Intercalibrating new paleogenomic methods to investigate the vulnerability of the Antarctic trophic levels to past climate change

The basis of the Southern Ocean ecosystem are large phytoplankton known as diatoms that thrive in the nitrate, phosphate and silicate rich waters, and provide the preferred food for krill, which support extraordinary Antarctic megafauna such as penguins, seals, and whales. Consequently, the Antarctic ecosystem is essentially entirely dependent on Southern Ocean phytoplankton. Climate change is now altering the Antarctic ecosystem at alarming rates, and its future is at risk. Projections from the IPCC consistently predict that primary productivity will be promoted in the Southern Ocean. But will this be enabled by the adaptation of existing diatom-based communities to warmer conditions in the coming decades, will the larger diatoms be replaced by smaller diatoms, or will other phytoplankton groups take over? Will smaller phytoplankton cells invade from warmer latitudes as temperatures increase? Will the crucial micronutrients released from melting glaciers and the tabular icebergs that detach from them stimulate phytoplankton blooms? Will these changes lead to the desertification of the Antarctic ecosystem as the current biogeochemical cycles and food webs become dysfunctional? Whatever the scenario, such changes will have a major impact on the food web. One way to evaluate the response of the diatoms and other phytoplankton groups/species to climate change is to investigate its evolution in the past using marine sediment archives. However, we are still limited by the existing methods, mostly based on the micropaleontological approach, due to the absence of some microfossil remains, especially for species that do not produce shells. To circumvent these issues, recent technological developments now allow us to scrutinize changes in all the marine species at an unprecedented level of details using the ancient DNA. This new and powerful genetic tool, along with other tracers (specific organic compounds and diatom fossil accounts) can qualitatively and quantitatively characterize the response of the phytoplankton group and species to past climate and environment changes over the last millennia, in particular during abrupt warming events. Nevertheless, different protocols have been recently developed to extract, purify and amplify DNA but, without any data lab intercomparison and intercalibrated methods. This project therefore aims at establishing (i) which protocol more efficiently extract ancient DNA in the Southern Ocean, (ii) how to adapt and optimize a common protocol, from the sampling to the sequencing steps and (iii) how statistically are robust these data in comparison with traditional markers.