Atlantic Ionian Stream Research Articles

Oceania armata Türünün Türk Sularındaki Muhtemel Havza Ölçekli Akıntı Kaynaklı Son Kaydı ve Diğer Jeli Organizmaların Yakın Geçmişteki Kayıtları

The present study reports the occurrence of Oceania armata in the Turkish Levantine Sea, and presents evidence to support a hypothesis established to link an increased recent and near-past records of many gelatinous zooplankton species in the Turkish seas, and particularly in the Turkish Levantine Sea to specific Mediterranean basin-scale currents (Atlantic-Ionian Stream and the Mid-Ionian Jet). One worldwide-distributed oceanic cnidarian specimen was collected from the surface water of a location of 36.59002 N and 29.02471 E by a SCUBA diver on January 18, 2019 in the eastern Mediterranean Sea. The hydrozoan specimen was then identified as O. armata and recorded for the first time in the Turkish Mediterranean coast and only second time in the Levant coast after about 30 years. This is the second report of the species from the Turkish waters, and the first report was from the Turkish Aegean coast. Recently, new records of the gelatinous species have increased from the Turkish marine coasts; Sea of Marmara, Aegean Sea, and Levantine Sea. Most of them are distributed in the West Mediterranean Sea, but are also present in the Adriatic Sea (East Mediterranean Sea). In the Mediterranean Sea, one branch of the Atlantic current (Atlantic-Ionian Stream) enters the eastern basin via the Mid-Ionian Jet, linked with the southern Adriatic current. Therefore, it is possible that zooplankton could have entered East Mediterranean by the Atlantic current through West Mediterranean.

Surface connection between the Ionian Sea and different areas of the Mediterranean derived from drifter data

The surface connection between the Ionian Sea (central Mediterranean Sea) and the surrounding areas is studied by looking at the statistical properties of 1632 near-surface Lagrangian trajectories. The choice of the area is due to the key role in the dynamics of the Mediterranean Sea and to the geographical distribution of data. The Lagrangian drifter data were taken from the OGS Mediterranean drifter database, which gathers drifter data collected in the Mediterranean Sea from various institutions and countries between 1986 and 2016. The database has proved to be sufficiently complete, but the spatial and temporal data coverage are less satisfactory in the case of selection of a specific study area and temporal range. The strategy used in this work aims to limiting the problem of data coverage by choosing many target boxes around the study area, choice based on drifter trajectories, current patterns and areas of interest. The pseudo-eulerian analysis obtained from all trajectories passing through the Ionian Sea show the main dynamic structure present in the central Mediterranean Sea (e.g. Atlantic Ionian Stream, Mid Ionian Jet, etc.).On the other hand, the data density decreases progressively toward the eastern and western sectors of the Mediterranean. The highest connection was observed with the Strait of Sicily, Eastern Ionian and Adriatic Sea, with connection percentages 30%, 25% and 16% respectively. The transit times between the Ionian Sea and these target boxes are about 20–50 days. The Ionian Sea is characterized by phenomena of inversion of the basin surface circulation, from cyclonic to anti-cyclonic, over a ten-year timescale, the so-called Adriatic-Ionian Bimodal Oscillating System (BiOS, e.g. Gačić et al., 2010; Gačić et al., 2011). An application of the “target box methodology” has been used to describe how the cyclic variability of the dynamic surface currents generates an equally cyclical fluctuation of the connectivity between the Ionian Sea and the surrounding areas during the BiOS phases.

Interannual Variations of Surface Currents and Transports in the Sicily Channel Derived From Coastal Altimetry

AbstractA 20 year coastal altimetry data set (X‐TRACK) is used, for the first time, to gain insight into the long‐term interannual variations of the surface circulation in the Sicily Channel. First, a spectral along with a time/space diagram analysis are applied to the monthly means. They reveal a regionally coherent current patterns from track to track with a marked interannual variability that is unequally shared between the Atlantic Tunisian Current and Atlantic Ionian Stream inflows in the Sicily Channel and the Bifurcation Tyrrhenian Current outflow northeast of Sicily. Second, an empirical altimetry‐based transport‐like technique is proposed to quantify volume budgets inside the closed boxes formed by the crossing of the altimetry tracks and coastlines over the study area. A set of hydrographic measurements is used to validate the method. The inferred altimetry transports give a well‐balanced mean eastward Atlantic Waters baroclinic flow of 0.4 Sv and standard deviations of 0.2 Sv on a yearly basis throughout the Sicily Channel and toward the Ionian Sea, which is fairly coherent with those found in the literature. Furthermore, the analysis allows to quantify the intrusions of Atlantic Waters over the Tunisian Shelf (0.12 ± 0.1 Sv) and highlights two main modes of variability of the main surface waters path over the Sicily Channel through the Bifurcation Atlantic Tunisian Current and Atlantic Ionian Stream systems. Some physical mechanisms are finally discussed with regards to changes in the observed currents and transports.

The Sicily Channel surface circulation revisited using a neural clustering analysis of a high‐resolution simulation

AbstractThe Sicily Channel surface circulation is investigated by analyzing the outputs of a high‐resolution ocean model MED12 forced during 46 years by the ARPERA atmospheric fields. Applying a neural network classifier, we show that the surface circulation in the Sicily Channel can be decomposed into 8 modes characterizing the major patterns of that circulation, particularly the Algerian Current separation at the entrance to the Sicily Channel, the features of the Atlantic Tunisian Current and of the Atlantic Ionian Stream. These modes reflect the variability of the circulation in space and time at seasonal and inter‐annual scales. Some modes preferably occur in winter whilst others are characteristic of summer. The mode sequence presents an inter‐annual variability in good agreement with observations. The topography of the Sicily Channel sill plays a major role in steering the circulation. In particular the summer upwelling along the southern coast of Sicily, which is present in several modes, could be explained by a large‐scale density forcing. A combination of barotropic/baroclinic double Kelvin waves generated on both sides of the sill provides a mechanism for explaining the complexity of the surface circulation advecting the surface waters from the Western Mediterranean toward the Eastern Mediterranean, the most salient features of which are the Atlantic Tunisian Current, the Atlantic Ionian Stream and the Tyrrhenian Sicilian Current which is a new feature highlighted by the present study.

Exploiting coastal altimetry to improve the surface circulation scheme over the central Mediterranean Sea

AbstractThis work is the first study exploiting along track altimetry data to observe and monitor coastal ocean features over the transition area between the western and eastern Mediterranean Basins. The relative performances of both the AVISO and the X‐TRACK research regional altimetric data sets are compared using in situ observations. Both products are cross validated with tide gauge records. The altimeter‐derived geostrophic velocities are also compared with observations from a moored Acoustic Doppler Current Profiler. Results indicate the good potential of satellite altimetry to retrieve dynamic features over the area. However, X‐TRACK shows a more homogenous data coverage than AVISO, with longer time series in the 50 km coastal band. The seasonal evolution of the surface circulation is therefore analyzed by conjointly using X‐TRACK data and remotely sensed sea surface temperature observations. This combined data set clearly depicts different current regimes and bifurcations, which allows us to propose a new seasonal circulation scheme for the central Mediterranean. The analysis shows variations of the path and temporal behavior of the main circulation features: the Atlantic Tunisian Current, the Atlantic Ionian Stream, the Atlantic Libyan Current, and the Sidra Gyre. The resulting bifurcating veins of these currents are also discussed, and a new current branch is observed for the first time.

Different key roles of mesoscale oceanographic structures and ocean bathymetry in shaping larval fish distribution pattern: A case study in Sicilian waters in summer 2009

Fish larvae data collected in year 2009 were used to examine the effects of particular environmental conditions on the structure of larval assemblages in two oligotrophic Mediterranean areas (the Southern Tyrrhenian Sea and the Strait of Sicily). For this purpose, relationships with environmental variables (temperature, salinity and fluorescence), zooplankton biomass, water circulation and bathymetry are discussed. Hydrodynamic conditions resulted very differently between two study areas. The Southern Tyrrhenian Sea was characterized by moderate shallow circulation compared to the Strait of Sicily. In this framework, distribution pattern of larval density in the Tyrrhenian Sea was mainly driven by bathymetry, due to spawning behavior of adult fish. There, results defined four assemblages: two coastal assemblages dominated by pelagic and demersal families and two oceanic assemblages dominated by mesopelagic species more abundant in western offshore and less abundant in eastern offshore. The assemblage variations in the western side was related to the presence of an anti-cyclonic gyre in the northern side of the Gulf of Palermo, while in the eastern side the effect of circulation was not very strong and the environmental conditions rather than the dispersal of species determined the larval fish communities structure. Otherwise in the Strait of Sicily the currents were the main factor governing the concentration and the assemblage structure. In fact, the distribution of larvae was largely consistent with the branch of the Atlantic Ionian Stream (AIS). Moreover, very complex oceanographic structures (two cyclonic circulations in the western part of the study area and one anti-cyclonic circulation in the eastern part) caused the formation of uncommon spatial distribution of larval fish assemblages, only partially linked to bathymetry of the study area. Typically coastal larvae (pelagic families: Engraulidae and Clupeidae) were mostly concentrated in the offshore areas and off Capo Passero, where the presence of a thermo-haline front maintained their position in an area with favourable conditions for larval fish feeding and growth.

Pathways of the Modified Atlantic Water across the Strait of Sicily

The purpose of this study is to study the medium-scale dynamics, as well as the dynamics of the sub-basin scale in the Central Mediterranean, and to elucidate the routes of the Atlantic waters in this region using a high-resolution numerical model of the eddy-resolving simplest equation. The seasonal variability of the two streams of modified Atlantic waters crossing the Sicilian Strait varies considerably. The main stream along the coast of Tunisia, giving rise to the Atlantic Tunisian current, is stronger than the Atlantic Ionian stream (AIP) from autumn to spring. The Atlantic Tunisian current, which, apparently, is present throughout the year, is characterized by high spatial and temporal variability from the simulation results. The high-resolution model is capable of well reproducing the flow and variability of AIP, including such associating characteristic structures as the Advent Benk Vortex, Moltis Channel Cross, Ionian Benc Vortex and the outflow to the northern Ionian Sea.

Lagrangian simulations and interannual variability of anchovy egg and larva dispersal in the Sicily Channel

AbstractThe interannual variability in the transport of anchovy eggs and larvae in the Sicily Channel, relatively to the period 1999–2012, is studied by means of numerical simulations of the Mediterranean Forecasting System (MFS) circulation model provided by INGV. Subgrid‐scale dynamics not resolved by the MFS model is parameterized in terms of kinematic fields. The latter affect small‐scale tracer relative dispersion, while leaving the mean large‐scale advection substantially unchanged. A Lagrangian Transport Index (LTI) can be defined to characterize the efficiency of the main currents, e.g., the Atlantic Ionian Stream, in connecting spawning and nursery areas to each other. In our case, this indicator comes from the first arrival time statistics of tracers traveling from a spawning area near Sciacca to a nursery area in proximity of Cape Passero. We observe, on the basis of LTI values, that there are years when the Lagrangian connectivity is very efficient (2004, 2008, 2012) and years when it is weak (2000, 2001, 2003, 2010). Lagrangian indicators like the LTI concur to explain observed fluctuations of larval density and, also, can be employed, more in general, in multivariate models of population dynamics.

Water masses and nutrient distribution in the Gulf of Syrte and between Sicily and Libya

This paper analyzes for the first time the water masses circulation in the Gulf of Syrte (Libya) and along a Sicily–Libya transect (central Mediterranean Sea) based on a new dataset of hydrological and nutrients data. The collected dataset highlights the presence of three main water masses with different chemical–physical features: Atlantic Water, Levantine Intermediate Water and Deep Water. Atlantic Water shows an intrusive low-salinity water near the Sicilian (≤37.6) and Libyan coasts (≤37.8), linked to the Atlantic Ionian Stream and the Atlantic Libyan Current respectively. The surface circulation evidences meandering structures throughout the area and the presence of an anti-cyclonic vortex in the central part of the Gulf of Syrte. In this latter area no coastal surface current is recognized, suggesting a seasonal character for such coastal circulation. In the Gulf the anti-cyclonic pattern characterizes also the intermediate water circulation. The nutrient distribution confirms the oligotrophic character of the area with a strong reduction in concentration in the surface layer due to the assimilation of phytoplankton in the euphotic zone. Furthermore, there is an evident increase in the deep water caused by the re-mineralization of organisms. The nitrate:phosphate ratio is ~10 and ~30 in the surface waters and deep waters, respectively, the latter being far in excess of the Redfield ratio (16:1) found in the oceans' deep waters. Nutrients data close to the Libyan coast do not show any enrichment pattern as a potential effect of the input of Saharan dust.

The key role played by the Augusta basin (southern Italy) in the mercury contamination of the Mediterranean Sea

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.

Nursery and Spawning Areas of Deep-water Rose Shrimp, Parapenaeus longirostris (Decapoda: Penaeidae), in the Strait of Sicily (Central Mediterranean Sea)

The identification of nursery and spawning areas of coastal fish and shellfish populations represents fundamental information for stock assessment essential for giving advice for managers within the framework of Ecosystem Approach to Fisheries. This study investigates the bathymetric and spatial distribution of young-of-the-year and mature females of the deep-water rose shrimp, Parapenaeus longirostris, in the Strait of Sicily (Central Mediterranean Sea) in order to describe the species nursery and spawning areas. Data were obtained from trawl surveys carried out yearly in spring and autumn from 1994 to 2004, and nursery and spawning areas were inferred by means of GIS techniques. Species maximum abundance occurred between 100 and 300 m. We found that young-of-the-year concentrated on the outer shelf while mature females occurred mostly between the outer shelf and the upper slope. We detected four large areas of aggregation of young-of-the-year, and three areas of aggregation of mature females. High concentrations of young-of-theyear and mature females persistently occupied some of these areas, representing stable nursery and spawning areas. Young-of-the-year and mature females aggregate where retention and enrichment processes occur, linked to the semi-permanent patterns resulting from the meanders of the Atlantic Ionian Stream. We highlight the importance of studying the spatial distribution pattern of commercial species to identify habitats essential to those species’ life cycle. We detected deep-water rose shrimp nursery and spawning areas in the Strait of Sicily and discuss their spatial pattern in relation to the hydrological characteristics of the area.

Impact of data assimilation of glider observations in the Ionian Sea (Eastern Mediterranean)

Glider observations of temperature, salinity and vertically averaged velocity in the Ionian Sea (Eastern Mediterranean Sea), made in the period October 2004–December 2004, were assimilated into an operational forecasting model together with other in situ and satellite observations. The study area has a high spatial and temporal variability of near surface dynamics, characterized by the entrance of the Atlantic Ionian Stream (AIS) into the Northern Ionian Sea. The impact of glider observations on the estimation of the circulation is studied, and it is found that their assimilation locally improves the prediction of temperature, salinity, velocity and surface elevation fields. However, only the assimilation of temperature and salinity together with the vertically averaged velocity improves the forecast of all observed parameters. It is also found that glider observations rapidly impact the analyses even remotely, and the remote impacts on the analyses remain several months after the presence of the glider. The study emphasizes the importance of assimilating as much as possible all available information from gliders, especially in dynamically complex areas.

Surface circulation patterns in the Sicily Channel and Ionian Sea as revealed by MODIS chlorophyll images from 2003 to 2007

The surface circulation in the Sicily Channel and in the Ionian Sea is investigated using MODerate-resolution Infrared Spectro-radiometer (MODIS) chlorophyll-a images collected from 2003 to 2007. The use of chlorophyll as surface tracer in the area is verified by comparison with satellite altimeter measurements available during the same period. The interaction between waters with different concentrations of chlorophyll adds new particulars to the surface circulation of the Atlantic Water (AW) in the study area. In the Sicily Channel, warm anticyclonic structures located in the southern end drive the AW flow along their northern boundary to the south-east, towards the Libyan coast. In winter, the anticyclonic structures contract in a stable nucleus (the Sidra gyre) close to the African coast allowing AW intrusion over the Tunisian shelf (Atlantic Tunisian Current). In summer, the anticyclonic structure expands westwards, limiting the Atlantic Tunisian Current, and northwards, grazing the Atlantic Ionian Stream. It also fragments, allowing occasional AW intrusion into the central part of the Sicily Channel along different pathways. Due to the activity of the Sidra gyre, no evidence of the extension of the Atlantic Tunisian Current along the Libyan coast (east of 15°E) is found in the observation period. AW spreads into the central Ionian for long periods in summer but rarely in winter. It reaches the northern Ionian Sea via anticyclonic eddies (already observed in thermal imagery) departing from the northern and eastern border of the anticyclonic structure, captured by the prevalent clockwise offshore circulation in the northern Ionian (except in summer 2003). The deduced circulation is in agreement with recent studies based on the altimetric Mean Dynamic Topography and trajectories of drifters released in the Sicily Channel in recent years.

Circulation over the southeastern continental shelf and slope of the Mediterranean Sea: Direct current measurements, winds, and numerical model simulations

Results are presented for the first time from an extensive, systematic campaign of direct current measurements that were conducted over the continental shelf and slope of the southeastern corner of the Mediterranean over a 10‐year period. Concurrent cross‐shelf hydrographic transects and coastal wind measurements were also conducted. The results are presented within the context of the general circulation of the Levantine Basin as simulated with a numerical model. The circulation over the shelf is northward throughout the year with strong seasonal variability, and maximum currents in winter and summer. In summer, the strong currents are confined to the upper layer with seaward intensification. Over the slope, a seasonally varying along‐slope baroclinic jet also appears during summer and early winter. The shelf and slope current system is part of the general circulation of the Levantine basin composed of the bifurcating Atlantic Ionian Stream, the Mid‐Mediterranean Jet, and the cyclonic basin‐wide current that follows the coast. During winter storms, the strong southwesterly winds drive the northward flowing current and downwelling over the shelf. At this time the deeper level currents near the shelf break are also intensified. The alongshore synoptic currents are weakly coherent and strongly affected by the alongshore pressure gradient. In late winter the slope jet remains offshore and does not intrude over the narrow shelf. Both the measurements and the simulations confirm the strong seasonality and variability of the shelf and slope current system and hint at the potential for intense shelf‐open sea exchanges in this region.

Effects of the 2003 European heatwave on the Central Mediterranean Sea: surface fluxes and the dynamical response

Abstract. The effects of the 2003 European heatwave on the sea surface layer of the Central Mediterranean were studied using a regional 3-D ocean model. The model was used to simulate the period 2000 to 2004 and its performance was validated using remotely-sensed and in situ data. Analysis of the results focused on changes in the Sea Surface Temperature (SST) and on changes to the surface and sub-surface current field. This permitted us to identify and quantify the anomalies of atmospheric and sea surface parameters that accompanied the heatwave. The dominant annual cycle in each variable was first removed and a wavelet analysis then used to locate anomalies in the time-frequency domain. We found that the excess heating affecting the sea surface in the summer of 2003 was related to a significant increase in air temperature, a decrease in wind stress and reduction of all components of the upward heat flux. The monthly averages of the model SST were found to be in good agreement with remotely-sensed data during the period studied, although the ocean model tended to underestimate extreme events. The spatial distribution of SST anomalies as well as their time-frequency location was similar for both the remotely-sensed and model temperatures. We also found, on the basis of the period of the observed anomaly, that the event was not limited to the few summer months of 2003 but was part of a longer phenomenon. Both the model results and experimental data suggest the anomalous heating mainly affected the top 15 m of ocean and was associated with strong surface stratification and low mixing. The skill of the model to reproduce the sub-surface hydrographic features during the heatwave was checked by comparison with temperature and salinity measurements. This showed that the model was generally in good agreement with observations. The model and observations showed that the anomalous warming also modified the currents in the region, most noticeably the Atlantic Ionian Stream (AIS) and the Atlantic Tunisian Current (ATC). The AIS was reduced in intensity and showed less meandering, mainly due to the reduced density gradient and low winds, while the ATC was enhanced in strength, the two currents appearing to modulate each other in order to conserve the total transport of Modified Atlantic Water.

A Mean Dynamic Topography of the Mediterranean Sea computed from altimetric data, in-situ measurements and a general circulation model

In the Mediterranean Sea, where the mean circulation is largely unknown and characterized by smaller scales and less intensity than in the open ocean, the interpretation of altimetric Sea Level Anomalies (SLA) is rather difficult. In the context of operational systems such as MFS (Mediterranean Forecasting System) or MERCATOR, that assimilate the altimetric information, the estimation of a realistic Mean Dynamic Topography (MDT) consistent with altimetric SLA to be used to reconstruct absolute sea level is a crucial issue. A method is developed here to estimate the required MDT combining oceanic observations as altimetric and in-situ measurements and outputs from an ocean general circulation model (OGCM). In a first step, the average over the 1993–1999 period of dynamic topography outputs from MFS OGCM provides a first guess for the computation of the MDT. Then, in a second step, drifting buoy velocities and altimetric data are combined using a synthetic method to obtain local estimates of the mean geostrophic circulation which are then used to improve the first guess through an inverse technique and map the MDT field (hereafter the Synthetic Mean Dynamic Topography or SMDT) on a 1/8° resolution grid. Many interesting current patterns and cyclonic/anticyclonic structures are visible on the SMDT obtained. The main Mediterranean coastal currents are well marked (as the Algerian Current or the Liguro–Provenço–Catalan Current). East of the Sicily channel, the Atlantic Ionian Stream divides into several main branches crossing the Ionian Sea at various latitudes before joining at 19°E into a unique Mid-Mediterranean Jet. Also, strong signatures of the main Mediterranean eddies are obtained (as for instance the Alboran gyre, the Pelops, Ierapetra, Mersa-Matruh or Shikmona anticyclones and the Cretan, Rhodes or West Cyprius cyclones). Independent in-situ measurements from Sea Campaigns NORBAL in the North Balearic Sea and the North Tyrrhenian Sea and SYMPLEX in the Sicily channel are used to validate locally the SMDT: deduced absolute altimetric dynamic topography compares well with in-situ observations. Finally, the SMDT is used to compute absolute altimetric maps in the Alboran Sea and the Algerian Current. The use of absolute altimetric signal allows to accurately follow the formation and propagation of cyclonic and anticyclonic eddies in both areas.

Seasonal variability of water transport through the Straits of Gibraltar, Sicily and Corsica, derived from a high-resolution model of the Mediterranean circulation

The variability of the water transport through three major straits of the Mediterranean Sea (Gibraltar, Sicily and Corsica) was investigated using a high-resolution model. This model of the Mediterranean circulation was developed in the context of the Mercator project. The region of interest is the western Mediterranean between the Strait of Gibraltar and the Strait of Sicily. The major water masses and the winter convection in the Gulf of Lions were simulated. The model reproduced the meso-scale and large-scale patterns of the circulation in very good agreement with recent observations. The western and the eastern gyres of the Alboran Sea were observed but high interannual variability was noticed. The Algerian Current splits into several branches at the longitude of the Strait of Sicily level, forming the Tyrrhenian branch, and, the Atlantic Ionian Stream and the Atlantic Tunisian Current in the eastern Mediterranean. The North Current retroflexed north of the Balearic Islands and a dome structure was observed in the Gulf of Lions. The cyclonic barotropic Algerian gyre, which was recently observed during the MATER and ELISA experiment, was evidenced in the simulation. From time-series of 10-day mean transport, the three straits presented a high variability at short time-scales. The transport was generally maximum, in April for the Strait of Gibraltar, in November for the Strait of Sicily, and in January for the Strait of Corsica. The amplitudes of the transport through the Straits of Gibraltar (0.11 Sv) and Sicily (0.30 Sv) presented a weaker seasonal variability than that of the Strait of Corsica (0.70 Sv). The study of the relation between transport and wind forcing showed that the transport through the Strait of Gibraltar is dependent on local zonal wind over short time-scales (70%), which was not the case for the other straits (less than 30%). The maximum (minimum) of the transport occurred for an eastward (westward) wind stress in the strait. An interannual event was noticed in November–December 2001, which corresponded to a very low transport (0.3 Sv), which was characterised by a cyclonic circulation in the western Alboran Sea. That circulation was also reproduced by the model for other periods than winter during the interannual simulation. The transport through the Strait of Sicily is not influenced by local wind. The wind stress curl of the northwestern Mediterranean influenced the transport through the Strait of Corsica.

Assessing the variability of hydrographic processes influencing the life cycle of the Sicilian Channel anchovy, Engraulis encrasicolus, by satellite imagery

AbstractThree oceanographic surveys carried out in the Sicilian Channel during the spawning season (June to July) of anchovy (Engraulis encrasicolus) showed a close relationship between anchovy reproductive strategy and important hydrographic structures. A time series of satellite‐derived sea surface temperature images of the Sicilian Channel were analysed by means of empirical orthogonal functions and the dominant empirical modes were studied in detail. The first empirical mode captured much of the original variance and reproduced the trajectory of the Atlantic Ionian Stream (AIS), the principal hydrodynamic feature of the area. The time coefficients of modes 1 and 2 had seasonal signals which, when combined, accounted for the enhancement of the thermal front, clearly visible off Cape Passero (southernmost coast of Sicily) during summer. As the area constituted the principal nursery ground of the Sicilian Channel anchovy, the combination of the time coefficients of these modes was considered a potential indicator of the food particle concentration usually associated with oceanic fronts, which provided the energy requirements for larval growth. Mode 3 described the north/south displacements of the mean AIS trajectory, which modified the surface temperature regime of the anchovy spawning habitat. Therefore, the time coefficients of this mode were used as a potential indicator of anchovy spawning habitat variability. The capability of time coefficients of modes 2 and 3 to modify the main pattern depicted by mode 1 were tested successfully against in situ oceanographic observations.

The dynamics of the Sicily Strait: a comprehensive study from observations and models

Abstract The dynamics of the Sicily Strait are investigated in a comprehensive study using recent in situ observations, Ocean General Circulation Model (OGCM) simulations and process model results. In particular, results of a very high-resolution Mediterranean model (MED16) developed in the context of the Mercator project are described. The circulation in the Sicily Strait can be described as a two-layer exchange of Atlantic Water (AW) and Eastern Mediterranean Outflow Water (EOW). The Algerian Current brings AW (the upper layer) eastwards and splits into two branches at the entrance to the Sicily Strait, one flowing to the Tyrrhenian Sea, the other into the Sicily Strait. The later is composed of two streams, referred to as the Atlantic Ionian Stream (AIS) and the Atlantic Tunisian Current (ATC). In winter, the ATC signature is more pronounced. In summer, the AIS is associated with a number of well-known semi-permanent features including the intermittent northward extension of the AIS (called NAIS) at the Ionian shelf break, which seems to be driven by the surface density contrast between waters of the Sicilian and the Ionian basins. New intermittent patterns are shown by the MED16 simulations, for example an anticyclonic eddy (called MCA) south of the Malta Channel and an anticyclonic gyre associated to the NAIS (called NAISA). Upwelling is well developed in August, with temperature lower than 24°C along the western and southern coasts of Sicily. The seasonal transport of the AW through the strait has a maximum value (1.4 Sv ) in winter, and a minimum value at the end of summer (0.8 Sv ) . In the lower layer, at the exit of the Sicily Strait, the EOW, mainly composed of Levantine Intermediate Water (LIW), outflows into the Tyrrhenian Sea and veers to the right. Then, as well known, the LIW flows along the northern coast of Sicily before reaching the Sardinia Channel. A new LIW path from the Sicily Strait towards the Sardinia Channel is shown by the MED16 model, and is due to intermediate eddy shedding at the exit of the Sicily Strait. The topography of the sill in the Sicily Strait plays a major role in the circulation. A combination of barotropic/baroclinic double Kelvin waves on both side of the sill provides a mechanism, for splitting the Algerian Current.

Anchovy egg and larval distribution in relation to biological and physical oceanography in the Strait of Sicily

The European Anchovy (Engraulis encrasicolus, Linnaeus, 1758) represents one of the most important fishery resources in some areas of the Mediterranean. This short-lived, small pelagic fish is characterized by large interannual fluctuations, probably as a result of environmental variability. As part of the European Project Med 98-070, the main aim of which was the study of the anchovy population in the Strait of Sicily, icthyoplankton surveys were carried out between 1999 and 2001, during the peak spawning season for anchovy. Present work reports the relationship between meso-zooplankton biomass and the abundance of anchovy eggs and larvae in the Strait of Sicily. Data on anchovy egg abundance showed that the main spawning area was located in the north-western region of the study area. The branch of the Atlantic Ionian Stream, running parallel to the southern Sicilian coast, acts as a transport mechanism for anchovy eggs and larvae towards the southernmost end of the island, off Cape Passero. Observed distributions were largely consistent with local hydrographic features, which allow larvae to be retained in areas providing the necessary feeding conditions for recruitment success.