P. Favali

Structural pattern and CO2–CH4 degassing of Ustica Island, Southern Tyrrhenian basin

Abstract Brittle tectonics and ground degassing, including fracture-field, soil–gas and exhalation flux analyses of CO 2 and CH 4 , were studied at Ustica Island, a Pleistocene volcanic complex in the Southern Tyrrhenian Sea. The mesoscopic fracture pattern perfectly fits an E–W-trending left-lateral strike–slip master fault, in agreement with the main morpho-structural submarine alignment including Ustica Island and Anchise Seamount. Along the SW–NE high-angle normal Arso Fault, geological evidence of reactivation with different kinematics (left- to right-lateral displacements) was recognised. Major CO 2 and CH 4 degassing (with fluxes up to 93,750 and 20 t km −2 a −1 , respectively, and soil–gas concentrations of 11.3% and 5.7 ppm) occur over the Arso Fault. Although this fault is mapped just in the SW sector of the island, soil–gas CO 2 anomalies point out its clear continuation up to the NE margin of the island. These data, together with those of previous geophysical and geochemical results from off-shore Ustica, suggest that the Arso Fault is the local evidence of a more important active, gas-bearing structure. This tectonic feature is interpreted as a reactivation of a preexistent SW–NE trend, inherited as a second-order structure of the E–W deep shear zone. The reactivation is related to the interplay among different structures of the Southern Tyrrhenian basin.

Warming, salting and origin of the Tyrrhenian Deep Water

[1]xa0Data collected from 1996 to 2001 down to 3,500 m in the Tyrrhenian sub-basin with ship-handled and moored instruments show 5-year T and S trends (0.016 °C/yr, 0.008/yr) that are the largest ever evidenced in Mediterranean deep waters. This is not consistent with the usual hypothesis that Tyrrhenian Deep Water (TDW) is a mixture of eastern water flowing from the Sicily Channel and western water flowing from the Sardinia Channel partly since both are reported to encounter lower trends. We argue that TDW might result from a dense water formation process occurring within the Tyrrhenian itself, in a region never reported up to now, east of the Bonifacio Strait. Whatever the validity of our hypothesis, climatic changes are occurring in the whole sea and are efficiently specified with long time series.

GEOSTAR: a GEophysical and Oceanographic STation for Abyssal Research

Publisher Summary This chapter describes the different aspects of GEophysical and Oceanographic STation for Abyssal Research (GEOSTAR), which is aimed at the realization of an observatory able to perform a long-term scientific mission in deep waters down to 4000 meters. GEOSTAR represents the first European reply to the challenges launched by the international scientific and technological community addressed to the realization of a worldwide network of benthic multidisciplinary permanent observatories. The Long-term Ocean Monitoring Station (LOMOS) concept for deployment and recovery, defined in a MAST 2 project, DESIBEL, and the feasibility study for Abyssal BEnthic Laboratory (ABEL), promoted by E.U., formed the basis of the design of GEOSTAR. The general architecture of GEOSTAR demonstrated its validity during the Adriatic Sea mission and consequently no substantial modification to the concept is foreseen. Improvements on some parts of the two main systems—the bottom station (BS) and mobile docker (MD)— are, however, projected in a view of the deep sea mission requirements.

The geological links of the ancient Delphic Oracle (Greece): A reappraisal of natural gas occurrence and origin

Recent studies have speculated that the prophetic powers of Pythia, the woman of the Delphic Oracle, at the Temple of Apollo in Greece, were induced by hydrocarbon vapors, specifically ethylene, rising from bedrock fissures at the intersection of the E-W Delphi fault with the NNW-SSE Kerna fault, and producing neurotoxic effects, including trance and delirium. New surveys including gas flux from soil, gas in groundwater, and isotopic analyses of spring scales, provide the experimental confirmation of the gas release in the Delphi area. Presently, methane, ethane, and carbon dioxide are being released from a thermogenic (catagenetic) hydrocarbon-prone environment. This environment is not prone to biogenic production of ethylene in amounts inducing neurotoxic effects (hundreds or thousands of ppmv). A WNW-ESE–trending subsidiary fault within the Delphi fault zone, extending for ∼2 km, passes under the Temple of Apollo and shrine of Athena. The Temple of Apollo, located above this fault, may have been the site of enhanced degassing in the past. If gas-linked neurotoxic effects upon Pythia need to be invoked, they should be sought in the possibility of oxygen depletion due to CO2-CH4 exhalation in the indoor temple. Alternatively, a plausible geological explanation behind the natural presence of sweet scents could be the occurrence of aromatic hydrocarbons, such as benzene, dissolved in the groundwater spring.

NEMO-SN1 Abyssal Cabled Observatory in the Western Ionian Sea

The NEutrino Mediterranean Observatory-Submarine Network 1 (NEMO-SN1) seafloor observatory is located in the central Mediterranean Sea, Western Ionian Sea, off Eastern Sicily (Southern Italy) at 2100-m water depth, 25 km from the harbor of the city of Catania. It is a prototype of a cabled deep-sea multiparameter observatory and the first one operating with real-time data transmission in Europe since 2005. NEMO-SN1 is also the first-established node of the European Multidisciplinary Seafloor Observatory (EMSO), one of the incoming European large-scale research infrastructures included in the Roadmap of the European Strategy Forum on Research Infrastructures (ESFRI) since 2006. EMSO will specifically address long-term monitoring of environmental processes related to marine ecosystems, climate change, and geohazards. NEMO-SN1 has been deployed and developed over the last decade thanks to Italian funding and to the European Commission (EC) project European Seas Observatory NETwork-Network of Excellence (ESONET-NoE, 2007-2011) that funded the Listening to the Deep Ocean-Demonstration Mission (LIDO-DM) and a technological interoperability test (http://www.esonet-emso.org). NEMO-SN1 is performing geophysical and environmental long-term monitoring by acquiring seismological, geomagnetic, gravimetric, accelerometric, physico-oceanographic, hydroacoustic, and bioacoustic measurements. Scientific objectives include studying seismic signals, tsunami generation and warnings, its hydroacoustic precursors, and ambient noise characterization in terms of marine mammal sounds, environmental and anthropogenic sources. NEMO-SN1 is also an important test site for the construction of the Kilometre-Cube Underwater Neutrino Telescope (KM3NeT), another large-scale research infrastructure included in the ESFRI Roadmap based on a large volume neutrino telescope. The description of the observatory and its most recent implementations is presented. On June 9, 2012, NEMO-SN1 was successfully deployed and is working in real time.

Gas seepage and seismogenic structures along the North Anatolian Fault in the eastern Sea of Marmara

[1]xa0We carried out a combined geophysical and gas-geochemical survey on an active fault strand along the North Anatolian Fault (NAF) system in the Gulf of Izmit (eastern Sea of Marmara), providing for the first time in this area data on the distribution of methane (CH4) and other gases dissolved in the bottom seawater, as well as the CH4isotopic composition. Based on high-resolution morphobathymetric data and chirp-sonar seismic reflection profiles we selected three areas with different tectonic features associated to the NAF system, where we performed visual and instrumental seafloor inspections, including in situ measurements of dissolved CH4, and sampling of the bottom water. Starting from background values of 2–10 nM, methane concentration in the bottom seawater increases abruptly up to 20 nM over the main NAF trace. CH4 concentration peaks up to ∼120 nM were detected above mounds related probably to gas and fluids expulsion. Methane is microbial (δ13CCH4: −67.3 and −76‰ versus VPDB), and was found mainly associated with pre-Holocene deposits topped by a 10–20xa0m thick draping of marine mud. The correlation between tectonic structures and gas-seepages at the seafloor suggests that the NAF in the Gulf of Izmit could represent a key site for long-term combined monitoring of fluid exhalations and seismicity to assess their potential as earthquake precursors.

Single-frame multiparameter platforms for seafloor geophysical and environmental observations: projects and missions from GEOSTAR to ORION

The paper presents an overview of recent seafloor long-term single-frame multiparameter platform developed in the framework of the European Commission and Italian projects starting from the GEOSTAR prototype. The main features of the different systems are described as well as the sea missions that led to their validation. The ORION seafloor observatory network recently developed, based on the GEOSTAR-type platforms and engaged in a deep-sea mission at 3300 m w.d. in the Mediterranean Sea, is also described

Continuous monitoring of noise levels in the Gulf of Catania (Ionian Sea). Study of correlation with ship traffic

Acoustic noise levels were measured in the Gulf of Catania (Ionian Sea) from July 2012 to May 2013 by a low frequency (<1000Hz) hydrophone, installed on board the NEMO-SN1 multidisciplinary observatory. NEMO-SN1 is a cabled node of EMSO-ERIC, which was deployed at a water depth of 2100m, 25km off Catania. The study area is characterized by the proximity of mid-size harbors and shipping lanes. Measured noise levels were correlated with the passage of ships tracked with a dedicated AIS antenna. Noise power was measured in the frequency range between 10Hz and 1000Hz. Experimental data were compared with the results of a fast numerical model based on AIS data to evaluate the contribution of shipping noise in six consecutive 1/3 octave frequency bands, including the 1/3 octave frequency bands centered at 63Hz and 125Hz, indicated by the Marine Strategy Framework Directive (2008/56/EC).

Deep submarine gas vents in the aeolian offshore

Abstract Consistent results, concerning the detection of deep submarine hydrothermal vents, were obtained during two cruises (1991 and 1996) offshore from the Aeolian Islands, by CTD profiling from sea surface down to seafloor, and water-sampling casts. In 1991 an echo sounder showed a wide plume at a depth of about 800 m, within which water samples displayed anomalies in He and NH a content, suggesting also the presence of a water-vapour phase. The latter, in 1996, was remarkably observed as a horizontally diffusing plume at about 350 m. Near-plume casts were characterised by high CO2 and CH4 and low O2 concentrations in seawater, disturbed light transmission profiles, and false bottom outputs appearing at ∼300–350 m down to the seafloor from the rosette-mounted altimeter. No significant temperature/salinity anomalies were noted during either events. These preliminary results show the presence of deep hydrothermal activity, over an area where, one century ago, the occurrence of submarine eruptions was detected.

Gas and seismicity within the Istanbul seismic gap

Understanding micro-seismicity is a critical question for earthquake hazard assessment. Since the devastating earthquakes of Izmit and Duzce in 1999, the seismicity along the submerged section of North Anatolian Fault within the Sea of Marmara (comprising the “Istanbul seismic gap”) has been extensively studied in order to infer its mechanical behaviour (creeping vs locked). So far, the seismicity has been interpreted only in terms of being tectonic-driven, although the Main Marmara Fault (MMF) is known to strike across multiple hydrocarbon gas sources. Here, we show that a large number of the aftershocks that followed the M 5.1 earthquake of July, 25th 2011 in the western Sea of Marmara, occurred within a zone of gas overpressuring in the 1.5–5u2009km depth range, from where pressurized gas is expected to migrate along the MMF, up to the surface sediment layers. Hence, gas-related processes should also be considered for a complete interpretation of the micro-seismicity (~Mu2009<u20093) within the Istanbul offshore domain.