Data report: Carbon isotopic composition of dissolved CO2, CO2 gas, and methane, Blake-Bahama Ridge and northeast Bermuda Rise, ODP Leg 172

Carbon isotopic data of interstitial dissolved CO2 (ΣCO2), CO2 gas, and methane show that a variety of microbial diagenetic processes produce the observed isotopic trends. Anaerobic methane oxidation (AMO) is an important process near the sulfate-methane interface (SMI) that strongly influences the isotopic composition of ΣCO2 in the sulfate reduction and upper methanogenic zones, which in turn impacts methane isotopic composition. Dissolved CO2 and methane are maximally depleted in 3C near the SMI, where C values are as light as –31.8‰ and –101‰ PDB for ΣCO2 and methane, respectively. CO2 reduction links the CO2 and methane pools in the methanogenic zone so that the carbon isotopic composition of both pools evolves in concert, generally showing increasing enrichments of C with increasing depth. These isotopic trends mirror those within other methane-rich continental rise sediments worldwide

Microevents produced by gas migration and expulsion at the seabed: A study based on sea bottom recordings from the Sea of Marmara

International audienceDifferent types of 4-component ocean bottom seismometers (OBS) were deployed for variable durations ranging from 1 week to about 4 months in 2007, over soft sediments covering the seafloor of the Tekirdag Basin (western part of the Sea of Marmara, Turkey). Non-seismic microevents were recorded by the geophones, but generally not by the hydrophones, except when the hydrophone is located less than a few tens of centimetres above the seafloor. The microevents are characterized by short durations of less than 0.8 s, by frequencies ranging between 4 and 30 Hz, and by highly variable amplitudes. In addition, no correlation between OBSs was observed, except for two OBSs, located 10 m apart. Interestingly, a swarm of ∼400 very similar microevents (based on principal component analysis) was recorded in less than one day by an OBS located in the close vicinity of an active, gas-prone fault cutting through the upper sedimentary layers. The presence of gas in superficial sediments, together with analogies with laboratory experiments, suggest that gas migration followed by the collapse of fluid-filled cavities or conduits could be the source of the observed microevents. This work shows that OBSs may provide valuable information to improve our understanding of natural degassing processes from the seafloor

A 500,000-year-long sediment archive drilled in eastern Anatolia

Sedimentary archives host a wealth of information that can be used to reconstruct paleoclimate as well as the tectonic and volcanic histories of specific regions. Long and continuous archives from the oceans have been collected in thousands of locations by scientific ocean drilling programs over the past 40 years. In contrast, suitable continental archives are rare because terrestrial environments are generally nondepositional and/or subject to erosion. Lake sediments provide ideal drilling targets to overcome this limitation if suitable lakes at key locations have existed continuously for a long time

Late Quaternary co-seismic sedimentation in the Sea of Marmara's deep basins

25 pages, 15 figures, 1 tableauInternational audienceThe deep, northern, part of the Sea of Marmara (northwestern Turkey) is composed of several aligned, actively subsiding, basins, which are the direct structural and morphological expression of the North Anatolian Fault's northern branch. The last 20 kyr of their sedimentary fill (lacustrine before 12 kyr BP) have been investigated through giant piston coring onboard R/V MARION-DUFRESNE (MARMACORE Cruise, 2001) and chirp subbottom profiler onboard R/V ATALANTE during MARMARASCARPS Cruise (2002). Especially during the lacustrine stage, the infilling of the deep basins (Tekirda?, Central, Kumburgaz, and Çinarcic Basins; up to 1250 m depth) was dominated by turbidites (with coarse mixed siliciclastic and bioclastic basal part), intercalated in “hemipelagic-type” finegrained calcareous and slightly siliceous clays. Often – especially in the thickest ones – the turbidites show strong segregation and a sharp boundary between coarse part and suspendedload part. In the Central Basin, 8 m of a unique sedimentary event include a 5 to 8m-thick “homogenite” well imaged on seismic profiles. The latter is interpreted as related to a major – possibly triggered - tsunami effect, as described in the Eastern Mediterranean by Kastens and Cita (1981). In the marine (Holocene) upper part of the sedimentary fill, repeated to-and-from structures, affecting silt or fine sand, are evidencing seiche-like effects and, thus, earthquake triggering. Detailed correlations between two deep coring sites (1250 and 1200 m) indicate more than 100 % overthickening in the deepest one; this implies specific processes of distribution of terrigenous input by dense hyperpycnal currents (high kinetic energy, seiche effect, complex reflections on steep slopes). The peculiar sedimentary infilling of the Sea of Marmara's Central Basin (and, by extrapolation, of the whole set) is tentatively interpreted as a direct consequence of the strong seismic activity; the imprint of the latter is more obvious prior to the base of the Holocene, as environmental conditions favoured marginal accumulation (especially on the southern shelf) of large amounts of erosion products available for mass wasting

Mediterranean-Black Sea gateway exchange: Scientific drilling workshop on the BlackGate project

The MagellanPlus workshop "BlackGate"addressed fundamental questions concerning the dynamic evolution of the Mediterranean-Black Sea (MBS) gateway and its palaeoenvironmental consequences. This gateway drives the Miocene-Quaternary circulation patterns in the Black Sea and governs its present status as the world's largest example of marine anoxia. The exchange history of the MBS gateway is poorly constrained because continuous Pliocene-Quaternary deposits are not exposed on land adjacent to the Black Sea or northern Aegean. Gateway exchange is controlled by climatic (glacio-eustatic-driven sea-level fluctuations) and tectonic processes in the catchment as well as tectonic propagation of the North Anatolian Fault Zone (NAFZ) in the gateway area itself. Changes in connectivity trigger dramatic palaeoenvironmental and biotic turnovers in both the Black Sea and Mediterranean domains. Drilling a Messinian to Holocene transect across the MBS gateway will recover high-amplitude records of continent-scale hydrological changes during glacial-interglacial cycles and allow us to reconstruct marine and freshwater fluxes, biological turnover events, deep biospheric processes, subsurface gradients in primary sedimentary properties, patterns and processes controlling anoxia, chemical perturbations and carbon cycling, growth and propagation of the NAFZ, the timing of land bridges for Africa and/or Asia-Europe mammal migration, and the presence or absence of water exchange during the Messinian salinity crisis. During thorough discussions at the workshop, three key sites were selected for potential drilling using a mission-specific platform (MSP): one on the Turkish margin of the Black Sea (Arkhangelsky Ridge, 400mb.s.f., metres below the seafloor), one on the southern margin of the Sea of Marmara (North Imrali Basin, 750mb.s.f.), and one in the Aegean (North Aegean Trough, 650mb.s.f.). All sites target Quaternary oxic-anoxic marl-sapropel cycles. Plans include recovery of Pliocene lacustrine sediments and mixed marine-brackish Miocene sediments from the Black Sea and the Aegean. MSP drilling is required because the JOIDES Resolution cannot pass under the Bosporus bridges. The wider goals are in line with the aims and scope of the International Ocean Discovery Program (IODP) "2050 Science Framework: Exploring Earth by Scientific Ocean Drilling"and relate specifically to the strategic objectives "Earth's climate system", "Tipping points in Earth's history", and "Natural hazards impacting society"

Development of Geochemical Exploration Techniques for Massive Sulphide Ore Deposits, Eastern Black Sea Region, Turkey.

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Marmesonet Leg I. Cruise Report. November 4th - November 25th, 2009

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 are systematically related to zones 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.La campagne constitue l’une des missions de démonstration soutenues par ESONET. Elle résulte d’un partenariat entre l’Ifremer, le CNRS, l’INSU, l’Université Technique d’Istanbul, l’Institut des Sciences Marines d’Izmir, le CNR-ISMAR (Bologne) et l’INGV (Rome). La plupart des objectifs du premier leg de la campagne Marmesonet, du 4 au 25 novembre 2009, ont été atteints, grâce à trois facteurs principaux: i) la météo exceptionnellement favorable ; ii) la bienveillance des garde-côtes de la Marine Turque ; iii) le professionnalisme des équipes (équipage et sédentaires