DATE2018-05-16 04:19:02
AUTHORSS Kyrikou (1), K Panagiotopoulos (1), O Peyron (2), K Kouli (3), A Francke (4), N Leicher (1), B Wagner (1)
  1. Institute of Geology and Mineralogy, University of Cologne, Germany
  2. Institut des Sciences de l’Evolution de Montpellie, University of Montpellier, France
  3. Department of Geology and Geoenvironment, University of Athens, Greece
  4. School of Earth and Environmental Sciences, University of Wollongong, Australia
ABSTRACTIn this study we present two new pollen records with centennial resolution from lakes Ohrid and Prespa that provide new insights into the flora composition, vegetation changes and climate variability over the last 17000 years. The Lake Ohrid (DEEP core) pollen record is the first continuous Late Glacial-Holocene sequence from Lake Ohrid that together with the new high-resolution pollen archive of the adjacent Lake Prespa allows examining the evolution of local and regional vegetation patterns. Moreover, we employ the modern analogue technique (MAT) on the new pollen data to reconstruct climate variability in the area over the study interval. A new surface sample calibration set was established by including a total of 30 modern surface samples collected across an altitudinal transect within the catchments of Ohrid and Prespa. From 17000 years onwards, pollen spectra from both lakes suggest a rather open landscape dominated by steppe elements (mainly Artemisia and Chenopodiaceae) along with grasslands. Pines appear to be the dominant trees at Ohrid and Prespa during the Late Glacial. During the Bølling/Allerød, deciduous oaks dominate tree percentages at Ohrid, while at Prespa pines remain dominant over this period. Throughout the Younger Dryas, the resurgence of steppe elements accompanied by Betula, Ephedra and Hippophae in both pollen records suggest that cold and arid conditions prevailed. Mean annual precipitation values reconstructed applying the MAT method are above 400 mm/year during the last 17000 years. These findings imply that moisture availability was most likely not a limiting factor for tree growth and support the refugial character of the region. The Holocene is characterized by an estimated twofold increase of mean annual precipitation compared to the Younger Dryas. The onset of the Holocene is characterized by the gradual expansion of mixed deciduous oak woodlands in the surroundings of Ohrid and Prespa, while during the Mid- and Late-Holocene, the closed forests diversify and percentages of other deciduous taxa such as Acer, Alnus, Carpinus, Fagus, Ostrya increase, especially at Prespa. Although Lake Ohrid is situated a 150 m lower than Lake Prespa at 693 m asl, the presence of Mediterranean elements such as Pistacia and Phillyrea in Ohrid pollen spectra is rather limited compared to Prespa. Intensifying anthropogenic activities during the last two millennia can be inferred in both records from the decline of tree percentages and the coeval increase in pollen of cultivated plants such as walnuts and cereals.