Geochemistry of Hydrothermal Particles in Shallow Submarine Hydrothermal Vents on Milos Island, Aegean Sea East Mediterranean

Abstract

Abstract—The study aims to contribute to submarine hydrothermal particle geochemistry knowledge on the central part of the Hellenic Volcanic Arc. Hydrothermal fluids collected by scuba diving from active shallow hydrothermal venting areas on Milos Island in the Aegean Sea in East Mediterranean. Analysis carried out in suspended particles for Fe, Mn, Cu, Pb, Cd, Ca, Ba, Sr, Li, Al and Si. During sampling, gas and water flux was measured and gas/water ratios were estimated. The data presented significant time and spatial variability. The gas flux values in Palaeochori Bay varied from 4.5 to 63 L/h and water flux varied from 25 to 92 L/h. In Voudia Bay varied from 0.8 to 32 L/h and the water flux found from 7 to 118 L/h while in Adamas Bay the gas flux values were from 2 to 13 L/h and the water flux found from 24 to 72 L/h. The suspended particulate matter (SPM) flux varied from 0.07 to 47 mg/L in Palaeochori Bay, between 2 and 19 mg/L and from 0.8 to 4 mg/L respectively in the three sites studied. Metal/Al ratios also vary significantly within a short distance between seeps in the same area. The pH of hydrothermal waters was from 5.21 to 6.63 in Palaeochori Bay, from 5.45 to 6.39 in Voudia Bay and from 5.69 to 6.10 in Adamas Bay suggesting either different mixing of fluids with seawater deeper in the substrate or perhaps that gases CO2 and H2S control pH values. Based on the geochemical properties found a common geothermal reservoir is suggested located below the surface of the island and annual fluxes of elemental particulates have been estimated. The main scope of this research is to evaluate the fluxes of gas and water and the main particulate geochemistry of hydrothermal venting fluids. Hydrothermal particles from the submarine vents studied were dominated by Fe, Ca, Si and Al and strongly enriched in Mn, Cu, Pb, Ca and Ba. The chemistry of particles emitted from seeps can strongly influence the local sediment geochemistry and element distribution on sea bottom locally while subjected to further transportation can also affect a much greater region.