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Recent field observations have identified the widespread occurrence of fluid seepage through the eastern Mediterranean Sea floor in association with mud volcanism or along deep faults. Gas hydrates and methane seeps are frequently found in cold seep areas and were anticipated targets of the MEDINAUT/MEDINETH initiatives. The study presented herein has utilized a multi-disciplinary approach incorporating observations and sampling of visually selected sites by the manned submersible Nautile and by ship-based sediment coring and geophysical surveys. The study focuses on the biogeochemical and ecological processes and conditions related to methane seepage, especially the anaerobic oxidation of methane (AOM), associated with ascending fluids on Kazan mud volcano in the eastern Mediterranean. Sampling of adjacent box cores for studies on the microbiology, biomarkers, pore water and solid phase geochemistry allowed us to integrate different biogeochemical data within a spatially highly heterogeneous system. Geophysical results clearly indicate the spatial heterogeneity of mud volcano environments. Results from pore water geochemistry and modeling efforts indicate that the rate of AOM is similar to 6 mol m(-2) year(-1), which is lower than at active seep sites associated with conditions of focused flow, but greater than diffusion-dominated sites. Furthermore, under the non-focused flow conditions at Kazan mud volcano advective flow velocities are of the order of a few centimeters per year and gas hydrate formation is predicted to occur at a sediment depth of about 2 m and below. The methane flux through these sediments supports a large and diverse community of micro- and macrobiota, as demonstrated by carbon isotopic measurements on bulk organic matter, authigenic carbonates, specific biomarker compounds, and macrofaunal tissues. Because the AOM community appears to be able to completely oxidize methane at the rate it is seeping through the sediments, ultimate sinks for methane in this environment are authigenic carbonates and biomass. Significant differences in organic geochemical data between this site and those of other cold seep environments, even within the eastern Mediterranean mud volcanoes, indicate that the microbiological communities carrying out AOM varies depending on specific conditions such as methane flux and salinity. (C) 2004 Elsevier B.V. All rights reserved.

Two mud volcano fields were explored during the French–Dutch MEDINAUT cruise (1998) with the submersible NAUTILE, one south of Crete along the Mediteranean Ridge at about 2000 m depth (Olimpi mud field) and the other south of Turkey between 1700 and 2000 m depth (Anaximander mud field) where high methane concentrations were measured. Chemosynthetic communities were observed and sampled on six mud volcanoes and along a fault scarp. The communities were dominated by bivalves of particularly small size, belonging to families commonly found at seeps (Mytilidae, Vesicomyidae, Thyasiridae) and to Lucinidae mostly encountered in littoral sulfide-rich sediments and at the shallowest seeps. Siboglinid polychaetes including a large vestimentiferan Lamellibrachia sp. were also associated. At least four bivalve species and one siboglinid are associated with symbiotic chemoautotrophic bacteria, as evidenced by Transmission Electronic Microscopy and isotopic ratio measurements. Among the bivalves, a mytilid harbors both methanotrophic and sulfide-oxidizing bacteria. Video spatial analysis of the community distribution on three volcanoes shows that dense bivalve shell accumulations (mainly lucinids) spread over large areas, from 10% to 38% of the explored areas (2500–15000 m 2 ) on the different volcanoes. Lamellibrachia sp. had different spatial distribution and variable density in the two mud volcano fields, apparently related with higher methane fluxes in the Anaximander volcanoes and maybe with the instability due to brines in the Olimpi area. The abundance and richness of the observed chemosynthetic fauna and the size of some of the species contrast with the poverty of the deep eastern Mediterranean.

The Florence Rise is a submarine feature extending from the island of Cyprus in the southeast to the Anaximander Mountains which form the northwestern end of the Cyprus Arc south of western Turkey, The eastern Florence Rise includes a topographic high near Cyprus while its central domain displays relatively low relief. Most of the major elements of relief appear to be bounded by faults, in the light of new geophysical data. An underlying 'core' ridge, likely made of pre-Pliocene nappes emplaced from the north, separates relatively undeformed sediments to the northeast from actively shearing sediments and seismic basement, to the southwest, A dextral arc-parallel wrench zone, at least 15 km wide, has created a lineated seafloor texture and accompanying flower structures within the central Florence Rise. Apparent Riedel type conjugate shears within this system cut across the Florence Rise and mark changes in the relief along the are, Several mud volcanoes are observed within the wrench zone and along associated faults. indicating that overpressuring at depth is relieved by these faults. There is no evidence for any typical subduction along this arcuate trend, which is considered to act as the present boundary between the African and Anatolian-Aegean plates. In contrast, both the nature of faulting and the morphology of the Florence Rise seem to indicate some degree of transpressional coupling between the two plates, even though they appear disconnected by a tectonic boundary in the form of a major shear zone. (C) 2002 Elsevier Science B.V. All rights reserved.