PALEOCEANOGRAPHY,VOL. 16,NO. 1, PAGES40-52, FEBRUARY 2001
Variability of the western Mediterranean Sea surface
temperature during the last 25,000 years and its
connectionwith the Northern Hemisphere
climatic changes
Isabel
Cacho,
•'2'3
JoanO.Grimalt,
• MiquelCanals,
4LauraSbaffi,
5
NickJ. Shackleton,
sJoachim
Sch6nfeld,
6andRainerZahn,
6'7
Abstract. Seasurfacetemperature
(SST)profilesoverthelast25 kyr derivedfromalkenonemeasurements
arestudied
in fourcoresfroma W-E latitudinaltransect
encompassing
theGulf of Cadiz(AtlanticOcean),theAlboranSea,andthe
southernTyrrhenianSea(westernMediterranean)..The
resultsdocument
the sensitivityof the Mediterranean
regionto
the shortclimatf•changesof theNorth AtlanticOcean,particularlythoseinvolvingthe latitudinalpositionof the polar
front.The amplitudeof the SST oscillations
increases
towardthe TyrrhenianSea,indicatingan amplificationeffectof
the Atlanticsignalby the climaticregimeof theMediterranean
region.All studiedcoresshowa shortercoolingphase
(700 years) for the Younger Dryas (YD) than that observedin the North Atlantic region (1200 years).This time
diachroneityis relatedto an intra-YD climaticchangedocumented
in the Europeancontinent.Minor oscillationsin the
southwarddisplacement
of the North Atlanticpolar front may alsohavedriventhis early warmingin the studiedarea.
Duringthe Holocenea regionaldiachroneitypropagating
westto eastis observedfor the SST maxima,11.5-10.2kyr
B.P. in the Gulf of Cadiz, 10-9 kyr B.P. in the Alboran Sea, and 8.9-8.4 kyr B.P. in the ThyrrenianSea. A general
coolingtrendfrom theseSST maximato presentday is observedduringthis stage,which is markedby shortcooling
oscillationswith a periodicityof 730+40 yearsandits harmonics.
1. Introduction
high resolutionin a transectof four marinecoresfor the last25
kyr. These cores are situatedat similar latitude but represent
differenthydrographicconditions,from openoceanwaters(Gulf
of Cadiz) to enclosed basin conditions (Thyrrhenian Sea)
includingthe Atlantic-Mediterranean
exchangearea (Alboran
Sea). The samplingresolutionand age models afford the
The Mediterranean Sea is a semienclosed water body
surroundedby large continentalmasseswith only one narrow
connectionto the Atlantic Ocean. The hydrodynamicsof the
basin is controlled by the North Atlantic water inflow, wind
regime,and climateof the surroundinglands.Recentresearchon
the last glacial period has demonstrateda dependenceof the
western
basin
from
the
millenial-centenial
climatic
identification
of
centennial-millennial-scale
oscillations.
The
resultsare discussed
in the contextof the previousknowledgeon
marine and terrestrialclimatic variability of the Mediterranean
and North Atlantic regions.
and
oceanographic
variability in the North Atlantic [Rohlinget al.,
1998; Cachoet al., 1999a; Paterne et al., 1999]. However,the
lastdeglaciationand Holoceneperiodswere alsocharacterized
by
short-term climatic variability, which was recorded either as
intense, e.g., the Younger Dryas (YD), or lower-amplitude
oscillations[Bondet al., 1997].
The presentstudyis devotedto elucidatethe significanceof
this shortterm variability for the westernMediterranean.For this
purpose,alkenone-derivedsea surfacetemperatures(SST) and
2. Core Location and OceanographicSetting
The coresstudiedencompass
a seriesof four sitesfrom similar
latitude, located on a W-E latitudinal transect from the Gulf of
Cadiz in the Atlantic Ocean to the southernTyrrhenian Sea
(Figure 1). CoreM39-008 (39ø22.8'N,7ø4.6'W,waterdepth576
m, core length of 570 cm) was recoveredfrom the northeastern
15180
profiles
of Globigerina
bulloides
havebeenanalyzed
at
Gulf of Cadizby RV Meteor [Schottet al., 1999].Pistoncore
MD 95-2043 was obtainedin the centralAlboran Sea (36ø 8.6'
N; 2ø 37.3' W; 1,841m waterdepth;corelength3600 cm) by RV
Environmental
Research
(CSIC),Barcelona,
Catalonia,
Spain.
Marion Dufresneduring the 1995 Intemationa!Marine Global
2 AlsoatG.R.C.
Marine
Geosciences,
Department
of Stratigraphy
and ChangeStudies(IMAGES) cruise.Cores BS79-38 (38ø24.7'N,
Paleontology,
University
of Barcelona,
Barcelona,
Catalonia,
Spain.
3 Nowat Godwin
Laboratory,
University
of Cambridge,
Cambridge 13ø34.6'E,waterdepthof 1489 m, 515 cm long) and BS79-33
(38ø15.7'N,14ø1.8'E,waterdepthof 1282m, 485 cm long)were
England,UnitedKingdom.
4 G.R.C.MarineGeosciences,
Department
of Stratigraphy
and recoveredfrom neighboringlocationsin the southernTyrrhenian
I Department
of Environmental
Chemistry,
Institute
of Chemical
and
Paleontology,
Universityof Barcelona,
Barcelona,Catalonia,Spain.
Sea.
s Godwin
Laboratory,
University
of Cambridge,
Cambridge
England,
The MediterraneanSea is a concentration
basinexchanging
water with the open oceanonly throughthe Strait of Gibraltar.
The water transportat this site is conformedby a low-salinity
surfacelayerof AtlanticWater enteringinto the Mediterranean
UnitedKingdom.
6GEOMAR
Research
Center
forMarine
Geosciences,
Kiel,Germany.
? Nowat Department
of EarthSciences,
CardiffUniversity,
Cardiff,
Wales,UnitedKingdom.
Seaanda deepsalt-richlayerof Mediterranean
waterflowingout
Copyright2001by theAmericanGeophysical
Union.
to the Atlantic Ocean.The Atlantic Water inflow comesdirectly
from the Gulf of Cadiz, entersinto the AlboranSea, whereit
describes
two anticyclonicgyres,and continueseastwardalong
the Algeriancoastformingeddies(Figure 1). Aboutonethird of
Papernumber2000PA000502.
0883-8305/01/2000PA000502512.00
40
CACHO ET AL.: WESTERN MEDITERRANEAN SEA TEMPERATURES
I
45 ø -
Gulf
of
41
I
.
..
_J
40 ø
ß
_)
'"adiz
F'"•.
•'
. A
35 ø
Sicily
ß
Sea /
• .........
l.......................
I.......
'
0ø
-5 ø
0ø
5ø
.
10 ø
15 ø
20 ø
25 ø
30 ø
35 ø
Figure1. Locationof thefourcoresconsidered
tbr studyThepresently
dominant
superficial
circulation
patternis
indicated.
the
flow
of
the
now
modified
Atlantic
Water
enters
the
Tyrrhenian Sea following the northern Sicilian coast. The
remainingtwo thirds of the Atlantic Water crossthe Strait of
Sicily to the eastern Mediterranean [Millot, 1987]. All cores
selectedfor this study are locateddirectly underthe present-day
pathof this AtlanticWater mass.
Vertical mixing in the Alboran Sea occursbecauseof the
strongshearat the interfacebetweeninflowing and outflowing
watermassesthroughthe relativelynarrowand shallowGibraltar
sill [Bray et al., 1995]. The anticyclonicgyre describedby the
inflowingAtlantic jet into the westernAlboran Sea fom-•san
upwellingcell which bringscold water to the surfacealong the
Spanishcoastbetween Gibraltar and Malaga [Perkinset al.,
1990]. In addition, noticeablyvertical and lateral fluxes are
relatedto frontalregionsdevelopedat theboundaries
betweenthe
Atlanticjet and surrounding
waters[Peinertand Miquel, 1994].
Therefore,althoughthe coresselectedfor studyare locatedat
almost the same latitude (36ø-38øN), they monitor different
stagesof alteration of the Atlantic Water entering into the
Mediterranean
Sea.
3. Experimental Section
3.1. Sea Surface Temperature (SST) Reconstruction
SST was obtained from the relative compositionof C37
unsaturated
alkenones
through
theuK'3,index[Brassell
et al.,
thickness
of 0.12 m). Hydrogenwasthe carriergas(50 cm/s).
The oven temperature
was programmed
from 90ø to 140øCat
20øC/rain,thento 280øCat 6øC/min(holdingtime 25 rain), and
finally,to 320øCat 10øC/rain(holdingtime of 6 min). The
injector
wasprogrammed
from90øC(holdingtimeof 0.3 rain)to
320øCat 200øC/min
(finalholdingtimewas55 rain).Forfurther
detailson analyticalconditions
usedin thisstudy,seeVillanueva
etal. [1997].Replication
of a sediment
sample
withsimilarlipid
content
anduK'3?
index(n = 5) showed
a standard
deviation
of
+0.15øC in temperatureestimation.
The coresfromthisstudyarelocatedwithinthe influenceof
the inflowing North Atlantic Surface Water. The most
appropriate
conversion
equation
is therefore
thegeneral
uK'3,
calibration
(UK'3,-0.033SST+ 0.044),whichincludes
sediment
samples
fromtheNorthAtlanticOcean[Miilleret al., 1998].
RecentuK'3,studies
carriedouton suspended
particulate
matter
from the Gulf of Lionsandsurrounding
areahaveshownthatthe
general
uK'3v
calibration
[Prahletal., 1988;Millletetal., 1998]
provides
anomalous
SST in this zone[Ternoiset al., 1997;
Bentalebet al., 1999;Cachoet al., 1999b].In thisareaIhe water
column measurements
reflect a good correlationwith present
SST datawhena specificcalibration
is used[Ternoiset al.,
1997].Nevertheless,
eveninthisparticular
zone,thesedimentary
UK'3?
indices
onlyprovidereliableaverage
annualSSTthrough
thegeneral
equation
[Cacho
etal., 1999b].Thisgeneral
equation
[Miiller et ai., 1998] is thereforethe one chosenfor
transformation
oftheuK'37
dataintoSSTin thepresent
study.
1986].Sedimentsamples(---2g) werefreeze-dried
andmanually
grounded. After addition of an internal standard mixture
containing n-nonadecan-l-ol, n-hexatriacontane,and n-
tetracontane,
dry sediments
wereextracted
in an ultrasonic
bath
with dichloromethane.The extractswere hydrolyzedwith 6%
potassiumhydroxide in methanol,and the alkenoneswere
recoveredwith hexane. The solventwas evaporatedto dryness
3.2. Isotopic Measurements
Stableisotope
measurements
of G. bulloides
forcoresMD 952043, BS79-33, and BS79-38 were made in a SIRA mass
spectrometer
at the GodwinLaboratory(Universityof
Cambridge)
usingsamples
of 25-30specimens
pickedfromthe
Themassspectrometer
is fittedwiththe
with a N2 stream,andthe extractswere finally redissolved
with 300-355gmsizerange.
VG isocarbcommonacidbathsystem.Analyticalreproducibility
tolueneandderivatized
withbis(trimethylsilyl)trifluoroacetamide
of laboratory
standards
is betterthan+0.08ø00
for •O.
beforeinstrumental
analysis.
Alkenones
wereanalyzedwith a VariangaschromatographCalibrationto Vienna Peedeebelemnite (VPDB) is via the
Model3400equipped
with a septurn
programmable
injectorand NBS 19 standard.
a flameionizationdetector.The instrumentwas equippedwith a
CPSIL-5 CB columncoatedwith 100% dimethylsiloxane
(film
In core M39-008, stableisotopemeasurements
were carried
outwith9-11 specimens
of G. hulloides
fromthesizefraction
42
CACHO ET AL.: WESTERN MEDITERRANEAN SEA TEMPERATURES
>250 gin, each5 cm. The testswere crackedandultrasonically
rinsedin methanolprior to analysis.Measurements
weredoneat
GEOMAR isotopelaboratorywith a CARBO KIEL automated
carbonate
preparation
devicecoupledto a FINNIGAN MAT 251
differentconnotations
(chronozones
andbiozones)andboundary
age uncertainties
[Ammannand Lotter, 1989; Broecker,1992;
•aIker, 1995; Wohlfarth, 1996; BjOrck et al., 1998]. To avoid
confusionderived from the classicalnomenclature,a new event
massspectrometer.
Reproducibility
for •5•80was:t:0.056%o
(1cr
stratigraphy
hasbeenproposedfor the North Atlanticregionon
value,n=42internalcarbonate
standard
measurements).
thebasisof the15180
fromGreenland
icecores[BjOrck
et al.,
1998;•alker et al., 1999].For thispurpose,
the GRIP •80
profile is divided in a seriesof Greenlandstadial (GS) and
interstadial(GI) periodsfollowingthe procedureusedin marine
isotopicstratigraphy.
This eventstratigraphyprovidea continuos
4.1. Age Models for Sediment Cores
and more.detailedsubdivisionfor the Last Glacial-Interglacial
Radiocarbon
agesfor all cores(Table 1) havebeenconverted transitionoscillations,fixing clearly the locationand timing of
into calendar
ageswith the Calib.4.1 programwhichusesan the differentboundarieswithout the problemsderived from the
4. Stratigraphy
and Lotter,1989;BfiSrck
et al., 1996;
updated
calibration
dataset[Stuiver
et al., 1998]andincludes
the •4C dating[Atomann
correction
foroceansurface
reservoir
effects[Bardet al., 1994]'. Hughenet al., 1998]. This new stratigraphyis usedin the present
Theagemodelfor coreM39-008hasbeenconstructed
by linear study,but the terminologyof someof the traditionaleventsis
interpolationbetween 10 calibrated •4C acceleratormass occasionallyused in the text. For clarification of possible
spectrometry
(AMS) carbonagesand two moreage control confusion,the new stratigraphyis comparedwith the traditional
points
determined
fromthe8180profileof G.bulloides.
The14C terminologyin Figure3.
ages were determined in monospecific samples of
Globigerinoides
tuber(white)containing
555-1037testsfromthe
>150/•m sizefraction.The sampleswere cleanedwith 15-30%
5. Results
H202in an ultrasonic
bathbeforeanalysis.
Radiocarbon
ages 5.1. Isotope Records
All studied
8•80profiles
fromG. bulloides
(Figure2) showa
were determinedat the Leibniz-LaborAMS facility of Kiel
University[Nadeauet al., 1997]. The precisionof the ages
rangesfromñ25 to ñ150 years(standarddeviation).
The two
additional
8t80points
wereselected
by correlation
withtheG.
buIloides
8•80profileof coreSU81-18,theneighbor
core
previously
datedby several
•4CAMSages[Bardetal., 1987].
Thesetwo pointsconfirm the timing of the ice-rafteddetritus
(IRD) layercorresponding
to HeinricheventH1 (Figure2).
CoreMD 95-2043has an accuratechronostratigraphy
based
on 18 •4CAMS agesfor the last20 kyr (Table1). AMS
measurements
were determinedin the Universityof Utrechtwith
a precisionrangingfrom ñ37 to 4-120years.The oldersectionhas
beendatedby correlationof the alkenoneSST profilewith the
8•O record
oftheGreenland
icecoreGISP2(seemore
details
in
the work by Cacho et al. [1999a]). The correlationcoefficient
betweenMD 95-2043 SST and GISP2/5•O overthe •4C dated
intervalis extremelyhigh (R=0.92).
SevenAMS carbonageshavebeenusedfor the agemodelof
core BS79-33 (Tyrrhenian Sea). These were measured in
monospecific
samples
of G. tuberor G. bulloides(Table1) in the
laboratoryof the Centre des FaiblesRadioactivit•s(Gif-surYvette), providinga precisionbetweenñ70 and :t:220years.
Subsequent
improvement
of the agemodelhasbeenobtainedby
correlationof the •.80 recordsfrom G. buIIoidesand G. tuber
with thoseof coresAC 85-4, GT 85-5 andET 91-18(Tyrrhenian
goodagreementin both the generaltrendsandthe timing of the
major oscillations.This featureverifies the consistency
of the
different core chronologies.The onsetof the isotopicdepletion
associated
to the last deglaciationappearsat-16.5 kyr B.P., and
a seconddepletion phase started at 15 kyr B.P.. The YD is
represented
in all the coresby a shortenrichment(0.25%oin the
Gulf of Cadiz and 0.75%0 in the Mediterraneancores), which
lasted-1100 years.All profiles reachedHolocenevalues at 10
kyr B.P..
Absolutevaluesare alwayslower in the Gulf of Cadiz than in
the Mediterraneancores, a difference that is larger during the
glacialperiod(1-1.5%o)than duringthe Holocene(0.5%o).All
Mediterraneancores show similar values during the Holocene,
while glacialanddeglaciationvaluesare lower by ~0.5%0in the
Alboran Seathanin the TyrrhenianSea.
5.2. Sea SurfaceTemperature Records
SST curvesdisplaysimilartrendsthan thosefrom the isotopes
(Figure 4) but in general,they show more abruptoscillations.
Minimumvaluesarerecordedduringthe glacialperiod.Warming
of the last deglaciationlasted •6000 years, with total SST
increases of ~7 ø and -•9øC in the Gulf
of Cadiz
and the
MediterraneanSea, respectively.Holocenevalueswere always
reached
before11 kyr B.P., arrivingto maximumtemperatures
in
Sea),whichwere datedwith a largenumberof •4C AMS
the early Holocene,althoughnot synchronously
betweenthe
measurements
[Capotondiet al., 1999]. Combinationof the age
differentareas.Thereafter,HoloceneSST follow a weak cooling
points resultingfrom the two dating serieshas provideda
trend towards present day. The major difference between
consistent
agemodel.In coreBS79-38the planktonic
•80
HoloceneSST in the differentareasconcernsthe first phaseof
profileshavebeencorrelated
withthosereportedfromCapotondi
the
deglaciation
warming.This occurredas an extremelyabrupt
et al. [1999].
pulse in the Gulf of Cadiz while it was slower in the
Mediterraneansites.The YD is well markedin all coresby a 3ø4øC coolingwhichlasted---700years.
4.2. Chronostratigraphyof the Last Deglaciation
Absolutevaluesarealwayshigherin the Gulf of Cadizthanin
Traditionally,paleoceanographical
and paleoclimatological the Mediterraneanwhich is in agreementwith the present-day
studiescoveringthe last deglaciation,TerminationI (T!), usea
oceanographicalpattern (see section 2). This Atlanticclassicalsequence
of climaticperiods(OldestDryas,Belling, Mediterraneangradientwas larger during the glacial period
Older Dryas,Allerod,YoungerDryas,and Preboreal),whichwas
(~4øC) than duringthe Holocene(-•1-2øC).Similar valuesare
firstproposedfor the Fenoscandian
regionon thebasisof pollen recorded between the Mediterranean cores, although the
evidence[Mangefurlet al., 1974]. The world wide use of this
Tyrrhenian cores always show larger amplitude in the short
terminologyhas been widely criticized becauseit has several oscillations,
especiallyduringtheHolocene.
CACHOET AL.: WESTERNMEDITERRANEANSEATEMPERATURES
43
Table1.DatedPoints
UsedintheAgeModels
Indicating
theMeasured
•4CYearsandthe
Calibrated
AgesObtained
WiththeCalib4.1Program
a
Depth, LaboratoryNumber
cm
Age
Dated
Source
CalendarSedimentation Sampling
Species 14C
age years Rates,
caffkyrResolution,
years
co•z MJ9O08(GuZfof Cact•z)
8
18
28
38
91
190
288
KIA6969
KIA7639
KIA7640
KIA7641
KIA7642
KIA7643
KIA7644
358
KIA8131
403
458
529
564
KIA8581
KIA8132
I4CAMS
•4CAMS
14CAMS
•4CAMS
•4CAMS
14CAMS
t4CAMS
G.ruber
G.ruber
G. ruber
G. ruber
G.ruber
G. ruber
G. ruber
14CAMS
'
2,660
4,195
4,875
5,910
7,755
8,445 ß
8,755
2,332
4,282
5,240
6,301
8,193
8,935
9,238
5.1
10.4 •
9.4
28.0
133.4
323.4
51.0
975
479
530
178
37
15
98
10,610
22.3
224
G. tuber
9,860
Bardetal.[1987]
Bardetal.[1987]
11,080
b
13,980
b
12,626 15.6
16,143 33.1
320
150
•4CAMS
•4CAMS
G. ruber
G. tuber
15,800 18,285
18,370 21,243
11.8
422
1,527
3,011
4,396
6,018
7,401
27.0
30.3
50.6
43.4
38.1
186
165
99
115
131
COREMD 95-2043 (AlboranSea)
14
54
96
178
238
•4CAMS
t4CAMS
•4CAMS
14CAMS
14CAMS
G. bulloides
G. bulloides
G. bulloides
G. bulloides
G. bulloides
298
•4CAMS
N.pachyderma8,530
8,976
58.8
85
348
t•CAMS
G.bulloides 9,200
9,827
70.9
71
418
487
512
588
•C AMS
•CAMS
•4CAMS
14CAMS
N.pachyderma
9,970
N.pachyderma10,560
N.pachyderma10,750
N.pachyderma11,590
10,815
11,659
12,021
13,081
81.8
69.1
71.7
22.0
61
72
70
227
595
682
incAMS
14CAMS
G.bulloides 11,880 13,399
G.bulloides 12,790 14,289
97.8
54.9
51
91
708
758
802
858
870
•4CAMS
•4CAMS
œ4C
AMS
•4CAMS
GISP2
14,762
16,617
17,871
21,116
21,310
27.0
35.1
17.3
61.9
11.4
185
143
290
81
438
23,410
24,000
24,740
25,530
26,850
27,740
28,290
29,030
30,100
33.9
35.1
12.7
25.8
18.0
18.2
40.5
13.1
20.5
148
142
395
194
278
275
123
382
244
19.2 ,
23.2
30.6
19.6
23.1
21.3
35.6
14.1
260
216
98
256
449
235
281
354
894
914
940
950
984
1000
1010
1040
1054
GISP2
GISP2
GISP2
GISP2
GISP2
GISP2
GISP2
GISP2
GISP2
37
65
150
210
237
282
333
405
470
boundary
1-2
boundary
2-3
boundary
3-4
boundary
4-5
boundary
5~6
boundary
6~7
boundary
7-8
boundary
8-9
boundary
9-10
1,980
3,216
4,275
5,652
6,870
N.pachyderma
13,100
N.pachyderma
14,350
N.pachyderma
15,440
N.pachyderma
18,260
-
-
COREBS79-38(Tyrrhenian
Sea)
2,800
*
4,000
*
7,200
*
9,000
ø
10,000
½
11,400
½
13,200
•
15,000
½
19,000
•
2,530
3,985
7,656
9,615
10,995
12,945
15,343
17,365
21,968
44
CACHO ET AL.: WESTERN MEDITERRANEAN
SEA TEMPERATURES
Table 1. (continued)
Depth, LaboratoryNumber
cm
Age
Dated
source
Calendar Sedimentation
Sampling
Species
... •4C.ageyears Rates,
cm/kyrResolution,
years
CORE BS79-33(TyrrhenianSea)
57
98
115
120
136
150
175
185
204
225
249
295
340
360
450
boundary
1-2
boundary
2-3
•4CAMS
boundary
3-4
•4CAMS
boundary
4-5
boundary
5-6
t4CAMS
boundary
6-7
•aCAMS
boundary
7-8
taCAMS
•aCAMS
boundary
9-10
•4CAMS
2,800c
4,000c
G.rubber 6,310
7,200•
G. rubber' 8,160
9,000•
10,000c
G. bulloides !0,830
11,400•
G. bulloides 12,910
13,200;
G. bulloides 15,480
G. bulloides 16,990
19,000;
G. bulloides 24,120
2,530
3,985
6,747
7,656
8,615
9,615
10,995
12,225
12,945
14,343
15,343
17,917
19,655
21,968
27,608
26.0
10.0
4.4
14.2
12.5
21.9
9.0
17.9
19.0
22.4
39.4
41.0
17.9
71.6
532
396
1,721
300
1,002
633
1,230
189
551
625
1,062
859
947
503
a SeeStuiveret al. [1998]for Calib4.1 program.
Sedimentation
ratesandthe averagetimeresolution
for the SST
measurements are also indicated.
bDataaretaken
fromBardetaI.[1987]
without
correction
forreservoir
effect.
cDataaretakenfromCapotondi
etal. [1999]withoutcorrection
forreservoir
effect.
6. Discussion
The isotopicandthermalgradientsbetweenthe Gulf of Cadiz
andthewestern
Mediterranean
Searemained
throughout
thelast
20 kyr B.P.. Thesegradientschangedin intensitybut neverin
direction, supporting the hypothesis that the wetern
Mediterranean
Seaworkedas a concentration
basinalongthis
full period[Rohlingand De Ro'k,1999].The largestdifferences
are observedin the glacialperiods,reflectingan increasing
isolation
of theMediterranean
Seawhichoperated
asanamplifier
All the SST profiles depict relatively stablevalues during
mostof GS-2 (GS-2b and GS-2c) followingan overall slightly
warmingtrend. Such a stability is in strongcontrastwith the
rapid SST variability documentedfor isotopicstage 3 in the
Alboran Sea [Cacho et al., 1999a]. A similar stablepatternis
observedduring isotopicstage2 in North Atlantic mid latitude
sites,asevidencedfrom foraminiferal-derived
paleotemperatures
(core SU90-03 at 40øN [Chapmanand Shackleton,1998] and
coreCH69-09 at 41øN [Waelbroecket al., 1998]) and alkenone
SST (coreMD 95-2037 at 37øN (E. Cairo et al., New insights
of theprevailing
coldandaridglacialconditions.
Thehighest into the glacial latitudinaltemperaturegradientsin the North
SSToscillations
recorded
in theTyrrhenian
coresmayreflectthe Atlantic:Results
from U}C37-sea
surfacetemperatures
and
strongercontinentalinfluence of this area in contrastto the more
terrigenousinputs,submittedto Earth and Planetary Science
oceanicregimeof the Atlantic site.
6.1. Glacial
Period
The SST profilesshowrelativelycold valuesfor the glacial
period, but the lowest values are not coincident with the Last
GlacialMaximum(LGM) (18.5-20 kyr B.P.).TheseSSTminima
areconfinedto rapideventsrelatedwiththeHeinrichevents(HE)
asobservedin coreMD 95-2043 [Cachoet al., I999a]. H1 and
H2 are well correlatedin the Alboran and TyrrhenianSST
profiles,whichhighlightsH2 asthecoldestperiodforthelast30
kyr (Figure 4). Polar water entrancethrough the Strait of
Gibraltarhasbeenproposedasthe main mechanism
responsible
for thiswatercoolingin theAlboran[Cachoet al., 1999a]andin
the Tyrrhenian[Paterneet al., 1999] Seas.This hypothesis
is
stronglysupportednow by the documentationof IRD occurrence
during H1 in the Gulf of Cadiz (Figure 2). However,
intensification
of the NorthernHemispherewind systemscould
alsohaveplayedan importantrole in theseMediterraneanwater
Letters, 2000)). In contrast,the cores from northern latitudes
showwell-definedSST minima coveringthe whole GS-2 (core
BOFS5K at .--51øN[Maslin et al., 1995]) or exhibitinga clear
coolingtrend(core SU90-08 at 43øN [Villanuevaet al., 1998;
Paterneet al., 1999]).This latitudinalcontrasthasbeendiscussed
by Chapmanand Maslin [1999] and was interpretedto result
from seasonal
insolationincreaseoverlow latitudes,which led to
enhanced
transport
of atmospheric
moisture.Higheratmospheric
moisture stimulatedNorthern Hemisphereice sheet growth
duringthe LGM.
The resultsof the presentstudyindicatethat the equatorial
SST warmingextendedinto the Mediterraneanregion by the
easternboundarycurrentfromtheAtlanticsubtropical
gyre.This
situationwould producea strongmeridionalgradientbetween
40øand50øNin theNorthAtlanticOcean[Chapman
andMaslin,
1999] in agreement
with the LGM positionof the polarfront
reconstructed
by Climate.'Long-RangeInvestigation,Mapping
andPrecipitation
(CLIMAP)ProjectMembers[1976].
coolings[Rohling et al., 1998; Cacho et al., 1999a]. An
6.2. First Phaseof the Last Deglaciation
atmospheric
transmission
of rapidclimatechangeissupported
by
the oscillations
in the relativeabundance
of treepollenat Lago
In all locationsconsideredin the presentstudy the last
Grandedi Monticchioand Lago di Mezzano (southernItaly)
deglaciation
warmingstartedimmediatelyafterH1, prior to the
following the HE and Dansgaard-Oeschger
(D-O) oscillations onset of the late glacial interstadial (GI-1) in the
[ Wattset al., 1996;Allen et al., 1999].
chronostratigraphic
controlof Greenland
ice cores(Figure3 and
CACHOETAL.:WESTERN
MEDITERRANEAN
SEATEMPERATURES
45
Cal. age in kyr
0
I
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 2.324 25 26 27
I
I
I
!
I
I
I
I
l:
I _l
.I
I
I
I . I
I
I
!
I
I
!
I
I
I
,
ß
HOLOCENE;
LGM
-32.5
-35-
-37.5-40 -42.5-
I
-45
I
I
I
I
!
.-. 0.75Gulf of Cadiz
-o
ß
(M39-008)
o
0.35
c•
_
o.•s- (MD95-2043)
!
I
I
I;
,
I
!.1_ !
i
:
!l
! . t_
ß
ß
...
ß
AlboranSea
O-
ß
ß
,
ß
ß
ß
ß
ß
_'
* ;.,
i !,ß
: :: :i
:
•
•
:,
:
-3
,
Tyrrhenian
Sea
!
(BS79-38)
ßi •* !"•"•'
,,•.•
ß
ß
ß
ß ß
ß
•:
'
i
:
ii
[
: ß
• 2'
O
ß
[
, i
•'
•
ß
i:
'ß:
•,
i
:
!
:
! ß
o
,,
-1
o...:
.
o
i :
:
,
-
4
:
3-
•o 4
0
I
I
I
I
I
J' I
!
I
I
2
3
4
5
6
8
9
7
I ' I •'I
10
11
12
;I
13
• :I
14
15
I
i'
I
16
17
18
19
20
21
22
I
!
I
i
23
24
25
26
27
Cal. age in kyr
* Calibrated•4CAMS ages
o
Coorrelation
with GISP2
ß Coorrelationwith Bard et al. (1987)
ß CoorrelationwithCapotondiet al (1999)
Figure2. Profiles
of G. bulloides
6t80fromthestudied
coresandice-rafted
detritus
(IRD)forcoreM39-008
compared
withtheb'gOrecordfromtheGISP2Greenland
icecore[Grootes
etal., 1993].Theeventchronology
proposedby the Integrationof Ice-core,MarineandTerrestrialrecords(IMITATE) group[BjOrcketal., 1998]
(seeFigme3) isindicated.
Thepoints
drawn
overthe5'•Ocurveof eachcoreindicate
thelocation
of thedated
pointsusedin theagemodels(seeTable 1).
4), the so-called
Bollingtransition.
This warmingphaseis the
most distinctivefeature amongstthe variousbasinsstudied.
Whilein theGulfof Cadiz,thiswarnting
occurred
asa singleand
extremelyrapid pulse at-16 kyr B.P.; in the Tyrrhenianand
AlboranSeasthewarmingfolloweda stepwise
pattern.
Thusall
Mediterranean
coresshowcolderSSTat thebeginning
of thelast
glacialinterstadial
(GI-le or Bollingperiod)thanattheend(GIla to Gl-lc or Allemdperiod),just the opposite
of whatis
observed in most temperature records previously reported.
Pollen, beatles, and also Greenland Ice Core records show that
the initial warming in North Atlantic borelandsoccurredas a
single and rapid pulse, teaciting maximum values at the
beginningof the B•lling episodefollowed by a coolingtrend
throughoutthe full B•lling-Allerod (B-A) period[Johnsenet al.,
1992; Lowe et al., 1994; Coope and Lemdahl, 1995; Stuiver et
a!., *.995; Walker, 1995]. In contrastwith the terrestrialrecords,
46
CACHO ET AL.- WESTERNMEDITERRANEAN SEATEMPERATUGS
theB-Amarine
pattern
variesfromplaceto place.Foraminifera- with colder internradianwaters, may have been the mechanism
derivedSSTfromnorthwest
Scotland
closelyparallel
tile
responsiblefor an intensivecoolingof the warm infiowing
coolingtrendof theterrestrial
records
[1tafiidason
et al., 1995,' waters, thus modifying the Atlantic signal. Enhanced water
Kroon et al., 1997], while diatomSST reconstructions
from the
exchangeduringthis period,probablyrelatedto sea level rise,
Norwegian
Seashowanalmost
fiatB-Aperiod[Ko½
Kaq9uz
and hasbeenpreviouslydocumentedby sedimentologicalandbenthie
Jansen,1992].This marineheterogeneity
pointsto a rather fauna analysesin the Gulf of Cadiz [Caralp, 1988; Grousse!et
complex
oceanographic
response
totileglobalwarming
related
to al., 1988; Sierro et al., 1999]. This vertical mixing shouldalso
the firstphaseof the TI.
drivea nutrientfertilizationof surfacewaters,increasing
primary
Thesharpness
of thiswarming
phase(4øCper---225 years) productivityas is supportedby studieson diatom assemblages
related
to GI-1in theGulfof Cadizhasalsobeenreported
inthe [Abrahies, 1988] and planktonic foraminifera [Ve•naudIberianmargin[Bardet al., 1987].It likelycorresponds
to the Grazzi)•iand Pierre, 1991]. The warm B-A SST were only
rapidnorthward
migrationof thepolarfrontaftertheoccurrence reachedafter-14.5 kyr B.P. probablydue to a weakeningof the
of HI, leading
to tilearrivalof surface
warmsubtropical
waters water mixing processesas is also suggestedby tile primary
to the Gulf of Cadiz.Surprisingly,
thisabruptchangein the productivity proxies [Abrarites, 1988; Vergnaud-Grazziniand
surface
watermasssource
isnotdetected
intheAlboran
Sea(4øC Pierre, 1991].
per-2000 years)nor in the Tyrrhenian
Sea(4øCper---3000
Tile SST profilesof the lastdeglaciationalsodocumentsome
years) which are under the direct influence of the surface
short-termvariabilityby the occurrence
of somebrief coolings
infiowingwaterfromtheGulfof Cadiz(seesection
2). Local
processes,
suchasan intensification
in theverticalwatermixing
profiles also report some short oscillations as the well
Greeland
ice
b•80
whichwere more illtensein the TyrrhenianSea. The
core
Greeland
IMITATE
- GRIP
event
stratigraphy
LD clasical
ice
core
Alboran
(5180- GISP2
sequence
over GISP2
(Bjdrck
etal.1998)•tuiver
etal.1995)
SST
(MD95-2043)
9 , 11
13 15 17 19 21
! , I , ! , ! , ! • I
_
_
I
_
,; ß
_
_
9.
-
o
('3
0:)
lO
-
"'
_
. 10
.
11
ß
12
GS-1
Younger-
''
-
- 12
D
r..Y..:..a...•..4•::
..............
i•iiiiiiiiiiiiiiiiiiiiii
iiii •-• G,.1Ga
S-1
o, ......... ....... 13
L
GI-lC
•' 14-
.•
•)
....
GI-1
e
ø"'ø"
15
O3
_
•/;ii•ng................
i}1111}11"'•
..............
- •-
14
•
ß
15
•c•
16
=
GS-2a
16
O 17
18-
GS-2b
9
.
GS
2a
17
'-,
18
19-
19
......................................
.............................
:'._.
...........
J.......................
1.1111...
2O
21................
GI-2
22-
i............................
.............
22
23'
23
...........
H2
24
H2
25
24
25
.
.
Isotopic
Stage 3
27.....•,.,,,
•5----•.,,,
•....•''....
-45
-42.5
-40
-37.5
-35
-32.5
...........
-45
-42.5
I ....
-40
-37.5
27
i ....
-35
-32.5
Figure
3. Correlation
between
8's0fi-orn
thetwoGreenland
icecores,
GISP2
[Grootes
etal.,1993]
andGRIP,
[Johnsenet al., 1992;Dansgaardet al., 1993;Grooteset al., 1993],andthe AlboranSeaalkenoneseasurface
temperature
recordfromcoreMD 95-2043.Figure3 shows
theclassical
lastdeglaciation
sequence
[Mangerud
et
al.,1974]indicated
overGISP2•5'•Oprofile
byStuiver
etal.[1995]anditscorrespondence
withthenewevent
chronology
proposed
by theIMITATE group[BjSrcket al., 1998].
26
CACHOET AL.' WESTERNMEDITERRANEAN
SEATEMPERATURES
47
Cal. age in kyr
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
i
I •
i
i
I
I
I
I
I
I
i
!
I
I
I
I
I
GS-2
HOLOCENE
'
::
GS-2a
GS-2b
H1
LGM
-32.5
I:
:GS-2c Of
J
,
,
"!
i
-35
.--. -37.5
o
Greenland
Ice
Core
GISP2
-40
-42.5
I
-45
I
I
I
I
!
!
I
cc1
Gulf of Cadiz
I
!
(M39-008)• •.*•,.•.••=••
(MD95-2043)
;I
I
:1
i
!
i_
i
i,
I
23
CC31
Alb:n
Se•a
22-
!!
cc2
-21
-19
....
AC2
/•c4
AC3
-17
•..
03
-15 •
2O
-13
'-'
-11
?
16
•
14
ß
9
12
Tyrrhenian
10
Sea
.
(BS79-38)
TC4
- 22
'
- 20
8
-18
03
-16
.-..
o
-14
ß
22
12
.
20
lO
18
•
16
•-
14
:
;
:
12
10
8
0
I
I
I
I
I
I
I
I
I
I
2
3
4
5
6
7
8
9
10
I
I
I
11
12
13
14
I
I
I
I
I
I
I
I
I
I
I
I
15
16
17
18
19
20
21
22
23
24
25
26
27
Cal. age in kyr
Figure4. Alkenone
SSTprofilescompared
to the8•s0record(toppanel)of theGreenland
icecoreGISP2
[Grootes
et al., 1993].Theeventchronology
proposed
bytheIMITATE group[BjOrck
etal., 1998](seeFigure3)
is shown.ArrowsoverSST profilesindicatethe positionof the coldHoloceneeventsdescribedin text and listed
in Table 2.
documented
enrichment
at---15kyrB.P.,whichseparates
in two
phases
the isotopic
depletion
trendof this period(Figure2).
cold spellsduringthisperiod[Lehmanand Keigwin, 1992; Ko•
Karpuzand Jansen,1992; Kroon et al., 1997], which have been
Palcoclimaticrecordsfrom the North Atlantic Oceanborderlands
related to events of decreased flux of warm surface water into the
havedocumented
severalminor,short-lived
climaticoscillations high latitudes. Similar short-term variability has also been
as the Older Dryas (OD) and the Intra-A!lemdCold Period
recognizedin biological productivity records from the Cariaco
(IACP)(Figure3) [Mangerud
et al., 1974;BjOrck
et al., 1996]. basin (10øN) being associatedto short periodsof trade wind
High-resolution studies from North Atlantic Ocean and
Norwegian
Seacoreshavealsoreported
theoccurrence
of few
strengthening
over the tropicalNorth Atlantic, leadingto the
intensification
of the upwelingcell [Hughen et al., 1996].
48
CACHO ET AL.: WESTERNMEDITERRANEANSEATEMPERATU•S
MediterraneanSST oscillations,especiallythe coolingrecorded
at--,15 kyr B.P. (the OldestDryas),which hasbeenalsoreported
in pollen recordsfrom Italian lakes [Huntley et al., 1999],
is strongly
supported
by thedatingof theVerdeashlayerpresent
in bothcores.Annuallylaminatedsediments
from Cariacobasin
(-•10øN)alsocorrelate
with the GISP2chronology
for the YD
[Hughen
etal., 1998].Thusthetimingandduration
of theYD in
Greenland
seemto providea realchronostratigraphy
for climatic
short-term variability. The atmosphericscenariodescribedby
oscillations
thatoccurred
in theNorthAtlantic
Hughen et al. [1996] may also involve strongernorthwesterlies andoceanographic
indicate that Mediterranean
climate was also sensitive to such
responsible
for shortMediterraneancoolingevents,similarto the
teleconnectionmechanismshypothesizedfor the cold D-O
stadials [Rohling et al., 1998; Cacho et al., 1999a]. Such
atmospheric
forcewouldexplainthehigherSST variabilityof the
TyrrhenianSea for this period, in contrastto the other studied
areas,whichwereunderhigheroceanicinfluence.
region.
AlborancoreMD 95-2043 has a robustagemodel including
two •4C AMS agesfor the YD termination.
The YD in the
Tyrrhenian.core
BS79-33
isalso14C
AMSdated.
Calibration
of
•4CAMS agesduringthe YD is particularly
difficultfor the
occurrence
of two•nCplateaus,
oneof themjustatthetimeof the
YD termination.
This lastplateauhasa durationof-•250 years
6.3. Younger Dryas
andends100-200yearsaftertheYD termination
[Goslaret al.,
The YD period or Greenland stadial I (GSI) is very well
marked in all the studiedprofiles(Figs. 4), showingthat SST
cooleddown (3ø-4øC)to glacialvaluesvery abruptly,in a 50-80
years interval.This rapid coolingoccurredin both sidesof the
GibraltarStrait.Rapid SST coolingand salinitydepletionduring
YD has been associated,in the Portuguesemargin, to fast
movementsof the polar front driven by changesin the global
thermohalinecirculation [Bard et al., !987; Duplessyet al.,
observeddifferencesin our study,and in m•y case,it would
1992]. If the polar front movedsouthwardenoughto reachthe
ventilationrateswereestimated
by Bard et al. [1994]whofound
Strait of Gibraltar latitude, this could also be the mechanism
responsiblefor the YD coolingrecordedin our cores[Cacho et
al., 1999a]. Nevertheless,an atmospherictransmissionfor the
YD SST cooling cannot been excluded. Model experiments
1995].However,
thepotential
calibration
errorissmaller
thanthe
introduce
a lagratherthana leadin ourcalibrated
ages.Another
potential
errorsource
consists
oftheventilation
ageof thewater
massesfrom the studiedarea. Since no major changein the
Mediterranean
circulation
patternoccurredandconsidering
that
the Mediterranean
waterrenewalperiodis 100 years,ventilation
ageswouldnotdifferstrongly
fromthoseof theAtlanticOcean,
at least those from the Alboran Sea. These Atlantic Ocean
anatmosphere-sea
surface
incdifference
of700-800
years
forthe
YD (aperiodof400yearsis already
corrected
in ouragemodels
[Stuiveret al., 1998]).
Bioturbation
is anotherpotentialfactorfor disturbance,
but
suggestthat atmosphericcirculationplayed an importantrole in
takingintoaccount
theextremely
highsedimentation
ratesfor
thehemispheric
propagation
of the YD coolingby intensification
of the wind systemin many regionsand southwarddisplacement
of the winter stormtracks[Renssenet aI., 1996; Mikolajewiczet
al., !997; Fawcett et al., 1997]. Such YD atmospheric
perturbations
are also documentedin Greenlandice coresby a
decreasein snowaccumulation[Alleyet al., 1993;Kapsneret al.,
1995] and an increasein the concentrations
of dustandseasalt
[Mayewskiet al., 1993;Tayloret al., 1997].
The mostsurprising
featureof SSTevolutionduringtheYD in
all our profilesconcernsto the brief durationof the coldphase
(--,700'years),
whichcontrasts
with extentof the isotopicplateau
recordedin the samecoresfor this period (---1100years).This
meansthat the onsetof the final YD warming started,--600years
earlierin the MediterraneanSST (12,250 yearsB.P.) than over
Greenland (11,650 years B.P.). This warming phase was
extremelyabruptin the AlboranSea (3.3øCper 55 years)and
was suddenlyinterruptedby a short(1øC) reversalwhichended
in parallelwith the GS-1 on GISP2. CoresM39-008 (Gulf of
Cadiz)andBS79-38(TyrrhenianSea)alsoshowa shortreversal
just afterthe YD warmingalthoughthe lowerresolution
and/or
age model uncertainties
preventa precisecorrelation
of this
extremelyshortevent(260 years).The causesof thesetiming
anomalyin ourYD recordscouldbe regarded
asa chronological
problemin the frameworkof the Greenland
Ice SheetProject2
(GISP2)icecoreand/orthestudiedprofiles.
The YD in Greenlandice recordslasted 1200 yearswith slight
differencesin the absolutetiming, 12,800-11,600 yearsB.P. in
GISP2 and 12,700-11,500 years B.P. in GreenlandIce Core
thisperiodin coreMD 95-2043(70-80cm/kyr)andtheresults
fromprevious
simulated
bioturbation
models
[Bardet al., 1994],
thiseffectcouldonly be of a few years.On the otherhand,the
studied
/5•80curvesprovidea clearproof,totallyindependent
fromtheagemodelconstraints,
thatthereis a leadin theYD end
warming
of thestudied
cores.SSTstarted
to increase
---400years
beforethe •5•80depletion
associated
to the lastphaseof the
deglaciation.
Therefore
the abovereportedSST risemustbe
consideredasa real warminglead.
Considering
thattheYD cooling
wasdrivenbytheentrance
of
coldwatersthroughthe Straitof Gibraltar,our timingwould
indicate
a rapidnorthward
retirement
of thepolarfrontin middle
YD. A displacement
of a few degrees
northwouldbe enoughto
avoidthe entranceof cold watersthroughthe Straitof Gibraltar.
The short SST reversal in Alboran core during the YD
termination
wouldprobablyindicatea secondbrief phaseof
southward
displacement
of the polarfrontbut lessintensethan
theprevious
one.Distinctperiodsof polarwaterreplacement
by
warm and saltywatershavebeenidentifiedin the YD profile
from the North Atlantic core 56/10/36 [Kroon et al., 1997].
Furtherwork on high-resolution
YD recordsfrom low North
Atlantic latitudes(---35øN)would be required for a better
assessment
of thepolarfrontmovement
duringthisperiod.
Several recordsfrom the northwesternEuropeancontinent
documentthe occurrenceof climaticchangesduring the YD,
pointingto a warmerepisodeduringthe latterphase[Walker,
Project(GRIP)[Johnsen
et al., 1992;Grooteset al., 1993].This
is not significantlydifferent from 230Th/234U dating of
1995].Sediments
from Lake Gosciaz(Poland)showtwo main
phases:
the earlier,whichwaslonger,colder,anddrier,andthe
latter,whichw•.sshorterandmilder[Goslaret al., 1993].The
Barbadoscorals,!3,000-11,700yearsB.P. [Fairbanks,1990],or
varved sedimentcountingestimationsfrom Europeanlakes,
before the YD end. This two fold character of the YD has also
transitionbetweenthesetwo phasesis assignedto--600 years
recentlyin a laminatedrecordfrom Meerfelder
12,700-11,500
yearsB.P. [Goslaret al., 2000 andreferences beenobserved
therein].Core 56/10/36from northwest
Scotland(--56øN) Maar(weternGermany),wherethischangetowardmorehumid
is datedat 12,250kyr B.P.[Braueret al, 2000]. This
provides
the presently
available
highest-resolution
YD record conditions
timingis synchronous
withtheageof ourpremature
warmingin
from the North AtlanticOceanand showsa goodmatchingwith
GISP2chronostratigraphy
[Kroonet al., 1997].Thiscorrelation the Alboran Sea. Greenland ice cores also show an intra-YD
CACHO ET AL.: WESTERN MEDITER/LANEAN SEA TEMPERATURES
weakoscillation
aroundthisagein the8•80 record,
whichis
better defined in the sea salt records [Grootes et al, 1993;
Mayewski
et al., 1993].Farther
south
a well•4CAMSdated
pollen
record
fromtheIberianPeninsula
alsoshows
thatthefinal
warmingof the YD advanced,in -600 years,the SST North
Atlantic warming recorded in core SU81-18 [Pe•alba et al.,
1997].Thiswarmingphasewasshortlyinterrupted
by a cooling
periodsimilarto thatrecorded
by SSTin AlboranSea.All this
evidence strongly supportsthat this climatic variation over
49
timingof the HolocenemaximumSST changebetweenthe areas:
11.5-10.2kyr B.P. in the Gulf of Cadiz, 10-9 kyr B.P. in the
AlboranSea,and 8.9-8.4 kyr B.P. in the TyrrhenianSea.This
indicatesa regionaldiachroneityin the occurrenceof the
Holocene.optimum,
whichpropagates
from westto east.
The generalHolocenecoolingtrendis shortlyinterrupted
by
theoccurrence
of someshortcoolingevents(1ø-2øC),whichare
more intensein the TyrrhenianSea (2.5ø-3øC).This short-term
.variabilitycanbe betteranalyzedin coreMD 95-2043,the one
at higher
resolution
andwithmoreabundant
•4CAMS
Europe
wasrelatedtotheYD signature
in ourcoresandtherefore studied
thatwind regimechangeswere involvedin this early warming
ages.Six shortcoldevents
(A,C1-AC6;
1ø-1.5øC)
havebeen
phase.
Comparison
of thediverse
YD records
mentioned
above identified(Figure4 and Table 2). The youngerevents(AC1seem to indicate that this climatic disturbance increased its
AC3) lasted900-1500years,whileth• olderevents(AC4-AC6)
amplitude
towardthesouth.
were considerablyshorter (250-400 years) but with the same
thermalintensity(1.5øC).
A perio•licity
of,-,730+40
yearsisobserved
between
theoldest
6.4. Holocene
All studiedareasshow the warmestSST valuesat the early
Holocenefollowed by a slow cooling trend. Nevertheless,the
cold spells(AC6-4; seeTable 2). Then, theseperiodslengthen
afterthe Holoceneoptimum,but theyalwaysoccurin harmonic
tonesof this 7304-40yearsperiodicity(AC3:---730 x 3; AC2:
Table 2. List of theRapidHoloceneCoolingEventsRecorded
in Eachof the StudiedAreas,
Indicating
TheirAge,Duration,andtheTimePeriodBetweenThemandListof theHoloceneCold
EventsDefinedin theNorthAtlanticOceanProposed
for Correlation
With ThoseDescribedin the
PresentStudya
Cold
EventMinimum
SST
Age, Time
Span
Since
the
.. lcyr
....Interval
Age
Duration,
'kYr
Previous
One,k•
Alboran Sea
AC 1
AC2
AC3
AC4
AC5
AC6
ACYD
1.38
5.36
8.24
10.28
11.01
11.70
12.47
TC 1
TC2
TC3
TC4
TC5
TC6
TYD
1.39
2.95
5.93
9.45
9.87
11.56
12.51
CC1
CC2
CC3
CYD
7.98
10
12.27
12.75
3.98
2.88
2.04
0.73
0.69
0.77
-
TyrrhenianSea
1.56
2.98
3.52
0.42
1.69
0.95
Gulf of Cadiz
2.02
2.27
0.48
-
1.01 - 1.90
4.75- 5.94
7.56- 9.08
9.95- 10.34
10.95 - 11.21
11.65- 11.91
12.00- 13.10
0.89
1.19
1.52
0.39
0.25
0.26
1.10
1.00- 1.91
2.5 - 3.45
5.28 - 6.58
9.!3- 9.62
9.62- 10.38
10.9- 11.78
12.00- 13.09
0.91
0.95
!.3
0.49
0.76
0.88
1.09
7.8 - 8.25
9.9 - 10.2
12.2-12.4
I2.6-12.9
0.45
0.3
0.2
0.3
NorthAtlantic Minimum
SST TimeSpanSincethe
Alboran
Cold
Events Age,
kyr
cold
eventsCold
Events Cold
Events
Previous
One,
kyr
1.4
2.8
NAC3
4.3
1.6
NAC4
NAC5
NAC6
5.9
8.2
9.5
2.3
1.3
0.8
NAC7
10.3
0.8
AC4
TC5
NAC8
11.1
1.4
AC5
-
-
-
AC6
TC6
CC3
-
AYD
TYD
CYD
12.5
AC1
-
Gulfof Cadiz
NAC1
NAC2
NAYD
1.4
1.5
Tyrrhenian
TC1
TC2
-
-
-
-
AC2
AC3
-
TC3
TC4
CC1
CC2
aSeetextforlistofcooling
events
inthestudied
areas,
andseeBond
etal.[1997]
forcoldevents
intheNorth
Atlantic Ocean.
50
CACHOET AL.' WESTERNMEDITERRANEAN
SEATEMPERATURES
-•730 x 4; ACI: •730 x 5). The cooling eventsobservedin the
other studiedcoresare generally coincident with the events in
MD 95-2043 (Table 2), althoughthe lower resolutionand less
accurateage model do not allow a strict correlationbetween
them. Only few of them, AC3 and AC4 in the AlboranSea and
CC1 and CC2 in the Gulf of Cadiz, can be well correlated(Figure
2 and Table 2), andthey are coincidentin agewith thepre-Boreal
oscillation and the Greenland 8.2 event, respectively.These
cooling eventshave been abundantlyreportedin the North
Atlantic as being associatedwith short freshwaterinfluxes
[Bj6rck et al., 1996;Alley et al., 1997, and references
therein].
However, in the context of the Mediterranean Holocene SST
recordsthey do not show remarkablydifferent characteristics
fi'omthe othercoolings,constitutingthe sequence
with the 730
yearsperiodicitypattern.
The Holocenerecordin Greenlandshowsfour shortperiodsof
increasedconcentrationsof sea salt and terrestrialdust [O'Brien
Mediterranean
basins[DeRo'ket al., 1999;MyersandRohling,
2000].
7. Conclusions
Bothlong-andshort-term
variability
in theNorthAtlantic
modulated
the climaticevolutionof the Mediterranean
SST over
thelast25kyr.Atmospheric
circulation
alsoplayed
a majorrole
during
some
periods,
whichcurrently
ledtoamplifications
ofthe
Atlantic
signal.
TheSSTand•5•80
gradients
between
theGulfof
Cadiz and the AlboranSea changedin intensitybut never in
direction,
pointing
totheoperation
of thewestern
Mediterranean
in concentration
basinconditionsall alongthisperiod.
SSTminimaarenotrecorded
duringLGM butduringH1 and
H2. Occurrence
of an IRD layer in the Gulf of Cadiz in
coincidence
with H1 supports
the hypothesis
that polarwater
enteredin the Mediterranean
Seathroughthe Straitof Gibraltar
et al., 1995]. Such atmosphericperturbationshave been
associated
to a groupof SST coolingevents(2øC) in the North
Atlantic Ocean[Bondet al., 1997]. A cyclicityof 1470ñ500
yearshasbeenrelatedto them and also seemsto be relatedto
changesin the deep-ocean
flow southof Iceland[Bianchiand
McCave,1999]andclimaticvariabilityovertheNorthAmerican
continent[Campbellet al., 1998].The exacttimingof theNorth
Atlanticcoolings[Bondet al., 1997] is listedin Table2, where
theyaretentativelycorrelatedwith mostof the coldeventsfound
in our cores.A periodicityof-•730+40 years in the earlier
during
theHE.In thefirstphase
ofthedeglaciation
a slowdown
Holocene can also be observedin the Atlantic coolings.This
watersthroughthe Straitof Gibraltarand alsodeterminethis
periodicityinvolvesn x 730 yearsharmonicsin the late stage.
Suchcyclicity(.--750years)hasalsobeenreportedin Holocene
records from Asian monsoon-driven sea surface salinity
oscillationsin the South China Sea [Wang et al., 1999] and
Indian monsoonrainfall from the Arabian Sea [Sakar et al.,
2000].
All this evidence indicates that this short-term Holocene
variabilitywasa wideextendedprocess.
Our datasuggest
thatat
leastpartof thiscoolingwastransmitted
throughtheinflowing
North Atlantic Water. Nevertheless,the larger Thyrrhenian
of the Atlantic Ocean warming signal is observedin the
Mediterranean Sea. This attenuation could reflect an
intensification
of surfacemixingprocesses
in thisarea.
SSTwarmingaftertheYD occurred
.--600yearsearlierthan
the warmingdescribed
in othermarineandcontinental
areas.
This advancement
is relatedto the occurrence
of two different
climatic
phases
during
thisperiod
whichhada stronger
effectin
southern
Europe.
Minoroscillations
in theAtlantic
thermohaline
circulationcould be sufficientto avoid the entranceof cold
earlier Mediterraneanwarming.
Holocene
SSTshowa coolingtrendfromstartto presentin all
the studiedareasand reflecta regionaldiachroneity,
occurring
earlier(10-11.5kyr B.P.) in the areasunderhigheroceanic
influenceandlater(8.4-8.9kyr B.P.)in theenclosed
basinsites.
A sequence
of shortSSTcoolingevents(1.5ø-3øC)
observed
in
the coresstudiedat highresolution
is consistent
with a climatic
periodicity
of---730ñ40years.Thesecoolings
arein agreement
withtheHolocene
variabilityrecorded
in otherareas.Theywere
transmitted
to the Mediterranean
Sea by the Atlanticinflowing
amplitude
for thisHoloceneoscillation
indicates
a Mediterranean water, but strongwinter winds may have amplifiedthese
amplification,
probablyinducedby changes
in thewindregime. oscillationsin the TyrrhenianSea.
Similar short Holocenecooling eventshave been previously
documented
in
some
remote
areas
from
the
eastern
AcknowLedgments.
WethankJoanVillanueva
foruseful
discussions
in theelaboration
of thispaperandTim Herbert,EelcoRohling,
and
Laurent
Labeyrie
for theirusefulcomments
in thereviewof thefirst
version.
Thepresent
study
wassupported
bytheHOLOCENE
important
roleforthesebriefcoolings.
Furtherworkisnecessary manuscript
Project
(ENV4-CT97-0162)
funded
by theEuropean
Union.Financial
for absolute correlation between Mediterranean and Atlantic
support
fromproject
MTPII-MATER
(MAS3-CT96-0051)
andCICYT
coolingsand alsofor full understanding
of the sequence
of
(AMB95-1284-E,CLI-96-226
l-E, CLI98-1002-CO2)is also
processes
involvedin their transmission.
Nevertheless,
it is
acknowledged.
Thestudies
of coreM39-008werealsosupported
bythe
interesting
to pointout that althoughthis variabilityinvolved Deutsche
Forschungsgemeinschaft
(GrantZa157/15-1
and-2).Wethank
of theFrench
agencies
MENRT,TAAF,CNRS/INSU,
and
onlyshortthermalchanges,
it couldbe relatedto drasticchanges thesupport
IFRTPtoMarionDufresneandIMAGESprogram.
in the deep water convectionof the easternand wetern
Mediterranean
Sea,theAegeanandAdriaticSeas[Rohlinget al.,
1997;De Ro'ket al., !999]. Theseareasarestronglyinfluenced
by the flow of wintercontinental
winds,whichcouldplay an
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