NW Africa Research Articles

Associated fauna of Sponge grounds in the Cantabrian Sea. SponGES Project. Crustacea Decapoda. Expansion of distribution and new records of unusual species.

Associated fauna of Sponge grounds in the Cantabrian Sea. SponGES Project. Crustacea Decapoda. Expansion of distribution and new records of unusual species.

Physical-biological interactions in the ocean: case studies from the northern Canary Current Upwelling Ecosystem

Physical-biological interactions in the ocean: case studies from the northern Canary Current Upwelling Ecosystem

Dissolved benthic phosphate, iron and carbon fluxes in the Mauritanian upwelling system and implications for ongoing deoxygenation

Benthic fluxes of total dissolved phosphate (TPO43-), dissolved iron (Fe2+), and dissolved inorganic carbon (DIC) were determined in situ using benthic chambers at nine stations along a depth transect between 47 and 1108 m water depth at 18°N off Mauritania (NW Africa) during the upwelling season in 2014 (RV Meteor cruise M107). Bottom water oxygen (O2) concentrations were always ≥ 25 µM, and all fluxes (TPO43-, Fe2+, DIC) were consistently directed from the sediments into the bottom water. The highest benthic TPO43- release of 0.2 ± 0.07 mmol m2 d−1 was found at 47 m water depth (50 µM O2). The highest diffusive Fe2+ flux of 0.03 mmol m2 d−1, determined from porewater Fe2+ concentrations, occurred at 67 m water depth (27 µM O2). This was much lower than the detrital Fe supply as indicated by constant Fe/Al ratios along the depth transect. TPO43- release rates decreased concurrently with DIC flux and water depth. A difference of up to one order of magnitude between benthic chamber and diffusive TPO43- fluxes indicated that the total TPO43- release was strongly enhanced by bioirrigation.The observed fluxes were similar to those measured during an earlier cruise in 2011, generally indicating comparable release rates during both upwelling seasons. Furthermore, ex situ oxygen manipulation experiments showed an increase of the nutrient release (e.g. TPO43-, Fe2+) after seven days of anoxic bottom water conditions. The fluxes were enhanced by a factor of 1.4 for P and 7.3 for Fe compared to the measured release under natural conditions and reached values as high as those measured in the anoxic oxygen minimum zone off Peru. Our observations support the hypothesis that increasing deoxygenation of the oceans will likely enhance sedimentary TPO43- and Fe2+ release and thus contribute to a positive feedback mechanism with increasing nutrient levels and increased ocean productivity.

A Barremian-?Aptian Tethyan precursor of the Cretaceous marine flooding of Morocco: Evidence from the red-bed series within the “Marginal Folds” of the eastern High Atlas

Stratigraphic, sedimentologic, and micropaleontologic studies have been undertaken on the “Infra-Cenomanian” continental red beds (= Dekkar Group) located on the northern side of the Moroccan eastern High Atlas. Rich charophyte assemblages containing Sphaerochara magna, Ascidiella stellata, Hemiclavator sp. A, Globator trochiliscoides, Atopochara trivolvis, At. triquetra, and Flabellochara harrisii indicate a late Barremian age for the lower part of the series. Within the continental deposits we have discovered in the Middle Member of the Dekkar 2 Formation limestones and marls containing echinoderms, dasycladacean algae and foraminifera (miliolids, Ammobaculites sp., Choffatella decipiens). The existence of two littoral to lagoonal-marine intercalations within the continental sedimentation reveals marine transgressive events during the late Barremian–?early Aptian. The lateral extension of these marine sediments allows the erection of paleogeographic boundaries that define a « Marginal Folds Gulf » characterized mainly by restricted marine paleoenvironments. This E-W directed gulf is a relatively long depression, a few tens of kilometers wide and one hundred kilometers long, developed in an area which is now at the foot of the eastern High Atlas. The infilling deposits is dominantly controlled by the distance from the North High Atlas Fault. The gulf terminated westward and probably opened northeastward into the Tethyan domain. This narrow gulf was separated from both the Tethyan Gulf known in the Central Middle Atlas during the Aptian and the coeval Atlantic Gulf located on the northern side of the Marrakech and Central High Atlas. Thus, the « Marginal Folds Gulf » is a new paleogeographic feature that documents marine incursions within the Jurassic–Early Cretaceous continental areas of the NW Africa.

A revised chronostratigraphic framework for the Aptian of the Essaouira-Agadir Basin, a candidate type section for the NW African Atlantic Margin

The Essaouira-Agadir Basin (EAB) of Morocco contains the most extensive exposure of Aptian to Lower Albian strata onshore the NW African Atlantic Margin. This paper documents the first high-resolution, multi-disciplinary stratigraphic approach for the Aptian to Lower Albian on the NW African Atlantic Margin. Previous biostratigraphic work almost exclusively relied on long-distance correlation of ammonoids to the Mediterranean – Caucasian Realm. Recent biostratigraphic work has questioned some of the previous interpretations, highlighting significant faunal endemism and complications with correlation to other key Aptian sections.This study focuses on 5 key sections: Tiskatine, Id Amran, Assaka, and DSDP 416/370. Distribution of ammonoids, foraminifera, and calcareous nannofossils are reported from a bed-by-bed collection made at Tiskatine.The analysis of foraminiferal and calcareous nannofossil assemblages enable correlation to standard zonation schemes; but also highlights the urgent need of revision and future work on the integration of these schemes across disciplines. The study, further, includes δ13Ccarb, δ13Corg, and total organic carbon (TOC) data that is compared to reference material from the Vocontian Basin.The combined litho-, bio-, chemo-, and sequence stratigraphic analysis establishes a robust chronostratigraphic framework for regional and super-regional correlations and a type section is proposed for the Aptian of NW Africa at Tiskatine.

Age, growth and natural mortality of blue jack mackerel Trachurus picturatus (Carangidae) from the Canary Islands, Spain (NW Africa)

Status assessment of exploited fish populations is a general requirement to ensure sustainability of fisheries in both global and local contexts. The blue jack mackerel Trachurus picturatus (Bowdich, 1825) remains unassessed in a data-limited fishery in the eastern central Atlantic, within the waters of the Canary Islands (Spain) off the coast of northwest Africa. This is the most southwestern targeted fishery in the species’ distributional range. To obtain basic life-history information, a total of 2 472 specimens were analysed, ranging from 10.2 to 31.9 cm total length, from samples collected monthly between March 2005 and March 2006. Length–weight relationships (a = 0.0023; b = 3.418; R 2 = 0.97) showed no significant difference between sexes. Deposition periodicity and coherence of the ageing criteria were verified by analysis of the monthly evolution of the otolith edge. Ages were estimated by counting annual growth rings on whole otoliths, with these fish ranging from age 0 to 6 years. The von Bertalanffy growth model, which was used to estimate growth parameters from both direct readings and back-calculated length-at-age data, gave good statistical fits. The parameters from the direct readings were: L∞ = 34.9 cm; k = 0.214 y–1; t 0 = −2.545 y (R 2 = 0.84), and the natural mortality rates estimated from empirical methods varied between 0.20 and 0.55 y–1.

Liassic age of an oceanic gabbro of the External Rif (Morocco): Implications for the Jurassic continent–ocean boundary of Northwest Africa

This work concerns the northernmost limit of the West African Craton (WAC) and Variscan WAC-related terranes of NW Africa. Based on newly obtained radiometric age of an oceanic gabbro from the “Mesorif Suture Zone” of the External Rif Belt, we propose a revised interpretation of this puzzling lineament. We report on a 190±2 Ma LA–ICP–MS U–Pb zircon age of a trondhjemite vein cross-cutting the Bou Adel gabbro, which is one of the largest oceanic units of the quoted suture zone. We previously interpreted the arcuate MSZ in terms of transported, hyper-extended margin of the Alpine Tethys, based on a K–Ar 166±3 Ma age ascribed to the Bou Adel gabbro in the literature. The new, Early/Middle Liassic age coincides instead with the onset of oceanic floor formation in the Central Atlantic. We hypothesize that the Mesorif suture zone corresponds to the transported trace of the West African Atlantic margin surrounding the northwestern Moroccan Meseta promontory and connecting with the ENE-trending North African Transform North African transform. The latter zone sharply bounded the North Africa margin and connected the Central Atlantic with the Alpine Tethys. We propose that transported elements from the North African transform constitute the “Mesorif Basalt–Breccias” lineament parallel to and more external than the Mesorif suture zone. If correct, this new interpretation provides an opportunity to develop detailed field and laboratory studies of an exhumed segment of the up-to-now conceptual Jurassic North African transform.

The Agadir Slide offshore NW Africa: Morphology, emplacement dynamics, and potential contribution to the Moroccan Turbidite System

A newly identified large-scale submarine landslide on the NW African margin (Agadir Slide) is investigated in terms of its morphology, internal architecture, timing, and emplacement processes using high-resolution multibeam bathymetry data, 2D seismic profiles, and gravity cores. The Agadir Slide is located south of the Agadir Canyon at a water depth ranging from 500 m to 3,500 m, showing an estimated affected area of approximately 5,500 km2. The analysis of the Agadir Slide's complex morphology reveals the presence of two headwall areas and two slide fairways (the Western and Central slide fairways). Volume calculations indicate that ∼340 km3 of sediment were accumulated downslope along the slide fairways (∼270 km3) and inside the Agadir Canyon (∼70 km3). Stratigraphic correlations based on five gravity cores indicate an emplacement age of 142±1 ka for the Agadir Slide. However, its emplacement dynamics suggest that the slide was developed in two distinct, successive stages. The presence of two weak layers (glide planes) is a major preconditioning factor for the occurrence of slope instability in the study area, and local seismicity related to fault activity and halokinesis likely triggered the Agadir Slide. Importantly, the Agadir Slide neither disintegrated into sediment blocks nor was transformed into turbidity currents. The emplacement timing of the Agadir Slide does not correlate with any turbidites cored downslope across the Moroccan Turbidite System.

Detrital zircon characterization of early Cambrian sandstones from East Avalonia and SE Ireland: implications for terrane affinities in the peri-Gondwanan Caledonides

AbstractThe Caledonides of Britain and Ireland include terranes attributed to both Laurentian and Gondwanan sources, separated along the Solway line. Gondwanan elements to the south have been variably assigned to the domains Ganderia and East Avalonia. The Midland Platform forms the core of East Avalonia but its provenance is poorly known. Laser ablation split-stream analysis yields information about detrital zircon provenance by providing simultaneous U–Pb and Lu–Hf data from the same ablated volume. A sample of Red Callavia Sandstone from uppermost Cambrian Stage 3 of the Midland Platform yields a U–Pb age spectrum dominated by Neoproterozoic and Palaeoproterozoic sources, resembling those in the Welsh Basin, the Meguma Terrane of Nova Scotia and NW Africa. Initial εHf values suggest that the Neoproterozoic zircon component was derived mainly from crustal sources < 2 Ga, and imply that the more evolved Palaeoproterozoic grains were transported into the basin from an older source terrane, probably the Eburnean Orogen of West Africa. A sample from Cambrian Stage 4 in the Bray Group of the Leinster–Lakesman Terrane shows, in contrast, a distribution of both U–Pb ages and εHf values closely similar to those of the Gander Terrane in Newfoundland and other terranes attributed to Ganderia, interpreted to be derived from the margin of Amazonia. East Avalonia is clearly distinct from Ganderia, but shows evidence for older crustal components not present in West Avalonia of Newfoundland. These three components of the Appalachian–Caledonide Orogen came from distinct sources on the margin of Cambrian Gondwana.

Birds of Libya / Oiseaux de Libye

na

On the transition from hunting-gathering to food production in NE Morocco as inferred from archeological Phorcus turbinatus shells

Processes behind the shift from hunting-gathering to food production lifestyle are multifaceted and not yet completely understood. The Mediterranean coast of NW Africa provides an eclectic transitional pattern, namely, a very hesitant transition to food production. The distribution and abundance of early Neolithic domesticated species is disparate and region specific. Climate and environmental change have been often considered as an important influencing factor for this transition. This hypothesis was tested using archeological shells of the rocky intertidal gastropod Phorcus turbinatus recovered from the Ifri Oudadane site in NE Morocco. The oxygen isotope composition (δ18O) of the shell was used to examine whether the hesitant transition to food production was linked to a local climate shift in the Mediterranean Maghreb. Intrashell δ18O values suggest a marked temperature increase from >7.6 to ~7.0 cal. ka BP, the time when Neolithic innovations first appear on site. An additional increase in temperature from ~7.0 to <6.8 cal. ka BP matches with the beginning of the main occupation phase and the doubtless breakthrough of cultivation at Ifri Oudadane. This apparent warming trend, although considered preliminary, seems to match well with warming tendency observed in several published regional climate proxies. Therefore, a temperature shift may have played a role in the timing and implementation of food production in the area. Last growth episode δ18O values suggest that shellfish were harvested throughout most of the year, with noticeable intensification during the cooler half of the year. This preliminary pattern was fairly consistent throughout the Epipaleolithic and early Neolithic phases, pointing to a probable near year-round site occupation rather than a single season settlement. Future research on Ifri Oudadane and other NW African archeological records are much needed to assess whether these patterns persist in Morocco and other Epipaleolithic and early Neolithic settlements in the western Mediterranean Maghreb.

Detrital zircon U–Pb provenance and palaeogeography of Triassic rift basins in the Marrakech High Atlas

AbstractThe Marrakech High Atlas contains some of the best exposures of the Triassic early‐rift strata related to Atlantic opening in NW Africa. We present the first detrital zircon U–Pb data of five Triassic redbed samples from the Tizi n'Test basin to quantify sediment provenance, transport and dispersal patterns during early rifting. These U–Pb ages document dominant sediment sourcing from the south, the Anti‐Atlas domain, with very limited to absent input from the Variscan Meseta domain to the north. This combined with stratigraphic and thermochronologic information points to a highly asymmetric palaeogeography during Triassic rifting. Furthermore, the occurrence of Archaean detrital zircon grains in Triassic sandstone, likely recycled from the Reguibat shield, suggests the presence of a fully developed regional drainage system with rivers and catchments reaching hundreds of kilometres into the hinterland of the rift flank.

Mass wasting along the NW African continental margin

Abstract The NW African continental margin is well known for the occurrence of large-scale but infrequent submarine landslides. The aim of this paper is to synthesize the current knowledge on submarine mass wasting off NW Africa with a special focus on the distribution and timing of large landslides. The described area reaches from southern Senegal to the Agadir Canyon. The largest landslides from south to north are the Dakar Slide, the Mauritania Slide, the Cap Blanc Slide, the Sahara Slide and the Agadir Slide. Volumes of individual slides reach several hundreds of cubic kilometres; run-outs are up to 900 km. In addition, giant volcanic debris avalanches are widespread on the flanks of the Canary Islands. All headwall areas are complex with clear indications of multiple failures. The most prominent similarity between all investigated landsides is the existence of widespread glide planes that follow the stratigraphy, which points to weak layers as most important preconditioning factor for the failures. Landslides with volumes larger than 100 m 3 are close to being evenly distributed over time, contradicting previous suggestions that landslides off NW Africa occur at periods of low or rising sea level. The risk associated with the landslides off NW Africa, however, is relatively low due to their long recurrence rates.

A two-dimensional layer-averaged numerical model for turbidity currents

Abstract Turbidity currents occur widely in submarine environments, but field-scale numerical simulations of the flow features have not been applied extensively. Here, we present a two-dimensional layer-averaged numerical model to simulate turbidity currents over an erodible sediment bed, and taking into consideration deposition, entrainment and friction. The numerical model was developed based on the open-source code, Basilisk, ensuring well-balanced and positivity-preserving properties. An adaptive spatial discretization was used, which allows multi-level refinement. The adaptive criterion is based on the dynamic features of the flow and sediment concentrations. The numerical scheme has a relatively high computational efficiency compared with models based on the Cartesian mesh. A hypothetical case based on a true large-scale landform (the Moroccan Turbidite System, offshore NW Africa) was studied. Compared with previous models, the current model accounted for the coupling between flow, sediment transportation and bed evolution. This approach may improve simulation results and also allow the simulation of complex field-scale landforms, while preserving the flow details.

Marine lobsters and lithodids (Crustacea: Decapoda) from Mauritanian deep-waters (NW Africa)

This paper deals with species of the deep-water marine lobsters and lithodids collected on soft and rocky bottoms during the four Spanish Maurit surveys from 2007 to 2010 in Mauritanian waters, at depths between 80 and 2000 m. The collection is represented by eight species included in the infraorders Astacidea, Achelata, and Polychelida, and by five species of the family Lithodidae. The true lobster Nephropsis atlantica, the blind lobster Stereomastis nana, and the king crab Paralomis cristulata are reported for the first time in Mauritanian waters, while the presence of the slipper lobster Scyllarus subarctus is confirmed in the area. New data on the bathymetric distribution of P. cristulata and Lithodes ferox are also included.

The porcelain crab Porcellana africana Chace, 1956 (Decapoda: Porcellanidae) introduced into Saldanha Bay, South Africa

The porcelain crab Porcellana africana Chace, 1956, a species native to NW Africa, between Western Sahara and Senegal, is reported from Saldanha Bay, South Africa, and both morphological evidence and DNA analysis are used to confirm its identity. The taxonomic history of P. africana is summarized, and the taxonomic implications of the DNA analysis are discussed. The observations that the South African population appeared suddenly and that it is located in and around a major international harbour, strongly suggest that it represents a recent shipping introduction. Porcellana africana was first detected at a single site within Saldanha Bay in 2012, but by 2016 was abundant under intertidal boulders and within beds of the invasive mussel Mytilus galloprovincialis across most of the Bay. It remains absent along the adjacent oceanic coastline and in other regional harbours, but these should be monitored to detect any subsequent range expansion.

A New Southern North Atlantic Isochron Map: Insights Into the Drift of the Iberian Plate Since the Late Cretaceous

AbstractThis paper presents a new southern North Atlantic plate model from Late Cretaceous to present, with the aim of constraining the kinematics of the Iberian plate during the last 83.5 Myr. This model is presented along with a detailed isochron map generated through the analysis of 3 aeromagnetic tracks and ~400 ship tracks from the National Centers for Environmental Information database. We present a new technique to obtain well‐constrained estimates of the Iberia‐North America plate motions from magnetic anomalies, overcoming the scarcity of large‐offset fracture zones and transform faults. We build an integrated kinematic model for NW Africa, Morocco, Iberia, Europe, and North America, which shows that the deformation is partitioned between Pyrenees and Betic‐Rif orogenic domain during the Late Cretaceous‐Oligocene time interval. In the Eastern Betics domain, the calculated amount of NW Africa‐Iberia convergence is ~80 km between 83.5 and 34 Ma, followed by ~150 km since the Oligocene. The motion of Iberia relative to Europe in the Central Pyrenees is characterized by overall NE directed transpressional motion during the Campanian and the Paleocene, followed by NW directed transpressional movement until the Lutetian and overall NNW directed convergence from Bartonian to Chattian. This motion occurs along the axis of the Bay of Biscay from the Santonian–Campanian boundary to the middle Priabonian, subsequently jumping to King's Trough at Anomaly 17 (36.62 Ma).

Whole Y-chromosome sequences reveal an extremely recent origin of the most common North African paternal lineage E-M183 (M81)

E-M183 (E-M81) is the most frequent paternal lineage in North Africa and thus it must be considered to explore past historical and demographical processes. Here, by using whole Y chromosome sequences from 32 North African individuals, we have identified five new branches within E-M183. The validation of these variants in more than 200 North African samples, from which we also have information of 13 Y-STRs, has revealed a strong resemblance among E-M183 Y-STR haplotypes that pointed to a rapid expansion of this haplogroup. Moreover, for the first time, by using both SNP and STR data, we have provided updated estimates of the times-to-the-most-recent-common-ancestor (TMRCA) for E-M183, which evidenced an extremely recent origin of this haplogroup (2,000–3,000 ya). Our results also showed a lack of population structure within the E-M183 branch, which could be explained by the recent and rapid expansion of this haplogroup. In spite of a reduction in STR heterozygosity towards the West, which would point to an origin in the Near East, ancient DNA evidence together with our TMRCA estimates point to a local origin of E-M183 in NW Africa.

Individual specialization and behavioral plasticity in a long-lived marine predator

Individual specialization in vertebrates is often related to morphological variability, but can also reflect a diversity of trajectories during the learning sensitive period in early life. In both cases the capacity of adults to adapt to new environments can be limited if further morphological or behavioral change is not possible. Adult loggerhead turtles Caretta caretta (Linnaeus, 1758) from Cape Verde (NW Africa) may forage in the open ocean or on the continental shelf. Oceanic foragers prevail in the population, but neritic foragers grow larger, have a higher reproductive output and produce best fitted offspring. Previous research suggests that the high prevalence of oceanic foragers is because the migratory routes followed by juvenile turtles during their early life results into a low probability of settlement on the African shelf. The stable isotope ratios of C and N in 60μm carapace layers from 14 adult females have been analyzed to reconstruct retrospectively their individual habitat use patterns and test the hypothesis that adult loggerhead turtles remain faithful to their foraging grounds even if sub-optimal. Only two turtles exhibited clear oceanic—neritic shifts, approximately 22 and 15years before sampling. The remaining turtles had foraged in neritic (3) or oceanic (9) habitat as long as recorded in the carapace scutes (approximately 8–37years), despite the smaller body size and the lower reproductive output associated to oceanic foraging. These results suggest that habitat shifts during adulthood are unlikely in this species and support the hypothesis that only during the juvenile stage loggerhead turtles are flexible enough to adapt to contrasting environments.

Species-specific sensitivity of dinoflagellate cysts to aerobic degradation: A five-year natural exposure experiment

Post-depositional sedimentary dinoflagellate cyst associations undergo species-selective degradation under oxic conditions. However, there is little known about the temporal relationship between oxygen concentration and bulk dinocyst degradation rate over the time scale of several years, and if this degradation is mainly microbial or chemical. Whilst the overall sensitivity of heterotrophic dinoflagellate cysts is well documented, sensitivity differences within this group have not been studied. Here we examine the rates of cyst degradation of heterotrophic species over short temporal scales across an anoxic–oxic gradient. Sediment with a known dinoflagellate cyst association largely dominated by heterotrophic dinoflagellates, were connected to trap arrays at two different locations, Cap Blanc (NW Africa) and Gotland Basin (central Baltic Sea) and exposed to four different ambient oxygen concentrations representing a complete oxic gradient from 5.1mL/L to sulphate bearing anoxic waters. Two treatments of either gauze or dialyse membrane in triplicate were established to investigate the effects of chemical or bacterial degradation. Cyst loss was significant at oxic settings, rapidly occurring within the first year of exposure (32%) whereas no significant degradation was observed for suboxic and anoxic exposures. Compiling the degradation rates of individual species under the different exposure settings reveals an overall species sensitivity ranking amongst cysts of heterotrophic species. Species of average resistance: Bitectatodinium spongium, Brigantedinium spp., Echinidinium spp., Echinidinium aculeatum, and Gymnodinium trapeziforme. Species more resistant than average: Stelladinium robustum and Trinovantedinium applanatum. We observe that oxic degradation of cysts of heterotrophic dinoflagellates is fast and selective with maximal cyst association changes during the first year of oxic exposure. These aspects have to be taken into account in palaeoenvironmental and palaeoceanographic reconstructions where bottom/pore water conditions of the upper sediments are oxygenated.