Deep Sea Management of abiotic resources in the Eastern Mediterranean

Dr. C. Perissoratis
Institute of Geology and Mineral Exploration
Athens
Greece.

In recent decades the efforts of the international scientific community has focused on the sustainability of natural resources on land and in the sea. This effort has provoked the interest and the awareness both of the general public and, in turn, of decision makers. This shift of the interest of the two most influential groups of society has resulted in a “feed back” reaction toward the scientific community to come forward with specific, clear and concrete proposals for solutions and actions, which must be presented without using scientific jargon and which go beyond intra scientific disagreements. A characteristic example of one such successful response of the scientific community in Greece is exemplified in the case of the conservation of the national monuments while the contrary holds true for earthquake forecasting methods and a public warning system.

Needless to say, the marine realm has been for some years of prime interest for sustainable management for two reasons. First because new and previously unknown resources have been discovered, a typical example being the occurrence of gas hydrates, and second, the fact that the marine abiotic resources remain in a state of manageable sustainability, whereas many terrestrial resources are irreversibly overexploited and depleted. Typical examples can be seen in the near shore freshwater resources of the islands, the erosion of the coastal areas and the ruining of the natural environment of the nearshore zone by construction projects.

In this context, this conference provides an opportunity and a challenge for a constructive input to the sustainable management focusing on our marine area, the Eastern Mediterranean and the Black Sea.

This presentation concerns the management of the abiotic resources. There are other presentations on the same topic dealing with the living resources, the ecosystems, the fisheries, and the deep sea resources. In general, therefore, it can be suggested that abiotic resources are those that have been and are formed mainly by geological processes, and their management must indicate means of their “handling” from research to exploitation, eventual or possible. This is important for resources for which the research is on-going, such as for gas hydrates and hydrothermal fluids.

Gas hydrates (G.H.) are ice-like compounds belonging to the clathrates and consist of ice cells formed by six to eight H2O crystals within which there is a gas molecule, mainly methane. They occur in vast quantities in the sea and also on the land, in permafrost regions. It has been estimated that the amount of methane contained in the world gas hydrate resources can be up to 3.1019 cubic meters, that is double the conventional gas in the recovered and non-recovered fossil fuels. In the marine realm, G.H occur in many deeper water areas because, as is indicated in the relevant stability curve, with increasing depth conditions there is a coincidence of rising pressure and diminishing temperature, that allows the stability of gas hydrates below a critical water depth (that is dependent on seabed temperature). The presence of gas hydrate also depends on a suitable supply of gas from the decay of fossil biogenic material. In shallower water depths, such gas is generally oxidized by biogenic activity at the seabed and thus is lost as a resource. The significance of gas hydrate is three fold due to the enormous methane quantities which they contain. First as a potential energy source, second as a probable cause of extensive submarine slumping in case of their dissociation, and third as a source of a greenhouse gas (methane) that can enhance the anticipated climate change.

In the Eastern Mediterranean, the presence of gas hydrates has been reported and sampled in submarine mud volcanoes in the Anaximander mountains south of Antalya Gulf and east of the Rhodes basin. There research was carried out in the previous decade at depths ranging from 1800 to 2200 m. We do not know the thickness of the gas hydrate bearing sedimentary formations, nor if the presence of GH nodules is the result of an ephemeral sea bottom processes or a surface manifestation of a thicker GH bearing sedimentary layer. The area where the GH occur is composed of a series of submarine mountains that have a crest depth from 670m. to 1120m. and consist of three separate submarine mountains, Anaximander, Anaxagoras and Anaximenes. In this area there is a widespread presence of gas within the sediments, that disrupts the sub bottom seismic profiling records making it difficult to estimate the amount of GH present. A recently-funded EU research project, Anaximander, has just been launched and will be carried out over the next three years in the area. Its target is to proceed beyond the given knowledge by using appropriate and innovative coring and other sampling instruments to obtain and study undisturbed “pristine” cores of the sediments and the GH present there. This we hope will lead us to the evaluation of the GH as a future energy source.

Although the area of the Anaximander mountains is the only area in the Eastern Mediterranean where GH have actually been sampled, there are indications that GH are also present on the Mediterranean Ridge in the south of Greece. In gravity cores retrieved from Milano and Napoli domes, violent fluid venting with low heat flow has been reported in water depth of about 2000m. This, combined with the abnormally high content of low salinity water led the scientists to postulate the presence of CH occurrence in deeper layers, which when dissociated provide fresh water and free gas, a reaction that results in a drop in temperature. Also evidence from ODP Leg 160 in the same area indicated the presence of GH in deeper horizons. As for the Black Sea area, unpublished reports indicate that in the western part of the sea, off Varna, Bulgaria, GH are present even in sea depths as shallow as 800 to 1000m. All these indicate that we must seriously investigate the nature and volume of the GH present in the eastern Mediterranean and the Black sea and strengthen the cooperation between neighboring countries.

Within the issue of the abiotic resources and their management we have to include the fluid flow within the seabed sediments that is particularly active in the Eastern Mediterranean, especially in the southern Aegean Volcanic Arc proper. This fluid flow is of two types. In the Mediterranean Ridge, it is the result of the compressive tectonics of the ridge dewatering by compaction of the piled up sediment. This results in mud volcanoes and the small anoxic basins in the Mediterranean Ridge. In the Volcanic Arc and particularly off the islands of Milos, Santorini and Kos hydrothermal circulation occurs, driven by the heat related to volcanism. The hydrothermal fluids in the arc directly affect the biocommunities present by the emanating sulfuric ions and the high quantities of the produced CO2 and CH4. Interesting also is the presence of the bacterial communities within the sea bottom sediments in the hydrothermal areas in the Volcanic Arc and their absence in the deeper anoxic basins in the Mediterranean Ridge.

The study of hydrothermal activity is necessary for the evaluation of their impact on the biocommunities and of course for the understanding of the formation of marine mineral deposits in a convergent plate environment like that of the Southern Aegean Volcanic Arc. Also of particular environmental interest is the evaluation of the high concentrations of the elements Fe, Ni, Co, Cu and Zn in the same area.

Within the subject of abiotic resources can also be included the management of pipelines, electrical cables and telecommunication cables that have been installed in the eastern Mediterranean and the Black Sea. It is known that it is planned to position a pipeline to transport natural gas across the Black Sea, from the Sea of Azov of Ukraine Georgia to Samsun northern Turkey, while a number of national and international telecommunication and electric power cables connect various sites. The surrounding sediments in these sea areas can be prone to slumping, triggered either by the frequent earthquake activity, by overloading or by excess pore pressure, causing damage to such installations. On the other hand the adverse impacts of the pipe line hazards in a land locked area like the Black Sea are magnified in comparison to those encountered in an more open marine system. Such impacts can include of course pollution of the marine biocommunities and of the surrounding coastal area. In areas of adverse seabed conditions, management of these transportation routes is necessary to ensure the effective use of the seabed by all possible users.

In most of the activities of seabed management of abiotic resources, the most difficult problems occur in waters deeper than a few hundred meters. There will be a requirement for a new generation of scientific and technological methodology in the eastern Mediterranean and Black Seas. This will include regional swath bathymetric mapping, improved near-bottom seismic-reflection techniques, and innovative sampling techniques for gas hydrates. Deployment of such expensive tools will require cooperation between all countries of the region.