Sedimentary ancient DNA from the sympagic dinoflagellate Polarella glacialis as a sea-ice proxy

Abstract Sea ice is a critical component of the Earth’s Climate System and a unique habitat. Sea-ice changes prior to the satellite era are poorly documented, and proxy methods are needed to constrain its past variability. Here, we demonstrate the potential of sedimentary ancient DNA from Polarella glacialis, a sea-ice microalga, for tracing past sea-ice conditions. Our observations confirm that this cyst-forming species is common in first-year sea ice and sinking particulate matter following sea-ice melt. Using species-specific primers targeting the nuclear ribosomal ITS1 region, we quantified Polarella glacialis DNA (Pgla-DNA) by digital PCR in marine and fjord surface sediments. Inferred Pgla-DNA gene copy numbers in sediments reflect the spatial variability of recent sea-ice cover, they increase for sites with 20-80% sea-ice concentration and decrease for sites with concentrations > 80%. Furthermore, Pgla-DNA was detected in a sediment core from northern Baffin Bay spanning ca. 12,000 years. Its detection is more efficient following a molecular approach than standard micropaleontological methods. Given that the species inhabits coastal and marine environments in the Arctic and Antarctic, Pgla-DNA has the potential to become a useful tool for circum-polar sea-ice reconstructions both in marine and glaciated fjord environments, where biomarker and microfossil approaches are limited.