Late Quaternary paleoenvironmental reconstruction and paleoclimatic implications of the Aegean Sea (eastern Mediterranean) based on paleoceanographic indexes and stable isotopes

Abstract

The Late Quaternary palaeoenvironmental evolution and the main palaeoceanographic changes of the Aegean Sea was reconstructed using planktonic foraminifera obtained from the sediments of a northern (SK-1) and a southern (NS-14) core site. Multivariate statistical approach, including Q-mode cluster and Principal Component (PCA) Analyses, gives an insight into the relationships between sea surface environmental changes between the north and south Aegean, and furthermore serves as a baseline data set for palaeoclimatic and palaeoceanographic reconstructions of the eastern Mediterranean Sea. Stable isotope analyses coupled with additional paleoceanographic (sea surface temperature (SST), productivity (SSP), stratification (S-index), upwelling (U-index), seasonality (Sn-index)) proxies provide insights into the sedimentological, hydrographic and trophic evolution and ecosystem dynamics of the Aegean Sea, and furthermore serve as a baseline data set for palaeoclimatic and palaeoceanographic reconstructions of the eastern Mediterranean Sea. Concentrating on the last ~19 ka, faunal and isotopic data concur, suggesting a series of climatic zones, corresponding to well-known climatic phases of the last glacial cycle. Cold and arid conditions during the late glacial period were followed by a warmer and wetter climate trend during deglacial time. A marked seasonality, characterized by homogenous water column favored by efficient upwelling during the winter and by warm stratified water column during the summer, has also been recognized during this period (BøllingeAllerød e BeA) in both basins. An abrupt switch to cool, arid climatic event (Younger Dryas e YD) suggests a strengthening of winter convection around 12.9 ka, which seems to be more evident in the north Aegean core. However, the more pronounced environmental changes between the north and south Aegean Sea were identified during the Holocene, and they coincide with the deposition of sapropel S1 and Sapropel-Mid-Holocene (SMH). The comparison between SK-1 and NS-14 records indicated significant changes in both the productivity and stratification patterns, with the former the main factor in north Aegean and the latter in south Aegean for S1 deposition. Regarding the localized deposition of SMH in the semi-enclosed shallow south Aegean site, the fully oxygenated and less productive water column conditions prevailing during that time (5.4 e4.3 ka) in the north Aegean were the limiting factor for its deposition.