DNA based primary producer reconstructions throughout the Holocene in the Northern Antarctic Peninsula)

The phytoplankton in the Southern Ocean are at the base of a marine food web adapted to cold conditions and, thus, extremely endangered by the current global climate warming. As an active biological carbon pump, it also represents a very efficient way to sequester anthropogenic CO2 . In addition, some phytoplankton species synthesize specific compounds, such as dimethyl sulfur (DMS) that affects cloud formation, albedo and, therefore, the radiative budget of the Southern Hemisphere . Despite its ecological and climatic importance, the future evolution of the phytoplankton in the Southern Ocean is highly uncertain. It is obviously urgent to gain information on Southern Ocean phytoplankton adaptability under very different mean climate conditions, especially when climate was warmer than present, and on larger spatial scales. In this context, the main objectives of this project are to better understand (i) what were the dynamics of the different phytoplankton groups and species in the NAP during the Holocene, especially during phases of rapid climate transitions, (ii) which factors controlled these dynamics and to what extent were regional marine ecosystems and climate affected (e.g. CO2, DMS) and (iii) which lessons can we draw for the future. Thanks to recent technology developments, it is now possible to study these soft-tissue groups and to an unprecedented level of details (species) using a new combined molecular approach. Indeed, phytoplankton synthesis specific organic compounds, in particular DNA, which is relatively resistant to biodegradation during its transport from the surface to the sediment as well as to diagenesis. The association of this powerful genetic tool along with other organic tracers such as fatty acids, some diatom-specific alkenes (highly branched isoprenoids, HBIs), diatom-sterols and micropaleontological tools will thus enable us to precisely qualitatively and quantitatively characterize the response of these groups/species to past climatic and environmental changes over the last millennia.