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In the eastern Black Sea, we determined methane (CH4) concentrations, gas hydrate volumes, and their vertical distribution from combined gas and chloride (Cl−) measurements within pressurized sediment cores. The total gas volume collected from the cores corresponded to concentrations of 1.2–1.4 mol CH4 kg−1 porewater at in-situ pressure, which is equivalent to a gas hydrate saturation of 15–18% of pore volume and amongst the highest values detected in shallow seep sediments. At the central seep site, a high-resolution Cl− profile resolved the upper boundary of gas hydrate occurrence and a continuous layer of hydrates in a sediment column of 120 cm thickness. Including this information, a more precise gas hydrate saturation of 22–24% pore volume could be calculated. This volume was higher in comparison to a saturation calculated from the Cl− profile alone, resulting in only 14.4%. The likely explanation is an active gas hydrate formation from CH4 gas ebullition. The hydrocarbons at Batumi Seep are of shallow biogenic origin (CH4 > 99.6%), at Pechori Mound they originate from deeper thermocatalytic processes as indicated by the lower ratios of C1 to C2–C3 and the presence of C5.

The Sorokin Trough (Black Sea) is characterized by diapiric structures formed in a compressional tectonic regime that facilitate fluid migration to the seafloor. We present acoustic data in order to image details of mud volcanoes associated with the diapirs. Three types of mud volcanoes were distinguished: cone-shaped, flat-topped, and collapsed structures. All mud volcanoes, except for the Kazakov mud volcano, are located above shallow mud diapirs and diapiric ridges. Beyond the known near-surface occurrence of gas hydrates, bottom simulating reflectors are not seen on our seismic records, but pronounced lateral amplitude variations and bright spots may indicate the presence of gas hydrates and free gas.

Long-range, low-resolution and deep-towed, high-resolution side-scan sonar records, high-resolution seismic profiles and core samples were used to study the relatively small canyon fed turbidite systems west of Corsica and Sardinia. The margin west of Corsica is dissected by deep (up to 1500 m), straight canyons that have steep axial gradients (10° slopes are common) and that extend from land to sea without a break in gradient. The submarine canyon axes are readily mapped by their stronger acoustic backscatter. The axes have scour holes and trains of gravel or pebble waves. Canyoned slopes have widespread, shallow sediment failures. Five separate depositional lobes are recognised, extending beyond the canyon mouths. Deep-towed, high-resolution seismic profiles across part of one lobe show stacked sedimentary sheets, a few tens of kilometres wide. Cores from these sheets contain coarse to medium sand beds that are up to 3 m thick, with some mud clasts in the middle of the beds and up to 3% clay in the sand matrix. A drape of nannofossil ooze on top of cores indicates that the main activity through the canyons is at times of low sea level. The lobes tend to appear as weak backscatter, with fringes of a braid-like pattern of stronger backscatter. The reasons for this acoustic pattern are not fully understood, though in general the sand bodies are found where backscatter is relatively weak. The size of the canyon-mouth lobes is proportional to the size of the subaerial drainage basins. The limited sediment supply accounts for the absence of a well-developed submarine ramp despite the sand-dominated input from multiple sources.

Tectonically active structures prone to cause devastating earthquakes and tsunamis, e.g. the Lisbon 1755 earthquake, were investigated during the UNESCO/IOC Training Through Research-10 (TTR-10) cruise on the southwest Portuguese Continental Margin using single channel seismic profiles, a 3.5-kHz hull-mounted sea-bottom profiler, 10-kHz OKEAN long range side-scan sonar, 30-kHz ORETECH deep-towed side-scan sonar, and a high-resolution deep-towed sea-bottom profiler. These data allowed the definition of new active faults and the establishment of morphological criteria for the classification of active faults in the study area. Landslides associated with the activity of a major tectonic structure, the Marquês de Pombal Fault, and other areas with clear signs of mass wasting phenomena were mapped. A slope-to-basin sedimentary system comprising 21 sedimentary ridges up to 20 km long was mapped and described. It was found that the sediments are mainly transported into the deep basins by mass transport processes across the steepest fault scarps forming a channel–levee system, while gravitational slides/slumps dominate the shallower slopes. The sedimentary ridges with an elevation of 40–50 m (50–60 ms TWT) above the seafloor are imaged on the high-resolution seismic profiles as an alternation of high and low amplitude reflectors. It is shown that the Pereira de Sousa Fault, its plateau and the Príncipes de Avis Plateau are experiencing uplift according to sedimentary and morphological criteria.