Tyrrhenian Waters Research Articles

Silting Process and Loss of Posidonia oceanica Meadows in the Tyrrhenian Waters of Calabria (Southern Italy)

In the Mediterranean Sea, two critical issues affect marine benthic biocenosis: sedimentation and the increasing trend in marine biodiversity loss. These processes are very marked along the western side of the Calabrian coastline, where siltation is one of the main reasons for the regression of Posidonia beds in the regional coastal waters. This study investigates the relationships between the geomorphological features of the debris source areas, represented by fluvial basins, and the distribution of Posidonia meadows. So, a concise geomorphological study of the Tyrrhenian fluvial basins with an area greater than 200 km2 was carried out, and we correlated the results with the mapping of the meadows in Calabria’s Tyrrhenian waters. Furthermore, to assess the increased level of burial in a Posidonia oceanica meadow and its health state over time, a program of Posidonia monitoring was undertaken between 2000 and 2010 in a test area located in the Marine Regional Park of Isca (Calabria, Southern Italy). The results of this survey highlighted that, at the beginning of the study period, the silting rate of 4–5 cm/year saw the meadow suffer a reduction in its photosynthetic ratio with a mortality rate of 50%. The siltation rate reached 12 cm/year in 2010, and the meadow began to disappear. Therefore, marine pollution via sedimentation represents a serious factor in the regression of Posidonia oceanica meadows and enhances the risk of a gradual loss of marine biodiversity.

Coastal mesozooplankton respond to decadal environmental changes via community restructuring

AbstractLong‐term ecological research has revealed the impact of climate on marine ecosystems at multiple time scales. Changes in the pelagic system have been detected at the LTER‐MC site in the Gulf of Naples (Tyrrhenian Sea, western Mediterranean) since 1984. Here we analyzed the time series to determine whether zooplankton had significantly changed over the three decades 1984–2015. In addition to the seasonal cycle as the main mode of temporal variability, we observed long‐term trends in the functional groups and species. Copepods, the most abundant group, declined over the years owing to a decrease in the abundance of Acartia clausi, Centropages typicus, the Paracalanus parvus complex, and Oithona spp. Increasing trends were observed for strict carnivores (chaetognaths) and typical filter feeders (cladocerans, appendicularians, and thaliaceans); the latter may be linked to a higher density of <5 μm phytoplankton. Two main temporal shifts were detected: (i) in 1985–87, similarly to the regime shifts registered in other basins of the Northern Hemisphere, and (ii) after 2011, likely related to local atmospheric forcing. The disappearance or decrease in some neritic copepods and the increased abundance of typical offshore species seem to reflect the enhanced influence of the open Tyrrhenian waters at the sampling site. Despite these changes, no significant trends were detected in the total zooplankton abundance and overall composition, which indicates restructuring within the whole community. These results underline the need to examine the entire zooplankton diversity spectrum and improve our knowledge of their ecological traits to detect and interpret long‐term variability.

First Evidence of Contourite Drifts in the North-Western Sicilian Active Continental Margin (Southern Tyrrhenian Sea)

We present the results of an integrated geomorphological and seismo-stratigraphic study based on high resolution marine data acquired in the north-western Sicilian continental margin. We document for the first time five contourite drifts (marked as EM1a, EM2b, EM2, EM3a, and EM3b), located in the continental slope at depths between ca. 400 and 1500 m. EM1a,b have been interpreted as elongated mounded drifts. EM1a,b are ca. 3 km long, 1.3 km wide, and have a maximum thickness of 36 m in their center that thins northwards, while EM1b is smaller with a thickness up to 24 m. They are internally characterized by mounded seismic packages dominated by continuous and parallel reflectors. EM2 is located in the upper slope at a depth of ca. 1470 m, and it is ca. 9.3 km long, more than 3.9 km wide, and has a maximum thickness of ca. 65 m. It consists of an internal aggradational stacking pattern with elongated mounded packages of continuous, moderate to high amplitude seismic reflectors. EM2 is internally composed by a mix of contourite deposits (Holocene) interbedded with turbiditic and/or mass flow deposits. EM1a,b and EM2 are deposited at the top of an erosional truncation aged at 11.5 ka, so they mostly formed during the Holocene. EM3a,b are ca. 16 km long, more than 6.7 km wide, and have a thickness up to 350 m. Both EM2 and EM3a,b have been interpreted as sheeted drift due to their morphology and seismic features. The spatial distribution of the contourite drifts suggests that the drifts are likely generated by the interaction of the LIW, and deep Tyrrhenian water (TDW) on the seafloor, playing an important role in the shaping this continental margin since the late Pleistocene-Holocene. The results may help to understand the deep oceanic processes affecting the north-western Sicilian continental margin.

Impact of Freshwater Inflow From the Volturno River on Coastal Circulation

The coastal area located in front of the Volturno river’s estuary (Gulf of Gaeta, central-eastern Tyrrhenian Sea) has been synoptically sampled during seven surveys, between June 2012 and October 2014. The vertical profiles of temperature and salinity have been acquired on a high resolution nearly-regular grid, in order to describe the spatial and temporal variability of the water masses characteristics. Moreover, to provide a first assessment of the steady circulation at small scale, the three-dimensional velocity field associated to each survey has been obtained through the full momentum equations of the Princeton Ocean Model. The data analysis has shown the entire water column characterized by an evident thermal cycle and a vertical thermohaline structure dominated by three types of water masses: the freshwater of river’s origin, the saltier coastal Tyrrhenian waters and transitional waters, resulting from the mixing of them. The freshwater inflow strongly affected the density distribution, causing a strong temporal variability in the upper layer. Its impact was more evident in winter inducing also a temperature inversion along the water column. In case of rainy events, its effect was clear also in condition of high vertical temperature stratification, forming a surface-trapper layer characterized by high density gradients. Together with wind forcing, they contributed to the formation of small scale shallow features, such as longshore currents, cyclonic and anticyclonic eddies. The latter influenced the vertical stratification and modify the coastal circulation preserving the transitional waters from the surrounding saltier ones.

Modelling the marine circulation of the Campania coastal system (Tyrrhenian Sea) for the year 2016: Analysis of the dynamics

Abstract The Campania coastal system (CCS), located in the Tyrrhenian Sea, is characterized by an interesting and complex morphology, being made by a sequence of three gulfs (Gaeta, Naples and Salerno, GG, GN, GS) of different sizes, shapes, and bathymetries. Until now, most of the oceanographic studies in the area have focused on the GN, whereas little is known about the circulation in the GG and GS. Here, for the first time, a high-resolution modelling study of the whole CCS has been carried out, which covers a whole year (2016), allowing for a detailed description of the seasonal variability throughout this year. For each season, the dynamics in the three gulfs have been characterized, assessing the relative roles of the wind forcing, the topographic constraints and the remote large-scale Tyrrhenian Sea circulation. As a first step, the surface circulation patterns in the CCS have been compared with altimeter observations and with the atmospheric forcing. A detailed analysis of the monthly mean surface and intermediate circulation within each gulf has then been performed. Besides, a more quantitative insight into the mechanisms controlling the circulation has been obtained using an integrated vorticity diagnostic, which allows one to separate different contributions to the total barotropic vorticity equation. The results show a strong seasonality of the circulation in the three gulfs, which is mainly controlled by the wind stress input during autumn and winter, whereas in spring and summer the main contribution comes from the combined effect of baroclinicity and topographic gradient (the JBAR term). The exchanges between the gulfs and the Tyrrhenian waters have also been quantified, through the analysis of the transport across specific sections. These transports are found to be highly correlated with the offshore large-scale circulation in the GG, whereas in the GS there is strong correlation with the local wind forcing. Finally, lower correlations are found for the more geometrically complex and semi-enclosed GN.

Microplastics occurrence in the Tyrrhenian waters and in the gastrointestinal tract of two congener species of seabreams

In this work it is reported for the first time the characterization of microplastics from sea water samples and in two congener species of seabreams: Pagellus erythrinus and P. bogaraveo, Mediterranean fish species of great commercial importance. An experimental survey was conducted on May–June 2017 in the southernmost part of the Tyrrhenian Sea. Microplastics found in the sea water and in the grastrointestinal tract of two teleosts were characterized by Raman and IR spectroscopies. Microplastics found in sea water samples appeared in the form of fragments made of plastics of low and high density (PVC and LPDE). All the microplastics found in fish belonged to Nylon 66, typical fibers used in industry and in fisheries. Our findings highlighted the importance of further studies along the food web chain for a better understanding of the diffusion and possible consequences of this terrible threat.

Water mass structure and deep mixing processes in the Tyrrhenian Sea: Results from the VECTOR project

In this study, we analyze data from observations conducted in the southern Tyrrhenian Sea, within the framework of the VECTOR project, initiated in 2006. In the six cruises organized as part of the project, in November 2006, in February, April and June 2007, in February 2008 and in January 2009, repeated hydrological measurements were collected along a transect. Data collected at the same stations in a subsequent cruise in November 2010 were also incorporated into the study.The main Tyrrhenian water masses were clearly identified in vertical sections. In particular, a positive salinity anomaly, observed both in the first (late autumn) and second (winter) cruise, associated with an anti-cyclonic structure, characterized the surface layer. The intermediate layer revealed salinity values higher than the climatological salinities, continuing the rising trend observed in the previous works, because of the influence of the Eastern Mediterranean Transient on the western basin hydrology.At the bottom, both temperature and salinity showed higher values with respect to the historical data, but were nearly constant during the study period. However, the water column between 600m and 2500m exhibited a trend of increases in temperature and salinity at a mean rate of 0.025°/y and 0.0075/y, higher than the findings in earlier studies. This discrepancy is likely due to the downward transfer of excess heat and salt from the intermediate depths.In the Tyrrhenian Sea, one of the main mechanisms responsible for transferring heat and salt in the deep layers is double diffusion, which is particularly active here. Double diffusion forms ‘staircase’ structures that are better developed and more stable than in other areas of the world’s oceans. Such structures are clearly seen in the analysis of the CTD data collected at an offshore station. These features occur at depths below 600m, where the Levantine Intermediate Water (LIW) encounters the Tyrrhenian Dense Water, and mixing processes occur.As the Tyrrhenian Sea represents the main area of deep mixing for the waters from the eastern and western Mediterranean, systematic monitoring and quantification of changes in the Tyrrhenian intermediate and deep hydrological characteristics is critical. These data will prove to be particularly relevant to studies of the impact of climatic variability on the Mediterranean Sea.

Sub-regional patterns of primary production annual cycle in the Ligurian and North Tyrrhenian seas, from satellite data

The annual cycle of pelagic primary production (PP) from ocean colour is analysed in a transition area between Ligurian and Tyrrhenian waters, where a general oligo-mesotrophic status is seasonally modified by anthropic impact near the Tuscany coast. Based on the common ecological features six different zones were delimited. Remote sensing data from different satellites (Meteosat, Aqua) were used as input in a primary production model. The daily production of the entire area was computed on pixel by pixel basis (4x4 km) using a modified GIS software. Overwhelming importance of oceanic bloom and high spatial variance of PP (90 ±54 gC m -2 y r -1 ) show that remote sensed data can allow a better

First record of the lessepsian fish Siganus luridus (Osteichthyes: Siganidae) in the Tyrrhenian Sea

The first record of the dusky spinefoot Siganus luridus in Tyrrhenian waters is reported. One specimen was caught in Capo d'Orlando in March 2004 by trammel net. Its morphometric and meristic characteristics are reported.

Rarely observed short‐period (5–10 s) suboceanic Rayleigh waves propagating across the Tyrrhenian Sea

Shallow earthquakes occurring in the southern part of the Tyrrhenian basin excite a long‐duration low‐frequency coda that propagates efficiently along paths crossing the Tyrrhenian Sea. Seismograms recorded at regional distances in the Italian peninsula are analysed in the frequency‐time domain and compared with synthetics computed in simple vertically varying media. Based on results of our modeling, we interpret the coda as short‐period (5–10 s) suboceanic Rayleigh waves. Their large amplitude and long duration, that we emphasize here, are explained as due to the influence of the Tyrrhenian water layer over a fast seafloor with little S‐wave attenuation (QS > 300). A satisfactory fit of amplitude and duration of the observed waveforms is obtained assuming a young oceanic model with an average water column of 1 to 2 km and relatively high S‐wave velocity (2.5 km/s) in the shallow crust.

Mucilages and climatic changes in the Tyrrhenian Sea

Abstract1. Pelagic mucilage aggregates are composed of phytoplankton and bacteria, whilst macro‐ and micro‐phytobenthos and bacteria make up the benthic ones. During the summer of 1991 massive mucilage aggregates, both pelagic and benthic, appeared in the Tyrrhenian Sea, seriously damaging fisheries, tourism and the benthic biocoenoses. Only a few, loose benthic mucilages have persisted during the last decade although the pelagic ones have shown a great resurgence during the last autumn.2. 14C autoradiographies show that the mucilage is photosynthesized and excreted by the micro‐ and macroalgae it contains. The mucilage aggregates are a microecosystem with biological and chemical composition, and a functionality that is different from the surrounding waters. The mucilages cannot be the result of a gelification of the Dissolved Organic Matter (DOM) in the water trapping the free algae present in the water.3. Since 1991 up to the present, variations of Dissolved Inorganic Nitrogen (DIN) and Dissolved Inorganic Phosphorous (DIP) and of their ratio have been observed in the surface waters. These variations could be assumed as the cause of mucilages, however, the mucilage occurrence cannot be directly related to the change of nutrient concentrations and ratios because: i) the higher N/P ratio was persistent also during years without mucilages; ii) nutrients and their ratios have a continuous spatial distribution while mucilages have a discontinuous spatial and temporal distribution. It is suggested that mucilage aggregates are the result of a hyperproduction as a pathological response of the algae to a microbial infection. This hypothesis is also supported by some laboratory experiments.4. The observed trophic changes in the surface Tyrrhenian waters have been related to the Levantine Intermediate Waters (LIW) as they are the main source of nutrients for the surface ones. Data collected from several areas between 1982 and 1998 show that changes in the temperature, salinity and nutrient concentrations and ratios took place in the LIW, so changing the Tyrrhenian climate. Copyright © 2001 John Wiley & Sons, Ltd.

Dynamics and mixing of the Eastern Mediterranean outflow in the Tyrrhenian basin

Hydrographic measurements in the Sicily Channel and in the southern Tyrrhenian Sea show that the water outflowing from the Eastern Mediterranean Basin enters the Tyrrhenian Sea directly, close to the Sicily coast. Two water types have been distinguished: the upper part constituted by the Levantine Intermediate Water (LIW), and the transitional Eastern Mediterranean Deep Water (EMDW) below. Current measurements taken about 50 km after the entrance into the Tyrrhenian evidence a well-developed mean flow from a depth of 500 m to the bottom. While the LIW flows at the known depth for this type of water (namely between 500 and 800 m), a considerable volume of transitional EMDW was seen to sink from a depth of about 300 m in the Sicily Channel to a maximum depth of 1850 m in the Tyrrhenian Sea, where it floats over the Tyrrhenian Deep Water (TDW). The sinking is a consequence of the higher density of the incoming water ( σ θ >29.10) with respect to that of the intermediate Tyrrhenian waters ( σ θ ∼29.00–29.05). The progressive sinking of the transitional EMDW along the principal route from the Sicily Channel to the Tyrrhenian Sea, can be observed in the evolution of the isotherms, isohalines and isopycnals. The isopycnals, in particular, clearly tend to follow the bottom slope. The mean hydrographic characteristics of this vein of Eastern Mediterranean water progressively change along the route, and two regions of strong mixing are identified. The first occurs immediately after the Sicily Channel, while the second is found following the entrance of the vein into the Tyrrhenian Sea. An estimation of the entrainment stress shows that it largely dominates over the acceleration term. When the bottom slope does not influence the water motion anymore, the mixing is entirely ascribable to molecular diffusion via finger instability. The transport of transitional EMDW through the Sicily Channel is estimated to be about 0.2–0.3 Sv, implying a salinity anomaly export of 0.05–0.075 psu per Sv to the deep layers of the Tyrrhenian Sea.

The seasonal characteristics of the circulation in the north Mediterranean basin and their relationship with the atmospheric‐climatic conditions

The greater heat losses sustained by the Ligurian‐Provençal basin in winter appear to be the major factor leading to the periodic intrusions of the warmer Tyrrhenian water from the east. This is the main conclusion of a 3‐year oceanographic investigation carried out in the eastern Ligurian‐Provençal basin in order to monitor the long‐term characteristics of its exchanges with the Tyrrhenian Sea. The analysis of the whole data set collected in this period shows that two currents converge north of Corsica after having flowed along the northwestern side of Corsica (the West Corsican Current) and through the Corsican Channel (the Tyrrhenian Current). While the former does maintain nearly steady properties year round, the latter crosses the strait only during the coldest season, thus showing a clear seasonal trend that begins again every year. The comparison with the meteorological parameters of the Ligurian‐Provençal basin indicates that the winter intrusions of the Tyrrhenian current are tightly associated with the heat and water losses through the rise induced in the upper basin density. In addition to reintegrating the heat lost to the atmosphere, the Tyrrhenian flow might also restore the volume of the basin upper layer involved in the deep water formation processes. This enables us to infer that a unique circulation pattern, mostly driven by atmospheric‐climatic conditions, involves the northern part of the western Mediterranean Sea.

Temporal variability of currents in the eastern Ligurian Sea

Surface and intermediate waters enter the Ligurian Sea from the Tyrrhenian and Algero‐Provencal basins via northward flows along the east and west coasts of Corsica. The temporal variability of these flows is examined by means of a 1‐year time series of current data (October 1986 to September 1987) and hydrographic data from December, March, and May cruises. The flow through the Corsica Channel increases suddenly during December and then gradually decreases after March, reaching its lowest values in late summer. The seasonal variability in the channel seems associated mainly with the steric sea level differences between the Tyrrhenian Sea and Ligurian Sea. The West Corsican Current appears more stable throughout the one year of data. The two flows converge just north of Corsica into the Ligurian Current. Because of the water‐masses differences between the two currents, in the area of convergence considerable smaller‐scaled structure is observed. During winter, the less dense Tyrrhenian water provides available potential energy to the Ligurian shelf area and thereby helps sustain the large‐scale cyclonic circulation in the Ligurian basin. During the other seasons the spatial structures over the Ligurian shelf are less organized and the spatial scale of the flow is a few tens of kilometers.

Tidal forcing of the water mass interface in the Strait of Messina

The tidal currents of the Strait of Messina and their effect on the displacement of the water‐mass interface are discussed utilizing the historical velocity data of Francesco Vercelli, taken from ∼100 anchor stations during 1922 and 1923. The data show a complex, strongly tidal behavior, in which speeds of 200–300 cm/s are attained over the sill. Messina is an amphidromic point for the tides of the two main basins of the Mediterranean Sea, and two distinct water masses flow through the strait at different stages of the tide: the subsurface Levantine intermediate water flowing north alternating with surface Tyrrhenian water flowing south. The time evolution of the interface between the two marine water layers at the semidiurnal periodicity is computed from the observed distribution of acceleration term for the baroclinic component. This interface shows large vertical oscillations with amplitudes of ∼100 m intersecting both the surface and bottom. The results are in reasonable agreement with recent satellite data and other recent field observations and numerical experiments. An estimate of the mean position of the interface is made by assuming that the potential energy required to uplift the interface, from the equilibrium depth of 150 m to the observed 30 m depth over the sill, is derived from the time‐independent contribution of the nonlinear field acceleration term. The results are in reasonable agreement with observations.

Heavy metals in ionian and tyrrhenian waters from a section of the sicilian coast

Heavy metals in ionian and tyrrhenian waters from a section of the sicilian coast