Table Of ContentMarineGeology214(2005)309–322
www.elsevier.com/locate/margeo
Late glacial to Holocene climate and sedimentation history
in the NW Black Sea
Andre´ Bahra,*, Frank Lamyb, Helge Arzb, Holger Kuhlmanna, Gerold Wefera
aDepartmentofGeosciences,Universita¨tBremen,Fachbereich5-Geowissenschaften,Postfach330440,D-28334,Bremen,Germany
bGeoForschungsZentrumPotsdam,Telegrafenberg,14473Potsdam
Received2June2004;receivedinrevisedform23November2004;accepted24November2004
Abstract
Gravitycoresfrom the continental slope inthe northwestern BlackSeawere studied usinghigh-resolution stable isotope,
grain size and XRF-scanning data. The measurements provide a 30000 years AMS 14C-dated record of variations in the
hydrological regime of the Black Sea and give insight into changing paleoenvironments in the surrounding areas. Stable
climatic conditions during the Last Glacial Maximum were followed by a series of meltwater pulses most likely originating
fromtheScandinavianicesheetbetween18000and15500yrBP.1ThismeltwaterinputrosetheleveloftheCaspianSeatoa
point that Caspian water could spill into the Black Sea via the Manych-depression north of the Caucasian mountains. High-
frequencyoscillationsintheXRF-dataduringthisperiodsuggestaprobablelinktothearcticclimateregime.Later,duringthe
Bblling/AllerbdandtheearlyHolocene,prevailinghightemperaturesledtoauthigeniccalciteprecipitationthroughincreased
phytoplanktonactivity,interruptedbytheYoungerDryasandtheb8200yrBPcoldeventQwithdominantclasticsedimentation.
D2004Elsevier B.V. All rightsreserved.
Keywords:BlackSea;paleoclimate;paleohydrology;lateglacial;Holocene;CaspianSea
1. Introduction the catchment. Whereas previous studies centered
mainly around the analysis of marine Holocene
The Black Sea as an almost isolated marginal deposits (e.g., Ross and Degens, 1974; Hay et al.,
sea reacts particularly sensitive to paleoenviron- 1991; Jones and Gagnon, 1994; Pilskaln and Pike,
mental changes. Black Sea sediments therefore 2001) and the establishment of the Black Sea–Sea
provide an excellent opportunity for high-resolution of Marmara–Mediterranean drainage corridor (e.g.,
studies of past climatic and hydrological changes in Ryan et al., 1997; Aksu et al., 1999; Cagatay et
al., 2000; Myers et al., 2003), first detailed
sedimentological and geochemical analyses of the
* Correspondingauthor.Tel.:+494212187109;fax:+49421
late glacial to Holocene limnic sediments were
2188916.
published only recently (Major et al., 2002; Ryan
E-mailaddress: [email protected](A.Bahr).
1 AlldatesarecalibratedtocalendaryearsB.P.(yrBP). et al., 2003).
0025-3227/$-seefrontmatterD2004ElsevierB.V.Allrightsreserved.
doi:10.1016/j.margeo.2004.11.013
310 A.Bahretal./MarineGeology214(2005)309–322
A main concern of any work on the limnic BlackSealeveltoriseabovetheBosphorussilldepth
sediments is to create a reliable stratigraphy, because ataround11.4to12.8kyrBPandallowedwaterfrom
the unknown reservoir effect during the lake stage of the Black Sea into the Sea of Marmara.
the Black Sea hampers precise radiocarbon dating. In Theaimofthisstudyistorefinetheunderstanding
their study of gravity cores from the northwestern of the late glacial to Holocene evolution of the Black
BlackSea,Majoretal.(2002)assumedareservoirage Sea and its surrounding areas. For this purpose we
of 0. To further reinforce this stratigraphy they conducted a high-resolution multi-proxy study on
correlated two distinct horizons from the Black Sea gravity cores from the northwestern Black Sea
with similar ones in the Caspian Sea: a series of continental slope. These data allow a detailed recon-
reddish-brown clays deposited from about 15.8–17.7 struction of climatic and hydrologic changes in the
kyrBPand,second,adiatom-richlayerfromthedeep western Black Sea basin during the last 30000 years.
basinfloorwithagesof10.6–10.7kyrBP(Ryanetal.,
2003),whichwascorrelatedwiththebStephanodiscus
horizonQ in the Caspian Sea (Zhakovshchikova, 2. Study area
1968). Both horizons were attributed to an outflow
of Caspian waters through the Manych-depression The studied gravity cores are located in the
into the Black Sea during periods of massive melt- northwestern Black Sea, south of the Danube delta,
waterpulsesfromtheFennoscandianandSiberianice onalowershelftoslopetransectfrom118mto1977
shields in the late glacial (Kroonenberg et al., 1997; m water depth (Table 1; Fig. 1). The area is
Grosswald and Hughes, 2002). characterised by the very broad northwestern Black
To decipher the evolution of the Black Sea, the Sea shelf, which comprises almost 94% of the total
timinganddevelopmentoftheconnectionviatheSea shelf area in the Black Sea (Panin and Jipa, 2002).
of Marmara with the Mediterranean Sea has to be Thecontinentalslopeisverygentleandshapedbythe
known.SomeresearchersproposeacontinuousBlack morphology of the pre-Holocene Danube fan, reach-
Sea outflow during the last glacial and Holocene ingfarouttowardsthecentreofthewesternBlackSea
(Ross and Degens, 1974; Lane-Serff et al., 1997) basin.
while other authors postulate an evaporative draw- Riverine input to the northwestern Black Sea
down of the Black Sea level through the Last Glacial continental margin derives mainly from the Danube,
Maximum (LGM) down to (cid:1)110 m (Aksu et al., the second largest river in Europe with a drainage
2002a)or(cid:1)150m(Winguthetal.,2000),wellbelow basin of over 817000 km2 (Panin and Jipa, 2002).
thepresentBosphorussilldepth((cid:1)32m).Ithasbeen Although the Danube delivers by far the largest
pointed out by several authors that the depth of the amount of water and sediment load of all rivers to
Bosphorussillplaysacentralrolefortheonsetofthe the Black Sea (multiannual mean discharge of water
Black Sea–Marmara connection (Major et al., 2002; before damming the river: 190.7 km3dyear(cid:1)1; mean
Myers et al., 2003; Sperling et al., 2003). A deep sediment discharge: 51.70 Mtdyear(cid:1)1; Bondar et al.,
Bosphorus ((cid:1)80 m) would allow intrusion of Med-
iterranean water as early as ca. 14 kyr BP (Major et
al., 2002), whereas a shallow sill depth of ca. (cid:1)35 m
is consistent with the so-called bNoah’s Flood Table1
hypothesisQ, in which Ryan et al. (1997) proposed a Locationandlengthofthesampledcores
catastrophicinundationoftheBlackSeafollowingthe Corename Latitude Longitude Waterdepth Corelength
N E (m) (cm)
breechingoftheBosphorusbyMediterraneanwaterat
around9400yrBP(Ryanetal.,2003).Sperlingetal. GeoB7604-2 42856.2V 30801.9V 1977 592
GeoB7607-2 43809.7V 29857.7V 1562 636
(2003) argue that a sill at least 7 m higher than today
GeoB7608-1 43829.2V 30811.8V 1202 685
would fit best to the salinity evolution of the Sea of
GeoB7609-1 43832.8V 30809.2V 941 655
Marmara and the Aegean Sea at around 8700 yr BP. GeoB7610-1 43838.9V 30804.1V 465 880
An opposing view offered Aksu et al. (2002b), GeoB7611-1 43841.8V 30800.1V 118 634
who assumed that a positive water balance led the GeoB7616-4 43841.0V 30802.5V 168 916
A.Bahretal./MarineGeology214(2005)309–322 311
27˚ 28˚ 29˚ 30˚ 31˚ 32˚ 33˚ 34˚
45˚ 45˚
ne
n i a Ukrai
a
Danube R o m 100 2222000000000640000 80011000 1200
44˚ 44˚
11640000 1800
a r i a 2000
43˚ g 43˚
u l
B
42˚ 42˚
T u r k e y
Sakarya
40˚ 40˚N
Fig.1.LocationofgravitycoresrecoveredduringRVMeteorcruiseM51-4(circles)andlocationoftwocorespresentedinapreviousstudyby
Majoretal.(2002)(stars).AlsoindicatedistheapproximatepositionoftheBlackSearimcurrent(afterOguzetal.,1993).
1991; Panin and Jipa, 2002), the outer shelf in the today.But,asdiscussedlater,itmayhavebeenlarger
studyareaisknowntobesediment-starved(Paninand during the deglacial.
Jipa, 2002). This is the result of the strong (N50 Climatically the western Black Sea is situated in
cmds(cid:1)1) cyclonic bRim CurrentQ (Oguz and Besik- the transition between the humid climatic regime of
tepe, 1999), which transports most of the suspended the mid-latitudes in SE Europe with a temperate
sedimentsalongthecoasttowardsthedeep-searegion mixed forest and precipitation N1000 mmdyear(cid:1)1, a
(Panin and Jipa, 2002, Fig. 1). Therefore, Holocene more continental climate in the northern part of the
sediments are only present as a very thin cover or Black Sea and the eastern Danube lowlands with
absent on this part of the shelf. savannah grasslands and b600 mm annual rainfall
ThesedimenttransportedbytheDanubeisderived and, third, the Mediterranean climate region in the
from a large drainage area in southeastern Europe. In south towards the Sea of Marmara (Mudie et al.,
its middle and lower course, the Danube flows 2002b).
through the Quaternary fluvial and eolian deposits
of the Hungarian and Walachian lowlands, through
Cretaceous and Tertiary flysch and molasse of the 3. Material and methods
northern Carpathian Mountains and through gneiss
and crystalline schists of the southern Carpathian 3.1. Material
Mountains. The southern drainage area is mostly
dominated by granites and crystalline schists of the Seven gravity cores retrieved during the RV
Balkans (Mu¨ller and Stoffers, 1974). Sediment input Meteor-cruise M51-4 in December 2001 were chosen
from the regions north of the Black Sea by the rivers for the present study (Table 1). All sediment cores
Dniester, Dniepr and Don is of minor importance from the continental slope show the subdivision in
312 A.Bahretal./MarineGeology214(2005)309–322
three units typical for sediments from the Black Sea Table2
basin (Ross and Degens, 1974): the marine units I RadiocarbonagesfromgravitycoresGeoB7608-1and7616-4
(finely laminated coccolith ooze) and II (sapropelic Lab.-ID Core 14Cage Calendar Material
sediments) at the top with a fairly constant thickness depth (yrBP) age
(cm) (yrBP)
of together ca. 45 cm, and the lowermost Unit III,
GeoB7608-1
which consists of homogeneous to (mostly) centi-
KIA21464 34 7735F50 7607F40 Ostracodes
meter-scale laminated muddy clay deposited under
KIA21463 88 11460F70 12342F215 Gastropod
lacustrine conditions. KIA21461 158 13350F80 14469F365 Gastropod
Thecoresfromthelowershelfarecharacterisedby KIA21460a 243 17080+150/ 18563F320 Ostracodes
homogeneoustocentimeter-scalelaminatedmudwith (cid:1)140 andbivalves
KIA21866 436 16360F70 17951F285 Ostracodes
abundant shells and shell fragments of bivalves and
andbivalves
gastropods representing entirely Unit III sediments.
KIA21459 596 20140+180/ 22499F265 Gastropod
Holocene sediments are nearly completely missing, (cid:1)170
exceptfortheuppermosthorizonofGeoB7611-1that KIA21457 652 24970+310/ 26891F480 Mixedmollusc
revealed a late Holocene age of 2585 yr BP. (cid:1)300 shells
GeoB7616-4
3.2. Methods
KIA18212 2 10470F60 12360F200 Dreissena
rostriformis
3.2.1. Profiling measurements KIA19681 184 10945F60 12855F50 D.rostriformis
A Minolta CM-2002k hand-held spectrophotom- KIA19680 386 11250F60 13055F90 D.rostriformis
KIA19678 579 11670F80 13435F140 D.rostriformis
eter was used to measure percent reflectance values
KIA19677 802 12040F130 13824F220 D.rostriformis
of sediment color at31 wavelength channels over the
KIA18213 899 13105F55 15452F105 D.rostriformis
visible light range (400–700 nm). The digital
For GeoB 7608-1 a correction of 1000 years was applied before
reflectance data of the spectrophotometer readings
calibrating,inGeoB7616-4calendarageswerecalculatedwith0
were obtained from the surface (measured in 1 cm yearcorrection.
steps) of the split cores. The red/blue ratio was a Thedatefrom243cmdepthinGeoB7608-1wasdiscarded
calculated as the ratio between the 700 nm and 450 becauseofitshighage.
nm wave lengths.
All cores listed in Table 1 except GeoB 7611-1 Germany; the AMS measurements were done at the
were scanned in 1 cm intervals with a X-ray Leibniz-Labor in Kiel, Germany (Nadeau et al.,
fluorescence scanner at the University of Bremen, 1997).
Germany. The XRF-core scanner, developed at the
Netherlands Institute for Sea Research, Texel, meas- 3.2.3. Stable isotopes measurements
ures the bulk intensities of major elements (e.g., K, For stable isotope analyses (y18O and y13C) on
Ca, Ti, Mn, Fe, Cu and Sr) on split sediment cores coreGeoB7616-4,atotalof288samplesrecoveredin
(Jansen et al., 1998; Ro¨hl and Abrams, 2000). These 4 cm intervals were collected and wet sieved with 63
data were used to correlate the cores along the slope and150Ammeshsize.FromthefractionN150Amwe
transect. collected 5 to 7 juvenile shells of the freshwater
bivalve D. rostriformis and analysed them at the
3.2.2. Radiocarbon dating Geoscience Department at the University of Bremen
For AMS 14C-dating on the shallow water core usingaFinniganMAT251massspectrometerwithan
GeoB 7616-4, 6 samples containing shells of the automated carbonate preparation device. The ratio of
bivalvespeciesDreissenarostriformis werecollected. 18O/16O is given in x relative to the PDB standard.
Due to the absence of D. rostriformis, we used 7 Analytical long-time standard deviation is about
samples with ostracodes and/or molluscs shells for F0.07x PDB.
dating the deeper core GeoB 7608-1 (Table 2). All data are available under the name of the
Carbonate hydrolysis and CO -reduction of the corresponding author through the PANGAEA server
2
sampleswereperformedattheUniversityofBremen, (www.pangaea.de/PangaVista).
A.Bahretal./MarineGeology214(2005)309–322 313
4. Chronology core top through extrapolation using the sedimenta-
tion rate computed for Unit II.
The stratigraphies of GeoB 7608-1 and GeoB Acentralproblemwhenworkingonthelastglacial
7616-4 are principally based on the linear interpola- lacustrine sediments of the Black Sea is the con-
tionbetween6AMS14Cdatesforeachcore(Table2). structionofaconsistentstratigraphy,primarilyforthe
For calibration to calendar years BP (1950) we used reasonthatradiocarbondatesdonotallowpreciseage
the program CALPAL (Version 2003; Weninger and assignments because of an unknown reservoir age.
Jo¨ris,2003)mainlybasedontheINTCAL-98(Stuiver Major et al. (2002) based their stratigraphy on 14C-
etal.,1998)calibrationset.Thedate at243cmdepth dates on individual mollusc shells assuming a 0 year
in GeoB 7608-1 was discarded because its age was reservoir correction and correlations with marker
regarded as too old, probably because it contains horizons from the Caspian Sea (see Introduction). In
reworked shell material. The stratigraphy of GeoB order to prove the validity of our radiocarbon dates,
7608-1 was further refined by using the 2700 yr BP especially those on shell debris from GeoB 7608-1,
UnitI/UnitIIboundary(JonesandGagnon,1994)at8 wetriedtolinkourcoreswiththosestudiedbyMajor
cmcoredepthand7540yrBPfortheUnitII/UnitIII et al. (2002), which are located adjacent to our study
boundary (Jones and Gagnon, 1994) at 31 cm core area (cores BLKS9809 and 9810, Fig. 1).
depthasadditionaltimemarkers.Althoughourdating The XRF Ca-curve from GeoB 7608-1 and the
of7600yrBPfrom34cmcoredepth(directlybelow carbonatecontentpublishedbyMajoretal.(2002)are
the Unit II/Unit III boundary) is in good agreement fairly congruent, if an age correction of 1000 years is
with the published data for this boundary we decided appliedtothemeasurementsonGeoB7608-1(Fig.2).
to use only the well-founded 7540 yr BP date. Since Incontrast,theoxygenisotopedatafromGeoB7616-
the upper part of Unit I is not preserved in GeoB 4 and those given by Major et al. (2002) seem to fit
7608-1, an age of 1380 yr BP was calculated for the without any age correction, although the low number
Fig.2.Correlationof(a)thecarbonatecontentofcoreBLKS9810afterMajoretal.(2002)with(b)theXRF-CacontentinGeoB7608-1and(c)
they18OofmolluscshellsincoresBLKS9809andBKLS9810afterMajoretal.(2002)with(d)y18OmeasurementsonDreissenarostriformis
juv.inGeoB7616-4.For(b)anagecorrectionof1000yearswasappliedbeforecalibrating,allothercurvesarecalibratedtocalendaryearswith
0yearagecorrection.
314 A.Bahretal./MarineGeology214(2005)309–322
of values in the published record only allows a rough of D. rostriformis used for dating GeoB 7616-4 were
comparison (Fig. 2). This discrepancy might be found articulated and in living position and thus may
explained by the different dating material: because beconsideredtobeautochthonous.Asaconsequence
of the scarcity of material in GeoB 7608-1, a mixture we adopted thepublished stratigraphy byMajoretal.
of ostracodes and shell debris was pooled for dating (2002) and applied the suggested age correction of
(Table 2); this may have introduced older material in 1000 years for GeoB 7608-1.
the samples. Because the radiocarbon dates in Major It is worth noting that the offset of 1000 years is
etal.(2002)andGeoB7616-4arebothbasedonadult fairlyconstantthroughoutthecoreGeoB7608-1.This
mollusc shells, the probability of contamination with could be coincidence, but may alternatively be
older material is smaller. Furthermore, the specimens explained by a stratification of the ancient Black Sea
Fig.3.CorrelationofgravitycoresfromtheslopetransectinthenorthwesternBlackSeausingtheXRF-Ca-intensity(uppergraph)andTi/Ca
ratio(lowergraph).ForGeoB7608-1theradiocarbondatesareindicatedincalendaryears.R1toR4indicatetheredlayers.
A.Bahretal./MarineGeology214(2005)309–322 315
lake:atleasttheupper400m(thepresentwaterdepth cores (especially for the red layers) Fe, Ti, K-
of the cores published by Major et al. (2002) are 240 intensities, Fe/Ca, Ti/Ca, K/Ca ratios and the spectral
m for BLKS98109 and 378 m for BLKS9810) of the red/blue ratio were the most useful parameters for
water column were ventilated and therefore show no correlation (Ca and Ti/Ca are shown in Fig. 3). The
reservoir age, whereas GeoB 7608-1 from 1202 m identification of the carbonate peaks in GeoB 7610-1
water depth may contain signals of an older, not is difficult, because the high amount of terrigenous
ventilatedwatermass.This assumes that apermanent material dilutes the Ca-signal.
stratification persisted throughout the glacial and The thickness of the Holocene units I and II is
deglacial period. fairly constant in all cores, while the limnic sedi-
ments show an at least fourfold increase in sed-
imentation rate towards shallower water depths. This
5. Results increase is most pronounced in the interval between
the end of the carbonate peaks and the onset of the
5.1. Slope transect red layers, but weakens during the deposition of the
red layers (Fig. 4).
The correlation of the five cores along the slope GeoB 7608-1 was chosen for further investigation
transect was done using the Ca-intensity to track the because it has a continuous sediment record without
Unit I/II boundary and the carbonate peaks in the any turbidites and represents a good compromise
upper 1–2 m of the cores. In the lower part of the between deep penetration and high resolution.
Fig.4.Thicknessofparticularhorizonsalongtheslopetransect.(R1=uppermostredlayer).
316 A.Bahretal./MarineGeology214(2005)309–322
5.2. Sedimentological data from GeoB 7608-1 ratio was chosen as a representative indicator for
variations in the relative proportion of terrestrial and
From the stratigraphy presented in chapter 4, the carbonate sedimentation.
core covers a continuous sequence since 30 kyr BP. The Ti/Ca-ratio is fairly constant during the LGM
An overview about different parameters measured in while the bulk grain size shows a rather high sand
GeoB 7608-1 is presented in Fig. 5, together with contentwithadecliningtrendupto18kyrBP.Apeak
y18O values from the GRIP ice core and y13C values in the sand content around 21 kyr BP is mainly
of core GeoB 7616-4. produced through the presence of a large amount of
As mainly reflecting biogenic and/or authigenic sulphidic concretions.
precipitated carbonate, Ca-intensities are inversely Theonthewholestableperiodfrom30to18kyrBP
related to the Fe, Ti and K-intensities, which are isterminatedatca.18kyrBPbytheoccurrenceoffour
linkedtosiliciclasticcomponents.SinceFe,TiandK- reddish-brownlayers,spanningatimeofroughly2500
intensities are very similar throughout the record and years. The terrigenous input sharply increased during
Ti is inert against diagenetic alterations, the Ti/Ca the deposition of these red layers, while the sand
Fig.5.OverviewaboutparametersmeasuredonGeoB7608-1.PlottedaretheXRFTi/Caratio,thespectralred/blueratio,bulkgrainsize,and
sedimentationrate.Forcomparisonthey13CfromcoreGeoB7616-4andcounts(inpercent)oftheplankticforaminiferG.bullidesfromtheSea
ofMarmara(Sperlingetal.,2003).Markedareasequenceofreddish-brownclaylayers(R)andthreeCa-peaks(C1toC3)andtheirpotential
correlationtotheGRIPice-core.
A.Bahretal./MarineGeology214(2005)309–322 317
contentshowsadecliningtrend,indicatingthatmostof proximal position of the core to the ancient Danube
theterrigenousmineralsweretransportedinthesiltand delta and higher river suspension load compared to
clayfraction.Thehighsedimentinputisalsoreflected the marine Holocene deposits which are constant in
byatwo-foldincreaseinsedimentationratefrom0.35 thicknessalongtheentireslope(UnitIIinFig.4;due
to0.8mdkyr(cid:1)1.Afterthisepisodeofhighterrigenous to core loss Unit I is not entirely preserved in all
input the sedimentation rate decreased again to a cores).
moderate value (ca. 0.33 mdkyr(cid:1)1) and successively
declined to 0.05 mdkyr(cid:1)1 in the late Holocene. Ca. 6.1. Last glaciation (28500–18000 yr BP)
1000 years after the occurrence of the uppermost red
layer, contemporaneous to the Bblling warm period, Thesedimentologicalparametersmeasuredoncore
the Ca-intensity shows the first of three separated GeoB7608-1showthatclimaticconditionshavebeen
maxima, which are related to an increased carbonate relatively stable throughout the LGM. The high sand
content.Whileinthelowerpartoftherecordmostof content between 28.5 and 25 kyr BP may reflect a
the carbonate in GeoB 7608-1 consists of biogenic moreproximalpositionrelativetotheDanubedeltaas
components(molluscorostracodeshellsandsubordi- it prograded towards the basin interior during this
nate detritical carbonate) all three Ca-maxima are period of low Black Sea lake-level.
producedbyahighquantityofsilt-sized,rhombohedric
authigeniccalcitethatwereclearlyidentifiedinsmear 6.2. Deposition of the red layers (18000–15500
slides. yr BP)
During the Ca-troughs the Ti/Ca-ratio increases,
especially in the upper Ca-trough at around 8 ka, Betweenca.18and15.5kyrBPaseriesofreddish-
whereitreachesitsabsolutemaximum.TheHolocene brownclaylayersweredepositedatalllocationsonthe
periodaftertheuppermostCa-peakischaracterisedby slope. To confine the source of the red clays, it is
arelativelyhighTi/Caratiowithdistinctfluctuations. importanttodistinguishbetweenmeltwaterdeliveryof
The final increase in the Ca-intensity marks the alpine and Scandinavian/Siberian provenance. The
beginning of the carbonate-rich Unit I (laminated retreat of alpine ice domes started at ca. 17.7 kyr BP
coccolith ooze). andfinishedaround17.3kyrBP(Dentonetal.,1999),
while17.2kyrBPmarkstheendofmeltwaterdelivery
5.3. Stable isotopes from glaciers in northeastern Europe through the
Dnieprwatershed(Majoretal.,2002).Thetermination
y18O values from core GeoB 7616-4 are in the oftheCaspianoverflowisdisputed,butmaynothave
range of the values reported by Major et al. (2002) persistedbeyond15.8kyrBP(Svitoch,1999).There-
with a trend from values around (cid:1)6x at 14 kyr BP fore,alpinemeltwatercanonlyaccountfortheincrease
towards lighter values around (cid:1)3.5x at 11 kyr BP insedimentationrateandterrigenousmaterialbetween
(Fig. 2). y13C values are enriched (up to +2.24x) 18 and 17.3 kyr BP, not for the entire period of 2500
during the maximum of the lowermost Ca-maximum years during the deposition of the red layers. Taken
and depleted (around +0.25x) before and afterwards together, the lesser increase in sedimentation rate
(Fig. 5). upslopecomparedtothesubsequentdeposits(Fig.4),
thesmallgrainsize,wide-spreadoccurrenceofthered
layers, and similarity to contemporaneous Caspian
6. Discussion deposits (see below) favour a distal sediment source
such as the Caspian Sea-Black Sea drainage corridor
The comparison of data measured on six cores (Manych-depression).
from theslope transect inthenorthwestern Black Sea Ryan et al. (2003) suggested a possible link of the
(Fig. 3) shows that the results obtained on GeoB reddish-brown layers to the bEarly Khvalynian trans-
7608-1arerepresentativefortheregionalsedimentary gressionQ in the Caspian Sea during the late glacial
history. The distinct increase in the pre-Holocene induced by meltwater pulses from glaciers in Fenno-
sedimentationratetowardstheupperslopeindicatesa scandia and/or Siberia that led to a lake-level rise in
318 A.Bahretal./MarineGeology214(2005)309–322
theCaspianSea(Kroonenbergetal.,1997;Grosswald complex internal structure with mm-scale lamina-
and Hughes, 2002). Thus, the Manych-depression tions, which may represent interannual or even
would represent one possible spillway for Scandina- annual pulses of meltwater discharge. The occur-
vianand/orSiberianmeltwaterduringthedeglaciation rence of the red layers may be linked to high latitude
(Ryan et al., 2003). The height of former beach climate variations as the red layers and the accom-
terracesintheCaspianSeaindicates+50m(abovethe panying increase in the terrigenous components
present lake level) as the maximum highstand during correspond to periods of slightly increased y18O
thedeglacial(Kroonenbergetal.,1997).Thisallowed (reflecting warmer conditions) during the GS-2
the flooding of the Manych-depression between the (Greenland Stadial 2) as recorded in the GRIP ice-
CaspianandBlackSeathatistoday+25mabovesea- core record (Fig. 6). This may indicate that the
level (Popov, 1983; Mangerud et al., 2001). During Scandinavian glaciers and ice-dammed lakes reacted
the maximum stage of the Early Khvalynian trans- very sensitive to climate forcing also on short time
gression, brownish bChocolate ClaysQ were deposited scales and, as also demonstrated by modelling
in the Caspian Sea (e.g., Kroonenberg et al., 1997), studies (Krinner et al., 2004), had themselves effects
resembling the colour of the red layers in the Black on the climate dynamics in northern Eurasia.
Sea.ThetimingoftheEarlyKhvalyniantransgression Inaddition,theredlayerintervalsarecharacterised
is uncertain—estimates are from 70 kyr BP (thermo- by reduced Mn contents (Fig. 6). Mn contents are
luminescence dating) to ca. 9000 yr BP (14C and U– often used as an indicator for changing redox
Th-dates, Kroonenberg et al., 1997; Svitoch, 1999). conditions-oxic conditions favour MnO-precipitation,
Within our stratigraphy and considering the dates of reducing conditions makes Mn2+ more soluble (Pei-
our red layers in GeoB 7608-1, the transgression nerud, 2000; Tekiroglu et al., 2001). Thus, the lower
occurred between 15.5 and 18 kyr BP. Mn-content would be consistent with at least tempo-
The origin of meltwater flowing into the Caspian rary more oxygen depleted deep waters during
Sea, i.e., whether it is derived from the Barents-Kara enhanced freshwater input into the Black Sea (see
ice sheetortheeasternScandinavian ice sheet,isstill also Mudie et al., 2002a). The at that time relative
discussed controversially. It is known that during the high lake level of the Black Sea (Ryan et al., 2003)
last glacial period huge ice masses blocked the rivers would have allowed the dissolved Mn2+ to leave the
flowing into the Arctic Ocean, diverted them to the Black Sea via the Bosphorus strait.
south, and dammed extensive lakes in northern
Siberia (Grosswald and Hughes, 2002). However, 6.3. Oldest Dryas (15500–14500 yr BP)
there isdisagreementabout the spatial advanceof the
Barents-KaraicesheetduringtheLGM.Someauthors From the end of the red layer deposition till the
(e.g.,Grosswald,1998;GrosswaldandHughes,2002) onset of the Bblling, a marked increase in bulk grain
claimthattheBarents-Karaicesheetexistedthrough- size at relative constant Ti/Ca ratios occurs. Beside
out the LGM and meltwater drained into the Caspian abundant iron sulphide concretions, the bulk grain
Sea, but recently published results (Mangerud et al., size changes mainly relate to an increase in the
2004) show that the Barents-Kara ice sheet was most accumulation of quartz grains. This interval also
likely restricted to the shelf areas of the Arctic Ocean shows a huge upslope increase in sedimentation rates
andtheicewasunabletoblockthenorthwardflowing along the slope transect, indicating a more proximal
rivers. Instead, the Scandinavian ice sheet reached its position to the Danube Delta during a relatively low
maximum extent at ca. 17–18 kyr BP and diverted Black Sea level.
rivers and meltwater from the Baltic Basin to the There is a lag of around 300 years between the
RiverVolgaandfurthertotheCaspianSea(Mangerud steady decline in the Ti/Ca-ratio when compared to
et al., 2004), which is contemporaneous to the theabruptdropofbulkgrainsizeattheOldestDryas/
development of the Black Sea red layers. Bblling transition at ca. 14.5 kyr BP (Fig. 5). We
Our data indicate four major episodes (equivalent interpretthelagasanimpactofdelayedreforestation,
to four layers) of Caspian water spilling into the which occurred around 200 years after the onset of
Black Sea. Additionally, each red layer has a warming in the Alps (Magny et al., 2003b; Denton et
