The Tyrrhenian Sea is characterised by many active features created by fluid escapes from the seafloor, linked to the tectonic evolution of this back-arc basin and the associated Apennine thrust belt. In particular, various CO2 emissions are located in active and quiescent volcanic areas (CampiFlegrei, Ischia, Palinuro Seamount, Pontine, and EolianArchipelagos), only one site with CH4 emissions is reported in the Tyrrhenian Sea at high depths offshore Calabria.
MARENDOGAS project aims to study a recently discovered shallow water site (Scoglio d¿Africa, Tuscan Archipelago) characterized by active CH4 emissions, and to compare it with well-known shallow-water CO2 dominated sites (i.e. Panarea). These sites are similar enough to be compared (shallow-water,climate, easy access for sampling and monitoring, occurrence of Posidonia oceanica meadows) but different enough (CO2 vs CH4, depressed areas versus mounds) to show contrast in geochemistry, mineralogy, sedimentary structures and impact on fauna.
The CO2 emissions have been studied extensively in terms of their impact on chemical and biological systems, and as sites to test monitoring equipment. In particular, the site offshore Panarea Island was studied within the European Community funded CCS project ECO2 (http://www.eco2-project.eu/) and ECCSEL (www.eccsel.org) and was subsequently transformed into an ERIC laboratory. Our long-term goal is to propose the Scoglio d¿Africa site as a natural laboratory, if it will be proved to be appealing enough to deserve it.
In fact, opposite the CO2 sites, knowledge regarding CH4 seeps is very limited, with few sites in shallow water worldwide, thus numerous scientific issues warrant study. These include, but are not restricted to, the origin and the conduits of the leaking CH4 (given that the majority of Tyrrhenian sites leak CO2), the impact of the CH4 on the surrounding ecosystems, and the quantification of the release CH4 (a strong greenhouse gas) directly to the atmosphere.
This proposal presents several innovative aspects, considering the targets of the investigation, the multidisciplinary approach proposed by the consortium and the wide area of application of the expected results.
It is noteworthy that SdA represents a rare up to unique example of shallow-water CH4 emissions in the Tyrrhenian Sea, where the majority of emissions are CO2 dominated. Not all geological processes and mechanisms generating these emissions have been studied in this context, and so the study area is unique in the Italian geological setting. In fact, most of the CH4 emission sites in Italy are located in the Adriatic domain, corresponding to the active front of the migrating Appennine chain, whereas the back arc domain, corresponding to the Tyrrhenian Sea, is the site of volcanic activity and CO2 emissions.
The fact that the summits and SdA CH4 leakages are in anomalously shallow waters (7-20m) is a clear advantage from a logistic point of view, both for survey operations from the sea surface, and for scuba-diving observations and sampling. Beside these fact, the impact of CH4 emissions in shallow water may differs from what is known in literature for authigenic minerals, biota living in photic zone and namely on the P. oceanica meadows.
The comparison between the CH4 SdA and the CO2 Panarea site (and in minor extent with the CO2 Zannone site) will also produce innovative results. All these sites lies in shallow water, with same climate and oceanographic regimes.
Also the real and deep multidisciplinarity of the research can be considered innovative: the consortium, almost completely composed by Sapienza University researchers (Department of Earth Sciences) or CNR researchers working in the same Department, has a wide experience in marine geology studies, and it is able to investigate the area under many scientific aspects. These will include the sea bottom morphology and its evolution, geochemical characterization, sedimentary facies distribution around the main positives structures, biological aspects (benthic foraminifers and ostracods in the sediments, the P. oceanica distribution and morphological characteristics in the area), as well as the definition of its physical-structural characters, such as active tectonics and the potential occurrence of over pressurized deep zones. Such interdisciplinary will be useful to describe and fully reconstruct the geological processes and may lead to identification of specific interaction and correlation among different aspects, such as the role of authigenic minerals in controlling the leakage system evolution, the presence of subsurface fluids in controlling biota, and the correlation between morphologies and sedimentary facies (to be compared with fossil examples).
The detailed characterization of SdA can support the discovery and interpretation of potentially similar sites everywhere and specifically in Italy, for instance among positive features of unknown origin that were mapped in the MaGIC project.
MARENDOGAS results will be a contribution in the recognition and interpretation of analogues fossil structures. It is noteworthy that fossil mud volcanoes are recognized in many places and ages, and their occurrence is usually associate with physical processes (paleo-seismicity, sediment liquefaction, over-pressures) that are characteristics of compressional domains like accretionary prisms[12,13].
The occurrence and characterization of mud volcanoes in back arc basin, may support a better reconstruction of the fossil and ancient geological paleo-domains. This latter aspect is very innovative because these studies will contribute to fill a lack of information both on present-day as well as on the ancient extensional settings.
In general fluid escape features and subsequent sediment mobilization can also have relevant impact on the marine environment, and paroxistic expulsion of fluids may jeopardize the safety of human activities and infrastructures. In the case of this proposal, the SdA site surely represents an area of altered submarine biological/geochemical equilibrium as well as marine geohazard areas.
Both CO2 and CH4 are greenhouse gas and due to the particularly shallow water of both SdA and Panarea sites, they can reach the atmosphere possibly by passing the whole water column, instead of dissolving into the water as happened for deeper vents. This study will evaluate the interaction between shallow gas released at the seafloor and the water column, and will contribute to the evaluation of the mode and amount of greenhouse gas released in the atmosphere.
Finally, the SdA site could be considered strategic for the future installation of a multidisciplinary permanent seafloor observatory to study such dynamic environment and the effects of CH4 enriched fluids, to be proposed to became part of European Infrastructure.