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Oceanographic processes play a key role in influencing the structure of the marine planktonic ecosystems. Taking advantage of the quasi-simultaneous collection of a large ichthyoplanktonic dataset in different regions of the Central Mediterranean Sea (Italian/Maltese, Tunisian and Libyan waters), this study aimed at the identification of the main environmental drivers that control the structure of the larval fish assemblages. Spatial distribution and taxa composition were related to physical forcings (geostrophic currents and wind stress) and environmental conditions (bottom depth, temperature, salinity, chlorophyll-a concentration). ANOSIM and SIMPER identified contribution of fish taxa to the average Bray-Curtis dissimilarity among regions. In Italian and Libyan waters, two assemblages (neritic and oceanic) were identified, while a mixed assemblage characterized only some stations. Two neritic and one oceanic assemblages were discriminated in Tunisian waters. Random Forest classification model highlighted the essential role of the bathymetry, while Lagrangian simulations evidenced the action of the hydrodynamics in mixing neritic and oceanic assemblages in the Italian/Maltese and partially in Libyan waters. These findings highlighted the importance of the multidisciplinary approach and shed light on the potential value of the ichthyoplanktonic surveys for the assessment of the state of the marine ecosystem and the conservation of the fishery resources. [ABSTRACT FROM AUTHOR]

This contribution describes projections of the maximum level that water will reach during a storm along the coast of the Mediterranean Sea in the next decades (2021-2050). The computation accounts for changes of marine storminess (maximum wave amplitude and maximum storm surge level) and for the steric contribution (thermosteric expansion, halosteric contraction) to the mean sea level, but not for addition of water mass to the basin through the Gibraltar Strait. This analysis is based on an ensemble of regional climate model simulations (produced by the CIRCE fp6 project) covering the period 1951-2050 under the A1B emission scenario, whose results have been used for forcing a hydro-dynamical shallow water mode and a wave model, obtaining estimates of storm surge levels and maximum amplitude of ocean waves, respectively. Data produced by high resolution models of the Mediterranean Sea circulation have been used for diagnosing the steric sea level change. The climate change signal is computed as the difference between maximum water level statistics in the 1971-2000 and 2021-2050 periods. Results show that the decrease of storm surge level and wave height will compensate for the positive steric effects in the next decades. [ABSTRACT FROM AUTHOR]

An analysis is made of the historical datasets covering almost 40 years (1976-2014) in the Ligurian Sea, in the North-Western Mediterranean. Two transects are studied: one at the boundary with the Tyrrhenian sea, in the Corsica Channel, the other between Nice on the French coast and Calvì on Corsica. The variability in the circulation patterns and changes in the hydrological properties of the water masses on seasonal and interannual time scales are investigated. For every cruise we chose the closest transect to the chosen ideal sections. [ABSTRACT FROM AUTHOR]

The real transfer function and the phase shift between sea surface height (SSH) and sea surface buoyancy (SSB) were estimated from the output of a realistic eddy-resolving model of the Mediterranean Sea circulation. The analysis of their temporal evolution unveiled the existence of a clear seasonal cycle closely related to that of the mixed layer depth. The phase shifts between SSH and SSB attain their minimum for deep mixed layers, which is different from zero. Besides, the spectral slope of the transfer function at scales shorter than 100 km fluctuates between k−1 and k−2. For deep mixed layers, it is close to k−1, as predicted by the surface quasigeostrophic (SQG) solution. At longer wavelengths, it is approximately constant under the different environmental conditions in all of the subbasins analyzed with the exception of the Gulf of Lions. The capability to observe sea surface temperature (SST) from satellites motivated the extension of this analysis to SST and SSH. Results showed a similar qualitative behavior but with larger phase shifts. In spite of the presence of a phase shift, even for deep mixed layers, results revealed that it is still possible to reconstruct surface dynamics from SST using a transfer function, provided that the mixed layer is deep enough. For the present study, a threshold value of 70 m was enough to identify the appropriate environmental conditions. In addition, the results revealed that a precise estimation of the transfer function significantly improves the reconstruction of the flow in comparison with the application of the classical SQG solution. [ABSTRACT FROM AUTHOR]

Different combinations of the EGM2008 global model and the GOCE space-wise solution are used to estimate the geodetic mean dynamic topography and the corresponding surface geostrophic circulation of the Mediterranean Sea. In order to assess the accuracy of the GOCE-derived products for oceanographic applications, the mean currents obtained from the geoid models are compared with the mean surface geostrophic velocities measured by drifters and satellite altimetry data. The mean dynamic topographies based on GOCE data combined with EGM2008 generally describe the main circulation patterns and dynamical features in the Mediterranean Sea, except in few coastal regions and in the semi-enclosed Adriatic and Aegean Seas, and improve the results obtained with previous geoid models. The root mean square differences between the geostrophic velocities and the GOCE/EGM2008-derived currents are smaller than 10 cm/s in all the sectors of the Mediterranean basin, whereas they are larger than 12 - 15 cm/s using the EGM2008 solution. The minimum discrepancies and the best complex correlation coefficient are achieved from the EGMSPWbc solution based on an order-wise block diagonal approximation of the GOCE error covariance structure. [ABSTRACT FROM AUTHOR]

Abstract: The study of mesoscale and submesoscale [hereafter (sub)mesoscale] hydrodynamic features is essential for understanding thermal and biogeochemical exchanges between coastal areas and the open ocean. In this context, a glider mission was conducted in August 2008, closely co-located and almost simultaneously launched with a JASON 2 altimetric pass, to fully characterize the currents associated with regional (sub)mesoscale processes regularly observed to the north of Mallorca (Mediterranean Sea). A synoptic view from satellite remote-sensing fields, before and during the glider mission, provided a descriptive picture of the main surface dynamics at the Balearic Basin scale. To quantify the absolute surface geostrophic currents, the coastal altimetry-derived current computation was improved and cross-compared with its equivalent derived from glider measurements. Model simulations were then validated both qualitatively and statistically with the multi-sensor observations. The combined use of modeling and multi-sensor observational data reveals the baroclinic structure of the Balearic Current and the Northern Current and a small-scale anticyclonic eddy observed northeast of the Mallorca coast (current∼15cm/s, <30km in extent and >180m deep). This mesoscale structure, partially intercepted by the glider and along-track altimetric measurements, is marked by relatively strong salinity gradients and not, as is more typical, temperature gradients. Finally, the use of the validated model simulation also shows that the geostrophic component of this small-scale eddy is controlled by sub-surface salinity gradients. We hypothesize that this structure contains recently modified Atlantic water arriving from the strait of Ibiza due to a northerly wind, which strengthens the northward geostrophic circulation. [Copyright &y& Elsevier]

Abstract: The surface currents of the Levantine sub-basin (Mediterranean Sea) are described using 18 years (1992–2010) of drifter data and satellite-derived sea level anomalies. The combination of drifter and satellite data allowed to estimate maps of surface geostrophic circulation and to obtain more accurate pseudo-Eulerian velocity statistics for different time periods. Seasonal and interannual variability of surface currents are investigated with particular focus on the main sub-basin eddies of the eastern Levantine. The mean velocity field depicts the typical patterns of the along-slope and offshore currents and outlines the sub-regions where eddies are generated recurrently (west Egyptian coast, Ierapetra, Mersa-Matruh, south-west of Cyprus, Israel–Lebanon coast, Latakia) or persist steadily (Rhodes Gyre). Highly variable and energetic currents are observed between the Ierapetra and Mersa-Matruh regions, as the result of the interaction of the Mid-Mediterranean Jet meandering in between, and interacting with, the eddies generated by the instability of the coastal current. Seasonal pseudo-Eulerian maps show the current field stronger in summer and weaker in winter, mainly in the western Levantine and in the Cyprus–Syria Passage. The Shikmona Eddy displays a periodic nature with higher intensities during the cold months and an enhanced activity in the period 1998–2005. The Cyprus Eddy has a less periodic nature, characterised by events of high activity and periods in which it dominates as a single enlarged eddy in the southeast Levantine, eventually including the Shikmona Eddy. The Latakia Eddy is mainly cyclonic with higher intensities in summer and fall; occasional weekly or monthly inversions of circulation from cyclonic to anticyclonic are triggered by the interaction between the MMJ and the northward coastal meandering current. [Copyright &y& Elsevier]

Coastal mesoscale eddies were evidenced during a high-frequency radar campaign in the Gulf of Lions (GoL), northwestern Mediterranean Sea, from June 2005 to January 2007. These anticyclonic eddies are characterized by repeated and intermittent occurrences as well as variable lifetime. This paper aims at studying the link between these new surface observations with similar structures suggested at depth by traditional acoustic Doppler current profiler measurements and investigates the eddy generation and driving mechanisms by means of an academic numerical study. The influence of the wind forcing on the GoL circulation and the eddy generation is analyzed, using a number of idealized configurations in order to investigate the interaction with river discharge, buoyancy, and bathymetric effects. The wind forcing is shown to be crucial for two different generation mechanisms: A strong northerly offshore wind (Mistral) generates a vortex column due to the bathymetric constraint of a geostrophic barotropic current, which can surface after the wind relaxes; a southerly onshore wind generates a freshwater bulge from the Rhône river discharge, which detaches from the coast and forms a well-defined surface anticyclonic eddy based on buoyancy gradients. These structures are expected to have important consequences in terms of dispersion or retention of biogeochemical material at local scales. [ABSTRACT FROM AUTHOR]

Abstract: Altimetry has become a powerful tool to understand the dynamics of the deep-sea ocean circulation. Despite the technical problems encountered in the coastal zone by this observational technique, resulting in large data gaps in those areas, solutions already exist to mitigate this issue and to allow the retrieval of coastal information from existing altimetric data. Using some of these solutions, we have reprocessed a new set of 14.5years of the TOPEX/Poseidon and Jason-1 satellite altimeter data over the Northwestern Mediterranean Sea, leading to a significant increase in the quantity of available data near coastlines. Time series of geostrophic surface velocity anomalies have been computed from the along-track altimeter sea level anomalies. In this paper, we evaluate the ability of these altimeter-derived currents to capture the main surface circulation features and the associated seasonal variability in the area of interest. In-situ ADCP current measurements are used to estimate the accuracy of altimeter geostrophic surface velocity anomalies at different locations on the shelf edge. The results indicate good qualitative altimeter performances at seasonal time scales, confirming that altimetry is reliable to observe synoptic variations of the Liguro–Provençal–Catalan Current System. The seasonal evolution of the shelf edge flow is then documented using results from satellite altimetry and from sea surface temperature (SST). The regional picture of the shelf edge circulation that emerges agrees fairly well with previous knowledge (the flow is much stronger during winter than during summer) but also reveals interesting aspects of the coastal current system: (1) the characteristics of the seasonal cycle observed appear highly consistent along the Northwestern Mediterranean shelf break, suggesting a continuous current from the Tyrrhenian to the Balearic Seas, (2) the relationship with the Balearic Current appears somewhat more complex and suggests that its evolution is controlled by another inflow contribution, at least in spring, (3) the seasonal variations of the shelf edge flow over a particular year can show large discrepancies with the averaged picture presented in this study, since large year to year differences are observed. [Copyright &y& Elsevier]

Abstract: The circulation of the Gulf of Lion, a large continental shelf north of the western basin of the Mediterranean Sea, is complex and highly variable. During stratified conditions, unexpected barotropic eastward currents can be detected, mostly in the western part of the gulf. Care is given to retrieve inertial oscillations when necessary. The primitive-equation free-surface model Symphonie is used to investigate the processes which can generate and influence these eastward currents. Three main wind forcing create these barotropic eastward currents: northwesterlies channelled in the western part of the gulf, northwesterlies and north winds both homogeneous throughout the gulf. In the first case, the wind stress curl of the channeled northwesterlies generates an elongated cyclonic circulation in the western part of the Gulf of Lion. The southern part of this cyclonic circulation is a barotropic eastward current, detected west of longitude 4.5°E. In the second case, a homogeneous northwesterly wind creates an intrusion of the along-slope geostrophic current on the shelf, generating a strong coastal jet going northward above Cap Creus. In stratified conditions, intrusion at this western end of the continental shelf only occurs during this type of wind forcing. The coastal jet goes north then detaches itself from the coast and goes eastward, north of the 100 m isobath. In the third case, a homogeneous north wind creates an eastward current which occupies the whole shelf north of latitude 43°N. The first two cases are studied in more details since cruise data corroborate the model simulations. The striking characteristic of these eastward currents is that they are barotropic despite the stratified conditions. Otherwise, their amplitude and exact locations are slightly different for the different cases of circulation. These eastward currents probably have an impact on the residence time of water masses in the Gulf of Lion, and hence on the total water budget of the gulf, as well as on primary production and biogeochemical fluxes. [Copyright &y& Elsevier]

Abstract: An intensive observational programme of the Balearic Front, in the Western Mediterranean Sea, was carried out using conventional (CTDs from a ship) and new technologies (gliders). The strategy consisted of repeated sampling of a section almost perpendicular to the Balearic Current situated to the north of Mallorca Island. This section is coincident with track 773 of the ENVISAT satellite. In this work we present results of missions undertaken in July and September 2007. In July the sampling was designed to collect in-situ data from a ship and a coastal glider, almost simultaneously with the passage of the radar altimeter on board the ENVISAT satellite. In September the sampling was done only by the glider platform, and also simultaneously with the passage of the satellite. The Balearic Front was clearly detected by salinity (not temperature), with lower values (37.4 PSU) near the coast that are likely to be related to the input of recent Atlantic Water through the Mallorca Channel. The observed width of the front was about 35–40 km, with a vertical extension of 200 m. It had a significantly different pattern between the July and September samplings, which confirms the high mesoscale variability of this frontal area. Using a reference depth level of 180 m we have obtained maximum geostrophic velocities of 40–45 cm/s, flowing northeastwards along the north Mallorca coast. These velocity estimates are not sensitive to the test reference level (600 m), indicating that the layer between 200 and 600 m does not play a key role in the dynamics of the upper layer (200 m). A dynamic height rise from July to September (in 70 days) of about 3–7 cm reflects the seasonal cycle of sea level due mainly to thermosteric expansion of the water column. This gives a rise rate in the range of 1.3–3 cm/month, which is in agreement with previous estimates in the Mediterranean Sea. Absolute dynamic topography from altimetry data reveals good coherence with the dynamic height from the glider data in the area where there are common observations. In September, ENVISAT captured the sharp gradient observed with in-situ data, with mean velocities of about 24 cm/s, but with a smaller variance than the glider due to the larger wavelength of the filter applied to the altimeter data. From the technological point of view the observational experiment has confirmed the feasibility of using a coastal glider to monitor the spatial and low-frequency variability of the coastal ocean. The coastal glider was appropriate in this particular case since the vertical extension of the front only reaches up to 200 m. The autonomous platform was shown to be strongly robust, and able to monitor the area even under adverse meteorological conditions. This represents an important achievement, since under the same conditions the CTD sampling from a traditional research vessel would normally have been cancelled. Moreover, this type of platform allows autonomous collection of CTD casts and biogeochemical measurements at high spatial resolutions and at very low costs compared to conventional methods. [Copyright &y& Elsevier]