Late postglacial paleoenvironmental change in the northeastern Mediterranean region: Combined palynological and molecular biomarker evidence

Quaternary International (Impact Factor: 2.06). 05/2012; 261:128-137. DOI: 10.1016/j.quaint.2011.10.036


Three gravity cores collected from the NE Mediterranean (NEMR) across a transect from the northern Aegean Sea (North Skyros basin) to the south Cretan margin (SCM), were investigated for pollen and terrestrial biomarkers derived from epicuticular waxes of vascular plants during the last w20 ky. Pollen data show diversified mixed temperate forest in the northern borderlands and enhanced Mediterranean vegetation in the southern areas, documenting an NeS climatic trend. Terrestrial plant biomarkers and their diagnostic geochemical indices exhibit latitudinal patterns which are interpreted in terms of the different delivery pathways (fluvial/runoff vs. atmospheric transport), resulting from the climate conditions during different periods. During the Late Glacial and early deglaciation periods (20e14 ka BP) relatively increased humidity (H-index) is recorded in the north Aegean Sea, while in the South drier climate was the limiting factor for vegetation development. During this interval, terrestrial n-alkanes showed increased accumulation rates, suggesting massive transport of terrestrial organic matter through runoffs and rivers, followed by weaker input after 14 ka BP. After w11 ka BP a major expansion of forest cover is evidenced in the NEMR, accompanied by a higher H-index because of the climatic amelioration. The forest vegetation exhibited regionally different characteristics, with cool temperate taxa being more abundant in the Aegean cores, while the SCM record is being featured by Mediterranean elements. At the onset of the Holocene and throughout the Holocene Climatic Optimum the delivery of terrestrial biomarkers increased and became more significant in the Aegean sites compared to the SCM site. Within the Holocene, the average chain length (ACL) of long chain n-alkanes exhibits lower values in the northern Aegean than in the southeastern Aegean and SCM, indicating the predominance of warmer species southwards. Finally, the H-index records a conspicuous humidity increase between 5.4 and 4.3 ka BP in the south Aegean that coincides with an increase in the terrestrial biomarker supply and the deposition of a distinct sapropel-like layer, SMH (Sapropel Mid Holocene). Similar trends in T (temperature) and H indices are slightly delayed and attenuated in the northern Aegean and are accompanied by an increase in the ACL index. A noticeable increase in the accumulation rates (ARs) of terrestrial biomarkers and the HPA index values during this period are clearly recorded in all three cores, indicative of enhanced terrigenous inputs of organic matter along with higher in-situ preservation.

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Available from: G. Rousakis, Oct 04, 2015
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    • "Evidence from eastern Mediterranean Quaternary sapropel studies indicate that freshwater stratification and organic carbon accumulation took place due to both enhanced productivity and hypoxia, during warm and wet climatic conditions (e.g., De Lange and Ten Haven 1983; Emeis et al. 2000a; Casford et al. 2003; Gogou et al. 2007; De Lange et al. 2008; Kuhnt et al. 2008; Triantaphyllou et al. 2009a, b, 2010, 2013; Katsouras et al. 2010; Schmiedl et al. 2010; Kouli et al. 2012; Triantaphyllou 2014). Calcareous nannofossils are one of the most important pelagic sediment micro-components (Müller 1985; De Kaenel and Villa 1996; Castradori 1998; Negri et al. 1999a, b; Negri and Villa 2000; Vázque et al. 2000), used mainly for biostratigraphy and paleoceanographic reconstructions. "
    Geo-Marine Letters 08/2015; 35(5). DOI:10.1007/s00367-015-0414-6 · 2.12 Impact Factor
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    • "Accordingly, the fresh water input in the SCM also ranged in low values (PC2; Fig. 6). The area was clearly less humid, following the north-south trend towards drier climate within the northeastern Mediterranean region (Kouli et al., 2012; Peyron et al., 2013). The stratification of the SCM water column (Fig. 6) has relatively increased values with a negative shift at about 8.0 ka BP, implying shoaling of the nutricline and higher production in the surface layer (Beaufort et al., 1997; Incarbona et al., 2008), linked to 8.2 ka BP Northern Hemisphere cooling (e.g., Alley et al., 1997). "
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    ABSTRACT: Recent paleoceanographic findings suggest that during the Holocene, NE Mediterranean climate was less stable than previously thought. Several recently generated Aegean paleoceanographic records of sapropel S1 suggest that during the Holocene short-term potentially global cooling episodes, reflecting the N. Atlantic climatic fluctuations and possibly related to solar variability, are superimposed on the underlying regional subtropical/tropical control on the hydrography and ecosystems. Detailed quantitative analyses of coccolithophores have been performed on the deep sea deposits of the NE Mediterranean Sea; four gravity core records from North Aegean Sea (SL- 152), SE Aegean (NS-14, NS-18) and South Cretan continental Margin/northern Levantine Sea (HCMR 2/22) respectively, with a focus on the regional expression of sapropel S1 deposition. In all sites, higher values of Florisphaera profunda, Helicosphaera carteri, Braarudosphaera bigelowii and the increase of stratification S-index within sapropel intervals can be interpreted as the result of elevated marine production in the deep photic zone and enhanced inflow of fresh water input during the S1 period. The stratification S-index is significantly higher in the North Aegean, in respect to SE Aegean and the South Cretan Margin (SCM), reflecting increased coccolithophore productivity at the lower photic zone, being associated with a remarkably stratified water column. The concomitant increased presence of B. bigelowii indicates the prominent riverine input in the North Aegean basins and possible influx of Black Sea waters after ∼9.0 ka BP. Consequently, the increased stratification of the water column is linked to the significant freshening of the North Aegean surface waters, particularly during the early stages of the Holocene Climatic Optimum (S1a depositional interval). A series of cooling events detected towards the end of sapropelic conditions (∼7.2 ka BP) mostly in the North Aegean site, may be linked to outbursts of cold northerly air masses and relevant pulses in the deep-intermediate water ventilation that caused the enhancement of surface marine productivity and the temporary cessation of S1 at ∼ 8.0 ka BP. In contrast, in the SE Aegean and the northern Levantine Sea, the water column remains still warm and stratified, influenced by moderate fresh water input, for at least 1 more ky.
    Quaternary International 02/2014; 345. DOI:10.1016/j.quaint.2014.01.033 · 2.06 Impact Factor
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    • "The low salinity water is delivered by the Black Sea outflow and also from an inundation event of the Black Sea by Mediterranean waters observed during 7500 cal BP (Theoharis et al., 1993) although land delivered material in the coast of Eastern Aegean Sea comes from land runoff and aolian transport (Chendes et al., 2004; Triantaphyllou et al., 2009; Kouli et al., 2012). "
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    ABSTRACT: The study area is located on the northeastern coast of Lemnos Island (North Aegean Sea, 40 degrees 2'30"N, 25 degrees 00'00"E). It covers the archaeological settlement of Hephestia located in the Purnia Gulf and the coastal area of Alyki Lagoon. Reconstruction of the palaeogeography used palaeoenvironment data delivered from foraminifera and sea-level changes, providing archeological data about the presence of a potential harbour in the area. Geomorphological mapping as well as sedimentological and micropalaeontological studies of the Holocene coastal deposits were conducted. Four boreholes were drilled from the Alyki Lagoon, reaching 2.5 m to 11 m at the deepest and two from Hephestia area, reaching a depth of 6 m. Twenty-four samples were dated using the AMS radiocarbon method, providing a chronology of the sedimentary units. The calculated age from the boreholes provides dates from 7050 cal BP to 990 cal BP There was a constant sea-level rise during the last 7000 cal BP in the study area. Results from the model of Lambeck sea level curve and sea level index point from Hephestia and Alyki show a vertical difference of 0.5-1.5 m below sea level. The foraminiferal fauna analysis shows the development of shallow marine conditions with fresh water influx during 7000-4000 cal BP and a temporary lagoon environment with fluctuations to shallow bay environment from 4000 to 990 cal BP.
    Quaternary International 10/2013; 308. DOI:10.1016/j.quaint.2012.06.024 · 2.06 Impact Factor
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