DOI: 10.20351/29he20260122
title: FLAIR-POLARIN Cruise, RV Hespérides
title: 29HE20260122

description: The Antarctic margin hosts one of the most complex hydrogeological systems on Earth, where multiple fluid phases—including free gas, groundwater, permafrost, and gas hydrates—interact with the seafloor. The migration, phase change, and seepage of these fluids can profoundly influence seafloor morphology, sediment stability, nutrient fluxes, and benthic ecosystems. While climate-driven fluid–seafloor interactions have been increasingly documented in the Arctic, equivalent observations in Antarctica remain sparse due to logistical constraints and historically limited access to high-resolution geophysical and geochemical data. The seafloor of the northern Western Antarctic Peninsula, particularly the Bransfield Basin and adjacent continental shelves around the South Shetland Islands, represents a natural laboratory for investigating these processes. This region is characterised by active tectonism related to back-arc rifting and subduction of the Phoenix Plate, elevated geothermal gradients, evidence for gas hydrates, and documented methane seepage to the water column. Sedimentary records indicate repeated glacial advances and retreats, with grounded ice extending to the outer shelf during the Last Glacial Maximum and retreating in multiple phases. These glacial dynamics are hypothesised to have emplaced extensive bodies of overpressured groundwater beneath the continental shelf through subglacial melting and drainage networks. The Western Antarctic Peninsula is currently experiencing among the fastest warming rates in the Southern Hemisphere. Despite this rapid environmental change, the response of subsurface fluid systems and their role in shaping seafloor geomorphology, sediment stability, and benthic habitats remain poorly constrained. Features such as pockmarks, slope failures, and chemosynthetic communities observed along the Bransfield Basin flanks suggest that fluid flow has played, and may continue to play, a key role in margin evolution. Understanding these interactions is critical for interpreting past ice–ocean–seafloor coupling and for assessing how ongoing climate warming may modify Antarctic seafloor processes. b. Aims of the cruise The primary objective of the FLAIR expedition was to investigate the interactions between subsurface fluid flow, seafloor geomorphic processes, and benthic habitats in the northern Western Antarctic Peninsula within the context of a rapidly changing climate. The working hypothesis guiding the expedition was that fluid migration and seepage are major drivers of seafloor evolution and chemosynthetic ecosystems in the Bransfield Basin and adjacent shelves, and that these processes may intensify under continued regional warming. The specific objectives of the cruise were to: 1. Characterise marine hydrogeological systems at targeted sites, including the extent, type, and source of fluids, preferential migration pathways, and the spatial distribution and timing of fluid seepage. 2. Assess the influence of past glacial cycles on subsurface fluid systems, with particular emphasis on the role of ice advance, retreat, and subglacial drainage in shaping present-day hydrogeology. 3. Evaluate the impact of fluid flow on seafloor geomorphology and benthic habitats, including the development of pockmarks, sediment instability, and chemosynthetic communities, and to assess potential long-term geomorphic consequences. To address these objectives, the expedition integrated high-resolution geophysical mapping, sediment coring, water-column and pore-water sampling, Remotely Operated Vehicle surveys, and controlled-source electromagnetic measurements, enabling a multidisciplinary assessment of fluid–seafloor interactions across climatically sensitive Antarctic margins.