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Quaternary International 293 (2013) 170e183

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Quaternary International

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First high-resolution marinopalynological stratigraphy of Late Quaternarysediments from the central part of the Bulgarian Black Sea area

Mariana Filipova-Marinova a,b,*, Danail Pavlov b, Marco Coolen c, Liviu Giosan c

aMuseum of Natural History e Varna, 41 Maria Louisa Blvd., 9000 Varna, Bulgariab Society of Innovative Ecologists of Bulgaria, 10 Dr. Bassanovich Str., 9010 Varna, BulgariacWoods Hole Oceanographic Institution, 360 Woods Hole Rd., Woods Hole, MA 02543, USA

a r t i c l e i n f o

Article history:Available online 7 May 2012

* Corresponding author. Museum of Natural HistoBlvd., 9000 Varna, Bulgaria.

E-mail addresses: marianafilipova@yahoo.comdanailpavlov@gmail.com (D. Pavlov), mcoolen@whowhoi.edu (L. Giosan).

1040-6182/$ e see front matter � 2012 Elsevier Ltd adoi:10.1016/j.quaint.2012.05.002

a b s t r a c t

Spores, pollen and dinoflagellate cysts of Late Pleistocene and Holocene sediments were analyzed fromGiant Gravity Core 18 from the Black Sea continental slope, recovered from a water depth of 971 m. Theinvestigated length of the core is 203.5 cm. It includes 3 lithological units: light grey clay, sapropels andcoccolith-bearing ooze. The core was sampled at 5e10 cm intervals. Sampling of the interval 141.5e126 cm was carried out at every cm. AMS radiocarbon dating of bulk organic carbon was performedon 18 selected sediment layers. This chronological data allowed the first high-resolution pollen stra-tigraphy of Late Quaternary sediments from the western Black Sea area to be presented. The percentagesporeepollen diagram is divided into 6 local pollen assemblage zones. The trends in the vegetationdynamics and climate changes and the early history of migration of the majority of the arboreal taxa thatnowadays occur in the Eastern Balkan Range were traced out. The palynological record suggests thatopen oak forests were spread in the Eastern Balkan Range at the beginning of the Holocene and showsearly migration of the major temperate arboreal species such as Quercus, Ulmus, Tilia and Carpinusbetulus. This vegetation palaeosuccession continues with the spreading of mixed oak forests from 8950until 2620 cal. BP (8650 � 40 until 3120 � 35 14C BP) followed by destructive changes due to humanimpact and climate deterioration. A cooling of Holocene climate that is well known in the North Atlanticregion as the “8200 yrs cold event” is identified for the first time in marine records from the BulgarianBlack Sea area. The assemblages of dinoflagellate cysts and acritarchs were investigated to providea reconstruction of surface seawater salinity and surface seawater temperature changes. Two maindinoflagellate cyst assemblages, one dominated by fresh- to brackish water species such as Spiniferitescruciformis and Pyxidinopsis psilata and a subsequent one, that is characterized by euryhaline marineMediterranean species such as Lingulodinium machaerophorum, Spiniferites belerius, Spiniferites bentorii,Operculodinium centrocarpum and acritarchs Cymatiosphaera globulosa testified a change in SSS from lowsalinity (<7&) to present day conditions after 7990 cal. BP. Substantial freshening of Black Sea surfacewaters at 2570 cal. BP is established and connected with the transition from a relatively dry and warm torelatively cold and wet climate.

� 2012 Elsevier Ltd and INQUA. All rights reserved.

1. Introduction

The palynostratigraphic method is one of the main biostrati-graphic methods used for correlation of sediments that are lackingin datable fossil material, which is a common problem for lakes ofthe Near and Middle East (Mudie et al., 2002). Pollen analysis of

ry e Varna, 41 Maria Louisa

(M. Filipova-Marinova),i.edu (M. Coolen), lgiosan@

nd INQUA. All rights reserved.

marine sediments offers the possibility of obtaining long andpresumably continuous records of coastal vegetation, which is thesource of the terrestrial plant microfossils found in the marinebasins (Mudie and McCarthy, 2006; Cordova et al., 2009). Studies ofmarine sedimentary sequences provide the opportunity to estab-lish high-resolution records of terrestrial events.

The Black Sea sediments provide an excellent opportunity forhigh-resolution studies of past climatic, vegetation and hydrolog-ical changes. According to Cordova et al. (2009) in contrast to shelfrecords which are affected by erosion during lowstands, pollenrecords from the continental slope and deep-water Black Seamarine cores are of particular interest as they can provide almost

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uninterrupted sequences covering the Pleistocene and Holoceneand can be used to derive an independent record of regional climatechange and aid in the land-based interpretation of the recon-structed vegetation. These reconstructions are able to describe theinteraction between climate and vegetation and also to clarify therole of coastline and other geomorphological changes, salinity andimpacts of human activities in the Black Sea region (Cordova et al.,2009).

Sediments from the Bulgarian sector of the Black Sea have beeninvestigated intensively by means of pollen analysis during the lastthree decades. The biostratigraphic investigations of Quaternarymarine sediments taken by Scientific-Research vessels “Atlantis-2”and “Glomar-Challenger” established a baseline chronostratig-raphy. Palynological investigations of sediments in the deep-waterzone allowed Traverse (1974, 1978a, b), Koreneva and Kartashova(1978) and Koreneva (1980) to outline the stratigraphy of sedi-ments, vegetation dynamics and climate changes along the BlackSea coast from the end of the Pliocene through the Pleistocene ata very low resolution of tens of thousands of years. The first detailedmarinopalynological investigations of the western Black Sea shelfare those of Roman (1974), Bozilova et al. (1979), and Komarov et al.(1979). Based onmarinopalynological data of the western Black Seasediments, the climatic changes during the Late Glacial and Holo-cene were estimated and considered to be the main drivers forvegetation changes along the Bulgarian Black Sea coast (Shimkuset al., 1977; Komarov et al., 1978; Bozilova et al., 1979;Chernyishova, 1980; Filipova and Dimitrov, 1987; Atanassova, 1990,1995, 1999, 2005; Atanassova and Bozilova, 1992; Mudie et al.,2007). Palaeoecological changes during the Quaternary andpossible sea-level fluctuations during the Holocenewere traced outby Filipova-Marinova and Christova (2004), Filipova-Marinova et al.(2004), Filipova-Marinova (2003a, b, 2007) and Hiscott et al.(2007). Mudie et al. (2007) showed that organic-walled microfos-sils including pollen, spores and dinocysts are well-preserved andabundant in deep-water Pleistocene and Holocene sediments.These authors presented pollen assemblages for the last 33 000years, and reported the first high-resolution Holocene pollen influxdata for SW Black Sea shelf. Mudie et al. (2002) also showed theclose correlation between marine pollen assemblage zones in theMarmara and southern Black Seawith lakes in northern Turkey andBulgaria. Quantitative palaeovegetation reconstruction and corre-lation of pollen data of 99 sequences from the Black, Marmara, andAzov Seas are presented by Cordova et al. (2009).

The aim of this study is to reconstruct the Late Quaternaryevolution of the western Black Sea area and the Eastern BalkanRange at a higher resolution than previously available that allowsdetection and attribution of millennial and sub-millennial envi-ronmental events. For this purpose, a high-resolution multi-proxystudy on Giant Gravity Core (GGC) 18 from the Black Sea conti-nental slope is conducted. Whereas previous palaeoecologicalstudies were centered mainly on the analyses of marine sedimentsfrom the southern and northern part of the Bulgarian Black Seaarea, its central part in front of the Cape of Emine was less inves-tigated. Therefore, the new data allows a better more detaileddescription of the pollen stratigraphy and more precise palae-oecological reconstructions of the Bulgarian sector of the Black Sea.

2. Regional setting

2.1. Geomorphology of the Bulgarian sector of the Black Sea

On the basis of the relief, shape, time of formation, character,and speed of sedimentological processes, three geomorphologiczones can be outlined in the western Black Sea shelf: littoral orinner, central, and peripheral or outer (Dimitrov, 1979). The littoral

zone is considered to be of Holocene age. It extends from the coastto a depth of 20e50m for the central part of the Bulgarian Black Seacoastal area. Active wave impact, erosion, and accumulation arecharacteristic processes for this zone (Khrischev, 1984). Thelittoral zone is separated from the central zone by a depression17e20 m deep on the northern Black Sea shelf and 65e70 m deepon the southern Bulgarian Black Sea shelf. The central zone liesbetween 50 and 72 m in depth. Within it, three subzones runparallel to the coast: an inner depression, an area of depositionalbars, and a depositional plain. This zone experiences a high sedi-mentation rate, typically about 2.5 m/kyr (Khrischev, 1984). Theperipheral zone extends to depths between 90 and 120 m. It issubdivided into an outer depression and an area of barrier bars, andits low sedimentation rate is due to sediment removal by strongbottom currents (Dimitrov, 1979).

Within the general morphostructural plan of the Black Seadeep-water basin (Alexiev, 2002), the continental slope covers 25%of its surface. The transition of the shelf to the continental slope isgentle and has a convex-up profile. The slope morphology isaffected by the development of broad submerged valleys, canyons,as well as accumulation zones connected to them. The transitionfrom the continental slope to the deep basin increases in thewestern Black Sea from 1100 m in the north to 2000m in the south.The continental slope of the Bulgarian Black Sea zone is charac-terized by deeply indented relief including land-sliding complexes,fault slopes, ledges, and submerged valleys and canyons. Ninesystems of submerged valleys are established in the area (Alexiev,2002).

The continental foot is formed by the confluence of the sedi-ment of the submerged delta valleys. The gentle transition of thesteep continental slope to the abyssal plain is accomplished by itsslightly undulating plain surface. The formation of the modernshape of the continental slope took place mainly during the Pleis-tocene. The large input of terrestrial sediments that are the mainconstructive material for the continental foot was disrupted by thebreaking-off access of the coastal rivers to the outer zone of thecontinental slope during the Holocene. The limit between thecontinental foot and the abyssal plain is difficult to be located.However, the isobaths 2000e2100 m form a typical abyssal plainwhich declines slightly towards the deepest part of the Black Seabasin. The abyssal plain is the earliest formed morphologicalelement of the Black Sea (Alexiev, 2002).

The modeling of the modern shape of the continental slope tookplace mainly during the Pleistocene. Large inputs of terrestrialsediments to the slope and deep basin discontinued in the Holo-cene as sea level rose and cut-off the access of rivers to the outershelf. The location of the core is on an interfluve zone locatedbetween submarine valleys and displays continuous hemipelagicdeposits for the entire study interval.

2.2. Climate

According to Velev (2002), the Bulgarian Black Sea coast belongsto the Continental-Mediterranean climatic area and is influencedby the proximity of the sea. Climate in the northern part is affectedby strong continental influences. Prevailing winds are northeast-erly, and annual precipitation is about 450e500 mm, witha maximum in June and a minimum in February. Mean Januarytemperature is around 0 �C, dropping to �2 �C inland. In the south,the climate is transitional Mediterranean. Mean annual precipita-tion is estimated at about 500e600 mm, with rainfall mostly in theautumn-winter seasons. Mean January temperature is 2e3 �C, andin July, it is 22 �C. The dry summer period lasts from July toSeptember. Winds blowmostly from the southeast and rarely from

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the northeast. Mean annual precipitation over the mountain areasof the coast (500 m asl) is about 600e1000 mm (Velev, 2002).

2.3. Recent vegetation

According to Bondev (1991), the study area falls within the BlackSea region of the Euxinian province of the European deciduousforest. The eastern Balkan Range area (Eastern Stara Planina Mts.)(Cape Emine area, Fig. 1) is characterized by dominance of xero-thermic forest vegetation with a prevalence of Quercus cerris L. and

Fig. 1. Scheme of the location o

Q. frainetto Ten. Typical for this region is the restricted presence ofstands of southeuxinian taxa such as Quercus polycarpa Schur. andFagus orientalis Lipsky on northern slopes and lower moistureravines together with Carpinus betulus L. with Acer campestre L.,Q. cerris, and Tilia tomentosa Moench. Only in the northernBulgarian Black Sea coastal area, in the South Dobrudzha region(Cape Shabla and Cape Kaliakra area, Fig. 1), there is steppe vege-tation, dominated by Agropyron brandzae Pantu et Solac., Koeleriabrevis Stev., Stipa lessingiana Trin. et Rupr., Artemisia lerchianaWeber, Adonis vernalis L., Paeonia tenuifolia L., among others. Forests

f the investigated GGC 18.

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containing Mediterranean elements, such as Carpinus orientalisMill., Phillyrea latifolia L., Fraxinus ornus L., Quercus pubescensWilld.,and Celtis australis L., are distributed along the southern Black Seacoast. Forests with more continental species grow in lowland sitesand on hilltops, as well as in the Strandzha Mountains. They arecomprised mainly of Q. cerris, Quercus frainetto, Q. polycarpa, and C.betulus. Relict southeuxinian forests of F. orientalis, with anundergrowth of evergreen shrubs (Rhododendron ponticum L., Ilexaquifolium L., and Daphne pontica L.) cluster within the more humidravines of the StrandzhaMountains (Veleka River and Sozopol area,Fig. 1). Riparian forests lining rivers and lakes are periodicallyinundated. Their components are mainly Fraxinus oxycarpa Willd.,Ulmus minor Mill., C. betulus, Quercus pedunculiflora C. Koch, andAlnus glutinosa (L.) Gaerth. The riparian forests are particularly richin lianas: Hedera helix L., Periploca graeca L., Smilax excelsa L., Vitisvinifera L., and Clematis vitalba L. Distributed along the periphery ofcoastal lakes, reed formations are dominated by Phragmites aus-tralis (Cav.) Trin. ex Steud., Typha latifolia L., T. angustifolia L. andSchoenoplectus lacustris (L.) Palla (Kochev and Jordanov, 1981).Psammophytic herb communities, mostly of Leymus racemosus(Lam.) Tzvel. ssp. sabulosus (Bieb.) Tzvel., Ammophilla arenaria (L.)Link, Centaurea arenaria Bieb. ex Willd., Galilea mucronata (L.) Parl,and shrub communities with Cionura erecta (L.) Grsb., grow on thesandy beaches and dunes.

3. Material and methods

3.1. Coring and sampling

The Giant Gravity Core GGC-18 was obtained from the westerncontinental slope of the Black Sea (42�46.5690 N; 28�40.6470E) ata water depth of 971 m (Fig. 1) during the cruise AK06 on the R/VAkademik (Institute of Oceanology, Bulgarian Academy of Sciences).The coring site is out of the submarine canyons and the core iswithout any unconformities caused by regional washouts. Theinvestigated length of the core is 203.5 cm. It includes 3 lithologicalunits: Unit III (203.5e128.5 cm) is represented by light grey clay;Unit II (128.5e58.5 cm) contained sapropels; Unit I (58.5e2.5 cm) iscomposed of coccolith-bearing ooze. The core was sampled at5e10 cm intervals. Sampling of the interval 141.5e126 cm wascarried out at every 1 cm.

3.2. Pollen analysis

All 54 samples were processed according to the standardprocedure of Faegri and Iversen (1992), and removing the mineralcomponents with sodium pyrophosphate and hydrofluoric acid(Birks and Birks, 1980). The laboratory technique includes serialtreatment with hot 10% HCl, hot 7% NaOH, cold 60% HF, glacialCH3COOH, 2 min acetolysis, glacial CH3COOH, cold 1% NaOH andglycerine. By this procedure, cysts of some insignificant dinofla-gellate species could be lost, but the main indicative taxa arepreserved. Pollen types were determined by comparison with thereference collection of the Museum of Natural History of Varna andthe keys of Erdtman et al. (1961), Beug (1961, 2004), Moore andWebb (1978), Faegri and Iversen (1992), and Reille (1992, 1995).The pollen sum (PS) used for percentage calculations was based onthe sum AP (arboreal pollen) þ NAP (non-arboreal pollen) and forthe calculation of the AP/NAP ratio. In most instances a PS of300e500 and a minimum count of 100 dinoflagellate cysts wasachieved. Excluded from PS are spores of mosses and pterido-phytes, pollen of aquatics and dinoflagellate cysts. Their represen-tation is expressed as percentages of the PS. Taxonomy of organic-walled dinoflagellate cysts follows that of Wall et al. (1973) andMarret and Zonneveld (2003). The computer programs TILIA

v.2.0.b.4 (Grimm, 1991) and TGVIEW v.1.5.12. (Grimm, 2011) areused for pollen percentage and pollen concentration calculations.Cluster analysis program CONISS (Grimm, 1987) is applied forzonation. Six local pollen assemblage zones named after thedominant taxa in the pollen spectra (LPAZ GGC-18-1 to GGC-18-6)and two dinocyst zones (DAZ-I and DAZ-II) were recognized (Figs. 2and 3).

3.3. Radiocarbon dating and age modeling

Eighteen sediment layers were selected for 14C AMS dating ofbulk organic carbon at the National Ocean Sciences AcceleratorMass Spectrometry (NOSAMS) Facility, WHOI. Radiocarbon datingof individual organic compounds in concert with bulk organiccarbon (Eglinton et al., 1997) suggests that pre-aged detrital organiccarbon is a minor component of the carbon pool in Holocene BlackSea sediments. This is supported by a new estimate for the onset ofsapropel at w8000 years BP (Bahr et al., 2006), which is signifi-cantly earlier than previously proposed (Jones and Gagnon, 1994).However, until a better understanding for the time variability ofdetrital organic carbon inputs is developed, and for reasons ofconsistency with previous studies, a detrital carbon correction of580 years (so called “reservoir effect”) was applied to the radio-carbon dates (Jones and Gagnon, 1994). An “age vs. depth” model(Fig. 4) for the core was then developed by calibrating the correctedradiocarbon dates to calendar years BP (1950) with CALIB 6.0.1(Stuiver and Reimer, 1993; Stuiver et al., 2005), using the IntCal09curve (Reimer et al., 2009) (Table 1).

4. Results

4.1. Chronology

The stratigraphy of Black Sea sediments deposited under sulfidicconditions has been well described (Jones and Gagnon, 1994; Bahret al., 2005). AMS radiocarbon (14C) dating was performed on 18selected sediment layers spanning all three lithological units(Table 1). According to the “age vs. depth”model (Fig. 4), every 1 cmrepresents on average w40 years of deposition in Unit I, and w60years of deposition in Unit II. A characteristic feature is the lowsedimentation rate ofw316 y of deposition at the boundary of UnitIII and Unit II in the interval 8950 and 7145 cal. BP (8650 � 40 and6840 � 40 14C BP).

4.2. Pollen and dinocyst zonation

Six local pollen assemblage zones (LPAZ) and two dinocystassemblage zones (DAZ) are established on the basis of CONISSanalysis and pollen spectra composition (Table 2).

5. Discussion

5.1. Vegetation dynamics

5.1.1. LPAZ GGC-18-1 (11,840e11,130 cal. BP)This zone is associated with the last most significant rapid

climate deterioration of the last Late Glacial Stage, i.e. the YoungerDryas Stadial. This cold period is of global importance and isrecognized everywhere in Europe as an episode of pronouncedcooling (Berglund et al., 1994) and is also clearly recognised in theMarmara Sea (Mudie et al., 2002, 2007) and in Lake Van sediments(Wick et al., 2003). This stage of the vegetation developmentreflects the expansion of xerophytic herb (steppe) vegetation. Thelight-demanding xerophytic and halophytic taxa such as Artemisiaand Chenopodiaceae prevailed. Palynological data show that many

Fig. 2. 1. Percentage sporeepollen diagram of GGC-18 (arboreals), 2. Continuation.Percentage sporeepollen diagram of GGC-18 (non-arboreals).

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Fig.

2.(con

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Fig. 3. Dinocyst assemblages of GGC-18: I. Stenohaline freshwater to brackish; II. Euryhaline marine.

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020406080100120140160180200

0 2000 4000 6000 8000 10000 12000Radiocarbon Age (cal. yrs BP)

De

pth

(c

m)

Fig. 4. Sedimentation rate of GGC-18 based on the established age vs. depth model.

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other taxa such as Poaceae, Aster-type, Achillea-type, Centaurea,Thalictrum, Apiaceae and Caryophyllaceae have also participated inthese steppe communities. Multiple factors may have beenimportant in determining the vegetation changes in this region,including climate oscillations, sea level and surface water salinitychanges, and possibly also human activities (Cordova et al., 2009).These sediments contain extremely high percentages of Artemisiaand Chenopodiaceae (more than 42% and 14% respectively), and at187.7 cm have an age of 11,870 cal. BP (10,450 � 80 14C BP). Thesedata confirm that Younger Dryas is the coldest and driest periodalong the central Bulgarian Black Sea coast during the whole LateGlacial. The continuous presence of Juniperus and the indicatorfor cold and dry climate Ephedra distachya also confirms the aridityof the climate. High percentage values of Artemisia and Chenopo-diaceaemay have also been a result of thewide extent of halophyticspecies such as Salsola ruthenica, Suaeda maritima, Salicorniaeuropaea and Artemisia maritima growing on the beach area and onthe part of the modern shelf after the withdrawal of the seato �100 m during the Neoeuxinian regression (Chepalyga, 2002).Stands of Pinus, Quercus, Corylus, C. betulus, Ulmus, Tilia and Betulawere sparsely distributed in favorable moisture localities in theEastern Balkan Range (Stara Planina Mts.). This supports thehypotheses of van der Hammen et al. (1971) and Beug (1975) thatthe refugia of deciduous trees would have been located at mid-altitude sites where the precipitation would have been higherthan on the plains during this arid glacial period. This informationis of great importance in tracing out the main migration routes ofthese deciduous trees along the Bulgarian Black Sea coast after the

Table 1Chronology of the investigated GGC 18.

Depth (cm) Lab. no Material dated Uncalibrated

10.5 OS-58560 Bulk 1020 � 3014.5 OS-58560 Bulk 1060 � 3034.5 OS-58602 Bulk 1910 � 3046.5 OS-58502 Bulk 2390 � 3048.5 OS-58501 Bulk 2450 � 2552.5 OS-58498 Bulk 2890 � 3056 OS-58559 Bulk 3120 � 3558 OS-58499 Bulk 3150 � 3571 OS-58559 Bulk 3700 � 3081 OS-58560 Bulk 4200 � 3095 OS-58561 Bulk 4990 � 30119 OS-58587 Bulk 6420 � 30126 OS-58500 Bulk 6840 � 40128 OS-58556 Bulk 6910 � 30133.5 OS-58504 Bulk 8650 � 40141.5 OS-58588 Bulk 9170 � 45163.7 OS-67911 Bulk 9660 � 50187.7 OS-68230 Bulk 10,450 � 80

a detrital carbon correction of 580 years is applied.

last glaciation. Probably the stands of Pinus nigra occupied thehigher parts of the coastal plateaux, where the conditions weremore favorable for the growth of trees because of higher atmo-spheric humidity.

Comparison with other pollen diagrams of marine cores fromthe western Black Sea shelf and deep-water zone (Filipova-Marinova, 2006) shows that this climate oscillation is clearlyapparent along the whole Bulgarian Black Sea coast (Table 3). TheYounger Dryas event in the western Black Sea area is also dated bythe Artemisia maximum at w10,660 cal. BP (Mudie et al., 2007). Alarge increase in NAP with peaks in Artemisia and Ephedra andincreased Chenopodiaceae is found in Core MAR 98-12 of thenearby Marmara Sea during the Younger Dryas (Mudie et al., 2002).According to Niklewski and van Zeist (1970) during the glacials notjust low temperature but primarily low humidity was the limitingfactor for the development of arboreal vegetation. Mudie et al.(2002) and Atanassova (2005) also suggest the presence of decid-uous trees taxa such as Quercus, Alnus, Corylus, Tilia, C. betulus andferns in addition to the steppe taxa such as Artemisia, Chenopo-diaceae, Asteraceae and Ephedra.

Palynolological record from the deep basins of the Marmara Seasuggest high abundance of Artemisia and Chenopodiaceae(respectively up to 30% and 20% in core MAR98-11) and cold anddry climate during the Late Glacial (Caner and Algan, 2002; Mudieet al., 2002).

5.1.2. LPAZ GGC-18-2 (11,130e9290 cal. BP)Palynological information of this zone is of great significance for

reconstruction of vegetation cover along the Bulgarian Black Seacoast as data concerning palaeoenvironment at the onset of theHolocene are scarce due to the unconformity and erosion of shelfsediments at the Pleistocene/Holocene boundary (Khrischev andGeorgiev, 1991). The uninterrupted record of this core from thecontinental slope suggests a forest-steppe phase during the LPAZGGC-18-2. According to the radiocarbon ages 10,010 and 9577 cal.BP (9660 � 50 and 9170 � 45 14C BP) this zone could be associatedwith the Preboreal. A characteristic feature is the replacement ofxerophytic herbs communities by arboreal species. The first step inthe afforestation began after 10,010 cal. BP (9660 � 50 14C BP) withthe rapid increase of arboreal taxa mainly of Quercus and Pinus. Inaddition to Quercus several temperate taxa such as Ulmus, Tilia andC. betulus were present in these forests. These species probablysurvived the severe conditions of the Late Glacial in suitable

BP Calibrated BP (2s range) Calendar BPa Error

803e1047 495 21927e1053 520 21

1740e1929 1198 1042344e2675 1725 972359e2701 1801 712926e3156 2270 873254e3441 2619 1293269e3448 2629 1283930e4147 3331 704627e4842 3954 1115644e5884 5062 1167279e7421 6649 877591e7755 7146 1217674e7423 7244 739538e9689 8950 124

10,236e10,486 9577 13710,786e11,204 10,010 14412,085e12,574 11,870 212

Table 2Description of the local pollen assemblage zones and dinoflagellate zones from GGC 18.

LPAZ GGC-18-1 (203.5e180.5 cm)11,840e11,130 cal. BPArtemisiaeChenopodiaceaeePinusDominant Artemisia (max. 44%), Chenopodiaceae (max. 31%) and Pinus diploxylon-t.

(max. 35%); gradual rise of Quercus (up to 11.2%) at zone top and first Carpinus betuluspollen. Low Corylus, Ulmus and Tilia (up to 1%). Presence of Ephedra distachya (up to 1%).Betula, Fraxinus excelsior-t. and Alnus present.

Continuous Poaceae (around 3.5%), Achillea-t. (1%) and Polypodiaceae (3%). SporadicApiaceae, Lamiaceae and Boraginaceae.

LPAZ GGC-18-2 (180.5e138.5 cm)11,130e9290 cal. BPQuercusePinuseArtemisiaGradual rise of Quercus (9e48.6%) at zone top, high Pinus diploxylon-t. (max. 42.5%) inthe middle part of the zone, then decreasing up to 11.4%, Artemisia (about 25%); slightincrease of Corylus (about 2e5%), constant presence of Carpinus betulus (2%), Ulmus (2%).Tilia, Fraxinus excelsior-t. Betula and Ephedra distachya sporadic. Fagus, Acer, Carpinus orientalisand Humulus/Cannabis appear. Decreasing Chenopodiaceae from 13.9 to 5.2%. Constant presenceof Poaceae, Achillea-t., Lamiaceae, Brassicaceae and Polypodiaceae. First appearance of anthropogenicindicators Polygonum aviculare, Plantago lanceolata, Centaurea cyanus, Carduus-t. and Filipendula.

LPAZ GGC-18-3 (138.5e129 cm)9290-7635 cal. BPQuercuseUlmuseArtemisiaQuercus peak (one spectrum) up to 38.8%, decreasing Pinus diploxylon-t. to 2.6%,

substantial Artemisia (max. 31%); rising Ulmus (1.7e5.6%) and Tilia (0.3e1.7%).Continuous Corylus (ca. 5.4%, at the end e 43%) Carpinus betulus (ca 3.2%).Nearly continuous Fagus, Alnus and Fraxinus excelsior-t (over 1%). First appearance ofHedera. Reduced values of Chenopodiaceae (4.8%). Poaceae, Achillea-t., Apiaceae, Lamiaceaeconstantly present. First appearance of Cerealia-t. and Triticum.

LPAZ GGC-18-4 (129e84 cm)7635-4085 cal. BPQuercuseCoryluseCarpinus betuluseUlmuseFagusDecrease and steadily presence of Quercus (23e28%), coincident sharp increase of Carpinus betulusfrom 2.3 to 18.9%. Corylus peak (one spectrum) up to 43.3% simultaneous with rise of Cerealia-t.up to 2.1% and Triticum up to 1.2%. Rising Ulmus and Fagus (up to ca. 9%), Tilia, Alnus andCarpinus orientalis (up to 2%). Decreasing Pinus to 8%. Juglans, Rhododendron and Erica appear andstart occurring regularly. Nearly continuous Hedera and Humulus Cannabis. Acer and Cornus massporadic. Decreasing Artemisia and Chenopodiaceae. Fluctuating Poaceae, Plantago lanceolata,Urtica and Filipendula.

LPAZ GGC-18-5 (84e59 cm)4085e2570 cal. BPQuercuseCarpinus betuluseFagusIncreasing Quercus from 28 to 37.6% at zone top, continuous Carpinus betulus

(about 16%) and Fagus (ca. 6.3%). Decreasing Corylus from 19 to 4.4%. ContinuousUlmus and Alnus (ca.5%). Slightly decreasing Tilia up to 0.7%. Nearly continuous Fraxinus excelsior andCarpinus orientalis (ca. 2.5%), Hedera and Humulus/Cannabis (0.7%). Slightly rising Artemisia to 19.1% andChenopodiaceae to 6.8% at zone top. Continuous Poaceae (3%), Cerealia-t., Achillea-t. and Plantago lanceolata (0.7%). Papaver, Rumex, Cenaturea cyanus and Centaurea jacea sporadic.

LPAZ GGC-18-6 (59e2.5 cm)2570e95 cal. BPQuercuseAlnuseCarpinus betuluseUlmuseFagusConstant presence of Quercus (ca. 14%), Fagus (6%), Ulmus (3%). Consistantly rising Alnus up to 14%,F. excelsior up to 1%, C. orientalis up to 2.1%. C. betulus and Corylus at decline to 8%, Tilia to 0.5%.Increasing Rhododendron up to 1.3%. Juglans, Ericaceae, Hedera and Acer sporadic. Small rise ofArtemisia (ca. 15%), low Chenopodiaceae and Poaceae (about 5%). Cerealia-t. and Triticum startingcontinuously from 0.4 to 1.7%. P. lanceolata, Taraxum, Rubiaceae, Apiaceae and Fabaceae nearlyconstantly present.

DAZ I (fresh- to brackish- water species)11,840e7990 cal. BPDominant dynoflagelate cysts of Pyxidinopsis psilata (173e24.8%) and Spiniferites

cruciformis (7.5e26.2%). Constant presence of green algal species Pediastrumsimplex var. simplex (3.7e12.0%). Botryococcus very low (0.9%).First appearance of dynoflagelate cysts of Lingulodinium machaerophorum,Spiniferites belerius, Spiniferites benthorii, Polykrikos kofoidii, Peridinium ponticum, andacritarchs Cymatiosphaera globulosa at 130 cm (DAZ-I/II boundary).

DAZ II (euryhaline marine species)7990e95 cal. BPDominant dynoflagelate cysts of L. machaerophorum f. clavatum (max. 56.1%), L. machaerophorum(max. 466.1%), Spiniferites belerius (ca. 8.1%), Spiniferites bentorii, Spiniferites ramosus and Peridiniumponticum (ca. 5%), Echinidinium transparantum (ca. 2%) and acritarchs C. globulosa (ca. 18%). All thosetaxa much oscillating. Spiniferites mirabilis and Polykrikos kofoidii sporadic. Reappearance of S.cruciformis (up to 1%) and P. simplex var. simplex at 59 cm. All dynoflagelate cysts strongly reducedfrom 59 cm to 2.5 cm.

M.Filipova-M

arinovaet

al./Quaternary

International293(2013)

170e183

178

Table 3Correlation between local and regional pollen assemblage zones and subzones (modified after Filipova-Marinova, 2006). Legend: Al¼Alnus, Art ¼ Artemisia, Be¼Betula,Cb¼ Carpinus betulus, Ce¼Cerealia-type, Ch¼ Chenopodiaceae, Co¼Corylus, Cor¼ Carpinus orientalis, F¼Fagus, P¼Pinus diploxylon-type, Po¼Poaceae, Q ¼ Quercus, Sa¼ Salix,Ti¼Tilia, Tr ¼ Triticum, U¼Ulmus;— missing stratigraphic units.

Lo c

alP

AZ

Polle

n as

sem

blag

es

Loc

alP

AZ

Polle

n as

sem

blag

es

Lo c

alP

AZ

Polle

n as

sem

blag

es

Loc

alP

AZ

Polle

n as

sem

blag

es

Lo c

alP

AZ

Polle

n as

sem

blag

es

Loc

alP

AZ

Polle

n as

sem

blag

es

Lo c

alP

AZ

Polle

n as

sem

blag

es

Lo c

alP

AZ

Polle

n as

sem

blag

es

Loc

alP

AZ

Polle

n as

sem

blag

es

Loc

alP

AZ

Polle

n as

sem

blag

es

Lo c

alP

AZ

Polle

n as

sem

blag

es

Lo c

alP

AZ

Polle

n as

sem

blag

es

Lo c

alP

AZ

Polle

n as

sem

blag

es

New Black Sea

Iron Epoch

Q-U-Al-Cb-Sa-

F5

Q-U-Al-Sa-F

8Q-U-Al-F

3Q-Al-Cb-Sa

4Q-Cb-Al-F-

U6

Q-Al-Cb-U-

F5

Q-Cb-Al-U-

F6

Q-Al-Cb-U-F

2 Q-Cb-F-Ce

3Q-Co-Cb-

Ti-F

1Q-Co-

Cb-U-F

aQ-Be-

Co -Art1 Q-Be-

Co-Art2 Q-P-

ArtYounger

Dryasd Art-Ch 2

Ch-Art

1Ch-Art

4Art-Ch

5 Art-Ch 1Art-Ch-P

1Art-Ch

2 Art-Ch

Allerød cP-Art-

Ch4

P-Art-Ch

1P-Art-

Ch

Older Dryas bArt-Ch-

Po3

Art-Ch-Po

Bølling a P-Art 2 P-Art

Oldest Dryas

P-Art-Ch-Po

3 P-Art-Ch-Po

Ch-Art-Po

2Ch-Art-Po

Ch-Art-P

1Ch-

Art-P1

Ch-Art-P

85 Aprilska structure-3

2345

5

3su

bzon

esR

egio

nal

PA

Z

Nor

ther

neur

opea

n cl

imat

ostr

atig

raph

y (B

lytt

187

6 –

Sern

ande

r 19

08) 84

230

270

870

8

12

13

15

30

9

10

11

11.8

unca

l. ky

rs. B

P

Art-Ch-P

1

strati-graphic hiatus

strati-graphic hiatus

strati-graphic hiatus

Q-Co-Art 2

3Q-U-Art

strati-graphic hiatus

Q-Co-U-F-Cb

5Q-Co-U-Ti-Cb-F

6 4

Art-QQ-Co-U-Cb-

Art

4

Q-Co-U-Cb-

Ti3

Q-Co-U-Cb

1

1

2

3

Günz

III

II

I

Riss I-II

Riss I

Uzunlarian

strati-graphic hiatus

Upper-New-euxinian

Upper eoeuxinian

Lower Tschaudinian

PL

EI

ST

OC

EN

E

Q-Cb-Co-F

Q-Cb-Co-U-F-Tr

4 2Q-Cb-

Co-Cor

Boreal

Wür

m

Bronze Age

B L

A C

K

S E

A

Old Black Sea

Pleniglacial

Atlantic

Preboreal

Lat

e G

laci

al

strati-graphic hiatus

Q-Co-U

149

Art-Ch-P

4

IV

V

b

VI

VIII

Urdoviza-F 1 544Sozopol-D Sozopol-I 18 19 GGC18

5Q-Cb-Co-F

Arc

h. c

hron

olog

y

(Tod

orov

a 19

86)

Q-Cb-Co

7Q-Cb-Co-F

Q-Co-Cb-U-

F

Q-Co-U-Ti-

Al3

Q-Cb-F-Cor

4

2Q-Co-Cb-U

Q-Cb-Co-F-U

Polle

n as

sem

blag

es

Reg

iona

l sta

ges

and

subs

tage

s

(Sho

pov

1991

)

Q-Co-Cb-U-Tr-Ce

IX

Transi-tional Period

Eneo-lithic

VII

Q-Cb-Co-F-

Cor-Ce

Neo-lithic

2 Q-Po-Tr-Ce

HO

LO

CE

NE

Subatlantic

Subboreal

Q-Co-Cb-U

Q-Co-U-Art

2Q-Co-

U

3

5Q-Cb-

F

4Q-Co-Cb-U-

F-

Q-Ti-F-Po-Tr 21

3Q-Cb-Co-F-Cor

M. Filipova-Marinova et al. / Quaternary International 293 (2013) 170e183 179

localities. The distribution of open oak forests during the Preborealwas probably stimulated by the temperature rise and the persis-tence of the dry continental climate. Brewer et al. (2002) considerthat climate of the Early Holocene acted as the strongest controllingfactor on the spread of the oak. According to Davis et al. (2003), theEarly Holocene warming and later equilibrium has been mainlymodulated by increased winter temperatures.

The primary role in this initial stage of vegetation palae-osuccesion was taken by Quercus in contrast to the central andNorthern Europe where Corylus appeared as a pioneer element onopen areas prior to the other migrating trees (Birks and Line, 1993).The warming at the start of the Holocene allowed also a rapiddispersal of oak along the Atlantic coast of Europe (Brewer et al.,2002). According to Berglund et al. (1994) such vegetation changeis probably a biotic reaction of the climate improvement beforeabout 10,000 yrs including the rise of temperature. Pinus diploxylonis known as the major contributor to the Early Holocene pollenassemblages (Mudie et al., 2002). Percentage values of Pinus dip-loxylon-type declines, while the deciduous arboreals expanded theirpresence in the pollen spectra. Taking into account the over-representation of Pinus pollen in modern surface samples from thewestern and central Balkan Range (Stara Planina Mts) (Filipovitchet al., 1997) and from the Black Sea Coast (Pardoe et al., 2010) thehigh values of Pinus pollen could be partly due to the long-distancetransport. The formation of isolated stands of P. nigra on higherplaces on the Eastern Balkan Range could not be excluded.

The reconstructed vegetation succession is in good agreementwith results of previous studies of sediments from the Bulgarian

Black Sea coast. The first increase of deciduous arboreal pollen,mainly of Quercus is dated at 9630 � 20 14C BP in deep-watersediments of the Black Sea (Filipova et al., 1989) and at9945 � 160 14C BP at the estuary of the Veleka River in theStrandzha Mountains, southern Bulgarian Black Sea coast (Filipova-Marinova, 2003a). Mudie et al. (2002) also reportfd that Quercus, C.betulus and Ulmuswere presented in the Early Holocene and beganto expand after 8500 BP. Similar changes in vegetation compositionalong the coast during that time have also been documented byAtanassova (2005). Such a vegetation change is classically observedat the beginning of the Holocene along the Mediterranean(Tzedakis, 2007).

5.1.3. LPAZ GGC-18-3 (9290e7635 cal. BP)This zone could be correlated to the Boreal chronozone. The AP/

NAP ratio suggests denser forest communities during this time dueto the increase of temperatures and humidity. The maximumextension of Quercus forests is characteristic. Probably, different oakspecies such as Q. cerris, Q. frainetto, Q. pubescens and Q. polycarpatook part in the composition of these forests. C. betulus is still aninsignificant component of the oak forests. A characteristic featureis also the increase of Corylus in the pollen spectra. This taxon wasa major component of the mixed oak forest. Tilia and Fagus increaseinsignificantly. The presence of Ulmus supports the assumption ofStojanov (1950) that in the past, Ulmus forests were importantcomponents of the vegetation of the lowlands.

At the end of the zone, however, a sharp and short forestdecrease event is established. A very low sedimentation rate of

M. Filipova-Marinova et al. / Quaternary International 293 (2013) 170e183180

w316 y/cm (Fig. 4), decrease of AP, mainly of Pinus and Ulmus,presence of E. distachya, and increase of Artemisia is observed at130.5 cm that corresponds to an age of 8344 cal. BP. This eventcould be associated with the “8200 y BP cold event” (Magny et al.,2003; Bahr et al., 2005) and is hereby identified for the first time bythe pollen analysis of sediments from the Black Sea. This event isalso identified in a Holocene sequence from the Lake Prespa byPanagiotopoulos et al. (2013) for the Balkan region. The shrinking oftemperate forests very likely also reflects a decrease in humidity(Combourieu Nebout et al., 2009; Dormoy et al., 2009).

5.1.4. LPAZ GGC-18-4 (7635e4085 cal. BP)The palynological record implies that the next stage of the

vegetation palaeosuccession could be correlated to the Atlanticchronozone. The mixed oak forests reached their maximal distri-bution at 5745 cal. BP. The extremely high values of AP suggestthat forests become denser. Quercus appears to be the majorarboreal constituent in the mixed oak forests with abundantUlmus, Corylus, Tilia, Carpinus betulus, Fraxinus excelsior, and Acer.The optimal climate conditions (high temperature and humidity)stimulated the extensive spreading of these forests. According toTonkov and Bozilova (1995) high humidity on Balkan Peninsulawas reached after 8000 BP and the climate was determined by thetransport of air masses from the Atlantic Ocean. The presence ofthe indicators Hedera and Humulus/Cannabis suggests an increaseof humidity and rise in mean annual temperatures. The mostcharacteristic feature of the Bulgarian Black Sea coastal zoneduring the Atlantic is the increase of C. betulus after 6650 cal. BP(6420 � 30 14C BP). In addition to being part of the mixed oakforests, C. betulus also formed separate communities at higheraltitudes and on northern slopes. In the western and central Bal-kan Range, hornbeam also formed separate belts (Filipovich, 1987).The areas occupied by Fagus were also enlarged. Corylus expandedand became widespread from 7245 to 6650 cal. BP (6910 � 30 to6420 � 30 14C BP). This taxon has high pollen productivity andpossibility of long-distance transport when growing in open pla-ces. Pollen data suggest the great extent of monodominantcommunities of Corylus in open areas, but probably also as anundergrowth of the oak forests. The maximum percentage valuesof Corylus could be also associated with clearance of mixed oakforests for enlargement of cultivated areas along the coast(Filipova-Marinova, 2006). The presence of single pollen grains ofCerealia-type and Triticum and ruderals such as Plantago lanceolataand Polygonum aviculare is connected with human activities.According to the Archaeological Chronology (Todorova, 1986) thisperiod could be referred to the Eneolithic (6420e5910 cal. BP).Human impact was significant along the western Black Sea coastas reflected in pollen diagrams from the Bulgarian Black seacoastal lakes (Bozilova and Filipova, 1991; Bozilova and Beug,1994). After 6650 cal. BP (6420 � 30 14C BP), when the forestcover became denser, a diminishing of Corylus pollen productionoccurred with subsequent restriction in its distribution under theforest canopy. The areas occupied by Fagus expanded after6650 cal. BP (6420 � 30 14C BP) reflecting favorable conditions forits spreading, and Fagus started to be better represented along theBlack Sea coast. Fagus forests were distributed in suitable localitiesat lower altitudes. However, the increase of Fagus in the southernpart of the Bulgarian Black Sea coast started as early as post-8355 � 75 14C BP (Filipova-Marinova, 2003a). Along the northernBulgarian Black Sea coast the spread of Fagus started later and itsexpansion maximum occurred around 3070 � 100 14C BP (Filipova,1985). Nowadays, communities of this species could be found onthe Eastern Balkan Range at altitudes between 170 and 450 m asl(Bondev, 1991). The presence of Alnus together with single pollengrains of Rhododendron confirms the increase of humidity and

temperature along the coast. The presence of Ericaceae pollensuggests spreading of some taxa from this family (such as Vacci-nium and Calluna) based on their recent distribution in the EasternBalkan Range. The submediterranean element C. orientalisappeared and probably occupied some areas after the degradationof mixed oak forests due to a human impact that influenced thenatural vegetation. The presence of Juglans throughout LPAZ GGC-18-4 is registered after 7120 cal. BP. However, the question ofwhether the presence of this taxon in the pollen diagrams fromthe Black Sea is connected with human culture or is a result of itsnatural spread along the coast is debatable. The earliest appear-ance of single pollen grains of Juglans along the southern BulgarianBlack Sea coast during the Holocene is registered for Preboreal, ca.10,000 cal. BP (Filipova-Marinova, 2003a), confirming the likelyrelict origin of this taxon in the Balkan Peninsula (Bottema, 1980).

5.1.5. LPAZ GGC-18-5 (4085e2570 cal. BP)The presence of themixed oak forests continued from4990� 30

14C BP to 3150 � 35 14C BP. The radiocarbon dates and the charac-teristic vegetation succession allow the correlation of this pollenzone with the Subboreal. Mixed oak forests were still dominant.Percentages of the non-arboreal pollen types are low. A maincharacteristic feature is the change in vegetation composition. C.betulus, Quercus, Ulmus, and Tilia show constant values. Apart fromtaking part in the composition of mixed oak forests, C. betulus verylikely also formed isolated communities in restricted areas onnorthern slopes, and along the river valleys. According to data fromFilipovitch et al. (1998), at about the same time this species formeda separate belt on higher areas in the Balkan Range. Hornbeam beltwas also common on eastern Carpathians during the Subboreal anddated to around 4210 � 35 14C BP (Tantau et al., 2011). The humanimpact during the Bronze Age coincides with the increase of C.orientalis and the presence of anthropogenic indicators, includingCerealia-type. The presence of Acer and F. excelsior suggest thatthese taxa also appeared in the mixed oak forests.

5.1.6. LPAZ GGC-18-6 (2570e95 cal. BP)This zone reflects vegetation dynamics after 3150 � 35 14C BP

and could be correlated to the Subatlantic. The most characteristicfeature is the formation of the modern vegetation communitiesalong the coast. At the onset of Subatlantic, mixed oak and horn-beam forest decrease probably due to the human impact during theIron Epoch. This is confirmed by the increase of cereals and otheranthropophytes such as Plantago lanceolata, Polygonum aviculare,and Filipendula. Most probably C. orientalis enlarged its spreading inthe areas previously covered by oak forests. The significant increaseof Alnus is due to the increase of humidity and cooling of climatethat is connected with the formation of the specific flooded “lon-goz” forests along the river valleys dominated nowadays by Alnusglutinosa, Fraxinus oxycarpa, Ulmus minor, C. betulus, and Q.pedunculiflora (Filipova-Marinova, 2006).

5.2. Dinocyst assemblages

The two main dinoflagellate cyst assemblages, DAZ-I dominatedby fresh- to brackish water species such as Spiniferites cruciformisand Pyxidinopsis psilata and DAZ-II respectively characterized byeuryhaline marine Mediterranean species such as Lingulodiniummachaerophorum, Spiniferites belerius, Spiniferites bentorii, Spinifer-ites mirabilis, Operculodinium centrocarpum and acritarchs Cyma-tiosphaera globulosa document a significant change in sea surfacesalinity (SSS) at around 7990 cal. BP from low salinity (<7&) to thepresent day conditions (Fig. 3).

DAZ-I is highly similar to the previously established freshwaterto brackish water New Euxinic Stage assemblage (Unit 3) of Wall

M. Filipova-Marinova et al. / Quaternary International 293 (2013) 170e183 181

and Dale (1974) as well as to the dinocyst assemblage zones B2 andB1c of Mudie et al. (2004). The overall low diversity was also notedby Wall et al. (1973) and Mudie et al. (2001, 2002). The assemblageis associated with SSS less than 7& (Deuser, 1972; Wall and Dale,1974; Mudie et al., 2001), while Chepalyga (2002) suggests thateven lower salinities (less than 5&) may have occurred during thisinterval. According to Wall et al. (1973), S. cruciformis and P. psilataare cool water, low salinity stenohaline species that were commonin Late Glacial to Early Holocene sediments. S. cruciformis alsooccurred in Late Glacial sediments from the Lake Kastoria, northernGreece (Kouli et al., 2001) and in the brackish Caspian and Aral Seas(Marret et al., 2004). The presence of all these dinoflagellate speciesis probably connected with the eustatic regression of the WorldOcean during the Late Glacial and the decrease of the Black Sealevel down to 90e110 m. It is also related with the ceasing of theconnection with the Mediterranean, as well as with the influx ofglacial meltwater from the European ice sheet during the LateGlacial (Stanley and Blanpied, 1980; Aksu et al., 1999; Chepalyga,2002). According to Major et al. (2002) these sea level changesare directly related to the river/precipitation input versus water lossby evaporation and periodic overflow of Caspian Sea waters to theBlack Sea. The draining of meltwater into the Black Sea led to risingof its level during the deglacial interval 10,000e7000 BP, intenseoverflow of freshwater into the Sea of Marmara, which precludedthe rapid invasion of Mediterranean species into the Black Sea.

An abrupt change in the composition of dinoflagellate cystsoccurred at 7990 cal. BP (boundary between DAZ-I and DAZ-II)(Fig. 3). Mudie et al. (2001) consider that the virtual disappear-ance of S. cruciformis and P. psilata suggests the inability of thesestenohaline taxa to survive an apparently abrupt salinity change tovalues as high as 10e12& (Deuser, 1972), or even 18& (Wall andDale, 1974). The appearance of euryhalinous marine dinoflagellatespecies Lingulodinium machaerophorum, Spiniferites ramosus andacritarchs C. globulosa indicate an increase of water salinity anda rise in the sea level around 7650 cal. BP (6880 � 260 14C BP)(Filipova-Marinova, 2003b). Such a dinoflagellate assemblagepoints to salinity values of 17e19& (Deuser, 1972). The isotopicsalinity estimates are in closed agreement with the present-daysurface salinity of 18& (Mudie et al., 2002), although highervalues of 18e22& were previously cited by Wall and Dale (1974).The low temperature tolerance of these species could be anotherfactor that controlled their demise (Wall et al., 1973).

The algal blooms, especially of euryhaline marine species Lin-gulodinium machaerophorum, Spiniferites benthorii, S. mirabilis andS. belerius coincide with high temperatures and salinity of surfacewaters during the Holocene climate optimum (7635e4085 cal. BP)and the high productivity of phytoplankton was connected to thefavorable climatic conditions along the Bulgarian Black Sea coast. Inother cores from the Black Sea continental slope, this change isdated at 7010 cal. BP (6135 � 75 14C BP) and 7565 cal. BP(6775 � 300 14C BP) (Atanassova, 1995). Based on molluscan anal-ysis, Ryan et al. (1997, 2003) proposed that Black Sea salinificationdid not start until 7925 cal. BP (7150 � 40 14C BP), and that post-glacial connection between the Mediterranean and the Black Seaoccurred as a catastrophic flood of saline water into the Black Seathat rapidly inundated the basin.

This GGC-18 palaeorecord is followed by a succession of speciessuggesting a decrease of temperature and salinity at 59 cm(2570 cal. BP). There is an unusual presence of S. cruciformis, as wellas of the freshwater green algae Pediastrum simplex var. simplex, andthe decrease of percentage values of the euryhaline marine speciesat the transition of the Unit II to Unit I, that coincides with thetransition from a relatively dry and warm climate (typical for theSubboreal) to relatively cold and wet climate (typical for the Sub-atlantic). This palaeoenvironmental change indicates a decrease of

SSS caused by the large freshwater input into the Black Sea from therivers Danube, Dniester, Dnieper and Don. Substantial freshening ofthe Black Sea surface waters from w29& to approximate 19&,based on alkenones of the coccolithophorid Emiliania huxleyi in thelast 3000 years was also reported by van der Meer et al. (2008).Combined lipid biomarkers and fossil DNA analysis of alkenones ofEmiliania huxley from the same GGC-18 sedimentary record indi-cate a gradual cooling from 19 �C to 15 �C after 2570 cal. BP (Coolenet al., 2009).

6. Conclusions

This new palynological record from the western Black Seasuggests that open oak forests spread in the Eastern Balkan Rangeat the beginning of the Holocene and clearly documents the earlymigration of the major temperate arboreal species such as Quercus,Ulmus, Tilia and C. betulus over the mainland. The vegetationpalaeosuccession continues with the spreading of mixed oakforests from 8650 � 40 until 3120 � 35 14C BP followed by serieschanges linked to the human impact and climate oscillations. Arapid cooling event that is documented around the NorthernHemisphere as the “8200 yrs cold event” is reported for the firsttime in both marine sediment records from the Bulgarian Black Seaarea, as well as by pollen analysis of such materials. An abruptchange in the composition of dinoflagellate cysts occurred at7990 cal. BP. Substantial freshening of Black Sea surface waters at2570 cal. BP is established and related with regional climatechanges.

Acknowledgments

We would like to thank R/V Akademik crew and IO-BASresearchers for their extensive organizational and participatoryhelp with the cruise. We are grateful for the financial support fromUS National Science Foundation grant OCE 0602423, as well asfunding from WHOI’s Access to the Sea program, and a grant fromthe Andrew W. Mellon Foundation Endowed Fund for InnovativeResearch. Constructive comments from the editor Daniel Veres,Professor Donatella Magri and the anonymous reviewer, are greatlyacknowledged.

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