Marmesonet Cruise. R/V Le Suroit. Leg1

The MARMESONET cruise is part of the Marmara Demonstration Mission Program supported by ESONET Network of Excellence (European Seafloor Observatory Network), within the 6th European Framework Programme. Main partners are: Ifremer, CNRS/CEREGE, Istanbul Technical University, TUBITAK, Institute of Marine Science and Technology of Dokuz Eylül Universitesi (Izmir), INGV (Rom) and ISMAR (Bologna). Marmesonet is also the follow-on of the Franco-Turk collaborative programme that resulted in numerous cruises in the Sea of Marmara since 2000. The objectives of the MARMESONET cruise were: 1) to study the relationship between fluids and seismicity along the Sea of Marmara fault system ; 2) to carryout site surveys prior to the implementation of permanent seafloor observatories in the Marmara Sea through ESONET. The cruise is divided in 2 parts: Leg I (from november 4th to november 25th, 2009), mainly dedicated to: i) the high resolution bathymetry at potential sites of interest for future permanent instrumentation using the Autonomous Unmanned Vehicle (AUV)Asterx of Ifremer/Insu ; ii) the systematic mapping of the gas emissions sites on the Marmara seafloor ; iii) the deployment of the Bubble Observatory Module (BOB) in the Çinarçik basin. Leg II (from november 28th november to december 14th, 2009), for 3D, High Resolution Seismic imagery of the fluid conduits below the observatory site planned at the Western High. The present report only concerns Leg I. A total of 19 dives were completed during Leg I: 16 with the multibeam echosounder SIMRAD EM2000 (200 kHz), among which 12 were successful and 4 failed ;3 with the CHIRP sédiment penetrator (1 test dive and 2 operational, both were unfortunately with early stop recording). Main results are: The absence of recent, visible deformation on the segment south of Istanbul. Wether or not this segment is locked or creeping remains an open question. The site south of Istanbul thus requires a massive effort to assess the deformation, particularly through submarine geodesy and piezometry. The plausible presence of a 4 km, right-lateral offset on the Western High, between N30 oriented structures related to cold seeps. Gas emission sites aresystematically related tozones of High reflectivity mapped on the AUV imagery AUV imagery reveals the traces of intensive, human activity, which shows the necessity to ensure the security of the future cables by enforcing a clearance area Last but not least, the exact position of the future observatories is now established, at the Central High and at the Western High sites. Some chirp profiles suggest that the 1912 earthquake probably extended up to the Western High, but not the fault is not visible on all of them. Further work is needed. The SIMRAD EM-302 multibeam echosounder was used to map the water column, providing a complete coverage ofslopes foot and ofthe central shear zone. Results require further analysis to establish the correlation between acoustic anomalies and active faults, as gas emissions appear to be a common feature in the the Sea of Marmara. A noticeable feature is the important gas emission activity along the base of thewestern of slope of the Tekirdag Basin, suggesting that the gas réservoirs from the Thrace Basin are presently leaking out into the Sea of Marmara. In addition, shipboard CHIRP data were collected along with EM-302. 23 cores were taken (13 with gravity corer, 3 with Küllenberg and 7 with interface corers). A total of 24 additional heat flow measurementswere also collected. Finally, 2 OBSs were deployed to complete the coverage of the OBSs dropped with R/V Urania in september 2009. The assistance of the Turkish Coast Guard largely contributed to the success of the operation. We greatly acknowledge the Coast Guard, as well as SHOD, the Department for Hydrography and Oceanography of Turkey, who made the cruise possible in a heavy trafic area. The captain, Jean-René Gléhen, and all crew members of R/V Le Suroit, are also greatly acknowledged.