New molecular approaches to investigate the Southern Ocean (past) soft-tissue pump)

The soft-tissue phytoplankton, such as haptophytes or cryptophytes, play an important role on Southern Ocean ecosystem as first trophic level, as well as on the carbon cycle as they represent up to 50% of the biomass. However, their modern distribution in the Southern Ocean is not very well known as few dedicated studies have been published so far. Even less is known about their past distribution and evolution because, as these soft species do not produce any tests, conventional micropaleontological studies cannot be applied. In this study, we applied a novel approach using ancient DNA (sedaDNA) preserved in the well-dated Holocene marine sediment cores retrieved in the northern Antarctic Peninsula (NAP) where important blooms of soft-tissue phytoplankton were observed, to track the distribution and the quantity of these groups over the last thousands years. We combine sedaDNA metabarcoding using eukaryotic specific amplicon sequences of the V9 region, to highly branched isoprenoid (HBI), alkenes (sea-ice proxy), and TEXL86 (ocean subsurface temperature proxy) to (1) determine the response and adaptive processes of the soft-tissue groups to past climate change over the last millennia, (2) constrain which parameters drove their past evolution and (3) gain information on their future variation. Those data will be then compared to previous reconstructions derived from marine sediments cores around the Antarctic Peninsula.