Modelling Thermohaline Properties in an Estuarine Upwelling Ecosystem (R?́a de Vigo: NW Spain) Using Box-Jenkins Transfer Function Models

Since 1987, twice weekly, hydrological variables have been monitored at a fixed station in the R?́a de Vigo (NW Spain), aiming to examine the time scales of variability and the relationships to meteorological conditions. The present paper analyses: (1) the advantage of Box-Jenkins transfer function (TF) models (single output–multiple input), a type of linear stochastic model, to describe the dynamic behaviour of the system; and (2) the coupling between the R?́a and meteorological events at the time scale of autonomy of this coastal inlet affected by the Iberian coastal upwelling, approximately a fortnightly period. In order to achieve these objectives, thermohaline properties have been used to characterize the estuarine ecosystem (output variables), while wind regime, runoff in the drainage basin and incoming solar radiation have been considered as the main forcing variables (input variables). The use of the amplitude time series, derived from principal component analysis (PCA) applied to the deseasonalized meteorological variables, is also explored as a different set of input variables.When compared with standard regression models, all TF models built to describe thermohaline behaviour had reduced residual variance. Similar TF models, as well as percentage of explained variance, were also obtained when meteorological variables or the amplitude time series were used as input variables. The fitted TF models provided an insight into the ‘ inertial ’ behaviour of the system and the time scales of coupling of the system with the forcing variables. The plausible physical mechanisms which link the response of the system with the observed meteorological variability are also discussed. As could be expected, bottom thermohaline properties show a stronger inertial behaviour than the surface ones, which is particularly marked for bottom temperature. Besides, the shelf domain, by means of upwelling-downwelling events, strongly influences surface and bottom temperature, as well as bottom salinity; by contrast, surface salinity is mainly influenced by the effect of wind along the main axis of the R?́a and runoff. In relation to the time scales of coupling between the system and the forcing variables, thermohaline properties show a dependance with the meteorological conditions in, at least, the immediately preceding fortnight period. It was concluded that: (1) TF models that incorporate meteorological information described the dynamic behaviour of the system adequately; and (2) this type of model can be useful as a first approximation to develop more sophisticated (deterministic) models, since, with the purpose of modelling any state variable of the system, both the coupling between different domains and the time scales of the interactions must be taken into account.     

P-T path determinations in the Tormes Gneissic Dome, NW Iberian Massif, Spain

The Tormes Gneissic Dome (TGD, NW sector of the Iberian Massif, Spain) is a high-grade metamorphic complex affected by a major episode of extensional deformation (D2). The syn-D2 P–T  path of the Lower Unit of the TGD was deduced from the analysis of reaction textures related to superimposed fabrics developed during exhumation, analysis of mineral zoning and thermobarometric calculations. It comprises an initial phase of decompression, determined using the tweequ thermobarometric technique, from 6.4–8.1 kbar at 735–750 °C (upper structural levels) and 7.2 kbar at 770 °C (lower structural levels) to 3.3–3.9 kbar and 645–680 °C. This evolution is consistent with the observed sequence of melting reactions and the generation of garnet- and cordierite-bearing anatectic granitoids. The later part of the syn-D2 P–T  path consisted of almost isobaric cooling associated with the thermal re-equilibration of the unit in the new structural position. This segment of the P–T  path is recorded by assemblages with And +Bt+Ms and Ms+ Chl +Ab related to the later mylonitic S2 fabrics, which indicate retrogression to low-amphibolite and greenschist facies conditions.     

Acid mine drainage and acid rock drainage processes in the environment of Herrerías Mine (Iberian Pyrite Belt, Huelva-Spain) and impact on the Andevalo Dam

The present work describes the process of acid water discharge into the Andévalo Dam (Iberian Pyrite Belt, Huelva-Spain) starting from the interpretation of rainfall data and chemical analyses regarding pH, conductivity, metal and sulphate content in water, from a time series corresponding to the sampling of two confluent channels that discharge water into the referred dam. Statistical data treatment allows us to conclude the existence of acid mine drainage processes in the Chorrito Stream, which are translated into very low pH values and high sulphate and metal concentrations in the water coming from Herrerías Mine. On the other hand, the Higuereta Stream shows, for the same parameters, much lower values that can be interpreted as the channel response to acid rock drainage processes in its drainage basin induced by the rocky outcrops of the Iberian Pyrite Belt.     

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.     

Upper Ordovician–Lower Silurian transgressive–regressive cycles of the Central Iberian Zone (NE Jaén,Spain)

A thick Upper Ordovician shelf sequence was developed in the northern Gondwana margin (southernmost exposures of the Central Iberian Zone). Integrated sedimentologic and stratigraphic studies allow distinction between pedogenetic processes (Facies association C), shoreline deposits (Facies association S), proximal to distal shelf (Facies association L, H₁, H₂, H₃) and outer shelf zone or open marine environments (Facies association M, Mo). The vertical distribution of facies is characterized by the presence of regressive high frequency sequences (partial shelf progradational sequences), affected by the presence of catastrophic phenomena (storms). These sequences, in turn, can be classified into higher‐order transgressive (T)–regressive (R) cycles. Two second‐order T‐R megacycles (MC. Ord‐2 and MC. Sil‐1) limited by a major sequence boundary are identified. Traces of emersion (palaeokarsts and palaeosols) are detected along the sequence boundary, and these are related to the eustatic sea‐level fall that occurred during the Ashgillian. The MC. Ord‐2 and MC. Sil‐1 megacycles extend respectively from the Middle Arenig to the Ashgillian and from Late Ashgillian to the Late Llandovery. Major transgressive peaks occurred at the Llanvirn and at the Middle Llandovery (Aeronian). The vertical distribution of the facies delineates successive genetically related units in relation to relative sea‐level changes. Within the upper part of the first megacycle (MC. Ord‐2) six third‐order cycles are proposed (Lla‐1, Car‐1, Car‐2, Car‐3, Car‐4, Ash‐1), in which a transgressive and a regressive interval can be distinguished. Within the lower part of the second megacycle (MC. Sil‐1) two transgressive–regressive third‐order cycles are proposed (Lly‐1, Lly‐2). Copyright © 2005 John Wiley & Sons, Ltd.