PAGEO: Palaeoecological reconstruction of Global Environmental changes at the Younger Dryas Onset

Facts:

Current climate changes and related changes in ecosystems have major socio-economic impacts on human society. Understanding of long-term climate variations (their causes and consequences, extent, and prediction of future development) are therefore one of the fundamental topics of today's science. Similarly, evidences of ecosystem changes caused by natural catastrophes, such as volcanic eruptions or impact events, in the youngest geological past are an important contribution for assessing environmental risks in the near future. This knowledge allows to predict environmental impacts in similar scenarios, both in terms of biological and abiotic parameters.

The end of the last ice age (=Late Glacial, ca 14,650-11,650 calibrated years before present) was characterized by abrupt climatic reversals. However, their causes have not yet been clearly elucidated. In this project, we will focus on determining the evidence of the Younger Dryas (12,800 cal. yr. BP) impact event and the Laacher See eruption (12,900 cal. yr. BP), and related rate of paleocommunity turnover, biodiversity changes, and level of “environmental contamination” in reconstructed paleoecosystems. A multiple evidence from increasing number of sites shows that a major cosmic impact occurred at the end of the Pleistocene epoch (see "Links" section). The so-called Younger Dryas Boundary layer (YDB or “black mat”) supports the hypothesis that a fragmented comet or unknown asteroid slammed into the Earth ~12,800 cal. yr. BP at the time of the Younger Dryas (YD) climatic period onset. The YDB contains a characteristic assemblage of impact-related glassy spherules formed by melting due to the extremely high temperatures, carbon spherules, glasslike carbon, aciform carbon, shock-melted and contorted quartz, nanodiamonds, fullerenes, and platinum-group elements. We have focused on lake sediment sequences in the Bohemian Forest, central Europe, and identified YDB markers in sediments of Stará Jímka paleolake together with the volcanic ash (tephra) from the Laacher See eruption (Kletetschka et al. 2018, The Journal of Geology 126 (6): 561-575). In this new project (PAGEO), we focus on environmental impact of this catastrophic event on lake communities on broad geographical scale. For this reason, sediments of two North American lake sites are studies and the Czech team established a collaboration with an American partner institution (University of Alaska, Fairbanks) represented by Dr. Nancy Bigelow, the head of the Alaska Quaternary Center.

Aims:

Thanks to a comprehensive and innovative approach, the response of both the living and non-living components of the systems formed by the lakes and their watershed to dramatic environmental changes around the onset of the Younger Dryas (YD) period will be reconstructed. We will focus mainly on:

Evidences of the YD impact event(s)
Related geochemical, geophysical and sedimentological changes in lake sediments
Relative abundances of selected indicator species
Biodiversity changes at the YD onset
Reconstructions of changes in lake productivity, pH, possible evidence of environmental contamination, changes in habitat quality, etc. Influence of the Laacher See volcano explosion on communities of organisms inhabiting Bohemian Forest lakes

Hypotheses:

H1: Laacher See volcanic explosion changed freshwater communities in Bohemian Forest lakes.

H2: Younger Dryas boundary (YDB) layer (well-known from many North American sedimentary sequences) is present in sediments of the Bohemian Forest lakes. This layer has characteristic geochemical and geophysical signal, contains impact-related micro-spherules (MSPs), and could be used as an important tool for regional chronostratigraphy.

H3: YDB is also present in sediment of lakes in central Alaska. If yes, YDB will be compared with YDB found at the Czech sites.

H4: Younger Dryas (YD) onset was characterized by changes in environmental chemistry, a decrease in biota abundances and biodiversity, or a shift in composition of ecological groups in the studied palaeoecosystems. If yes, which factors were responsible for the ecosystem damage and transformation? Was the YD onset more pronounced in Alaskan lakes or in the Czech lakes?