Cosmic-Impact Event in Lake Sediments from Central Europe Postdates the Laacher See Eruption and Marks Onset of the Younger Dryas
Abstract
The Younger Dryas (YD) climate episode (similar to 12,850-11,650 calendar years before present [cal BP]) is an event recorded widely across the Northern Hemisphere. We conducted multiple analyses at high resolution of a YD-age sedimentary sequence from Stara Jimka, a paleolake in the Bohemian Forest, Czech Republic. Age-depth modeling indicates that a central European warming trend was interrupted at similar to 13,020 +/- 110 cal BP by the sudden onset of cooling (<20 y) known as the Gerzensee climate oscillation and marked by the deposition of fine-grained sediment at this location. That cooling episode ended at similar to 13,001 +/- 66 cal BP and was followed by a similar to 121-y-long warming trend. After that, the Laacher See tephra depositional event, dating to similar to 12,820 +/- 20 cal BP, continued an overall warming trend. The composition of Laacher See volcanic tephra in this section likely corresponds to the middle eruption sequence. Finally, the deposition of glassy microspherules marked the onset of the YD climate change at 12,755 +/- 92 cal BP. The sequence across the YD onset is marked by (1) a peak in glassy microspherules (117,000/kg), (2) a peak in framboidal spherules (14,000/kg), (3) significant changes in the lake's weathering proxies, and (4) major changes in fauna and flora, showing a shift to unfavorable environmental conditions (decrease in temperature and lake trophy status). Collectively, this evidence is consistent with the YD impact hypothesis and evidence of one or more cosmic airburst events occurring at this time.