NW Iberian Peninsula Research Articles

Multidata Study to Evaluate the Impact of Submarine Outfall in a Beach Sedimentary Dynamic: The Case of Samil Beach (Galicia, Spain)

The Ria de Vigo (NW Iberian Peninsula) is one of the most impacted coastal areas of Galicia, due to demographic and industrial pressure. One of the main consequences of this pressure is the need to extend the current wastewater treatment plant of the city of Vigo (295,000 inhabitants). This extension includes a new submerged pipeline construction to discharge the treated water in the central channel of the Ria. The new planned pipeline must cross Samil Beach, the most important urban beach of the city. Based on a multitool strategy, this work characterizes the interactions between the new pipeline route alternatives and the sediment dynamics of Samil Beach. This approximation improves the reliability of the results in the subtidal area of the beach, where studies are scarce due to the complexity of the data acquisition. The present study is based on high resolution bathymetry data, seabed physical characterization, a granulometric study of the superficial sediment, and a numerical simulation of the tide, wave climate, and sediment transport in low and high energy conditions using open source Delft3D software. The results showed that the area of interest is a low energy area, which is significantly shielded from wave attack, where fine sand predominates. However, the field data indicated an interaction (accretion-erosion) in the submerged obstacles between 0 and 12 m deep. The model revealed that there is significant sediment movement above a 7.4 m isobath, and that the pipeline would not alter the general transport dynamics of the beach, but would interact in the shallowest section. The main conclusion of this work states that the future structure would not alter the global sediment dynamics of the beach. In addition, in order to guarantee the safety of the new pipeline, it should emerge above an 8 m isobath. The multiapproach methodology presented can be applied to other studies of the interaction between coastal structures and the environment.

High-resolution patterns of palaeoenvironmental changes during the Little Ice Age and the Medieval Climate Anomaly in the northwestern Iberian Peninsula

A high resolution core (9.7 ​yr ​cm−1) from the Chao de Veiga Mol raised bog (NW Iberian Peninsula) was analyzed to identify plant macrofossils, estimate peat humification and calculate hydroclimatic indices based on current bog species, with the overall aim of determining the climate conditions associated with evolution of the bog during the Medieval Climate Anomaly and the Little Ice Age. These proxies, together with historical and climate data, proved to be good indicators of the changes in bog surface wetness. Analysisof the core led to identification of 9 different periods: two corresponding to the so-called Medieval Climate Anomaly (930 to 1345 AD, 1075–665 calibrated years before present [cal. yr BP]); four corresponding to the Little Ice Age (1345 to 1905 AD; 665–105 ​cal ​yr BP); and three corresponding to the last century (1905 to 2000 AD). The findings revealed a generally dry climate that lasted until the 14th century, followed by a transition to a long period with a more humid, but characteristically very variable climate, which ended at the beginning of the 20th century and was followed by a rapid transition to more humid conditions and finally, a change to drier conditions.The Medieval Climate Anomaly was indicated by the abundance of dry-adapted mosses (Leucobryum glaucum, Hypnum cupressiforme) and characterized by warm dry conditions and high levels of peat humification, with alternating wet phases. The LIA period was dated by a large abundance of Sphagnum species (an indicator of wetness) and a gradual increase in the humification index. However, four different climate phases were differentiated in this period.High-resolution reconstruction of the evolution of the CVM bog and the multiproxy approach have together enabled a more detailed identification of climatic variations in this area, which are generally consistent with the global models, as well as better definition of the elusive climatic oscillations in the last millennium and confirmation of the importance of local modulation of global models.The study provides new information and a detailed chronology of climatic events that will help to refine local modulation of the climate evolution model in the still quite unexplored region of the NW Iberian Peninsula, a key area for understanding the paleoclimatic dynamics in SW Europe.

Trace metal accumulation in the commercial mussel M. galloprovincialis under future climate change scenarios

The current trend of climatic alterations will accelerate the modification of the ocean system by, among other aspects, changing the metal speciation and its bioavailability which may have an impact in their accumulation by marine organisms. Understanding the impact of these potential changes is essential for future risk assessment of metal contamination. In the present study, we selected the species Mediterranean mussel (Mytilus galloprovincialis) as the main European aquaculture production bivalve and due to its widespread use for biomonitoring purposes. A long-term test (2 months) was carried out to explore the impact that global change in the marine environment (warming and CO2 increase) may exert on the accumulation of dissolved trace metals (Cu, Co, Pb, Cd, Cr, As and Ni) in different body parts of mussels (foot and rest of soft tissues).Studied mussels were collected at two different climatic locations (Atlantic and Mediterranean Sea) and exposed to unspiked, unpolluted seawater from the Vigo Ria (NW Iberian Peninsula). Results showed that under the global change conditions proposed in this study (1100 pCO2 and 25 °C), the increase in temperature resulted in a lower condition index and byssus strength for mussels from Atlantic Sea, while Mediterranean sea mussels, adapted to higher temperatures, did not show remarkable variations. According to trace metals accumulation in different body parts of the studied mussels, it was observed that the effect of increasing CO2 alone did not show to have an impact in the bioaccumulation, but the combined stressors (increase in CO2 and temperature) may lead to an increase in the bioaccumulation for some elements. The increase in temperature resulted in a decrease of the Cu content of foot tissue (byssus gland) in mussels from Atlantic Sea, which is in accordance with the lower byssus strength observed under such conditions. Our results indicate that the expected seawater temperature increase, which will be produced gradually during next decades, should be further study to ensure the species adaptability and aquaculture production.

Regional and global changes during Heinrich Event 1 affecting macrobenthic habitat: Ichnological evidence of sea-bottom conditions at the Galicia Interior Basin

Abstract Heinrich events (HEs) are climatic changes, occurring during the Pleistocene, related to massive discharge of freshwater from the Laurentide Ice Sheet, through the Hudson Strait, recognized in the sedimentary record through distinctive layers of ice-rafted detritus (IRD), the so-called Heinrich layers (HLs). Environmental changes during HEs influence significantly in marine biota (i.e. modifications in composition and abundance of assemblages), with ecological and evolutionary consequences. This point has been only partially addressed in particular groups (e.g. microorganisms), whereas interactions with other groups remain understudied. Here, we analyse ichnological features of the Heinrich layer 1, associated to Heinrich Event 1 (HE1), from several gravity cores at the Galicia Interior Basin (NW Iberian Peninsula) to test the influence of this HE1 on environmental parameters, such as bottom and pore-water oxygenation, as well as benthic food availability, conforming the macrobenthic habitat. Freshwater input during the first phase of the HE1 caused unfavorable conditions (probably highly dysoxic to anoxic) for tracemakers, as revealed by the absence of both discrete traces and a well-developed mottled background. However, the tracemaker community was reestablished shortly after deposition of the ice-rafted detritus layer (Heinrich layer) of HE1, as reflected by the significant increase in diversity and abundance of traces (Planolites, Thalassinoides, Thalassinoides-like, Chondrites, and Zoophycos), revealing a major shift to oxic bottom and pore waters and likely benthic food. This global/general pattern, though, is affected by the regional setting and by the associated predominant sedimentation processes, leading to a variable incidence of paleoenvironmental changes associated with HE1. The ecological impact on macrobenthic biota, in term of changes in diversity and abundance of tracemakers, by HE1 soon attenuates, resulting in a negligible evolutionary impact.

Assessment and timing of the anthropogenic imprint and fisheries richness in marine sediments from Ría de Muros (NW Iberian Peninsula)

Textural, geochemical and geochronological analyses on two gravity and two box cores recovered from the outer and inner sectors of the Ría de Muros allowed reconstructing and timing the anthropogenic imprint on the sedimentary record from this ría. The chronological framework for the last 8 kyr was built based on Pb-210 dating (Constant Rate of Supply model) and C-14 dating. Recent sedimentation rates were an order of magnitude higher than those of the oldest analyzed sediments, and the periods of upwelling enhancement were constrained.Assessing the human influence on sediment metal contents required the establishment of local background levels. Since the 16th century the enrichment factors of copper, zinc and lead increased (up to 2.7, 1.5 and 2.1, respectively, at or close to present), and a remarkable increase in the fine-grained particles’ content happened in the outer ría sector, due to deforestation. The anthropogenic signature identified in the sedimentary record is assigned to fishing, harbor activities, mining, salting, and, or canning activities, depending on the considered period, which caused a local demographic increase since the 16th century in the region. Such population growth caused a rise in the marine signature of the organic matter, which likely results from enhanced primary production due to eutrophication caused by increased soil erosion and human and livestock waste inputs. Furthermore, the metal enrichment trend during the 20th century, which was more significant in the inner than in the outer ría sector, follows the different demographic evolution of the villages (related to urban and industrial development).The present study highlights the need for conjunction of varying dating techniques when reconstructing the anthropization trends in coastal environments.

100 myr cycles of oceanic lithosphere generation in peri-Gondwana: Neoproterozoic–Devonian ophiolites from the NW African–Iberian margin of Gondwana and the Variscan Orogen

Abstract The Variscan Orogen in Iberia and the Anti-Atlas Mountains in Morocco contains a set of ophiolites formed between Neoproterozoic and Devonian times, during the complex evolution of the NW African–Iberian margin of Gondwana. During this time interval, the margin evolved from an active margin ( c. 750–500 Ma: the Reguibat–Avalonian–Cadomian arc) to the final collision with Laurussia in Devonian times to form Pangaea. In this context, one of the oldest recognized ophiolites is the Bou Azzer Ophiolite from the Anti-Atlas Mountains, dated at c. 697 Ma and containing two types of mafic rocks, the youngest of which has a boninitic composition. To the north, in the SW Iberian Massif, the Calzadilla Ophiolite contains mafic rocks also of boninitic composition dated at c. 598 Ma. Farther north, in the NW Iberian Massif, the Vila de Cruces Ophiolite is formed by a thick sequence of mafic rocks with an arc tholeiitic composition and minor alternations of tonalitic orthogneisses dated at c. 497 Ma. In the same region, the Bazar Ophiolite has a similar age of c. 495 Ma. Also in NW Iberia, there is a group of ophiolites with varied lithologies and dominant mafic rocks with arc tholeiitic composition (Careón, Purrido and Moeche ophiolites) dated at c. 395 Ma. The composition of all these peri-Gondwanan ophiolites is of supra-subduction zone type, showing no evidence of preserved mid-ocean ridge basalt type oceanic lithosphere. Consequently, these ophiolites were generated in the peri-Gondwanan realm during the opening of forearc or back-arc basins. Forearc oceanic lithosphere was promptly obducted or accreted to the volcanic arc, but the oceanic or transitional lithosphere generated in back-arc settings was preserved until the assembly of Pangaea. Based on the ages of the described ophiolites, the peri-Gondwanan realm has been a domain where the generation of oceanic or transitional lithosphere seems to have occurred at intervals of c. 100 myr. These regularly spaced time intervals may indicate cyclic events of mantle upwelling in the peri-Gondwanan mid-ocean ridges, with associated higher subduction rates at the peri-Gondwanan trenches and concomitant higher rates of partial melting in the mantle wedges involved. The origin of the apparent cyclicity for mantle upwelling in the peri-Gondwanan ocean ridges is unclear, but it could have possibly been related to episodic deep mantle convection. Cycles of more active deep mantle convection can explain episodic mantle upwelling, the transition from low- to fast-spreading type mid-ocean ridges and, finally, the dynamic context for the episodic generation of new supra-subduction zone type oceanic peri-Gondwanan lithosphere.

Understanding divergences between ecological status classification systems based on diatoms

A large number of diatom-based classification systems have been developed worldwide in recent years. These new systems, together with the oldest, emerged on the need to assess the water quality of rivers, but knowledge on possible divergences resulting from their simultaneous application within a territory is limited. This study aimed to compare the ecological status classification provided by conceptually different methodological approaches, of use or potential use within the same region. 402 monitoring samples were collected from Atlantic siliceous streams (NW-Iberian Peninsula) and temporary Mediterranean streams (Balearic Islands, Spain). Two multimetric indices specifically developed for these areas (MDIAT and DIATMIB, respectively) were calculated, as well as the Specific Polluosensitivity Index (IPS). Multimetric indices were more sensitive methods at diagnosing degradation than IPS since they took directly account of abundance (i.e. chlorophyll a in DIATMIB) or indirectly by its proved inverse relationship with Chl a (MDIAT), together with their use of the regional reference diatom community. Alteration gradients were identified in both studied regions based on the distribution of diatoms, with the first axis of distance-based redundancy analyses (dbRDA) being related to nutrient enrichment and organic loads. Threshold Indicator Taxa ANalysis (TITAN) performed on diatoms sampled along environmental (dbRDA axis 1 and phosphate) and biological gradients (as Ecological Quality Ratio scores of classifications), pointed to lower than current Good/Moderate boundaries for phosphate maximum values (e.g. 22.5 and 71.6 μg L−1 for Galicia and the Balearic Islands, respectively) as well as for higher Good/Moderate boundaries for the MDIAT and IPS classifications. A ‘transition group’ of species was classified as sensitive or as tolerant depending on the regional nutrients range. Findings of the present study highlight the need to perform auto-ecological studies to increase the knowledge on regional diatoms and their optimal survival ranges across regions prior to adopt other non-regional diatom indices.

Industrial supply of trace elements during the “Anthropocene”: A record in estuarine sediments from the Ria of Ferrol (NW Iberian Peninsula)

This work addresses the study of a sediment core retrieved in the estuary of the Grande-de-Xubia River (Ria of Ferrol), which is among the first industrialized areas in the Iberian Peninsula and has links to the shipbuilding industry since 1750. The chemical analysis of trace elements (i.e. As, Cd, Co, Cr, Cu, Hg, Mo, Ni, Pb, V, and Zn) was coupled with 210Pb dating. The results span a period of about 130 years and cover the whole of the 20th century. Trace element anthropogenic fluxes accumulating in the sediments were calculated and show that human inputs are the most important sources for Cu, Cd, Hg and Zn, being, on average, well over the natural loads. The temporal variation in the anthropogenic contaminants allows the identification of four main phases describing the human-natural input interactions, which in chronological order, are: (i) early industrialization, (ii) industrial acceleration or first industrial transition, (iii) industrial collapse, and (iv) an industrial maturity or a second industrial transition.

First occurrence of musk ox Ovibos moschatus in the Late Pleistocene (MIS 3) record from NW Iberia: Paleobiogeographic and paleoenvironmental implications

A remarkable musk ox (Ovibos moschatus) assemblage was recovered at Cowshead Cave (Picos de Europa Mountains, NW Spain). This find is of special paleobiogeographic relevance since it involves the first occurrence of this species in NW Iberia and extends the boundary of its Eurasian distribution range to the SW.Fossils correspond to at least two individuals: one young male about 20 months old, which includes an extraordinarily well-preserved skull, and one subadult of about 38–44 months. The bone deposit, dated to 34.9 ± 0.4 cal ka BP (MIS 3), accumulated in a karst cave that acted as a natural trap, agreeing with the geomorphology and the good preservation of the remains.Considering that musk ox skulls of young individuals are extremely rare in the Pleistocene record, the detailed comparative study of the skull here presented provides new and relevant information. The skull from Cowshead is larger than modern specimens of similar individual age from Greenland; additionally, some remarkable morphological peculiarities in skull and teeth were identified.One metacarpal of the subadult individual was compared to recent and Pleistocene specimens and was among the largest in the entire sample. Significant differences in morphology and size between fossil and recent metacarpals were detected.Teeth microwear analysis suggests a browsing diet based on twigs and leaves at the time of death, which is consistent with a winter diet.The cold and arid environment inferred from the presence of musk ox is consistent with the paleontological record, since cold-adapted mammals occurred at other contemporary assemblages from NW Iberia.

Atmospheric mercury pollution deciphered through archaeological bones

Mercury is a major environmental pollutant extensively used by humans, whose pollution dates back at least to c. 3250 BCE (South Iberian Peninsula). As it happens today, past populations were mostly affected by low dose chronic mercury exposure, with levels that varied with the intensity of some anthropogenic activities (mining and metallurgy in particular). Despite its toxic nature, mercury impact in humans themselves has been hardly addressed by Archaeology. The aim of this research is to increase our knowledge on mercury levels in past populations by 1) analysing human (cortical) bone from skeletons recovered in a necropolis from NW Iberia covering contrasting periods of atmospheric pollution: Roman, AD 1st to 4th centuries, and post-Roman, AD 5th to 7th centuries; 2) considering bone type variability; 3) contextualizing our findings with previous works. Samples from 3 types of bone (n = 143) as well as soils/sediments associated to the burials (n = 34) were analysed. Mercury concentrations in soil were below 5 ng g−1, while the average in bone was 36 ± 52 ng g−1, making post-depositional incorporation unlikely. We found significant differences between the two periods (Romans: 54 ± 60 ng g−1, post-Romans: 21 ± 23 ng g−1), but no effect of type of bone, sex, age, social status or diet of the individuals. Our results agree with the chronology of mercury pollution reconstructed from a local peatland, which suggests a predominant atmospheric source. This fact contrasts with previous research in which high mercury concentrations were mainly related to post-mortem burial customs and pre-mortem medical treatment and poisoning. Thus, mercury distribution in past communities was possibly more complex than previously thought, with different pre- and post-mortem sources interacting. Furthermore, our research also supports the use of archaeological bone as environmental archive of metal pollution, when metal cultural exposure is low.

A multidisciplinary overview of the lower Miño River terrace system (NW Iberian Peninsula)

The Miño River basin represents one of the main fluvial catchments draining the Atlantic side of the Iberian Peninsula. The extensive sedimentary deposits of this basin have been documented since the 19th century, but limited research has been undertaken on these features historically, and the Quaternary record of the basin has remained understudied until recently. Research carried out over the last decade on the Spanish margin of the Miño River has enabled more detailed classification and mapping of the main fluvial landforms, as well as numerical (luminescence, electron spin resonance, cosmogenic) dating of some of the deposits associated with Palaeolithic archaeological sites. Here we synthesise the existing Quaternary fluvial record for the basin, and present new geospatial and chronological analyses for the lower catchment area. Our latest examination has enabled the identification of nine fluvial terrace levels and other regionally significant sedimentary features (e.g., alluvial fans) formed in response to tectonics, eustatic changes and associated global climate changes. The chronological data and calculated incision rates indicate that the various fluvial terraces were formed during the Early to Late Pleistocene. Numerous Palaeolithic sites have been found in association with the middle terrace levels (between +40 and +13 m above present-day river level). Primarily, these archaeological sites preserve assemblages that feature large flake Acheulean (LFA) tools, though a number of Middle Palaeolithic sites have also been documented. Direct dating of these sites, together with morphostratigraphic correlations across the terrace system, suggest that the basin has been extensively occupied by human populations during the last 300 thousand years.

Living at the edge: population differentiation in endangered Arnica montana from NW Iberian Peninsula

Arnica montana (Asteraceae) is a herbaceous species with high interest for pharmaceutical industry due its anti-inflammatory properties. However, commercial collection in wild, habitat loss, abandonment of land, reforestation and the ongoing climate change threaten the conservation of the species throughout its natural distribution. Galicia (north-western Spain) is one of the main flower suppliers, but no legislation on A. montana exploitation is currently applied. In order to assess the genetic status and population structure in this region, 27 locations were genotyped for 14 microsatellite loci and sequenced for 2 plastid DNA (cpDNA) markers. The relationship of environmental, biochemical and morphological variables with genetic differentiation was also evaluated. Two different cpDNA groups previously described were found. One of them was widely distributed while the other was restricted to heathlands of the O Courel Mountains. The percentage of clonality was low (< 10%). Genetic diversity based on microsatellites (He = 0.245) was lower than in Central European populations, with high levels of population differentiation (FST = 0.441), suggesting strong effects of genetic drift. Bayesian clustering methods revealed the presence of four genetically distinct population units, one of them corresponding to the O Courel Mountains group described by cpDNA analysis. Environmental and biochemical factors were related to genetic differentiation, suggesting local adaptation. Necessary conservation measures include the overdue implementation of the Habitats Directive by the Galician Regional Administration, establishing sustainable harvesting regimes, and aim to conserve genetic variation in these endangered populations at the southern range edge.

Evaluating wind datasets for wave hindcasting in the NW Iberian Peninsula coast

ABSTRACT The available wind datasets can be exploited to support the setup of accurate wave models, able to reproduce and forecast extreme event scenarios. It is of utmost importance in the actual context of climate change. This study focuses on evaluating the performance of a numerical wave model, using different wind datasets, helping to create a tool to assess coastal risks, and further on to support the future implementation of reliable warning systems based on numerical models. The numerical model SWAN was implemented, configured and validated for the NW Iberian Peninsula coast, as a test case region. A period of two months, from December 2013 to January 2014, was simulated due to the winter storms that crossed the area. Six distinct wind datasets were selected to test their suitability in regional wave modelling. The results were validated against several sets of wave buoy data, considering wave parameters such as significant wave height, mean wave period and peak direction. The implemented wave model configuration allowed the representation of the wave evolution with relatively good accuracy. All the wind datasets were able to produce reasonably good wave condition estimates. The dataset that best represented the wave properties varied from one wave parameter to another, but the most reliable for the selected region was the reanalysis product generated at the European Centre for Medium-Range Weather Forecasts.

Single subduction zone for the generation of Devonian ophiolites and high‐P metamorphic belts of the Variscan Orogen (NW Iberia)

AbstractWithin the Variscan Orogen, Early Devonian and Late Devonian high‐P belts separated by mid‐Devonian ophiolites can be interpreted as having formed in a single subduction zone. Early Devonian convergence nucleated a Laurussia‐dipping subduction zone from an inherited lithospheric neck (peri‐Gondwanan Cambrian back‐arc). Slab‐retreat induced upper plate extension, mantle incursion and lower plate thermal softening, favouring slab‐detachment within the lower plate and diapiric exhumation of deep‐seated rocks through the overlying mantle up to relaminate the upper plate. Upper plate extension produced mid‐Devonian suprasubduction ocean floor spreading (Devonian ophiolites), while further convergence resulted in plate coupling and intraoceanic ophiolite imbrication. Accretion of the remaining Cambrian ocean heralded Late Devonian subduction of inner sections of Gondwana across the same subduction zone and the underthrusting of mainland Gondwana (culmination of NW Iberian allochthonous pile). Oblique convergence favoured lateral plate sliding, and explained the different lateral positions along Gondwana of terranes separated by Palaeozoic ophiolites.

Characteristics, vulnerability and conservation value of active tufa-forming springs on coastal cliffs in the NW Iberian Peninsula

Tufa-forming hard water springs are classified as a priority natural habitat of community interest and described in Annex I of Community Directive 92/43/EEC as “ (Natura, 2000 habitat type 7220* Petrifying springs with tufa formation [Cratoneurion])”. This type of habitat is scarce along the European Atlantic coast. In this study, petrifying springs in 36 coastal locations in the NW Iberian Peninsula were described on the basis of their physiographical characteristics, geomorphologic context, water chemistry, floristic composition and the types of disturbance endangering their conservation. The springs under study differed from other coastal and inland examples of this type of habitat in relation to the abiotic factors controlling their distribution and also some botanical traits. They are the southernmost petrifying springs reported to date on the Atlantic coast of Europe. Unfortunately, one third of the study sites lie outside of the protected areas delimited in the European Natura 2000 Network. This suggests that the network should be extended in order to conserve biodiversity and natural heritage in Atlantic Europe.

Analysis of the Spatial Distribution of Stable Oxygen and Hydrogen Isotopes in Precipitation across the Iberian Peninsula

The isotopic composition of precipitation provides insight into the origin of water vapor, and the conditions attained during condensation and precipitation. Thus, the spatial variation of oxygen and hydrogen stable isotope composition (δp) and d-excess of precipitation was explored across the Iberian Peninsula for October 2002–September 2003 with 24 monitoring stations of the Global Network of Isotopes in Precipitation (GNIP), and for October 2004–June 2006, in which 13 GNIP stations were merged with 21 monitoring stations from a regional network in NW Iberia. Spatial autocorrelation structure of monthly and amount weighted seasonal/annual mean δp values was modelled, and two isoscapes were derived for stable oxygen and hydrogen isotopes in precipitation with regression kriging. Only using the GNIP sampling network, no spatial autocorrelation structure of δp could have been determined due to the scarcity of the network. However, in the case of the merged GNIP and NW dataset, for δp a spatial sampling range of ~450 km in planar distance (corresponding to ~340 km in geodetic distance) was determined. The range of δp, which also broadly corresponds to the range of the d-excess, probably refers to the spatially variable moisture contribution of the western, Atlantic-dominated, and eastern, Mediterranean-dominated domain of the Iberian Peninsula. The estimation error of the presented Iberian precipitation isoscapes, both for oxygen and hydrogen, is smaller than the ones that were reported for the regional subset of one of the most widely used global model, suggesting that the current regional model provides a higher predictive power.

The collapse of the Variscan belt: a Variscan lateral extrusion thin-skinned structure in NW Iberia

ABSTRACT The Iberian Massif of the Variscan Belt is a big area of exposed Palaeozoic rocks holding an S-shaped regional bend. Profuse data and genetic models support the existence of the northern arch (Ibero-Armorican Orocline: IAO) created by Late-Variscan buckling. The southern arch (Central-Iberian Orocline: CIO) was proposed near a century ago but it remains controversial. Tectono-metamorphic studies in the core of the CIO constrain its geometry and kinematics and provide crucial data to unravel the geological evolution of the region. The CIO is here envisaged as produced by the lateral thin-skinned extrusion of a fan-like wedge (with fragments of the NW Iberia allochthonous complexes) onto the Iberian autochthon, using the parautochthon as the lower tectonic sheet. The progression of a roughly E-W linear orogen towards the W (today’s NW Iberia) controlled by the obliquity of the continental collision of Gondwana and Laurussia created an escape way for the collapsing materials coming from the accretionary prism. The extrusion wedge expanded westwards along the orogenic extensional vector and progressively curved areas to the west, dragging the previous structures and the stratigraphy while incorporating the Variscan foreland basins at the base. We propose the French Massif Central (FMC) as a provenance area for the extrusion. In this sector, evidences of Eo-Variscan (~410-360Ma) subduction-obduction stages match to those described in the NW Iberia allochthonous complexes. The synorogenic extension towards NW and gneiss-dome formation in the FMC at 370-355 Ma fits with the known ages and kinematics (after restoring the IAO) of the first compressive stages in the parautochthon/autochthon of NW Iberia (360-340Ma) evidencing the relationship between regions. Tightening of the CIO occurred in the late-Variscan compressive stage, due to the formation of the IAO that wrapped the entire CIO thus rotating the extrusion fan more than 90ºcounter-clockwise in the latest Palaeozoic.

Habitat use and food sources of European flounder larvae (Platichthys flesus, L. 1758) across the Minho River estuary salinity gradient (NW Iberian Peninsula)

The European flounder (Platichthys flesus Linnaeus, 1758) exhibits plasticity for several life traits throughout its distribution range, including ontogenetic habitat shifts during early life, as well as the timing and duration of spawning. Estuaries are preferred as nursery habitat; however, the importance of specific salinity zones for larval development is not well-understood. Therefore, we aimed to identify the significance of distinct estuarine salinity habitats (i.e., tidal freshwater, brackish) along the Minho River estuary (NW-Iberian Peninsula, Europe) for larval development by combining field observations with carbon (C) and nitrogen (N) stable isotope analysis. Sampling occurred between January 2015 and January 2016 in six sampling stations across the estuarine salinity gradient. A total of 29 larvae were collected in the Minho River estuary from March till September 2015. Spawning likely occurred near the river mouth because the highest abundance of larvae occurred in the brackish estuary. Timing for migration towards freshwater was variable with metamorphosis likely occurring in both brackish and freshwater habitats. European flounder larvae obtained their diet from the benthic food web, indicating that benthic habitat is fundamental for larval development, including prior to settlement. This study provides further evidence on the behavioral plasticity of European flounder during early life regarding both habitat use and timing of migration towards freshwater habitats. Additionally, this study demonstrates the importance of preserving estuarine connectivity for this migratory species.

δ18O and Mg/Ca Thermometry in Planktonic Foraminifera: A Multiproxy Approach Toward Tracing Coastal Upwelling Dynamics

AbstractPlanktonic foraminifera δ18O and Mg/Ca ratios are widely considered as a powerful proxy to reconstruct past seawater‐column temperature. Due to the complex interpretation of planktonic foraminifera δ18O data in regard to past seawater temperatures, temperature determination based on the foraminifera shell Mg/Ca ratio is believed to be more accurate. Scarce Mg/Ca calibration data exists for coastal upwelling regions, resulting in incoherent results of past seawater reconstructions. The current study along the NW Iberia coastal upwelling system intends to define the best Mg/Ca temperature equation for the most representative species of this region (Neogloboquadrina incompta, Globigerina bulloides, and Globorotalia inflata). Seawater temperature from δ18O and Mg/Ca of these three planktonic foraminifera species was compared with the surface sediments alkenone derived SST and with the in situ temperatures measured at the depths where these foraminifera species currently live and calcify. The equations that better reflect each species calcification depth were selected as our regional equations for δ18O and Mg/Ca temperature reconstructions. The δ18O‐estimated temperatures for surface sediment specimens were comparable with in situ seawater‐column temperature measurements, whereas the Mg/Ca derived temperatures seem to underestimate in situ values, in special for G. bulloides from samples affected by stronger coastal upwelling. The G. bulloides δ18O and Mg/Ca estimated temperatures from samples located offshore, further from coastal upwelling influence, are comparable to surface sediment alkenone derived temperatures. Our study shows that in upwelling areas, regional calibration of planktonic foraminifera Mg/Ca temperature equations is necessary for reliable interpretations of high‐resolution past temperature variability in these important environments.

Crops behind closed walls: Fortified storage at Castelinho in the Late Iron Age of NW Iberia

The site of Castelinho (Torre de Moncorvo, northeast of Portugal) is a fortification strategically placed on a small elevation, near the river Sabor, built in the Late Iron Age and occupied until the Early Roman period. It is characterized by impressive defensive features, including large walls with turrets, ditches and complex entrances, inside of which no clear evidences of domestic areas were found. On the contrary, this monumental defensive apparatus seems to have served mostly to protect several storage facilities, mainly elevated granaries, in which abundant archaeobotanical remains were recovered.The excavation of Castelinho comprised the systematic sampling of sediment in a wide diversity of contexts, ultimately leading to the recovery of large amounts of charcoal, fruits and seeds. Most came from secondary or tertiary refuse deposits but some seem to have been actually related to the destruction of granaries by fire.Carpological results show the predominance of naked wheat (Triticum aestivum/durum) while hulled barley (Hordeum vulgare) and broomcorn millet (Panicum miliaceum) were found in smaller amounts. These crops were stored fully processed, taking into account the almost absence of chaff and the scarce presence of weeds. Charcoal analysis suggest Pinus pinaster and Quercus evergreen provided most of the wood used in the construction of the granaries.In this study, this data will be presented, discussed and compared with archaeobotanical and archaeological information from other sites excavated in the Sabor Valley and in the surrounding region. The size and monumentality of Castelinho, combined with the fact that it provided few evidences of other activities besides storage, suggests this site had a relevant role for local communities. This will be discussed together with other evidence of the social relevance of storage for Late Iron Age communities in the region.