1,721,104 research outputs found
Massive benthic litter funnelled to deep sea by flash-flood generated hyperpycnal flows
Full text linkMarine litter is an emerging environmental threat affecting all world’s oceans including the deep seafloor, where the extent of the phenomenon is still largely unknown. We report the spatial patterns of macro-litter distribution within the Messina Strait’s channels (Central Mediterranean), focusing on the transfer mechanisms responsible for its emplacement, a key information to better understand litter distribution. Litter is patchy but pervasive on all surveyed channels, reaching densities up to ~200 items/10 m, the highest reported for the deep sea until now. Litter is often arranged in large accumulations formed by hundreds of land-sourced items, mixed to vegetal and coarse-grained debris, indicating an emplacement from sedimentary gravity flows. Such impressive amount of litter can be explained by the superposition of a very efficient source-to-sink sedimentary transport and a strong urbanization of the coastal area. These findings point out that macro-benthic litter pollution is a major, often overlooked, threat for deep-sea ecosystems. Further explorations are thus required in similar marine settings to fully understand the magnitude of the problem, since they may represent the largest litter hotspots in the deep-sea
The key role of canyons in funnelling litter to the deep sea. A study of the Gioia Canyon (Southern Tyrrhenian Sea)
No full textLitter is a significant environmental issue, threatening all ocean environments including the deep sea, where little is known about the extent of the threat. This study collected underwater videos on shelf-indenting canyons (the Gioia and Petrace Canyon) and adjacent sectors to characterize benthic litter and its distribution patterns. A high density of litter was present in the canyon thalwegs (up to 56.3 items/100 m), where ∼95 % of observed debris was concentrated. Litter primarily comprised of plastic (∼90 %). The presence of household objects intermingled with vegetal material indicates a strong influence of land-based sources for litter in these areas. Sedimentary gravity flow processes transported natural and anthropogenic debris downslope and may determine its burial beneath the seafloor. Another litter transport mechanism is the presence of light items, observed while drifting above the seafloor under the action of down-canyon bottom currents. This phenomenon was frequently documented within Gioia Canyon, where up to 74 drifting items were counted in one hour of video. Conversely, a lower litter concentration was found along the continental margin, where items were mostly fishing-related. Findings from this study confirm that canyons act as conduits for land-sourced debris and litter transport from coastal to deep-sea environments. The funnelling of a large amount of plastic to the deep sea through multiple processes indicates that the magnitude of this pollution may be greater than expected. This pollution could concentrate in canyons along continental margins and possibly at the mouths of canyons at the base of the slope. This issue requires urgent attention, as understanding of deep-sea litter distribution is still limited and potential impacts to benthic ecosystems are poorly understood
Amino acids in surface sediments of the Zannone Island shelf (Western Mediterranean Sea): Possible bioindicators of submarine hydrothermal activity
No full textThis study shows results from amino acid analysis of seafloor sediment sampled between ~80 and ~130 m depth, within an active hydrothermal field located off Zannone Island (Tyrrhenian Sea). The total hydrolysable amino acid (THAA) content was determined at eight stations, three located within the main hydrothermal depression (i.e. the Zannone Giant Pockmark, ZGP) and five located in the surrounding seafloor. THAA concentration ranged between ~2 and ~11 nmol mg−1 dw and the lowest THAA concentrations were found at stations located within the ZGP. Amino acids resistant to degradation or originating from bacteria (β-alanine, histidine, leucine, arginine and lysine) had higher relative abundances inside the ZGP, whereas amino acids susceptible to degradation or originating from cellular plasma (proline, phenylalanine and tyrosine) showed higher relative abundances outside the ZGP. Degradation and reactivity indices were calculated, and the sedimentary organic matter in the three outside ZGP stations B07, B08 and B09 was found to be the most labile and reactive. Together with THAA concentrations, sediment grain size and carbon percentages were measured at 12 stations, five located within the ZGP and seven located outside the ZGP. At all stations, the percentage of sand was ~75% or higher. Carbon percentages were lower in samples located inside the ZGP than in the surrounding stations. The southern outside ZGP station B12 was found to be similar in terms of amino acids composition to the three inside ZGP stations, suggesting the influence of the hydrothermal fluids at this station
Kinematics and the tsunamigenic potential of Taranto Landslide (northeastern Ionian Sea): Morphological analysis and modeling
No full textIn the northeastern sector of the Ionian Sea, offshore of Taranto coast, there is an impressive landslide. This landslide, named Taranto Landslide, has an estimated volume of 0.30 km3, and it is larger than other landslides identified across the Apulian slope. The Taranto Landslide is classified as a slide; the headwall is at a depth of 370 m, the toe is at a depth of 900 m, for a total length of about 9 km. The sediment accumulation area, starting from a depth of 570 m and ending at a depth of 900 m, is due to processes of rapid emplacement. The landslide tsunamigenic potential has been assessed by empirical calculation assuming a mass translation of the involved sediments, the height of the wave that could be generated is about 1.75 m. Values of this magnitude are potentially dangerous for coastal infrastructures
Morpho-stratigraphic evolution of a tectonically controlled canyon-channel system in the Gioia Basin (Southern Tyrrhenian Sea)
No full textThe Gioia-Mesima Canyon-Channel System (GMS) incises the northern part of the Gioia Basin, a post-Tortonian
intra-slope basin located along the south-eastern Tyrrhenian margin. Integration of multibeam, side scan sonar
and seismic reflection data allowed to reconstruct the morpho-stratigraphic evolution of the GMS and the main
factors controlling its development and maintenance. The GMS drains the entire continental margin and displays
a complex morphology consisting in two main courses: the Gioia-Petrace Canyon and the Mesima CanyonChannel. These courses run parallel to each other, changing from narrow straight to meandering geometry
until they merge into a single, relatively straight lower reach, which debouches in the Stromboli Valley. Seismic
reflection profiles and morphometric analysis highlight a strong tectonic control on GMS location and
morphology throughout its course. At large scale, tectonic structures cross cutting the GMS caused both the
formation of a mini-basin in the upper slope and a larger confined sub-basin downslope. These features promote
abrupt changes in slope gradients that in turn are reflected on the plan-view morphology and stratigraphic architecture (seismic facies and sediment depocenters) of the GMS. Particularly, the progressive infilling of the
confined sub-basin caused changes in the GMS base level, determining a polyphased evolution of the system
encompassing repeated erosional and depositional events. The complete infill of the sub-basin promoted a bypass of turbiditic flows in the lower slope, leading to the development of the lower reach of the GMS and its
connection with the Stromboli Valley. This connection favoured a base level lowering of the GMS, causing its
rejuvenation by retrogressive upslope erosion. This stage was recorded only in the shelf-indenting Gioia Canyon,
characterized by a narrow and entrenched course, with irregular longitudinal profile and multiple knickpoints.
Based on these results, we propose an evolutionary architectural model of the GMS to point out how erosional
and depositional processes of channel/canyon system in a tectonically controlled margin can rapidly change in
space and time in relation to multiple factors
Morpho-sedimentary characteristics of the volcaniclastic apron around Stromboli volcano (Italy).
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Megafauna distribution along active submarine canyons of the central Mediterranean: Relationships with environmental variables
Full text linkThe tectonically-controlled margins off Southern Italy are carved by several shelf-indenting submarine canyons that are periodically flushed by sedimentary gravity flows. In this study, the distribution of benthic and demersal megafauna within the thalweg of some of these canyons (i.e. the Gioia-Petrace and Caulonia Marina canyons in the Tyrrhenian and the Ionian Calabrian margins, respectively, and the Sant'Agata, San Gregorio, Tremestieri and Messina canyons in the Messina Strait) was studied using Remotely Operated Vehicle video transects. The relationships between fauna distribution and environmental conditions (i.e. seafloor type, depth, slope, aspect and canyon system) extracted from video footage and bathymetric data were assessed to identify the main physical drivers influencing the megafaunal assemblages within active submarine canyons. These latter have their heads in shallow water, so representing highly dynamic environments affected by present-day sediment transport. Hierarchical Cluster Analysis allowed to distinguish seven different assemblages occurring in the study areas. PERMANOVA analysis showed significant differences among species groups associated to different seafloor types, depth ranges and canyon systems. Distance-based linear modeling (DistLM) identified the canyon system as the main factor explaining the variability of the megafaunal assemblages across the study areas. In the Gioia and Petrace canyons, both characterized by homogenous fine-grained sediment, the assemblages were mainly dominated by Polychaeta Sabellidae and Ceriantharia. The almost total absence of sessile fauna at the canyons’ head was interpreted as an effect of a strong physical disturbance due to the impact of sedimentary flows. In the canyons of the Messina Strait, the presence of more varied seafloor encompassing fine and coarse sediment along with an higher spatial heterogeneity of physical disturbance, determined more diversified faunal assemblages, featuring species associated with hard and soft substrates. More in detail, in the Sant'Agata, San Gregorio and Messina canyons the colonization of cobbles and boulders by slow-growing species vulnerable to physical disturbance such as the gorgonians Acanthogorgia hirsuta and Swiftia dubia was recorded. For the Tremestieri canyons a stronger impact by sedimentary flows was reflected both by a very high abundance of land-based litter and the lowest values of species richness. Interactions between megafauna and marine litter, whose widespread occurrence was recorded on the floor of all these canyons, have been also presented and discussed. Although in several cases litter caused entanglement of benthic species, the anthropogenic debris was also used as growing substrate or shelter by some invertebrates and fishes, suggesting complex fauna-litter interactions that should be better explored. Overall, the large variability in morphology and seafloor characteristics across the studied canyons is reflected on the variability of megafauna assemblages, suggesting a strong influence of the physical conditions specific of each canyon in controlling fauna distribution
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