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Abstract: High-resolution pollen, conifer stomata and plant macrofossil analyses of two glacial lake sediments (1740 and 1990 m a.s.l.) are used to reconstruct Lateglacial (LG) and early Holocene (EH) vegetation and tree line changes in the Retezat Mountains. Our results show that during the LG, tree line was between 1750 and 1800 m a.s.l. formed by Larix decidua, Pinus mugo and Picea abies. Early LG spread to high altitudes suggests refugia of these tree species in the mountain. The Younger Dryas cooling resulted in regional steppe-tundra expansion, but tree line position and composition showed little change. The abundance of trees and shrubs decreased at 1740 m a.s.l., but species richness increased with the arrival of Pinus cembra. Our data support climate-model hindcasts for only modest decrease in accumulated growing season heat at mid-high altitudes. Regionally the pollen records suggest enhanced aridity and seasonality. In the EH, tree line reached 2000 m a.s.l. (higher than today) by ∼11,100 cal yr BP. P. mugo, P. cembra, P. abies established around the upper lake suggesting rapid increase in summer temperatures. The EH maximum of L. decidua between 11,200–10,600 cal yr BP was connected to high summer insolation. High altitude expansion of Abies alba between 10,600–10,300 cal yr BP suggested summer mean temperatures ∼2.8 °C higher then today. In comparison with other mountain sites in Europe, LG interstadial tree line was at similar altitude in the S Alps and ∼350 m higher in the Pirin Mountains. LG tree line fluctuation had similar low amplitude in the SE Alps, Retezat and Pirin Mts suggesting relatively weak influence of the North Atlantic thermohaline circulation changes on growing season temperatures. [Copyright &y& Elsevier]

Abstract: A multi-proxy approach is widely used for reconstructing climatic change in alpine lake sediments. This study applied bulk sediment geochemistry to reconstruct lateglacial and early Holocene climatic change in a glacial lake (Lake Brazi, 1740 m a.s.l.) in the Retezat Mts. (South Carpathians, Romania). The lowermost 1 m part of a 4.9-m long sediment core, covering the period between 9950 and 15,750 cal BP, was used for high resolution bulk analysis of major elements (Al2O3, SiO2, TiO2, CaO, MgO, K2O, Na2O, Fe2O3, MnO, SO3). Linear discriminant analysis (LDA) was used to compare a priori classified main chemical groups. Subsamples from the core were priory ordered to “warm” and “cold” groups respectively, according to their age and evidence of cold and warm events in the record, as suggested by proxy correlation with the lateglacial event stratigraphy of North Greenland Ice Core Project (NGRIP). The discriminant function was calculated using concentrations of Al2O3, TiO2, CaO, MgO, K2O, Na2O, Fe2O3, and MnO after log ratio transformation. Loss-on-ignition, silicon and sulphur concentrations were not used for the discriminant analysis, but regarded as comparison proxies for checking up the validity of outputs. Sediments deposited during “cold” and “warm” events were separated significantly by the LDA function; 85.1% of the originally grouped cases were correctly classified under the LDA analysis. The calculated discriminant scores indicated four “cold” and four “warm” events. Sediments ordered into the “warm” group contained larger amounts of organic matter and sulphur, while sediment samples of the “cold” group were characterized by the overall predominance of major oxides bound into inorganic silicates. The discriminant scores showed strong correlation with the NGRIP δ18O data (r = 0.8135) and with the pollen percentage sum of trees and shrubs (r = 0.9460). Loss-on-ignition showed a somehow weaker, but still conclusive linear relationship with the discriminant scores (r = 0.7505). Discriminant analyses of bulk sediment major oxide chemical data may be a useful tool to identify the impact of climatic events upon the nature and composition of materials delivered to a lake basin. [Copyright &y& Elsevier]