Dr. Jessica L. Ray
Uni Research Climate and Uni Research Environment, Bergen, Norway
Abstract: Traditional proxies for sea ice reconstruction include microfossils and chemical bio-markers in marine sediments, as indicators of past phytoplankton abundance in the overlying water column. We performed a pilot study to assess whether ancient environmental DNA (aDNA) from marine sediments can complement these traditional proxies to provide a more robust assessment of sea ice cover in the Arctic over the last ~100 kyr. We have a developed a semi-automated DNA extraction method that combines high levels of replication, high extraction efficiency of a commercial kit and the speed of an automated DNA extraction platform, to map patterns of biodiversity throughout geological time in the Ice2Ice Core GS15-198-38CC from the east of Greenland. Biodiversity was assessed through PCR amplification of the V7 region of the SSU ribosomal RNA gene using universal Eukaryote primers. Replicate amplicon pools were combined prior to Illumina MiSeq paired-end sequencing. We performed OTU clustering (97% similary, singletons excluded) using the UPARSE pipeline and taxonomically assigned OTUs using the CREST classifier with SilvaMod as reference database. Evaluation of OTU- and order-level taxonomic diversity demonstrated clear differences in microbial eukaryote community structure in the different sediment samples, with youngest samples (14 - 25 kyr) forming a distinct cluster from oldest samples (60 - 100 kyr), and interim samples (38-50 kyr) clustering distinctly between the two extremes. Interestingly, the 34 kyr sample, for which analysis of dinocyst assemblages and organic geochemistry markers indicate seasonal sea ice, clustered separately from all other samples.
To provide a framework upon which to assess the ecological, economical and political consequences of a future sea-ice free Arctic, an in-depth understanding of the forcing and feedback mechanisms that naturally regulate Arctic sea ice is essential. This pilot study represents a first and very promising use of aDNA as a proxy for past sea ice reconstruction in the Arctic. In the new three-year project aDNAPROX, we will expand our analyses to include multiple sediment cores from the Arctic. Furthermore we will quantify DNA degradation rates as a function of time, we will investigate the individual contributions of time and sea ice cover on sediment DNA signatures, and we will identify and quantify sea ice indicator taxa using correlation analysis of the sequence data with traditional proxies. This interdiscplinary project therefore aims to increase our understanding of natural variability in sea ice cover by exploring the link between climate and biology.