Southwestern Iberian Peninsula Research Articles

Comparisons of ocean scatterometer and anemometer winds off the southwestern Iberian Peninsula

A set of 25-km QuikSCAT wind measurements have been compared with 10-m winds from anemometer stations in the southwestern Iberian Peninsula. Comparisons were made for anemometer observations co-located in time to the QuikSCAT pass and scatterometer vectors with direction differences not exceeding a fixed directional threshold co-located in space within a number of spatial co-location radii. Low-pass filtering of the anemometer winds improves vector correlations but reduces the data quality as the wind speed difference and its rms are sharply magnified. The information provided by both measurements agrees over a zone-dependent area of variable extent surrounding each of the stations. West of Cape St. Vincent anemometer winds are largely coherent with ocean winds over distances greater than 150 km from the stations, whereas anemometer winds acquired in the Gulf of Cádiz represent ocean winds over a much more confined nearby ocean sector west of the cape. As a result, anemometer stations west of 7 ∘ W fail at representing ocean winds in the eastern Gulf of Cádiz, and vice versa. Based on the temporal and spatial variations of the wind field a ‘frozen-field’ coinciding with the areas of maximum correlation is noted. Since these regions appear spatially constrained by the coastline features, sharp spatial heterogeneity of ocean winds is inferred. Part of it is attributed to coastal effects associated with Cape St. Vincent while a secondary source of discrepancy is due to coastal rectification and land effects. As for the vector correlations, dissimilar vector responses emerge for the comparisons with wind data from each of the anemometer stations. At Sagres and Cádiz the winds exhibit speed and direction differences (and rms) of the same order of magnitude as aimed at by QuikSCAT mission requirements. Contrarily, the Sines and Faro station data exhibit large deviations from the scatterometer ocean winds, as a result of stronger land and coastal effects taking place at these sites. Based on these results we conclude that anemometer wind vectors can be used for descriptive purposes of the nearby ocean winds although the underlying underestimation of ocean wind speeds must be accounted for when evaluating the Ekman transport or forcing ocean models with anemometer wind data. Where QuikSCAT wind retrievals of quality are able to resolve the spatial and temporal scales of the wind forcing relevant to the ocean circulation, these provide region-independent and more robust estimates of the ocean winds than low-pass filtered in situ wind measurements obtained at coastal locations.

Impact of evergreen oaks on soil fertility and crop production in intercropped dehesas

Dehesa, open oak woodland, is the most extended agroforestry system in Europe, with more than 3 million hectares existing in the southwestern Iberian peninsula. However, today, thousands of trees are still being lost every year and soils that are more fertile have already been completely deforested. A better understanding of the effects of oak trees on crops could help in designing management practices to ensure sustainability of this traditional agroforestry system. The aim of this study was to examine the effect of Holm-oak (Quercus ilex L.) on soil nutrient concentration and its consequent effect on the production of understorey crops (oats: Avena sativa L.) in intercropped dehesas of central-western Spain. Crop production, crop plant characteristics (weight and size), the nutritional status of crop plants (N, P, K and Mg) and soil nutrient content in the topsoil layer (0–30 cm: texture, pH, soil organic matter (SOM), total and mineral N, available P, cation exchange capacity (CEC) and base cations) were determined. Samples were taken around 6 trees per plot at distances ranging from 2 to 30 m from the tree trunk, in 16 intercropped plots differing in soil fertility and fertilisation rate. Soil fertility increased near the trees, with a significant increase of SOM, total N, available P, CEC and exchangeable Ca 2+ and K + . By contrast, pH and soil particle size did not vary significantly with the distance from the tree. In unfertilised plots, trees had a positive effect on crop production, with higher crop production occurring beneath trees than beyond tree canopy projection. Fertilisers outweighed the positive effect of trees in fertilised plots, where crop production was reduced near to the trees. This could be explained mainly by management practices (biased distribution of seeds and fertilisers by broadcast spreaders), whereas light reduction probably played a minimal role (explained only 2% of the crop yield variability). # 2006 Elsevier B.V. All rights reserved.

Sedimentary characterization of bed types along the Guadiana estuary (SW Europe) before the construction of the Alqueva dam

The Guadiana River estuary is one of the most important mesotidal fluvio-marine systems of the south-western Iberian Peninsula. The river mouth was formed as a narrow channel that was excavated by fluvial incision during the Pleistocene lowstand and was then flooded 6500 years ago. The estuary is in an advanced state of sediment infilling in its proximal part, due to its narrow morphology, which prevents passage of sediment through to the open coast. Consequently, sediment is accumulating in the river mouth, which causes progradation. The analysis of the sediments into the estuarine channel (grain size, organic carbon content) and bedform distribution (Side-Scan Sonar) allows a distinction between two types of sedimentation to be made: a fluvial–marine sedimentation (favoured by tidal action) and an autochthonous sedimentation that is related to water mixing. The net transport of sediments is towards the sea because of the tidal current asymmetry. The autochthonous deposits and the sediments from the extreme fluvial floods that tides are unable to rework are preserved on the meandering convex margins under low tidal velocities. These areas acquire a lateral tidal-bar morphology with cohesive beds because the narrow geometry of the estuary inhibits the presence of longitudinal tidal bars, as may be expected in tide-dominated systems. The higher energy zones (deeper zones of the channel) become bypassing channels where the flocculated material cannot be settled on the bottom; this part of the channel then develops sandy beds with mesoforms as ebb-oriented two-dimensional and three-dimensional dunes (sand waves and megaripples).

Cenozoic seismic stratigraphy and tectonic evolution of the Algarve margin (offshore Portugal, southwestern Iberian Peninsula)

The Cenozoic seismic stratigraphy and tectonic evolution of the Algarve margin (southwestern border of the Iberian Peninsula) are documented from multichannel seismic reflection data, isochron and time–structure maps. Six seismic units (B to G), bounded by unconformities and probably ranging in age from Campanian to Holocene, are identified. Their ages are derived from: 1) oil exploration wells drilled in the margin; 2) geometrical relationship with the Guadalquivir Allochthonous Unit; 3) correlation with the onshore stratigraphic record of the Algarve basin; and 4) lateral correlation with unconformities dated in adjacent basins and related to tectonic events that affected Iberia during the Cenozoic. Three main tectonic domains, bounded by major fault zones that segment the Algarve margin, are characterised: a western central domain, bounded to the west by the N–S Portimão–Monchique Fault Zone and to the east by the N–S Albufeira Fault Zone; an eastern central domain, bounded to the east by the N140° São Marcos–Quarteira Fault Zone; and an eastern domain located east of this latter structure. The Cenozoic evolution of the Algarve basin results from both Hercynian basement reactivation and thin-skinned contraction above a relative thick evaporitic unit (probably Upper Triassic–Hettangian) that acted as the main décollement, controlling synchronous extensional and thrust detachments and generating both salt structures and salt-withdrawal sub-basins. A persistent halokinesis is identified, with two climax phases: during the deposition of Unit C (Lutetian to Oligocene), and at Unit E (Upper Tortonian to Messinian). The increasing flexure of the Algarve margin is mainly expressed by spatial and temporal variations of the subsidence. The overall tectonic regime is considered to be compressive, and the close juxtaposition of compressed and extended areas is related to the orientation and geometry of preexisting basement tectonic structures and to the syncline evolution of the Guadalquivir foredeep basin in response to the westward migration of the Gibraltar Arc.

Study of desert dust events over the southwestern Iberian Peninsula in year 2000: two case studies

Abstract. Strong desert dust events occurring in 2000 over the southwestern Atlantic coast of the Iberian Peninsula are detected and evaluated by means of the TOMS Aerosol Index (A.I.) at three different sites, Funchal (Madeira Island, Portugal), Lisboa (Portugal) and El Arenosillo (Huelva, Spain). At the El Arenosillo station, measurements from an AERONET Cimel sunphotometer allow a more precise retrieval of the spectral AOD and the derived alpha Ångström coefficient. After using different threshold values of these parameters, we conclude that it is difficult to establish reliable and robust criteria for an automatic estimation of the number of dust episodes and the total number of dusty days per year. As a result, additional information, such as airmass trajectories, were used to improve the estimation, from which reasonable results were obtained (although some manual editting was still needed). A detailed characterization of two selected desert dust episodes, a strong event in winter and another of less intensity in summer, was carried out using AOD derived from Brewer spectrometer measurements. Size distribution parameters and radiative properties, such as arefractive index and the aerosol single scattering albedo derived from Cimel data, were analyzed in detail for one of these two case studies. Although specific to this dust episode, the retrieved range of values of these parameters clearly reflect the characteristics of desert aerosols. Back-trajectory analysis, synoptic weather maps and satellite images were also considered together, as supporting data to assess the aerosol desert characterization in this region of study.

Transpressional collision tectonics and mantle plume dynamics: the Variscides of southwestern Iberia

Abstract In southwestern Iberia, three continental domains (the South Portuguese Zone (SPZ), Ossa-Morena Zone (OMZ) and Central Iberian Zone (CIZ) collided in Devonian-Carboniferous time. The collision was transpressional, with left-lateral kinematics, and was interrupted by extensional tectonics during the earliest Carboniferous, when bimodal magmatism (with associated mineral deposits) and basin development were the dominant orogenic features. Transpression was renewed in Visean time, and persisted until the end of the Carboniferous. The IBERSEIS deep seismic reflection profile helps to define the 3D geometry of transpressional structures: out-of-section displacements concentrate in bands, which bound wedges of upper crust; this crustal wedging strongly modifies the geometry of the sutures between continental blocks. A mid-crustal strongly reflective thick band (the Iberseis Reflective Body, IRB) is interpreted as a huge body of basic rocks. The IRB magma trapped in the middle crust was linked to the Early Carboniferous mantle-derived magmatism that crops out in the SPZ, OMZ and CIZ. Magmatism at the surface and trapped in the crust, high thermal gradients and basin development reflect a thermal anomaly in the underlying mantle, influencing both the thermal and the stress state of the orogen at that time. A mantle plume is inferred to have existed in the Early Carboniferous, the transpressional tectonic regime dominating again after its decay.

Invasibility Patterns of Knotgrass (Paspalum distichum) in Portuguese Riparian Habitats

Spatial patterns of the exotic riverine knotgrass (Paspalum distichum L.) were examined in Mediterranean river basins in Southwestern Iberia. The major goals of this study were to assess the degree of invasibility of riparian habitats by this species and to determine the influence of environmental factors and human-induced disturbances that this knotgrass has on both the landscape and the habitat scales. The present study demonstrates the ability of knotgrass to invade riparian habitats in Portuguese freshwater ecosystems. However, most of the spatial variation of the knotgrass cover seemed to be driven by local factors, such as fine sediment enrichment and the fragmentation of riparian woods, and by other anthropogenic interferences in relation to both the fluvial system and the surrounding landscape.

Seasonal and interannual dynamics in dwarf rush vegetation in the Southwestern Iberian Peninsula

Seasonal and interannual dynamics in dwarf rush vegetation in the Southwestern Iberian Peninsula

Environmental patterns and plant communities of the ephemeral wetland vegetation in two areas of the Southwestern Iberian Peninsula

Environmental patterns and plant communities of the ephemeral wetland vegetation in two areas of the Southwestern Iberian Peninsula

An archaeological approach to regional environmental pollution in the south-western Iberian Peninsula related to Third millennium BC mining and metallurgy

The development of the first inter-settlement hierarchical framework in the South of the Iberian Peninsula in the Third millennium BC lead to a territorial division of labour, in which intensification of mining activities caused the first significant environmental impact on local and regional scales. To evaluate this impact we have selected the prime mining district in south-western Europe, the Iberian Pyrite Belt, and a method based on the correlation of pollen, charcoal and chemical analysis. The latter analyses were carried out on marine mollusc shells from spatially and chronologically contextualised archaeological records from a sequence ranging from the Sixth to the Second millennium BC. The results reveal that the copper metallurgy which developed in the south-western Iberian Peninsula in the Third millennium BC augmented deforestation, increased the rate of erosion processes and contaminated, at a regional scale, the waters of the Gulf of Cádiz – corresponding to the mouth of the Tinto and Odiel rivers – with heavy metals.

Nutrients, light and phytoplankton succession in a temperate estuary (the Guadiana, south-western Iberia)

Seasonal changes in freshwater flow, leading to alteration of the nutritional environment and hence affecting phytoplankton composition, will probably be enhanced in the Guadiana estuary (SW Iberia) by the recently built Alqueva dam. The main goal of this study is to assess the relationship between dissolved inorganic macronutrient concentrations and ratios, light availability and phytoplankton succession in the upper estuary of the Guadiana River prior to the completion of the dam. From April to October 2001 three locations along the upper estuary were sampled fortnightly. Several physical and chemical parameters were analysed and phytoplankton composition, abundance and biomass were determined through inverted and epifluorescence microscopy. Phytoplankton showed a uni-modal cycle with a biomass maximum during spring. A relationship between phytoplankton succession and nutrient ratios seemed to exist. In early spring, N:P was high, Si was abundant and a diatom bloom occurred. This bloom collapsed and an increase in green algae abundance was observed later in spring, with low Si and high N:P. In the summer, N:P and Si were low, and a cyanobacteria bloom developed. This bloom included the potentially toxic Microcystis. Light was probably limiting throughout the sampling period, particularly to non-motile cells. Enhancement of cyanobacteria blooms can be expected, and as the river water is used by local human populations, continued monitoring of the Guadiana estuary will be necessary to evaluate the effects of the Alqueva dam construction on phytoplankton dynamics.

Lithospheric structure under the western African‐European plate boundary: A transect across the Atlas Mountains and the Gulf of Cadiz

We present a two‐dimensional lithospheric thermal and density model along a transect running from the southwestern Iberian Peninsula to the northwestern Sahara. The main goal is to investigate the lithosphere structure underneath the Gulf of Cadiz and the Atlas Mountains. The model is based on the assumption of topography in local isostatic equilibrium and is constrained by surface heat flow, gravity anomalies, geoid, and topography data. The crustal structure has been constrained by seismic and geological data where available. Mantle density is supposed to vary linearly with temperature, providing the link between thermal and density‐related data. The lithospheric thickness varies strongly along the profile, going from near 100 km under the Iberian Peninsula to at least 160–190 km under the Gulf of Cadiz and the Gharb foreland basin in Morocco and to 70 km underneath the Atlas Mountains, coinciding with a region of Neogene volcanism. The thickening of the lithosphere is interpreted as a SW trending lithospheric slab extending from the western Betics to the Gulf of Cadiz and the Gharb Basin, whereas the thin lithosphere underneath the Atlas may be interpreted as plume‐like asthenospheric upwelling similar to those observed in the west European Alpine foreland or as a side effect of a slab penetrating the less viscous asthenosphere.

MANTLE EXHUMATION PROCESSES IN THE OCEAN CONTINENT TRANSITION OF MAGMA-POOR RIFTED MARGINS

MANTLE EXHUMATION PROCESSES IN THE OCEAN CONTINENT TRANSITION OF MAGMA-POOR RIFTED MARGINS

Biennial acorn maturation and its relationship with flowering phenology in Iberian populations of Quercus suber

Since the XIX century, there is a controversy about the existence of biennial maturation of the acorns in Quercus suber L. While some authors recognised biennial cycles as an adaptation to habitats with short vegetative periods, other authors discarded the biennial pattern. Successive flowering events from spring to autumn and annual acorn ripening are proposed as an explanation of the multiple acorn crops typical of Iberian forests. To clarify this discussion, the presence of annual and biennial acorns was assessed in seven cork oak stands, covering a wide range of environmental conditions. In each stand, 100 individuals were sampled once in spring and once in autumn. Biennial acorns were observed with variable frequencies in all populations. There was a significant and positive relationship between latitude and the percentage of trees with biennial acorns within northern and central populations. On the contrary, this trend was not significant among southern populations. The hypothesis that the presence of biennial acorns in Quercus suber is related to individual female flowering phenology was confirmed in four populations located in the southwestern Iberian Peninsula. Unregarding local differences in the distribution of phenological stages anticipated trees bore significantly less biennial acorns than delayed individuals of the same stand. This result is coherent with the idea that the length of the vegetative period plays a crucial role in the frequency of annual and biennial acorn ripening patterns. The relationship between annual and biennial ripening cycles and the multiple acorn crops is discussed.

THE AGUABLANCA Ni Cu PGE DEPOSIT, SOUTHWESTERN IBERIA: MAGMATIC ORE-FORMING PROCESSES AND RETROGRADE EVOLUTION

The Aguablanca Ni–Cu–PGE ore deposit, in southwestern Iberia, has a magmatic origin, and has been reworked by later skarn-related hydrothermal activity. Base-metal sulfides are associated with igneous cumulates displaying subvertical layering consisting of gabbro, norite and dolerite, with fragments of pyroxenite and peridotite. These rocks show a pervasive retrograde alteration with an early overprint of actinolite ± chlorite ± epidote ± albite ± serpentine, followed by later growth of talc ± chlorite ± carbonates. The base-metal sulfides are concentrated in two subvertical bodies and consist of pyrrhotite, pentlandite and chalcopyrite, overprinted by fluid-deposited pyrite. The following types of mineralization have been recognized: 1) disseminated ore (1 < Ni/Cu < 1.5), with sulfides occurring interstitially to the igneous silicates, 2) semimassive to massive ore (2 < Ni/Cu < 5), with net-textured to poikilitic sulfides, 3) breccia ore, consisting of fragments of unmineralized ultramafic rocks in a massive sulfide matrix, 4) nodules of sulfides, 5) pyrrhotite veinlets, and 6) chalcopyrite veinlets. The PGE content and (Pt + Pd):(Ru + Ir + Os) ratio have their highest values in the Cu-rich disseminated ore and associated veinlets of chalcopyrite. The platinum-group minerals (PGM) associated with the base-metal sulfides at Aguablanca include michenerite, merenskyite, moncheite, palladian melonite and sperrylite. These mostly occur enclosed within sulfide minerals or close to contacts between them. The PGE tellurides show an extensive substitution of Bi for Te, indicating temperatures of formation below 500°C. A PGE oxide assemblage has also been discovered in samples from the surface gossan developed above the sulfides. The composition of the PGM and their association with magmatic base-metal sulfides suggest that they exsolved from the sulfides during subsolidus recrystallization, although some remobilization may have occurred in areas of pervasive circulation of fluid.

Allelic variation at the VHa locus in natural populations of rabbit (Oryctolagus cuniculus, L.).

The large interallelic distances between the three rabbit Ig V(H)a lineages, a1, a2 and a3, suggest that the persistence time of the V(H)a polymorphism could amount to 50 million years, which is much longer than that of MHC polymorphisms. Rabbit originated in the Iberian Peninsula where two subspecies coexist, one of which is confined to Southwestern Iberia (Oryctolagus cuniculus algirus). We studied the V(H) loci in the original species range to obtain a better understanding of the evolutionary history of this unusual polymorphism. Serological surveys revealed that sera from the subspecies algirus, when tested with V(H)a locus-specific alloantisera, showed either cross-reactivity ("a-positive" variants) or no reaction at all ("a-blank"). Using RT-PCR, we determined 120 sequences of rearranged V(H) genes expressed in seven algirus rabbits that were typed as either a-positive or a-blank. The data show that the V(H) genes transcribed in a-positive rabbits are closely related to the V(H)1 alleles of domestic rabbits. In contrast, a-blank rabbits were found to preferentially use V(H) genes that, although clearly related to the known V(H)a genes, define a new major allotypic lineage, designated a4. The a4 sequences have hallmark rabbit V(H)a residues together with a number of unprecedented amino acid changes in framework region 2 and 3. The net protein distances between the V(H)a4 and the V(H)a1, a2, and a3 lineages were 20, 29, and 21% respectively. We conclude that at least four distantly related lineages of the rabbit V(H)a locus exist, one of which seems to be endemic in the Iberian range.

High-Resolution Seismic Stratigraphy of a Narrow, Bedrock-Controlled Estuary: The Guadiana Estuarine System, SW Iberia

ABSTRACT The late Quaternary sedimentary architecture of the Guadiana estuary (southwestern Iberian Peninsula), a narrow, bedrock-controlled estuary with moderate sediment supply, was studied by applying concepts of high-resolution seismic stratigraphy. The estuarine sedimentary infill consists of a discontinuous basal interval overlain by five seismic units bounded by laterally continuous seismic horizons. The correlation between seismic facies and a stratigraphic section of the Guadiana valley enables the proposal of a detailed sequence stratigraphic interpretation of the estuarine infill. During the last glacial lowstand, the Guadiana was a subaerial valley with no significant accumulation of fluvial deposits because of increased sediment bypass towards the present-day middle and outer shelf. Towards the end of the postglacial transgression, the subaerial valley was transformed into an estuary, and sediments began preferentially accumulating in structural depressions. Furthermore, flood tidal currents constrained by basement highs enhanced sand deposition in the upper part of the estuary. Wave influence was reduced and confined to the lower estuarine system. Here, the narrow morphology of the valley led to an increased sediment export to the shelf during the Holocene highstand period. The lower part of the estuarine infill consists of four fifth-order depositional sequences, composed of regressive deposits (HST). The last glacial maximum is recorded by a distinct stratigraphic surface, representing simultaneously the sequence boundary and the transgressive surface. A tidal ravinement surface is characterized by strong erosion and channel formation in the outer estuarine zones. The maximum flooding surface is identified by change of stratal patterns between landward-prograding transgressive deposits and downlapping highstand deposits. Both transgressive (TST) and regressive tracts (HST) were deposited during the final part of the postglacial transgression and subsequent highstand.

Comparative seasonal and spatial distribution of decapod larvae assemblages in three coastal zones off the south-western Iberian Peninsula

Plankton studies over the long southern coast of Iberian Peninsula are very scarce and restricted to a few specific taxonomic groups. In order to know the dynamic of decapod larvae coastal assemblages from south-western of Iberian Peninsula, three zones were studied: Guadalquivir Estuary, Cadiz Bay and Algeciras Bay. The three zones differ by their freshwater inflow and turbidity (highest in Guadalquivir Estuary), primary production (highest in Cadiz Bay) and nutrient concentrations (lowest in Algeciras Bay). The material is based upon plankton samples (250 μm mesh) collected monthly at eight stations distributed between these zones, during 1 year. Maximum values of abundance and diversity were found in Cadiz Bay, while the lowest were recorded in Algeciras Bay. Brachyura was the main abundant taxonomic group in larval decapod assemblages, while Dendrobranchiata, Palinura, Stenopodidea, and Astacidea were scarcely represented or absent. From the 69 taxa identified, 11 were considered rare and 12 taxa constituted 87% of the total larvae collected. Liocarcinus spp. was the most representative taxon, being present in all stations and showing high abundance and dominance values. The annual distribution was specifically studied for Liocarcinus spp., Carcinus maenas, Xantho spp., Ilia nucleus, Uca tangeri, Brachynotus spp., Hippolyte spp., Philocheras spp., Pisidia longicornis, Diogenes pugilator, Pilumnus spp. and Upogebia sp. Attending to the temporal distribution of dominant taxa, three abundance patterns are shown for decapod larvae at study zones: (i) species present in non-warm months; (ii) species present in warm months; (iii) species present through all year.

Seasonal and wind-induced variability of Sea Surface Temperature patterns in the Gulf of Cádiz

The evolution of thermal structures in the Gulf of Cádiz is analysed with a set of 325 weekly composite Sea Surface Temperature (SST) images derived from NOAA–AVHRR sensor, and covering a time span of 7 years, from 1993 to 1999. A spatial Empirical Orthogonal Function (EOF) analysis has been performed in order to identify the main SST spatial patterns. The first EOF mode explains 60% of the temperature variance of the images, and shows a quasi-permanently warmer than the mean region in the southern part of the area of study. The second mode (13% of variance), has a strong temporal variability, and is the main responsible for the cooling and warming of the shelf waters in southwestern Iberia. These two modes explain together most of the seasonal variability of SST over the basin, particularly the variation and strength of the upwelling area located southeast of Portugal. The third mode explains 6% of variance and is well correlated with the local zonal wind. Two wind-induced upwelling can be clearly identified in this mode. The first one, located at the southwestern end of the Strait of Gibraltar, takes place during easterlies events. The second one, related to westerlies, is located to the east of Cape Santa Marı́a, and is associated with a southeastward transport of cold surface waters from that Cape.

Synchroneity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the Mediterranean region

Land–sea climatic proxies have been obtained from the Last Glacial section of IMAGES core MD95-2043 (western Mediterranean Sea). Vegetation and alkenone derived SST curves indicate rapid (∼150 years) and synchronous terrestrial and marine climatic changes, paralleling the Dansgaard–Oeschger (D–O) climatic variability over Greenland. This frequency of climate change can be related to shifts between the two modes of operation of the North Atlantic Oscillation (NAO). Transfer functions applied to the pollen data indicate that there was an amplification of the climatic signal during Heinrich events (HEs) in comparison with other D–O stadials. The development and persistence of both Scandinavian and Atlantic Mobile Polar Highs over southwestern Europe may explain the extreme cooling (∼10 °C) and dryness (400 mm) during Heinrich events 5 and 4 in the Mediterranean region. Comparison of the results of core MD95-2043 with similar climatic data from IMAGES core MD95-2042, located off Portugal, indicates that thermal and precipitation gradients occurred between the Mediterranean and the Atlantic sides of Iberia within HEs. HEs 4 and 5 are associated with more humid conditions in the Atlantic (by 200 mm) than in the Mediterranean site, as is the case at the present time. This comparison also illustrates the different behaviour of these areas during the D–O stadials. In contrast with the Mediterranean site, the Atlantic site shows similar precipitation and temperature drops for all the D–O stadials, including those related to the HEs. Here we propose the operation of different Mobile Polar Highs (MPH) as the driving mechanism for this difference in behaviour between the Atlantic and Mediterranean sides of Iberia. HEs are related to a stronger influence of the Scandinavian MPH, forcing a severe aridification and cooling of the full Iberian Peninsula. The Atlantic MPH may have been dominant during the other stadials, which would preferentially affect Southwestern Iberia.