Models of hydrothermal plumes by submarine diffuse venting in a coastal area: a case study for Milos, South Aegean Volcanic Arc, Greece

The hydrothermal activity of Milos Island has been studied with respect to its economic potential and its significance for marine ecosystems. This study aims at assessing the hydrothermal plumes close to the southeastern coast of Milos forming from submarine diffuse vents covered by sediment in shallow water. It contributes to the knowledge about hydrothermal plumes at such conditions as a large part of research effort so far has been applied to hydrothermal plumes from focused vents in sediment- starved settings in the deep sea. Fluid and gas samples from submarine vents were taken showing different portions of high- and low salinity fluids originating in the hydro-thermal system. This seems to be controlled by the distance to the hydrothermal system and by the thickness of the sedimentary canope. Seawater samples were taken in the regions of active venting revealing a strong impact by low-salinity fluids on the seawater forming extended surface layers of lower salinity. High salinity fluids were encountered only as locally confined small plumes delineated by enrichments of main components. this suggests that the flux of low-salinity fluids is of greater importance at Milos than high-salinity fluids. ... mehrUsing the hydromechanical simulation programme CORMIX, the spatial dimensions and dilution characteristics of hydrothermal plumes were calculated. The models revealed a high dilution efficiency resulting in small plumes of a few cm to m extent. The development of the dilution in each model case is expressed by an equation that enables to calculate the concentration of any tracer at any position in the model plume. Based on a new estimate of the extent of degassing hydrothermal vents around Milos Island, the chemical fluxes were calculated using the equations derived from the CORMIX models.