OS037-0008
Shallow water hydrothermal systems: Constraints on distribution, nature, and heat fluxes of outflow from Milos (Greece)

Monday, 14 December 2020
Poster
Valentine Puzenat1, Javier Escartin2, Jean-Emmanuel Martelat3, Thibaut Barreyre4, Sven Le Moine Bauer4, Nuno Gracias5, Paraskevi Nomikou6, Philippe Grandjean3, Anders Schouw4, Paraskevi Polymenakou7 and Pascal Allemand3, (1)Institut de Physique du Globe de Paris, Université de Paris, Paris, France, (2)Laboratoire de Géologie, Ecole Normale Supérieure de Paris, Paris, France, (3)Laboratoire de Géologie, Université de Lyon, Villeurbanne, France, (4)Department of Earth Science, University of Bergen, Bergen, Norway, (5)Underwater Robotics Research Center, Computer Vision and Robotics Institute, Universitat de Girona, Girona, Spain, (6)Faculty of Geology and Geoenvironment, National and Kapodistrian University of Athens, Athens, Greece, (7)Institute of Marine Biology Biotechnology and Aquaculture, Hellenic Center for Marine Research, Anavyssos, Greece
Abstract:
Hydrothermal activity is well-studied in deep sea settings and is responsible for heat and chemical exchanges through the seafloor. While particularly abundant at volcanically active areas, shallow-water hydrothermal systems (SWHS) have been identified around the globe, but are less studied. Their geometry, temporal evolution and associated heat fluxes are not well constrained.

Using aerial drones, an AUV, and temperature measurements at 10-40 cm subseafloor, we investigated in 2019 one of the most extensive SWHS known to date, in Paleochori (south of Milos, Greece). Hydrothermal venting, found from the shore to almost 500m, shows emissions of gases and high-temperature fluids, often associated with bacterial mats and/or hydrothermal mineral precipitates, that are visible in satellite imagery (Martelat et al., 2020). Our study provides extensive drone mapping coupled with local AUV surveys for seafloor characterization and ground-truthing, that provide a context to samples, measurements and observations carried in situ.

We interpret our photomosaics to define distinct seafloor types. First, we observe white hydrothermal patches (WHPs), often showing a clear polygonal organization, together with outflow areas that are both more dispersed and distributed. Polygonal patterns likely result from fluid convection in a sandy porous medium heated from below. These WHPs display elevated temperatures, typically >50°C, with maximum values of ~100°C. Second, we identify textures of biological origin, including seagrass and bioturbation patterns. In particular, we observe that bioturbation by burrowing shrimp is often associated with WHPs, bounding them, in addition to its presence on sandy seafloor away from hydrothermal patterns. Subseafloor temperatures at these bioturbated areas are of ~30-40°C, and are thus transitional between hot WHPs and sedimented seafloor unaffected by hydrothermal activity (~24°C). In addition to linking temperature data and interpreted photomosaics, our study provides a comprehensive general overview of this SWHS, of the organization of hydrothermal outflow, and in fine of the associated thermo-chemical energy fluxes. It also gives a background for other studies on the nature and distribution of microbial communities, which are controlled by this hydrothermal activity.

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