Geochemical survey of Lake Balaton sediments: holocene paleoenvironment and paleoclimate

Abstract

<p>In the winter of 2017 three undisturbed sediment cores were retrieved from the Szemes Basin of Lake Balaton. The sediments were sampled for AMS <sup>14</sup>C dating and we used 8 of the radiocarbon dates for age-depth modelling. Based on this, the investigated sediment sequence covers the entire Holocene and Late Glacial period and the bottom of the sediment is ca. ~16,000 cal yr BP old. X-ray fluorescence spectrometry (XRF) was used to reconstruct rapid changes in the element content of the lake sediment. The evaluation of the measured results makes it possible to reconstruct the changes in the discharge environment and lake water level that can be related to the climate and human impact. Based on the data, two major evaporation events can be observed at 5500 BP and 8100 BP. These results were also verified by oxygen isotope studies. To reconstruct the energy of the deposition environment, particle size analysis was performed. The obtained results confirmed that river sediments are common at the bottom of Lake Balaton sediments, while biogenic carbonate dominates in the upper, Holocene part of the sediment core. To identify each mineral phase in the sediment, X-ray diffraction (XRD) studies were used to determine the ratio of calcite to Mg-calcite. Based on our XRF measurements, focusing primarily on quantitative changes in magnesium and calcium, transmission electron microscopy (TEM) studies were performed, mainly in the Mg enrichment layer around 8100 BP. The precipitation of biogenic carbonate in Lake Balaton is still taking place, mainly in the form of calcite and Mg-calcite. Their relative proportions strongly depend on the Mg saturation of the water and the substrates on which they are separated. From our results we can draw conclusions about the possible previous deeper phases of the lake and the evaporation conditions of the water. The data obtained from transmission electron microscopy shows a good agreement with the results of the XRF measurement, the proportion of Mg-calcite increases around 8100 BP that likely indicate drier climatic conditions connectable to the well know 8.2 ka cal BP climatic reversal.</p>

Pathways of carbonate sediment accumulation in a large, shallow lake

“…On the basis of zebra mussel (Dreissena polymorpha) remains, the sediment accumulation rate was estimated at ~5.5 mm•y −1 year for the topmost (40 cm) sediment (Korponai et al, 2011), whereas seismic measurements in the Eastern part of the lake were interpreted to reflect a ~8.8 mm•y −1 year accumulation since ~1980 (Zlinszky et al, 2010). Dating of a sediment core obtained in the middle of the lake using a combination of 14 C, 210 Pb and 137 Cs data suggested that the upper 32 cm of the sediment accumulated over just ~150 years (Pálfi et al, 2021), yielding an accumulation rate of 2.1 mm•y −1 , slightly larger than (but generally consistent with) our estimates. Since turbulence and currents move and redeposit sediment material, the sediment accumulation rate varies by location, as was shown by both sediment stable isotope (Cserny et al, 1995) and seismic measurements (Zlinszky et al, 2010;Visnovitz et al, 2021).…”

“…However, such small changes in the water budget did not result in noticeable differences in the average composition of Mg-bearing calcite or the relative amount of protodolomite in our suspended matter samples. Studies of sediment cores showed the presence of either one (Müller et al, 1978) or two distinct, protodolomite-rich layers ~5,300 and 8,100 years before present (Pálfi et al, 2021), attesting to specific events in the history of the lake with higher Mg concentration in lakewater and presumably much drier conditions than today.…”

Review on vegetation, landscape and climate changes in the Carpathian Basin during the Neolithic and Chalcolithic period

“…Finally, stable isotope and geochemical studies on the sediments of Lake Balaton and mussel shells of Unio pictorum from its lakeshore CA settlement provided valuable insight into the CA climate of Transdanubia (Schöll-Barna et al 2012;Pálfi et al 2021). These studies found considerable negative excursions in the δ 13 C and δ 18 O values of the studied bivalve shells around 5,310 cal bp (~ 3360 cal bc) that pointed to a short wet-cold interval in the transitional phase of the CA settlement (prior to the classical Baden occupation).…”

“…When this short term cooling event is examined in the context of a larger age interval in the biogenic carbonate sediments of Lake Balaton, then a slightly different picture emerges. In the δ 13 C and δ 18 O curves of the Holocene well dated sediment sequence from the Szemes Sub-basin of the lake, 5,500-4,800 cal bp (3,550-2850 cal bc; ~ LCA) is characterised by higher δ 13 C and δ 18 O values suggesting an overall increase in summer evaporation that can arise from lower summer precipitation, or a combination of low summer precipitation and increased summer temperatures (Pálfi et al 2021). The 5.3 ky bp reversal is intercalated to this lengthier dry summer interval.…”