Boreal forest bi-stability around Lake El’gygytgyn (NE Russia) during interglacial of the last 2.15 Million years

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Ecosystem services of boreal forests are of critical importance for humanity and differ markedly between evergreen and summergreen needle-leaf forests. The proposed project will address the timely questions “Why is northern Asia dominated by larch forests during the Holocene while it was covered by evergreen needle-leaf forests during previous interglacials of seemingly similar climate conditions?"Our overall hypothesis is that summergreen and evergreen needle-leaf forests represent alternative quasi-stable states that can occur under similar climate conditions during interglacials of the last 2 Myr, being triggered by different environmental conditions and the composition of northern tree refugia during the preceding glacials.We will address this hypothesis by a multiproxy investigation of Lake El'gygytgyn sediments (Chukotka, NE Asia) that were collected as part of the ICDP programme.Investigations in Work Package 1 (group M. Melles) aim to track regional vegetation change of the last 2 Myrs using pollen data which includes new analyses of ~500 pollen samples as well as its integration with available data.The sedimentary ancient DNA analyses to be performed in Work package 2 (group U. Herzschuh) will aid the interpretability of pollen data. In particular, the regional vegetation signal of pollen will be verified, the composition of the regional tree refugia and the species-specific taxa composition will be revealed to allow the separation tree vs. shrub growth forms of certain woody genera. In Work Package 3 (group H. Meyer), regional climate change of selected glacial/interglacial cycles of the last 2.15 Myrs will be reconstructed from stable oxygen isotope analyses of diatom valves. Gained results will be used to assess globally available high-resolution paleoclimate records for its suitability to represent NE Asian climate change at glacial/interglacial time-scale.Gained results will be compiled and re-analysed to assess the stated hypothesis jointly by all working group members in Work Package 4 (synthesis).