The promise of sedimentary ancient DNA as a proxy to understand Arctic Ocean palaeoecology and palaeoenvironments

The Arctic Ocean is changing rapidly due to global warming, but how this will impact marine Arctic ecosystems remains uncertain. Several Pleistocene interglacials, like Marine Isotope Stages (MIS) 5e, 9 and 11 form potential analogues to a future warmer Arctic and can give important insights on how Arctic ecosystems may respond to climate warming. However, micro- and nannofossils are scarce in many Pleistocene marine sediment cores, and are often not in agreement with biomarker data. Sedimentary ancient DNA (sedaDNA) is an emerging method that does not require the preservation of fossils and can therefore be used to detect taxa without any hard body parts, like most protist groups and zooplankton. Thanks to this method, it is now possible to detect organisms from all trophic layers of marine ecosystems. SedaDNA provides us with new opportunities to reconstruct past sea ice conditions, changes to ocean currents, and borealisation of the Arctic Ocean. Developments in bioinformatics software and new techniques like shotgun metagenomics and hybridisation capture, now enable the study of ancient DNA from Middle and even Early Pleistocene sediments. Moreover, the marine sedaDNA field is working towards detecting within-species genetic variation, which can provide information on population bottlenecks, recolonisation histories, and may lead to important insights for marine conservation. Combined with traditional proxies, sedaDNA is a powerful tool for Arctic Ocean palaeo-environmental reconstructions and can help provide critical proxy data to facilitate climate model calibrations and ultimately improve climate and environmental predictions for the Arctic.