Diatom-inferred lateglacial and Holocene climatic variability in the South Carpathian Mountains (Romania)

Abstract

Climatic and environmental changes were studied using siliceous algae (diatoms and chrysophycean cysts) analyses in a mountain lake in the South Carpathian Mountains for the lateglacial and Holocene. Lake Brazi (1740 a.s.l.) is a small, shallow lake in the Retezat Mountains. According to the basal radiocarbon dating of the core, the lake was formed around 15,750 cal BP and sediment accumulation has been continuous ever since. High resolution diatom analyses were carried out together with loss-on-ignition and biogenic silica measurements. Total epilimnetic phosphorus (TP) concentrations and pH were reconstructed quantitatively. Ten statistically significant zones were distinguished, six of which appeared in the lateglacial and Early Holocene suggesting the instability of diatom assemblages after deglaciation. The uppermost zone covered six thousand years, which suggests that diatom assemblages remained quite stable during the second half of the Holocene. High lake level occurred between 9500 and 9000 cal BP. After 6300 cal BP the lake level gradually increased again until 5800 cal BP. A further increase was detected at 3000 cal BP, while after 1500 cal BP water level decreased. Although there is limited knowledge regarding the environmental constraints of several diatom taxa present in the sequence (e.g. Aulacoseira laevissima), which makes the precise environmental interpretation of the diatom record more difficult, the available data provide an important new insight into the environmental history of Lake Brazi and the Carpathian Mountains. The most remarkable changes in the aquatic ecosystem were observed at 6000 cal BP in the Holocene and 12,800 cal BP, at the onset of the Younger Dryas. Marked changes were also detected at 10,500–10,300; 9800; 9500–9000; 8900–8800; 8300; 6300–5800 and 3100–3000 cal BP.