MARE NIGRUM SLOGARO II-cancelled

EUROFLEETS cruise AK211 with RV AKADEMIC served in 2012 to execute geophysical investigations at gas release sites along the Bulgarian margin of the Black Sea. In the course of the project seafloor depressions aligned with such seep sites were interpreted to be caused by weakening of the sediment due to gas migration. Proximity of the depressions to headwalls and slumps lead to the question if gas migration might cause slope failure. Cruise MSM-34 with the RV MARAIA S MERIAN showed that mass transport deposits occurred with up to 600 km3 in the Danube Fan. 3D seismic data images showed that deposition sequences may prevent vertical gas migration pathways from active gas release. On the other hand slope failure caused the hydrate stability zone to shrink and may cause additional gas supply along the slope. Similar depressions like those investigated along the Bulgarian margin were mapped during following cruises M-142 & M-143 with RV METEOR along the Romanian margin in the area where massive slope failure has been documented before. PARASOUND images identified extensional seafloor depressions above faults at various stages of development. Due to limited signal penetration the base of the faults and connection to the gas plumbing system could not be revealed. This proposal sets out to collect new seismic data, gravity cores, cone-penetrometer across the observed seafloor depressions. Data analyses should help to evaluate if the development of these structures represents a new mechanism of slope failure development. During the last glacial maxima limnic conditions caused reduced salinity in the sediments. Since then the equilibration is still underway and will cause a deepening of the top of the hydrate stability zone. This process will release further free gas in the margins sediments and may accelerate this process. Therefore, heatflow measures will be undertaken as well to support new calculations on hydrate distribution.