Marine biodiversity responses to Holocene climate off NW Greenland: a sedimentary ancient DNA trait-based approach

Biodiversity plays an essential role in the functioning of ecosystems, and ultimately their health and resilience. Yet, as an overwhelming number of functional groups do not leave a fossil record (e.g., zooplankton, jellyfish, worm-like fauna), our understanding of past biodiversity changes is inadequate to make confident projections. The retrieval of sedimentary ancient DNA (sedaDNA), the molecular footprints of past biota, has been a game changer in this regard. It allows us to trace species, e.g. with soft body parts or skeletal components prone to dissolution, ultimately allowing us to identify responses to environmental changes on ecosystem level.
Our goal is to move beyond taxonomic characterizations and capture key aspects of functionality in the arctic marine ecosystem over time. For this, we focused on ecological strategies via traits known to be directly related to fitness or to ecosystem functioning. These traits include morphology (size, shape), energy acquisition (trophic mode and behaviour), survival (motility, defense structures, toxin production) and potential for bioturbation (biodiffusors, surficial modifiers).
The functional framework was applied to a Holocene marine sediment core from the Northwest Greenland shelf, an area affected by accelerating sea ice retreat and freshwater discharge from the Greenland Ice Sheet, and an important migration corridor for seabirds and marine mammals. We applied DNA metabarcoding of a diatom-specific (rbcL) and a broad eukaryotic (18S V7 region) marker to a well-dated marine sediment core (AMD14-204C) retrieved on the shelf off the Upernavik Ice Stream.
Our 8,500 year-record of sedaDNA was rich in phyto- and zooplankton groups, characterizing the lower trophic levels of the food web at an unprecedented detail in the study area. Different functional groups responded to different potential drivers: while benthic infauna was negatively correlated with our proxy for seasonal sea ice, nano-sized phytoplankton was positively correlated with atmospheric temperature, whereas diatoms and benthic epifauna showed periodic biodiversity pulses potentially related to ocean circulation patterns. We will discuss the exceptional potential of sedaDNA to improve predictions of marine productivity and biodiversity.