The potential of sedimentary ancient DNA for reconstructingpast sea ice evolution

Abstract

Sea ice is a crucial component of the Arctic climate system, yet the tools to document the evolution of sea ice conditions onhistorical and geological time scales are few and have limitations. Such records are essential for documenting andunderstanding the natural variations in Arctic sea ice extent. Here we explore sedimentary ancient DNA (aDNA), as a noveltool that unlocks and exploits the genetic (eukaryote) biodiversity preserved in marine sediments specifically for past sea icereconstructions. Although use of sedimentary aDNA in paleoceanographic and paleoclimatic studies is still in its infancy, weuse here metabarcoding and single-species quantitative DNA detection methods to document the sea ice conditions in aGreenland Sea marine sediment core. Metabarcoding has allowed identifying biodiversity changes in the geological recordback to almost ~100,000 years ago that were related to changing sea ice conditions. Detailed bioinformatic analyses on themetabarcoding data revealed several sea-ice-associated taxa, most of which previously unknown from the fossil record.Finally, we quantitatively traced one known sea ice dinoflagellate in the sediment core. We show that aDNA can berecovered from deep-ocean sediments with generally oxic bottom waters and that past sea ice conditions can be documentedbeyond instrumental time scales. Our results corroborate sea ice reconstructions made by traditional tools, and thusdemonstrate the potential of sedimentary aDNA, focusing primarily on microbial eukaryotes, as a new tool to betterunderstand sea ice evolution in the climate system.