Volcanic Rejuvenation and Hydrothermal Systems: Implications for Conservation and Resource Assessment in the Southeastern Tyrrhenian Sea

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We provide a concise overview of prospective seafloor sites in the southeastern Tyrrhenian Sea with potential for future deep-sea mining, within the context of the Italian Exclusive Economic Zone and newly established Ecological Protection Zones.

Abstract

The Southeastern Tyrrhenian Sea is a back-arc basin characterized by the onset of volcanism over the past ~11 million years and the development of numerous volcanic seamounts. Hydrothermal venting is predominantly concentrated in the southeastern sector, encompassing the Aeolian volcanic arc and major volcanic edifices, such as Palinuro and Marsili. These systems frequently exhibit zones of localized magnetic depletion (demagnetization) within otherwise magnetized volcanic structures, often linked to hydrothermal alteration. Notably, volcanic rejuvenation phases are commonly associated with active hydrothermal circulation. In response to mounting ecological concerns, the Italian government has delineated extensive Ecological Protection Zones (EPZs), including those in the Eastern Tyrrhenian sector. These EPZs encompass a series of prominent seamounts—Palinuro, Marsili, Vercelli, Vavilov, Magnaghi, Enarete, and Anchise—that exhibit morphological evidence of rejuvenation and magnetic anomalies consistent with hydrothermal modification. Such features are indicative of potentially mineralized systems, relevant for future resource exploration. A comprehensive evaluation of both the ecological significance and the mineral potential of these areas is now imperative. Balancing environmental conservation with the strategic assessment of deep-sea mining prospects will be essential to mitigate biodiversity loss while promoting the sustainable use of marine mineral resources.

1. Introduction

Deep-sea mining is a relatively new and controversial industry that has gained significant attention in recent years, in response to a growing demand for metals [1]. However, the process of deep-sea mining is not without challenges and risks. Environmental concerns and potential damage to fragile ecosystems have raised questions about the sustainability of this industry. Overall, there is still much that is unknown about the potential environmental impacts of deep-sea mining. Many scientists argue that the precautionary principle should be applied to this industry, meaning that mining should not proceed until its potential impacts have been fully assessed [1,2,3]. There are concerns about the potential impacts linked to the process of extraction, which can disrupt fragile oceanic ecosystems, while the release of sediment and other materials into the water column during the extraction and processing of minerals can have negative effects on marine life [4,5,6,7]. Moreover, there is still much that is unknown about the long-term effects of removing large quantities of nodules from the ocean floor and the impact of large-scale sediment plumes generated by mining vehicles [8,9]. Finally, several studies pointed out the risks related to the release of toxic chemicals into the ocean during the extraction and processing phases [10]. Despite these concerns, interest in potential marine mining resources continues to grow. In fact, deep-sea minerals hold significant potential due to their abundant deposits, mainly consisting of polymetallic nodules (deep-sited seafloor), Fe-Mn crusts (on seamounts), and massive sulfides (on hydrothermal chimneys). According to conservative estimates in the Clarion–Clipperton Zone (CCZ, Pacific Ocean), quantitative studies indicate potential stocks of around 21.1 billion dry metric tons of polymetallic nodules, which equates to 600% of the world’s existing terrestrial reserves of cobalt, 340% of nickel, 30% of copper, and more than 100% of manganese [11,12,13]. Other, more accessible (shallower) potential sites of marine resources have also been identified and confirm the overall potentiality [14], which is especially related to back-arc basins.

The purpose of this manuscript is to shed light on the state of the art of the knowledge of hydrothermal vents of the SE Tyrrhenian basin (Western Mediterranean Sea; Figure 1A), where there is a strong inclination to further explore the economic aspects of the frontier constituted by deep-sea mining, in terms of private companies that greatly believe in the potential and future of this sector. The SE Tyrrhenian Sea is a geodynamically unique area, shaped by active back-arc extension above a subducting slab, which has led to the formation of one of the highest concentrations of volcanic seamounts in the Mediterranean. This region hosts hydrothermal systems known to produce polymetallic sulfide deposits rich in copper, zinc, iron, and rare earth elements (REE). Its relatively young seafloor enhances mineral preservation, while its proximity to Europe offers logistical advantages. The overlapping features of tectonic activity, hydrothermal mineralization, and ecological sensitivity make the Southeastern Tyrrhenian a natural laboratory for studying the intersection of deep-sea mining potential and marine conservation. The coexistence of ecologically totally and/or partially protected areas makes it a distinctive setting for evaluating both the deep-sea mining potential and the conservation priorities. Naturally, the growth of this sector is inevitably linked to the sustainability of the processes, to maintain a good environmental status of the sea. In particular, research on vent areas, especially applied and certainly oriented, translates into a race that has already produced significant efforts in terms of funding (consider the large injections of funds from the European community and excellent results in the industry of sampling demonstrators, as well as for extraordinary robotics capable of handling the enormous complexities of collecting minerals located in abyssal areas [15,16], at thousands of meters of depth. Despite the high number of excellent research centers engaged in these projects, there are many voices in the literature today that express generalized alarm about the potential destruction of some of the most intriguing and fascinating environments on the planet. These alarms are certainly motivated and significant from both a geological and biogeochemical perspective, especially due to the radical changes potentially introduced by extraction activities, but little progress has been made to date on quantitative assessments of the importance of these environments and the risks associated with the extraction potential of deep-sea mining.

1.1. Legal Aspects of Deep Sea Mining

The evolution of the legal framework related to the exploitation of abiotic resources in the marine environment is currently undergoing a delicate phase. To date, regulations and policies surrounding deep-sea mining are still evolving, as the industry is relatively new and there are still many unknowns about its potential impacts [17].

The International Seabed Authority (ISA) is an autonomous international organization established by the United Nations Convention on the Law of the Sea (UNCLOS) of 1982. With the 1994 Agreement relating to the implementation of Part XI of the United Nations Convention on the Law of the Sea [18,19], the ISA tried to establish a set of protocols and rules with the common aim of organizing and controlling all activities related to developing resources from the seabed (generally defined as the ‘Area’) for the benefit of mankind as a whole (UNCLOS, Section 3; [20]). In doing so, the ISA is mandated to ensure the effective protection of the marine environment from the harmful effects that may arise from seabed-related activities. The agreement on the implementation of UNCLOS charges the ISA with developing a system for the exploration and exploitation of these resources, including creating the necessary rules, regulations, and procedures (Article 153 of UNCLOS [20]). Some countries have developed their own regulations and policies for deep-sea mining within their Exclusive Economic Zones (EEZs; Figure 1B). The Italian Parliament has approved a law that authorizes the declaration, by presidential decree, of an Exclusive Economic Zone (EEZ) in all or part of the waters beyond the territorial sea, based on a decision by the Council of Ministers upon the proposal of the Minister of Foreign Affairs and International Cooperation [21,22].

The evolution of maritime law led to a precautionary management of marine natural and biotic resources within the framework of an ecosystem approach to their use, namely Maritime Spatial Planning (MSPD), and the need to protect the marine environment beyond national waters. In recent years, Italy established a vast Ecological Protection Zone to avoid activities that may constitute sources of pollution. Furthermore, conservation actions for these environments stem from recommendations in the Third National Report on Natural Capital (2019), emphasizing their intrinsic economic value and the ecosystem services they provide [23]. With the adoption of Resolution 73/284, the United Nations Decade on Ecosystem Restoration (2021–2030) recommends a conservation-oriented vision, as adopted by the International Seabed Authority (ISA) for achieving the Sustainable Development Goals of Agenda 2030 [24]. Finally, recommendations from the Marine Strategy Framework Directive for achieving GES and its targets strongly discourage activities that could have significant environmental impact and promote the protection of the deep sea from mining and deep-sea fishing, as also requested and supported by many research entities and NGOs and already adopted by some countries, such as New Zealand and Polynesia. It is evident that this national and international regulatory scenario, although currently not a direct prohibition against mining, strongly discourages it both scientifically and productively, and in fact, it emphasizes and accelerates the need to develop studies and research aimed at its geochemical, biological, and ecological characterization.

1.2. Further Detail on Regulatory Aspects of Reference (The Italian Case)

The current regulatory landscape governing deep-sea environments in the Southeastern Tyrrhenian Sea is shaped by a combination of Italian national initiatives and international legal frameworks, which can sometimes result in overlaps, gaps, or tensions in terms of implementation and enforcement. At the international level, Italy is bound by multiple frameworks, including the United Nations Convention on the Law of the Sea (UNCLOS), which grants coastal states sovereign rights over the resources within their Exclusive Economic Zone (EEZ), while simultaneously imposing obligations to protect and preserve the marine environment. Furthermore, Italy is a signatory to the Barcelona Convention and its SPA/BD Protocol, which commits parties to the establishment of a coherent network of Marine Protected Areas (MPAs) in the Mediterranean and to the application of a precautionary approach in managing human activities.

On the national level, Italy has proactively established Ecological Protection Zones (EPZs) under Law No. 61/2006, extending Italian jurisdiction beyond the territorial sea with the aim of safeguarding marine biodiversity and controlling pollution. These zones, particularly those encompassing seamounts such as Marsili and Palinuro, reflect an increasingly conservation-oriented national policy. In 2011, Italy enacted DPR 209/2011, the “Regulation establishing Ecological Protection Zones in the Northwestern Mediterranean, the Ligurian Sea, and the Tyrrhenian Sea”, which prohibits any activity that may adversely affect the marine ecosystem. Furthermore, following the enactment of Law No. 12 of 11 February 2019, and in particular Article 11, which mandates the adoption of the Plan for the Sustainable Energy Transition of Suitable Areas (PiTESAI), and the revision of royalties under Article 18 of Legislative Decree No. 625 of 25 November 1996, the Ministry of Economic Development (MiSE) launched a comprehensive environmental planning and assessment process. The aim of this process is to identify a clearly defined framework for areas where hydrocarbon exploration, research, and extraction may be permitted, based on criteria of environmental, social, and economic sustainability (as stated in Decree Law No. 135/2018, Article 11, converted with amendments by Law No. 12/2019). This includes the drafting of a Preliminary Report to initiate the Strategic Environmental Assessment (VAS), intended to outline the scope and detail of the Environmental Report required under Legislative Decree No. 152/06 and the subsequent amendments.

Conflicts may arise when economic interests, such as the exploration of mineral-rich hydrothermal sites, clash with international environmental commitments. For instance, while national laws may authorize marine research and even preliminary resource assessments, these may be restricted by broader international obligations to avoid biodiversity degradation or non-compliance with regional conservation targets. Moreover, no specific legal instrument currently exists at either the EU or international level governing deep-sea mining in the Mediterranean, leading to regulatory uncertainty and potential jurisdictional disputes. Nonetheless, synergies also exist. Italy’s EPZs may serve as a model for the integration of marine spatial planning with science-based zoning, in accordance with EU directives such as the Marine Strategy Framework Directive (2008/56/EC) and the EU Biodiversity Strategy for 2030. The alignment between national protective measures and international commitments can enhance policy coherence, especially when conservation areas are designated based on robust geophysical and ecological criteria, as demonstrated by the findings of this study. In this context, it is significant to recall the official communication sent by the Italian Ministry of the Environment and Protection of Land and Sea to the EU in 2019, in which Italy committed to the designation of two new Natura 2000 Sites of Community Importance (SCIs) under habitat type 1170—rocky reefs, specifically for the Palinuro and Vercelli Seamounts. This decision was taken in response to a formal request from the European Union through EUPILOT 8348/16/ENV. This commitment strengthens the ecological significance of Italy’s EPZs by integrating them into the Natura 2000 Network established under the Habitats Directive (92/43/EEC), and confirms the conservation priority of the Palinuro Seamount over extractive activities, such as deep-sea mining. Thus, a more integrated governance framework—one that explicitly links geoscientific data with conservation obligations and resource management—is urgently needed to balance resource potential and ecosystem vulnerability. This would require stronger coordination between national regulatory bodies, scientific institutions, and international organizations to harmonize objectives and avoid conflicting mandates.

2. Geological Background

The Tyrrhenian Sea

The Tyrrhenian Sea (Western Mediterranean; Figure 1A), is a small extensional back-arc basin formed due to the subduction of the Ionian lithosphere beneath the Calabrian Arc in the broader context of the Africa–Eurasia convergence [25], which led to widespread volcanism that is characterized by high heat flow values (>150 mW m⁻²) [26], thin crust (averaging 7 km) and lithosphere (averaging 30 km) [27,28], a youthful oceanic crust [29,30] and the emplacement of several seamounts with huge, and partially still active, hydrothermal vents [31].

The initiation of the Tyrrhenian Sea’s opening occurred approximately 11 million years ago, marked by an extension oriented from east to west. During this phase, extensive extension prevailed in the northern region, while rift activity dominated the western portion of the southern region [32], leading to the creation of oceanic crust in the Southern Tyrrhenian area and the development of the Vavilov ocean-like basin (Figure 1A). Subsequently, a transition to extension directed from east to east–southeast occurred concurrently with frontal accretion in the Southern Apennines thrust belt. This shift primarily impacted the Southeastern Tyrrhenian Sea and resulted in the formation of the Marsili ocean-like basin (1.8 to 0.2 million years ago) [30]. This huge extension led to widespread volcanism across the Tyrrhenian Sea and its adjacent coasts [33].

The Aeolian Archipelago consists of seven islands (Stromboli, Panarea, Vulcano, Lipari, Salina, Alicudi, and Filicudi) and several seamounts (Figure 2) with a strong volcano-structural control [34,35] and arranged in a ring-like formation, located at the southern edge of the Tyrrhenian Sea [36]. This area lies just a few tens of kilometers from the northern coast of Sicily and the southwestern coast of Calabria. The archipelago’s location, structure, and geochemical makeup, along with the region’s deep seismic activity, suggest that the volcanic activity in the Aeolian Archipelago is due to a subduction zone [37,38]. Volcanic activity in the Aeolian island arc started around 1 million years ago on continental crust (Figure 1A).

The Palinuro Volcanic Chain (PVC), approximately 90–100 km long, consists of 15 volcanoes aligned in an east–west direction, with heights up to 3200 m above the surrounding seafloor [39]. The presence of calderas (to the west), fracture systems, and canyons provides evidence of instability [40,41]. Additionally, the PVC is influenced by hydrothermal activity that can weaken volcanic rocks [42,43]. Lower seismicity, possibly related to hydrothermal activity, has also been detected [44]. Different styles of volcanism are clearly visible, grouped into three sectors that differ in morphologic characteristics [40], including cones, calderas, and structurally controlled volcanic features [45], and located at depths ranging −84/−2600 m below sea level.

Marsili Seamount MS refers to the spreading ridge of the Marsili back-arc basin [46]. The most recent activity of MS, estimated to have occurred around 2–3 thousand years ago, was linked to a vent in the central–northern part of the volcano responsible for the last explosive eruption [47,48]. Today, the volcano is active, with shallow seismic activity and hydrothermal emissions [49]. Its actual morphology represents the surface expression of different ridge segments controlled by the larger-scale spreading processes and by the local occurrence of an active hydrothermal field [50,51].

3. Data and Methods

3.1. Bathymetry

A bathymetric map of the SE Tyrrhenian Sea was created by joining high-resolution multibeam data with the lower resolution data provided by the European Marine Observation and Data Network (EMODnet) [52]. High-resolution multibeam data (Palinuro and Marsili volcanic chains) were collected by using a Reson Seabat 8160 multibeam sonar system, which is effective at depths ranging from 50 to 3500 m. This system is integrated with differential global positioning and characterized by a 50 kHz ping source, 150° beamwidth for the transmitted pulse, and a 126-beam receiver. The sound velocity in seawater was measured using a sound velocimeter profile, with real-time recordings and updates made every 8 h during data acquisition. Data were processed with partial, real-time beam filtering, swath and spatial mode editing, despiking, and digital terrain model (DTM) rendering. The final DTM is reported with a 20 m grid cell size (Figure 3).

3.2. Magnetics

In the framework of the qualitative analysis of the Tyrrhenian crustal magnetic anomaly field, the magnetic map of Italy [53] is presented in Figure 4. The analysis aims to describe the general pattern of the field and to identify potentially productive areas from a mining perspective, as defined by their magnetic properties. The map here reported represents the integration of various marine and terrestrial surveys and was created using data acquired by the Osservatorio Geofisico Sperimentale (OGS) between 1965 and 1972, as well as data from measurement campaigns conducted by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) within the framework of the Geodynamics Finalized Project of the National Research Council from 1977 to 1981. The marine dataset used for the compilation of the map refers to oceanographic campaigns organized by the National Research Council (CNR) between 1965 and 1972 in the Mediterranean and conducted by the National Institute of Oceanography (OGS). The surveys in the Tyrrhenian Sea and in the study area form a dense set of acquisition lines striking mostly in the NS and EW directions. Measurements were taken at a speed of 10–12 knots using a proton precession magnetometer whose sensor, mounted on a fish, is towed 200–300 m below the boat. The Loran C system was used for positioning the measurements. Data processing involved the reduction of the diurnal variations using the geomagnetic observatory of L’Aquila (centrally located with respect to the extent of the marine surveys) and data reduction to a common epoch (1979.0). The magnetic anomaly is then obtained by removing the core magnetic main field (CMT) using the Molina and De Santis, 1987, model (ItGRF) [54]. Measurement leveling and the removal of the residual line errors were applied by using a crossover analysis and filtering of the total magnetic intensity field (TMI).

Digital enhancement of the magnetic anomaly field involves operations aimed at highlighting its variations and extracting components that improve the ability to derive geological information from geophysical data. To achieve this, a series of filters are typically applied, such as field derivatives, regional and local field separation, and anomaly source edge detection. In this work, we successfully applied the analytic signal tool.

The analytic signal (the square root of the sum of the squares of the total field derivatives, hereafter AS; Equation (1)) combines the horizontal and vertical derivatives of potential field data [55]. The horizontal derivative enhances the location of the source edges, while the vertical derivative narrows the anomaly width. As a result, this filter exhibits its maximum values above the magnetization contrast, regardless of the inducing field’s direction, the magnetization directions, and without requiring prior information about the source.

Analytic Signal = √(〖dx〗^2 + 〖dy〗^2 + 〖dz〗^2)

(1)

Therefore, geological contacts or faults characterized by significant magnetization contrast can be efficiently mapped using AS features. These features are located directly over the edges of causative structures (Figure 5).

4. Results and Discussion

4.1. Back-Arc Spreading Vents and Deposits

Many similarities exist between the contemporary marine geologic formation of back-arc areas and deposits that are currently mined on land [56,57]. Sulfide deposits are reported in back-arc spreading, like Central Manus Basin [58] and the Mariana Trough [59,60]. These findings prompted extensive exploration of marginal basins, arc systems, and back-arc systems in the Western and Southwestern Pacific during the late 1980s. Since then, a wide range of mineral deposits have been found in back-arc rifts at various stages of development (immature versus mature), on volcanoes along the active volcanic fronts of arcs, and in rifted fore-arc environments. Notable examples of polymetallic massive sulfide deposits have been reported from mature back-arc spreading centers such as the North Fiji Basin [61], along propagating back-arc rifts like the Valu Fa Ridge in the southern Lau Basin [62], and in embryonic back-arc rifts such as the Okinawa Trough [63].

In 1991, extensive sulfide deposits were discovered in association with felsic volcanism in the Eastern Manus Basin [64]. Hydrothermal deposits have also been located in the Western Woodlark Basin, where seafloor spreading extends into the continental crust of Papua New Guinea [65]. Later, more than 100 sites of hydrothermal mineralization have been identified on the seafloor [66], including at least 25 sites with high-temperature (350–400 °C) black smoker venting

In the Santorini Archipelago (Eastern Mediterranean Sea), the deposition of iron oxide occurred at an exceptionally high rate. It was also found that deposition in the central part of the Santorini Bay proceeded within specific vertical zones in the water column, and deposition was mediated by bacteriological processes that varied in intensity depending on their specific location in the inner bay of the archipelago [67,68,69]. Many other episodes are reported for the Aegean Arc but remain poorly explored in terms of active fluid flows or associated deposits. However, the rocky substrate varies in terms of the thickness and chemistry of marine sediments and mineral deposits, and the variability is extreme, often even for two very close vent-sites [70,71].

4.2. Magnetic Source Boundaries in the SE Tyrrhenian Sea

The Tyrrhenian Sea magnetic anomaly field is complex and extremely articulated. The different wavelengths reflect the extraordinary variability of the geological and tectonic environments developed over time and space from the Oligocene and Holocene to the Present time in an area extending 580 by 560 km in longitude and latitude, respectively. Particularly, this area encompasses the submerged sections of the Apennine and Maghrebide mountain ranges, along with the Marsili and Vavilov oceanic-like basins (Figure 1A and Figure 2). Additionally, it features active volcanoes, including the subduction-related Stromboli and Vulcano of the Aeolian Arc and wide sedimentary basins hosted in tectonic depressions (Figure 5).

These different geodynamic settings lead to marked lateral and vertical lithology variations and their magnetization and density properties, which in turn, generate intense geophysical anomalies. Particularly, volcanic and intrusive activities and the corresponding heat fluxes in the upper crust have favored specific settings with an increasing or lowering of the magnetic properties, respectively. Local conditions may have promoted re-mineralization phenomena with specific magnetic signatures. The reduction, modeling, and interpretation of the magnetic anomalies provide important information on these relevant sources, illuminating otherwise unattainable depths. This can occur at different scales depending on the measurement spacing and density. However, determining the geological significance of potential field observations is challenging due to the considerable anomalous spatial complexity and overlap because of the inherent ambiguity of the method regarding depth. Nonetheless, a first indication of the presence of large magnetized bodies characterized by axial shapes (which is a potential expression of tectonic control) arise from the application of the analytic signal (Figure 5), thus indicating the Aeolian Arc islands and the Palinuro, Marsili, Vavilov, Magnaghi, Enarete, and Anchise seamounts as the most interesting in terms of the presence of large volcanic bodies linked to the opening of the Tyrrhenian sea (Figure 1A, Figure 2, Figure 3, and Figure 5).

4.3. Hydrothermal Vents and Products of the SE Tyrrhenian Sea

The SE Tyrrhenian Sea has several seamounts characterized by wide and diffuse vents [72,73,74,75,76,77,78,79,80] that give rise to peculiar, site-specific bio-associations [81,82,83,84,85,86,87,88,89,90,91,92]. These sites of active (or that were active in the recent past) hydrothermal vents are located on its SE sector, i.e., in the Aeolian Arc, and on the Marsili and Palinuro volcanic chains. The Aeolian Islands archipelago, located in the Southern Tyrrhenian Sea off the northeastern coast of Sicily, consists of seven main islands (Lipari, Vulcano, Salina, Stromboli, Filicudi, Alicudi, and Panarea) and numerous seamounts of volcanic origin. The formation of the archipelago occurred around one million years ago, following the subduction process induced by the movement of the Ionian Sea lithosphere beneath the Calabrian arc. The volcanic activity, which is still ongoing on some of the islands and in the surrounding seabeds, has also produced hydrothermal vents, particularly in Vulcano and Panarea. The geochemical characterization of the gases emitted revealed a dominant presence of CO₂, naturally leading to a decrease in pH levels. Vulcano Island is characterized by the presence of numerous sulfurous fumaroles that can reach 400–550 °C and hosts one of the most active and studied submarine CO₂ emissions [93,94,95,96]. The composition of the gases emitted consists mainly of CO₂ (around 97–99% vol.), while small concentrations of toxic gases, such as H₂S (not exceeding 2.2%), appear to be limited to the primary vent and decrease sharply over short distances (20 m). Additionally, as an indirect effect of the acidification of the area, trace elements, such as Ba, Fe, As, and Cd, have been found in sediments even at significant distances from the primary source. Panarea Island represents the emerged part of an underwater volcano more than 2 km high and approximately 20 km wide, eroded over time by marine erosion and tectonic processes, as well as the presence of hydrothermal vents [97,98,99,100,101,102]. Off the eastern coast, there is a field of submarine hydrothermal emissions at depths of around 10–15 m. Fluid emissions reach the water column through fractures, and numerous areas have been identified where warm waters and gases permeate through the sand of the seafloor. The emissions (predominantly volcanic CO₂) have a flow of approximately 106–107 L per day, with temperatures between 48 and 54 °C and pH values around 4.7–5.4. ROV (remotely operated vehicle) images have enabled the discovery and location of a hydrothermal system situated southwest of the Isolotto di Basiluzzo at around 70–80 m depth, known as ‘smoking land’, with the release of Fe-rich fluids [103] and characterized by the presence of over 200 volcanic chimneys, typically conical in shape, ranging from 1 to 4 m in height, some of which are active and emit a mixture of warm waters and gases.

Of course, deep-sea areas potentially eligible for mining activities are more interesting because they are less exposed to environmental damage. In this sense, partially demagnetized sectors inside magnetic bodies are more interesting because these are the areas presumably affected by demagnetization due to the presence of hydrothermal vents. Crustal demagnetization is a common feature in basalt-hosted hydrothermal vent fields at slow- and ultra-slow-spreading mid-ocean ridges and caldera hydrothermal areas, primarily due to the removal of magnetic minerals by hydrothermal alteration processes and thermal demagnetization [104,105].

The Palinuro Seamount (Figure 6) shows E to W morphologic changes with distinct groups of calderas (westernmost sector), cones (central sector), and dissected shapes (eastern sector; Figure 5). The Palinuro Volcanic Chain is completed by coalescent volcanic items named Glabro, Enotrio, the Ovidio Seamount, and Diamante. Active or fossil hydrothermal vents have been widely documented along the entire Palinuro chain thanks to seafloor sampling (minerals and copper crusts, iron and manganese nodules and crusts, and other cobalt-rich nodules), as well as from the geochemistry of the water column (He³/He⁴ isotopic ratio), geophysics (demagnetization of rocks altered by hydrothermalism), and OBS with seismic activity due to active hydrothermalism detected by seismic waveforms recorded with ocean bottom seismometers [31,39,43,44,45,106,107,108,109,110,111,112,113]. All these activities reveal that the rejuvenation sector included in the easternmost caldera area could be the most promising for DSM purposes.

The Marsili Seamount (Figure 7) is 70 km long and 30 km wide ridge that is elevated ca. 3000 m from surrounding seafloor [50], which represents the inflated spreading ridge [46] of the 2 Ma old Marsili back-arc basin associated to the subduction of the Ionian Sea below the Calabrian Arc and the Tyrrhenian Sea. Its morphology shows signs of differentiated eruptive styles, also including mono- and polygenetic central cones, fissural volcanic features, and hydrothermal mounds [51]. Petrologic analysis [72,112] and visual inspection by ROV [114,115] indicate the presence of active or past hydrothermal activities on its top. Magnetic and gravity data suggest the presence of demagnetized sectors due to hydrothermal alteration in the central sector of the Seamount, while geochemical analyses of the water column and local seismicity are consistent with the presence of active hydrothermal phenomena from the top of the seamount itself [31,49]. Magnetic data indicate (like for Palinuro Seamount) rejuvenation areas as the most interesting for hydrothermal vent products [111,115,116].

The spatial resolution of the available magnetic data, while informative, remains too coarse to resolve fine-scale hydrothermal features. Moreover, the link between magnetic demagnetization and specific mineral deposit types remains partly inferential and must be confirmed through ground-truthing via ROV surveys, coring, and geochemical assays. Additionally, the long-term ecological consequences of mining activity in these unique environments remain poorly understood. To address these gaps, future research should focus on (1) high-resolution geophysical and geochemical surveys at priority sites to better constrain the nature and extent of subsurface mineralization, also including advanced facies recognition with reflection seismic profiles acquired with deep-towed systems and specifically processed to properly understand the real dimensions of DSM facies (e.g., [117]) and (2) in situ biological and ecological studies to assess vulnerability and species endemism in hydrothermal vent communities and integrated impact assessments that model the cumulative effects of potential DSM operations within sensitive volcanic and hydrothermal ecosystems.

In the Southeastern Tyrrhenian Sea, where ecologically sensitive seamounts coincide with hydrothermally active areas, evaluating the environmental impacts of potential deep-sea mining is crucial. Long-term studies [4,8] show that seabed disturbances cause persistent ecological degradation, including sediment plumes that affect regions far beyond the immediate impact zone. Modeling efforts [7,10] warn of risks to benthic food webs and metal bioaccumulation, highlighting potential long-term toxicity. Recent findings [118] at a site in the Clarion-Clipperton Zone reveal minimal ecosystem recovery more than 26 years after disturbance. Key benthic organisms, including sponges and invertebrates, remain scarce, and the sediment structure has not fully returned. These findings underline the long-lasting ecological damage of deep-sea mining and the need for precautionary frameworks. Our study emphasizes that magnetic demagnetization and volcanic rejuvenation indicators can help identify hydrothermally altered—and potentially mineral-rich—areas. Yet, these same features often coincide with ecologically valuable habitats. Therefore, an integrated approach to deep-sea policy is urgently needed, combining geophysical assessments with ecological data, long-term monitoring, and robust governance mechanisms to balance conservation with resource development.

5. Conclusions

The SE Tyrrhenian Sea hosts a large number of volcanic seamounts, many of which are characterized by active hydrothermal vents or features associated with past volcanic and hydrothermal activity. Magnetic data serve as a powerful tool for delineating the boundaries of magnetized sources, providing a first-level indication of the potential presence of mineral deposits, such as nodules, massive sulfides, and ferromanganese crusts—features of growing interest in the context of deep-sea mining. High-resolution analyses can further reveal localized, partially demagnetized zones within volcanic structures, which are frequently associated with hydrothermal systems, particularly in areas where volcanic activity has experienced rejuvenation. Geophysical anomalies arise from variations in rock magnetization and density and volcanic and intrusive activity that alter crustal heat flow and hydrothermal re-mineralization, resulting in localized demagnetization. Notably, the Palinuro and Marsili seamounts exhibit clear geophysical and morphological signatures of such processes. The Palinuro volcanic chain (including the Palinuro Seamount, as well as Glabro, Enotrio, Ovidio, and Diamante) is well known for its active and fossil hydrothermal fields, hosting metal accumulation in a tectonically controlled setting. On the other hand, Marsili, the largest submarine volcano in Europe, shows evidence of recent volcanic activity and widespread demagnetized areas, suggesting ongoing or past hydrothermal circulation. In response to the increasing awareness of the ecological value and vulnerability of these environments, the Italian government has adopted a precautionary approach by establishing extensive Ecological Protection Zones aimed at safeguarding these fragile and largely unexplored marine ecosystems.

A comparative analysis of the SE Tyrrhenian hydrothermal systems reveals a diverse spectrum of geological settings, from emergent island volcanoes to deeply submerged spreading ridges. Vulcano and Panarea represent shallow, highly accessible analogs to mid-depth vent systems, with a strong emphasis on ecosystem sensitivity and biogeochemical cycling. In contrast, Palinuro and Marsili display larger-scale tectono-magmatic processes with well-developed hydrothermal imprints, localized demagnetization, and a greater potential for polymetallic resource accumulation. While Palinuro exhibits strong tectonic segmentation and metal-rich deposits, Marsili appears as a classic ridge-type volcanic system with axial hydrothermalism.

From an environmental perspective, shallow sites like Panarea are critically sensitive to anthropogenic disturbance due to their established biota and shallow venting, while deeper structures may offer more controlled access for future DSM evaluation, albeit with considerable ecological uncertainty. These distinctions highlight the need for site-specific assessments that integrate geological potential and environmental vulnerability before advancing any resource-related activities.

Going forward, integrated studies that combine geophysical imaging, geochemical sampling, and ecological monitoring are essential to assess the feasibility of any DSM initiatives. A site-specific and precautionary approach must guide future exploration strategies, ensuring that scientific understanding and environmental stewardship evolve in tandem. The SE Tyrrhenian region exemplifies both the promise and the complexity of seabed mineral resources in active volcanic arcs, offering valuable insights but also demanding rigorous safeguards.