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Continuous monitoring has been carried out at a fluvial flood-plain site near Rome for over a year. There is a mix of biogenic CO2 and deep geogenic CO2 at the site at relatively low concentrations and fluxes compared with other natural CO2 seepage sites studied previously. Factors such as temperature and soil moisture clearly affect the CO2 concentration and flux and seasonal and diurnal influences are apparent. Statistical approaches are being used to try to define these relationships and separate out the two gas components, which would be necessary in any quantification of leakage from CO2 storage.

Discoveries from multibeam bathymetry and geochemical surveys performed off Zannone Island (western Pontine Archipelago, Tyrrhenian Sea) provide evidence of an undocumented hydrothermal field characterized by ongoing fluid emissions and morphologically complex giant depressions located in shallow water (250 m) that host pockmarks, mounds, small cones, and active fluid vents, which are interpreted as complex fluid-escape features developed both through vigorous-explosive events and steady seepage. Their spatial distribution suggests that the NE-SW trending faults bounding the Ponza-Zannone structural high and the shallow fractured basement are favorable conditions for the upward migration of hydrothermal fluids. Moreover, we performed a detailed geochemical study to investigate the source of the hydrothermal fluids. The geochemical signature of the collected fluids provides information of active CO2-dominated degassing with a significant contribution of mantle volatiles, with measured 3He/4He values>3.0 Ra that are similar to those recorded at Stromboli and Panarea volcanoes. The hydrothermal system produces volatiles that may originate from residual magma batches, similar to the Pleistocene trachytes cropping out in the SE sector of Ponza Island that were probably intruded in the shallow crustal levels and never erupted. The discovery of the Zannone hydrothermal field updates the record of active hydrothermal areas of the Mediterranean Sea. Moreover, the recognition of several giant hydrothermal depressions characterized by a complex morphology is peculiar for the Mediterranean Sea.

Monitoring the surface composition of CO2 derived from subsurface reservoirs is an important part of the carbon capture and storage (CCS) chain. Most approaches use geochemical or geophysical instrumental approaches but these have the drawback that no long-term time series are available, which depend on a predefined monitoring location. We test a flexible approach using natural archives based on the measurement of radiogenic 14C concentrations in tree rings to detect geogenic CO2 fluxes derived from natural springs in the Latera Caldera, central Italy. The approach can be used as a preliminary check to evaluate natural CO2 leaks from sites designated for CO2 storage, as well as evaluating the extent of leakage in an unforeseen area. An extensive database of soil gas composition and fluxes is available for that site, permitting direct comparison of the tree ring isotopic composition and point sources of CO2 from the subsurface against the mean atmospheric standard. We sampled oak trees (Quercus cerris and Quercus pubescens) directly at the CO2 source (ON), and at short (50m, NEAR), intermediate (500m, FAR) and long distances (~3000m, CONTROL) from CO2, sources, and measured the radioactive 14C concentration in tree rings at ~10 year intervals from 2012 back to 1976. To accurately date the tree rings we constructed a tree-ring chronology using standard dendrochronological methods. We tested whether variation in 14C concentration in tree rings and ring-width are related to distance of trees from CO2 source, as well as climate factors, i.e. precipitation and temperature. Results show that local point sources of CO2 at the location where the tree grows are effectively recorded by the 14C concentration in the cellulose of this tree. The fossil CO2 signal is sharply delineated since already at short distance from the source (~50m, NEAR) the 14C incorporation is at the detection limit of the tested approach. Tree-ring width of the oaks at Caldera Latera is mainly limited by the amount of precipitation during the growing season, from March to October, while distance to the CO2 point source has no detectable effect on radial growth, likely due to the continuous presence of the enhanced CO2 flux to which the trees adapt their physiology from germination. While the approach is promising and permits data collection at any forested site, a more detailed sampling transect between 0 and 50m from a point source of CO2 is needed to determine the exact detection limit of the signal in the 14C concentration of the tree ring cellulose. © 2013 Elsevier Ltd.

The relation between acoustic seafloor backscatter and seep distribution is examined by integrating multibeam backscatter data and seep locations detected by single-beam echosounder. This study is further supported by side scan sonar recordings, high-resolution 5 kHz seismic data, pore-water analysis, grain-size analysis and visual seafloor observations. The datasets were acquired during the 2003 and 2004 expeditions of the EC-funded CRIMEA project in the Dnepr paleo-delta area, northwestern Black Sea. More than 600 active methane seeps were hydro-acoustically detected within a small (3.96 km by 3.72 km) area on the continental shelf of the Dnepr paleo-delta in water depths ranging from -72 m to -156 m. Multibeam and side scan sonar recordings show backscatter patterns that are clearly associated with seepage or with a present dune area. Seeps generally occur within medium- to high backscatter areas which often coincide with pockmarks. High-resolution seismic data reveal the presence of an undulating gas front, i.e. the top of the free gas in the subsurface, which domes up towards and intersects the seafloor at locations where gas seeps and medium- to high-backscatter values are detected. Pore-water analysis of 4 multi-cores, taken at different backscatter intensity sites, shows a clear correlation between backscatter intensity and dissolved methane fluxes. All analyzed chemical species indicate increasing anaerobic oxidation of methane (AOM) from medium- to high-backscatter locations. This is confirmed by visual seafloor observations, showing bacterial mats and authigenic carbonates formed by AOM. Grain-size analysis of the 4 multi-cores only reveals negligible variations between the different backscatter sites. Integration of all datasets leads to the conclusion that the observed backscatter patterns are the result of ongoing methane seepage and the precipitation of methane-derived authigenic carbonates (MDACs) caused by AOM. The carbonate formation also appears to lead to a gradual (self-)sealing of the seeps by cementing fluid pathways/horizons followed by a relocation of the bubble-releasing locations.