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Abstract The intrusion of relatively warm water onto the continental shelf is widely recognized as a threat to Antarctic ice shelves and glaciers grounded below sea level, as enhanced ocean heat increases their basal melt. While the circulation of warm water has been documented on the East Antarctic continental shelf, the modes of warm water transport from the deep ocean onto the shelf are still uncertain. This makes predicting the future responses of major East Antarctic marine-grounded glaciers, such as Totten and Ninnis glaciers, particularly challenging. Here, we outline the key role of submarine canyons to convey southward flowing currents that transport warm Circumpolar Deep Water toward the East Antarctic shelf break, thus facilitating warm water intrusion on the continental shelf. Sediment drifts on the eastern flank of the canyons provide evidence for sustained southward-directed flows. These morpho-sedimentary features thus highlight areas potentially prone to enhanced ocean heat transport toward the continental shelf, with repercussions for past, present, and future glacial melting and consequent sea level rise.

Abstract This paper presents the results of the interpretation of a set of high‐resolution seismic lines integrated with multibeam echosounder data acquired in a coastal area in the Northern Adriatic Sea. The aim of the study was to reconstruct the stratigraphic evolution of a late Quaternary sedimentary succession offshore the town of Bibione, North‐Eastern Italy, by recognising the key unconformities, identifying the main depositional units, dating them and reconstructing the depositional environments in relation to relative sea‐level variations. Specifically, four sedimentary units, separated by erosional unconformities associated with the development of deep channels, were identified and dated based on literature information. By interpreting the seismic data, sedimentary dynamics were reconstructed and palaeoenvironments identified. The lower unit corresponds to a paludal environment, showing abundant gas seeps and accumulations (bright spots); the two intermediate units correspond to fluvial deposits, filling the deep incisions that characterise the bounding surfaces. Finally, the shallowest unit, bounded by a wave‐ravinement surface incised by tidal currents, corresponds to the Holocenic progradation of the coastal wedge. In addition, several vertical gas chimneys were identified, ranging in width from a few metres to 20–30 m. These were present in all units, often reaching the sea floor. Finally, elongated mounds, about 300 m wide, at the sea floor were recognised. The bathymetric and seismic characteristics of these elongated bodies and their relationship to adjacent sedimentary bodies suggest that they are probably methane‐derived carbonate formations known as ‘Trezze’ or ‘Tegnùe’. These names recall the fact that the trawls of the local fishermen were often hindered (‘tegnù’ in the Venetian language) or even cut off by these formations.

Widespread volcanism has been known in the Sicilian Channel for a long time, even if some submarine volcanoes have only recently been discovered. Most of this volcanism formed along the NNE-trending transfer zone known as the Capo Granitola–Sciacca Fault Zone, while others, such as the islands of Pantelleria and Linosa, are associated with the continental rift zone that has developed since the early Pliocene in the central part of the Sicilian Channel through the formation of three deep tectonic troughs (Pantelleria, Linosa and Malta). However, the origin of a group of five volcanoes (here called “Tetide volcanic cluster”) that form a NW-SE alignment on the eastern edge of the Adventure Plateau is not yet known. In this work, we hypothesize that this volcanic alignment may represent the remnants of a failed rift attempt that was unable to generate another tectonic trough in the Sicilian Channel. Based on seismic sections and gravimetric data, three phases in the formation of this volcanic alignment can be identified: (i) a major magmatic intrusion in the early Pliocene associated with a NW-SE normal fault that formed during the opening of the Pantelleria graben, leading to the uplift and deformation of the host sedimentary rocks; (ii) a late Pliocene-Quaternary tectono-magmatic quiescent phase; and (iii) a renewed magma intrusion through fissures or cracks that led to the formation of the volcanoes in the late Quaternary. This process was not able to cause significant extension and only limited volcanism, which is why the “Tetide volcanic cluster“ is interpreted as the morphological expression of a failed rift.

The Pantelleria Vecchia Bank, a fascinating shoal in the Sicilian Channel, exhibits enigmatic underwater morphological and geological features. These have led to speculation about the possibility that this site may once have hosted an ancient settlement, dating back to a time around 9000 years ago when this bank was still above sea level. In this paper, we focus on a previously little-explored area in the northeastern part of the shoal, where a sequence of regularly arranged concentric half-rings was found in water depths of 30–34 m, the origin and purpose of which is still unclear. Using multibeam echosounder bathymetry, high-resolution seismic profiles, underwater imagery and petrographic analysis, we are beginning a comprehensive investigation of these concentric semicircles. Analysis of the data and examination of their geometry and structure suggest an artificial rather than a natural origin, leading us to hypothesize various possible meanings and functions.

Engineers need to know properties of shallow marine sediments to build piers, pipelines and even offshore windfarms. We present a method for estimating the density, P velocity and thickness of these sediments. The traveltime inversion of primary and multiple reflections enables their semiquantitative estimation in marine surveys when using a minimal acquisition system such as a monochannel Boomer. Picking errors, ambient noise and interfering events lead to significant errors in the estimates. Similar, albeit milder, instabilities occur when inverting the signal amplitudes to determine the reflectivity of the layer interfaces. In this paper, we introduce a coupling between the separate inversion of amplitudes and traveltimes to obtain a better Earth model. The P velocity shows up in two stable terms provided by the separate inversions: the acoustic impedance of shallow sediments (through the amplitudes) and the transit time across the sediment layer (through the traveltimes). We couple the two inversion engines by imposing a smoothness condition on velocity and density and thickness of the layer while keeping the impedance and traveltime constant. We thus exploit the ambiguity of the solution to introduce geological criteria and reduce the noise contribution. We validated the proposed method with synthetic and real data.

The Pantelleria Vecchia Bank is a submerged calcareous-arenitic shoal in the NW sector of the Sicilian Channel. Together with other morphological heights, some of which are volcanic in origin, this shoal punctuates the shallow Adventure Plateau, which was above sea level from the Last Glacial Maximum until at least 9000 years ago. The rise in sea level caused by the melting of the ice caps gradually flooded the plateau, isolating the heights and creating a broad archipelago until the area was finally submerged. High-resolution Multibeam bathymetric mapping shows that the Pantelleria Vecchia Bank has an 820 m long rectilinear ridge connecting the two main shoals of the bank, and an 82 m long ridge perpendicular to the 820 m ridge 100 m from its southern end. The top of the 820 m ridge lies in a water depth of 35 m, its base in about 42 m, and the seaward side has a fairly uniform slope of 16°–22°. The 82 m ridge has an average width of ∼7 m and rises ∼1 m above the surrounding seafloor. Underwater photographs document that the entire seaward side of the 820 m ridge consists of juxtaposed blocks, the largest measuring about 3 × 4 m, some of which are rectangular in shape, while the upper part consists of horizontally arranged blocks and the lower part of sub-vertical blocks embedded in the sediments. Petrographic analyses show that the blocks forming the seaward side of the 820 m ridge can be classified as late Pleistocene calcirudites, while the 82 m ridge consists of bioclastic calcarenites of Tortonian age. A series of high-resolution seismic profiles crossing both ridges and composite mosaics of the seafloor obtained from underwater videos provide a comprehensive panorama of these two peculiar and in many ways enigmatic structures. The structures described and the palaeogeographical context in which they are embedded do not exclude the possibility that they are artefacts indicating an ancient temporary or permanent human presence in the Pantelleria Vecchia Bank.

The ancient Greek colony of Selinunte, with its acropolis on a promontory on the south-western coast of Sicily, is flanked by two valleys where two modest rivers flow today: the Modione to the west and the Cottone to the east. Archaeological reconstructions, historical documents from various sources, and recent remote sensing surveys indicate two important bays corresponding to the ancient mouths of these two rivers, now completely covered by a thick layer of sediments. It is believed that the ports of the colony were located in these bays, although the remains of these ports are still sparse and contradictory. Here we present a multibeam bathymetric map of part of the marine area immediately off Selinunte and a series of high-resolution seismic profiles acquired parallel to the coastline. They show the geometries and stratigraphic context of the two buried river valleys offshore, from which information about the palaeoenvironmental setting and evolution of the landscape can be derived and which may be used in adequately guiding future archaeological excavation programs.

The lithological characterization of the seafloor is key information for offshore engineering, especially when it comes to pier and platform design. Undetected shallow gas pockets may cause the collapse of heavy platforms for hydrocarbon production. Unconsolidated sediments are not ideal for the basement of wind farms for electric power production. Drilling and coring can be used for local sampling, but continuous profiles or even areal coverage are far more preferable. High-resolution seismic profiles are successfully used when ports are not too busy, but otherwise, single-channel systems must be used. We show in this paper that even these simpler systems can be used to estimate parameters such as the acoustic impedance of shallow sediments directly beneath the seafloor. We exploit the amplitude decay of the multiple reflections between the seafloor and the surface, which does not depend on the source energy. If the offset between source and receiver is not too small, we can estimate the shallow P velocity and, via acoustic impedance, also the rock density.

The Sciacca basin extends in the southwestern part of Sicily and hosts an important geothermal field (the Sciacca Geothermal Field) characterized by hot springs containing mantle gasses. Newly acquired high-resolution seismic profiles (Boomer data) integrated with a multichannel seismic reflection profile in close proximity to the Sciacca Geothermal Field have documented the presence of numerous active and shallow fluid-related features (pipes, bright spots, buried and outcropping mud volcanoes, zones of acoustic blanking, and seafloor fluid seeps) in the nearshore sector between Capo San Marco and Sciacca (NW Sicilian Channel) and revealed its deep tectonic structure. The Sciacca Geothermal Field and the diffuse submarine fluid-related features probably form a single onshore–offshore field covering an area of at least 70 km2. This field has developed in a tectonically active zone dominated by a left-lateral transpressive regime associated with the lithospheric, NNE-striking Sciacca Fault System. This structure probably favored the rising of magma and fluids from the mantle in the offshore area, leading to the formation of a geothermal resource hosted in the Triassic carbonate succession that outcrops onshore at Monte San Calogero. This field has been active since the lower Pleistocene, when fluid emissions were likely greater than today and were associated with greater tectonic activity along the Sciacca Fault System.

Conventional multichannel surveys provide good images in 2D and 3D of the Earth in depth, which are successfully used for the oil and gas industries. However, their cost and environmental impact make them rarely affordable for engineering applications, especially for offshore infrastructures. In this case, monochannel systems, such as Boomers, having cables that are a few-meters long, provide time-domain images that are useful but miss relevant lithological information for engineers, such as the P-wave velocity of shallow layers. In this paper, we present a tomographic approach that exploits multiple reflections, in addition to primaries and direct arrivals, which work for monochannel surveys with a short offset. It can detect lateral variations of velocity and thickness of the first layer under the sea floor. Two complementary algorithms are compared: a pure tomographic inversion, and a tuning exploiting the classical Dix formula; the first one is more precise, while the second is more robust with respect to noise. A two-step inversion with incidence-angle parametrization performs slightly better than a single-step algorithm based on the direct traveltime inversion. We validate the method by synthetic and real data examples.

The shallow P velocity provides relevant information for offshore engineers, in planning pipelines, piers, and platforms. Standard multichannel surveys trailing long cables provide good estimates but may require stopping other ongoing operations or may affect the environment. Monochannel surveys by Boomer systems involve a very short cable, so those drawbacks are minimized; however, this comes at the cost of loss of information for estimating the P velocity of shallow layers. In this paper, we present a new method exploiting multiple reflections for characterizing the seafloor. After validation of the algorithm by a synthetic example, we tested this approach in a marine survey acquired by a Boomer system at the Gulf of Trieste (Italy).

The increasing demand for freshwater requires the identification of additional and less-conventional water resources. Amongst these, offshore freshwater systems have been investigated in different parts of the world to provide new opportunities to face increasing water requests. Here we focus on the north-eastern Adriatic Sea, where offshore aquifers could be present as a continuation of onshore ones. Geophysical data, in particular offshore seismic data, and onshore and offshore well data, are interpreted and integrated to characterise the hydrogeological setting via the interpretation of seismo-stratigraphic sequences. We focus our attention on two areas located in the proximity of the Tagliamento and Isonzo deltas. Well and seismic data indicate that the Quaternary sediments, that extend from onshore to offshore areas, are the most promising from an offshore freshwater resources point of view, while the several kilometres thick pre-Quaternary carbonate and terrigenous sequences likely host mainly salty waters.