The deep ocean was long assumed to be in a quasi-stationary state, and therefore excluded from studies on climate variability. The awareness of the unsteady state of the deep ocean is a fairly recent achievement, but despite its pivotal role in the assessment of climate variability, the understanding of abyssal ocean dynamics remains largely unknown, primarily due to the scarcity of observations. This is why any observations below 2000 m depth, although poor or widely dispersed, constitute valuable knowledge that is mandatory to enhance and make available. This work presents validated oceanographic time series collected by benthic multidisciplinary observatories across key locations in the Mediterranean Sea region. It includes details on the data processing and quality control methods used to ensure reliability and aims to deliver high-quality data, as well as standardization in the quality control procedures for deep-sea measurements. The dataset provides a comprehensive description of seafloor observations collected over different time periods during the past decade, contributing to the long-term characterization and understanding of abyssal ocean variability in the region (MOIST, https://doi.org/10.13127/MD/MOIST, Azzarone et al., 2010).

Offshore earthquakes can cause widespread destruction due to directly propagating seismic vibrations and/or the generation of tsunamis. Early warning of offshore earthquakes is vital, but their location complicates identification of clear early warning (EW) signatures. Distributed acoustic sensing (DAS), applied to offshore fibre-optic cables offers the prospect to improve early warning of offshore events. We use a DAS dataset acquired from a 30 km submarine cable spanning a complex bathymetry, offshore Sicily, to contribute to a proof-of-concept using five regional earthquakes to investigate factors impacting incident body wave detection capabilities. We demonstrate observations for P- and S-waves incident parallel and perpendicular to the cable, and that cable coupling to the surrounding medium exerts far more control on signal quality than incidence azimuth. Compared to the nearest land station, an EW signal for a Mw5.8 earthquake was triggered 1.59 seconds earlier using P-wave arrivals on the fibre, and 3.89 seconds earlier using S-waves. We show that effective warnings can be made despite spatially decimating data by factors of 10 and 100 for P-waves and S-waves, respectively. This data volume reduction allows DAS on legacy seafloor cables to be integrated with EW systems for offshore earthquakes and other geohazards which threaten coastal populations.

Marine seismic surveys contribute to acoustic pollution, and the sounds they produce may be audible by marine mammals at several hundred kilometers distance. To evaluate the potential effects of such sounds on fauna and translate them into effective policies and mitigation measures, stakeholders require quantitative estimations of acoustic fields. We compare simulations of airgun-array signals produced during the Upper LIthosphere Ship Subduction Exploration survey in the Ionian Sea with the signals recorded 650 kilometers away at the cabled seabed observatory NEMO-SN1. JASCO's Applied Sciences' Airgun Array Source Model was used to predict the sound levels for two configurations of 18-element airguns, and the signal was then propagated in a realistic environment utilizing JASCO's Full-Waveform Range dependent Acoustic Model from the source to the position of the receiver station. There is a qualitative agreement between the simulated, denoised, and recorded signals of the airgun arrivals. However, the signal simulated at 650 kilometers from the source stretches and shows fewer high-frequency components compared to the received one. Our study quantitatively shows that the peaks produced by a large airgun array during a scientific cruise, at 160–180 Hz are not masked by ambient noise even in busy shipping locations at a distance of 650 km.

Autonomous Ocean Bottom Seismometer (OBS) deployments have often involved a degree of “drop-and-hope” due to the inherent lack of seismic data communication during installation as well as waiting extended periods before data collection. Cabled solutions provide real-time data during and immediately after deployment, sometimes with opportunity to adjust the instrument before it is left to operate remotely. However, cabled solutions are inherently financially and logistically challenging both in terms of seismic hardware and arguably more significantly, deployment hardware (ships, ROVs, cables etc.). The geographical reach of these experiments is also often limited to within a few hundred kilometres of the coast. These constraints often mean cabled OBS are beyond the scope of most scientific bodies. Güralp Systems, in collaboration with INGV, has successfully manufactured and demonstrated a method of reducing financial and logistical constraints and extending geographical range by utilising force-feedback seismic instrumentation in cabled OBS systems. The recent successful deployment of the InSEA Wet Demo SMART (Science Monitoring And Reliable Telecommunications) cable displays a world first in how science can partner with industry to achieve this. SMART cables are primarily telecommunication cables that secondarily serve as hosts for scientific monitoring equipment. Commercial viability for these systems relies on the cable being laid as if the science element did not exist, thereby minimising additional deployment costs and reducing barriers to cooperation with cable laying companies. GSL and INGV deployed 3 seismometer-accelerometer pairs housed inline repeaters along the 21km cable length using standard cable-laying techniques to show proof of concept. This pioneering installation using telecommunication cables marks a significant step towards drastically improving local knowledge of inaccessible oceanic regions as well as global azimuthal coverage for teleseismic events, all in real time.

Continuous seismic and environmental monitoring at remote seabed sites always faced a major challenge due to technical, logistical and financial effort. Commercial Telecommunication submarine cables continuously expand the coverage of ocean seafloor following society's needs to increase connectivity between distant countries and remote sites. Cables over thousands of kilometres long are equipped with in-line repeaters which compensate for optical losses due to such long distances. A Science Monitoring And Reliable Telecommunications (SMART) Subsea Cables, designed by a Joint Task Force (JTF) across the International Telecommunication Union, World Meteorological Organization, the UNESCO Intergovernmental Oceanographic Commission, may host, inside repeaters, scientific sensors for seismic, ocean and climate monitoring and disaster risk reduction in cases of tsunamis. The recent successful deployment at the Western Ionian Sea, one of EMSO (European Multidisciplinary Seafloor and water column Observatory) Regional Facilities, of the InSEA Wet Demo SMART Cable displays a world first demonstrating the feasibility of such installation using standard cable-laying techniques to show proof of concept. Commercial viability for these systems relies on the cable being laid as if the scientific element did not exist, thereby minimising additional deployment costs and reducing barriers to cooperation with cable laying companies. Güralp Systems Ltd and INGV deployed three seismometer-accelerometer pairs housed in inline repeaters along the 21km cable long. Each repeater also provides temperature and pressure devices which respectivley enable the real time monitoring of sea environment state and of sea surface level for tsunami detection.This pioneering installation demonstrates the feasibility of smart cable initiative which may lead to global coverage of ocean seafloor with a network of scientific sensors enabling the real time monitoring of seismicity and tsunami events at remote locations thanks to a collaboration between scientific and commercial parties.

The Mediterranean fin whale emits two types of 20-Hz calls, known as “classic” and “backbeat”, that can be produced in irregular series or in patterned sequences called songs. The analysis of songs is recognized as a meaningful approach to study baleen whales and can be used to investigate populations’ identities. Mediterranean fin whale songs have been studied previously, but only in the western Mediterranean Sea. This work describes the structure of the songs recorded in the Ionian Sea. The inter-note intervals and the alternation of 20-Hz note types were considered to assess the occurrence of recurring patterns. Differences between patterned songs and irregular sequences were also investigated. Acoustic data were sampled continuously for about 10 months by the cabled observatory NEMO-SN1, deployed at 2100 m depth, 25 km offshore Catania; 28 call sequences were isolated and 10 of these were classified as either patterned songs or irregular sequences. Significant differences were observed in the spectral features of classic notes between songs and irregulars; four-note patterns were found repeatedly over different months, indicating a regular structure in detected songs. This work establishes a reference to interpret Mediterranean fin whale songs, and to assess the acoustic behavior of the population.

<p>Although it is now known that deep marine processes play a crucial role in the study and assessment of climate variability, deep-sea ocean dynamics remain largely unknown. This is due to the lack of data above 2000 m of depth. </p> <p>Given the paucity of observation of the deep ocean environment, is essential to improve the availability and accessibility of in-situ high-quality datasets, standardized in accordance with the FAIR principles. This allows enhanced knowledge of local deep variability, and contributes to maximizing the utility of data, also supporting ocean modeling which so far has been unable to realistically depict the deep-layers state. </p> <p>Several high sampling frequency dataset collected by benthic multidisciplinary observatories in key sites such as Mediterranean Sea, Marmara Sea and Atlantic Ocean has been elaborated, verifying the sensor efficiency through post-calibration and standardized Quality Control (QC) procedures, adapted from international protocols and recommendations specifically for deep-sea observations. QC tests were automated as much as possible aiming for a standardized procedure while taking into account the specificity of each different technology used.</p> <p>The aim of this work is to disseminate verified in-situ dataset, together with properly formatted raw data and metadata, providing high-quality open-access data including Ocean Essential Variables  ready for user analysis intended to fill the gap in deep ocean knowledge.</p>

The oceans are a fundamental source for climate balance, sustainability of resources and life on Earth, therefore society has a strong and pressing interest in maintaining and, where possible, restoring the health of the marine ecosystems. Effective, integrated ocean observation is key to suggesting actions to reduce anthropogenic impact from coastal to deep-sea environments and address the main challenges of the 21st century, which are summarized in the UN Sustainable Development Goals and Blue Growth strategies. The European Multidisciplinary Seafloor and water column Observatory (EMSO), is a European Research Infrastructure Consortium (ERIC), with the aim of providing long-term observations via fixed-point ocean observatories in key environmental locations across European seas from the Arctic to the Black Sea. These may be supported by ship-based observations and autonomous systems such as gliders. In this paper, we present the EMSO Generic Instrument Module (EGIM), a deployment ready multi-sensor instrumentation module, designed to measure physical, biogeochemical, biological and ecosystem variables consistently, in a range of marine environments, over long periods of time. Here, we describe the system, features, configuration, operation and data management. We demonstrate, through a series of coastal and oceanic pilot experiments that the EGIM is a valuable standard ocean observation module, which can significantly improve the capacity of existing ocean observatories and provides the basis for new observatories. The diverse examples of use included the monitoring of fish activity response upon oceanographic variability, hydrothermal vent fluids and particle dispersion, passive acoustic monitoring of marine mammals and time series of environmental variation in the water column. With the EGIM available to all the EMSO Regional Facilities, EMSO will be reaching a milestone in standardization and interoperability, marking a key capability advancement in addressing issues of sustainability in resource and habitat management of the oceans.

The European Multidisciplinary Seafoor and water Column Observatory (EMSO, www.emso.eu) is a distributed research infrastructure (RI), composed of fxed-point deep-sea observatories and shallow water test sites at strategic environmental locations from the southern entrance of the Arctic Ocean all the way through the North Atlantic through the Mediterranean to the Black Sea. Working as a single powerful system, it is a valuable new tool for researchers and engineers looking for long time series of high-quality and high-resolution data to study and continuously monitor complex processes interactions among the geosphere, biosphere, hydrosphere and atmosphere, as well as to test, validate and demonstrate new marine technologies.

Extreme events have long been underestimated in the extent to which they shape the surface of our planet, our environment, its ecological integrity, and the sustainability of human society. Extreme events are by definition rarely observed, of significant impact and, as a result of their spatiotemporal range, not always easily predicted. Extremes may be short-term catastrophic events such as tsunamis, or long-term evolving events such as those linked to climate change; both modify the environment, producing irreversible changes or regime shifts. Whatever the driver that triggers the extreme event, the damages are often due to a combination of several processes and their impacts can affect large areas with secondary events (domino effect), whose effects in turn may persist well beyond the duration of the trigger event itself. Early studies of extreme events were limited to opportunistic approaches: observations were made within the context of naturally occurring events with high societal impact. Given that climate change is now moving us out of a relatively static climate regime during the development of human civilization, extreme events are now a function of underlying climate shifts overlain by catastrophic processes. Their impacts are often due to synergistic factors, all relevant in understanding process dynamics; therefore, an integrated methodology has become essential to enhance the reliability of new assessments and to develop strategies to mitigate societal impacts. Here we summarize the current state of extreme event monitoring in the marine system, highlighting the advantages of a multidisciplinary approach using Research Infrastructures for providing the temporal and spatial resolution required to monitor Earth processes and enhance assessment of associated impacts.

EMSO is a distributed Research Infrastructure currently comprising nine Regional Facilities (RFs) and three shallow water test sites, strategically located all the way from the southern entrance of the Arctic Ocean across to the North Atlantic through the Mediterranean to the Black Sea. Since the beginning of 2021 Norway has been integrated as a new EMSO ERIC member, extending the geographical coverage to the Nordic Sea and the Arctic. EMSO’s extension will benefi t from an experienced team managing moored observatories, ocean gliders and the Mohn Ridge Seafl oor and Water Column Observatory.

MarsiteCruise was undertaken in October/November 2014 in the Sea of Marmara to gain detailed insight into the fate of fluids migrating within the sedimentary column and partially released into the water column. The overall objective of the project was to achieve a more global understanding of cold-seep dynamics in the context of a major active strike-slip fault. Five remotely operated vehicle (ROV) dives were performed at selected areas along the North Anatolian Fault and inherited faults. To efficiently detect, select and sample the gas seeps, we applied an original procedure. It combines sequentially (1) the acquisition of ship-borne multibeam acoustic data from the water column prior to each dive to detect gas emission sites and to design the tracks of the ROV dives, (2) in situ and real-time Raman spectroscopy analysis of the gas stream, and (3) onboard determination of molecular and isotopic compositions of the collected gas bubbles. The in situ Raman spectroscopy was used as a decision-making tool to evaluate the need for continuing with the sampling of gases from the discovered seep, or to move to another one. Push cores were gathered to study buried carbonates and pore waters at the surficial sediment, while CTD-Rosette allowed collecting samples to measure dissolved-methane concentration within the water column followed by a comparison with measurements from samples collected with the submersible Nautile during the Marnaut cruise in 2007. Overall, the visited sites were characterized by a wide diversity of seeps. CO2- and oil-rich seeps were found at the westernmost part of the sea in the Tekirdag Basin, while amphipods, anemones and coral populated the sites visited at the easternmost part in the Cinarcik Basin. Methane-derived authigenic carbonates and bacterial mats were widespread on the seafloor at all sites with variable size and distributions. The measured methane concentrations in the water column were up to 377 mu mol, and the dissolved pore-water profiles indicated the occurrence of sulfate depleting processes accompanied with carbonate precipitation. The pore-water profiles display evidence of biogeochemical transformations leading to the fast depletion of seawater sulfate within the first 25-cm depth of the sediment. These results show that the North Anatolian Fault and inherited faults are important migration paths for fluids for which a significant part is discharged into the water column, contributing to the increase of methane concentration at the bottom seawater and favoring the development of specific ecosystems.

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, 25 th 2011 in the western Sea of Marmara, occurred within a zone of gas overpressuring in the 1.5–5 km 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 (~M < 3) within the Istanbul offshore domain.