Research Article |
Corresponding author: Mariana Filipova-Marinova ( marianafilipova@yahoo.com ) Academic editor: Snejana Moncheva
© 2024 Mariana Filipova-Marinova, Danail Pavlov, Krasimira Slavova.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Filipova-Marinova M, Pavlov D, Slavova K (2024) Paleoclimate changes and ecosystem responses of the Bulgarian Black Sea zone during the last 26000 years. Nature Conservation 55: 201-248. https://doi.org/10.3897/natureconservation.55.121842
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Multi-proxy analysis (spore-pollen, dinoflagellate cysts, other non-pollen palynomorphs (NPPs), radiocarbon dating and lithology) was performed on marine sediments from three new cores retrieved during the two cruise expeditions on board the Research Vessel “Akademik” in 2009 and 2011. The Varna transect comprises three cores extending from the outer shelf, continental slope and deep-water zone. The record spans the last 26000 years (all ages obtained in this study are given in calendar years BP (cal. yrs BP)). The pollen record reveals the spreading of steppe vegetation dominated by Artemisia and Chenopodiaceae, suggesting cold and dry environments during the Late Pleniglacial – Oldest Dryas (25903–15612 cal. yrs BP). Stands of Pinus and Quercus reflect warming/humidity increase during the melting pulses (19.2–14.5 cal. ka BP) and the Late Glacial interstadials Bølling and Allerød. The Younger Dryas (13257–11788 cal. yrs BP) coldest and driest environments are clearly demonstrated by the maximum relative abundance of Artemisia and Chenopodiaceae. During the Early Holocene (Preboreal and Boreal chronozones, 11788–8004 cal. yrs BP), Quercus appeared as a pioneer species and, along with other temperate deciduous arboreal taxa, formed open deciduous forests as a response to the increased temperature. The rapid expansion of these taxa indicates that they survived in Glacial refugia in the coastal mountains. During the Atlantic chronozone (8004–5483 cal. yrs BP), optimal climate conditions (high humidity and increased mean annual temperatures) stimulated the establishment of species-rich mixed temperate deciduous forests. During the Subboreal chronozone (5483–2837 cal. yrs BP), Carpinus betulus and Fagus expanded simultaneously and became more important components of mixed oak forests and probably also formed separate communities. During the Subatlantic chronozone (2837 cal. yrs BP to pre-industrial time), climate-driven changes (an increase of humidity and a cooling of the climate) appear to be the main drivers of the specific vegetation succession expressed by increased abundance of Alnus, Fraxinus excelsior and Salix along with lianas, suggesting formation of flooded riparian forests (so called ‘Longoz’) lining the river valleys along the Black Sea coast. The first indicators of farming and other human activities have been recorded since 7074 cal. yrs BP. The dinoflagellate cyst (dinocyst) assemblages have been analysed to assess the changes in the Black Sea environment over the last 26000 years in terms of fluctuation in paleoproduction and surface water conditions related to changes in climate, freshwater input and Mediterranean water intrusion. Two major dinocyst assemblages were distinguished: one dominated by stenohaline freshwater/brackish-water species and a successive one dominated by euryhaline marine species. The changes in the composition of the assemblages occurred at 7668 cal. yrs BP. The abrupt decrease of stenohaline freshwater/brackish-water species Pyxidinopsis psilata and Spiniferites cruciformis was followed upwards by a gradual increase in euryhaline marine species, such as Lingulodinium machaerophorum, Spiniferites belerius, S. bentorii and acritarch Cymatiosphaera globulosa. The first occurrence of euryhaline marine species took place synchronously with the onset of sapropel deposition. Modern marine conditions were established after 6417 cal yrs BP when an abundance of Mediterranean-related species, such as Operculodinium centrocarpum and Spiniferites mirabilis, along with other heterotrophic species, occurred. After the stable cold and dry environment during the Last Glacial Maximum, the phytoplankton record of core AKAD 11-17 shows that Pediastrum boryanum var. boryanum has a cyclical abundance associated with the deposition of four red-brown clay layers between 19.2 and 14.5 cal. ka BP. This event is associated with the major melting phase of European Ice drained by the Danube and Dnieper Rivers in response to climate warming observed after the end of the Last Glacial Maximum. During the Early Holocene, P. psilata, characterised by a preference to warmer temperatures, demonstrates its ecological optimum for growth concerning SST reaching maximum relative abundance of 94% between 11072 and 8638 cal. yrs BP. This maximum was interrupted by an abrupt significant short-term decrease in the relative abundance of P. psilata centred between 8500 and 8300 cal. yrs BP reflecting cold conditions similar to those of Younger Dryas. This finding, also confirmed by the rapid significant decrease of arboreal pollen, particularly of Quercus in the same studied core, is considered a regional expression of the well-known ‘8.2 ka cold event’ which is commonly linked to a meltwater-related perturbation of the Atlantic Meridional Overturning Circulation (AMOC) and associated collapse of oceanic northward heat transport. Our fossil pollen and dinocyst data confirm that the high amplitude temperature anomaly associated with ‘the 8.2 ka cold event’ may have also occurred in south-eastern Europe, at lower latitudes of the western Black Sea coastal area, most probably due to atmospheric transition and/or river discharge.
Dinoflagellate cyst, non-pollen palynomorphs, radiocarbon dating, spore-pollen analysis
The Black Sea, as an almost isolated marginal sea, is particularly sensitive to paleoenvironmental changes and, therefore, Black Sea sediments provide an excellent opportunity for high-resolution studies of past climatic, vegetation, human activity and hydrological changes in the catchment (
The Black Sea sediments have been intensively investigated by multi-proxy analysis during the last five decades. The biostratigraphic investigations of Quaternary marine sediments taken by the Scientific-Research vessels ``Atlantis-2” and “Glomar-Challenger’’ established a baseline chronostratigraphy. Palynological investigations of sediments from the deep-water zone allowed
The pioneer work of
Recent studies in the western Black Sea are focused mainly on palaeoecological changes during the Late Glacial and Holocene. There is a lack of uninterrupted Late Quaternary sediments from the northern Bulgarian Black Sea area adjacent to Varna. Therefore, in order to obtain appropriate records which would allow a better more detailed description of the pollen and dinocyst stratigraphy and more precise palaeoecological reconstructions of the Bulgarian sector of the Black Sea, two expeditions by the Research Vessel “Akademik” in 2009 and 2011 were carried out. A total of 105 new samples were taken for multi-proxy analysis of sediments from three representative cores: AKAD 11-17 (deep-water zone, water depth: 1805 m, core length: 228.5 cm), AKAD 09-10 (zone of the continental slope, water depth: 1000 m, core length: 240 cm) and AKAD 09-15 (outer shelf zone, water depth 164 m, core length 377 cm).
The aim of this study is to establish the palaeoclimatic, palaeohydrological and environmental dynamics of the Bulgarian Black Sea coastal area during the Late Pleistocene and Holocene, as well as to evaluate the timing and extent of the passage between various events previously described in other studies, based on multi-proxy analysis.
The Black Sea (Fig.
The most recent pelagic sediment layers in the Black Sea can be divided into three units:
The large continental shelf in the north-western Black Sea narrows in the southerly direction. On the basis of the relief, shape, time of formation, character and speed of sedimentological processes, three geomorphological zones can be outlined in the western Black Sea shelf: littoral or inner, central and peripheral or outer (
According to the general morphostructural plan of the Black Sea deep-water basin, the continental slope covers 25% of its surface. The transition of the shelf to the continental slope is gentle and has a convex-up profile. The continental slope of the Bulgarian Black Sea zone is characterised by deeply-indented relief including land-sliding complexes, fault slopes, ledges and submerged valleys and canyons. Nine systems of submerged valleys are established in the area (
The continental foot is formed by the confluence of the sedimentation materials of the submerged delta valleys. The gentle transition of the steep continental slope to the abyssal plain is accomplished by its slightly undulating plain surface. The formation of the modern shape of the continental slope took place mainly during the Pleistocene. The large input of terrestrial sediments that are the main constructive material for the continental foot was disrupted by the breaking-off access of the coastal rivers to the outer zone of the continental slope during the Holocene. The limit between the continental foot and the abyssal plain is difficult to be located. However, the isobaths 2000–2100 m localise a typical abyssal plain which declines slightly towards the deepest part of the Black Sea Basin. The abyssal plain is the earliest formed morphological element of the Black Sea (
According to
The Bulgarian Black Sea coast covers a narrow strip of land located to the west of the Black Sea coastline. It is 375 km long and 30 to 50 km wide and includes Southern Dobrudzha, the Eastern Stara Planina Mountains (Balkan Range), Burgas Plain and the Eastern Strandzha Mountains. Climate controls and local topography play a dominant role in determining the pattern of highly-varied natural vegetation. This area is considered as a major pollen source area for the investigated core sediments with consideration of wind pattern, river input and gyre systems in the Black Sea. In addition to the vegetation distribution map, simplified characteristics of vegetation types are presented by
Sediments pertinent to this study were collected during expeditions in 2009 and 2011 onboard the Research Vessel Akademik owned by the Institute of Oceanology of the Bulgarian Academy of Sciences. The two cruise expeditions recovered a series of sediment cores on a number of shallow-to-deep transects from the Bulgarian Black Sea area. The Varna transect consists of three cores taken from the shelf, continental slope and deep-water zone of the Black Sea (Fig.
Lithological and geochronological correlations of the studied cores AKAD 11-17, AKAD 09-10 and AKAD 09-15.
Core Akad 11-17 (42°51'13.50"N, 29°01'08.50"E) was recovered from a water depth of 1805 m in the Black Sea deep-water zone (Fig.
Core Akad 09-10 (42°54.8'N, 28°45.6'E) was recovered from a water depth of 1000 m on the Bulgarian Black Sea continental slope (Fig.
Core Akad 09-15 (42°58.628'N, 28°33.147'E) was recovered from a water depth of 164 m on the Bulgarian Black Sea shelf (Fig.
A total of 105 samples were selected for palynological, dinoflagellate cyst and other non-pollen palynomorph analyses. Each sample consists of 1 cm3 of wet sediment. The sampling interval was 10 cm. Sediments characterised by much higher sedimentation rates were sampled with varying resolution (Figs
Pollen types were identified using the reference collection of modern pollen types of the Museum of Natural History of Varna, keys in
Percentage diagram of dinocysts, other algae and non-pollen palynomorphs (NPPs) in Core AKAD 11-17 (Black Sea deep-water zone).
Percentage diagram of dinocysts, other algae and non-pollen palynomorphs (NPPs) in Core AKAD 09-10 (Black Sea continental slope).
The stratigraphic subdivision of sediments from the western Black Sea area is based on qualitative interpretation of the pollen and spore assemblages and the vertical and spatial distribution of selected indicator taxa. The pollen assemblage zones distinguished are based entirely on the percentage abundances of the predominant and indicator pollen and spores in the assemblages. Pollen spectra delimited for each assemblage zone were obtained from several samples in each sediment core and provide a picture of vegetation changes for the period represented by sediments. According to
Radiocarbon (14C) dating was performed on 15 selected sediment layers (Table
Core AKAD | Depth (cm) | Lab. No | Material dated | Uncalibrated yrs BP | Calibrated yrs BC (2σ range) | Calendar yrs BP* |
---|---|---|---|---|---|---|
11-17 | 27 | GdA-2598 | Bulk | 3345±20 | 909–732 | 2759 |
11-17 | 58.5 | GdA-2599 | Bulk | 7470±25 | 5722–5537 | 7584 |
11-17 | 134.5 | GdA-2601 | Bulk | 12850±35 | 12170–11866 | 13971 |
11-17 | 145.5 | GdA-2602 | Bulk | 13660±40 | 13687–13233 | 15395 |
11-17 | 179.5 | GdA-2603 | Bulk | 15860±45 | 16587–16175 | 18346 |
11-17 | 228.5 | GdA-2604 | Bulk | 16950±50 | 17798–17343 | 19534 |
09-10 | 126 | OS-79014 | Bulk | 6920±40 | 5271–4978 | 7074 |
09-10 | 180 | OS-79016 | Bulk | 19850±170 | 21500–20592 | 22985 |
09-10 | 212 | OS-79017 | Bulk | 21100±170 | 23073–22054 | 24451 |
09-10 | 240 | OS-79018 | Bulk | 22400±230 | 24444–23510 | 25903 |
09-15 | 10 | OS-79753 | Mollusk | 10300±50 | 9151–8757 | 10906 |
09-15 | 120 | OS-79754 | Mollusk | 10950±45 | 10181–9582 | 11877 |
09-15 | 170 | OS-90808 | Mollusk | 11500±40 | 10807–10603 | 12648 |
09-15 | 300 | OS-79756 | Mollusk | 12900±50 | 12234–11892 | 14021 |
09-15 | 375 | OS-74855 | Mollusk | 13000±60 | 12562–11954 | 14144 |
On the pollen diagrams, six LPAZ from Core AKAD 11-17 (LPAZ AKAD 11-17 1–6) and four LPASZ (LPASZ AKAD 11-17 2 a, b, c, d) (Fig.
Description of the local pollen assemblage zones and subzones (LPA(S)Z) and local dinoflagellate cyst assemblage zones and subzones (LDA(S)Z) from cores AKAD 11-17, AKAD 09-10 and AKAD 09-15.
LPAZ AKAD11-17-1 (228.5–147.5 cm) | LPASZ AKAD11-17-2a (147.5–136.5 cm) | LPASZ AKAD11-17-2b (136.5–134.5 cm) |
19546-15612 cal. yrs BP | 15612-14295 cal. yrs BP | 14295-14036 cal. yrs BP |
Artemisia-Chenopodiaceae-Pinus | Pinus-Artemisia-Chenopodiaceae | Artemisia-Chenopodiaceae |
Dominant non-arboreal pollen (NAP) (up to 72%), mainly Artemisia (around 50%) and Chenopodiaceae (10%). Continuous Poaceae (ca. 2%), Aster-t. (1%) and Brassicaceae (1%). Sporadic Achillea-t., Caryophyllaceae and Scleranthus. Arboreal pollen (AP) dominated by Pinus diploxylon-t. (up to 25%). Regular presence with low values (up to 1%) of Picea, Abies, Juniperus and Ephedra distachya. Gradual decrease of Quercus from 12% up to 3% and of Corylus (3.8-0.5%) at zone top. Continuous low Betula and Ulmus (up to 0.8%). Sporadic Alnus, Carpinus betulus, Fagus and Tilia. | Maximum of Pinus diploxylon-t. (up to 42%), coincident with decrease of Artemisia (50 to 35%), constant Chenopodiaceae (to 12.8%). Constant presence of Quercus (ca. 4%), Corylus, Ulmus and Salix (ca. 1%). Sporadic Hippophae. Poaceae, Cichoriaceae, Aster-t., Achillea-t., Brassicaceae and Centaurea jacea-t. are continuously presented. | One spectrum: Rapid rise of Artemisia (35-70%) and Chenopodiaceae (up to 16%). Presence of Poaceae (2%) and Achillea-t. (2%). Rapid decrease in Pinus diploxylon-t. (from 42% to 6%). Slight increase in Juniperus and Ephedra distachya. Decline of Quercus (from 4% to 1.5%). |
LPASZ AKAD11-17-2c (134.5–125.5 cm) | LPASZ AKAD11-17-2d (125.5–99.5 cm) | LPASZ AKAD11-17-3 (99.5–63 cm) |
14036-13257 cal. yrs BP | 13257-11072 cal. yrs BP | 11072-8004 cal. yrs BP |
Pinus-Artemisia | Artemisia-Chenopodiaceae | Quercus-Artemisia-Chenopodiaceae |
Two spectra: Rapid rise of Pinus diploxylon-t. (from 6% to 25%), decrease of Artemisia (from 70% to 58%) and Chenopodiaceae (from 15% to 10%). Continuous Poaceae (around 2%). Presence of Picea, Quercus, Corylus, Juniperus and Ephedra distachya. | Sharp rise of NAP (up to 86%), including highest values of Artemisia (around 67%), max. at the zone bottom. (up to 82%). Gradual increase of Chenopodiaceae (11-16%) and Poaceae (1-3%) at the zone top. Pinus diploxylon-t. after sharp decrease is stabilised below 11%. Constant Quercus (around 2-3%), increased Corylus (up to 1%) at the zone top. Regular low presence of Picea, Juniperus, Ericaceae, Ephedra distachya, Betula, Salix and Hippophae. Presence of numerous heliophytes including Helianthemum, Scleranthus, Caryophyllaceae, Centaurea jacea-t. | Gradual rise of Quercus (1-16%), coincidently with decrease of Artemisia (from 64% to 34%). Abrupt decrease in Pinus diploxylon-t. (up to 5%) at the zone top. Trend to rise of Picea, Betula, Corylus and Salix (up to 2%) at the zone top. First significant presence of Carpinus betulus (6%). Presence of Ephedra distachya (0.8%) and Hippophae (0.2%). Typha angustifolia/Sparganium-t., Athyrium and Dryopteris/Thelypteris-t. appear. |
LPAZ AKAD11-17-4 (63–44.5 cm) | LPAZ AKAD11-17-5 (44.5–27.5 cm) | LPAZ AKAD11-17-6 (27.5–3.5 cm) |
8004-5483 cal. yrs BP | 5483-2837 cal. yrs BP | 2837 cal. yrs BP-preindustrial time |
Quercus-Corylus-Carpinus betulus-Ulmus-Cerealia-Triticum | Quercus-Carpinus betulus-Corylus-Fagus-Carpinus orientalis-Cerealia | Quercus-Alnus-Ulmus-Carpinus betulus-Fagus |
Dominant Quercus (max. 29%) and Corylus (max. 27%). Consistent increase in Ulmus (0.5-7 %) and Tilia (up to 1.2%). Abundance of Salix and frequent Betula (about 1.1%). Rise of Alnus (up to 3.1%) and Fagus (up to 5.4%) at the zone top. Sporadic Fraxinus excelsior-t., Acer, Pistacia and Hippophae. Constant presence of Hedera. Carpinus orientalis and Fraxinus ornus appear. Decrease in Pinus haploxylon-t. (from 20% to 2.4%). Increase in Picea (up to 1.1%). Abies, Juniperus and Ericaceae are sporadic. Decrease in Artemisia (from 64.4 to 13%) and Poaceae (from 8.5 to 2.6%). Decline of Chenopodiaceae (from max. 24.9% to 2.4%). Appearance of Cerealia-t. (1.3%) and Triticum. Achillea-t., Aster-t., Cichoriaceae, Brassicaceae, Scleranthus, Plantago lanceolata, Polygonum aviculare, Caryophyllaceae and Centaurea jacea-t. present. Polypodiaceaе (around 0.8%), Typha angustifolia/Sparganium-t., Typha latifolia and Cyperaceae are continuously present. | Dominant Quercus (about 28.4%). Gradual rise and maximal presence of Carpinus betulus (12.2-18.4%). Decrease in Corylus within the zone (16.8 to 8.1%). Constant presence of Alnus (around 6.1%), Tilia (1.8%), Carpinus orientalis (0.7%), Fagus (6%), Betula (0.1%), Pinus diploxylon-t. (9.5%). Decrease inof Ulmus (6-2.3%) at the zone top. Rise of Ericaceae (up to 0.9%). Sporadic Salix, Acer and Ephedra distachya. Continuous Hedera; Humulus/Cannabis appear. Reduced Artemisia (34% to 8%), Chenopodiaceae (21% to 3.6%) and Poaceae (6.6% to 3.6%). Cerealia-t. and Triticum are continuously presented (around 0.6%). Presence of Aster-t., Achillea-t., Cichoriaceae, Carduus-t., Plantago lanceolata, Polygonum aviculare, Scleranthus, Filipendula and Apiaceae. Polypodiaceae, Cyperaceae, Typha angustifolia/Sparganium-t., Myriophyllum spicatum and Alisma are sporadic. | Gradual rise of AP (69 to 84%). Dominant Quercus (around 20%). Rise of Alnus (max. 20%) at the zone top. Continuous Ulmus (around 3.7%) and Fagus (around 5%). Increase in Carpinus betulus (up to 8%) and Corylus (up to 7%). Constant Carpinus orientalis and Tilia (around 1%). Constant Hedera (0.3%). Vitis and Humulus/Cannabis appear. Reduced Artemisia (to 8.4%) at the zone top. Chenopodiaceae and Poaceae are low (2-3%). Continuous Cerealia-t. (1%) and Triticum (0.2%). Plantago lanceolata, Polygonum aviculare, Centaurea cyanus and Rumex are also presented. |
LDAZ AKAD11-17-1 (228.5–59 cm) | LDASZ AKAD11-17-2a (59–27.5 cm) | LDASZ AKAD11-17-2b (27.5–3.5 cm) |
19546-7668 cal. yrs BP | 7668-2837 cal. yrs. BP | 2837 cal. yrs. BP – present |
Pyxidinopsis psilata-Spiniferites cruciformis | Lingulodinium machaerophorum-Spiniferites belerius-Spiniferites bentorii | Lingulodinium machaerophorum-Spiniferites ramosus |
Dominant dynoflagelate cysts of Pyxidinopsis psilata (two max. 93.7 and 80.5%), then disappearing. Continuous Spiniferites cruciformis (two max. 20.9% and 23.2% at the zone top), then disappearing. Rise of Pediastrum boryanum var. boryanum (up to 5.1%), Pediastrum simplex var. simplex (around 3.7%), Pediastrum simplex var. sturmii and Pyxidinopsis reticulata are also presented. Other NPPs such as acritarchs Cymatiosphaera globulosa and Hexasteria problematica and fungal spores of Bactrodesmium-type, Sordaria-type, Valsaria valsaroides, Ascospore-type, Biscriate conidium of Alternaria and animal remains of Anthoceras are sporadic. | Increase of Spiniferites bentorii (max. 14%) and S. belerius (max. 10.5%) at the zone bottom, followed by rapid increase in Lingulodinium machaerophorum with long processes (max. 107.7%). Substantial presence of S. ramosus, S. mirabilis and S. hyperacanthus. Operculodinium centrocarpum (3.4%), Brigantedinium cariacoense (3.8%), Impagidinium centrocarpum (1.4%) and Echinidinium transparantum (1.5%) appear at the zone bottom and then decrease to 0.1%. Peridinium ponticum, Spiniferites mirabilis, Protoperidinum stellatum and Spiniferites hyperacanthus are sporadic. Increase in acritarchs Cymatiosphaera globulosa (up to 17.2%), then decreasing. First appearance of Micrhystridium cf. ariakense (max. 11.5%), Polykrikos kofoidii (0.6%) and Copepod eggs (0.5%). Sporadic Polykrikos schwartzii, Pleurospora-t.3B, Spirogyra sp. and Selenopemphix quanta. Other NPPs such as Biscriate conidium of Alternaria, Pentaphrasodinium dalei and Glomus-type are rare | Decrease of Lingulodinium machaerophorum (48.9% to 1.7%), Spiniferites bentorii (to 0.4%) and S. belerius (to 0.2%). Increase in S. ramosus (up to 4.7%) and Peridium ponticum (to 4.5%). Sporadic presence of Ataxodinium choane, Achomosphaera cf. andalousiense, Fungal spores-type 980, Biscriate conidium of Alternaria, Pediastrum boryanum var. boryanum, Pediastrum simplex var. sturmii. Constant values of acritarchs Cymatiosphaera globulosa (15-5.7%). Presence of Micrhystridium cf. ariakense (max. 5.9%) |
LPAZ AKAD09-10-1 (240–160 cm) | LPAZ AKAD09-10-2 (160–142 cm) | LPAZ AKAD09-10-3 (142–130 cm) |
25903-17092 cal. yrs BP | 17092-11788 cal. yrs BP | 11788-8253 cal. yrs BP |
Artemisia-Chenopodiaceae-Pinus | Pinus-Artemisia-Chenopodiaceae | Quercus-Artemisia-Corylus |
Dominant Artemisia (28-49%), constant Chenopodiaceae (6-16%), high Pinus diploxylon-t. (max. 33%). Sporadic Picea and Abies. Maximum of Juniperus (5-10%). Low Quercus (2.7%) and Corylus (1.6-4.3%). Sporadic Ericaceae, Betula, Carpinus betulus, Salix, Ulmus and Alnus. Continuous Polypodiaceae (2%). Many Late-Glacial heliophytes are presented. | Dominant Pinus diploxylon-t., decreasing Juniperus (from 7.1% to 1.7%). Appearance of Pinus haploxylon-t. and Ephedra distachya. Decrease in Artemisia (from 42% to 24.2%) and Poaceae (from 7.1% to 3.8%). Constant Chenopodiaceae (around 10%). Rise of Quercus (from 4.3% to 19.8%), constant Corylus (around 2%). | Two spectra: Pinus diploxylon-t. strongly reduced to ca. 8% at the zone top. High Quercus (max. 32.5%), increased Corylus (from 5.5% to 15%), Ulmus (up to 4%) and Fagus (to 1.6%). Frequent Carpinus betulus and Betula. Sporadic Humulus/Cannabis and Ephedra distachya. Decreased Artemisia (up to 17.3%), Chenopodiaceae (up to 4.8%) and Poaceae (up to 2.5%). |
LPAZ AKAD09-10-4 (130–100 cm) | LPAZ AKAD09-10-5 (100–36 cm) | LPAZ AKAD09-10-6 (36–10 cm) |
8253-ca.5500 cal. yrs BP | ca.5500-ca.2800 cal. yrs BP | ca.2800 cal. yrs BP – present |
Quercus-Corylus-Carpinus betulus-Ulmus-Cerealia-Triticum | Quercus-Carpinus betulus-Fagus-Corylus-Carpinus orientalis-Cerealia | Quercus-Alnus-Ulmus-Carpinus betulus-Fagus |
Dominant Quercus (around 30%), Corylus at max. (28.3%) in the middle of the zone. Increase of Carpinus betulus (from 1.2% to 16.3%), Fagus (from 0.9% to 7.1%) and Alnus (from 1.2% to 4.6%) at the zone top. Continuous Ulmus (around 7%), Fraxinus excelsior-t. (2.8%) ant Tilia (1.9%). Constant Hedera (ca. 0.5%). Appearance of Cornus mas and Acer. Ephedra distachya disappear. Reduced Artemisia (from 24% to 0.6%), Chenopodiaceae (from 3.8% to 0.7%) and Poaceae (from 2.5% to 1.4%). Substantial Cerealia-t. (0.8%) and Triticum (0.8%). Frequent Aster-t. and Achillea-t. (up to 1%). Appearance of Plantago lanceolata and Urtica. Sporadic Filipendula and Scleranthus. | Dominant Quercus (from 20% to 28%), Carpinus betulus at max. (17.5%), followed by a decrease to 1.5%. Maximum of Fagus (7.5%), followed by decrease to 2.8%. Decline of Corylus (from 20% to 5.8%) and Ulmus (from 3.7% to 1.6%). First appearance of Carpinus orientalis (1.3%). Continuous presence of Pinus diploxylon-t. (10%). Increase in-Artemisia (from 6.5% to 24.6%). Chenopodiaceae and Poaceae are low (ca. 3-4%). Substantial Cerealia-t. (1%) and Triticum (1%). Presence of Plantago lanceolata (1.2%), Polygonum aviculare, Centaurea jacea and Filipendula. | Dominant Quercus (26%); increasing of Alnus (up to 10%) and Ulmus (up to 3%). Constant Carpinus betulus (17%), Fagus (3%), Fraxinus excelsior (1.6%) and Hedera (1.3%). Decrease in Artemisia (from 24.6% to 7.7%), Chenopodiaceae (from 5.5% to 1.1%). Increase in Poaceae (ca. 7.6%). Significant Cerealia-t. (1.6%) and Triticum (0.6%). Appearance of Plantago lanceolata, Scleranthus and Carduus-t. |
LDAZ AKAD09-10-1 (240–128 cm) | LDASZ AKAD09-10-2a (128–40 cm) | LDASZ AKAD09-10-2b (40–10 cm) |
25903-7663 cal. yrs BP | 7663-ca.2800 cal. yrs. BP | ca.2800 cal. yrs. BP – present |
Pyxidinopsis psilata-Spiniferites cruciformis | Lingulodinium machaerophorum-Spiniferites belerius-Spiniferites bentorii | Lingulodinium machaerophorum-Peridinium ponticum |
Dominant dinoflagelate cysts of Pyxidinopsis psilata (max. 28.2%) and Spiniferites cruciformis (1.4 to 10.7%). Constant presence of green algal species Pediastrum boryanum var. boryanum (2.2% to 3.4%), Pediastrum simplex var. sturmii (around 3.7%), Botryococcus sporadic. High Glomus-t.207 (1.5% to 6.3%). Multiplicasphaeridium-t., Pleurospora-t.3B, Ascospores-t.20, Achomosphaera cf. andalousiense and Cymatiosphaera globulosa are sporadic. First appearance of Spiniferites ramosus at the zone top. Lingulodinium machaerophorum appear sporadically at the zone top. | Rapidly increasing dominant Lingulodinium machaerophorum with long processes (two max. 446% and 166%). L. machaerophorum f. clavate at max 28.7% at the zone bottom, followed by sharp decrease. Spiniferites belerius (max. 26.2%) and S. bentorii (max. 12.9%) form peaks at the zone bottom, then decreasing up to around 6%. High Brigantedinium cariacoense (around 10%). Substantial S. mirabilis, S. membranaceus and S. hyperacanthus. Constant Polykrikos kofoidii (0.7-5%), S. ramosus (2.2%), Operculodinium centrocarpum (0.9-7.2%), Echinidinium transparantum (0.6-5.4%) and Impagidinium aculeatum (0.5-1.8%). Sporadic Tectatodinium pellitum, Polykrikos schwartzii, Protoperidinum stellatum and Bitectatodinium tepikiense. Rising of acritarch Cymatiosphaera globulosa (18.3%), Micrhystridium cf. ariakense (max. 20%). Pleurospora-t.3B and Copepod eggs are also presented. | Dominant Peridinium ponticum (10%). Decrease in Lingulodinium machaerophorum (3.7%), Spiniferites bentorii and S. belerius. Polykrikos schwartzii increase (up to 2%). Protoperidinum nudum and Operculodinium centrocarpum are sporadic. Decrease in acritarchs Cymatiosphaera globulosa (1.8%). Pleurospora sp.-t.3B, Fungal spores-t.200, Sordaria and Copepod eggs are also presented. |
LPAZ AKAD09-15-1 (377–320 cm) | LPAZ AKAD09-15-2 (320–200 cm) | LPAZ AKAD09-15-3 (200–10 cm) |
14147-14054 cal. yrs BP | 14054-12965 cal. yrs BP | 12965-10906 cal. yrs BP |
Artemisia-Chenopodiaceae-Pinus | Pinus-Artemisia-Chenopodiaceae | Artemisia-Chenopodiaceae |
Dominant Artemisia (max. 44%), constant Chenopodiaceae (11%), high Pinus diploxylon-t. (39-42%). Continuously low Quercus (2.7%), Corylus (1.5%), Salix (1%), Betula (1%), Ulmus (0.6%), Juniperus (2%), Hippophae (0.5%). Presence of Ephedra distachya (up to 0.8%). Continuous Poaceae (around 7%). Numerous Late-Glacial heliophytes are presented. | Dominant Pinus diploxylon-t. (max. 61%) decreasing Artemisia (from 31.5% to 12%); Chenopodiaceae peak in the middle of the zone (23.6%). Increase in Poaceae to 10%. Many Late-Glacial heliophytes are presented. Constant Quercus (4%), Salix (2%), Betula (2%), Corylus (1%). | Dominant Artemisia (max. 67%) and Chenopodiaceae (24.6%); constant Poaceae (6-8%). Late-Glacial heliophytes are abundant. Typha angustifolia/Sparganium and Cyperaceae appear. Increase of Polypodiaceae (1-2%). |
LDAZ AKAD09-15-1 (377–10 cm) | ||
14147-10906 cal. yrs BP | ||
Pyxidinopsis psilata-Spiniferites cruciformis | ||
Dominant dynoflagelate cysts of Pyxidinopsis psilata (10%) and Spiniferites cruciformis (4%). Constant presence of green algal species Pediastrum boryanum var. boryanum (2%). Sporadic acritarchs of Pseudoschizaea circula. Constant presence of Glomus-type 207 (max. 11% at the zone bottom). |
Regional Pollen Assemblage Zone IV (Artemisia – Chenopodiaceae – Pinus)
25903–15612 cal. yrs BP
RPAZ IV has a Late Pleniglacial-Oldest Dryas/Upper Neoeuxinian age (25903–15612 cal. yrs BP). It is represented in cores AKAD 09-10 (LPAZ AKAD 09-10 1 and 2) (Fig.
Correlation between local and regional pollen assemblage zones and subzones (modified after
cal. kyrs. ВР (Fig. |
Northerneuropean climatostratigraphy ( |
Regional stages and substages ( |
Archaeological Chronology ( |
Regional PAZ | subzones | Pollen assemblages (Filipova-Marinova 2006) | 2345 | 09-15 | GGC18 | 09-10 | 544 | 11-17 | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Local PAZ | Pollen assemblages ( |
Local PAZ | Pollen assemblages (Table |
Local PAZ | Pollen assemblages ( |
Local PAZ | Pollen assemblages (Table |
Local PAZ | Pollen assemblages ( |
Local PAZ | Pollen assemblages (Table |
|||||||||||
2.8 | H O L O C E N E | Subatlantic | B L A C K S E A | New Black Sea | Iron Epoch | IX | Q-U-Al-Cb-Sa-F | 8 | Q-U-Al-F | 6 | Q-Al-Cb-U-F | 6 | Q-Al-U-Cb-F | 6 | Q-Al-Cb-U-F | 6 | Q-Al-U-Cb-F | |||||
5.5 | Subboreal | Old Black Sea | Early Bronze Age | VIII | Q-Cb-Co-F-Cor-Ce | 7 | Q-Cb-Co-F | 5 | Q-Cb-F | 5 | Q-Cb-F-Co-Cor-Ce | 5 | Q-Cb-Co-F | 5 | Q-Cb-Co-F | |||||||
8.2 | Atlantic | Transi-tional Period | VII | Q-Co-Cb-U-Tr-Ce | 6 | Q-Co-U-Cb-Ti | 4 | Q-Co-Cb-U-F- | 4 | Q-Co-Cb-U-Ce-Tr | 4 | Q-Co-U-F-Cb | 4 | Q-Co-Cb-U-Ce-Tr | ||||||||
Late Eneolithic | ||||||||||||||||||||||
Neolithic | ||||||||||||||||||||||
11.7 | Boreal | VI | b | Q-U-Co-Art | stratigraphic hiatus | 3 | Q-U-Art | 3 | Q-Art-Co | 3 | Q-Co-U-Cb-Art | 3 | Q-Art-Ch | |||||||||
Preboreal | a | Q-P-Art | 2 | Q-P-Art | ||||||||||||||||||
13 | P L E I S T O C E N E | Late Würm | Late Glacial | Younger Dryas | Upper-New-euxinian | V | d | Art-Ch | 5 | Art-Ch | 3 | Art-Ch | 1 | Art-Ch-P | 2 | P-Art-Ch | 2 | Art-Ch | 2d | Art-Ch | ||
14 | Allerød | c | P-Art-Ch | 4 | P-Art-Ch | 2 | P-Art-Ch | 1 | P-Art-Ch | 2c | P-Art | |||||||||||
14.3 | Older Dryas | b | Art-Ch-Po | 3 | Art-Ch-Po | 1 | Art-Ch-P | 2b | Art-Ch | |||||||||||||
15.6 | Bølling | a | P-Art | 2 | P-Art | 2a | P-Art-Ch | |||||||||||||||
25.9 | Oldest Dryas | IV | Art-Ch-P | 1 | Art-Ch-P | 1 | Art-Ch-P | |||||||||||||||
Late Pleniglacial | 1 | Art-Ch-P |
Paleovegetation reconstruction, based on typical high values of non-arboreal taxa and the presence of cold-resistant and heliophilous taxa such as Artemisia and Chenopodiaceae, suggest spreading of cold and dry steppes. Different taxa of Poaceae were also important elements in the steppe communities along the coast together with other heliophilous taxa from Asteraceae, Cichoriaceae, Apiaceae, Brassicaceae, Caryophyllaceae and Helianthemum. According to
Temperate deciduous arboreal taxa such as Quercus, Corylus, Ulmus, Betula and Alnus show constant presence in the pollen diagrams. The presence of single pollen grains of Tilia, Carpinus betulus, Abies, Ulmus, Fraxinus excelsior and fern spores of Polypodiaceae suggests an increase of temperature that is seen in the paleotemperature record of Greenland Ice sheet-2 (GISP-2) (
The Paleoclimate model of
These marine deposits are found below the 30 m isobath in almost all investigated cores of the western Black Sea shelf. In the peripheral (outer) shelf zone, they form clearly defined depositional bodies of coastal or barrier type sediments at the depth of 100 to 120 m (
Regional Pollen Assemblage Zone V
15612–11788 cal. yrs BP
This zone is distinguished in all cores studied and could be correlated with the Late Glacial/Neoeuxinian age. All stadials and interstadials were determined palynologically and four subzones were presented.
Regional Pollen Assemblage Subzone Va (Pinus – Artemisia)
15612–14295 cal. yrs BP
Subzone Va corresponds to the Bølling Interstadial of the European Late Glacial and can be referred to as the Upper Neoeuxinian. It is clearly separated only in core AKAD 11-17 (LPASZ AKAD 11-17 2a) (Fig.
Regional Pollen Assemblage Subzone Vb (Artemisia – Chenopodiaceae – Poaceae)
14295 – 14036 cal. yrs BP
Subzone Vb suggests stadial environmental conditions. The available Age vs. Depth model (Fig.
Regional Pollen Assemblage Subzone Vc (Pinus – Artemisia – Chenopodiaceae)
14036 – 12965 cal. yrs BP
Subzone Vc is considered as an interstadial sequence analogous with the Allerød Interstadial of the Late Glacial and correlated to the Upper Neoeuxinian. It is represented in cores AKAD 09-15 (LPAZ AKAD 09-15 2) (Fig.
Regional Pollen Assemblage Subzone Vd (Artemisia – Chenopodiaceae)
12965 – 11788 cal. yr BP
Subzone Vd is associated with the last most significant rapid climate deterioration of the last Late Glacial Stage, i.e. the Younger Dryas Stadial and has an Upper Neoeuxinian age. This cold period is of global importance and is recognised everywhere in Europe as an episode of pronounced cooling (
This succession reflects the expansion of xerophytic herb (steppe) vegetation. Palynological data show that, in addition to the predominant light-demanding xerophytic and halophytic taxa such as Artemisia and Chenopodiaceae, many other taxa, such as Poaceae, Aster-type, Achillea-type, Centaurea, Thalictrum, Apiaceae and Caryophyllaceae have also participated in these steppe communities. The extremely high percentages of Artemisia suggest that the Younger Dryas climate of the Bulgarian Black Sea coast is analogous to that of the Last Glacial maximum. Chenopodiaceae is always subdominant to Artemisia during the Pleniglacial and the Late Glacial Stadials (
Multiple factors may have been important in determining the vegetation changes in this region, including climate oscillations (
Regional Pollen Assemblage Zone VI (Quercus – Pinus – Artemisia)
11788 – 8004 cal. yrs BP
This zone could be correlated with the Preboreal-Boreal chronozone/Old Black Sea Substage and is represented in cores AKAD 09-10 (LPAZ AKAD 09-10 3) (Fig.
The most characteristic feature for the Early Holocene vegetation palaeosuccession is the early appearance of Quercus as a pioneer element in open pine forests, while, in central and northern Europe, the light-demanding species Corylus avellana started to spread in open forests dominated by Pinus and Betula where interspecies competition was probably of little importance (
The characteristic expansion of Quercus is due to the increase in temperatures and humidity. Probably, different oak species, such as Q. cerris, Q. frainetto, Q. pubescens and Q. polycarpa, took part in the composition of these forests. In addition to Quercus, several temperate taxa, such as Ulmus and Tilia, were also present in these forests. The presence of Ulmus supports the assumption of
The first increase of deciduous arboreal pollen, mainly of Quercus is dated at about 9630 ± 520 14C yrs BP at Core-544 of the deep-water zone (
The Sofular Cave (Zonguldak Province, north-western Turkey) record also suggests a fast re-vegetation with trees and shrubs at the onset of the Early Holocene (
Warming at the onset of the Holocene also allowed a rapid spread of oak along the Atlantic coast of Europe (
Pinus diploxylon is noted as the major contributor to the Early Holocene pollen assemblages (
A rapid and very short-term steep decline of arboreals is established in marine core AKAD 11-17 from the deep-water zone at 8500 to 8300 cal. yrs BP (70–65 cm) and in core AKAD 09-10 from the continental slope at 8253 cal. yrs BP at the transition of Boreal and Atlantic chronozones (130 cm) (Figs
Regional Pollen Assemblage Zone VII
(Quercus – Corylus – Carpinus betulus – Ulmus – Triticum – Cerealia)
8004 – 5483 cal. yrs BP
This RPAZ can be correlated to the Atlantic chronozone of the Middle Holocene that corresponds to the Old Black Sea Substage. It is represented in cores AKAD 09-10 (LPAZ AKAD 09-10 4) (Fig.
Corylus expanded in the local stand mainly at the expense of Ulmus and became widespread from 7584 to 5483 cal. yrs BP. This taxon has high pollen productivity in open areas. Pollen data suggest the great extent of monodominant communities of Corylus in open areas, but probably also as an undergrowth of the oak forests. The maximum percentage values of Corylus could be associated with a short-term fluctuation of climate parameters, but also with a clearance of mixed oak forests for enlargement of cultivated areas along the coast as is seen by the synchronous maximum values of Cerealia-type pollen (
The presence of Alnus, together with several occasional pollen grains of Hedera, confirms the increase in humidity and temperature along the coast. Submediterranean elements such as Carpinus orientalis and Fraxinus ornus also occurred near the coastline. Carpinus orientalis appeared and probably occupied some areas after the degradation of mixed oak forests due to a human impact that influenced the natural vegetation. The first occurrence of Juglans is registered at 7584 cal. yrs BP in LPAZ AKAD 11-17 4. The earliest appearance of several occasional pollen grains of Juglans along the southern Bulgarian Black Sea coast during the Holocene is registered for Preboreal, ca. 10000 cal. yrs BP (
The first appearance of pollen of anthropophytes, such as Cerealia-type, Triticum, Plantago lanceolata and Polygonum aviculare, coincides with the decline of Corylus and Ulmus, marking human impact during the Late Eneolithic period, 6790–6320 cal. yrs BP (
Regional Pollen Assemblage Zone VIII
(Quercus – Carpinus betulus – Corylus – Fagus – Carpinus orientalis – Cerealia)
5483 – 2837 cal yrs BP
The characteristic vegetation succession and the available Age vs. Depth model allow correlation of this RPAZ to the Subboreal chronozone of the Middle Holocene that also corresponds to the Old Black Sea Substage. It is represented in cores AKAD 09-10 (LPAZ AKAD 09-10 5) (Fig.
Regional Pollen Assemblage Zone IX
(Quercus – Ulmus – Alnus – Carpinus betulus – Salix – Fagus)
2837 cal. yrs BP – pre-industrial time
This RPAZ can be correlated with the Subatlantic chronozone of the Late Holocene and coincides with the New Black Sea Substage. It is represented in cores AKAD 09-10 (LPAZ AKAD 09-10 6) (Fig.
For a more correct and detailed reconstruction of the natural environment of the Black Sea, the changes in the relative abundance of dinoflagellate species and their assemblages recorded in three cores from the NW Black Sea were studied (Fig.
Regional dinocyst assemblage zone 1 (RDAZ 1)
(Pyxidinopsis psilata – Spiniferites cruciformis)
25903 – 7668 cal. yrs BP
This zone comprises sediments deposited between 25903 and 7668 cal. yrs BP and could be correlated to the Late Pleniglacial, Late Glacial and Early Holocene (Neweuxinian stage). This assemblage is represented in all three cores studied: AKAD 11-17 from 19546 to 7668 cal. yrs. BP (230–59 cm) (Fig.
The dinocyst record shows the low abundance or absence of stenohaline brackish-water species P. psilata from 19 to 15.5 ka yrs BP in core AKAD 11-17 and to 17.1 ka yrs BP in core AKAD 09-10 probably connected with the lack of a favourable environment for the growth of this species due to the strong melt-water and terrigenous input during that time. Pediastrum boryanum var. boryanum (considered a good indicator of freshwater input) has cyclical abundance associated with the deposition of four red-brown clay layers between 19 and 14 ka BP. The red-brown layers have been previously distinguished and dated from the north-western Black Sea shelf from 18.3 to 15.5 ka BP, in several pulses (
Regional dinocyst assemblage subzone 2a (RDASZ 2a)
(Lingulodinium machaerophorum – Spiniferites belerius – Spiniferites bentorii)
7668 – 2837 cal. yrs. BP
A prominent change of the composition of dinocyst assemblages from freshwater/brackish-water is observed at the boundary of LDAZ AKAD 11-17-1 and LDAZ AKAD 11-17-2a. The abrupt decrease of stenohaline freshwater/brackish-water species S. cruciformis and P. psilata at 7668 cal yrs BP indicating, according to
Regional dinocyst assemblage subzone 2b (LDASZ 2b)
(Lingulodinium machaerophorum – Spiniferites ramosus – Peridinium ponticum)
2837 cal. yrs. BP – pre-industrial time
The composition of the Late Holocene LDASZ AKAD 11-172b is identical to that of LDASZ AKAD 11-17-2a, but the decrease in the relative abundance of almost all marine euryhaline species since 2837 cal. yrs BP is noticeable. The increase in abundance of species that tolerate low-salinity water conditions, such as P. ponticum and S. ramosus, indicate certain freshening. Since P. ponticum is a heterotrophic species (
Vegetation successions and environmental changes along the north-western Black Sea coastal area during the last 26000 years were reconstructed by multi-proxy analysis including radiocarbon dating of sediments from three new marine cores. The following main conclusions from this study are: (1) The coastal landscape during the Late Pleniglacial (25903–17092 cal. yrs BP) was dominated by steppe vegetation composed of Artemisia, Chenopodiaceae, Poaceae and other cold-resistant and heliophilous herbs suggesting cold and dry environments. Sparse stands of Pinus and Quercus, partly enlarged during the melting pulses (19.2–14.5 cal. ka BP) and during the Late Glacial interstadials Bølling and Allerød reflecting warming and humidity increase. (2) During the Younger Dryas (13257–11788 cal. yrs BP), enlargement of steppe vegetation dominated by Artemisia and the shrubland of Juniperus-Ephedra indicates return to the coldest and driest climate. (3) In the Early Holocene (Preboreal-Boreal) (11788–8004 cal. yrs BP), pioneer forests of Quercus with groups of Ulmus, Tilia, Alnus and Betula spread and clearly confirm the presence of refugia of these taxa in the coastal mountains and their rapid migration due to the climate warming. (4) The short-term decline of arboreal pollen, particularly manifested by Quercus, between 8.5–8.3 ka BP can be explained as a vegetation response to the known in north Atlantic region ‘8.2 ka cold event’. This climatic oscillation is confirmed for the second time in Black Sea sediments. (5) During the Atlantic chronozone (8004–5483 cal. yrs BP), species-rich mixed oak temperate deciduous forests developed in the lowlands following climate optimal conditions (high humidity and increased mean annual temperatures). (6) During the Subboreal chronozone (5483–2837 cal. yrs BP), mixed oak forests dominate alongside a slight enlargement of Carpinus betulus. (7) During the Subatlantic chronozone (2837 cal. yrs BP – pre-industrial time), a specific vegetation succession manifested by the increased abundance of Alnus, Fraxinus excelsior and Salix along with lianas and the formation of flooded riparian forests (e.g. ‘Longoz’) lining the river valleys along the Black Sea suggests a climate shift (an increase of humidity and a cooling of the climate). (8) The first indications of farming and other human activities along the Black Sea coast were recorded during the Late Eneolithic (6790–6320 yrs BP). (9) Two main dinoflagellate cyst assemblages were distinguished: one dominated by stenohaline freshwater/brackish-water species and the successive one dominated by euryhaline marine species. (10) During the Early Holocene, Pyxidinopsis psilata revealed a wide ecological range and demonstrated its ecological optimum of growth concerning the increased sea surface temperature reaching a maximum relative abundance at 9475 cal yrs BP. (11) An abrupt short-term cooling centred between 8.5 and 8.3 ka BP associated with the ‘8.2 ka cold event’ is evidenced by an abrupt decline in the abundance of P. psilata and Spiniferites cruciformis to values close to those characteristic for the Younger Dryas. This climate oscillation is described for the first time in dinocyst records from Black Sea sediments (Core Akad 11-17). This finding confirms that the high amplitude temperature anomaly, associated with the ‘8.2 ka cold event’ may have also occurred in a southern direction possibly through atmospheric transmission of the signals. (12) The change in the composition of dinocyst assemblages occurred at 7668 cal yrs BP. The abrupt disappearance of freshwater/brackish-water species Pyxidinopsis psilata and Spiniferites cruciformis was followed upwards by a gradual increase in euryhaline marine species Lingulodinium machaerophorum, Spiniferites belerius, S. bentorii and acritarch Cymatiosphaera globulosa. (13) A certain freshening of the Black Sea waters after 2837 cal. yrs BP has been established.
The authors have declared that no competing interests exist.
No ethical statement was reported.
The studied gravity cores Akad 09-10, Akad 09-15 and Akad 11-17 were collected by an international scientific team during both expeditions, with financial support by the Bulgarian National Science Fund within the Project DO 02-337, led by Prof. Petko Dimitrov. The study was partly supported by the Project “Upgrading of distributed scientific infrastructure – Bulgarian Network for Long-Term Ecosystem Research” (LTER-BG), (agreement with Ministry of Education and Science, DO1-163/28.07.2022).
All authors have contributed equally.
Mariana Filipova-Marinova https://orcid.org/0000-0002-0786-9476
Danail Pavlov https://orcid.org/0000-0001-7382-2054
Krasimira Slavova https://orcid.org/0000-0002-0622-8490
All of the data that support the findings of this study are available in the main text.