Tracing Mid-Holocene Climate Change in Bosnia

As part of the DOMINO-CLIMATE project led by Enikő Magyari, we visited Lake Prokoško at the end of August. The lake is a glacial lake situated at 1,670 m in the Vranica Mountains, Bosnia. Its sediments were first cored by German researchers in 2007, and the project’s postdoctoral researcher, Aneta Formáčková, is now analyzing the fossil chironomid fauna from these cores. The aim of the study is to produce a quantitative July temperature reconstruction for this poorly studied region over the last 15,000 years. About 32 km from the lake, in the Bosna River valley, lie the remains of several Neolithic settlements linked to the Butmir culture, the largest of which is Okolište. Archaeologists from Kiel University have identified nine settlement phases at this site. The Butmir culture began spreading through the valley around 7,200 years ago, but its settlements were suddenly abandoned around 6,500 years ago, similar to the fate of Tisza culture sites on the Hungarian Plain. Our research seeks to shed light on the climate changes, particularly summer temperature trends, that occurred during the decline of this culture.

Lipid biomarker analyses are also being carried out on the lake sediments. Doctoral student Anna Hellner, in collaboration with ETH Zurich, is examining bacterial cell wall lipids (GDGTs) preserved in the sediments, the chain length of which is temperature-dependent. Using a European calibration dataset, her goal is to reconstruct annual temperature changes over the past 15,000 years.

During our summer fieldwork, we sampled the modern chironomid fauna by collecting pupal exuviae with nets and surface sediments using a gravity corer, from which chironomid larvae will be identified. The present-day fauna of the lake is expected to show signs of eutrophication and to differ from Holocene assemblages due to pollution from the increasing number of bungalows around the lake in recent decades. Although strictly protected, with national park rangers collecting entry fees, fish have been introduced into the lake. Fishing is prohibited, but the photographs illustrate well how the lake has become a tourist attraction. Most visitors now come from Arab countries, creating a striking impression in this Muslim-populated part of Europe. Along our route we passed through villages with mixed Serb Catholic and Bosniak Muslim populations, where the muezzin’s call to prayer can be heard in the evenings.

Together with Gusztáv Jakab, we surveyed the vegetation surrounding the lake and collected soil samples from different plant communities for lipid biomarker analyses.

The slopes around the lake are today dominated by dwarf pine, spruce, and mountain pastures. Beech occurs sporadically, with its uppermost occurrence at 1,750 m. Its highest individuals grow within the dwarf pine Krummholz zone, merging into shrubby associations. Spruce, in turn, mixes with fir at this elevation.

Small flocks of sheep and herds of cattle graze on the slopes, along with a few horses, which mainly serve the needs of tourism around the lake.