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Sea cucumbers are benthic marine invertebrate members of the phylum Echinodermata. Due to the absence of a rigid skeleton, these species have developed chemical defenses based on the production of saponins (triterpene glycosides). These secondary metabolites are bioactive molecules with a broad biological, ecological, and pharmaceutical spectrum. However, the saponin profiles of several species of sea cucumbers are not known yet. The present study aims to highlight the mixture of saponins in two sea cucumber species from the Algerian coast, namely Holothuria (Holothuria) algeriensis, which has been recently described in central and western Algerian waters, and Holothuria (Roweothuria) arguinensis, originating from the Atlantic Ocean and reported in Algeria for the first time in 2014. Saponin extracts from three individuals of H. (H.) algeriensis and two individuals of H. (R.) arguinensis were analyzed using mass spectrometry, i.e., Matrix-assisted Laser Desorption/Ionization mass spectrometry (MALDI-MS), MALDI-High Resolution MS (MALDI-HRMS), Liquid Chromatography MS (LC-MS) and tandem MS (LC-MS/MS). These analyses allow us to detect 11 and 18 elemental compositions for H. (H.) algeriensis and H. (R.) arguinensis, respectively, each presenting several isomers. In total, 13 new saponin structures are proposed, of which four are common between the two species, six are specific to H. (H.) algeriensis and three to H. (R.) arguinensis. The saponin profiles of the two species were compared to those of other species of the same genus existing on the Algerian coast and the results showed that they share non-sulfated saponins with Holothuria (Panningothuria) forskali and Holothuria (Platyperona) sanctori and sulfated saponins with Holothuria (Holothuria) tubulosa and Holothuria (Roweothuria) poli. [ABSTRACT FROM AUTHOR]

The study of echinoderms in the Mediterranean region has generated considerable interest and has led to significant advancements in systematic research. Numerous species have been identified, with 35% of them belonging to the Holothuroidea class. This paper provides pertinent information on the echinoderm fauna of the Algerian coast, specifically focusing on the sampling conducted at Plane Island in western Algeria. Additionally, it includes an updated account of previously recorded species. The recent research findings consist of a total of 288 specimens: 284 ophiuroids and 4 echinoids. The research provides a comprehensive list of all the species identified. Additional species have been discovered at Paloma (Plane) Island. Several of these species have not previously been recorded on the Algerian coastline, such as the pencil urchin Stylocidaris affinis. A map of its distribution has been created to monitor its establishment in the Mediterranean. Our findings show that S. affinis is more abundant in shallow waters ranging from 50 to 150 m. A total of 70 species were documented along the Algerian coast, with the majority belonging to the classes Holothuroidea and Ophiuroidea. The class Crinoidea, however, only counts three species: Antedon bifida moroccana, A. mediterranea, and Leptometra celtica. The majority of species (65.2%) have a distribution that spans the region of the Atlantic Ocean and the Mediterranean Sea. Approximately 33% of species are potentially exclusive to the Mediterranean region, and only one species (1%) is found worldwide. Three echinoderms are now indexed as endangered or threatened in Barcelona’s Appendix II. Moreover, to provide a comprehensive understanding, this study compares the fauna of the Algerian coast with that of adjacent seas.

The western Mediterranean Sea has traditionally served as a primary foraging ground for juvenile loggerhead turtles from three distinct regional management units: the North‐western Atlantic, the Mediterranean and Cape Verde. Nesting activities were sporadic.Recently, nesting activity on the beaches of eastern Spain has increased, due to warmer sand and water temperatures during the summer months.The study has integrated stable isotope analysis of carbon (C), nitrogen (N) and sulphur (S) with satellite telemetry to identify the foraging grounds of these new colonizers nesting on Spanish beaches.Results indicate that the majority of these adult females forage oceanically in the Algerian Basin, with a few exhibiting distinct stable isotope signals, tentatively associated with foraging in shallow coastal areas in the central Mediterranean Sea.The dominance of oceanic foragers in this new population is noteworthy, given the Algerian Basin's oligotrophic nature. This contrasts with the prevalence of neritic foraging in adult females nesting in the central and eastern Mediterranean Sea.The use of the Algerian Basin as a foraging ground for adult loggerhead turtles exposes them to bycatch from drifting longlines. The authorities should refrain from increasing bluefin quotas imposed on longliners in the Algerian Basin unless the fishery avoids using squid as bait and agrees to deploy hooks deeper than 25 m to reduce loggerhead turtle bycatch. [ABSTRACT FROM AUTHOR]

Field analogues illustrating the early stage of deformation of shortening structures in salt‐bearing orogenic fold‐and‐thrust belts are not yet well illustrated in literature. The relatively young Messinian salt of the Algerian basin could represent a good case example of such systems. The Algerian Basin is a deep‐water Miocene back‐arc basin including a layer of mobile Messinian evaporites up to 2 km thick. The Messinian salt was deposited in an already inverted basin, after its extensive stage. Its inversion initiated in the Tortonian, with a N‐NW shortening induced by the north‐westward motion of the African plate. In this study, we use new 2D multichannel seismic data to identify, classify and map salt structures throughout the central Algerian Basin and re‐assess its structural style. We interpret contractional salt tectonic structures, such as buckle folds, squeezed diapirs and related salt sheets as evidence of regional thick‐skinned shortening episodes. We conclude that horizontal displacement loading has driven salt deformation within the basin since its deposition. We also show spatial variations in the structural style of the central Algerian Basin, both along‐ and down‐dip. We demonstrate that the initial shortening‐related salt deformation in the late Messinian was focussed along the Algerian margin and later shifted outward toward the Balearic margin in the Plio‐Quaternary. The shifting of the deformation front is interpreted to be a result of the thickening and strengthening of the overburden. The second peak of deformation may have reactivated faults along the Emile‐Baudot escarpment with thick‐skinned deformation. We also observe a variation in the intensity of the salt deformation along the margin from SW to NE, which may be due to variable tectonic loading applied along the Algerian margin or the pre‐shortening distribution of salt. [ABSTRACT FROM AUTHOR]

The aim of this work is to study the biometric and reproductive characteristics of a population of Holothuria poli from the west Algerian coast. The study was carried out on 256 individuals (33.25 ± 12.38 g wet weight and 196.44 ± 37.81 mm relaxed length) collected from Oran Bay between October 2016 and September 2017. All individuals showed negative allometric growth (b = 1.586) and the population had a sex ratio of 1: 1 (male: female). Sexual maturity occurred at a relaxed length of 137 mm and at gutted body weight of 18 g. Macroscopic examination of the gonadal tubules revealed four sexual maturity stages (growth, maturity, spawning and post-spawning) and a reproductive pattern characterized by a single summer spawning period and autumnal sexual rest. The obtained data may constitute a database for the management of natural stocks of this sea cucumber species in Algerian waters. [ABSTRACT FROM AUTHOR]

This study investigates a long-term assessment of the wave energy resource propagated along the Algerian basin, based on a 39-year wave hindcast. The wave energy hindcast dataset was developed using the Simulating WAve Nearshore (SWAN) model, calibrated and validated [1] against wave measurements performed on the Algerian coast. A detailed spatial and local analysis was performed following the hindcast results. We have determined several parameters including; hourly, monthly, seasonal and annual variations of wave energy resources, the probability of occurrence distribution for different wave power ranges with different directions, the probability of calm sea states, the wave energy development index (WEDI) and the total annual wave energy and their distribution as a function of significant wave height and energy period. All these results enabled a very important benchmark for decision making regarding the future implementation and design of wave energy converters (WECs) and other offshore structures in the Algerian basin. Our findings have shown that the Algerian coasts are characterized by a considerable wave energy potential with a large hotspot area in the eastern coasts. Thus, we have recorded a significant variability in the wave energy characteristics available in each zone along the Algerian coast. The western zone was characterized by an average energy of ∼7.5 kW/m with a low monthly and seasonal variation (<1.2), the central zone was characterized by a significant total annual wave energy of 63 MWh/m/year and a considerable WEDI of 0.019, and the eastern Algerian coast was characterized by one of the highest energy potential in the Mediterranean basin with a total annual energy exceeding 100 MWh/m for less than 15 km from the coast and a calm sea state probability lower than 18%. Thus, it has been concluded that since 1995, wave energy resources have tended to increase further. • A first detailed long-term assessment of wave energies in the Algerian coast. • Largest hotspot area in the W-Med basin is located in the Eastern coast of Algeria. • High resolution SWAN model (∼3 km) calibrated for the Algerian basin was used. • A new accurate 39-year wave energy hindcast dataset has been developed. • Wave energy resources tend to increase further since 1995 in the Algerian coast. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the population distribution and some biological aspects for fish stock assessment of the greater forkbeard Phycis blennoides along the Algerian basin. The distribution of P. blennoides (3418 individuals) was studied using data collected between 170–779 m depth during two bottom trawl surveys developed on 2003 and 2004. Additionally, some biological parameters were obtained from 1050 individuals sampled from commercial fisheries in Algerian ports (i.e. Annaba, Azeffoun, Dellys, Cap Djinet, Zemmouri, Bouharoun, Algiers, La Madrague, Cherchell, Tenes and Mostaganem) during the period 2013–2017. P. blennoides sampled from bottom trawl surveys showed a depth related distribution with the largest individuals being found at 600–800 m depth and the smallest at shallower depths. Density and biomass varied with depth and density also with longitude, while biomass showed no pattern with longitude. Recruitment was recorded in the eastern sector of Algeria during winter, for individuals sampled by bottom trawl surveys. Young P. blennoides entered commercial fisheries in summer, with an overall sex ratio skewed towards males (1F:2.18M). The size at first maturity (L50) was 24.30 cm and 30.39 cm for males and females, respectively. The age at 50% maturity was 2–3 years for specimens collected by a bottom trawl survey in 2003 and commercial fisheries, but 3–4 years for the bottom trawl survey in 2004. [ABSTRACT FROM AUTHOR]

Marine phytoplankton forms the basis of the marine food web. Its diversity (size and pigmentation) has a significant impact on biogeochemical processes such as photosynthetic efficiency, trophic interactions, and global carbon fluxes. To date, little is known about the Algerian Basin regarding phytoplankton quality and quantity. In this study, we analyzed the distribution of phytoplankton communities in the Algerian Basin based on HPLC/Chemotaxonomy analysis for the summer season of 2014. The chemical taxonomy software CHEMTAX v1.95 was used to estimate the contributions of various phytoplankton groups to total Chlorophyll a (TChl a). The results showed that prymnesiophytes were the dominant group (16%) in the nanoplankton and occupied the entire water column, whereas cryptophytes were observed exclusively in the western region of the basin, and contributed about 6% to the TChl a. Diatoms had the highest contributions (18%) to the TChl a , and their emergence was linked to nutrient enrichment. Dinoflagellates had a contribution of about 12% with little variation throughout the basin. Prochlorococcus had a contribution of about 13% and prevailed in the deep layers (60–100 m) following the nitracline, while Synechococcus (11%) occupied the shallower layers (10–60 m) (beneath the MLD) following the nutrient depletion. Moreover, it is noteworthy that phytoplankton communities in the western part of the basin showed greater diversity and abundance, influenced by Atlantic waters and deep nutrient enrichment. In contrast, the eastern part of the basin displayed lower productivity, characterized by reduced diversity and the prevalence of nano- and picoplankton. • Phytoplankton communities in the Algerian basin are characterized by the CHEMTAX approach. • Nano- and micro-phytoplankton prevail in the Algerian basin. • Diatoms, prymnesiophytes, and Prochlorococcus are the major phytoplankton groups in the Algerian basin. • Phytoplankton communities are more abundant and diverse in the west of the Algerian basin than in the east. • Phytoplankton community composition is linked to the Algerian Basin's physical-chemical dynamics. [ABSTRACT FROM AUTHOR]

Highlights • A high resolution hindcast model SWAN was calibrated and validated for the Algerian Basin. • Janssen (1991) formulation with C ds1 = 1 for whitecapping in the W-Med Sea has a better performance. • Komen et al. (1984) formulation for wind growth in the W-Med Sea presents a better accuracy. • The calibrated SWAN performs better using Komen formula compared to the new ST6. Abstract This study aims to present an evaluation and implementation of a high-resolution SWAN wind wave hindcast model forced by the CFSR wind fields in the west Mediterranean basin, taking into account the recent developments in wave modelling as the new source terms package ST6. For this purpose, the SWAN model was calibrated based on one-year wave observations of Azeffoune buoy (Algerian coast) and validated against eleven wave buoys measurements through the West Mediterranean basin. For the calibration process, we focused on the whitecapping dissipation coefficient C ds and on the exponential wind wave growth and whitecapping dissipation source terms. The statistical error analysis of the calibration results led to conclude that the SWAN model calibration corrected the underestimation of the significant wave height hindcasts in the default mode and improved its accuracy in the West Mediterranean basin. The exponential wind wave growth of Komen et al (1984) and the whitecapping dissipation source terms of Janssen (1991) with C ds = 1.0 have been thus recommended for the western Mediterranean basin. The comparison of the simulation results obtained using this calibrated parameters against eleven measurement buoys showed a high performance of the calibrated SWAN model with an average scatter index of 30% for the significant wave heights and 19% for the mean wave period. This calibrated SWAN model will constitute a practical wave hindcast model with high spatial resolution (˜3 km) and high accuracy in the Algerian basin, which will allow us to proceed to a finer mesh size using the SWAN nested grid system in this area. [ABSTRACT FROM AUTHOR]

The Algerian Basin is a key component of the general circulation in the Western Mediterranean Sea. The presence of both fresh Atlantic water and more saline Mediterranean water gives the basin an intense inflow/outflow regime and complex circulation patterns. Energetic mesoscale structures that evolve from meanders of the Algerian Current into isolated cyclonic and anticyclonic eddies dominate the area, with marked repercussions on biological activity. Despite its remarkable importance, this region and its variability are still poorly known and basin-wide knowledge of its meso- and submesoscale features is still incomplete. Studying such complex processes requires a synergistic approach that involves integrated observing systems. In recent years, several studies have demonstrated the advantages of combined use of autonomous underwater vehicles, such as gliders, with a new generation of satellite altimetry. In this context, we present results of an observational program conducted in the Algerian Basin during fall 2014 and 2015 that aimed to advance our knowledge of its main features. The study was carried out through analysis of high resolution glider observations, collected along the Algerian BAsin Circulation Unmanned Survey (ABACUS) chokepoint, in synergy with co-located SARAL/AltiKa altimetric products and CMEMS numerical simulations. Results show that glider-derived dynamic height and SARAL/AltiKa absolute dynamic topography have similar patterns, with RMS of the differences ranging between 1.11 and 2.90 cm. Even though larger discrepancies are observed near the Balearic and Algerian coasts, correlation coefficients between glider and satellite observations seem mostly to be affected by reduced synopticity between the measurements. Glider observations acquired during the four surveys reveal the presence of several water masses of Atlantic and Mediterranean origin (i.e., AW and LIW at different modification levels) with marked seasonal variability. [ABSTRACT FROM AUTHOR]

The Algerian Basin is a key area for the general circulation in the western Mediterranean Sea. The basin has an intense inflow/outflow regime with complex circulation patterns, involving both fresh Atlantic water and more saline Mediterranean water. Several studies have demonstrated the advantages of the combined use of autonomous underwater vehicles, such as gliders, with remotely sensed products (e.g., altimetry, MUR SST) to observe meso- and submesoscale structures and their properties. An important contribution could come from a new generation of enhanced satellite sea surface salinity (SSS) products, e.g., those provided by the Soil Moisture and Ocean Salinity (SMOS) mission. In this paper, we assess the advantages of using Barcelona Expert Center (BEC) SMOS SSS products, obtained through a combination of debiased non-Bayesian retrieval, DINEOF (data interpolating empirical orthogonal functions) and multifractal fusion with high resolution sea surface temperature (OSTIA SST) maps. Such an aim was reached by comparing SMOS Level-3 (L3) and Level-4 (L4) SSS products with in situ high resolution glider measurements collected in the framework of the Algerian Basin Circulation Unmanned Survey (ABACUS) observational program conducted in the Algerian Basin during falls 2014−2016. Results show that different levels of confidence between in situ and satellite measurements can be achieved according to the spatial scales of variability. Although SMOS values slightly underestimate in situ observations (mean difference is −0.14 (−0.11)), with a standard deviation of 0.25 (0.26) for L3 (L4) products), at basin scale, the enhanced SMOS products well represent the salinity patterns described by the ABACUS data.

The Yaddene complex, located in Lesser Kabylia (northeastern Algeria), is composed of Tertiary mafic and ultramafic rocks that outcrop within syn-rift sedimentary rocks of the Algerian marginal basin, in the Maghrebide belt of North Africa. Petrographic observations show that the Yaddene complex is composed mainly of two distinct lithologies: (1) a layered quartz-bearing gabbro at the bottom, which consists mainly of plagioclase (An 93), clinopyroxene (altered to actinolite) and rare interstitial quartz; and (2) layered plagioclase-bearing lherzolites composed of olivine (Fo 86-88) orthopyroxene (En 86 – 87), clinopyroxene (diopside and augite), rare plagioclase (anorthite) and amphibole of pargasitic composition. The trace element concentrations in pyroxenes and olivine of the Yadenne complex show a depletion in light rare earth elements (LREE) similar to basalts of the Mid-Ocean Ridge (N-MORB), which reflects the depletion of the mantle source. In addition, high #Cr in spinel reflects a high degree of partial melting of the mantle source. On the other hand, slight enrichment in Large Ion Lithophile Elements (Cs, Rb, Ba), weak but significant negative Nb, Ta, Zr, Hf and Ti anomalies, and positive Pb spikes are observed in both whole-rocks and minerals. These patterns are best explained by interaction between parental mantle and fluids and/or siliceous melts derived from a subducting oceanic slab. The tectonic discrimination diagrams of minerals and whole rocks indicate that the most likely geodynamic setting for emplacement of the Yaddene Complex is a back arc basin environment. In situ U-Pb dating of euhedral zircons and titanite from a quartz-bearing gabbro yields an age of 18.97 ± 0.12 Ma (2σ), which is interpreted as the crystallization age of magmatic zircons and the gabbroic magma. Zircons from a plagioclase-bearing lherzolite gave a consistent age of 19.05 ± 0.39 Ma (2σ), which is attributed to zircon growth during metamorphic/metasomatic processes coeval to gabbroic magma emplacement. The mafic/ultramafic rocks of the Yaddene complex are intercalated within fine-grained sediments of the syn-rift "Oligo-Miocene Kabyle" and the obtained early Burdigalian ages are interpreted as the early stages of an extensional regime that ultimately led to the opening of the oceanic Algerian Basin. • Minerals composition reflects the very high rate of partial melting of the mantle source. • Trace element contents indicate a slightly metasomatized mantel and suggest a back-arc basin environment proximal to the arc. • The thermobarometric calculations show very high temperatures (≈1000 °C) for low pressures (1–3 Kbar). • U-Pb zircon dating yields ages of 19 Ma attributed to emplacement of gabbroic magma from the Yadenne complex. [ABSTRACT FROM AUTHOR]

Despite an extensive bibliography for the circulation of the Mediterranean Sea and its sub-basins, the debate on mesoscale dynamics and their impacts on bio-chemical processes is still open because of their intrinsic time scales and of the difficulties in their sampling. In order to clarify some of these processes, the “Algerian BAsin Circulation Unmanned Survey-ABACUS” project was proposed and realized through access to the JERICO Trans National Access (TNA) infrastructure between September and December 2014. In this framework, a deep glider cruise was carried out in the area between the Balearic Islands and the Algerian coast to establish a repeat line for monitoring of the basin circulation. During the mission a mesoscale eddy, identified on satellite altimetry maps, was sampled at high-spatial horizontal resolution (4 km) along its main axes and from the surface to 1000 m depth. Data were collected by a Slocum glider equipped with a pumped CTD and biochemical sensors that collected about 100 complete casts inside the eddy. In order to describe the structure of the eddy, in situ data were merged with next generation remotely sensed data: daily synoptic sea surface temperature (SST) and chlorophyll concentration (Chl-a) images from the MODIS satellites, as well as sea surface height and geostrophic velocities from AVISO. From its origin along the Algerian coast in the eastern part of the basin, the eddy propagated northwest at a mean speed of about 4 km/day, with a mean diameter of 112–130 km, mean amplitude of 15.7 cm; the eddy was clearly distinguished from the surrounding waters thanks to its higher SST and Chl-a values. Temperature and salinity values over the water column confirm the origin of the eddy from the Algerian Current (AC) showing the presence of recent Atlantic water in the surface layer and Levantine Intermediate Water (LIW) in the deeper layer. The eddy footprint is clearly evident in the multiparametric vertical sections conducted along its main axis. Deepening of temperature, salinity and density isolines at the center of the eddy is associated with variations in Chl-a, oxygen concentration and turbidity patterns. In particular, at 50 m depth along the eddy borders, Chl-a values are higher (1.1–5.2 μg/l) in comparison with the eddy center (0.5–0.7 μg/l) with maximum values found in the southeastern sector of the eddy. Calculation of geostrophic velocities along transects and vertical quasi-geostrophic velocities (QG-w) over a regular 5 km grid from the glider data helped to describe the mechanisms and functioning of the eddy. QG-w presents an asymmetric pattern, with relatively strong downwelling in the western part of the eddy and upwelling in the southeastern part. This asymmetry in the vertical velocity pattern, which brings LIW into the euphotic layer as well as advection from the northeastern sector of the eddy, may explain the observed increases in Chl-a values. [ABSTRACT FROM AUTHOR]

In May 1998 a big and deep open ocean anticyclonic eddy (AE 98-1) was sampled in the Algerian basin (western Mediterranean sea) in a region south of the Balearic islands. Fifteen surface Lagrangian buoys, tracked by satellite, were released across the eddy and were used for a few months to observe the continuity of the anticyclonic motion and the westward drift of the eddy. This kind of big and intense eddies in the Mediterranean can be detected by satellite altimeter radars. Using a new method, based on the Okubo-Weiss criterion, to identify mesoscale eddies in Sea Level Anomaly maps derived from measurements of the ERS and TOPEX/POSEIDON altimeters, an independent tracking of the same eddy was performed. There is a remarkable agreement between the two results despite the different nature of the information, mainly due to the fact that SLA maps contain interpolated and smoothed measurements while the drifter? trajectories are in situ data obtained from individual drifter fixes. The location of the eddy centre during two months with the two methods agrees within an average distance lower than the spatial resolution of the altimetric maps (0.2º). The size of the eddy, when it is possible to determine it, is also highly coincident in both cases (96.5% in diameter), and its average westwards translation speed is reasonably similar (24% lower from drifters). These results can be considered a good validation of the new tracking method in SLA maps in this specific case.

We report for the first time the discovery of diamond inclusions (5–30 μm in size), identified by Raman spectroscopy and the characteristic sharp band at 1332 cm − 1 for crystalline diamond, in a garnet megacryst (≥ 5 cm) from the Edough Massif (NE Algeria). The garnet is adjacent to actinolite and ultramafic boudins and slices of marbles that are inserted within a major mylonite–ultramylonite band. This tectonic contact sharply delineates the Kef Lakhal oceanic unit from the granite-gneiss core below. The host garnet is almandine-dominant and is rich in exsolution of acicular rutile needles. Major and trace elements show a gradual but significant zonation from core to rim, and a sharp increase in grossular component in the rim. Trace element analyses of prismatic rutile inclusions up to 300 μm in size indicate that the host metamorphic rock was a mafic protolith of MORB affinity. The Zr-in-rutile thermometry indicates a temperature range of 724–778 °C that we relate to rutile growth, either during prograde metamorphism or under peak UHP metamorphic conditions of ≥ 3.6 GPa that were reached during subduction of the UHP-rock precursors. We suggest that the mafic protolith originates from the subducted retreating Calabrian branch of the Tethyan slab, that broke or tore, and which fragments were dragged upward and thrust onto the North African margin along with the Kef Lakhal unit, shortly followed by formation of the Edough dome and opening of the Algerian basin. [ABSTRACT FROM AUTHOR]

The pelagic decapod crustacean fauna of two different zones (Sóller and Cabrera) with different hydrographic dynamics and oligotrophy levels was studied around Mallorca (western Mediterranean), the latter with a higher degree of oligotrophy than the former. Samples were taken with a Pelagic Trawl and an IKMT in the upper 600 m of the water column, targeting larger and middle-sized nektonic species, respectively. Fourteen species were collected: five dendrobranchiate shrimps, eight caridean shrimps and one scyllarid lobster. Some species were restricted to the shelf-break: Chlorotocus crassicornis and Plesionika heterocarpus . Others were exclusive of the middle slope: Pasiphaea multidentata , and Sergia robusta . Pasiphaea sivado and Gennadas elegans occurred in all pelagic strata. Multivariate analyses showed several distinct assemblages related to bathymetry and sampling depth. No significant differences were found concerning zone or sampled seasons. Bathymetrically, Deep Scattering Layers showed the highest diversity. No decapod crustaceans occurred in epipelagic daytime samples. The pelagic decapod community sampled was structured by both the geomorphology (and associated hydrographic characteristics over the shelf-break) and the influence of light in the water column. Size analysis showed species-specific patterns concerning size/age movements into the water column throughout the day–night cycle. [ABSTRACT FROM AUTHOR]

Abstract: The Maghrebides, Betics and some parts of the Calabrian, NE Sicilian and Tuscan allochtons constitute dismembered fragments of the Alpine belt that resulted from the Cenozoic collision between Africa and Eurasia and the opening of the Western Mediterranean basin. Mineral and whole-rock geochemical analyses have been performed on three distinct outcrops of mantle material from the Edough Massif of NE Algeria, namely the Bou Maiza (BM) gabbros, the La Voile Noire (LVN) amphibolites and the Sidi Mohamed (SM) peridotites. In all samples, Sr isotopes are largely affected by seawater alteration (87Sr/86Sract. >0.70384 and up to 0.70888) and cannot be used to evaluate the nature of the source reservoirs. SM peridotites display variable depleted mantle Nd isotopic signatures (εNdact. from +7.0 to +12.2) and geochemical features suggesting no significant chemical depletion as a result of partial melting and melt extraction (Mg#<90; slightly LREE-depleted patterns with La/YbN =0.33–0.39). These rocks are interpreted as parts of the subcontinental lithospheric mantle incorporated into the crustal units of the Edough Massif during the early stages of opening of the Algerian basin. BM gabbros and LVN amphibolites show geochemical signatures indicating derivation from a common depleted mantle reservoir (εNd >+7.9) and are likely cogenetic, but without filiation with the SM peridotites. Pb isotopes indicate a contribution of sediments in the source reservoir, which is attributed to contamination solely by hydrous fluids released from a sedimentary component. This observation, together with a LILE-enrichment, suggests a back-arc basin environment. These results indicate that BM and LVN units were obducted onto the North African margin and subsequently fragmented, probably during doming and exhumation of the lower continental crust of the Edough massif. Doming resulted in opposite movements of the overlying oceanic units, southward for the BM units and northward for LVN amphibolites. [Copyright &y& Elsevier]

The position of the middle-upper Miocene volcanic arc, encompassing the Maghrebides, the Sardinia Channel and the Sardinia-Corsica block, implies that the Algerian and Tyrrhenian basins developed, respectively, as backarc and forearc extensional zones in the Western-Central Mediterranean. The opening of the Western-Central Mediterranean Neogene extensional basin has been commonly interpreted as a two-step process: the opening of the Provençal-Algerian basin during the early-middle Miocene, followed, in the late Miocene, by the formation of the Tyrrhenian Basin. This article is an attempt to synthesize knowledge about the hinge zone between Algerian and Tyrrhenian basins by combining the analysis of seismic reflection profiles with dredge and borehole data in order to investigate how the transition between the eastern Algerian backarc and Tyrrhenian forearc geodynamic settings took place. We identified three sectors: the western Tyrrhenian characterized by a Tortonian forearc extension; the Sardinia Channel, which preserves the architecture of the lower Miocene Maghrebian thrust belt formed during the collision between Europe and Africa plates; and the easternmost Algerian basin-Sicily Channel where a backarc–thrust belt system developed during the Tortonian stage. During the extensional events, we hypothesize the re-activation of inherited structures during Tortonian rifting, (that is a negative tectonic inversion of pre-existing Eocene and early Miocene thrust faults). The contemporaneity of two different geodynamic environments, the forearc extension in the northern area and backarc–thrust belt system in the southern area, can be directly related with a lateral variation of the lower plate paleogeography of the Africa continental margin. This evidence contributes to the understanding of how the paleogeography of the lower plate can control, to a certain extent, the tectonic evolution of the upper plate in a subduction setting. • We study the area between Algerian backarc and Tyrrhenian forearc geodynamic settings. • We combine the analysis of seismic reflection profiles, dredge and borehole data. • An older thrust belt lies between Tortonian forearc rift and backarc–thrust belt. • We propose a link among upper plate and paleogeography of the lower plate. [ABSTRACT FROM AUTHOR]

Abstract: Caesium-137 and 239,240PU were analysed in the water column along the Algerian coast. The 137Cs activity concentration in surface water increased from the west to the east from 1.6 to 3.3mBqL−1, documenting a presence of Modified Atlantic Water (MAW) in the region. Higher concentrations observed in deep waters may be due to an intrusion of Levantine Intermediate Water (LIW), which has been carrying higher levels of 137Cs from Chernobyl accident. The 239,240Pu sub-surface concentration peaked at about 250m water depth as a result of biogeochemical processes in the water column. The observed 239,240Pu/137Cs activity ratio at the surface (0.003) was significantly lower than that in global fallout (0.04). This decrease exceeds that expected from radioactive decay of 137Cs, and confirms that Pu due to its adsorption on sinking particles is more effectively removed from surface layers than is 137Cs. An increase of the 239,240Pu/137Cs activity ratio with depth suggests that 239,240Pu, similarly as 137Cs, should be also transported by advection to maintain the observed ratios in deep waters. An intrusion of LIW may enhance therefore both the 137Cs and 239,240Pu concentrations in deep waters. The average 238Pu/239+240Pu activity ratio in seawater was 0.03±0.02, confirming a global fallout origin of Pu in the Algerian Basin. Caesium-137 and 239,240Pu inventories in the water column were estimated to be from 2.7±0.5kBqm−2 to 3.8±0.7kBqm−2, and from 13.8±2.6Bqm−2 to 41±7Bqm−2, respectively. The 137Cs massic activities in surface sediment were almost constant, the average activity was 9.0±0.8Bqkg−1. Sedimentation rates obtained using the 210Pb method were from 0.1 to 0.7cmy−1, and resulting penetration depths of 137Cs in the sediment cores were from 15 to over 40cm. The 137Cs peaks found in the sediment cores were associated with the Chernobyl accident (1986) and global fallout (1964). The 137Cs inventories in the sediment were increasing from the west (180Bqm−2) to the east (350Bqm−2). [Copyright &y& Elsevier]

The tectonic history of the Western Mediterranean region during the Oligocene and Early Miocene is illustrated through a series of plate reconstructions, from chron C13n to chron C6n. The reconstructions are based on a new interpretation of published magnetic anomaly data and two-ships seismic data, and their integration with known geological constraints, in order to determine style and timing of the backarc extension processes in the Liguro-Provençal, Valencia and Algerian basins. In particular, a reinterpretation of the regional magnetic anomaly field allowed the calculation of the instantaneous Euler poles associated with the motion of 11 microplates relative to Eurasia and Iberia. Furthermore, a quantitative analysis of the acoustic basement morphology and the balancing of deep crustal profiles were used to estimate the closure and pre-rift rotation angles associated with the Euler poles of opening of the Ligurian, Provençal, Valencia and Algerian basins. This rigorous reconstruction of the geometry of the pre-rift continental margins of Iberia and Eurasia could furnish important insights into the study of Mediterranean tectonics for older times. [ABSTRACT FROM AUTHOR]

Abstract: This work represents a first step in understanding the impact of hydrodynamic features on the zooplankton dynamics in the Algerian Basin (southwestern Mediterranean Sea). The mesoscale distribution of mesozooplankton abundance, biomass, specific composition and size structure was investigated during ELISA-1 campaign (1997) in the framework of the program ELISA (Eddies and Leddies Interdisciplinary Study off Algeria, 1997–1998), partly dedicated to study the mesoscale features during 1997. Physical, biogeochemical and biological measurements were made on transects through two hydrodynamic features, one anticyclonic eddy and a small secondary shear cyclonic eddy. The use of combined zooplankton descriptors, i.e. biomass, abundance, size structure (e.g. NB-SS slope) and taxonomic structure, and of cumulative function allowed us to extract spatial trends in the anticyclonic eddy (AE 96-1). It is hypothesized here that the eastern edge of AE 96-1, characterized by thick layer of chlorophyll (between 100 and 150m) due to the downward entrainment of chlorophyll down to 200m, was favorable for small organisms (Paracalanus/Clausocalanus, Calocalanus, and Calanus) while higher abundance of large active swimmer such as chaetognaths was observed in the center. In the cyclonic eddy, the highest abundance of filter-feeders (ostracods, cladocerans, doliolids and salps) was related to enhance trophic conditions, i.e. highest chlorophyll concentration (4–8mgm−3). These results show that cyclonic and anticyclonic eddies strongly influence the mesoscale characteristics of zooplankton in the Algerian basin during summer. Higher chlorophyll concentrations observed in spring suggest that such eddies can have an even more pronounced impact on the structuring of the ecosystem during high productive season. [Copyright &y& Elsevier]

Kinetic energy spectra appeared similar at all observational depths in the 3000m deep Algerian Basin, Western Mediterranean Sea. They were featureless except for a single peak at ∼2% above the local inertial frequency (f), even at depths (z) where stratification was very weak, . At great depths a second peak was observed at ∼0.99f. However, at a single point, we observed rotary spectra varying considerably with stratification and depth. Where that is between 600 and 1200m in a series of homogeneous layers associated with a double diffusion process and below 2200m in a dense homogeneous water formed nearby, all near-inertial horizontal motions were almost rectilinear. The observation of near-rectilinear inertial motions was in contrast with common observations of near-circularly polarized inertial motions, which were found, for example, from the same mooring at depths where , that is in continuously stratified waters encountered near the surface (100m) and at intermediate depths (1800m). Our observations suggested that the near-inertial motions in the Algerian Basin did not always represent internal gravity waves, but also dominant inertio (gyroscopic) waves. These waves could have been generated after excitation of the surface layer by atmospheric disturbances and the surface pressure gradient (barotropic) excitation of a simple 2-layer model via a coastal boundary condition, a process common in shelf seas. [Copyright &y& Elsevier]

The westward evolution of an open-sea anticyclonic eddy along the western Algerian Basin is shown, for the first time, by means of 15 buoy trajectories and remote sensing observations. For ∼3 months, the buoy trajectories described several anticyclonic loops in periods of 4–21 days. The eddy''s movement, translation, and rotation were separated with a kinematic model, resulting in a mean translation speed of ∼2 km/day, which fits the self-propulsion speed predicted on theoretical models for isolated eddies on a beta plane. Fluctuations in translation speed were associated with advection of the mean flow and topographic interactions. Both mechanisms changed the eddy''s horizontal shape from circular to elliptical, inducing fluctuations in its swirl velocity and solid-body rotation. The initial stage of the eddy is an isolated asymmetric dipole, comprised by a small cyclone and a large anticyclone, the latter generated from a frontal instability, which under the Coriolis term acquires anticyclonic relative vorticity. During its first days of life, the anticyclonic eddy was shallow Ro=0.9 and small (diameter less than 50 km). Later on, it reached a diameter of ∼150 km and a vertical structure of 3 km (Ro=0.1). A retrospective analysis with infrared images shows that the eddy''s generation took place at about 3–4°E. Then, the eddy completed a counterclockwise circuit never before reported in other studies and ended up at the entrance of the Algerian Basin, where the interaction with the topography and the coastal instability induced its decay. The eddy''s life span was ∼10 months. Computations of the heating rate following clusters of buoy trajectories show fluctuations throughout the eddy''s journey, induced by advection and a seasonal warming. [Copyright &y& Elsevier]

The Algerian Basin dynamics is dominated by the presence of very energetic mesoscale structures. Deep open sea eddies are key features that influence the regional circulation of water masses at all depths. In May 1998, an open sea eddy was sampled near 38°N 2°E by means of CTD, Acoustic Doppler Current Profiler (ADCP) and surface Lagrangian drifters. For the first time, it has been possible to characterise one of these mesoscale structures in its full depth, down to 2800 m. The density distribution indicated the presence of lighter water in the centre of the eddy from the surface to the bottom. The direct velocity measurements in the surface layer, plus the determination of the baroclinic shear from CTD data, evidenced that the anticyclonic motion was present in the whole water depth. [Copyright &y& Elsevier]

Recent studies have provided a better understanding of carbonate system parameters and their spatial and temporal variability in several areas of the Mediterranean Sea. This study uses a new dataset that covered the entire Algerian Basin during the summer of 2014 (SOMBA cruise) to describe the distribution of carbonate system parameters. The findings show that almost the entire basin was a source of CO 2 to the atmosphere during the studied period. Besides the well-known TrOCA (Tracer combining Oxygen, Carbon and total Alkalinity) approach, the study proposes new parametrization for the standard back calculation method to assess the anthropogenic carbon concentration. The results of both approaches yield similar distributions and concentration ranges (81 ± 4.3 and 69 ± 5.2 μmol/kg, respectively). This study assesses the errors for both approaches and emphasizes the importance of mesoscale and submesoscale structures on anthropogenic carbon sequestration and the distribution of carbonate parameters in the Algerian Basin. It shows that these features enhance basin ventilation and acidification. The first inventory of the anthropogenic carbon trapped by the Algerian Basin is estimated at 0.44–0.53 ± 0.06 Pg C, based on the new dataset. • The first high resolution spatial coverage of the Algerian Basin allowed a detailed study of the carbonate parameters. • A refitted back-calculation method is applied to estimate anthropogenic carbon concentrations. • Highlighting the role of the submesoscale processes in the increase of anthropogenic carbon sequestration. • The estimated acidification of the Algerian Basin, from the preindustrial era to 2014, range between −0.19 and −0.1 pH unit. • The first estimate of the anthropogenic carbon inventory trapped by the Algerian Basin is at 0.44–0.53 ± 0.06 Pg C. [ABSTRACT FROM AUTHOR]

The Algerian Basin is a key area for the general circulation in the western Mediterranean Sea. The basin has an intense inflow/outflow regime with complex circulation patterns, involving both fresh Atlantic water and more saline Mediterranean water. Several studies have demonstrated the advantages of the combined use of autonomous underwater vehicles, such as gliders, with remotely sensed products (e.g., altimetry, MUR SST) to observe meso- and submesoscale structures and their properties. An important contribution could come from a new generation of enhanced satellite sea surface salinity (SSS) products, e.g., those provided by the Soil Moisture and Ocean Salinity (SMOS) mission. In this paper, we assess the advantages of using Barcelona Expert Center (BEC) SMOS SSS products, obtained through a combination of debiased non-Bayesian retrieval, DINEOF (data interpolating empirical orthogonal functions) and multifractal fusion with high resolution sea surface temperature (OSTIA SST) maps. Such an aim was reached by comparing SMOS Level-3 (L3) and Level-4 (L4) SSS products with in situ high resolution glider measurements collected in the framework of the Algerian Basin Circulation Unmanned Survey (ABACUS) observational program conducted in the Algerian Basin during falls 2014–2016. Results show that different levels of confidence between in situ and satellite measurements can be achieved according to the spatial scales of variability. Although SMOS values slightly underestimate in situ observations (mean difference is −0.14 (−0.11)), with a standard deviation of 0.25 (0.26) for L3 (L4) products), at basin scale, the enhanced SMOS products well represent the salinity patterns described by the ABACUS data. [ABSTRACT FROM AUTHOR]