Volcanism and collisions between the Earth and extraterrestrial bodies (so-called impact events) are potential triggers of abrupt environmental changes, as their destructive power may cause global changes in the atmosphere. Major volcanic eruptions and impacts represent a significant threat to humanity. Evidence from many sites across both the Northern and Southern Hemispheres suggests that a major cosmic impact occurred 12,900 years ago, potentially triggering or reinforcing the Younger Dryas (YD) cooling over the North Atlantic and particularly in Greenland (see "Links" section). The sudden onset of the YD cooling was marked by intense wildfires and resulted in a major decline in Upper Paleolithic human populations, along with extinctions or reductions of many large mammal species. Around the time of the YD onset, there was also intense volcanic activity, which complicates efforts to disentangle the specific environmental effects of impact-related processes.

We propose an interdisciplinary study of lake sediments from the early YD period to evaluate responses of lake-catchment ecosystems to events at the YD onset. Because the impact left consistent traces across a broad area, we aim to define the geographic extent of these markers and identify any regional differences. Our study sites are located in five nature conservation areas: Šumava National Park and Krkonoše National Park (Czechia), Acadia National Park (Maine, USA), Alt Pirineu Natural Park (Catalonia, Spain), and Denali National Park (Alaska, USA). These locations provide the opportunity to study volcanic ash layers (tephras) and impact markers across a wide geographic scale in both regions affected (Bohemian Forest (Šumava) Mts, Krkonoše Mts) and probably unaffected (Acadia, Pyrenees, Alaska Range) by the preceding catastrophic eruption of the Laacher See volcano in western Germany (13,000 years ago). All selected study sites are small mountain lakes with sediment records extending back to the end of the last ice age (ca 14,700 years ago). These lakes were formed either by the retreat of the Laurentide Ice Sheet (in the case of Acadia NP) or by mountain glaciers (in the other regions). We will also focus on testing for the presence of extraterrestrial admixture in melt grains and for volcanic tephra in early YD lake sediments. In addition, we will test a newly developed method for identification of circannual cycles of sediment deposition using statistical analysis of μXRF scanning data. This method, developed by our team, will considerably improve the dating of environmental changes in non-varved lake sediments. The final objective is to evaluate the impact of volcanic eruptions and the cosmic impact event on lake ecosystems and their surrounding catchments. This will be done by analyzing the remains of aquatic and terrestrial organisms preserved in lake sediments.

To archive these goals, we are currently implementing a Czech-American research project in collaboration with two American research institutions, the University of Maine and the University of Alaska Fairbanks.

Hypotheses:

H1: Impact-related melt grains of Younger Dryas onset age are present in lake sediments of all selected European and American sites, but the Laacher See tephra is not detectable outside the Bohemian Forest and the Krkonoše Mountains.

H2: These melt grains contain an admixture of extraterrestrial material.

H3: Although pedogenesis and increased export of phosphorus from the watershed began identically at all sites more than 13,000 years ago, environmental disturbance during the Younger Dryas onset was greatest in the current Acadia NP (New England, Maine).

H4: μXRF scanning can be used to obtain data suitable for identifying circannual cycles of sediment deposition and improving the relative dating of non-varved lake sediments of the Younger Dryas onset age.