Palinuro Seamount Research Articles

Environmental DNA Metabarcoding of Cephalopod Diversity in the Tyrrhenian Deep Sea

The deep sea, the largest biome on Earth, is the least explored and understood. This lack of knowledge hampers our ability to understand and protect this important environment. In this study, water and sediment samples were collected at different depths in the central Mediterranean (224–780 m), specifically, within the Dohrn Canyon and the Palinuro Seamount, to investigate the diversity of cephalopods and establish a baseline knowledge of their distribution in these sites to preserve their habitats and estimate the impacts of human-driven environmental changes. Key taxa identified included Heteroteuthis sp., Loligo sp., and Histioteuthis sp., which were the most abundant across all sampling stations. A low overlap in species detection was observed between water and sediment samples, confirming previous findings that the typology of environmental matrices used in eDNA metabarcoding has a significant impact on the organisms detected and, therefore, the integrated use of different matrices to better represent local biodiversity is recommended. Furthermore, this study highlights the limitations posed by gaps in reference databases, particularly for deep-sea organisms, and addresses these by emphasising the need for improved multi-marker approaches and expanded reference databases to enhance the accuracy of eDNA-based biodiversity assessment.

Magnetic Expression of Hydrothermal Systems Hosted by Submarine Calderas in Subduction Settings: Examples from the Palinuro and Brothers Volcanoes

Volcanism is the most widespread expression of cyclic processes of formation and/or destruction that shape the Earth’s surface. Calderas are morphological depressions resulting from the collapse of a magma chamber following large eruptions and are commonly found in subduction-related tectono-magmatic regimes, such as arc and back-arc settings. Some of the most impressive examples of seafloor hydrothermal venting occur within submarine calderas. Here, we show the results of magnetic investigations at two hydrothermally active submarine calderas, i.e., Palinuro Seamount in the Southern Tyrrhenian Sea, Italy, and Brothers volcano of the Kermadec arc, New Zealand. These volcanoes occur in different geodynamic settings but show similarities in the development of their hydrothermal systems, both of which are hosted within calderas. We present a new integrated model based on morphological, geological and magnetic data for the Palinuro caldera, and we compare this with the well-established model of Brothers caldera, highlighting the differences and common features in the geophysical expressions of both hydrothermal systems. For consistency with the results at Brothers volcano, we build a model of demagnetised areas associated with hydrothermal alteration derived from 3D inversion of magnetic data. Both these models for Brothers and Palinuro show that hydrothermal up-flow zones are strongly controlled by caldera structures which provide large-scale permeability pathways, favouring circulation of the hydrothermal fluids at depth.

A first application of a marine inductive source electromagnetic configuration with remote electric dipole receivers: Palinuro Seamount, Tyrrhenian Sea

ABSTRACTWe study a new marine electromagnetic configuration that consists of a ship‐towed inductive source transmitter and a series of remote electric dipole receivers placed on the seafloor. The approach was tested at the Palinuro Seamount in the southern Tyrrhenian Sea, at a site where massive sulphide mineralization has been previously identified by shallow drilling. A 3D model of the Palinuro study area was created using bathymetry data, and forward modelling of the electric field diffusion was carried out using a finite volume method. These numerical results suggest that the remote receivers can theoretically detect a block of shallowly buried conductive material at up to ∼100 m away when the transmitter is located directly above the target. We also compared the sensitivity of the method using either a horizontal loop transmitter or a vertical loop transmitter and found that when either transmitter is located directly above the mineralized zone, the vertical loop transmitter has sensitivity to the target at a farther distance than the horizontal loop transmitter in the broadside direction by a few tens of metres. Furthermore, the vertical loop transmitter is more effective at distinguishing the seafloor conductivity structure when the vertical separation between transmitter and receiver is large due to the bathymetry. As a horizontal transmitter is logistically easier to deploy, we conducted a first test of the method with a horizontal transmitter. Apparent conductivities are calculated from the electric field transients recorded at the remote receivers. The analysis indicates higher apparent seafloor conductivities when the transmitter is located near the mineralized zone. Forward modelling suggests that the best match to the apparent conductivity data is obtained when the mineralized zone is extended southward by 40 m beyond the zone of previous drilling. Our results demonstrate that the method adds value to the exploration and characterization of seafloor massive sulphide deposits.

A self-potential investigation of submarine massive sulfides: Palinuro Seamount, Tyrrhenian Sea

The self-potential (SP) method detects naturally occurring electric fields, which may be produced by electrically conductive mineral deposits, such as massive sulfides. Recently, there has been increasing interest in applying this method in a marine environment to explore for seafloor massive sulfide (SMS) deposits, which may contain economic resources of base and precious metals. Although SMS sites that are associated with active venting and are not buried under sediment cover are known to produce an SP signal, the effectiveness of the method at detecting inactive and sediment-covered deposits remained an outstanding question. We built an instrument capable of recording SP data in a marine setting. We carried out a test of the instrument at the Palinuro Seamount in the Tyrrhenian Sea. Palinuro is one of only a few known sites containing an SMS occurrence that is buried under sediment and not associated with active hydrothermal venting, although diffuse seepage of hydrothermal fluids is known to occur at the site. Elevated electric field strengths recorded in and near the site of previously drilled massive sulfide samples are on the order of [Formula: see text]. A second zone of high field strengths was detected to the north of the drilling area where gravity coring later confirmed the existence of massive sulfides. Our observations indicate that an SP signal can be observed at the site of SMS mineralization even when the mineralized zone is shallowly buried and active hydrothermal venting is not present. These observations could aid in the planning of future marine research expeditions that use the SP method in the exploration of seafloor massive sulfides.

Descriptions of eight species from the superfamilies Axioidea Huxley, 1879 and Callianassoidea Dana, 1852, with a revised key to the species of the genus Acanthaxius Sakai & De Saint Laurent, 1989 (Decapoda, Callianassidea)

In the present paper, two new species, Acanthaxius kashimaensis sp. nov. and A. pseudopolyacanthus sp. nov., are described and a revised key to the species of the genus Acanthaxius Sakai & De Saint Laurent, 1989 is presented. In addition, Balssaxius habereri (Balss, 1913) and Boasaxius princeps (Boas, 1880) of the family Axiidae Huxley, 1879, Neaxius glyptocercus (Von Martens, 1869) of the family Strahlaxiidae Poore, 1994, together with Trypaea truncata (Giard & Bonnier, 1890) of the family Callianassidae Dana, 1852, and two species, Calliax lobata (De Gaillande & Lagardère, 1966) and Calliaxina punica (De Saint Laurent & Manning, 1982), of the family Eucalliacidae Manning & Felder, 1991 [sensu Sakai, 2011], are commented upon. The descriptions given herein result from the examination of specimens collected from Ise-Shima, Mie Prefecture and Ôfunato-City, Iwate Prefecture, as well as from Iriomote Island, Ryukyu Islands, Japan, and from material collected from Salamis, Saronikos Gulf, Greece, and the Palinuro Seamount, southern Tyrrhenian Sea, Italy.

Seafloor mapping using high-resolution multibeam backscatter: The Palinuro Seamount (Eastern Tyrrhenian Sea)

ABSTRACTWe present a seafloor map of the summit of Palinuro Seamount, an E–W elongated volcanic ridge located in the Eastern Tyrrhenian Sea. The seafloor was mapped using multibeam backscatter and seafloor samples collected between 80 and 1000 m below the sea level. The high-resolution imaging of the Palinuro seafloor was obtained by merging a Digital Terrain Model with a 2.5 m-sized grid and a backscatter mosaic with 2.5 m pixel. The resulting 1:20,000 scale map includes six main facies recognized based on their backscatter properties. These six facies reflect different lithologies. The Palinuro seafloor map represents a useful tool for morphological and geological studies of the Palinuro volcanic ridge.

Factors influencing the abundance of deep pelagic bioluminescent zooplankton in the Mediterranean Sea

Measurements of the density of deep pelagic bioluminescent zooplankton (BL) were made with the Intensified Silicon Intensifier Target (ISIT) profiler in the Ligurian, Tyrrhenian, Adriatic, Ionian Seas and the Strait of Sicily from ∼300 m to near seafloor. Mean BL densities ranged from 2.61 m −3 at 500–1000 m depth in the Adriatic Sea to 0.01 m −3 at 4000–5000 m depth in the E Ionian Sea. We investigated drivers of spatial variation of deep pelagic BL density. Linear regression was applied between surface chlorophyll a (Chl a) concentration and underlying BL density. Chl a values were determined from satellite derived 100 km radius composites (six 10-day means per ISIT deployment, over preceding 60 days). At 500–1000 m depth we found a significant positive relationship between mean BL density and mean Chl a in the period prior to 0–10 days (at 1% level) and prior to 10–40 days (at 5% level). Beyond 40 days no relationship between BL density and Chl a was found at this depth. At depths 1000–1500 m BL density values were low and no significant relationship with Chl a was detected. Generalised additive modelling (GAM) was used to assess the influence of benthic hotspots (seamount; cold water coral mound; mud volcano) on overlying BL density. A reduction in BL density was found downstream of the Palinuro seamount from 300 to 600 m. No effect on BL density in the overlying water column was detected from the presence of cold water corals. Higher BL densities were detected over the W Madonna dello Ionio mud volcano than at other sites sampled in the NW Ionian Sea. We find surface Chl a to be a good predictor of BL density in the mesopelagic zone; below this depth we hypothesise that processes affecting the efficiency of particle export to deep water may exert greater influence on BL density.

The use of high-resolution elevation histograms for mapping submerged terraces: Tests from the Eastern Tyrrhenian Sea and the Eastern Atlantic Ocean

Histogram plots can be used as a cost- and time-efficient tool to detect horizontal or gently dipping geomorphic surfaces within a background regional topography. One of the main classes of these surfaces is typified by terraces formed during marine still-stands. This contribution uses elevation histogram plots as morphometric indicators for detecting the possible existence of concealed terrace orders in Digital Elevation Models (DEMs) derived by the processing of bathymetric data. The approach is particularly useful when dealing with submerged terraces and platforms, because of the obvious difficulties in mapping those surfaces. The advantage of using this indicator consists in the rapid identification of DEM recurrent bathymetric values. This tool is most powerful when dealing with shortly developed terraces and/or multiple terrace orders, whose detection could have been missed by direct observation. Two case studies characterized by the presence of a single terracing event are tested: the southern slope of the Ischia Island and the top of the Palinuro Seamount, both located in the Eastern Tyrrhenian Sea Margin. Elevation histograms are used for terrace order computation in a more complex setting, the Gorringe Bank, located offshore SW Portugal in the Eastern Atlantic Ocean. The results show that a joint use of elevation histogram computation and geomorphologic analysis can be particularly efficient in the study of planar surfaces.

DTM-based morphometry of the Palinuro seamount (Eastern Tyrrhenian Sea): Geomorphological and volcanological implications

We present a high resolution DTM of the Palinuro Seamount (PS, Tyrrhenian Sea, Italy) resulting from the processing of multibeam swath bathymetry records acquired during the second leg of the “Aeolian 2007” cruise. PS consists of several superimposed volcanoes aligned along a N100°E strike and measures 55 × 25 km. The western and the central sectors result from the coalescence of collapse structures (calderas) with younger volcanic cones. The eastern sector reveals a more complex and articulated structure. In the central sector, a volcanic crater with a well-preserved rim not obliterated by erosional events suggests a volcanological rejuvenation of this sector. The presence of flat surfaces on the top of the seamount may be due to the formation of marine terraces during the last sea-level lowering. Lateral collapses on the northern and southern flanks of the seamount are probably related to slope instability, as suggested by the presence of steep slopes (25–40°). The main fault affecting PS strikes N65°E and shows a right lateral component of movement. E–W and N10°E striking faults are also present. Assuming that the N100°E deep-seated fault, which is responsible for the emplacement of PS, moved with sinistral slips, we interpret the N65°E and the N10°E faults as right-lateral (second order) shear and left-lateral (third order) shear, respectively. Due to the particular location of the Palinuro Seamount, the data presented here allow us to better understand the volcanism and the geodynamic processes of the Tyrrhenian Sea.

Rapid 3‐D forward model of potential fields with application to the Palinuro Seamount magnetic anomaly (southern Tyrrhenian Sea, Italy)

We show a set of forward model equations in the Fourier domain for calculating the 3‐D gravity and magnetic anomalies of a given 3‐D distribution of density or magnetization. One property of the potential field equations is that they are given by convolution products, providing a very simple analytic expression in the Fourier domain. Under this assumption, the domain of the density or magnetization parameters is connected by a biunivoc relationship with the data space, and potential field anomalies can be seen as filtered versions of the corresponding density or magnetization distributions. A very fine spatial discretization can be obtained by using a large number of points within a unique 3‐D grid, where both the source distributions and field data are defined. The main advantage of this formulation is that it dramatically reduces execution times, providing a very fast forward model tool useful for modeling anomalies at different altitudes. We use this method to evaluate an average magnetization of 8 A/m for the Palinuro Seamount in the Tyrrhenian Sea (southern Italy), thus performing a joint interpretation of morphological and newly acquired magnetic data.

Tephrostratigraphy study for the last 18,000 14C years in a deep-sea sediment sequence for the South Adriatic

A detailed tephrostratigraphy supported by accelerator mass spectrometry (AMS) 14C dating and isotopic and geochemical analyses has been carried out for a deep-sea core collected from the Southern Adriatic Sea, which spans the last 18 14C kyr. Fourteen ash layers have been recognized in the marine core and the origin was determined by comparing their age and geochemistry with tephra detected in terrestrial deposits. The geochemical signatures of marine ash layers indicate a prevailing Campanian and subordinate Etnean and Eolian provenances. Collectively, they are attributed to sources in the Phlegraean Fields (LAM-Lagno Amendolare; LN1/LN2-GM1; C-2/NYT-Neapolitan Yellow Tuff; C-1-Agnano Pomici Principali; AMS/PF-Agnano Monte Spina; AST-Astroni), Somma-Vesuvius (L9-Pomici di Base; L8-Greenish), Mount Etna (Et1-Y1-Biancavilla Ignimbrite), Lipari (E-1-Gabellotto-Fiumebianco) and Palinuro seamount (Pal 1). Some of these eruptions have been detected for the first time in marine cores (Astroni, LAM, L9, L8), and three were detected and dated by marine tephra (LN1, LN2, and Pal 1) providing new more precise stratigraphic markers for the last 18 kyr in the South Adriatic marine record.

Copper-ore grade hydrothermal mineralization discovered in a seamount in the Tyrrhenian Sea (Mediterranean): Is the mineralization related to porphyry-coppers or to base metal lodes?

A luzonite and tennantite-tetrahedrite-bearing massive sulfide mineralization was discovered when sampling the crater of the Palinuro seamount, located within a probable island-arc or marginal basin tectonic setting. The mineralization is made up of indurated sulfide crusts interpreted to have been deposited by a seawater/sediment interface and mixed with ooze of organic and volcanic origin. A preliminary investigation of the economic minerals showed besides luzonite and tennantite-tetrahedrite, native (rare) copper?, all associated with pyrite predominantly and baryte. Native silver, bismuthinite and stibnite were also found. A dust-like white precipitate was observed by submersible close to the mineralized zone but no structures or edifices resembling black smokers have yet been identified. Massive pyrite deposits associated with such uncommon mineral assemblages are found in the high level volcanic parts of porphyry copper systems, or associated with base metal lodes. The massive sulfide discovery is suggested to have a volcanogenic exhalative origin and a genetic relationship with porphyry coppers or base metal sulfide lodes.

The Palinuro volcano and magmatism of the southeastern Tyrrhenian Sea (Mediterranean)

The Palinuro Seamount is a complex volcano located along an E-W trending, possibly strike-slip fault system extending seaward of the Calabrian Arc in the southeastern Tyrrhenian Sea. The lavas from its top are Pleistocene in age and display a marked calcalkaline affinity. Age and petrochemistry are almost identical to those of the Aeolian island arc, that have been interpreted as generated by subduction of the eastern Mediterranean beneath the Calabrian Arc. The bathyal plain between these volcanic areas is presently undergoing distension, possibly with marginal oceanization. Here, a third volcano, the Marsili Seamount, again displays in its topmost portions Pleistocene lavas with calc-alkaline affinity. In the southeastern Tyrrhenian sea calc-alkaline magmas thus seem not to be confined to the island arc system, but also characterize volcanics emplaced in apparently quite different structural settings.