HAL Id: hal-02917095
https://hal.archives-ouvertes.fr/hal-02917095
Submitted on 9 Oct 2020
HAL is a multi-disciplinary open access
archive for the deposit and dissemination of
sci-entific research documents, whether they are
pub-lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d’enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.
Mg/Ca-paleothermometry in the western Mediterranean
Sea on planktonic foraminifer species Globigerina
bulloides: Constraints and implications
Soumaya Boussetta, Nejib Kallel, Franck Bassinot, Laurent Labeyrie,
Jean-Claude Duplessy, Nicolas Caillon, Fabien Dewilde, Hélène Rebaubier
To cite this version:
Soumaya Boussetta, Nejib Kallel, Franck Bassinot, Laurent Labeyrie, Jean-Claude Duplessy, et al..
Mg/Ca-paleothermometry in the western Mediterranean Sea on planktonic foraminifer species
Glo-bigerina bulloides: Constraints and implications. Comptes Rendus Géoscience, Elsevier Masson, 2012,
344 (5), pp.267-276. �10.1016/j.crte.2012.02.001�. �hal-02917095�
External
geophysics,
climate
Mg/Ca-paleothermometry
in
the
western
Mediterranean
Sea
on
planktonic
foraminifer
species
Globigerina
bulloides:
Constraints
and
implications
Le
pale´othermome`tre
Mg/Ca
applique´ a` l’espe`ce
de
foraminife`re
planctonique
Globigerina
bulloides
en
Me´diterrane´e
occidentale
:
contraintes
et
implications
Soumaya
Boussetta
a,*
,
Nejib
Kallel
a,
Franck
Bassinot
b,
Laurent
Labeyrie
b,
Jean-Claude
Duplessy
b,
Nicolas
Caillon
b,
Fabien
Dewilde
b,
He´le`ne
Rebaubier
ba
UniversityofSfax,FSS,laboratoireGEOGLOB,routedeSoukra,BP802,3028Sfax,Tunisia
b
LSCE(CEA/CNRS/UVSQ),domaineduCNRS,baˆtiment12,avenuedelaTerrasse,91198Gif-sur-Yvette,France
C.R.Geoscience344(2012)267–276
ARTICLE INFO Articlehistory: Received31May2011
Acceptedafterrevision2February2012 Availableonline11March2012 PresentedbyMichelPetit Keywords:
Mediterranean Mg/Ca
Planktonicforaminifera SeasurfaceTemperature Salinity Diagenesis Vitaleffect Motscle´s: Me´diterrane´e Mg/Ca Foraminife`resplanctoniques Tempe´raturedesurface Salinite´ Diagene`se Effetvital ABSTRACT
We generated a high-resolution SSTMg/Ca record for the surface-dwelling planktonic
foraminiferaGlobigerinabulloidesfromthecoreMD99-2346collectedintheGulfofLion, andcomparedittothatobtainedusingmodernanaloguetechniques appliedtofossil foraminiferalassemblages(SSTMAT).Thetwotemperaturerecordsdisplaysimilarpatterns
duringthe last 28,000years but the SSTMg/Caestimatesare several degrees warmer
(+48C)thanSSTMAT.The temperatureshiftbetween SSTMg/Caand SSTMATremained
relativelyconstantovertime.ThisseemstoexcludeabiasontheMg/Carecordassociated withsalinityorsecondaryMg-richcalciteencrustationontheforaminiferaltestsduring earlydiagenesis.Therefore,anomalouslyhighMg/Casuggestseither:(1)theempirical equationforG.bulloidesofElderfieldandGanssen(2000)isincorrect;or(2)thereisa specificMediterraneangenotypesofG.bulloidesforwhichaspecificMg/Ca-temperature calibrationisneeded.
ß2012Acade´miedessciences.PublishedbyElsevierMassonSAS.Allrightsreserved.
RE´ SUME´
Nousavonsreconstitue´ l’e´volutiondes tempe´raturesde surfacelelong de lacarotte MD99-2346,pre´leve´edans leGolfedu Lion,a` l’aide dedeuxpale´othermome`tres :la mesuredurapportMg/Cadestestsduforaminife`replanctoniqueGlobigerinabulloides,etla me´thode des plus proches analogues, applique´e aux assemblages de foraminife`res planctoniques. Les re´sultats montrent une co-variance entre les deux courbes de tempe´raturependantlesderniers28000ans.Lestempe´raturesbase´essurlesmesuresdu rapportMg/Casontcependantsyste´matiquementpluschaudesquecellesobtenuesparles associationsdeforaminife`resetl’e´cartentrelesdeuxcourbesestreste´ constant(+48C) aucoursdutemps.CetteconstancesembleexclureunbiaissurlesmesuresdurapportMg/ Caassocie´ a` lasalinite´ ouaude´poˆtd’unecalcitericheenMg,lorsdeladiagene`sepre´coce. De`slors,lesSSTMg/Caanormalemente´leve´essugge`rent:(1)quelacalibrationdisponible
pour l’espe`ce G. bulloides en oce´an Atlantique est errone´e ; ou (2) qu’il existe en
* Correspondingauthor.
E-mailaddress:Soumaya.Boussetta@lsce.ipsl.fr(S.Boussetta).
ContentslistsavailableatSciVerseScienceDirect
Comptes
Rendus
Geoscience
w ww . sc i e nce d i re ct . co m
1631-0713/$–seefrontmatterß2012Acade´miedessciences.PublishedbyElsevierMassonSAS.Allrightsreserved. doi:10.1016/j.crte.2012.02.001
1. Introduction
Amongthe variousproxies developed toreconstruct pastseasurfacetemperatures(SST),theMg/Cameasured onplanktonicforaminiferahasbeengivenmuchattention theserecentyears(Anandetal.,2003;Barkeretal.,2005;
de Garidel Thoron et al., 2005; Eggins et al., 2003;
ElderfieldandGanssen,2000;Levietal.,2007;Mashiotta
etal.,1999).Anadvantageofthismethodisthatthesame biotic carrier can be used for both Mg/Ca and oxygen isotope analyses, which makes it possible to estimate seawater
d
18O,aproxy forsalinity. Nevertheless,recentstudiespointedoutseveralpotentialbiasesthatmayaffect the incorporation of Mg in foraminiferal tests or its preservation during early diagenesis. Regarding the incorporation of Mg into foraminiferal calcite, previous works have addressedthe potentialeffects of seawater carbonateionconcentration(BarkerandElderfield,2002;
Bijmaetal.,1998;Speroetal.,1997)andsalinity(Ferguson
et al., 2008; Kisaku¨rek et al., 2008; Lea et al., 1999;
Mathien-Blard and Bassinot, 2009). The Mg/Ca ratio of
foraminiferacanbealsomodifiedinthesurfacesediment eitherbypartialdissolutionofMg-richshellcomponents inwatersunder-saturatedwithrespecttocalcite(Brown
andElderfield,1996;Dekensetal.,2002;Regenbergetal.,
2009)orbytheovergrowthofMg-rich,secondary-calcite likely formed near the sediment–seawater interface, in areaswhereinterstitialwatersare super-saturatedwith respecttoCaCO3(Boussettaetal.,2011).
Given the moderntemperature range of thesurface waters in the Mediterranean Sea, foraminiferal Mg/Ca valuesmeasured oncore topsedimentsarehigherthan what can be expected from the recent Mg/Ca-isotopic temperatureempiricalcalibrationsbasedon open-ocean sedimenttraps(Anandetal.,2003)orcoretops(Elderfield
andGanssen,2000).Recently,Fergusonetal.(2008)have
attributed such anomalously high values to the higher salinities in the Mediterranean Sea compared with the AtlanticOcean.Thehighestvalueshavebeenobservedon GlobigerinoidesruberfromtheeasternMediterraneanbasin (Levantinebasin).Inthisarea,Mg/Cavaluesarenotonly high,butalsodisplayaverylargescattering,whichcannot be explained by a temperature or a salinity effect
(Boussetta et al., 2011). SEM observations and X-ray
diffractometryanalysesexhibitclearlyapost-depositional precipitation of inorganic, Mg-rich (10–12%) calcite on foraminiferal shells. This inorganic calcite coating is considerablylesspronouncedinthewestern Mediterra-neanbasin than in theeastern basin, where diagenetic calcite can represent up to21% of the totalvolume of calciteforG.ruber(Boussettaetal.,2011).
In the western Mediterranean Sea, the planktonic foraminiferG.bulloidesisabundantandthegeochemistry ofits test couldbeusedtoreconstruct past changesin surfacewaterconditions.However,thesmall,modernsea
surfacetemperature(SST)gradient(48C)(Stephensetal., 2002)inthisareadoesnotallowustodevelopanaccurate calibrationoftheMg/CathermometerbasedonG.bulloides specimens picked from surface sediments. In order to betterconstraintheincorporationofMgintoforaminiferal testsoverawidertemperaturerange,wegenerateda high-resolutionMg/CarecordofG.bulloidespickedfromcore MD99-2346collectedintheGulfofLionandwhichcovers thelast28,000years.ThisMg/Carecordwascomparedto temperaturesinferredusingamodernanaloguetechnique appliedtofossilforaminiferalassemblages.Inthewestern Mediterraneanbasin,ithasbeenshownthatseasurface temperature (SST) reconstructions using foraminiferal associationsaregenerallyobtainedwithlowdissimilarity coefficient indicating reliable estimates (Kallel et al.,
1997b,2004;Melkietal.,2009).Conditionsare,however,
different during the Last Glacial Maximum when fossil assemblageshavenogoodmodernanaloguesparticularly intheeasternMediterraneanSea.Thiscomparisonstudy has been completed by the data obtained on seven Mediterraneancoretops.
2. Materialandmethods 2.1. Studymaterial
Mg/Ca analyses were performed on G. bulloides retrieved from well-preserved core tops spanning the western Mediterranean Sea (Boussetta et al., 2011)and alongthecoreMD99-2346(42802.610N,4809.040E,2100m
ofwaterdepth,10.61mlong;Fig.1)collectedintheGulfof Lion.TheMD99-2346core,whichis10.63mlong,iswell dated using accelerator mass spectrometry (AMS) 14C dating. Theage model of core MD99-2346, for the last 28kyr, hasbeen established using AMS 14Cdatesfrom
13planktonicforaminiferalevels(Melkietal.,2009).For this core, in addition to micropaleontological analysis, which have been used for reconstructions of past sea surface temperatures (SST), the oxygen stable isotope analysesmeasuredontheG.bulloides(
d
18O)areavailable(Melkietal.,2009).
2.2. Oxygenisotopicanalyses
Oxygenisotopic(
d
18O)measurementswereperformedonG.bulloidesspecimensalongthecoreMD99-2346and ontheavailablewesternMediterraneancoretops.About sixforaminifertests(60
m
g)persamplewerepickedfrom the 200–250m
m size fractionfor each oxygen isotopic measurement. Shells were ultrasonically cleaned in a methanolbathtoremoveclaysandotherimpurities.They wereroasted undervacuumat 3808Cduring45minto eliminateorganicmatter.Sampleswereanalyzedwitha FinniganD
+massspectrometer.Allresultsareexpressed asd
18Oin%versusPDBviathecalibrationwithrespecttoMe´diterrane´e une sous-espe`ce ende´mique pour laquelle il faut de´velopper une calibrationspe´cifiqueenraisond’uneffetvitalsurl’incorporationduMg.
the international standards NBS-19 and NBS-18. The analytical reproducibility as determined from replicate measurementsofaninternalstandardis0.05%(1
s
). 2.3. Mg/CaanalysesAbout20–30specimensofG.bulloidespersamplewere usedfromthe200–250
m
msizefractionforeachMg/Ca measurement.Theseshellsweregentlycrushedtoopenthe chambers. Prior to analysis, samples were cleaned following the procedure of Barker et al. (2003), which includes several ultrasonic treatments in water then ethanol to remove adhesive clays, and then a reaction withhydrogenperoxidetreatment1%at1008Ctoremove any organic matter. A very slight acid leaching with 0.001M nitric acid was finally applied to eliminate contaminants adsorbedon foraminiferal tests. Analyses wereperformedonaVarianVistaProInductivelyCoupled
Fig.1.Mapsofthewatersalinity(psu)andtemperature(8C)ofthewesternMediterraneanSeaattheappropriatedepthhabitatoftheplanktonic foraminiferaGlobigerinabulloides.Locationofthecoretops(greencircles)andofcoreMD99-2346(bluecircle)areshown.
Fig.1.Cartesdessalinite´s(psu)etdestempe´ratures(8C)deseauxdelaMe´diterrane´eoccidentale,a` laprofondeurapproprie´ed’habitatduforaminife`re planctoniqueGlobigerinabulloides.Sontmontre´ese´galement,leslocalisationsdessommetsdecarotte(cerclesverts)etdelacarotteMD99-2346 (cerclebleu).
Plasma Atomic Emission Spectrometer (ICP-AES) at the Laboratoiredessciencesduclimatetdel’environnement (LSCE),amemberofaninterlaboratorycomparisonstudy ofcalibrationstandardsforforaminiferalMg/Ca thermo-metry (Greaves et al., 2008), following the method of
deVilliersetal.(2002).Themeanexternalreproducibility
ofastandardsolutionofMg/Ca=5.23mmol.mol10.5%
(RSD).
Onaverage, claymineralscontainbetween 1and 10 weight%Mg(Deeretal.,1992).Claycontaminationmay cause,therefore,a significantbiasin foraminifer Mg/Ca ratios.Barkeretal.(2003)showedthatthecovariancesof Fe/Ca and Mg/Ca, as well as Fe/Mg values exceeding 0.1mol.mol1areindicatorsofclaycontamination.Allour
cleaned samples showed a Fe/Mg ratio smaller than 0.1mol.mol1,andneitherFe/CanorAl/Cacorrelatewith
Mg/Ca.
This clearly shows the efficiency of the cleaning procedureinremovingsilicatecontaminants.
2.4. Seasurfacetemperaturereconstructionusingthe modernanaloguetechnique
Sea surface temperature reconstructions were per-formed using foraminiferal assemblages along the core MD99-2346 based on the modern analogue technique
(Hutson,1980;Overpecketal.,1985;Prell,1985;Prentice,
1980), Fig. 1. This technique is used to compare fossil planktonicforaminiferalsamples toa modernreference databaseandtoidentify,foreachfossilassociation,theten best modern analogues. The mean degree of similarity betweeneachfossilassemblageandthecorrespondingten best modern analogues is measured by a dissimilarity coefficient.TheSSTestimatesareconsideredreliablewhen thiscoefficientislowerthan0.25(Prell,1985).Abovethis thresholdvalue,SSTestimateshavetobeconsideredwith caution.Thereferencedatabaseusedforthepresentstudy hasbeenfirstdevelopedbyKalleletal.(1997a)andthen improvedbyHayesetal.(2005)andcorrespondsto274 core-topsediments,145fromtheMediterraneanSeaand 129fromtheNorthAtlanticOcean.IntheMediterranean Sea, it has been found that modern analogues of foraminiferalfossilassemblagesarefoundinthe Mediter-ranean Sea itself during warm periods of the Upper Quaternary. However, during glacial periods, the best modern analogues originate mainly from the North Atlantic (Essallami et al., 2007; Kallel et al., 1997b,
2000;Melkietal.,2009).
2.5. Seasurfacesalinityreconstruction
BycombiningSSTestimatesderivedfromforaminifera usingmodernanaloguetechnique andtheforaminiferal
d
18O values, we reconstructed the Gulf of Lion surfacesalinityrecord(Fig.1)followingthemethodintroducedby
Duplessyetal.(1991)andKalleletal.(1997a).Takinginto
account the SST estimates, the
d
18O surface watervariationswerecalculated bysolvingthe paleotempera-tureequation(Shackleton,1974).
In the Mediterranean Sea, surface water
d
18O (dw
)changes reflect both changes in the
d
18O value of theincomingAtlanticwaterandvariationsofthelocal fresh-waterbudget(PrecipitationpluscontinentalRunoffminus Evaporation,P+RE)oftheMediterraneanbasin(Kallel
et al., 1997b). The effect of continental ice volume
variations on global seawater
d
18O is assumed to beequal to the sea-level curve of Lambeck and Chapell
(2001)multipliedbyaconstantcoefficientof1.1%/130m
fromWaelbroecketal.(2002).AstheMediterraneanSeais
linkedtotheNorthAtlanticOceanthroughtheStraitsof Gibraltar,wesupposethattheeffect of continentalice volumevariationswasrecordedinasimilarmannerinthe twoareas.Wethereforeestimatedthelocal Mediterra-nean Sea surface
d
18Osw variations with respect to
the modern situation as the difference between calculated and modern seawater
d
18Osw, corrected
for the global effect:
d
18Oanomaly=calculated
d
18Osw[modern
d
18Osw+global
d
18Osignal].Toconvertthe
d
18Oanomalytoasalinityanomaly,weusedthemodernseawater
d
18Osw-salinityrelationshipfor
the western Mediterranean Sea (1% change in local salinitywillresultin0.41%changeinlocal
d
18Osw;Kallel
etal.,1997a).
CoreMD99-2346exhibitsfourstrongnegativesalinity anomalies(Fig.3)duringH2,H1,theYoungerDryasand the Middle Holocene period between about10,000 and 4,000yrsB.P.(3.5,3.3,1.7and1%respectively).TheGulfof Lionsalinitydecreaseeventsaresimilartothoseobserved inotherMediterraneancoresrecoveredintheAlboranSea
(Cacho etal.,1999), in theTyrrhenian Sea (Kallel etal.,
1997b,Paterneetal.,1999)and intheSicilian–Tunisian
Strait(Essallamietal.,2007).
To understand better the origin of these salinity changes,Melkietal.(2009)comparedthemwiththose obtainedfromthecoreSU81-18recoveredintheNorth AtlanticOceanoffPortugal(Duplessyetal.,1992,1993). They found thatthe first threeevents wereassociated withasimilarsalinitydecreaseoftheincomingAtlantic waterenteringtheMediterraneanSeaintheupperpartof the Gibraltar Strait, but the western Mediterranean freshwater balance was not affected at these epochs. The basin acted as today as a concentration basin (P+R<E), whereas the Holocene event, absent in the NorthAtlanticOcean,wasfoundtobeoflocalorigin.It indicates an increase of precipitation over the whole Mediterraneanregion.
Consequently,theeffectofthedeglaciationmeltwater intheGulfofLionwasmainlytransferredfromtheNorth AtlanticviatheGibraltarStrait,whereastheAlpineglaciers contribution in the last deglaciation could have been potentiallysignificantonlyforthenorthernMediterranean sites(Stocchietal.,2005).ItwasrestrictedtotheAdriatic SeaandtheGulfofGenoa(Lambecketal.,2004). 3. Results
3.1. Dataofsurfacesediments Valuesof
d
18OforaminiferameasuredonG.bulloidesfrom
theMediterraneancoretops(Fig.1)andtheir correspon-dingcalcificationtemperatures(Tiso)aresummarizedin
usingthepaleotemperatureequationofShackleton(1974) bycombiningthese
d
18Ofmeasurementswiththeoxygen
isotopic ratio of seawater (
d
18Osw) extracted from a
gridded atlas (LeGrande and Schmidt, 2006) at the appropriate location of each core. Results for Mg/Ca measured onG.bulloidesarealsoshowninTable1.The Mg/Ca of G. bulloides were converted to temperatures (SSTMg/Ca)based on Elderfieldand Ganssen(2000) (Mg/
Ca=0.81e0.081T)empiricalequationforG.bulloides.Using
this Mg/Ca-temperature empirical calibration results in surface temperatures (SSTMg/Ca) that are systematically
higherthantheisotopictemperatures(Tiso).
3.2. Modernanaloguetechnique:selectionofseasonand results
Undermodernconditions,G.bulloidesdevelops prefe-rentiallyduringthespringbloomintheMediterraneanSea
(PujolandVergnaud-Grazzini,1995).Thisis
demonstrat-ed, for instance, by the strong correlation over all the Mediterranean Sea, between modern April-May SSTs
(Levitus,1982)andisotopictemperaturesestimatedusing
d
18OvaluesofG.bulloides(Kalleletal.,1997a).However, ifwefocus onlyon datafromthewestern MediterraneanSea,particularlyintheGulfofLion(Table 1), we notethat isotopic temperatures estimated using
d
18OvaluesofG.bulloidesfromcoretopsaverage16.58C, and are, therefore, 28C warmer than April-May SST (AtlasWOA5).Inthisarea,theplanktonicspringbloomis mainlylinkedtothestartoftheverticalstratificationofthe water column associated withthewater warmingafter winteroverturning.Astheverticalwinteroverturningis particularlyintenseintheGulfofLion,itislikelythatthe stratificationanddevelopmentofG.bulloidesspreadovera longerperiodand/orstartlaterthanintheotherareasof theMediterraneanSea.Thus,intheGulfofLion,thebest correlationwiththeisotopictemperaturesestimatedusing
d
18OvaluesofG.bulloidesisobtainedwiththemeanspring(April,May,June)SST,andnotwithApril-MaySST.
PastApril-May-JuneSST(SSTMAT)wereestimatedalong
the core MD99-2346 from the counts of planktonic foraminifera publishedby Melki etal. (2009), usingthe modern analogue technique. These temperatures esti-matesareshowninFig.2A.Thedissimilaritycoefficients associatedwiththisSSTreconstructionaregenerallylower than0.25exceptfortheLastGlacialMaximum(Fig.2B; between21.09and18.07calkyrBP.)whentheycanreach 0.3 (Fig. 2C). All estimates were obtained with low standarddeviations(notexceeding1.258C).
3.3. SSTMg/CarecordalongthecoreMD99-2346
Thehigh-resolutionSSTMg/Carecordforthelast28kyr,
canbecomparedtothatobtainedusingmodernanalogue technique applied to fossil foraminiferal assemblages (SSTMAT) (Fig. 2A). Records display similar patterns. In
both cases, thelast glaciationis colderthan theUpper Holocenebyabout78Candthepost-glacialwarmingofthe Bollı¨ng/Allero¨d (B/A), which began at about 14.7calkyr BP., wasinterrupted by a climatic deterioration and an abrupt coolingat thesame epoch as theEuropean and NorthAtlanticYoungerDryas(YD)betweenabout12.8and
11.5kyr BP. (Bard et al., 1987; Duplessy et al., 1991;
Rasmussen et al., 2006). This pattern of temperature
changeissimilartothatobservedinotherMediterranean areas such as theAlboran Sea, the Tyrrhenian Sea, the Sicilian-Tunisian Strait and the eastern Mediterranean basin (Cacho et al., 1999; Emeis et al., 2000, 2003;
Essallamietal.,2007;Kalleletal.,1997b;Paterneetal.,
1999).
Significantdifferencesbetweenthetworecordsofthe Gulfof Lion areobserved,however,duringtheYounger DryasandtheLowerHolocene. TheYDcoolingphaseis shorterintheMg/Carecord(of12.93at11.49kyrBP.)than in the modern analogue technique record (of 13.45 to 11.49 kyrBP.).ThetimingoftheSSTMg/Cacoolingismore
consistentwiththatdefinedintheNorthAtlanticforthe Younger Dryas (12.8 to11.7kyrBP.; Bard et al., 2000;
Table1
HydrologicparametersatthelocationofcoretopsandgeochemicaldataobtainedonGlobigerinabulloides.Valuesofd18
OfweremeasuredonG.bulloides,
andtheisotopictemperature(Tiso)wascalculatedusinganequationfromShackleton(1974).ValuesofMg/CaweremeasuredonG.bulloides,andthe
correspondingtemperatures(SSTMg/Ca)werecalculatedbasedoncalibrationfromElderfieldandGanssen(2000)forG.bulloides.April-MaySSTand
April-May-JuneSSTareextractedfromAtlas(LevitusandBoyer,1994). Tableau1
Parame`treshydrologiquesa` l’emplacementdessommetsdecarottesetdonne´esge´ochimiquesobtenuessurGlobigerinabulloides.Lesvaleursded18
Ofsont
mesure´espourleforaminife`replanctoniqueG.bulloides,etlestempe´raturesisotopiquesonte´te´ estime´esa` partirdel’e´quationdespale´otempe´raturesde
Shackleton(1974).LesrapportsMg/Casontmesure´ssurG.bulloidesetlestempe´raturescorrespondantes(SSTMg/Ca)onte´te´ de´duitesa` l’aidedel’e´quationde
calibrationd’ElderfieldetGanssen(ElderfieldandGanssen,2000)pourG.bulloı¨des.Lestempe´raturesd’avril-maietd’avril-mai-juinonte´te´ estime´esa` partir d’unatlasoce´anographique(LevitusetBoyer,1994).
Core Mg/Ca (mmol/mol) d18O f(PDB) Tiso (8C) April-May SST (8C) April-May-JuneSST (8C) SSTMg/Ca(8C) MD90-901 4.0 1.18 16.3 16.2 17.7 19.9 MD99-2344 5.3 1.14 17.3 13.9 15.6 23.1 MD99-2346 4.8 1.29 16.5 14.7 16.4 22.0 KET80-22 5.1 1.36 16.4 16.0 17.7 22.7 DED87-07 4.3 1.06 17.4 16.5 18.1 20.7 KET80-03 4.6 1.46 17.7 16.5 18.2 21.4 KET80-19 4.9 1.14 15 16.6 18.2 22.3
Heinrich, 1988; Rasmussen et al., 2006). Moreover, the foraminiferalrecordindicatedthatSSTswerehigheratthe beginningoftheHolocenethantheUpperHoloceneSSTs byabout2to38C.Suchastructureisnotasmarkedonthe Mg/Carecord.
Moreimportantly,Fig.2Aclearlyindicates thatwhile the structures of two temperature records are broadly similar; the SSTMg/Ca estimates are, however, several
degreeswarmerthanSSTMAT.Theshiftisconstantduring
thelastglaciationandHolocenebutchangessignificantly throughtimeduringthelastdeglaciation.Thisisprobably duetotheoffsetofthebiologicalresponseswithrespectto
hydrological changes in temperature. Thus, in order to determinetheaverageoffsetbetweenthetwo tempera-ture records, we suggest to retrieve the deglaciation interval,and wecalculatedthemeandifferencesforthe interval0–8kyrBP.(Holocene)and15–25kyrBP.(glacial period).OvertheHolocene,thetemperatureoffsetisabout 3.88C,andis+48Cfortheglacialperiod.
4. Discussion
4.1. MgenrichmentinG.bulloidesfromcoreMD99-2346: potentialeffectofearlydiagenesisprocesses
ArecentworkpointedoutthatanomalouslyhighMg/ Ca ratios measured byconventional ICP-AES analysisof planktonicforaminifersfromtheMediterraneanSea(and inparticularintheeasternbasin)aremainlyrelatedtothe presenceofearlydiagenesis,highMg-calciteovergrowths (10–12%)(Boussettaetal.,2011;Hoogakkeretal.,2009;
vanRadenetal.,2011).However,alongthecore
MD99-2346,aninterpretationoftheXRDprofiles,deconvoluted usingtheIGOR1
software,didnotrevealanymeasurable amountofMg-richcalciteonG.bulloidesshells.Ifitexists, in trace amounts, it is below the XRD detection-limit
(Sabbatini et al., 2011). Nevertheless, thedeposition of
secondaryinorganiccalcitecontaining10–12%ofMg,even insmallquantities,hasthepotentialtochangenoticeably Mg/Cavaluesobtainedonwholeplanktonicshells(which contain only a few mmol mol-1 Mg/Ca; Sexton et al.
(2006)).
IntheeasternMediterraneanbasin,wherethe diage-netic coating appears to be generally more important,
Boussetta(2011)showedthatthereisconsiderablelocal
variability in its amount even at the sample scale. Unpublished data, dealing with the evolution of the diageneticcoatingalongacorerecoveredintheLevantine basin, show that the amount of diagenetic calcite also varies over time (Boussetta, 2011, PhD thesis). Such variabilityintheMg-richcalciteencrustation,bothspatial and temporal, is not compatible with the relative constancy, within the rather stable time period of the HoloceneandtheLGM,ofthetemperatureshiftbetween SSTMg/CaandSSTMATthatwenoteinthecoreMD99-2346.
Wecanthereforereasonablyconcludethatthepresenceof adiageneticcoatingcannotaccountforthissystematicMg enrichmentobservedincoreMD99-2346.
4.2. CanasalinitybiasexplainG.bulloideshighMg/Ca values?
The Mediterranean Sea is a semi-enclosed basin showing a strong salinity gradient fromwest (36 psu neartheStraitofGibraltar)toeast(40psu)(Boyeretal.,
2002;Lascaratosetal.,1999).Thesesalinitiesarehigher
than theaverage fortheWorldOcean.Recently, several studieshaveemphasizedthepotentialroleofhighsalinity asabiasonMg/Cathermometry,withsensitivitiesranging from43%Mg/Caperpsuunitobservedinculturestudies
(Kisaku¨reketal.,2008;Leaetal.,1999;Nu¨rnbergetal.,1996)
up to 15–59% per psu suggested by field studies on Mediterraneancoretopsamples(Fergusonetal.,2008).
Fig. 2.Climatic records of core MD99-2646: (A) Oxygen isotope composition of Globigerina bulloides; (B) Sea surface temperatures (SSTs)obtainedbytheuseofMg/CaratiosinG.bulloides(greencurve), andplanktonicforaminiferaassemblagesforApril–May-June(inblue); (C)dissimilaritycoefficientfortemperaturesgeneratedusingmodern analoguetechnique.LevelsreportedinredwereanalyzedbyXRD. Fig. 2.Enregistrements climatiques de la carotte MD99-2346: (A) Composition isotopique de l’oxyge`ne de Globigerina bulloides; (B) Pale´otempe´raturesdesurfaceestime´esparlamesuredurapportMg/ Caduforaminife`replanctoniqueG.bulloides(courbeverte)etparla techniquedesanaloguesactuels(MAT)pourAvril-Mai-Juin(enbleu);(C) coefficientsdedissimilarite´ quicontroˆlentlafiabilite´ desestimationsde pale´otempe´raturesparlatechniquedesanaloguesactuels.Lesniveaux signale´senrougeonte´te´ analyse´sparDRX.
In order to evaluate the possibility that Mg/Ca temperatureanomaliesfromthewesternMediterranean Seaareaffectedbysurfacesalinity,wereconstructedthe Gulf of Lion surface salinity record, by combining SST estimates derived fromforaminifera usingmodern ana-logue technique and the foraminiferal
d
18O values,following the method introduced by Duplessy et al.
(1991) and Kallel et al. (1997a). Then, these salinities
arecomparedwiththepotentialshift(
D
T)betweenMg/Ca temperatures(SSTMg/Ca)andinferredtemperaturesusingmodernanaloguetechnique(SSTMAT).
As can be seen (Fig. 3), the surface salinity record obtained fromcore MD99-2346reveals large-scale fluc-tuationsthatareneithercorrelatedwithMg/Ca tempera-turesnorwiththeshift(
D
T)betweenSSTMg/CaandSSTMAT.This is particularly visible during the cold periods synchronoustotheHeinrich events2 and1,duringthe Younger Dryas and during the Lower to the Middle Holocene. Abruptand strong salinitydecreaseevents of 2to3%areobservedduringtheseperiods(Melkietal., 2009)andtheyarenotreflectedbycorrespondingchanges inMg/CatemperaturesorintheshiftrelativetoSSTMAT.
Toconfirmthehypothesisthatsalinitydoes notplay anydominantroleintheMg uptakeintoMediterranean foraminiferal tests,we looked ifa salinity effectcanbe detected fromMg/Cameasuredin G.bulloidescoretops samples(Boussettaetal.,2011)andfromplanktontows
(van Raden et al., 2011) recovered from the western
MediterraneanSea.
InthewesternMediterraneanbasin,SEMobservations andX-RayDiffractometryAnalysesindicatethatthe post-mortem calcite overgrowth is minor (Boussetta et al., 2011)andthatthemostofthiscalcitebeinglikelyremoved duringthechemicalcleaningforMg/Caanalyses(Sabbatini
etal.,2011).
Forthesesamplesweestimatedthedifference(
D
Mg/ Ca) between the measured Mg/Ca ratio (Mg/Cameasured)and that expected (Mg/CaT) from the calibration of
Elderfield and Ganssen (2000),by the useof estimated
temperatures from oxygen isotope composition of G.bulloides.Theresiduals(
D
Mg/Ca)werethencompared withsalinitychanges(Fig.4).Thisfigureclearlyshowsthat there is no significant correlation between salinity and planktontoworcoretopsampleD
Mg/Casupportingour conclusionthattheMg/CaenrichmentofG.bulloidesalong coreMD99-2346cannotbeexplainedbysalinity. 4.3. Mg/CathermometryinthewesternMediterraneanSea:is thereaspecificvitaleffectfortheincorporationofMginto G.bulloidescalcite?TheMg/Ca-temperaturecalibrationforG.bulloidesthat weusedinthis studyhasbeenestablishedbyElderfield
andGanssen(2000)usingsurfacesedimentmaterialfrom
open ocean, particularlythe North Atlantic Ocean on a latitudinaltransect from,308to608N at about258W. It shouldbenotedthatElderfieldandGanssen(2000)have removedfrom their databaseseveral G.bulloidesMg/Ca values, which appeared ‘‘unusually high’’ compared to values obtainedin thesamesurface temperature condi-tions on other planktonic foraminiferal species. These
authorsobservedthatMg-enrichedsamplesofG.bulloides aremainlyfoundonshallowercoretops,buttheydonot provideaclearexplanationaboutwhyonlytheG.bulloides speciesappearstoshowsuchanomalousMg/Cavalues.We believethattheexistenceofanomalouslyhighG.bulloides Mg/Caratiosclearlysuggesttheproblemofdevelopinga Mg/Cathermometryon this species,although —at this stage—noclearexplanationexistsaboutitscause.
ThisMg enrichment seems, therefore,tobe a signal acquiredduringthedevelopmentofG.bulloidesandnotat thesedimentsurface.Thisinterpretationissupportedby thedataobtainedbyvanRadenetal.(2011)showingthat thehighMg/CavaluesalsocharacterizeG.bulloidesshells
Fig. 3.Climatic recordsof coreMD99-2646 against age: (A)Mg/Ca temperature;(B)comparisonofthedifference(DT)betweenSSTMg/Caand
SSTApril-May-June(B)Seasurfacesalinityandd18Owatercalculatedfromthe
SST estimates derived from foraminifera using modern analogue techniqueand the foraminiferal d18
O values, following the method introducedbyDuplessyetal.(1991)andKalleletal.(1997a). Fig.3.Enregistrementsclimatiquesenfonctiondel’aˆgedelacarotte MD99-2646:(A)teme´raturesMg/Ca;(B)e´carts(DT)entreles tempe´ra-tures Mg/Ca et les tempe´ratures des plus proches analogues; (C) pale´osalinite´s et d18
Oeau reconstitue´s en combinant le d18O du
foraminife`replanctoniqueG.bulloidesetlesestimationsdes tempe´ra-turesparlatechniquedesAnaloguesActuels,selonlame´thodeintroduite parDuplessyetal.(1991)etKalleletal.(1997a).
retrievedfromplanktontowsin thewestern Mediterra-nean.Thehighcalcitesaturationstateof Mediterranean surfacewaterscannotexplainthisMgenrichment.Culture experiments on planktonic foraminifera, including G.bulloides, have shownthat less Mg rather thanmore Mg isincorporated intothetestsduring calcificationat highersaturationstates(Kisaku¨reketal.,2008;Leaetal.,
1999;Russelletal.,2004).
Twohypotheseswillhavetobetestedinthefuture,but unfortunately it cannot be done with the currently availabledataset:
1.is the empirical equation obtained by Elderfield and
Ganssen(2000)incorrectbecauseitshouldhavetaken
intoaccounttheG.bulloidesMg/Cavaluesconsideredby theseauthorsas‘‘abnormally’’high?;
2.is the Mediterranean G. bulloides associated to a particular genotype that has developed a specific processofbiomineralizationcharacterizedbyhighMg uptake(vitaleffect)?
Darlingetal.(2003)demonstrate,intheSantaBarbara
Channel (Pacific Ocean), that the same genotype of G.bulloides(type IId)occurs in all thechanging hydro-graphicregimesassociatedwiththisregionthroughoutthe annual cycle withthe exceptionof January,when they recorded the additional presence of the high-latitude G.bulloidestypeIIa.Ontheotherhand,ithasbeenshown that differentmorphotypes of G. ruber, which are most likelyrepresentativeofdifferentgenotypeshavedistinct Mg/Ca (Steinke et al., 2005). Consequently, genotype difference, if it exists, between G. bulloides individuals usedintheAtlanticcalibrationandthoseanalysedinthe MediterraneanSeamightberesponsiblefortheobserved anomalouslyhighMg/CaintheMediterraneanSea.
DecipheringtheoriginofthisconsistentMgenrichment of G. bulloides shellsin the Mediterranean Sea requires furtherinvestigations,basedonmodernmaterial. 5. Conclusions
1.Measurement ofMg/Caratios ofthesurface-dwelling planktonic foraminifera G. bulloides along the core MD99-2346 have allowed us, using the Atlantic calibrationofElderfieldandGanssen(2000),to recon-structtheseasurfacetemperatures(SST)intheGulfof Lionduringthelast28,000years.
2.ThecomparisonbetweenMg/Catemperatures(SSTMg/ Ca)recordobtainedforG.bulloidesalongthecore
MD99-2346 with that inferred using modern analogue technique,appliedtofossilforaminiferalassemblages inthesamecore, showsa strikingsimilaritybutalso emphasizes that the SST Mg/Ca estimates are several
degrees warmer than SSTMAT during the last 28,000
years.Theshiftisconstantduringthelastglaciationand Holocenebutchangessignificantlythroughtimeduring thelastdeglaciation.Thisisprobablyduetotheoffsetof thebiological responseswith respectto hydrological changesintemperature.
3.ThehighMg-calcitediageneticcoating(10–12%),which appears to be generally important in the eastern Mediterranean basin, cannot account for the anoma-lously high Mg/Caratios and the constant shift (
D
T) between the two palaotemperature records (SSTMg/CaandSSTMAT).
4.Comparisons of Mg/Ca data obtained on G. bulloides fromcoretopandplanktontowsamplesaswellasalong thecoreMD99-2346withmodernandpaleosalinitiesof the western Mediterranean Sea exclude any surface salinityeffectontheMguptakeintoG.bulloidestests. 5.We mustthereforeconsiderthat eithertheempirical
equation for G. bulloides of Elderfield and Ganssen
(2000)isincorrectorthereisaspecificMediterranean
genotypesof G. bulloidesfor which a specific Mg/Ca-temperaturecalibrationisneeded.Furtherstudiesare requiredtoconfirmthesetwohypotheses.
Acknowledgements
We aregratefultotwoanonymousreviewersoffered helpful suggestions that improved the manuscript. S. Boussetta and N.Kallel, gratefullyacknowledge LSCE, UniversityofSfax,‘‘Ministe`reTunisiendel’Enseignement Supe´rieur’’ and European FP7 MedSeA Project for their technicalandfinancialsupport. Thisworkhasbeenalso supportedbytheFrenchANR-LAMAproject.
References
Anand,P.,Elderfield,H.,Conte,M.H.,2003.CalibrationofMg/C:a ther-mometryinplanktonicforaminiferafromasedimenttraptimeseries. Paleoceanography18(2),1050.
Antonov,J.,Locarnini,R.,Boyer,T.,Mishonov,A.,Garcia,H.,2006.World OceanAtlas2005,vol.2.In:LevitusSalinity,S.(Ed.), NOAAAtlas NESDIS,vol.62.NOAA,SilverSpring,Md,p.182.
Bard,E.,Arnold,M.,Maurice,P.,Maurice,P.,Dupart,J.,Moyes,J.,Duplessy, J.-C.,1987.RetreatvelocityoftheNorthAtlanticpolarfrontduringthe Fig.4.Difference(DMg/Ca)betweentheMg/CaratiosmeasuredinG.
bulloidesfromcoretops(Boussettaetal.,2011)andplanktontowsamples (vanRadenetal.,2011)ofthewesternMediterraneanSeaandthevalue expectedfromthecalibrationofElderfieldandGanssen(2000)versus Mediterranean surface water salinity. Salinities were estimated by averagingWorldOceanAtlas2005data(Antonovetal.,2006). Fig.4.Diffe´rence(DMg/Ca)entrelerapportMg/Camesure´ surG.bulloides dessommetsdecarottes(Boussettaetal.,2011)etdespie`gesa` se´diments (vanRadenetal.,2011)delaMe´diterrane´eoccidentaleetceluipre´ditpar l’e´quationdecalibrationd’ElderfieldetGanssen(ElderfieldandGanssen, 2000)enfonctiondelasalinite´ desurfacedelaMe´diterrane´e.Lessalinite´s observe´esdeseauxdesurfacesontalorsestime´esa` partirdesdonne´esde l’Atlasoce´anographiqueWOAD05(Antonovetal.,2006).
lastdeglaciationdeterminedby14Cacceleratormassspectrometry.
Nature328,791–794.
Bard,E.,Rostek,F.,Turon,J.L.,Gendreau,S.,2000.Hydrologicalimpactof Heinrich events inthe Subtropical NortheastAtlantic (Research: reports).Science289(5483),1321–1324.
Barker,S.,Elderfield,H.,2002.Foraminiferalcalcificationresponseto glacial interglacial changes in atmospheric CO2. Science 297
(5582),833–836.
Barker,S.,Greaves,M.,Elderfield,H.,2003.Astudyofcleaningprocedures usedforforaminiferalMg/Capaleothermometry.Geochem.Geophys. Geosyst.4(9).
Barker,S.,Cacho,I.,Benway,H.,Tachikawa,K.,2005.Planktonic forami-niferalMg/Caasaproxyforpastoceanictemperatures:a methodo-logicaloverviewanddatacompilationfortheLastGlacialMaximum. QuaternarySci.Rev.24,821–834.
Bijma,J.,Spero,H.J.,Lea,D.W.,1998.Oceaniccarbonatechemistryand foraminiferalisotopes:newlaboratoryresults.Paperpresentedat SixthInternationalConferenceonPaleoceanography,Lisbon. Boussetta,S.,2011.E´tudege´ochimiquedesse´dimentsmarinsprofondsde
laMe´diterrane´ependantleQuaternairesupe´rieur:relationentrele rapportMg/Cadestestsdesforaminife`resplanctoniquesetles pale´o-tempe´raturesdesurface.The`se,Universite´ deSfax,210p. Boussetta,S.,Bassinot,F.,Sabbatini,A.,Caillon,N.,Nouet,J.,Kallel,N.,
Rebaubier, H., Klinkhammer, G., Labeyrie, L., 2011. Diagenetic Mg-rich calciteinMediterraneansediments:quantification and impact on foraminiferal Mg/Ca thermometry. Marine Geology (280)195–204.
Boyer,T.P., etal.,2002.WorldOceanAtlas2001,Volume2:Salinity.In: Levitus,S.(Ed.), NOAAAtlasNESDIS50.U.S.GovernmentPrinting Office,Washington,D.C,165pp.
Brown,S.,Elderfield,H.,1996.VariationsinMg/CaandSr/Caratiosof planktonicforaminiferacausedbypostdepositionaldissolution: Evi-denceofshallowMg-dependentdissolution.Paleoceanography11 (5),543–552.
Cacho,I.,Grimalt,J.O.,Pelejero,C.,Canals,M.,Sierro,F.J.,Flores,J.A.,et Shackleton, N., 1999. Dansgaard–Oeschger and Heinrich event imprints inAlboranSeapaleotemperatures.Paleoceanography14 (N.6),698–705.
Darling,K.F.,Kucera,M.,Wade,C.M.,vonLangen,P.,PakD,2003.Seasonal distributionofgenetictypesofplanktonicforaminifermorphospecies intheSantaBarbaraChannelanditspaleoceanographicimplications. Paleoceanography18(2)articleno
1032.
deGaridelThoron,T.,Rosenthal,Y.,Bassinot,F.,Beaufort,L.,2005.Stable seasurfacetemperaturesinthewesternPacificwarmpooloverthe past1.75millionyears.Nature433,294–298.
deVilliers,S.,Greaves,M.,Elderfield,H.,2002.Anintensityratiocalibration methodfortheaccuratedeterminationofMg/CaandSr/Caofmarine carbonatesbyICP-AES.Geochem.Geophys.Geosyst.3(1),1001. Deer, W.A., Howie, R.A., Zussman, J., 1992.An introduction to the
rock-forming minerals:Essex.Longman Scientificand Technical, England,696p.
Dekens,P.,Lea,D.,Pak,D.,Spero,H.,2002.CoretopcalibrationofMg/Cain tropical foraminifera:refiningpaleotemperatureestimation. Geo-chem.Geophys.Geosyst.3(4),1.
Duplessy,J.C.,Labeyrie,L.,Juilletleclerc,A.,Maitre,F.,Duprat,J.,Sarnthein, M.,1991.SurfacesalinityreconstructionoftheNorth-AtlanticOcean duringtheLastGlacialMaximum.OceanologicaActa14(4),311–324. Duplessy,J.-C.,Labeyrie,L.D.,Arnold, M.,Paterne,M.,Dupart, J.,Van Weering,T.C.E.,1992.ChangesinsurfacesalinityoftheNorthAtlantic Oceanduringthelastdeglaciation.Nature358,485–487. Duplessy,J.C.,Bard,E.,Labeyrie,L.,Duprat,J.,Moyes,J.,1993.Oxygen
isotope recordsandsalinitychangesinthenortheasternAtlantic Oceanduringthelast18,000years.Paleoceanography8,341–350. Eggins,S.,DeDeckker,P.,Marshall,J.,2003.Mg/Cavariationinplanktonic
foraminiferatests:implicationsforreconstructingpalaeo-seawater temperatureandhabitatmigration.EarthPlanet.Sci.Lett.212(3–4), 291–306.
Elderfield,H.,Ganssen,G.,2000.Pasttemperatureand(d18Oofsurface
oceanwatersinferredfromforaminiferalMg/Caratios.Nature405, 441–445.
Emeis,K.C.,Struck,U.,Schulz,H.M.,Rosenberg,R.,Bernasconi,S., Erlen-keuser,H.,Sakamoto,T.,Martinez-Ruiz,F.,2000.Temperatureand salinityvariationsofMediterraneanSeasurfacewateroverthelast 16,000yearsfromrecordsofplanktonicstableoxygenisotopesand alkenoneunsaturationratios.Palaeogeogr.Palaeoclimatol. Palaeoe-col.158,259–280.
Emeis,K.-C., etal.,2003.EasternMediterraneansurfacewater tem-peraturesandd18
Ocompositionduringdepositionofsapropelsin theLateQuaternary.Paleoceanography18(1),1005,doi:10.1029/ 2000PA000617.
Essallami,L.,Sicre,M.-A.,Kallel,N.,Labeyrie,L.,Siani,G.,2007. Hydrologi-calchangesintheMediterraneanSeaoverthelast30,000years. Geochem.Geophys.Geosyst.8(7).
Ferguson,J.,Henderson, G.,Kucera,M.,Rickaby,R.,2008. Systematic changeofforaminiferalMg/Caratiosacrossastrongsalinitygradient. EarthPlanet.Sci.Lett.265,153–166.
Greaves,M.,etal.,2008.Interlaboratorycomparisonstudyofcalibration standardsforforaminiferalMg/Cathermometry.Geochem.Geophys. Geosyst.9,Q08010,doi:10.1029/2008GC001974.
Hayes,A.,Kucera,M.,Kallel,N.,Sbaffi,L.,Rohling,E.J.,2005.Glacial Mediterraneanseasurfacetemperaturesbasedonplanktonic fora-miniferalassemblages.QuaternarySci.Rev.24,999–1016. Heinrich,H.,1988.Originandconsequencesofcycliciceraftinginthe
NortheastAtlanticOceanduringthepast130,000years,.Quat.Res. 29,142–152.
Hoogakker,B.A.A.,Klinkhammer,G.P.,Elderfield,H.,Rohling,E.,Hayward, C.,2009.Mg/Capaleothermometryinhighsalinityenvironments. EarthPlanet.Sci.Lett.,doi:10.1016/j.epsl.2009.05.027.
Hutson,W.H.,1980.TheAghulascurrentduringtheLatePleistocene: analysisofmodernanalogs.Science207,64–66.
Kallel,N.,Paterne,M.,Duplessy,J.C.,Vergnaud-Grazzini,C.,Pujol,C., Labeyrie,L.,Arnold,M.,Fontugne,M.,Pierre,C.,1997a.Enhanced rainfallintheMediterraneanregionduringthelastsapropelevent. OceanologicaActa.20(5),697–712.
Kallel,N.,Paterne,M., Labeyrie,L.,Duplessy, J.C.,Arnold,M.,1997b. Temperatureandsalinityrecordsofthelast18000years. Palaeo-geogr.,Paleoclimatol.,Paleoecol.135,97–108.
Kallel,N.,Duplessy,J.-C.,Labeyrie,L.,Fontugne,M.,Paterne,M.,Montacer, M.,2000. Mediterranean pluvial periodsand sapropel formation duringthelast200,000years.Palaeogeogr.Palaeoclimatol.Palaoecol. 157,45–58.
Kallel,N.,Duplessy,J.C.,Labeyrie,L.,Fontugne,M.,Paterne,M.,2004. MediterraneanSeapalaeohydrologyandpluvialperiodsduringthe LateQuaternary.In:Battarbee,R.W.,Gasse,F.,Stickley,C.E.(Eds.), PastclimatevariabilitythroughEuropeandAfrica.KluwerAcademic, Dordrecht, pp.307–324.
Kisaku¨rek,B.,Eisenhauer,A.,Bo¨hm,F.,Garbe-Scho¨nberg,D.,Erez,J.,2008. ControlsonshellMg/CaandSr/Cainculturedplanktonic foraminif-eran,Globigerinoidesruber(white).EarthPlanet.Sci.Lett.273(3–4), 260–269.
Lambeck,K.,Chapell,J.,2001.Sealevelchangethroughthelastglacial cycle.Science292,679–686.
Lambeck,K.,Antonioli,F.,Purcell,A.,Silenzi,S.,2004.Sealevelchange alongtheItaliancoastfromthepast10,000yr.QuaternarySci.Rev. 23,1567–1598.
Lascaratos,A.,Roether,W.,Nittis,K.,Klein,B.,1999.Recentchangesin deepwaterformationandspreadingintheeasternMediterranean Sea:areview.ProgressinOceanography44(1–3),5–36.
LeGrande, A., Schmidt, G., 2006. Global gridded data set of the oxygenisotopiccompositioninseawater.Geophys.Res.Lett.33 (12).
Lea,D., Mashiotta, T., Spero, H.,1999. Controls onmagnesium and strontiumuptake in planktonicforaminifera determined by live culturing.Geochim.Cosmochim.Acta63(16),2369–2379. Levi,C.,Labeyrie,L.,Bassinot,F.,Guichard,F.,Cortijo,E.,Waelbroeck,C.,
Caillon,N.,Duprat,J.,deGaridel-Thoron,T.,Elderfield,H.,2007. Low-latitudehydrologicalcycleandrapidclimatechangesduringthelast deglaciation.Geochem.Geophys.Geosyst.8(5).
Levitus,S.,1982.Climatologicalatlasoftheworldocean. NOAAProfes-sionalPaper.Rockville,Maryland,USA.
Levitus,S.,Boyer.,T.P.,1994.WorldOceanAtlas1994Volume4: Tem-perature,number4.
Mathien-Blard,E.,Bassinot,F.,2009.SalinitybiasontheforaminiferaMg/ Ca thermometry:correctionprocedureand implicationsforpast oceanhydrographicreconstructions.Geochem. Geophys.Geosyst. 10(12),doi:10.1029/2008GC002353.
Mashiotta,T., Lea,D.,Spero,H.,1999.Glacial-interglacialchangesin Subantarcticseasurfacetemperatureandd18O-waterusing
forami-niferalMg.EarthPlanet.Sci.Lett170(4),417–432.
Melki,T.,Kallel,N.,Jorissen,F.J.,Guichard,F.,Dennielou,B.,Berne´,S., Labeyrie,L.,Fontugne,M.,2009.Abruptclimatechange,seasurface salinityandpaleoproductivity inthe westernMediterraneanSea (GulfofLion)duringthelast28kyr.Palaeogeogr.,Palaeoclimatol., Palaeoecol.,doi:10.1016/j.palaeo.2009.05.005.
Nu¨rnberg,D.,Bijma,J.,Hemleben,C.,1996.Assessingthereliabilityof magnesiuminforaminiferalcalciteasaproxyforwatermass tem-peratures.Geochim.Cosmochim.Acta60(5),803–814.
Overpeck,J.T.,WebbIII,T.,Prentice,I.,1985.Quantitativeinterpretation offossilpollenspectra:dissimilaritycoefficientsandthemethodof modernanalogs.QuaternaryResearch23,87–103.
Paterne,M.,Kallel,N.,Labeyrie,L.,Vautravers,M.,Duplessy,J.-C., Ros-signol-Strick,M.,Cortijo,E.,Arnold,M.,Fontugne,M.,1999. Hydro-logical relationship between the North Atlantic Ocean and the MediterraneanSeaduring thepast 15-75kyr. Paleoceanography 14(5),626–638.
Prell,W.,1985.Thestabilityoflow-latitudesseasurfacetemperatures:an evaluationoftheCLIMAPreconstitutionwithemphasisonthe posi-tiveSSTanomalies.P.60,Technical report.TR025,UnitedStates DepartmentofEnergy,Washington,DC.
Prentice,I.C.,1980.Multidimensionalscalingasaresearchtoolin Qua-ternarypalynology:areviewoftheoryandmethods.Rev.Palaeobot. Palynol.31,71–104.
Pujol,C.,Vergnaud-Grazzini,C.,1995.Distributionpatternsoflive plank-tonicforaminifersasrelatedtoregionalhydrographyandproductive systemsoftheMediterraneanSea.MarineMicropaleontology 25, p.187–p.217.
Rasmussen,S.O.,Andersen,K.K.,Svensson,A.M.,Steffensen,J.P.,Vinther, B.M.,Clausen,H.B., Siggaard-Andersen,M.-L.,Johnsen,S.J.,Larsen, L.B.,Dahl-Jensen,D.,Bigler,M.,Ro¨thlisberger,R.,Fischer,H., Goto-Azuma,K.,Hansson,M.E.,Ruth,U.,2006.AnewGreenlandicecore chronologyforthelast glacialtermination.J.Geophys. Res.111, D06102.
Regenberg,M.,Steph,S.,Nu¨rnberg,D.,Tiedemann,R.,Garbe-Scho¨nberg, D.,2009.CalibratingMg/Caratiosofmultipleplanktonic foraminif-eralspecieswithd18O-calcificationtemperatures:paleothermometry
fortheupperwatercolumn.EarthPlanet.Sci.Lett.278,324–336. Russell, A.,Ho¨nisch,B.,Spero, H., Lea,D.,2004. Effects ofseawater
carbonateionconcentrationandtemperatureonshellU,Mg,and Srinculturedplanktonicforaminifera.Geochim.Cosmochim.Acta68 (21),4347–4361.
Sabbatini,A.,Bassinot,F.,Boussetta,S.,Negri,A.,Rebaubier,H.,Dewilde,F., Nouet,J.,Caillon,N.,2011. Furtherconstraints onthediagenetic influences and salinity on Globigerinoides ruber (white) Mg/Ca
thermometry: implications in the Mediterranean Sea. Geochem. Geophys.Geosyst.12(10),doi:10.1029/2011GC003675.
ShackletonN.,1974.Attainmentofisotopeequilibriumbetweenocean waterandthebenthicforaminiferaGenusUvigerina:isotopechanges in theoceanduring the last glacial,Lesme´thodes quantitatives d’e´tudedesvariationsduclimataucoursduPleistocene.Colloques InternationauxdeCentreNationaldelaRechercheScientifiqueCNRS, Paris,pp.203–210.
Sexton,P.,Wilson,P.,Pearson,P.,2006.Microstructuralandgeochemical perspectivesonplankticforaminiferalpreservation:‘‘glassy’’versus ‘‘frosty’’.Geochem.Geophys.Geosyst.7(12),Q12P19,doi:10.1029/ 2006GC001291.
Spero,H.J.,Bijma,J.,Lea,D.W.,Bemis,B.E.,1997.Effectsofseawater carbonate concentrationonforaminiferalcarbonandoxygen iso-topes.Nature390(6659),497–500.
Steinke,S.,etal.,2005.Mg/CaratiosoftwoGlobigerinoidesruber(white) morphotypes:implicationsforreconstructingpast tropical/subtropi-calsurfacewaterconditions.Geochem.Geophys.Geosyst.6. Stephens,C.,etal.,2002.WorldOceanAtlas,2001,Volume1:
Tempera-ture.In:Levitus,S.(Ed.),NOAAAtlasNESDIS49.U.S.Government PrintingOffice,Wash.,D.C,167pp.
Stocchi,P.,Spada,G.,Cianetti,S.,2005.Isostaticreboundfol-392lowing theAlpinedeglaciation:impactonthesealevelvariationsandvertical 393movementsintheMediterraneanregion.Geophys.J.Int.394, 162,doi:10.1111/j.1365-246X.2005.02653.x.
vanRaden,U.J.,Groeneveld,J.,Raitzsch,M.,Kucera,M.,2011.Mg/Cainthe planktonicforaminiferaGloborotaliainflataandGlobigerinoides bul-loidesfromWesternMediterraneanplanktontowandcoretop sam-ples.Mar.Micropaleontol.78,101–112.
Waelbroeck,C.,Labeyrie,L.,Michel,E., Duplessy,J.C.,McManus,J.A., Lambeck,K.,Balbon,E.,Labracherie,M.,2002.Sealevelanddeep watertemperaturechangesderivedfrombenthicforaminifera isoto-picrecords.QuaternaryScienceReviews21,295–305.
