Determination of fluid sources in the Paleochori Bay hydrothermal system, Milos Island (Greece)
Mineralogy, Petrology and Geochemistry
Final Report Abstract
Historically most research on marine hydrothermal venting focused primarily on deep-sea, black smoker-type locations, although approximately 70 locations of marine shallow-water hydrothermal vent systems (MSWHS) were documented. MSWHS usually consist of a combination of gas vents and hydrothermal springs, discharging into the shallow coastal marine environment where they can have a considerable impact on the biology by creating microenvironments due to the discharge of reduced, hot hydrothermal fluids often containing potentially toxic elements, such as, As and Hg. One of the best studied MSWHS is located in Paleochori Bay on the south side of Milos Island, which due to its peculiar biogeochemistry has been the focus of numerous scientific studies. However, despite more than 25 years of research we do not have a dependable biogeochemical model concerning the interaction between hydrothermal and biological processes, nor do we have reliable repeat measurements at single locations. This was owed to the fact there are no GPS coordinates given for any of the sites studied and thus, although descriptions of the general locations and characteristics of vent sites exist for most of the investigations, returning to those specific sites was virtually impossible. With this in mind we generated a geo-referenced map of Paleochori Bay with the help of aerial orthophotography and we correlated hydrothermal features between their actual occurrence and their representation on the photographic map, i.e., we did ground-truth (verified) the aerial map. That was possible, because due to their shallow nature, hydrothermal features were noticeable from the surface. With the possibility to obtain GPS coordinates directly from the map it was possible to pick exact locations for sample collection, including temperature, pore water samples and flux measurements. We collected 150 fluid samples and temperature measurements. The water samples were analyzed for major and minor elements, as well as, for their isotopic composition (δ2H and δ18O). The geo-referenced map was further processed in ArcGIS to map the distribution of white microbial mats, former microbial mats, sea grass and “normal” sand down to a depth of 15 m. This allowed to calculate the extend of the hydrothermal areas and together with temperature measurements and chemical data allowed an estimate of overall total hydrothermal flux of arsenic (As) in Paleochori Bay.
Publications
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2020. Hydrothermal areas, microbial mats and sea grass in Paleochori Bay, Milos, Greece. Journal of Maps, 16(2): 348-356
Khimasia, A., Rovere, A. and Pichler, T.
