Centimeter repeatability of the VLBI estimates of European baselines

Summary In the last three years, the European Geodetic Very Long Baseline Interferometry (VLBI) Network has grown to a total of six fixed antennas placed in Germany, Italy, Spain and Sweden, all equipped with the standard geodetic VLBI instrumentation and data recording systems. During this period of time, several experiments have been carried out using this interferometer providing data of very high quality due to the excellent sensitivity and performance of the European stations. The purpose of this paper is to study the consistency of the VLBI geodetic results on the European baselines with respect to the different degrees of freedom in the analysis procedure. In order to complete this study we have made use of both real and simulated data sets, two different software packages (OCCAM 3.0 and CALC 7.4/SOLVE) and a variety of strategies in the data analysis. The results we have obtained show that the repeatability of the VLBI estimates of the baseline lengths in the European network is better than one centimeter, independent of the different analysis methods, and is consistent with the formal error levels expected from the data analysis. This consistency should be enough to produce geophysically significant information in Europe from VLBI data within a relatively short time span.     

Post-fire management effects on sediment (dis)connectivity in Mediterranean forest ecosystems: Channel and catchment response

Forest fires and post-fire practices influence sediment connectivity (SC). In this study, we use the ‘aggregated index of connectivity’ (AIC) to assess SC in five Mediterranean catchments (198–1090 ha) affected by a wildfire in 2012 in south-eastern Spain. Two temporal scenarios were considered, immediately after the fire and before post-fire management, and 2 years after the fire including all practices (hillslope barriers, check-dams, afforestation, salvage logging and skid trails). One LiDAR (light detection and ranging)-derived digital elevation model (DEM, 2 m × 2 m resolution) was generated, per scenario. The five catchment outlets were established as the computation target (AIC_OUT), and structural and functional SC were calculated. Index outputs were normalized to make the results of the non-nested catchments comparable (AIC_N-OUT). The output analysis includes the SC distribution along the catchments and at local scale (929 sub-catchments, 677 in the burned area), the hillslope and channel measures' effect on SC, and a sedimentological analysis using observed area-specific sediment yield (SSY) at 10 new (built after post-fire practices) concrete check-dams located in the catchments (SSY = 1.94 Mg ha⁻¹ yr⁻¹; σ = 1.22). The catchments with more circular shapes and steeper slopes were those with higher AIC_N-OUT. The structural SC maps – removing the rainfall erosivity influence – allowed evaluating the actual role played by the post-fire practices that reduced SC ( $\overline{x}$= − 1.19%; σ = 0.41); while functional SC was linked to the actual change of SC ( $\overline{x}$= + 5.32%; σ = 0.62). Hillslope treatments resulted in significant changes on AIC_N-OUT at sub-catchment scale with certain disconnectivity. A good and positive correlation was found between the SSY and the changes of AIC_N-OUT. However, the coarse DEM resolution explained the lack of effect of the rock check-dams – located on the secondary channels – on AIC_N-OUT. AIC_N-OUT proved to be a useful tool for decision making in post-fire restoration, but an optimal input data is still necessary to refine calculations.     

A Numerical Study of the Impact of Greenhouse Gases on the South Atlantic Ocean Climatology

The National Center for Atmospheric Research Community Climate SystemModel (NCAR CCSM, version 3) numerical coupled model is used tounderstand the climatic impacts on the South Atlantic Ocean due toindustrialization and consequent increase of greenhouse gasemission. Two experiments are analyzed: the first one withtrace/greenhouse gases at pre-industrial levels and a second one wherepresent day levels were adopted. The results show that the annualaveraged sea surface temperature, sea level pressure and barotropictransport intensify and precipitation weakens from one period to thenext. With respect to the seasonal cycle, the sea surface temperaturewarms relative to the pre-industrial period mainly during the winterand spring; while sea level pressure presents higher values in summerand autumn. Barotropic transport has revealed significant differencesbetween the two experiments at middle and high latitudes. Increasedtransport is associated with the intensification of the SubtropicalGyre and the Antarctic Circumpolar Current. Changes in barotropictransport and sea surface temperature leads to an intensification ofthe Polar Front and associated gradients. Examination of theprecipitation field differences showed an increase over the Amazonregion and along the South Atlantic Convergence Zone, during summer.The changes in sea surface temperature, sea-level pressure andbarotropic transport from the pre-industrial period to the present daywere more pronounced at high latitudes. These reach almost 1 °Cand 11Sv between 45-60° S, respectively. Majordifferences in precipitation are confined to the tropics.     

The natural attenuation of two acidic effluents in Tharsis and La Zarza-Perrunal mines (Iberian Pyrite Belt, Huelva, Spain)

The geochemical evolution of two acid mine effluents in Tharsis and La Zarza-Perrunal mines (Iberian Pyrite Belt, Huelva, Spain) has been investigated. In origin, these waters present a low pH (2.2 and 3.1) and high concentrations of dissolved sulphate and metals (Fe, Al, Mn, Cu, Zn, As, Cd, Co, Cr, Ni). However, the natural evolution of these acidic waters (which includes the bacterial oxidation of Fe(II) and the subsequent precipitation of Fe(III) minerals) represents an efficient mechanism of attenuation. This self-mitigating process is evidenced by the formation of schwertmannite, which retains most of the iron load and, by sorption, toxic trace elements like As. The later mixing with pristine waters rises the pH and favours the total precipitation of Fe(III) at pH 3.5 and, subsequently, Al compounds at pH 4.5, along with the sorption of trace metals (Mn, Zn, Cu, Cd, Co, Ni) until chemical equilibrium at circumneutral conditions is achieved.     

Influence of Decarbonisation and Phosphate Dosage on Copper Corrosion in Drinking Water Systems

The effect of softening/decarbonisation and dosage of orthophosphate on copper corrosion was studied in pipe rigs according to the German standard DIN 50931, part 1. A literature study with regard to the effects of phosphate dosing on copper corrosion has shown that on the one hand and in most of the cases a dosage of phosphate led to lower copper concentrations. On the other hand phosphate aggravated the copper corrosion in some cases. The mechanisms are not yet clear and the influence of phosphate on the corrosion of copper remains a question to be answered. Using standardised on‐site corrosion tests (DIN 50931‐1) with virgin copper pipes softening/decarbonisation has decreased the copper concentration. Two effects of phosphate on copper corrosion were noticed: Phosphate dosing decreased the copper oxidation and resulted in lower copper concentration in water. Likewise phosphate hindered the precipitation of cupric ions, which prolonged the existence of copper in water and resulted in a higher copper concentration. As a consequence, dosing phosphate can decrease or increase the copper corrosion, this depends on which effect is dominating.     

Gravimetric determination of an intrusive complex under the Island of Faial (Azores): some methodological improvements

We present some improvements of a gravity inversion method to determine the geometry of the anomalous bodies for priori density contrasts. The 3-D method is based on an exploratory process applied, not for the global model, but for the steps of a growth approach. The (positive and/or negative) anomalous structure is described by successive aggregation of cells, while its corresponding gravity field remains nearly proportional to the observed one. Moreover, a simple (e.g. linear) regional trend can be simultaneously adjusted. The corresponding program is applied to new gravity data on the volcanic island of Faial (Azores archipelago). The inversion approach shows a subsurface anomalous structure for the island, the main feature being an elongated high-density body. The body is interpreted as a compact sheeted dyke swarm, emplaced along Faial-Pico Fracture Zone, a leaky transform structure that forms the current boundary between Eurasian and African plates in the Azores area. The new results in this paper are (1) a Bouguer gravity anomaly map, (2) several improvements in the inversion process (robust process, optimal balance fitness/model magnitude), (3) a new gravimetric method for estimating the mean terrain density, (4) a 3-D model for subsurface mass anomalies in Faial and (5) some interpretative conclusions about a main intrusive complex detected under the island as a wall-like structure extending from a depth of 0.5 to 6 km b.s.l., with a N100°E trend and corresponding to an early fissural volcanic episode controlled by the regional tectonics.     

人工回灌对地下水年龄分布规律的影响

地下水可更新能力是评价地下水开发可持续性的关键指标,可更新能力可以用地下水年龄来定量表达。在人类活动影响下,地下水的实际更新状况已与自然条件下截然不同。基于台兰河流域地下水库建设和人工回灌工作现状,通过物理试验和数值模拟相结合的方法分别研究了入渗池位置,回灌强度和包气带厚度对地下水年龄分布规律的影响。结果表明:人工回灌使地下水年龄整体变年轻;入渗池位置和回灌强度的改变对地下水年龄分布的影响显著;包气带厚度的增大使回灌水滞留时间延长,导致地下水年龄增大,该研究可为合理评价区域地下水可更新能力提供技术指导。     

First identification and characterization of Borrobol‐type tephra in the Greenland ice cores: new deposits and improved age estimates

Contiguous sampling of ice spanning key intervals of the deglaciation from the Greenland ice cores of NGRIP, GRIP and NEEM has revealed three new silicic cryptotephra deposits that are geochemically similar to the well‐known Borrobol Tephra (BT). The BT is complex and confounded by the younger closely timed and compositionally similar Penifiler Tephra (PT). Two of the deposits found in the ice are in Greenland Interstadial 1e (GI‐1e) and an older deposit is found in Greenland Stadial 2.1 (GS‐2.1). Until now, the BT was confined to GI‐1‐equivalent lacustrine sequences in the British Isles, Sweden and Germany, and our discovery in Greenland ice extends its distribution and geochemical composition. However, the two cryptotephras that fall within GI‐1e ice cannot be separated on the basis of geochemistry and are dated to 14358 ± 177 a b2k and 14252 ± 173 a b2k, just 106 ± 3 years apart. The older deposit is consistent with BT age estimates derived from Scottish sites, while the younger deposit overlaps with both BT and PT age estimates. We suggest that either the BT in Northern European terrestrial sequences represents an amalgamation of tephra from both of the GI‐1e events identified in the ice‐cores or that it relates to just one of the ice‐core events. A firm correlation cannot be established at present due to their strong geochemical similarities. The older tephra horizon, found within all three ice‐cores and dated to 17326 ± 319 a b2k, can be correlated to a known layer within marine sediment cores from the North Iceland Shelf (ca. 17179‐16754 cal a BP). Despite showing similarities to the BT, this deposit can be distinguished on the basis of lower CaO and TiO₂ and is a valuable new tie‐point that could eventually be used in high‐resolution marine records to compare the climate signals from the ocean and atmosphere.     

Pseudo-nitzschia spp. (Bacillariophyceae) and dissolved organic matter (DOM) dynamics in the Ebro Delta (Alfacs Bay, NW Mediterranean Sea)

Samples were collected during one annual cycle (April 2007–March 2008) at Alfacs Bay (NW Mediterranean Sea) central station in order to assess the influence of organic nutrients in the growth of the microalgae assemblage, with special reference to Pseudo-nitzschia spp. This potentially toxic diatom forms natural and recurrent blooms in the study area. To assess further the relationship between Pseudo-nitzschia spp. and nutrients an enrichment experiment with high molecular weight dissolved organic matter (HMWDOM) was performed with field samples obtained during a Pseudo-nitzschia spp. bloom. HMWDOM was extracted from water collected at Alfacs Bay. Five bioassays were prepared: N + P (seawater with addition of nitrate and phosphate), DOM (addition of HMWDOM), (−N + P) + DOM (nitrogen deficient, with addition of phosphate and HMWDOM), (N + P) + DOM (addition of nitrate, phosphate and HMWDOM), seawater control (without added nutrients), and B + DOM (control of bacteria, without microalgae). The experiment was run in batch mode over 4 days. Results from the field study revealed that the concentrations of organic nutrients mostly surpassed the inorganic pool. Pseudo-nitzschia spp. was the most frequent and abundant taxa of the microalgae community. The micro-planktonic assemblage was arranged according to a seasonal factor (ANOSIM and cluster analysis). DON, nitrate and silicate were the most important abiotic parameters contributing to the dissimilarities between seasons (SIMPER analysis) and thereby potentially influencing the seasonal distribution of microalgae in the representative station. In the experimental investigation, Pseudo-nitzschia cells increased by the end of the experiment in the DOM bioassay but no respective increase was observed for chlorophyll a. This could point to an acquisition of nutrients through the DOM fraction that would conjointly reduce the need of chlorophyll a. The data obtained suggest that organic nutrients may exert an important role in the development of microalgae, including Pseudo-nitzschia spp., in the selected location.