Coastal hydrodynamics at the sub-Antarctic Possession Island (Crozet archipelago) inferred from bedform structures and sediment properties

Within the Southern Ocean, sub-Antarctic regions are anticipated to face significant impacts related to climate change. The alteration of the circulation and properties of the water masses is expected to have widespread impacts on sub-Antarctic nearshore marine ecosystems. Satellite data provides valuable insights into the global ocean circulation but information on fine-scale, local coastal dynamics remain limited and imprecise for the isolated sub-Antarctic territories. The present study aims to infer coastal hydrodynamic processes from the analysis of bedforms using seafloor imagery and sediment samples at two sites located on the eastern coast of Ile de la Possession (Crozet archipelago), Baie du Marin and Crique du Sphinx. Sedimentological and mineralogical analyses conducted on samples have revealed a typical volcanic nature of sediments, with a high proportion of pyroxenes, olivines and large plagioclases. Sediments were characterized by low carbonate and nitrogen contents, suggesting that organic matter is either rapidly depleted by microbial degradation, consumed by benthic detritus feeders, or the lithogenic material transported away from the coastal production area by local currents. Sedimentary structures analyses suggested that ocean circulation at Baie du Marin and Crique du Sphinx is influenced by residual flows that are likely driven by wind and ocean circulation at regional scales and that may result as well from tidal rectification by topography between Ile de la Possession and Ile de l'Est. This study provides a first attempt to analyze local, fine-scale hydrodynamic processes occurring along the eastern coast of Ile de la Possession and link these field observations to large-scale, regional processes formerly studied in the region.