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1.
Hydrocarbons in the Mediterranean Sea were analyzed from 1 m depth during the winter of 1974–1975. Petroleum hydrocarbons averaged from 6.9 to 25.8 μg/l, with the Alboran Sea and the area off Libya having the highest concentrations. The freshest petroleum material was found off Libya and in the Tyrrhenian Sea.Considerable amounts of biologically produced hydrocarbon material were also present (0.8–22.8 μg/l). They could only be identified semi-qualitatively but appeared to be quite similar, with the exception of the material from the Tyrrhenian Sea.  相似文献   

2.
Vertical profiles of dissolved organic carbon (DOC) from eight hydrological stations in the Tyrrhenian Sea, Sardinia Channel and Algerian Sea, are reported. DOC exhibits concentrations ranging from 58 to 88 μM in surface water, 43–57 μM in the intermediate layer and 49–63 μM in deep waters. The assessment of the hydrological characteristics allows different water masses in the study area to be identified; moreover, different hydrological processes are observed in the Tyrrhenian and Algerian basins. DOC exhibits different values in the different water masses. The lowest DOC concentrations (43–46 μM) were found in the Tyrrhenian Levantine Intermediate Water (LIW). Correlations between DOC and apparent oxygen utilization (AOU), investigated within each water mass, exhibit different behaviors in the intermediate and deep waters, suggesting the occurrence of different processes of oxygen consumption in the different water masses.  相似文献   

3.
Study of clay sedimentation in the Tyrrhenian area during late Miocene time allows to distinguish continental, synsedimentary, and diagenetic influences on the composition of sedimentary rocks, according to the geographic location. In south Sicily smectite-rich assemblages were mainly eroded from soils developed under subarid conditions. On the eastern margin of Sardinia abundant micaillite was supplied from exposed areas tectonically rejuvenated during the opening of the Tyrrhenian Sea. In the westernmost part of the Tyrrhenian Basin evaporative environments combined to strong geothermal gradient allowed the formation of sediments rich in euhedral chlorite.  相似文献   

4.
《Oceanologica Acta》1999,22(3):281-290
The hydrological structure and the seasonal variability of marine currents in the Tyrrhenian Sea, off the coasts of Latium, are analysed using a data set obtained during several cruises between February 1988 and August 1990. Of particular interest is the fact that the hydrological surveys show the intermittent presence of a current of Levantine Intermediate Water (LIW) flowing anticlockwise along the Italian slope, at 250–700 m. This current is of particular importance in inferring the pathways of the Levantine Intermediate Water in the western Mediterranean Sea and in particular in the Tyrrhenian basin, downstream of the Strait of Sicily. These phenomena remain an open problem: our observations give support to the Millot's proposed general scheme, on the existence of a general cyclonic circulation of the LIW from the Strait of Sicily to the western Mediterranean, as opposed to a direct injection of LIW towards the Algerian basin.  相似文献   

5.
Numerous sapropels and sapropelic strata from Upper Pliocene and Pleistocene hemipelagic sediments of the Tyrrhenian Sea show that intermittent anoxia, possibly related to strongly increased biological productivity, was not restricted to the eastern Mediterranean basins and may be a basin-wide result of Late Pliocene-Pleistocene climatic variability. Even though the sapropel assemblage of the Tyrrhenian Sea clearly originates from multiple processes such as deposition under anoxic conditions or during spikes in surface water productivity and lateral transport of organic-rich suspensates, many “pelagic sapropels” have been recognized. Stratigraphic ages calculated for the organic-rich strata recovered during ODP Leg 107 indicate that the frequency of sapropel formation increased from the lowermost Pleistocene to the base of the Jaramillo magnetic event, coinciding with a period when stable isotope records of planktonic foraminifera indicate the onset of climatic cooling in the Mediterranean. A second, very pronounced peak in sapropel formation occurred in the Middle to Late Pleistocene (0.73-0.26 Ma). Formainifers studied in three high-resolution sample sets suggest that changes in surface-water temperature may have been responsible for establishing anoxic conditions, while salinity differences were not noted in the faunal assemblage. However, comparison of sapropel occurrence at Site 653 with the oxygen isotopic record of planktonic foraminifers established by Thunell et al. (Proc. ODP, Sci. Results 107, 1990) indicates that sapropel occurrences coincide with negative δ18O excursions in planktonic foraminifers in thirteen of eighteen sapropels recognized in Hole 653A. A variant of the meltwater hypothesis accepted for sapropel formation in the Late Pleistocene eastern Mediterranean may thus be the cause of several “anoxic events” in the Tyrrhenian as well. Model calculations indicate that the amount of oxygen advection from Western Mediterranean Deep Water exerts the dominant control on the oxygen content in deep water of the Tyrrhenian Sea. Inhibition of deep-water formation in the northern Adriatic and the Balearic Basin by increased meltwater discharge and changing storm patterns during climatic amelioration may thus be responsible for sapropel formation in the Tyrrhenian Sea.  相似文献   

6.
In this contribution we document an anomalous mucilage growth which occurred in June 2003 along the rocky cliffs of the Portofino Promontory (Ligurian Sea, NW Mediterranean Sea), and we describe its dynamics and its negative effects on many benthic taxa. The zooxanthellate scleractinian Cladocora caespitosa underwent ‘bleaching’ and about 40% of biomass of the erect algae was detached by mucilage ‘lianas’ created and strengthened by bottom currents. The 2003 event differed from any other previously occurred in the northern Tyrrhenian Sea, in that the mucilage aggregates were formed by the free‐living form of the Phaeophyceae Acinetospora crinita (Harvey) Kornmann, a not usually dominant species in mucilage aggregates from the north Tyrrhenian Sea. The damage suffered by the benthic organisms living in this area was curtailed by a severe storm, occurred in July, which removed the mucilage to deeper depths, preventing irreversible damages. Only slow growing, perennant organisms, such as corallinales or scleractinians, were seriously affected, but a survey carried out 1 year later, in June 2004, allowed to appreciate a complete recovery of those organisms. This anomalous mucilage event occurred in coincidence of the 2003 European heatwave, and the anomalous temperature increase of seawater has to be regarded as the major contributing event that led to the mucilage outbreak.  相似文献   

7.
This paper shows the results of a detailed reprocessing of aeromagnetic data, obtained by the downward projection to the seabed. The area of interest is centered over the Tyrrhenian Basin, whose bathymetric–topographic lay-out is characterized by a somewhat irregular trend. The origin of the intense depth variations depends on the Tyrrhenian structural setting, that is associated with the presence of several tectonic lineaments, seamounts or volcanic islands. The data were characterized by good quality and dense sampling, but they have been reprocessed in order either to solve some problems in the original compilation, and to reduce the distortion of the geomagnetic anomaly field caused by the difference of distance between the survey level and the magnetic source. The reprocessed magnetic map is proposed as an effective analysis tool for the Tyrrhenian area that is characterized by high susceptibility lithotypes. Downward projection of the aeromagnetic data by BTM algorithm increases the definition of the anomalous magnetic signal without distortions in the geometric pattern of the field, thus showing a more stable and effective association between the magnetic anomalies and their geological sources. This effect is particularly true for high frequency anomalies that are directly comparable after the topographic projection because the depth filtering effect is attenuated. Moreover, the BTM method has been applied for the first time to a regional scale survey that shows substantial advantages because no fictitious anomalies in the high frequency sector of the spectrum were generated. This has been a typical effect of the traditional downward projection methods widely used before. The final result is a BTM anomaly map that is able to show the structural connections between the geological magnetic sources of the Tyrrhenian Sea area.  相似文献   

8.
Cuvier's beaked whale (Ziphius cavirostris, G. Cuvier 1823) is a poorly known species and many international agreements have asked for a better understanding of its biology for conservation purposes. In the present study, systematic cetacean surveys were carried out from ferries along a trans‐regional fixed transect in the Central Tyrrhenian Sea (Civitavecchia, Latium – Golfo Aranci, Sardinia), just outside the southeastern border of the Pelagos Sanctuary. This research provided long‐term, consistent data on Cuvier's beaked whale during two research periods (1990–1992 and 2007–2011). The objective of the research was to compare the presence, distribution and habitat use of Cuvier's beaked whale between the two investigated periods. Summer data (June–September) from the two periods were compared in terms of frequency of sightings, group size and spatial distribution related to the main ecogeographical features. A presence‐absence model (generalized additive modelling) was performed to predict habitat suitability in the two study periods. The results highlight long‐term site fidelity of Cuvier's beaked whale in the Central Tyrrhenian Sea with encounter rates comparable to the ones reported for other key areas. Separate suitability models based on 1990s and 2000s data appeared to work for each individual time period but differences were evident between the two periods, indicating changes in habitat selection over time. Our findings of the study appear to expand the definition of suitable beaked whale habitat and underline how the temporal scale of the analysis can affect the results in habitat studies. Moreover, this research highlights the importance of the Central Tyrrhenian Sea marine region for Cuvier's beaked whale and the ability of continuous monitoring to identify changes in cetacean frequency and distribution, necessary for adaptive conservation management approaches.  相似文献   

9.
《Marine Geology》1999,153(1-4):253-274
The planktic foraminiferal distribution identified in 60 cores collected in different basins of the Mediterranean Sea allowed to establish an ecostratigraphical scheme which provides a very important tool for the biochronological subdivision of the uppermost Quaternary. We identified a succession of ten ecozones during the last 23 ka in the Tyrrhenian basin and eight ecozones in the Adriatic Sea during the last 15 ka. The ecozones boundaries have been calibrated by 14C AMS radiometric data and by the stable oxygen isotope record. The chronological framework defined by the successive bioevents shows a very high resolution (millenary scale) and evidences that the changes in the planktic microfauna occurred more or less synchronously throughout the central Mediterranean Sea. Differences due to different oceanographic settings of the basins do not affect the general distributional pattern of planktic foraminifera.  相似文献   

10.
A hindcast study of extreme wave conditions in the Tyrrhenian Sea is described. The paper covers the different steps of the work, including the identification and the statistics of the weather patterns in the area, the choice of the storms to be hindcasted, the wind and wave models, a check of the best extremal distributions for the estimate of the extreme values probability, and the estimate of the accuracy of the final results. Detailed examples of the results are given, followed by a discussion of their reliability.  相似文献   

11.
Signals from an explosive source backscattered from the seafloor and received at long range by hydrophones of a towed array are processed to estimate the directional distribution of energy for a given time increment. As assembly of these data shows the time and amplitude of scattering features, and after conversion to distance, the geographic location of the return. A frequency-domain beam-forming procedure is used in which beam levels are averaged over a given band of a broad-band source. The processing is applied to experimental data obtained in the southern Tyrrhenian Sea. The major backscattering occurred at the Baconi Seamounts and the coastal margin of Sardinia.  相似文献   

12.
Marine surficial sediments, intertidal molluscs and reed leaves collected in the Bay of Follonica are slightly contaminated by Pb, Ni, Zn and Fe. The main pollution sources are the waste water and the atmospheric emission of industrial plants. Probably, the weathering of the pyrite deposits along the eastern coast of Elba Island and adsorption and coprecipitation with hydrous Fe-Mn oxides increase the trace metal concentrations in sediments from the Piombino Channel. Mussels and limpets are contaminated by Hg because of the higher background level of the northern Tyrrhenian Sea.  相似文献   

13.
High-resolution seismic reflection data are used in the identification of the stratigraphic succession filling Naples Bay, a tectonically active half-graben located in the extensional margin of the eastern Tyrrhenian Sea. The architecture of the basin infill is characterized by fourth-order depositional sequences correlated to Quaternary eustatic oscillations. These depositional sequences form aggrading and prograding stacking patterns bounded by tectonically enhanced unconformities. The changes that the stacking patterns undergo record variations in accommodation space rates. These variations are a result of the tectonic subsidence produced during the evolution of the half-graben. Received: 7 July 1998 / Revision received: 29 March 1999  相似文献   

14.
Recolonization patterns of benthic assemblages after relict sand dredging were investigated in an area offshore of Capo d’Anzio (central Tyrrhenian Sea). Surveys were performed before, during, and after dredging in 2007. Sampling stations were located within and outside the dredging site in water depths between 40 and 56 m. Defaunation due to sand extraction was the main impact observed in the inner stations and in stations located in proximity of the dredging site. At the inner stations, 9 months after dredging, a significant increase in species richness and diversity was observed: the sediment removal led to an increase of the sandy sediment fraction, favouring the settlement of sabulicolous species. A decrease in number of individuals and species was also observed in most of the outer stations, probably due to fine sediment redeposition. Recolonization of macrobenthic assemblages was essentially achieved at inner stations both in terms of abundance and species richness, while at outer stations it was still in progress. Results of this study, providing a picture of recovery times and processes in the Tyrrhenian Sea, could be used to develop predictions of the effects of future offshore sand dredging projects in comparable areas. Monitoring programs and research have a key role to provide a more detailed overview of biological recovery processes and times in different regions and with different dredging intensity.  相似文献   

15.
In the present paper some numerical simulations and experiments were carried out to study jet-wall interaction in shallow waters. Namely, modifications of the hydrodynamic field concerning the interaction of river run-off with a shallow coastal water body, due to the presence of marine structures, were investigated. Stratification effects due to salinity and temperature were neglected, and the interest was focused on barotropic features (Coanda effect). The numerical analysis was carried out by means of shallow water equations, numerically solved by finite difference, and the present method was validated by means of a typical simple-shaped test case. The experiments were carried out in a shallow water tank, flow visualizations were performed, and the velocity field was obtained by PIV. The main features of jet-wall interaction flow were investigated in simple-shaped geometries, and applications were shown for two practical cases: Pescara channel harbour (Adriatic Sea, Italy) and the proposed design of Latina harbour (Tyrrhenian Sea, Italy).  相似文献   

16.
Determination of the actual mercury concentration in Mediterranean basin seawater was achieved by means of an instrument based on fluorescence spectrometry developed for this purpose, during a field study aboard the oceanographic ship “L.F. Marsili”, between August 1980 and May 1982.Dissolved ·total’ and ·reactive’ mercury and mercury associated with particulate matter were determined on surface and subsurface waters in the Tyrrhenian Sea from La Spezia to Sicily.Concentrations in the range 1.4–19.7 ng l−1 for ·total dissolved mercury’, 0.5–5.9 ng l−1 for ·reactive dissolved mercury’ and 0.3–8.0 ng l−1 for mercury associated with the particulate matter, were measured on surface and subsurface waters in the Tyrrhenian Sea from La Spezia to Sicily.Even if the mean value of the total mercury concentration (dissolved + particulate) was found to be about twice as high as those observed for the oceans, the difference does not seem to be as high as predicted by the model proposed by Buffoni and co-workers to explain the large difference of mercury levels between tunas caught, respectively, in the Mediterranean and in the Oceans.  相似文献   

17.
Most of the recent models which aim at explaining the origins of canyons call on mechanisms of retrogressive failure. The interpretation of high-resolution seismic reflection profiles permitted the recognition of the shelf and slope evolution of Naples Bay (eastern Tyrrhenian Sea margin) during the formation of the Dohrn canyon. Stratigraphic and structural data collected from this area suggest that the factor which triggered off the formation of the canyon was the tectonic uplift of both the outer shelf and fluvial valley mouth which took place during the eustatic fall of sea level. Received: 12 May 1999 / Revision accepted: 19 May 2000  相似文献   

18.
Meteor Cruise 22 (April 1971) successfully recovered numerous samples of unconsolidated marine sediments from the SE Tyrrhenian Sea in the vicinity of the Aeolian Islands (Italy). The sedimentological investigations disclosed a highly dynamic environment in which the pelagic realm was being invaded by volcanic and terrigenous detritus, transported and deposited by gravity slumping, debris flow, and turbidity currents. This was the first detailed investigation of sediments in the region, the results augmenting the findings of the more recent studies by Kidd et al. and Lucchi and Kidd. Received: 24 February 1999 / Revision accepted: 6 January 2000  相似文献   

19.
The Sardinia Channel dataset was collected as part of the European Geotraverse (EGT)—a 4000 km seismic refraction line running from Northern Norway to the Sahara, designed to investigate the structure of the lithosphere beneath Europe. Wideangle seismic data recorded by ocean bottom seismometers deployed in the Sardinia Channel as part of the Southern Segment of the EGT, together with gravity data, were used to constrain the final crustal model. In the centre of the Channel the crust is identified as thinned continental in nature, with a crystalline thickness of 10 km overlain by 4 km of sediments and 2.5 km of water in the most extended region. High velocities in the lower crust in the central region are thought to represent an area of underplating or intrusion by igneous material caused by extension related to the opening of the Tyrrhenian Sea. The crust overlies an anomalously low velocity upper mantle.  相似文献   

20.
Abstract. The amphipod population of the Fusaro coastal lagoon (Tyrrhenian Sea, Italy) was studied on a spatial-temporal scale. During a one-year period, samples were collected on hard and soft bottoms along a transect from the inland to the seaward side of the lagoon. Thirteen species were identified. The dominant taxa included species typical of lagoon environments, such as Corophium insidiosum and Microdeutopus gryllotalpa , and species typical of marine environments yet also inhabiting sheltered or semi-closed areas, such as Corophium acutum, Ericthonius brasiliensis , and Elasmopus rapax.
An inner-outer gradient was not evident, while a seasonal pattern was recognizable. At the community level, clear differences between the two substrata were not evident because of high algal growth and organogenic detritus on the soft bottoms. The importance of hydrodynamic forces in a euhaline lagoon in selecting amphipod communities - characterized by a typical trophic behaviour and way of life – is discussed. Information on the ecology of the collected species and a list of Mediterranean lagoons where they are present are also provided.  相似文献   

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