and thus precipitation over the tropical Atlantic.Moreover, intense convection in the tropical Pacific associ-ated with El Nino leads to suppression of rainfall over north-ern South America and the Amazon Basin (Garreaud et al.,2009). Although there are arguments that ENSO activity wasreduced in the mid-Holocene (Clement et al., 1999; Tudhopeet al., 2001), we find that the 6.22 ka coral record shows asimilar relationship between reconstructed salinity and SSTat interannual timescales. On multidecadal timescales, theAMO is known to play a critical role in controlling trop-ical Atlantic SST and precipitation anomalies (Sutton andHodson, 2005). During the AMO warm phase, the tropicalAtlantic and Caribbean experience positive SST and positivesummer precipitation anomalies, whereas summer precipi-tation over northern South America and the Amazon Basinshows an inverse relationship with the AMO (Sutton andHodson, 2005).

Given the positive correlation between SST and salinityas documented in Bonaire coral records for a wide range oftimescales, it is hypothesised that a single physical mecha-nism controlled this correlation over the last 6.2 ka. We pro-pose that changes in the strength of zonal surface winds mod-ulate both SST and the advection of tropical Atlantic fresh-water into the southern Caribbean Sea (Fig. 13). In a previ-ous study (Giry et al., 2012), we reported quasi-biennial tomultidecadal variability of southern Caribbean SST as doc-umented in our Bonaire coral Sr/Ca records. Since SST andsurface winds are strongly correlated around Bonaire (Fig. 9from Wang, 2007), we assume that interannual to multi-decadal changes of surface winds drive southern CaribbeanSST variations on these timescales. Moreover, as the modernCaribbean throughflow shows strong wind-driven variations(e.g. Johns et al., 2002), we suggest that zonal surface windsforce the inflow of fresher tropical water into the Caribbean

Salin

ity (

psu

)

AmazonOrinoco

Guyana Current

More heat loss

Less heat loss Weak wind

Strong wind

70°W 60°W 50°W80°W

37

36

35

34

33

32

Bonaire

Caribbean Current

Guyana CurrentCaribbean Current

Main surfacecirculation

Dominant wind direction

CCGC

Currents

Transect

Amazon

Orino

co

Bon

aire

Longitude

Guyana CurrentCaribbean Current

a)

b)

c)

d)

Fig. 13. (a)Map showing the transect of interest (red line) and thedominant surface currents (Guyana Current, GC; Caribbean Cur-rent, CC).(b) Observed sea surface salinity (SSS) in the upper 60 malong a transect from the western tropical Atlantic to the south-eastern Caribbean Sea. Freshwater discharged by the Amazon andOrinoco rivers contribute to freshening of the western tropical At-lantic that extend northwestward due to transport by Guyana andCaribbean Currents.(c) and(d) Response of sea surface conditionsunder two different surface wind strength scenarios.(c) Weak windscenario: reduced extent of fresh water (contour colour lines) trans-port northwestward due to reduced Guyana/Caribbean current sys-tem, and reduced heat loss and vertical mixing at sea surface that inturn contribute to warmer sea surface temperature (SST).(d) Strongwind scenario: intensification of surface water transport from thewestern tropical Atlantic to the Caribbean by surface current systemand enhanced heat loss and vertical mixing at sea surface which inturn reduce SST, thus contributing to colder and less saline condi-tions around Bonaire.

via Ekman transport through the North Brazilian–Guyana–Caribbean current system. This is further supported by thehigh correlation coefficient found between annual mean SSTand zonal surface wind and current at Bonaire (Fig. S2 in theSupplement). Moreover, this is consistent with a coral-basedstudy from Puerto Rico (Kilbourne et al., 2007) which indi-cated that equatorial water is transported to the Caribbean by



Ekman transport and is related to trade-winds variability. AtBonaire, strengthened easterlies contribute to stronger heatloss that cool down SST, while it forces Ekman transport andoceanic surface circulation that transport fresher tropical At-lantic water into the Caribbean, and thus contribute to colderand fresher conditions on interannual timescales in the south-ern Caribbean.

5.6 Enhanced inter- to multidecadal variability ofsurface hydrology at 6.2 ka

The Bonaire coral1δ18O records indicate pronounced inter-to multidecadal periodicities (Fig. 7) suggesting a prominentfeature of southern Caribbean Sea surface hydrology over thelast 6.2 ka. The 6.22 ka coral1δ18O record shows enhancedvariability at inter- to multidecadal timescales (Figs. 2, 7and 8). Since Caribbean hydrology at 6 ka was influenced byincreased precipitation and more river runoff, theδ18Osw-salinity linear regression known in today’s oceans might notbe valid for the mid-Holocene (Craig and Gordon, 1965;Delaygue et al., 2000; Rohling and Bigg, 1998; Schmidt,1999), thus hindering accurate quantification of past1δ18O-related salinity changes. Nevertheless, the amplitude of thismultidecadal1δ18O signal (∼ 0.3 ‰) is larger than the cor-responding annual cycle, thus providing evidence for en-hanced multidecadal variability of southern Caribbean Seasurface hydrology during the mid-Holocene.

A coral δ18O-based study from the Dominican Republicsuggested interdecadal variability of tropical Atlantic pre-cipitation in the mid-Holocene (Greer and Swart, 2006). Itwas suggested that the latitudinal migration of the ITCZor increased storm activity have modulated interdecadalchanges of northern Caribbean precipitation. In line with this,Knudsen et al. (2011) showed that precipitation over northernSouth America as inferred from the Cariaco Titanium record(Haug et al., 2001) has experienced multidecadal fluctuationslinked to the AMO over the last 8 ka. A recent study showedthat the southern Caribbean Sea experienced inter- to multi-decadal variability of SST during the mid-Holocene Giry etal., 2012). All of which points to the important role of the at-mospheric circulation in the inter- to multidecadal variabilityas documented in Bonaire corals records.

However, other mechanisms could explain the positivecorrelation between SSS and SST and possibly the en-hanced inter- to multidecadal variability in the mid-Holoceneas documented in Bonaire coral records. On multidecadaltimescales, the AMO can be assumed to be partly linkedto the strength of the AMOC (Delworth and Mann, 2000;Knight et al., 2005; Wei and Lohmann, 2012). There is a gen-eral agreement from water hosing experiments that a slow-down of the AMOC cools down most of the North Atlantic(Stouffer et al., 2006). However, similar experiments usinga high-resolution coupled ocean-atmosphere model (Wan etal., 2009) revealed that a weakened AMOC indeed producessurface cooling in the North Atlantic, whereas a narrow strip

of warmer surface water appears along the northern coast ofSouth America. Wan et al. (2009) suggested that a weakeningof the AMOC produces a weakening of the western boundarycurrent, which in turn creates a strong subsurface warmingthat extends to the surface mixed layer (such feature is actu-ally seen also in coarse-resolution models, e.g. in Lohmann,2003 and some of the models mentioned in Stouffer et al.,2006). In addition, there is a general consensus in water hos-ing experiments that the mean position of the ITCZ is shiftedsouthward during a weakened AMOC resulting in negativeprecipitation anomalies over the northern tropical Atlanticand northern South America (e.g. Stouffer et al., 2006; Zhangand Delworth, 2005; Lohmann, 2003; Vellinga and Wood,2002). This is consistent with the modelling results of Wan etal. (2010), indicating that atmospheric responses to reducedAMOC would increase salinity in the Caribbean. Given thatchanges from warm and saline to cold and fresh conditions inthe southern Caribbean Sea were observed during periods ofweakened large-scale ocean circulation (e.g. Younger Dryas)(Ruhlemann et al., 1999; Schmidt et al., 2004), our study in-dicates that on inter- to multidecadal timescales, a scale rele-vant for ocean circulation, changes in AMOC strength couldpartially explain the positive relationship between SST andSSS derived from Bonaire coral records. Moreover, if thiswere proven true, enhanced climate variability observed inthe mid-Holocene Caribbean climate (e.g. Greer and Swart,2006; Giry et al., 2012) would reflect multidecadal variabilitypotentially linked to changes in the strength of the AMOC.Finally, this would suggest that in-phase variations betweenthe ocean and the atmosphere would create strong inter- tomultidecadal climate variability.

6 Conclusions

Seasonality and interannual to multidecadal variability ofsurface hydrology in the southern Caribbean Sea are inves-tigated for time windows of several decades throughout themid- to late Holocene, by using monthly resolved Sr/Ca andδ18O records of Bonaire corals. Derived coral1δ18O is usedas a proxy for the oxygen isotopic composition of the sur-face seawater (δ18Osw). While this study indicates less salinemean conditions during the mid-Holocene compared to to-day, seasonality and interannual to multidecadal variabilityof the sea surface hydrology can be summarised as follows:

1. Consistent with modern southern Caribbean surface-water hydrology, the large positive deviation of the coral1δ18O annual cycle in the late part of the year sup-ports that enhanced evaporation and reduced advectionof fresher surface waters from the Orinoco and Ama-zon rivers in winter are the dominant factors controllingthe annualδ18Osw cycle as inferred from three moderncorals.



2. The 6.22 ka coralδ18O record indicates increased sea-sonality of the annual hydrological cycle during themid-Holocene. This increased seasonality is very likelyinduced by enhanced precipitation in summer as in-ferred from both climate model simulations and the cor-responding annual1δ18O cycle.

3. On interannual to multidecadal timescales, coral Sr/Caand1δ18O reveal that warmer than average conditionsat the sea surface were characterised by more salineconditions and vice versa. Since this systematic rela-tionship is found for very short timescales relevant foratmospheric circulation, we propose that the surfacewind-driven advection of fresher surface waters fromthe Amazon and Orinoco rivers to the Caribbean ex-plains the positive correlation between SST and salin-ity documented in Bonaire coral records. A potentiallink to variations in the strength of the AMOC on thesetimescales is hypothesized.

4. Our mid-Holocene coral1δ18O record provides evi-dence for enhanced inter- to multidecadal variability ofthe sea surface hydrology at that time. Although an ac-curate quantification of the relative salinity changes isdifficult to infer, the record indicates that the amplitudeof the inter- to multidecadal variability exceeds the cor-responding annual cycle at 6.22 ka BP.

This study identified both the freshwater fluxP − E andoceanic advection of fresher surface waters by wind-drivensurface currents as the prevailing factors influencing thefreshwater budget of the southern Caribbean during the mid-to late Holocene. Since the density structure of North At-lantic water can have drastic impacts on ocean circulationpatterns and heat transport from low to high latitudes, we pro-pose further investigating interannual to multidecadal vari-ability of the western tropical Atlantic and riverine dischargefrom South American tropical rivers as a potential feedbackmechanism affecting the strength of the AMOC.

Supplementary material related to this article isavailable online at:http://www.clim-past.net/9/841/2013/cp-9-841-2013-supplement.pdf.

Acknowledgements.We thank the government of the IslandTerritory of Bonaire (former Netherlands Antilles) for researchand fieldwork permission, E. Beukenboom (STINAPA BonaireNational Parks Foundation) for support, J. Patzold for supportwith coral drilling and discussion, M. Segl and her team for stableisotope analysis, and S. Pape for operating and maintaining theICP-OES. This work was funded by Deutsche Forschungsgemein-schaft (DFG) under the Priority Programme INTERDYNAMIK,through grants to T. F. (FE 615/3-1, 3-2; CaribClim).

Edited by: M. Schulz

References

Abram, N. J., Gagan, M. K., Liu, Z., Hantoro, W. S., McCulloch, M.T., and Suwargadi, B. W. : Seasonal Characteristics of the IndianOcean Dipole during the Holocene epoch, Nature, 445, 299–302,2007.

Abram, N. J., McGregor, H. V., Gagan, M. K., Hantoro, W. S., andSuwargadi, B. W.: Oscillations in the southern extent of the Indo-Pacific Warm Pool during the mid-Holocene, Quaternary Sci.Rev., 28, 2794–2803, 2009.

Alexander, M. and Scott, J.: The influence of ENSO on air-sea interaction in the Atlantic, Geophys. Res. Lett., 29, 1701,doi:10.1029/2001gl014347, 2002.

Andrade, C. A. and Barton, E. D.: The Guajira upwellingsystem, Continental Shelf Research, 25, 1003–1022,doi:10.1016/j.csr.2004.12.012, 2005.

Andrade, C. A., Barton, E. D., and Mooers, C. N. K.: Ev-idence for an eastward flow along the Central and SouthAmerican Caribbean Coast, J. Geophys. Res., 108, 3185,doi:10.1029/2002JC001549, 2003.

Antonov, J. I., Locarnini, R. A., Boyer, T. P., Mishonov, A. V., andGarcia, H. E.: World Ocean Atlas 2005, in: Volume 2: Salinity,edited by: Levitus, S., NOAA Atlas NESDIS 62, US GovernmentPrinting Office, Washington, DC, 182 pp., 2006.

Antonov, J. I., Seidov, D., Boyer, T. P., Locarnini, R. A., Mishonov,A. V., Garcia, H. E., Baranova, O. K., Zweng, M. M., and John-son, D. R.: World Ocean Atlas 2009, in: Volume 2: Salinity,edited by: Levitus, S., NOAA Atlas NESDIS 69, US Govern-ment Printing Office, Washington, DC, 184 pp., 2010.

Beck, J. W., Edwards, R. L., Ito, E., Taylor, F. W., Recy, J.,Rougerie, F., Joannot, P., and Henin, C.: Sea-Surface Temper-ature from Coral Skeletal Strontium/Calcium Ratios, Science,257, 644–647, 1992.

Cahyarini, S. Y., Pfeiffer, M., Timm, O., Dullo, W.-C., andSchonberg, D. G.: Reconstructing seawaterδ18O from pairedcoral δ18O and Sr/Ca ratios: Methods, error analysis and prob-lems, with examples from Tahiti (French Polynesia) and Timor(Indonesia), Geochim. Cosmochim. Acta, 72, 2841–2853, 2008.

Carlson, A. E., Oppo, D. W., Came, R. E., LeGrande, A. N.,Keigwin, L. D., and Curry, W. B.: Subtropical Atlantic salin-ity variability and Atlantic meridional circulation during thelast deglaciation, Geology, 36, 991–994,doi:10.1130/g25080a.1,2008.

Carriquiry, J., Risk, M. J., and Schwarcz, H. P.: Stable isotope geo-chemistry of corals from Costa Rica as proxy indicator of the ELNino/southern Oscillation (ENSO), Geochim. Cosmochim. Acta,58, 335–351, 1994.

Carton, J. A. and Giese, B. S.: A Reanalysis of Ocean Climate UsingSimple Ocean Data Assimilation (SODA), Mon. Weather Rev.,136, 2999–3017, 2008.

Cherubin, L. M. and Richardson, P. L.: Caribbean current variabilityand the influence of the Amazon and Orinoco freshwater plumes,Deep-Sea Res. Pt. I, 54, 1451–1473, 2007.

Chiang, J. C. H., Kushnir, Y., and Giannini, A.: Deconstructing At-lantic Intertropical Convergence Zone variability: Influence ofthe local cross-equatorial sea surface temperature gradient andremote forcing from the eastern equatorial Pacific, J. Geophys.Res., 107, 4004,doi:10.1029/2000jd000307, 2002.


http://www.clim-past.net/9/841/2013/cp-9-841-2013-supplement.pdf

http://www.clim-past.net/9/841/2013/cp-9-841-2013-supplement.pdf

http://dx.doi.org/10.1029/2001gl014347

http://dx.doi.org/10.1016/j.csr.2004.12.012

http://dx.doi.org/10.1029/2002JC001549

http://dx.doi.org/10.1130/g25080a.1

http://dx.doi.org/10.1029/2000jd000307


Clement, A. C., Seager, R., and Cane, M. A.: Orbital Controls onthe El Nino/Southern Oscillation and the Tropical Climate, Pale-oceanography, 14, 441–456,doi:10.1029/1999pa900013, 1999.

Correge, T.: Sea surface temperature and salinity reconstructionfrom coral geochemical tracers, Palaeogeogr. Palaeoclimatol.Palaeoecol., 232, 408–428, 2006.

Craig, H. and Gordon, L. I. (Eds.): Deuterium and oxygen 18 vari-ations in the ocean and the marine atmosphere. Stable Isotopesin Oceanographic Studies and Paleotemperatures, Cons. Naz. diRech., Spoleto, Italy, 121 pp., 1965.

Delaygue, G., Jouzel, J., and Dutay, J.-C.: Oxygen 18-salinity re-lationship simulated by an oceanic general circulation model,Earth Planet. Sci. Lett., 178, 113-123, 2000.

Delworth, T. L. and Mann, M. E.: Observed and simulated multi-decadal variability in the Northern Hemisphere, Clim. Dynam.,16, 661–676,doi:10.1007/s003820000075, 2000.

Dima, M. and Lohmann, G.: A Hemispheric Mechanism for theAtlantic Multidecadal Oscillation, J. Climate, 20, 2706–2719,doi:10.1175/jcli4174.1, 2007.

Etter, P. C., Lamb, P. J., and Portis, D. H.: Heat and FreshwaterBudgets of the Caribbean Sea with Revised Estimates for theCentral American Seas, J. Phys. Oceanogr., 17, 1232–1248,doi:10.1175/1520-0485(1987)017<1232:HAFBOT>2.0.CO;2,1987.

Felis, T., Patzold, J., and Loya, Y.: Mean oxygen-isotope signaturesin Poritesspp. corals: inter-colony variability and correction forextension-rate effects, Coral Reefs, 22, 328–336, 2003.

Felis, T., Lohmann, G., Kuhnert, H., Lorenz, S. J., Scholz, D.,Patzold, J., Al-Rousan, S. A., and Al-Moghrabi, S. M.: Increasedseasonality in Middle East temperatures during the last inter-glacial period, Nature, 429, 164–168, 2004.

Felis, T., Suzuki, A., Kuhnert, H., Dima, M., Lohmann, G., andKawahata, H.: Subtropical coral reveals abrupt early-twentieth-century freshening in the western North Pacific Ocean, Geology,37, 527–530, 2009.

Felis, T., Merkel, U., Asami, R., Deschamps, P., Hathorne, E.C., Kolling, M., Bard, E., Cabioch, G., Durand, N., Prange,M., Schulz, M., Cahyarini, S. Y., and Pfeiffer, M.: Pro-nounced interannual variability in tropical South Pacific tem-peratures during Heinrich Stadial 1, Nat. Commun., 3, 965,doi:10.1038/ncomms1973, 2012.

Fleitmann, D., Burns, S. J., Mudelsee, M., Neff, U., Kramers, J.,Mangini, A., and Matter, A.: Holocene Forcing of the IndianMonsoon Recorded in a Stalagmite from Southern Oman, Sci-ence, 300, 1737–1739,doi:10.1126/science.1083130, 2003.

Fratantoni, D. M.: North Atlantic surface circulation during the1990’s observed with satellite-tracked drifters, J. Geophys. Res.,106, 22067–22093,doi:10.1029/2000jc000730, 2001.

Gagan, M. K., Ayliffe, L. K., Hopley, D., Cali, J. A., Mortimer, G.E., Chappell, J., McCulloch, M. T., and Head, M. J.: Temperatureand Surface-Ocean Water Balance of the Mid-Holocene TropicalWestern Pacific, Science, 279, 1014–1018, 1998.

Garreaud, R. D., Vuille, M., Compagnucci, R., and Marengo, J.:Present-day South American climate, Palaeogeogr. Palaeoclima-tol. Palaeoecol., 281, 180–195, 2009.

Ghil, M., Allen, M. R., Dettinger, M. D., Ide, K., Kondrashov, D.,Mann, M. E., Robertson, A. W., Saunders, A., Tian, Y., Varadi, F.,and Yiou, P.: Advanced spectral methods for climatic time series,Rev. Geophys., 40, 1003,doi:10.1029/2000rg000092, 2002.

Giannini, A., Kushnir, Y., and Cane, M. A.: Interannual Variabilityof Caribbean Rainfall, ENSO, and the Atlantic Ocean, J. Climate,13, 297–311, 2000.

Giannini, A., Chiang, J. C. H., Cane, M. A., Kushnir, Y., andSeager, R.: The ENSO Teleconnection to the Tropical AtlanticOcean: Contributions of the Remote and Local SSTs to RainfallVariability in the Tropical Americas, J. Climate, 14, 4530–4544,doi:10.1175/1520-0442(2001)014<4530:TETTTT>2.0.CO;2,2001.

Giry, C., Felis, T., Kolling, M., and Scheffers, S.: Geochemistryand skeletal structure ofDiploria strigosa, implications forcoral-based climate reconstruction, Palaeogeogr. Palaeoclimatol.Palaeoecol., 298, 378–387, 2010a.

Giry, C., Felis, T., Scheffers, S., and Fensterer, C.: Assess-ing the potential of Southern Caribbean corals for reconstruc-tions of Holocene temperature variability, IOP Conference Se-ries: Earth and Environmental Science, 9,doi:10.1088/1755-1315/9/1/012021, 2010b.

Giry, C., Felis, T., Kolling, M., Scholz, D., Wei, W., Lohmann,G., and Scheffers, S.: Mid- to late Holocene changes in trop-ical Atlantic temperature seasonality and interannual to multi-decadal variability documented in southern Caribbean corals,Earth Planet. Sci. Lett., 331–332, 187–200, 2012.

Gordon, A. L.: Circulation of the Caribbean Sea, J. Geophys. Res.,72, 6207–6223,doi:10.1029/JZ072i024p06207, 1967.

Gray, W. M.: Atlantic Seasonal Hurricane Frequency, Part I:El Nino and 30 mb Quasi-Biennial Oscillation Influences,Mon. Weather Rev., 112, 1649–1668,doi:10.1175/1520-0493(1984)112<1649:ASHFPI>2.0.CO;2, 1984.

Greer, L. and Swart, P. K.: Decadal cyclicity of regional mid-Holocene precipitation: Evidence from Dominican coral proxies,Paleoceanography, 21, PA2020,doi:10.1029/2005PA001166,2006.

Hastenrath, S.: Interannual Variability and Annual Cycle: Mecha-nisms of Circulation and Climate in the Tropical Atlantic Sec-tor, Mon. Weather Rev., 112, 1097–1107,doi:10.1175/1520-0493(1984)112<1097:IVAACM>2.0.CO;2, 1984.

Hastenrath, S. and Lamb, P. J.: Heat Budget Atlas of the Tropi-cal Atlantic and Eastern Pacific Oceans, University of WinconsinPress, 104 pp., 1978.

Haug, G. H., Hughen, K. A., Sigman, D. M., Peterson, L. C., andRohl, U.: Southward Migration of the Intertropical ConvergenceZone Through the Holocene, Science, 293, 1304–1308, 2001.

Hellweger, F. L. and Gordon, A. L.: Tracing Amazon River waterinto the Caribbean Sea, J. Mar. Res., 60, 537–549, 2002.

Hendy, E. J., Gagan, M. K., Alibert, C. A., McCulloch, M. T.,Lough, J. M., and Isdale, P. J.: Abrupt Decrease in Tropical Pa-cific Sea Surface Salinity at End of Little Ice Age, Science, 295,1511–1514, 2002.

Hernandez, Guerra, A., and Joyce, T. M.: Water masses and circu-lation in the surface layers of the Caribbean at 66◦ W, Geophys.Res. Lett., 27, 3497–3500,doi:10.1029/1999gl011230, 2000.

Hetzinger, S., Pfeiffer, M., Dullo, W.-C., Ruprecht, E., and Garbe-Schonberg, D.: Sr/Ca andδ18O in a fast-growing Diplo-ria strigosa coral: Evaluation of a new climate archive forthe tropical Atlantic, Geochem. Geophy. Geosy., 7, Q10002,doi:10.1029/2006GC001347, 2006.


http://dx.doi.org/10.1029/1999pa900013

http://dx.doi.org/10.1007/s003820000075

http://dx.doi.org/10.1175/jcli4174.1

http://dx.doi.org/10.1175/1520-0485(1987)017<1232:HAFBOT>2.0.CO;2

http://dx.doi.org/10.1038/ncomms1973

http://dx.doi.org/10.1126/science.1083130

http://dx.doi.org/10.1029/2000jc000730

http://dx.doi.org/10.1029/2000rg000092

http://dx.doi.org/10.1175/1520-0442(2001)014<4530:TETTTT>2.0.CO;2

http://dx.doi.org/10.1088/1755-1315/9/1/012021

http://dx.doi.org/10.1088/1755-1315/9/1/012021

http://dx.doi.org/10.1029/JZ072i024p06207

http://dx.doi.org/10.1175/1520-0493(1984)112<1649:ASHFPI>2.0.CO;2

http://dx.doi.org/10.1175/1520-0493(1984)112<1649:ASHFPI>2.0.CO;2

http://dx.doi.org/10.1029/2005PA001166

http://dx.doi.org/10.1175/1520-0493(1984)112<1097:IVAACM>2.0.CO;2

http://dx.doi.org/10.1175/1520-0493(1984)112<1097:IVAACM>2.0.CO;2

http://dx.doi.org/10.1029/1999gl011230

http://dx.doi.org/10.1029/2006GC001347


Hetzinger, S., Pfeiffer, M., Dullo, W.-C., Garbe-Schonberg, D., andHalfar, J.: Rapid 20th century warming in the Caribbean and im-pact of remote forcing on climate in the northern tropical Atlanticas recorded in a Guadeloupe coral, Palaeogeogr. Palaeoclimatol.Palaeoecol., 296, 111–124, 2010.

Hodell, D. A., Curtis, J. H., Jones, G. A., Higuera-Gundy, A., Bren-ner, M., Binford, M. W., and Dorsey, K. T.: Reconstruction ofCaribbean climate change over the past 10,500 years, Nature,352, 790–793, 1991.

Hulme, M., Osborn, T. J., and Johns, T. C.: Precipitation sen-sitivity to global warming: Comparison of observations withHadCM2 simulations, Geophys. Res. Lett., 25, 3379–3382,doi:10.1029/98gl02562, 1998.

Jaeschke, A., Ruhlemann, C., Arz, H., Heil, G., and Lohmann, G.:Coupling of millennial-scale changes in sea surface temperatureand precipitation off northeastern Brazil with high latitude cli-mate shifts during the last glacial period, Paleoceanography, 22,PA4206,doi:10.1029/2006PA001391, 2007.

Johns, W. E., Townsend, T. L., Fratantoni, D. M., and Wilson, W.D.: On the Atlantic inflow to the Caribbean Sea, Deep-Sea Res.Pt. I, 49, 211–243, 2002.

Kilbourne, K., Quinn, T., Guilderson, T., Webb, R., and Tay-lor, F.: Decadal- to interannual-scale source water variations inthe Caribbean Sea recorded by Puerto Rican coral radiocar-bon, Clim. Dynam., 29, 51–62,doi:10.1007/s00382-007-0224-2,2007.

Knight, J. R., Allan, R. J., Folland, C. K., Vellinga, M., and Mann,M. E.: A signature of persistent natural thermohaline circula-tion cycles in observed climate, Geophys. Res. Lett., 32, L20708,doi:10.1029/2005gl024233, 2005.

Knudsen, M. F., Seidenkrantz, M.-S., Jacobsen, B. H., and Kuijpers,A.: Tracking the Atlantic Multidecadal Oscillation through thelast 8,000 years, Nat. Commun., 2, 178, 2011.

Larsen, J. C.: Transport and Heat Flux of the Florida Current at27 degrees N Derived from Cross-Stream Voltages and ProfilingData: Theory and Observations, Philos. T. Phys. Sci. Eng., 338,169–236, 1992.

Leduc, G., Vidal, L., Tachikawa, K., Rostek, F., Sonzogni, C., Beau-fort, L., and Bard, E.: Moisture transport across Central Americaas a positive feedback on abrupt climatic changes, Nature, 445,908–911, 2007.

LeGrande, A. N. and Schmidt, G. A.: Global gridded data set of theoxygen isotopic composition in seawater, Geophys. Res. Lett.,33, L12604,doi:10.1029/2006gl026011, 2006.

Linsley, B. K., Kaplan, A., Gouriou, Y., Salinger, J., deMeno-cal, P. B., Wellington, G. M., and Howe, S. S.: Track-ing the extent of the South Pacific Convergence Zone sincethe early 1600s, Geochem. Geophy. Geosy., 7, Q05003,doi:05010.01029/02005GC001115., 2006.

Lohmann, G.: Atmospheric and oceanic freshwater transport dur-ing weak Atlantic overturning circulation, Tellus A, 55, 438–449,doi:10.1034/j.1600-0870.2003.00028.x, 2003.

Mann, M. E. and Lees, J. M.: Robust estimation of back-ground noiseand signal detection in climatic time series, ClimateChange, 33, 409–445,doi:10.1007/bf00142586, 1996.

Marsland, S., Haak, H., Jungclaus, J., Latif, M., and Roske, F.: TheMax-Planck-Institute global ocean/sea ice model with orthogo-nal curvilinear coordinates, Ocean Model., 5, 91–127, 2003.

Martis, A., van Oldenborgh, G. J., and Burgers, G.: Predicting rain-fall in the Dutch Caribbean—more than El Nino?, Int. J. Clima-tol., 22, 1219–1234,doi:10.1002/joc.779, 2002.

McCulloch, M. T., Gagan, M. K., Mortimer, G. E., Chivas, A. R.,and Isdale, P. J.: A high-resolution Sr/Ca andδ18O coral recordfrom the Great Barrier Reef, Australia, and the 1982–1983 ElNino, Geochim. Cosmochim. Acta, 58, 2747–2754, 1994.

Molinari, R. L., Johns, E., and Festa, J. F.: The AnnualCycle of Meridional Heat Flux in the Atlantic Ocean at26.5◦ N, J. Phys. Oceanogr., 20, 476–482,doi:10.1175/1520-0485(1990)020<0476:TACOMH>2.0.CO;2, 1990.

Muller-Karger, F. E., McClain, C. R., Fisher, T. R., Esaias, W. E.,and Varela, R.: Pigment distribution in the Caribbean sea: Obser-vations from space, Prog. Oceanogr., 23, 23–64, 1989.

Oppo, D. W., Schmidt, G. A., and LeGrande, A. N.: Seawater iso-tope constraints on tropical hydrology during the Holocene, Geo-phys. Res. Lett., 34, L13701,doi:10.1029/2007gl030017, 2007.

Paillard, D., Labeyrie, L., and Yiou, P.: Macintosh program per-forms time-series analysis, EOS Trans. AGU, 77, 379, 1996.

Raddatz, T., Reick, C., Knorr, W., Kattge, J., Roeckner, E., Schnur,R., Schnitzler, K. G., Wetzel, P., and Jungclaus, J.: Will the trop-ical land biosphere dominate the climate–carbon cycle feedbackduring the twenty-first century?, Clim. Dynam., 29, 565–574,doi:10.1007/s00382-007-0247-8, 2007.

Ren, L., Linsley, B. K., Wellington, G. M., Schrag, D. P., andHoegh-guldberg, O.: Deconvolving theδ18O seawater compo-nent from subseasonal coralδ18O and Sr/Ca at Rarotonga inthe southwestern subtropical Pacific for the period 1726 to 1997,Geochim. Cosmochim. Acta, 67, 1609–1621, 2003.

Reverdin, G., Kestenare, E., Frankignoul, C., and Delcroix, T.:In situ surface salinity in the tropical and subtropical AtlanticOcean, Part I. Large scale variability, Progr. Oceanogr., 73, 311–340, 2007.

Roeckner, E., Bauml, G., Bonaventura, L., Brokopf, R., Esch,M., Giorgetta, M., Hagemann, S., Kirchner, I., Kornblueh, L.,Manzini, E., Rhodin, A., Schlese, U., Schulzweida, U., andTompkins, A.: The Atmospheric General Circulation ModelECHAM5, Part One: Model Description Report No. 349, MaxPlanck Institute for Meteorology, 2003.

Rohling, E. J. and Bigg, G. R.: Paleosalinity andδ18O:A critical assessment, J. Geophys. Res., 103, 1307–1318,doi:10.1029/97jc01047, 1998.

Ruhlemann, C., Mulitza, S., Muller, P. J., Wefer, G., and Zahn, R.:Warming of the tropical Atlantic Ocean and slowdown of ther-mohaline circulation during the last deglaciation, Nature, 402,511–514, 1999.

Schmidt, G. A.: Forward Modeling of Carbonate Proxy Datafrom Planktonic Foraminifera Using Oxygen Isotope Tracersin a Global Ocean Model, Paleoceanography, 14, 482–497,doi:10.1029/1999pa900025, 1999.

Schmidt, M. W. and Spero, H. J.: Meridional shifts in themarine ITCZ and the tropical hydrologic cycle over thelast three glacial cycles, Paleoceanography, 26, PA1206,doi:10.1029/2010pa001976, 2011.

Schmidt, M. W., Spero, H. J., and Lea, D. W.: Links between salin-ity variation in the Caribbean and North Atlantic thermohalinecirculation, Nature, 428, 160–163, 2004.


http://dx.doi.org/10.1029/98gl02562

http://dx.doi.org/10.1029/2006PA001391

http://dx.doi.org/10.1007/s00382-007-0224-2

http://dx.doi.org/10.1029/2005gl024233

http://dx.doi.org/10.1029/2006gl026011

http://dx.doi.org/10.1034/j.1600-0870.2003.00028.x

http://dx.doi.org/10.1007/bf00142586

http://dx.doi.org/10.1002/joc.779

http://dx.doi.org/10.1175/1520-0485(1990)020<0476:TACOMH>2.0.CO;2

http://dx.doi.org/10.1175/1520-0485(1990)020<0476:TACOMH>2.0.CO;2

http://dx.doi.org/10.1029/2007gl030017

http://dx.doi.org/10.1007/s00382-007-0247-8

http://dx.doi.org/10.1029/97jc01047

http://dx.doi.org/10.1029/1999pa900025

http://dx.doi.org/10.1029/2010pa001976


Schott, F. A., Lee, T. N., and Zantopp, R.: Variability of Structureand Transport of the Florida Current in the Period Rangeof Days to Seasonal, J. Phys. Oceanogr., 18, 1209–1230,doi:10.1175/1520-0485(1988)018<1209:VOSATO>2.0.CO;2,1988.

Sepulcre, S., Vidal, L., Tachikawa, K., Rostek, F., and Bard, E.:Sea-surface salinity variations in the northern Caribbean Seaacross the Mid-Pleistocene Transition, Clim. Past, 7, 75–90,doi:10.5194/cp-7-75-2011, 2011.

Smith, S. V., Buddemeier, R. W., Redalje, R. C., and Houck, J. E.:Strontium-Calcium Thermometry in Coral Skeletons, Science,204, 404–407,doi:10.1126/science.204.4391.404, 1979.

Smith, T. M., Reynolds, R. W., Peterson, T. C., and Lawrimore, J.:Improvements to NOAA’s Historical Merged Land-Ocean Sur-face Temperature Analysis (1880–2006), J. Climate, 21, 2283–2296, 2008.

Stouffer, R. J., Yin, J., Gregory, J. M., Dixon, K. W., Spelman, M.J., Hurlin, W., Weaver, A. J., Eby, M., Flato, G. M., Hasumi, H.,Hu, A., Jungclaus, J. H., Kamenkovich, I. V., Levermann, A.,Montoya, M., Murakami, S., Nawrath, S., Oka, A., Peltier, W.R., Robitaille, D. Y., Sokolov, A., Vettoretti, G., and Weber, S.L.: Investigating the Causes of the Response of the ThermohalineCirculation to Past and Future Climate Changes, J. Climate, 19,1365–1387,doi:10.1175/JCLI3689.1, 2006.

Sutton, R. T. and Hodson, D. L. R.: Atlantic Ocean Forcing of NorthAmerican and European Summer Climate, Science, 309, 115–118,doi:10.1126/science.1109496, 2005.

Taylor, G. T., Muller-Karger, F. E., Thunell, R. C., Scranton, M. I.,Astor, Y., Varela, R., Ghinaglia, L. T., Lorenzoni, L., Fanning,K. A., Hameed, S., and Doherty, O.: Ecosystem responses in thesouthern Caribbean Sea to global climate change, P. Natl. Acad.Sci., 109, 19315–19320,doi:10.1073/pnas.1207514109, 2012.

Tudhope, A. W., Chilcott, C. P., McCulloch, M. T., Cook, E. R.,Chappell, J., Ellam, R. M., Lea, D. W., Lough, J. M., and Shim-mield, G. B.: Variability in the El Nino-Southern OscillationThrough a Glacial-Interglacial Cycle, Science, 291, 1511–1517,2001.

Urey, H. C.: The thermodynamic properties of isotopic substances,J. Chem. Soc., 1947, 562–581, 1947.

Vellinga, M. and Wood, R. A.: Global Climatic Impacts of aCollapse of the Atlantic Thermohaline Circulation, ClimaticChange, 54, 251–267,doi:10.1023/a:1016168827653, 2002.

Wan, X., Chang, P., Saravanan, R., Zhang, R., and Schmidt, M.W.: On the interpretation of Caribbean paleo-temperature recon-structions during the Younger Dryas, Geophys. Res. Lett., 36,L02701,doi:10.1029/2008gl035805, 2009.

Wan, X., Chang, P., and Schmidt, M. W.: Causes of tropical Atlanticpaleo-salinity variation during periods of reduced AMOC, Geo-phys. Res. Lett., 37, L04603,doi:10.1029/2009gl042013, 2010.

Wang, C.: Variability of the Caribbean Low-Level Jet andits relations to climate, Clim. Dynam., 29, 411–422,doi:10.1007/s00382-007-0243-z, 2007.

Watanabe, T., Winter, A., and Oba, T.: Seasonal changes in seasurface temperature and salinity during the Little Ice Age inthe Caribbean Sea deduced from Mg/Ca and 18O/16O ratios incorals, Mar. Geol., 173, 21–35, 2001.

Wei, W. and Lohmann, G.: Simulated Atlantic Multidecadal Os-cillation during the Holocene, J. Climate, 25, 6989–7002,doi:10.1175/JCLI-D-11-00667.1, 2012.

Wei, W., Lohmann, G., and Dima, M.: Distinct Modes of InternalVariability in the Global Meridional Overturning Circulation As-sociated with the Southern Hemisphere Westerly Winds, J. Phys.Oceanogr., 42, 785–801,doi:10.1175/jpo-d-11-038.1, 2012.

Wellington, G. M., Dunbar, R. B., and Merlen, G.: Calibration ofStable Oxygen Isotope Signatures in Galapagos Corals, Paleo-ceanography, 11, 467–480,doi:10.1029/96pa01023, 1996.

Wust, G.: Stratification and Circulation in the Antillean–CaribbeanBasins, Part 1, Spreading and mixing of the water types withan oceanographic atlas, Columbia University Press, New York,201 pp., 1964.

Yokoyama, Y., Suzuki, A., Siringan, F., Maeda, Y., Abe-Ouchi, A.,Ohgaito, R., Kawahata, H., and Matsuzaki, H.; Mid-Holocenepalaeoceanography of the northern South China Sea using cou-pled fossil-modern coral and atmosphere-ocean GCM model,Geophys. Res. Lett., 38, L00F03,doi:10.1029/2010GL044231,2011.

Zhang, D., Msadek, R., McPhaden, M. J., and Delworth, T.: Multi-decadal variability of the North Brazil Current and its connectionto the Atlantic meridional overturning circulation, J. Geophys.Res., 116, C04012,doi:10.1029/2010jc006812, 2011.

Zhang, R. and Delworth, T. L.: Simulated Tropical Response to aSubstantial Weakening of the Atlantic Thermohaline Circulation,J. Climate, 18, 1853–1860,doi:10.1175/JCLI3460.1, 2005.


http://dx.doi.org/10.1175/1520-0485(1988)018<1209:VOSATO>2.0.CO;2

http://dx.doi.org/10.5194/cp-7-75-2011

http://dx.doi.org/10.1126/science.204.4391.404

http://dx.doi.org/10.1175/JCLI3689.1

http://dx.doi.org/10.1126/science.1109496

http://dx.doi.org/10.1073/pnas.1207514109

http://dx.doi.org/10.1023/a:1016168827653

http://dx.doi.org/10.1029/2008gl035805

http://dx.doi.org/10.1029/2009gl042013

http://dx.doi.org/10.1007/s00382-007-0243-z

http://dx.doi.org/10.1175/JCLI-D-11-00667.1

http://dx.doi.org/10.1175/jpo-d-11-038.1

http://dx.doi.org/10.1029/96pa01023

http://dx.doi.org/10.1029/2010GL044231

http://dx.doi.org/10.1029/2010jc006812

http://dx.doi.org/10.1175/JCLI3460.1

Documents

Controls of Caribbean surface hydrology during the mid- to