Trial lecture and disputation - MSc Aloïs Revéret

Later, at 12.15 he will defend his thesis entitled: "Reconstruction of long-term postglacial succession of subpolar terrestrial ecosystems from sedimentary ancient DNA".

Professor Monica Alterskjær Sundset at AMB will lead the disputation.

Popular Science Summary

For the last 20 000 years, polar ice sheets have retreated, and new ecosystems developed on the newly liberated lands. Sedimentary ancient DNA (sedaDNA) is a powerful tool that allows to reconstruct past ecosystem changes across the last ice age, and more specifically to study the transition from the glaciation to modern times.

We used sedaDNA on sediment cores from 14 sites along the Norwegian Atlantic coast, plus another one from the sub-Antarctic archipelago of Kerguelen, in the Southern Indian Ocean. We used 'meta-barcoding' of ultra-short DNA fragments to identify plants and mammals from these time periods.

Our results show that the sedaDNA record from aquatic plants informs us about past lake conditions, such as water acidity, temperature, nutrient content, etc. thanks to the analysis of individual preferences of each detected species. We reconstituted the postglacial development of aquatic vegetation in Northern Norway, as well as individual lake histories; for instance we record an increase of water acidity when the pine forest establishes nearby. In southern Norway, we show that climatic oscillations between warmer and colder periods of several millennia strongly influenced vegetation development, as plant diversity remained constant during cold periods but increased rapidly during climate warmings. In complex sediments from the bottom of the North Sea, we found a rich record of nearly 300 plant species, as well as records from large ice age mammals including reindeer, woolly mammoths, and woolly rhinoceroses. Moreover, we present the first detection in sediments of the giant deer (Megaloceros giganteus). Lastly, we reconstructed 10 000 years of vegetation history in the Kerguelen Archipelago, critically expanding the analysis to mosses and liverworts.

Reindeer was found on both sides of the Norwegian Channel during the Allerød warm period 13 000 years ago, suggesting that it crossed directly from 'Doggerland', i.e. the landbridge that once joined Great Britain to Denmark, into Norway. Doggerland likely served as an ecological 'hotspot' during the height of the last glaciation, and was a northern vegetation outpost that helped ecosystem development on the Scandinavian Peninsula. Our results demonstrate the potential of sedaDNA to carry out broad palaeo-ecological reconstructions, tracking post-glacial ecosystem build-up across millennia with high precision.

Evaluation Committee

• Senior researcher Dr Ole Bennike, GEUS, Denmark (1. opponent)
• Professor Robin Allaby, University of Warwick, UK (2. opponent)
• Researcher Dr Inger Marie Garfelt Paulsen, AMB (internal member and leader of the committee)

Supervisors

• Professor Inger Greve Alsos, the Arctic University Museum of Norway
• Senior researcher Dr Dorothee Ehrich, the Arctic University Museum of Norway
• Associate Professor Dilli Prasad Rijal, the Arctic University Museum of Norway
• Researcher Dr Peter Heintzman, Stockholm University, Sweden

Streaming

Both the trial lecture and defense and will be streamed and recorded:

• Trial lecture
• Defense

Thesis

 The thesis is available in Vitenarkivet