Kordella S., Etiope G., Christodoulou D., Papatheodorou G., Marinaro G., Lo Bue N., Geraga M. and Ferentinos G.
The submarine seepage area of thermogenic gas along the Katakolo offshore fault, was investigated and monitored by two underwater systems, equipped with a series of gas and oceanographic sensors, in order to study the methane release from bubble plumes and its effect on the oxygen distribution in the seawater. The underwater system MEDUSA (Module for Environmental Deep UnderSea Applications) performed areal surveys at the seepage area, while for the long-term monitoring, a benthic station, named Gas Monitoring Module (GMM) was deployed within a field of gas bubble plumes inside the Katakolo harbour for 101 days. The MEDUSA system allowed the underwater visual inspection of 68 bubble plumes along the offshore Katakolo fault area, and it detected variations of CH4 (increase) and O2 (decrease) related to numerous gas seeps and carbonate mounds. Notwithstanding the open sea conditions, O2 decreases locally close to the main seep fields where methane concentration in seawater is higher. Preliminary GMM data analysis showed 8 main periods of enhanced O2 depletion, associated with CH4 increase and wind and current regime that needs to be further investigated.