Determination of fluid sources in the Paleochori Bay hydrothermal system, Milos Island (Greece)

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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 micro-environments 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 is 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 is virtually impossible.A likely solution to this quandary at Milos and a potential aide to many other studies of MSWHS could be the generation of geo-referenced maps with help of aerial photography, because due to their shallow nature, hydrothermal features are discernable from the surface. With the possibility to obtain GPS coordinates directly from the map it will be possible to pick exact locations for sample collection, including temperature and flux measurements. Furthermore, it is possible to correlate hydrothermal features between their actual occurrence and their representation on the photographic map, i.e., to ground-truth the aerial map.The creation of a digital aerial map whose features were confirmed by direct observation will be the basis for a GIS platform to be used for past and ongoing research in Paleochori Bay, while the developed techniques will be easily transferred to other sites of shallow-water hydrothermal venting. Generation of such a map would, for the first time, allow unprecedented understanding of locations and chemistry of each vent site, as well as to provide an estimate of overall total hydrothermal fluxes and the associated Hg and As concentrations. This work has significance beyond Paleochori Bay since this approach will be easily transferable to other sites of MSWHS worldwide.