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.


Available from: G. Rousakis
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    • "The second is around 5200 cal yr BP and is also well-known in the eastern Mediterranean (e.g., Matthews and Ayalon, 2011; Kuzucuoğlu et al., 2011; Roberts et al., 2011). The third, less marked, is observed around 5000 cal yr BP in southeastern Aegean (Kouli et al., 2012). This suggests that northern Greece underwent the same pattern of climatic instability with three dry cold events than central and eastern Mediterranean areas (Zanchetta et al., 2014 ). "
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    • "At the same time, low values of F. profunda percentages (Fig. 5 ) indicate elevated in-situ productivity, presumably triggered by increases in nutrient availability, which further support the hypothesis of enhanced continental inputs during this time. From ca. 850 to 950 AD, SSTs at warming are in line with increases of the HPA index (Fig. 7), indicating higher preservation of organic matter due to reduced water column mixing (e.g., Kouli et al., 2012). From ca. 1000e1300 AD, fluctuating SSTs (Fig. 7), together with higher values of F. profunda and B. bigelowii (Fig. 5), support the establishment of low-salinity stratified waters and the presence of nutrient-rich environment in the deep photic zone (e.g., Molfino and McIntyre, 1990; Triantaphyllou et al., 2009a; Triantaphyllou, 2014). "
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    Full-text · Article · Feb 2016 · Quaternary Science Reviews
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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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