Impact of the hydrothermal activity on the seawater chemistry above the Kolumbo volcano (southern Aegean Sea - Greece)

Within the framework of SANTORY (SANTORini’s seafloor volcanic observatorY) project, funded by the Hellenic Foundation for Research and Innovation and with the financial support of the Municipality of Thira, three oceanographic cruises were performed in December 2022 and June and October 2023, with the research vessels PHILIA and AEGAEO of the HCMR at the submarine volcano Kolumbo, 7 km NE of Santorini. Kolumbo is considered to be one of the most active submarine volcanic complexes in the Eastern Mediterranean Sea, while being easily accessible from land.. The oceanographic surveys were mainly aimed at the deployment of a new generation observatory along with several multiple innovative sensors such as temperature sensors, inclinometers, pressure gauges, optical cameras, multispectral and stereo camera, radioactivity sensor gSniffer and the γ-radiation imager. During the surveys, several water column profiles were also performed in order to collect seawater samples for chemical analysis. At the bottom of the Kolumbo crater (500m depth), acidic and slightly reducing conditions prevail, due to the presence of several active hydrothermal vents. This agrees with previous studies and with the data recorded by the deployed observatory. Collected samples have been analyzed for the chemical and isotope (carbon, helium and argon) composition of the dissolved gases as well as for the major, minor and trace element concentrations. The results indicate that the morphology of the crater allows the buildup of persistent anomalies that extend from the bottom up to the lowest crater-rim level at about 250-meter depth. We will discuss the temporal variability of the Kolumbo venting dynamics and the explore in detail the resulting vertical gradients in the crater funnel.