Climate variability in SE Europe since 1450 AD based on a varved sediment record from Etoliko Lagoon (Western Greece)

To achieve deeper understanding of climate variability during the last millennium in SE Europe, we report new sedimentological and paleoecological data from Etoliko Lagoon, Western Greece. The record represents the southernmost annually laminated (i.e., varved) archive from the Balkan Peninsula spanning the Little Ice Age, allowing insights into critical time intervals of climate instability such as during the Maunder and Dalton solar minima. After developing a continuous, ca. 500-year-long varve chronology, high-resolution μ–XRF counts, stable-isotope data measured on ostracod shells, palynological (including pollen and dinoflagellate cysts), and diatom data are used to decipher the season-specific climate and ecosystem evolution at Etoliko Lagoon since 1450 AD. Our results show that the Etoliko varve record became more sensitive to climate change from 1740 AD onwards. We attribute this shift to the enhancement of primary productivity within the lagoon, which is documented by an up to threefold increase in varve thickness. This marked change in the lagoon's ecosystem was caused by: (i) increased terrestrial input of nutrients, (ii) a closer connection to the sea and human eutrophication particularly from 1850 AD onwards, and (iii) increasing summer temperatures. Integration of our data with those of previously published paleolake sediment records, tree-ring-based precipitation reconstructions, simulations of atmospheric circulation and instrumental precipitation data suggests that wet conditions in winter prevailed during 1740–1790 AD, whereas dry winters marked the periods 1790–1830 AD (Dalton Minimum) and 1830–1930 AD, the latter being sporadically interrupted by wet winters. This variability in precipitation can be explained by shifts in the large-scale atmospheric circulation patterns over the European continent that affected the Balkan Peninsula (e.g., North Atlantic Oscillation). The transition between dry and wet phases at Etoliko points to longitudinal shifts of the precipitation pattern in the Balkan Peninsula during the Little Ice Age

Palynological and geochemical data from Lake Vouliagmeni, Greece

Palynological (pollen and dinoflagellate cysts) and geochemical (X-Ray fluorescence [XRF], radionuclides, loss on ignition [LOI]) data from Lake Vouliagmeni, Greece, were generated to reconstruct climate and environmental changes in SE Europe during the past 300 years. The analyses were carried out on five cores recovered from the deepest part of the lake at a water depth of ~49 m, with coordinates between 38° 1' 33 – 38° 1' 43'' N and 22° 52' 49''– 22° 53' 14'' E. A total of 36 palynological samples, were prepared using standard palynological techniques including freeze-drying, weighing, spiking with Lycopodium spores (Batch Nr. 3140) treatment with HCl and HF, sieving (10 µm), and mounting of the residues on glass slides using glycerin jelly. The XRF core scanning for the elements Si, S, Cl, K, Ca, Ti, Mn, Fe, Br, and Sr was performed with an ITRAX core scanner equipped with a chromium X-ray tube at 200 μm step size, 30 kV tube voltage, 30 mA tube current, and a counting time of 10 s. To minimize sample-geometry effects related to differences in water content, surface irregularities, and sediment density, raw-element intensities (cps) were normalized by center-log-ratio (CLR) transformation. Radionuclide dating was carried out on 1 cm thick samples following freeze-drying, homogenization and placement in cylindrical transparent polystyrene containers that were sealed with an aluminum-composite foil in order to keep the samples Radon-tight. The activity concentrations of the radionuclides were measured gamma-spectrometrically after at least 3 weeks using Canberra-Eurisys Broad Energy Germanium (BEGe-5030) detectors. The activity concentrations were calculated with the LabSOCS (Canberra) calibration software taking into account the self-absorption of γ-rays in both samples and beakers as well as the summation-effects due to simultaneous emissions of several gammas from one nuclear decay. Measuring time was up to 24 h per sample until counting uncertainties of <5 % were achieved. The organic-matter content was determined by measuring loss on ignition (LOI). Bulk samples were freeze-dried for 24 h, and 1 g of the dried, homogenized sediment was dry-ashed at 550 °C for 4 h and subsequently weighed. The weight lost was used to estimate the organic-matter content of the sample (LOI550)