Fluid escape submarine geomorphological features in the NW Black Sea

By means of Digital Terrain Models, produced based on multibeam echosounding data and underwater photography, spectacular sea floor geomorphologies and features have been discovered and mapped.

In some parts of the NW Black Sea, the submarine geomorphology is characterized by the presence of fluid escape features. These very specific features are present in the flexure area and the upper continental slope. There are prevailing the so-called pockmarks (large depressions on the sea floor) and carbonate chimnies - positive small morphological items on top of the sea bottom, micro-biogeochemically build as the result of the fluid escapes from the sea floor. These kind of submarine geomorphologies are the result of the high dynamics of the fluid escapes that occur in areas with high sedimentation rates, both of sediments and organic matter. The sediments are of Quaternary age and are subject of consolidation processes, that means expulsion of pore water, sometimes accompanied by important amounts of gases, mainly biogenic methane. These submarine sea bottom elements are the best testimonies for the high dynamics of fluids in the pile of young sediments and point out that subjacent to these underwater morphologies could be located hot spots of organic matter accumulations.

The pockmarks could be isolated or clustered in groups of scattered elements or linear patterns. Often, mostly the linear clusters of pockmarks, are associated to the local highs of the sea floor geomorphology. The carbonate chimnies cannot be detected by means of multibeam technologies, but in some upper parts of the Danube and Dnieper deep sea fans such structures can by observed by means of underwater photography.