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- Author or Editor: Mihály Braun x
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A high-resolution paleolimnological record from Lake Brazi (TDB-1; 45°23’47″N, 22°54’06″E, 1740 m a.s.l.), a small, glacial lake in the Retezat (South Carpathian Mountains, Romania) provides a sensitive record of the impacts of late glacial climatic change on siliceous algal assemblages. The sequence, ranging from 15,700 cal yr BP to 9500 cal yr BP, suggests that the most significant changes in diatom assemblages took place at 12,800 and 10,400 cal yr BP, when alkaliphilous fragilarioid taxa were replaced by acidophilous diatoms. Altogether eight zones were distinguished with sharp and rapid changes of diatom assemblages. The paper discusses the application of siliceous algae in multi-proxy paleolimnological analyses, demonstrates the advantages and disadvantages of this proxy and presents the story of floristic discovery of unique diatom assemblages, the closest recent analogs of which are found in the arctic region.
the Retezat Mountains, this study discusses radiocarbon chronology and sediment accumulation rate changes in two sediment profiles in relation to lithostratigraphy, organic content, biogenic silica and major pollenstratigraphic changes. A total of 25 radiocarbon dates were obtained from sediments of two lakes, Lake Brazi (TDB-1; 1740 m a.s.l.) and Lake Gales (Gales-3; 1990 m a.s.l.). Age-depth modeling was performed on TDB-1 using calibrated age ranges from BCal and various curve-fitting methods in psimpoll. Our results suggest that sediment accumulation began between 15,124–15,755 cal yr BP in both lakes and was continuous throughout the Late Glacial and Holocene. We demonstrated that local ecosystem productivity showed delayed response to Late Glacial and Early Holocene climatic changes in the subalpine and alpine zones most likely attributable to the cooling effect of remnant glaciers and meltwater input. However, regional vegetation response was without time lag and indicated forestation and warming at 14,450 and 11,550 cal yr BP, and cooling at ca. 12,800 cal yr BP. In the Holocene one major shift was detected, starting around 6300 cal yr BP and culminating around 5200 cal yr BP. The various proxies suggested summer cooling, shorter duration of the winter ice-cover season and/or increasing size of the water body, probably in response to increasing available moisture.