Sediments of Bohemian Forest lakes (Central Europe) show evidence of a high-temperature event at the Allerod-Younger Dryas transition
Abstrakt
Near 12,850 cal. yr. BP, the Younger Dryas stadial (YD) abruptly reversed the warming trend from the last glacial to the present interglacial at high northern latitudes.
The main trigger of this ca. 1200-year-long extreme climate event has been attributed to major reconfigurations of the oceanic and atmospheric circulation in the North Atlantic, a large release of meltwater from the area of Laurentide Ice Sheet, volcanic gas aerosols from the cataclysmic Laacher See (LS) eruption (13,006±9 cal. yr. BP; Volcanic Eifel, Germany), or a cosmic body impact/airburst.
We retrieved lake sediment cores from three sites located in the Bohemian Forest Mts, a Czechia-Germany-Austria border area. All of them contained characteristic LS (crypto) tephra glass shards that were documented using X-ray fluorescence scanning, magnetic susceptibility measurements, and direct observation using SEM.
Chemical characterization and quantification of the glass shards were performed using an electron probe microanalyzer (EPMA) and a TESCAN Integrated Mineral Analyzer (TIMA). In addition to the cryptotephra, we observed magnetically extracted iron-rich melt grains (microspherules) with signs of high-temperature melting and quenching in all studied sediment cores.
Their maxima (3–36 objects per 1 g of dry sediment) were situated 2.2–3.1 cm above peaks in the cryptotephra shard concentrations showing ages that correspond well to the YD onset. Such exotic objects of similar age were reported from numerous sites on several continents, where more impact-related proxies were documented.
However, the dating of the previously published records is based only on 14C age-depth models which are always affected by measurement errors and calibration uncertainties. Based on this new evidence with a good age control (LS cryptotephra), we hypothesize that the Allerød-YD transition in Central Europe was likely affected by a high-temperature event, likely related to an impact.
The ongoing study is supported by the Czech Grant Foundation (20-08294S – PROGRESS).