Agostino Semprebello

Methane (CH4) is recognised as one of the most powerful greenhouse gases but yet it represents a relevant energy resource. Therefore it is important to decipher the various sources that can provide inputs to the atmosphere (Saunois et al. 2016). To determine the actual need for future emission reductions, a precise quantification of the global CH4 budget is required, however, according to the most recent modelling, significant uncertainties still affect these calculations (Saunois et al., 2020). The most important source of uncertainty is attributable to natural emissions. While the open ocean CH4 emissions are relatively well constrained, the global marine flux appears to be mainly influenced by shallow near-shore environments (0-50 m b.s.l.), where CH4 released from the seafloor could escape to the atmosphere before oxidation (Weber et al., 2019). The factors that govern the magnitude of methane transfer through the water column to the atmosphere remain poorly understood and are highly site dependent, with water depth playing a critical role. Nevertheless, quantifying methane emissions from shallow coastal environments remains a challenge due to the complex thermo-fluid dynamics of bubble-mediated transport.The present study, within the framework of the NRPP-PRIN project MEFISTO, focuses on advancing passive hydroacoustic techniques to improve gas flux detection and estimation at two distinct Mediterranean sites: the Panarea hydrothermal field ('hot seeps') and a seepage zone off the Marano and Grado lagoon, North Adriatic Sea ('cold seeps'), which exhibit contrasting degassing regimes. A central objective of the research is to enhance the Signal-to-Noise Ratio (SNR) in recorded acoustic data, which is often compromised by ambient coastal noise. We employ innovative acoustic inversion models based on the spectral analysis of bubble formation and detachment (pinch-off) events using a single hydrophone. By characterizing the unique acoustic signatures of individual bubbles and gas jets, and applying spectral denoising and an adaptive thresholding approach to detect non-overlapping individual bubbles, we aim to minimize the masking effects of the soundscape, allowing for a more precise reconstruction of the Bubble Size Distribution (BSD). These hydroacoustic flux estimates are integrated with and validated by water column geochemical investigations. This multidisciplinary approach allows us to track the fate of CH4 from the sediment-water interface to the surface, evaluating how different degassing regimes (hydrothermal vs. biogenic) and physical forcings influence the efficiency of gas transfer to the atmosphere. The acquired data revealed that different degassing styles are strongly influenced by natural forces driving the temporal evolution of degassing activity, particularly in gentle or low flux emissions. Preliminary results from four seasonal campaigns demonstrate that the synergy between acoustic monitoring and geochemical tracing significantly reduces uncertainties and provides new insights into gas migration mechanisms through the use of non-invasive techniques, the temporal variability of emissions, and the fate of dissolved methane, ultimately contributing to a more refined marine methane budget for coastal systems.

From 18 January to 23 October 2021, 58 paroxysmal events occurred at Mt. Etna volcano by the South East Crater (SEC). Three events, that occurred on 4, 12 March and 24 June, were selected to be studied through a plume dispersion modelling approach. All the selected paroxysms generated ash-SO2 rich plumes ranging from 6 to 8.5 km above the main vent.In this work, we explored the spatial dispersion of the volcanic SO2 plume in each paroxysmal event by using the Weather Research and Forecasting Chemistry (WRF-Chem) model coupled with the time-variable ground-based SO2 flux emission data recorded by FLAME (FLux Automatic MEausurement) scanning spectrometers network managed by INGV-OE (Osservatorio Etneo). In this context, WRF-Chem was specially configured to run with variable Eruption Source Parameters (ESPs), reading at each integration time-step experimentally measured SO2 flux values.The SO2 maps resulting from the WRF-Chem simulations were compared with the dispersion pattern detected by TROPOMI sensor onboard Sentinel-5p satellite, in order to validate the capability of the model in reproducing the volcanic plume dispersion. The comparison for each simulation highlights a very good agreement between simulated data and those observed by the satellite.The ash transport was also modelled in each simulation, considering an ash Mass Eruption Rate (MER) which was inverted from the plume height. The spatial evolution of the ash patterns was compared with data retrieved from the MGS-SEVIRI satellite. The comparison shows a good agreement between simulated and observed maps. Particularly for the 12 March event, the ash comparison clearly shows that the WRF-Chem model was able to well reproduce the eastward path of the ash cloud, even at long distances, as the simulated plume reached Greece about 10 hours after the paroxysm, in agreement with satellite observations.In conclusion, the obtained results testify that the WRF-Chem model can efficiently reproduce the dispersion of both SO2 and ash plume emitted from Mt. Etna volcano over the Mediterranean basin, representing a powerful tool for assessing air quality, flying security and other hazard factors due to volcanic plume transport and deposition from local to Mediterranean scale. In addition, the performed simulations highlighted that the ground-based data measured by the FLAME network play a key role in improving the accuracy in simulating the SO2 dispersion pattern as it allows us to take into account the fluctuating and not stationary nature of volcanic plume emissions.

The underwater volcanic activity associated with deep-seated mantle processes represents a primary driver of the chemical and biogeochemical evolution of the global oceans. Hydrothermal activity is often a manifestation of submarine volcanism, where fluxes of heat and magmatic volatiles confer both potential hazard and opportunities of resource exploitation. Despite this, research on shallow submarine arc volcanoes is still in an early stage and only a few continuous seafloor observing infrastructures have been developed until now. The Kolumbo underwater volcano, located in the Aegean Sea, hosts one of the most active and dynamic hydrothermal vent fields, marking it - along with the proximity to the world-known Santorini island - a severe geohazard for a combination of reasons. Within the framework of the SANTORY (SANTORini’s seafloor volcanic observatorY) project, funded by the Hellenic Foundation for Research and Innovation and with the financial support of the Municipality of Thira, between 2022 and 2023, three oceanographic cruises were performed on submarine Kolumbo volcano. The oceanographic surveys were mainly aimed at the deployment of integrated operating sensors of state-of-the-art technology, for in situ monitoring. A new-generation stand-alone multiparametric observatory has been developed at INGV Palermo and deployed at the bottom of the crater (500 meters depth) for the first time in December 2022. The battery powered module has been able to operate autonomously for a 10-month-long period, collecting a dense, heterogeneous dataset able to describe the activity of the hydrothermal reservoir, highlighting its intense dynamic along the time.In June 2023, the observatory was recovered and re-deployed after brief maintenance operations including battery charging and data downloading. Finally, in October 2023, the observatory was definitely recovered.Here we present for the first time a mid-term-long chemical-physical data series acquired (pH, temperature, hydrostatic pressure, turbidity, conductivity, dissolved methane) along with passive acoustic and the preliminary findings of the system evolution within the observing window. A variety of local VT events likely sourced in the deeper portion of the plumbing system, together with several other minor seismic events related to fluid dynamics inside “fluid-filled” cracks and conduits has been revealed by passive acoustic data. Moreover the acoustic sensor recorded all the signals generated by the bubbles along the water column. The obtained results gave back an up to date picture of the ongoing Kolumbo degassing dynamics, hydrothermal and seismic activity.

Submarine hydrothermal systems attract increasing interest from the scientific community, as they emit huge amounts of both elements and energy. However, in relation to their extreme environmental conditions (e.g. high temperature and pressure, low Ph) direct measurements can be challenging to perform.In this context, passive hydroacoustics may represent a powerful technique for both short- and long-term monitoring as the typical source mechanisms of the hydrothermal fields, directly related to ascending fluids, radiate sound pressure following different acoustic modes.Here we present preliminary results obtained by using a spectral approach for estimating the gas flow emission rate starting from the acoustic dataset collected between 22nd and 26th August 2022 on a stationary flux vent located at ~1.8 metres depth, inside the shallow hydrothermal field at Baia di Levante in Vulcano island (Aeolian Islands, Italy).To carry out the estimation of the gas flow emission rate emitted by the hydrothermal vent, we implemented a customised inverse modelling algorithm based on a spectral method founded upon the assumption that the acoustic signature of a single bubble event evolves over time as a sinusoid that exponentially decays. According to this approach, we refined the formulation of a forward model for the sound radiated by a stationary, high-flux bubbles’ plume, then the path was backward analysed through the proposed inversion algorithm, which allowed us to obtain the estimated value of the flow emission rate.High-resolution audio frames were recorded by using hydrophones [1 - 12800] Hz, that were deployed in the proximity of the investigated vent, collecting a total amount of 7 bursts of ~10 hour-long each. Preliminary analyses of the Power Spectral Density (PSD) and Pressure Power Spectrum highlighted the presence of different persistent energetic frequency peaks over the environmental background noise coherently with the dynamics of the hydrothermal field. The most energetic ones, likely due to the acoustic signal radiated by a large, resonant bubble plume, consistently confirmed the coupling of the estimated radius with direct observations. The performed analysis allowed us to identify the main features of the vent, characterised by bubbles radii up to 0.03 m that produce the main energetic peak centred at ~100 Hz, along with smaller bubbles generating less energetic peaks up to 2 kHz. Therefore, the algorithm was set to work in a wide frequency range, spanning from 60 Hz to 2060 Hz, in order to estimate all the gas released by the vent.The estimated flow emission rate for the investigated period retrieved values spanning from 3.31 to 6.98 litres per minute, with a mean value of 4.97 litres per minute, in good agreement with the direct observations. These results confirm that passive acoustic methods represent a valid and robust tool for both monitoring and research activity in submarine hydrothermal fields, providing a long-lasting instrument able to detect the fluctuations connected to the variations of such natural systems.

Shallow Hydrothermal Vents (SHVs) are fluid emission spots in which water dynamics are characterised by interactions between seawater and free gas due to low hydrostatic pressure. This characteristic marine environment represents a peculiar natural laboratory where the study of geo-biological conditions needs a multidisciplinary approach to better understand the extreme ecosystem dynamics.Although many studies have been already performed on physical-chemical conditions, analysing major chemical species, just a few studies have adopted multidisciplinary approaches, giving a broader and more detailed view of the observed phenomenon.We propose a multidisciplinary study carried out in the period May-August 2022, based on the geophysical, geochemical and biological analysis of Black Point (23m b.s.l.), a hydrothermal spring belonging to the system located at about 2 miles off the coast of Panarea island (Aeolian Archipelago, Italy). Here a multiparametric seafloor observatory is installed (IPANEMA Project funds), equipped with chemical-physical sensors, a hydrophone and a seismometer. The area is periodically monitored by scientific divers performing discrete geochemical sampling, in addition, acoustic radiation studies are regularly conducted close to the emission, to characterise their acoustic signatures and peculiarities in turn. The gained expertise has led to the development of custom algorithms to perform spectral analysis of the acoustic features.Comparing the variation of the flux, investigated through the inversion of acoustic energy (radiated in the band [35 - 55] Hz likely associated with the mass flux variation), with fluctuations related to the environmental seafloor temperature, both series exhibit synchronous relative maxima over the investigated period.Coupling these trends with geochemical and biological variations in terms of Minor, Trace elements and Rare Earth Elements (REEs) concentrations and in the microbial community, simultaneous variations have been highlighted as well.In detail, the highest concentrations of minor elements (Al, Fe, Mn), trace elements (As, V) and REEs correspond to spectral energy and temperature peaks. Moreover, pH is inversely correlated to Fe, Al and Mn, indicating its role in dissolution/precipitation of Fe, Al and Mn oxy-hydroxides; inversely, REEs are positively correlated to Fe, Al and Mn indicating the role of the oxy-hydroxide ligands in fractionation of these elements, as a consequence, REEs patterns shapes show LREE depletion (Lan/Ybn < 1).Furthermore, the composition and diversity of microbial communities were investigated by extracting metagenomic DNA from different matrices (vent fluid, marine sediment near the vent and seawater at a short distance from the vent) and through the next-generation sequencing of a bacterial marker gene (16S rRNA gene). The results show significant differences in the microbial community between the samples and in the two samplings (May and August), especially in the fluid vent. These results are in accordance with the geochemical flux variations and the seafloor temperature, suggesting that each sample carries its specific bacterial fingerprint and the microbial community changes depending on the physicochemical conditions.This study confirms the importance of a multidisciplinary approach as the key to highlight different features of SHVs and how geo-biological fields are strictly linked in extreme environments.

Here we discuss the development of IPANEMA project “PAnarea Natural laboratory of ECCSEL and MArine observatory”. This project aims, through technological innovation, at identifying the most appropriate techniques and methodologies for monitoring, protection and management of the marine ecosystem in the hydrothermal systems. This is strongly correlated to the national decarbonisation needs and to the international research initiatives. A seafloor observatory was installed in the hydrothermal system offshore Panarea island (area with naturally high CO 2 ), implementing multidisciplinary sensors (chemical-physical, oceanographic and geophysical) for the acquisition of measurements in continuous mode. The system consists of a Pole beacon anchored to the bottom on a mooring post and connected via umbilical cable and via acoustic modem to the seafloor observatory. The module provides the opportunity to better study dissolved carbon dioxide diffuses passively into sea waters and causes not only an increase in the partial pressure of the CO 2 but also a reduction in seawater pH, through the monitoring system in near real-time. Between the cabled real-time system and short-term research carried out currently; an objective should be to achieve a 10-year time span of operation. This would provide long-term environmental monitoring but also make a major contribution to science. Monitoring, obtaining time series data, is essential to understand oceanic processes from the surface to the oceanic sub-bottom.

Late Quaternary crustal uplift is well recognized in northeast Sicily, southern Italy, a region also prone to damaging earthquakes such as the 1908 “Messina” earthquake (Mw 7.1), the deadliest seismic event reported within the Italian Earthquake Catalogue. Yet it is still understudied if, within the Milazzo Peninsula, crustal uplift rates are varying spatially and temporally and whether they may be either influenced by (i) local upper‐plate faulting activity or (ii) deep geodynamic processes.To investigate the long‐term crustal vertical movements in northeast Sicily, we have mapped a flight of Middle‐Late Pleistocene marine terraces within the Milazzo Peninsula and in its southern area and refined their chronology, using a synchronous correlation approach driven by published age controls. This has allowed a new calculation of the associated crustal uplift rates, along a north–south oriented coastal‐parallel transect within the investigated area. Our results show a decreasing uplift rate from south to north across the Milazzo Peninsula and beyond, and that the associated rates of uplift have been constant through the Late Quaternary. This spatially varying yet temporally constant vertical deformation helps to constrain the amount of uplift, allowing us to explore which is the driving mechanism(s), proposing a few related scenarios.We discuss our results in terms of tectonic implications and emphasize the importance of using appropriate approaches, as such applying a synchronous correlation method, to refine chronologies of undated palaeoshorelines when used for tectonic investigations.

Volcanic emissions (ash, gas, aerosols) dispersed in the atmosphere during explosive eruptions generate hazards affecting aviation, human health, air quality, and the environment. We document for the first time the contamination of airspace by very fine volcanic ash due to sequences of transient ash plumes from Mount Etna. The atmospheric dispersal of sub-10 μm (PM10) ash is modelled using the WRF-Chem model, coupled online with meteorology and aerosols and offline with mass eruption rates (MERs) derived from near-vent Doppler radar measurements and inferred plume altitudes. We analyze two sequences of paroxysms with widely varied volcanological conditions and contrasted meteorological synoptic patterns in October–December 2013 and on 3–5 December 2015. We analyze the PM10 ash dispersal simulation maps in terms of time-averaged columnar ash density, concentration at specified flight levels averaged over the entire sequence interval, and daily average concentration during selected paroxysm days at these flight levels. The very fine ash from such eruption sequences is shown to easily contaminate the airspace around the volcano within a radius of about 1000 km in a matter of a few days. Synoptic patterns with relatively weak tropospheric currents lead to the accumulation of PM10 ash at a regional scale all around Etna. In this context, closely interspersed paroxysms tend to accumulate very fine ash more diffusively at a lower troposphere and in stretched ash clouds higher up in the troposphere. Low-pressure, high-winds weather systems tend to stretch ash clouds into ~100 km wide clouds, forming large-scale vortices 800–1600 km in diameter. Daily average PM10 ash concentrations commonly exceed the aviation hazard threshold, up to 1000 km downwind from the volcano and up to the upper troposphere for intense paroxysms. Vertical distributions show ash cloud thicknesses in the range 0.7–3 km, and PM10 sometimes stagnates at ground level, which represent a potential health hazard.

Volcanic emissions (ash, gas, aerosols) dispersed in the atmosphere during explosive eruptions generate hazards affecting aviation, human health, air quality and the environment. We document for the first time the contamination of airspace by very fine volcanic ash due to sequences of tran-sient ash plumes from Mount Etna. The atmospheric dispersal of sub-10 μm (PM10) ash is mod-elled using the WRF-Chem model coupled online with meteorology and aerosols and offline with Mass Eruption Rates (MER) derived from near-vent Doppler radar measurements and inferred plume altitudes. We analyse two sequences of paroxysms with widely varied volcanological conditions and contrasted meteorological synoptic patterns in October–December 2013 and on 3-5 December 2015. We analyse the PM10 ash dispersal simulation maps in terms of time-averaged columnar ash density, concentration at specified flight levels averaged over the entire sequence interval, and daily average concentration during selected paroxysm days at these flight levels. The very fine ash from such eruption sequences is shown to easily contaminate the airspace around the volcano within a radius of about 1000 km in a matter of a few days. Synoptic patterns with relatively weak tropospheric currents lead to the accumulation of PM10 ash at a re-gional scale all around Etna. In this context, closely interspersed paroxysms tend to accumulate very fine ash more diffusively in the lower troposphere and in stretched ash clouds higher up in the troposphere. Low-pressure, high-winds weather systems tend to stretch ash clouds into ~100 km-wide clouds forming large-scale vortices 800-1600 km in diameter. Daily average PM10 ash concentrations commonly exceed the aviation hazard threshold up to 1000 km downwind from the volcano and up to the upper troposphere for intense paroxysms. Vertical distributions show ash cloud thicknesses in the range 0.7–3 km, and PM10 sometimes stagnating at ground level, represent a potential health hazard.