Submarine hydrothermal activity off Santorini and Milos in the Central Hellenic Volcanic Arc: A synthesis

Geochemical investigations carried out for a long period on Santorini and Milos submarine hydrothermal fields in the central Hellenic Volcanic Arc are reviewed. They showed significant spatial and time variability in their dissolved element concentration levels. In the Santorini hydrothermal field Fe, Mn and As are the most enriched elements both in the hydrothermal waters and associated sediments. Average Fe and Mn showed little systematic variation in the Santorini waters during the period 1982–97. Milos hydrothermal waters the most Fe–Mn enriched were encountered near the Airport. Time series analysis for Fe and Mn at a very strong vent there showed the same semi-diurnal pattern for three consecutive days with strong element concentration variability. The results of monitoring this vent for ten years (1987–1997) showed significant increase of Mn from 1987 to 1994 and a decrease afterwards. Iron showed a similar variability. nt cores recovered from Palaea and Nea Kameni embayments of Santorini showed that the former consists mainly of pyrite, diatoms and amorphous iron hydroxides. In the later, amorphous Fe oxyhydroxides prevail with substantial amounts of Si, S and Na and minor amounts of Zn, P, As and organic C. Except for Sr, Ni, Pb, As and Bi all other elements determined showed statistically different mean concentrations in sediments between the two embayments. n Santorini and Milos sediment cores distinct Fe–Mn rich layers were located at depth suggesting pulses of hydrothermal activity in the recent past.