Renato Tonielli

Marine Geology and Morphobathymetry in the Bay of Naples (South-Eastern Tyrrhenian Sea, Italy)

Recent multibeam bathymetry (Elac, Bottomchart MK2) and high resolution seismics (Subbottom Chirp and 1–4 kJ Sparker source), acquired in the frame of an on-going programme of sea-floor mapping of Naples and Salerno Bays (south-eastern Tyrrhenian margin, Italy) and financed by the National Geological Survey of Italy, allows to put new insights into the recent evolution of the bay. The morphology and stratigraphy of the continental shelf and slope appear strongly controlled by the interplay of volcanism and canyoning that acted along the Magnaghi and Dohrn axes. Detailed bathymetry reveals the complexity of the drainage pattern which consists of a previously unknown, dense network of minor tributary channels. At places, the Dohrn and Magnaghi canyon walls are intensively affected by slope instability, as evidenced by numerous submarine slides and scars involving large volumes of sediments. Previously unreported mound-shaped morphological highs (“Bacarozzi” Facies), Holocene reworked sediments and sea-bottom creep appear on acoustic Chirp profiles in the inner sectors of the bay and seem to be related to volcano-sedimentary processes. On the contrary, sedimentation over the shelf at the southern edge of the bay (Sorrento-Capri) seems less influenced by volcanic activity and seabed features include Late Pleistocene regressive sand bodies and Holocene patch reefs, coastal dunes and depositional terraces.

Sandy beaches characterization and management of coastal erosion on western Sardinia island (Mediterranean Sea).

ABSTRACT 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.

Biogenic sediments from coastal ecosystems to Beach-Dune Systems: implications for the adaptation of mixed and carbonate beaches to future sea level rise

Coastal ecosystems produce and store carbonate particles, which play a significant role in the carbonate dynamics of coastal areas and may contribute to the sediment budget of adjacent beaches. In the nearshore seabed of temperate zones 10 (e.g. Mediterranean Sea and South Australia), marine biogenic carbonates are mainly produced inside seagrass meadows. This study quantifies the contribution of biogenic sediments, mainly produced in Posidonia oceanica seagrass meadows and secondarily in photophilic algal communities, to the sediment budget of a Mediterranean beach-dune system (San Giovanni beach, western Sardinia, western Mediterranean Sea). A set of geophysical, petrographic and sedimentological data were used to estimate the sediment volume and composition of the beach-dune system as a whole. The San Giovanni beach-dune 15 system contains 3,797,000±404,000 tons of sediments, 83% (3,137,000±404,000 tons) of which are located in the coastal wedge, 16% (619,000±88,000 tons) in the dune fields and 1% (41,000±15,000 tons) in the subaerial beach. The sediments are composed of mixed modern bioclastic and relict bioclastic and non-bioclastic grains from various sources. The system receives a large input of modern bioclastic grains, mainly composed of Rhodophytes, Molluscs and Bryozoans, which derive from sediment production by present-day carbonate factories, particularly P. oceanica seagrass meadows. Radiocarbon 20 dating of modern bioclastic grains indicated that they were produced during the last 4.37 ka. This value was used to estimate the long-term deposition rates of modern bioclastic sediments in the various beach compartments. The total deposition rate of modern bioclastic grains is 46,000±5,000 tons century, mainly deposited in the coastal wedge (39,000±4,000 tons century) and dunes (7,000±1,000 tons century), and 46,000 tons represents ~ 1.2% of the total beach-dune sediment mass. Carbonate production from coastal ecosystems was estimated to be 132,000÷307,000 tons century, 28% (15%÷34%) of 25 which is transported to the beach-dune system, thus significantly contributing to the beach sediment budged. The contribution to the beach sediment budget represents a further ecosystem service provided by P. oceanica, which our data can help quantify. The value of this sediment-supply service is in addition to the other important ecological services provided by seagrass meadows. The dependence of the beach sediment budget on carbonate production associated with coastal ecosystems has several implications for the adaptation of mixed and carbonate beaches to the loss of seagrass 30

Distribution of Posidonia oceanica (L.) Delile meadows around Lampedusa Island (Strait of Sicily, Italy)

ABSTRACT We present a seabed map around Lampedusa, the largest island of the Pelagie Islands Marine Protected Area (Italy, western Mediterranean). The seafloor was mapped using bathymetry and backscatter multibeam systems along with an underwater camera for direct observations and ground truthing, from the coastal area to about 50 m depth. The map was produced to monitor the present-day distribution of the Posidonia oceanica meadows around the Island. P. oceanica is the most important endemic seagrass species of the Mediterranean Sea and it can form meadows or beds extending from the surface to 40–45 m depth. These meadows provide habitat for a large marine community, thus increasing biodiversity of the coastal zone, stabilizing sediments and reducing coastline erosion. The seagrass meadows are susceptible to regression in response to specific impacts, thus their presence and abundance is an indicator of the overall environmental quality of the coastal zone. Recently, within the Marine Strategy Framework Directive (2008/56/EC), P. oceanica has been selected as an indicator of the Good Environmental Status for marine areas. Consequently, the Pelagie Islands Marine Protected Area launched a project to assess the conservation status and map the distribution of P. oceanica meadows. The resulting 1:15,000 scale map includes information about the Mediterranean seagrass and the distribution of five acoustic facies reflecting hard lithologies and soft substrates. The Lampedusa seabed map provides new information, which contributes to the development of a detailed benthic habitat map and a more comprehensive maritime spatial planning of this Marine Protected Area.

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

ABSTRACT We 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.

Seabed mapping in the Pelagie Islands marine protected area (Sicily Channel, southern Mediterranean) using Remote Sensing Object Based Image Analysis (RSOBIA)

In this paper we present the seabed maps of the shallow-water areas of Lampedusa and Linosa, belonging to the Pelagie Islands Marine Protected Area. Two surveys were carried out (“Lampedusa 2015” and “Linosa 2016”) to collect bathymetric and acoustic backscatter data through the use of a Reson SeaBat 7125 high-resolution multibeam system. Ground-truth data, in the form of grab samples and diver video-observations, were also collected during both surveys. Sediment samples were analyzed for grain size, while video images were analyzed and described revealing the acoustic seabed and other bio-physical characteristics. A map of seabed classification, including sediment types and seagrass distribution, was produced using the tool Remote Sensing Object Based Image Analysis (RSOBIA) by integrating information derived from backscatter data and bathy-morphological features, validated by ground-truth data. This allows to create a first seabed maps (i.e. benthoscape classification), of Lampedusa and Linosa, at scale 1:20 000 and 1:32 000, respectively, that will be checked and implemented through further surveys. The results point out a very rich and largely variable marine ecosystem on the seabed surrounding the two islands, with the occurrence of priority habitats, and will be of support for a more comprehensive maritime spatial planning of the Marine Protected Area.

Late Quaternary palaeoenvironmental reconstruction of sediment drift accumulation in the Malta Graben (central Mediterranean Sea)

The Malta Graben is a deep tectonic depression in the Sicily Channel, bounded by NW–SE normal faults and filled by thick Pliocene–Quaternary deposits. A previous analysis of a giant piston core (LC09) from the Malta Graben had revealed a wide range of sedimentary features (carbonate turbidites, bioturbated mud and scours), although the chronostratigraphic constraint of the stacking pattern has remained elusive. After establishing a reliable chronological framework based on seven radiocarbon dates for a shorter core from the Malta Graben (ANSIC03-735), a down-core analysis of planktonic foraminifer and coccolith abundance, stable isotopes and sediment grain size was carried out. Since the last glacial maximum, palaeoenvironmental conditions (surface fertility and deep chlorophyll maximum during the last glacial and the Younger Dryas; warm and oligotrophic water masses, with a deep nutricline and intense winter mixing during the Holocene) as well as selected calcareous plankton taxa trends and peaks seem to be similar to those reported for other central and western Mediterranean sites, possibly in spite of a unique response of these areas to late Quaternary climatic fluctuations. Four distinct layers, each tens of centimetres thick, are barren of foraminifers but not of coccoliths. Morphobathymetric data as well as new high-resolution and high-penetration seismic profiles show that prolonged contouritic activity has persisted on the western side of the Malta Graben. It is thus likely that layers barren of foraminifers are due to the overflow of fine-grained (clayey) material beyond drift channel dikes.

Sorted Bedforms Along the Continental Shelf of Western Sardinia

Two sorted bedforms fields located at the western Sardinian margin are described. Bedforms are developed at the edge of prograding sedimentary wedges related to the last sea-level rise and in a small basin of the inner shelf, surrounded by rocky outcrops. The mechanisms of formation and evolution are discussed in relation with sea-level oscillations, hydrodynamic forcing and complex seabed morphology.

Pinna nobilis within a Posidonia oceanica meadow: evidences of how hydrodynamics define this association in the Gulf of Oristano (West Sardinia, Italy)

The fan mussel Pinna nobilis is the largest bivalve of the Mediterranean Sea, declared protected since 1992. It is a sessile suspension feeder endemic of this basin which lives mainly on soft sediments colonized by seagrass meadows. This study considers a population living within a Posidonia oceanica bed in the Gulf of Oristano (W Sardinia, Italy), a site included within a Marine Protected Area and in two Sites of Community Importance. Based on field surveys conducted in 2007, 2009 and 2014 differences in density, size, and shell burial level of P. nobilis were investigated in relation to meadows distribution and characteristics. Moreover, the spatial differences in density and orientation of P. nobilis were related to hydrological features. P. nobilis showed a mean density of 4.06±1.13 ind./100 m2 and a significant increase in population size was observed between 2009 and 2014. A high-resolution multibeam survey revealed that the P. oceanica bed was characterized by a striped structure. Toward the inner sheltered sector of Gulf, the meadow became hillshaped. A comparison between meadow structure and P. nobilis distribution showed that specimens are mainly located at the edge of the channels within the striped meadow, whereas the edge effect resulted less noticeable within the hill-shaped meadow. The compactness of the seabed influences the shell stability: the burial level decreased with the increasing of fine sediments. Bottom current direction and speed are the main factors influencing shell orientation, whereas wave action is negligible. Where bottom current speed exceeded 0.07 m/s specimens resulted in line with the prevalent current direction with the ventral side exposed to incoming flow. These features suggest that feeding strategy is an important factor in determining shell orientation, possibly in addition to drag. Food availability could be the driving force in determining the patchiness distribution of P. nobilis population with higher values in those sites close to the mouth of the lagoons, in sedimentation area or in the meadow channels where the water flow is conveyed. These findings contribute to increase the knowledge on the P. nobilis-P. oceanica association and provide useful information for improving conservation measures.