Comparative analysis of upwelling influence between the western and northern coast of the Iberian Peninsula

Upwelling conditions have been simultaneously analyzed along the western and northern coast of the Iberian Peninsula in terms of wind forcing and water temperature response. The wind forcing analysis showed that the season under more upwelling favorable conditions corresponds to spring-summer (April-September) along the western coast and only to summer (June-August) along the northern one. Taking into account the upwelling period common to both coasts (June-August), it was observed that the occurrence of upwelling events simultaneously along both coasts is the most probable situation (∼46%) followed by upwelling unfavorable conditions also along both coasts (∼26%). The analysis of sea surface temperature data also showed the existence of an upwelling season in spring-summer along both coasts, although upwelling events are more frequent and intense along the western coast than along the northern one. Chlorophyll concentrations showed a high seasonal variability at the western coast with the highest concentrations values in spring-summer months while at the northern coast the maximum values were observed in spring and autumn.     

http://www.sciencedirect.com/science/article/pii/S1674987110000150

Phase and group velocities of 15–70 s Rayleigh waves propagating across the Iberian Peninsula have been transformed into local dispersion curves by linear inversion of travel times. The procedure permits that the waveform dispersion to be obtained as a continuous period-dependent velocity function at grid points belonging to the area probed by the waves, thus providing phase- and group-velocity contour maps for several periods within the interval of interest. The regionalization process rests on a homogeneous initial data set in which the number of observations remains almost constant for all periods of reference. Damped least-squares inversion of the local dispersion curves for shear-wave velocity structure is performed to obtain depth-dependent S-wave velocity profiles at the grid points covering the model region. The reliability of the results should improve significantly owing to the use of phase and group velocities simultaneously. On this basis, we have built horizontal depth sections that give an updated view of the seismic velocity structure of the peninsula at lithospheric and upper mantle depths (20–200 km). After averaging all the pure-path S-wave velocities previously determined at each grid point, the velocity-depth models so obtained for major tectonic units allow the comparison between the Hercynian basement and other areas of Mesozoic folding and Tertiary basins.     

Orbital- and sub-orbital-scale climate impacts on vegetation of the western Mediterranean basin over the last 48,000 yr

High-resolution pollen analysis of Alborán Sea core MD95-2043 provides a 48-ka continuous vegetation record that can be directly correlated with sea surface and deep-water changes. The reliability of this record is supported by comparison with that of Padul (Sierra Nevada, Spain). Marine Isotope Stage (MIS) 3 was characterised by fluctuations in Quercus forest cover in response to Dansgaard-Oeschger climate variability. MIS 2 was characterised by the dominance of semi-desert vegetation. Despite overall dry and cold conditions during MIS 2, Heinrich events (HEs) 2 and 1 were distinguished from the last glacial maximum by more intensely arid conditions. Taxon-specific vegetation responses to a tripartite climatic structure within the HEs are observed. In MIS 1, the Bölling-Allerød was marked by rapid afforestation, while a re-expansion of semi-desert environments occurred during the Younger Dryas. The maximum development of mixed Quercus forest occurred between 11.7 and 5.4 cal ka BP, with forest decline since 5.4 cal ka BP. On orbital timescales, a long-term expansion of semi-desert vegetation from MIS 3 into MIS 2 reflects global ice-volume trends, while Holocene arboreal decline reflects summer insolation decrease. The influence of precession on the amplitude of forest development and vegetation composition is also detected.     

Amphipoda assemblages in a disturbed area (Alicante,Spain, Western Mediterranean)

The distribution and composition of Amphipoda assemblages were analysed off the coasts of Alicante (Spain, Western Mediterranean), a disturbed area affected by several co‐occurring anthropogenic impacts. Although differences among sampled stations were mainly related to natural parameters, anthropogenic activities were linked with changes in amphipod assemblages. Expansion of the Port of Alicante, a sewage outfall and a high salinity brine discharge could be causing the disappearance of amphipods at stations closer to these disturbances. However, the completion of port enlargement works and mitigatory dilution of the brine discharge has led to the recovery of the amphipod assemblage. Among the natural parameters, depth determines the distribution of some of the species. While Siphonoecetes sabatieri was abundant at shallow stations, Ampelisca spp., Photis longipes, Pseudolirius kroyeri, Apherusa chiereghinii and Phtisica marina were more abundant at deeper stations. Grain size and percentage of organic matter also influenced amphipod distribution, resulting in changes in species composition and in the relative percentages of different trophic groups. Species such as Ampelisca brevicornis, Perioculodes longimanus, Urothoe hesperiae and Urothoe elegans were more abundant at stations with a high content of fine sand. Carnivorous species, mainly of the Oedicerotidae family, were more abundant at those stations with a low organic matter content, while detritivorous species were more abundant at stations with a higher mud content. Among 62 identified species, three were reported for the first time from the Spanish Mediterranean coast, two species were recorded for the second time and a new species of Siphonoecetes was found, Siphonoecetes (Centraloecetes) bulborostrum. These results confirm the need for further data on amphipods from the Mediterranean Spanish coast.     

Testing the model of oblique transpression with oblique extrusion in two natural cases: Steps and consequences

Kinematic models of various types of transpression have been used to explain fabric features and strain in many natural deformation studies. Here, a mathematical model that encompasses all monoclinic and triclinic transpressional deformations including triclinic deformation with inclined simple shear (ϕ) and/or inclined extrusion orientations (υ) can be tested using a step-by-step approach with available field evidence. Two cases are presented. The first case from the Wabigoon–Quetico boundary in the Archean Superior Province utilizes both fabric orientation and quantified strain data. The best fit of the field evidence to the model indicates that deformation likely took place along subvertical shear zones via transpression with subhorizontal simple shear (ϕ = 0–20°) and variable inclined extrusion direction (extrusion can be either east or west and υ typically indicates extrusion orientations between 0 and 50° from vertical). The second case of the South Iberian shear zone has fabric orientation data, but no quantifiable strain possibilities. The best fit of the field evidence to the model indicates that deformation likely took place along a moderately inclined shear zone via transpression with subhorizontal simple shear (ϕ = 0–20°) and variable inclined extrusion direction (υ values between 0° and 80° from the true dip of the shear zone). Using this protocol in other examples of natural deformation will allow further constraints to be applied to kinematic models.     

Last glacial ice‐rafted debris off southwestern Europe: the role of the British–Irish Ice Sheet

Ice‐rafted debris (IRD) seeded into the ocean from Northern Hemisphere ice sheets is found in ocean cores along the southwestern European margin through the last glacial period. It is known that the origin of this IRD, especially off Iberia, can vary between North America and western Europe during short‐lived episodes of greatly enhanced iceberg flux, known as Heinrich events, although in most Heinrich events the IRD has a North American source. During the longer times of much lower IRD fluxes between Heinrich events, use of an intermediate complexity climate model, coupled to an iceberg dynamic and thermodynamic model, shows that background levels of IRD most likely originate from western Europe, particularly the British–Irish Ice Sheet. Combining modelling with palaeoceanographic evidence supports reconstructions of a short‐lived, but substantial, Celtic and Irish Sea Ice Stream around 23 ka. Copyright © 2010 John Wiley & Sons, Ltd.     

Chemical characteristics of groundwater around two massive sulphide deposits in an area of previous mining contamination, Iberian Pyrite Belt, Spain

A detailed chemical study of groundwater was carried out to elucidate the processes controlling the oxidation and dissolution of sulphide minerals at two massive sulphide deposits in the Iberian Pyrite Belt (IPB), i.e. the mined La Zarza deposit and the unmined Masa Valverde deposit. It was found that major-element compositions varied according to the hydrological regime, La Zarza being in a relatively high area with groundwater recharge (and disturbance due to the human factor) and Masa Valverde being in a relatively low area with groundwater discharge. The variations mainly concern pH, Eh, SO₄ and Na concentrations. Metal concentrations were determined (a) by ICP-MS after filtration, and (b) in some cases by voltammetric measurement of Cu, Pb, Zn, Cd and Mn using the Voltammetric In situ Profiling (VIP) System, which allows detection of only the mobile fractions of trace elements (i.e., free metal ions and small labile complexes a few nanometers in size). If one compares the results obtained by each of the two methods, it would appear that the groundwater shows significant enhancement of metal solubility through complexing with organic matter and/or adsorption onto colloids and/or small particles. In areas of sulphide oxidation, however, this solubility enhancement decreases according to Cu>Zn>Cd>Pb. Under very low redox conditions, the attained metal concentrations can be several orders of magnitude (up to 10⁸–10⁹ for Cu and 10²–10³ for Pb) larger than those expected from equilibrium with respect to sulphide minerals as calculated with the EQ3NR geochemical code; Zn concentrations, however, are close to equilibrium with respect to sphalerite. The implication of these results is discussed with respect both to mineral exploration and to environmental issues.     

地下水资源评价中降水量的时间序列--马尔可夫模型

降水量的预报精度对以其为直接或间接补给源的地下水资源评价具有重要的影响，将时间序列方法与随机过程离散状态的马尔可夫链理论相结合，提出了时间序列－马尔可夫模型以预报大气降水量，模型根据降水序列的特征，采用一维非平衡时间序列模型进行预测，预测结果总体效果较好，但峰值点处误差较大，为了提高模型对波动性较大随机变量的预报精度，利用随机过程马尔可夫概率状态转移矩阵预报方法对其预测值进行二次拟合，实例计算表明，时间序列－马尔可夫模型预报效果良好，预报精度明显高于单一的时间序列模型精度，该结果拓宽了时间序列预报模型的应用范围，且对以大气降水为最终补给源的地下水资源评价具有重要的实用价值及理论意义。     

The Jiloca karst polje-tectonic graben (Iberian Range, NE Spain)

The Jiloca depression, one of the largest morpho-structural units of the Iberian Range and traditionally considered as a neotectonic graben, is interpreted as a karst polje developed within an active halfgraben. This polje, 705 km² in area, constitutes one of the largest documented poljes. Several evidences—(1) a sequence of eight-stepped levels of corrosion surfaces, (2) the reduced thickness of the basin fill, (3) fault-controlled mountain fronts with topographic scarps much higher than the structural throws—demonstrate that great part of the topographic relief of the depression has been generated by corrosional lowering rather than by tectonic subsidence. The height difference between the highest corrosion surface and the polje bottom indicate that the depression has been deepened around 300 m by corrosion processes. The initiation of the karst polje was determined by the creation of the Jiloca halfgraben by normal faults, which deformed a Pliocene regional erosion surface. The development of the polje has been controlled largely by the asymmetric structure and the slight neotectonic activity of the graben. Changes in the position of the polje bottom inferred from the slopes of the different corrosion surfaces (polje paleotopography) may have been controlled by neotectonic movements.