Tracing Holocene marine ecosystem changes off West Greenland with ancient DNA

The West Greenland shelf is a unique ecoregion harboring marine areas of international value like the North Water polynya and the Melville Bay Wildlife Sanctuary, yet it is among one of the most vulnerable regions to climate change. According to model projections, this region will be increasingly affected by sea-ice loss and freshwater discharge from the Greenland Ice Sheet. Large uncertainties prevail on how diversity and ecosystem structure will change, due to the complexity of ecological responses and the fact that modern observations cover mostly timeframes already affected by climate change. This is raising questions on how to define baselines for evaluating observed changes, and on how to disentangle the effects of human impact and natural climate variability. Ocean sediments are archives of the past and provide invaluable insights into long-term ecosystem responses. Here, we use sedimentary ancient DNA to explore past marine ecosystem dynamics to climate variability off West Greenland over the past 8,500 years. We applied DNA metabarcoding using a eukaryotic (18S) and a diatom-specific marker (rbcL) to a well-dated marine sediment core retrieved on the shelf off the Upernavik Ice Stream (AMD14-204C; Lat. 73.261, Long. -57.899, 987 m water depth). We uncovered a high taxonomic diversity (251 families in 31 phyla), including many taxa whose body parts are usually not preserved in sediments, such as copepods, polychaetes or jellyfish. We will discuss the unique potential of ancient DNA to improve predictions of marine productivity and biodiversity, and to support ocean and cryosphere risk assessment and conservation efforts.