Search

A previously unknown submerged volcanic field offshore western Sardinia (western Mediterranean Sea), has been identified based on swath bathymetric data collected in 2009, 2010 and 2013, and high-resolution seismic profiles collected in 2011 and 2013. About 40 conical-shaped volcanic edifices (maximum width of about 1600 m and maximum height of about 180 m) and several lava outcrops (up to 1,200 m wide) were recognized at 20 to 150 m water depth over an area of 800 km. The volcanic edifices are mainly eruptive monogenic vents, mostly isolated with a rather distinct shape, or grouped to form a coalescent volcanic body in which single elements are often still recognizable. High-resolution seismics enabled identifying relationships between the volcanic bodies and continental margin successions. The edifices overlie a major erosional surface related to the margin exposure following the Messinian salinity crisis, and are overlain by or interbedded with an early Pliocene marine unit. This seismo-stratigraphic pattern dates the volcanic activity to the early Pliocene, in agreement with the radiometric age of the Catalano island lavas (4.7 Ma) reported in earlier studies. The morphometry of the volcanic bodies suggests that cone erosion was higher at shallow water depths. Indeed, most of the shallow edifices are strongly eroded and flattened at 125 to 130 m water depth, plausibly explained by recurrent sub-aerial exposure during Pleistocene sea-level lowstands, whereas cones in deeper water are much better preserved. Volcanic vents and lava deposits, hereafter named the Catalano volcanic field (CVF), are emplaced along lineaments corresponding to the main directions of the normal fault system, which lowered the Sinis Basin and the western Sardinia continental margin. The CVF represents a volumetrically relevant phase of the late Miocene - Quaternary anorogenic volcanic cycle of Sardinia, which is related to the first stage of the extensional tectonics affecting the island since the late Miocene. [ABSTRACT FROM AUTHOR]

Multibeam echosounder data collected along the shelf of the western Sardinia margin (western Mediterranean Sea) revealed the occurrence of isolated dunes at a water depth of 35–40 m, linear and crescent-shaped sorted bedforms in the depth range of 43–70 m and crescent and irregular-shaped dunes at deeper sectors of the shelf, at a 73–87 m depth range. The morphodynamics of the seabed was analyzed by coupling multibeam backscatter data calibrated with ground truth sediment samples. The linear and crescent-shaped sorted bedforms in the depth range of 43–70 m are formed by a sequence of slight depressions characterized by coarse-grained sediments which alternated with elongated bodies, composed of finer sand, spaced ten to hundred meters apart and < 1 m high. The shelf sector, where the sorted bedforms occur, shows a terraced morphology, with planar sectors connected by gentle slopes. The sorted bedforms are generally oriented southwest to northeast, forming sequences of parallel crests which are located at the edge of the terraces. The analysis of very high-resolution seismic records suggests that the terraces are transgressive depositional sedimentary bodies forming prograding wedges. The analysis of the threshold hydrodynamic conditions for the motion of the sediment which forms the bedforms and the comparison of multibeam and sidescan sonar data collected over a 7-year time span revealed that the sorted bedforms migrate, and they are subjected to a regular forcing by the most severe storm waves from the NW. Sorted bedforms were not found in shallower water, where they are probably ephemeral features rapidly degraded by multi-directional waves and currents. At deeper sectors, > 70 m, wave energy is not strong enough to transport sediments and mud deposition prevails. We proposed an evolutionary model of the formation of prograding wedges and sorted bedforms off the western Sardinia shelf during the last sea-level rise. The landward migration of the shoreline subsequent to pulses of sea-level rise caused the deposition of prograding sandy wedges at different depths. Based on the present-day depth distribution, we can infer that the formation of persistent sorted bedforms over the edges of the terraces started after the sea level rose to a depth of 40 m over the seafloor where these bedforms occur. [ABSTRACT FROM AUTHOR]

De Falco, G., Budillon, F., Conforti A., De Muro, S., Di Martino G., Innangi, S., Perilli, A., Tonielli, R., Simeone, S. 2014. Sandy beaches characterization and management of coastal erosion on western Sardinia island (Mediterranean sea). In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 395-400, ISSN 0749-0208. Coastal erosion is a global problem which affects sandy and rocky shores worldwide. Coastal erosion can be triggered by several causes. Local processes can generate erosion hot spots, whereas at the global scale, the main forces are sea level rise, changes in storm climate and human interference. Beaches along the Mediterranean sea are strongly affected by coastal erosion. Recently, the Protocol on Integrated Coastal Zone Management in the Mediterranean (PAP/RAC 2007) recommended the prevention of erosion processes by restoring the natural adaptive capacity of the coast and by improving the knowledge on the state, development and impact of coastal erosion. In order to achieve the objective of the PAP/RAC protocol, we characterized 24 sandy beaches along ~270 km of the western coastline of the Sardinia island (western Mediterranean). Grain size and mineralogy of the foreshore sediments were analyzed and the intertidal elevation/bathymetric profile were measured using the Differential Global Positioning System. Aerial photos were used to identify the shoreline configuration, the number of bars and morphodynamic features. A digital elevation model (DEM) of the adjacent shelf was produced and acoustic backscatter, grab and box-corer sediment samples were collected in order to characterize the seafloor and to identify the substrate lithology, particularly the distribution of sandy sediments. The investigated coastline is characterized by linear, multibarred beaches and wide transgressive dune fields formed by terrigenous and coarse sand. These linear beaches are alternated with embayed beaches which locally show a mixed terrigenous/bioclastic carbonate composition. Large sandy bodies were found in the inner shelf, often forming dune fields which were uncovered by mud drapes. A database was created to facilitate the characterization of the beach systems along the studied coastline and adjacent inner shelf. It is anticipated that the database will be used by policy makers in support of the implementation of coastal erosion management strategies. [ABSTRACT FROM AUTHOR]

The Bulgheria canyon-fan system in the eastern Tyrrhenian Sea displays well-developed, small-scale, fluvial-like features and has formed alongside the northern slope of the Sapri peri-Tyrrhenian basin. This study reveals, for the first time, the morphology and course of the present-day system as well as the buried elements based on a Digital Terrain Model and high-resolution seismic profiles interpretation. Two adjacent canyons (Infreschi and Luna) originate in the Cilento outer shelf at a short distance from each other and feed an intraslope basin fan through two main sub-parallel channels that run about 12 and 8 km, respectively. Channel and levee development seems to be controlled primarily by the local slope gradient and by Coriolis forces that induce a faster vertical growth of the right-side features, as is often observed in the Northern Hemisphere. Centrifugal forces, on the other hand, have induced episodic flow-stripping at the meander loops and bends, causing local destruction of the main channel levees rather than new levee growth at the outer bends. Overbank deposits are associated with overspill turbidite deposition in the mid fan where a topographic constraint occurs, whereas large-sediment, low-angle wave fields are mainly developed on the outer fan. Buried features and relict morphologies suggest that the Infreschi channel experienced at least two phases of re-incision since the final stages of the middle Pleistocene. Local re-adjustment of outer lobe growth due to channel avulsion and meander abandonment is possibly a consequence of relative base-level fluctuations. The sedimentary record of the mid and outer fan includes outrun mass wasting deposits from extensive failures of the Sapri slope. Indeed, a marked scar is present on the eastern side of the modern outer lobe that indicates the persistency of mass flow passages up to recent times. In addition to the environmental factors that are currently considered to cause canyon formation on the shelf margin, this study proposes the possibility that the head canyon branch close to the mainland was incised by massive and persistent underground freshwater flow from the adjacent aquifer when the sea-level was lower than at present. [ABSTRACT FROM AUTHOR]

The Mediterranean Sea is a miniature ocean ideal to test the response of marine ecosystems to amplified orbital and suborbital climate changes. Here we present coccolith data from a Sardinia Channel gravity core (Arcose C_33) analysed over the last 145,000 years, with a mean resolution of about 900 years. The study highlights that regional phytoplankton assemblages underwent significant modifications between the penultimate glacial and the last interglacial, as well as between the last glacial and the Holocene. The N ratio palaeoproductivity index suggests reduced productivity levels and the development of a deep nutricline during the last interglacial and the Holocene. Within the last glacial period, many taxa exhibit abundance fluctuations that parallel oscillations in δ 18 O values of Globigerina bulloides tests. Heinrich events and stadials seem to be associated with drops in primary productivity levels, as already observed in the Alboran Sea and the Sicily Channel. A total of 19 ecobioevents were identified in the Sardinia Channel sediments, including abundance fluctuations of Emiliania huxleyi > 4 μm, Florisphaera profunda and Gephyrocapsa oceanica . The comparison of events across the Mediterranean Sea suggests that traceability applies to the Sicily Channel, Balearic and Tyrrhenian Seas, supporting the adoption of a common ecobiostratigraphic scheme. Less certain is the correlation with the Alboran Sea, although peaks of Helicosphaera carteri and Syracosphaera histrica during Heinrich events and stadials suggest similar nutrient dynamics in response to suborbital climatic variations in the Sicily Channel, southern Tyrrhenian and Alboran Seas. The traceability of events within eastern Mediterranean cores is strongly limited, possibly due to different physico-chemical properties and nutrient dynamics. [ABSTRACT FROM AUTHOR]

This contribution discusses an example of potential multi-hazard effects resulting from an earthquake in a highly seismogenic area of the Mediterranean Sea, the Augusta Bay, which presents high levels of contamination in sediments and seawater, due particularly to high-concentrations of mercury as a result of a long-term industrial exploitation. In particular, a high-resolution hydrodynamic and transport model is used to calculate the effects of enhanced mercury spreading in the open sea after significant damage and collapse of the artificial damming system confining the embayment where a very high concentration of Hg occurs in seafloor sediments and seawater. Coupling high-resolution 3D dynamic circulation modelling and sediment-seawater Hg fluxes calculated using the HR3DHG diffusion-reaction model for both inorganic and organic Hg species offers a valuable approach to simulating and estimating the effects of spatial dispersion of this contaminant due to unpredictable hazard events in coastal systems, with the potential attendant enhanced effects on the marine ecosystem. The simulated scenario definitely suggests that a combination of natural and anthropogenic multi-hazards calls for a thorough re-thinking of risk management in marine areas characterised by significant levels of contamination and where a deep understanding of the biogeochemical dynamics of pollutants does not cover all the aspects of danger for the environment.

The Augusta basin, located in SE Sicily (southern Italy), is a semi-enclosed marine area, labelled as a highly contaminated site. The release of mercury into the harbour seawater and its dispersion to the blue water, make the Augusta basin a potential source of anthropogenic pollution for the Mediterranean Sea. A mass balance was implemented to calculate the HgT budget in the Augusta basin. Results suggest that an average of ∼0.073 kmol of HgT is released, by diffusion, on a yearly basis, from sediments to the seawater, with a consequent output of 0.162 kmol y(-1) to coastal and offshore waters; this makes the Augusta area an important contributor of mercury to the Mediterranean Sea. Owing to the geographical location of the Augusta basin, its outflowing shelf-waters are immediately intercepted by the surface Atlantic Ionian Stream (AIS) and mixed with the main gyres of the eastern Mediterranean Sea, thus representing a risk for the large-scale marine system.