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Mud volcanoes (MV's) are structures that can be found on land and on the seafloor at passive and continental margins. The eruptions are triggered by the overpressure occurring at depth and resulting from excess gas and water pressure. Gas, fluids, and sediments are then mobilized and migrate through the sedimentary column (often via faults), building mud domes.
At all mud structures investigated in the eastern Mediterranean, enhanced concentrations of hydrocarbon gases, namely methane, ethane, and propane, have been observed not only in the sediment, but also in the water column. These gas plumes can extend up to several hundreds of meters above the seafloor or even upto the sea surface at shallow sites such as at North Alex MV, in the central part of the Nile area. Moreover, these gas plumes are associated with enhanced light scattering, which can be associated to the release of gas bubbles and/or sedimentary particles. Part of the hydrocarbons may been altered by (microbial) oxidation.
The signature of the gases that resembles most the intial composition can be found in the deepest core samples. Several of the water column plumes closely resemble these, thereby confirming their direct emission via bubble transport into the water column. On the basis of gas concentrations and isotope composition, a thermogenic origin with a smaller but variable biogenic contribution can be deduced for the hydrocarbon gases at most mud expulsion structures.
Here, we present results of gas, carbon and hydrogen isotopic composition of the migrating hydrocarbons as well as some essential elemental and isotope pore water data in order to highlight the processes involved, and to assess the origin of the gases and the water. Results will be presented from water and sediment samples from the Nile, Anaximander and Olimpi areas collected from 1999-2006.
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