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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    • "During the so-called Holocene Climatic Optimum (HCO; approx. 10.0–6.0 ka), a distinct positive shift in the Aegean Sea's freshwater budget—possibly supplemented by precipitation and riverine contribution from the Aegean borderland and also inflow of Black Sea Water (BSW)—weakened the basin's deepwater circulation, resulting in oxygen-starved conditions at the seafloor and deposition of sapropel layer S1 (e.g., Aksu et al. 1995, 2002; Gogou et al. 2007; Kuhnt et al. 2007; Abu-Zied et al. 2008; Kotthoff et al. 2008; Geraga et al. 2010; Katsouras et al. 2010; Schmiedl et al. 2010; Kouli et al. 2012; Triantaphyllou 2014; Triantaphyllou et al. 2014). Aegean Sea sites of high sedimentation rates are associated with S1 sapropelic layers characterized by low organic carbon (OC) contents of <2% (e.g., Roussakis et al. 2004; Triantaphyllou et al. 2009a), reflecting strong dilution by lithogenic input (e.g., Mercone et al. 2000). "
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    ABSTRACT: Combined micropaleontological and geochemical analyses of the high-sedimentation gravity core M-4G provided new centennial-scale paleoceanographic data for sapropel S1 deposition in the NE Aegean Sea during the Holocene Climatic Optimum. Sapropel layer S1a (10.2–8.0 ka) was deposited in dysoxic to oxic bottom waters characterized by a high abundance of benthic foraminiferal species tolerating surface sediment and/or pore water oxygen depletion (e.g., Chilostomella mediterranensis, Globobulimina affinis), and the presence of Uvigerina mediterranea, which thrives in oxic mesotrophic-eutrophic environments. Preservation of organic matter (OM) is inferred based on high organic carbon as well as loliolide and isololiolide contents, while the biomarker record and the abundances of eutrophic planktonic foraminifera document enhanced productivity. High inputs of terrigenous OM are attributed to north Aegean borderland riverine inputs. Both alkenone-based sea surface temperatures (SSTs) and δO18 G. bulloides records indicate cooling at 8.2 ka (S1a) and ~7.8 ka (S1 interruption). Sapropelic layer S1b (7.7–6.4 ka) is characterized by rather oxic conditions; abundances of foraminiferal species tolerant to oxygen depletion are very low compared with the U. mediterranea rise. Strongly fluctuating SSTs demonstrate repeated cooling and associated dense water formation, with a major event at 7.4 ka followed by cold spells at 7.0, 6.8, and 6.5 ka. The prominent rise of the carbon preference index within the S1b layer indicates the delivery of less degraded terrestrial OM. The increase of algal biomarkers, labile OM-feeding foraminifera and eutrophic planktonic species pinpoints an enhanced in situ marine productivity, promoted by more efficient vertical convection due to repeated cold events. The associated contributions of labile marine OM along with fresher terrestrial OM inputs after ~7.7 ka imply sources alternative/additional to the north Aegean riverine borderland sources for the influx of organic matter in the south Limnos Basin, plausibly related to the inflow of highly productive Marmara/Black Sea waters
    Geo-Marine Letters 10/2015; DOI:10.1007/s00367-015-0426-2 · 2.12 Impact Factor
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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. "
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    ABSTRACT: Quantitative analyses of calcareous nannofossils in the sediments of Pissouri South section on the island of Cyprus have produced a paleoceanographic record reflecting the paleoclimatic conditions during the Zanclean/Piacenzian transition. Pissouri South cyclical lithological alternations between organic-rich laminated layers and grey marls reflect the Earth’s orbital precession. According to the calcareous nannofossil biostratigraphy which has been performed, the studied section is correlated with MNN14/15 and MNN16 calcareous nannofossil biozones and is astronomically dated between 4.065 and 3.217 Ma. Intervals of increased organic carbon content, along with the positive values of Florisphaera profunda, Helicosphaera sellii, Discoaster spp. and the subsequent increase of stratification S-index, correspond to the sapropel deposition during periods of wetter climate and intense continental runoff, especially from the river Nile. These layers alternate with grey marly intervals, featured by the increased values of small placoliths of Reticulofenestra and Gephyrocapsa species, which are indicative of eutrophic conditions during intense surface-water mixing. Our data support the prevalence of a generally warm phase characterized by the absence of high-frequency climate variations in the southeastern Mediterranean during the Zanclean/Piacenzian (Early/Late Pliocene) transition.
    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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