Antarctic península tectonic and climatic controls on Southern Ocean frontal system dynamics, biogeochemistry and biological productivity since the Middle Miocene. Implications for the future

The Cenozoic history of the opening, widening and deepening of tectonic passages, and of the initiation and variability of the SO fronts within the ACC and its ecosystems, is archived in ocean basins around Antarctica. Geophysical data provides insights regarding the break-up of the Gondwana super-continent and the separation of the two last landbridges with Antarctica that gave place to the Drake and Tasman ocean corridors . Seismic reflection profiles and sediments around Antarctica have demonstrated that deep-water deposits (e.g., hemipelagites, turbidites and contourites) can provide information about climate variability, sea-ice coverage, ocean currents/water masses, paleotemperatures, and inferences about ice-sheet dynamics and stability. AntOcean aims at combining these tools to: (1) determine the mechanisms (tectonic vs. climatic) forcing in the establishment of the modern-like vigorous and deep-reaching SO frontal system, which has been a subject of debate for more than four decades, and (2) contribute to the advance of our knowledge about the functioning of the SO by reconstructing the physical, biogeochemical and biological changes across the SO fronts under past glacial-interglacial cycles, with emphasis in warmer-than-present times and terminations (i.e., deglaciation at the end of a glacial cycle). Reconstructions of past hydrological, biological, biogeochemical cycling and sea ice variability are based on environmental indicators preserved in marine sediments that have been developed, validated and sometimes calibrated. However, some reconstructions are limited partly due to the lack of robust calibration of some of these indicators to present day conditions and observations. While some tools are better constrained than others (e.g., diatoms vs organic compounds as proxies for presence/absence of sea ice), the mechanisms controlling their seasonal distribution or abundance are not fully understood. An improved understanding of their locus of production is thus needed to quantitatively assess the information preserved in the sediment record, and to reliably use these proxies in paleoclimate studies. To address this shortcoming in our reconstructions, AntOcean will conduct SO water sampling at the surface and at depth and test which indicators obtained in water filters are exported and preserved at the seafloor in sediment traps and sediment cores. This innovative interdisciplinary approach in AntOcean covering a large range of time scales (from paleoclimate proxies to in situ observations) provides a unique opportunity to construct snapshots (i.e., low-resolution time series) to help us advance in our now scarce knowledge of the complex SO system and to identify relations between physical, chemical, and biological processes.