Aloïs Revéret

Over the last 20 000 years, ice sheets and permafrost have been receding globally, and new ecosystems developed on barren deglaciated grounds. Sedimentary ancient DNA (sedaDNA) is a powerful palaeoecological proxy that allows to reconstruct past ecosystem changes across the Quaternary ice age, and more specifically over the transition from the Late Glacial into the Holocene.

We leveraged or generated sedaDNA records from 14 sites scattered along the Atlantic margin of the Fennoscandian Ice Sheet, as well as one lake from the sub-Antarctic Kerguelen Archipelago (Southern Indian Ocean). We used metabarcoding of the trnL P6 loop marker to reconstruct past plant communities, and the 16S marker for mammals.

Our results demonstrate that the sedaDNA record from freshwater macrophytes allows to reconstruct past limnological conditions, through the combined analysis of aquatic plants environmental traits and of the temporal turnover within the macrophyte community. We reconstituted the postglacial development of freshwater vegetation in northern Fennoscandia, as well as individual lake trajectories; capturing tipping points such as the groundwater acidification following the encroachment of pine taiga into the catchment. In southern Norway, we show that climate forcing strongly influenced vegetation succession, as fast warmings triggered episodes of new plants establishment, whereas colder periods capped floral diversity. An unprecedented diversity of nearly 300 plant species was captured in detritic estuarine North Sea sediments, supporting a lush megafauna including reindeer, woolly mammoths, and woolly rhinoceroses. Moreover, we present the first environmental detection of the giant deer (Megaloceros giganteus). Lastly, we reconstructed the Holocene vegetation history of Kerguelen Archipelago, critically expanding the taxonomic coverage to the mosses and liverworts community.

Reindeer detections on both sides of the Norwegian Channel during the Allerød interstadial suggest a direct crossing from this land bridge that once joined Great Britain to Denmark, alias ‘Doggerland’. This area likely served as an ecological hotspot during the Last Glacial Maximum, and was a northern vegetation outpost that fostered postglacial succession on the Fennoscandian mainland. Our results demonstrate the potential of sedaDNA to carry out broad palaeoecological reconstructions, tracking postglacial ecosystem build-up across millennia with high precision.