Incorporating circulation statistics in bias correction of GCM ensembles: hydrological application for the Rhine basin

An adapted statistical bias correction method is introduced to incorporate circulation-dependence of the model precipitation bias, and its influence on estimated discharges for the Rhine basin is analyzed for a historical period. The bias correction method is tailored to time scales relevant to flooding events in the basin. Large-scale circulation patterns (CPs) are obtained through Maximum Covariance Analysis using reanalysis sea level pressure and high-resolution precipitation observations. A bias correction using these CPs is applied to winter and summer separately, acknowledging the seasonal variability of the circulation regimes in North Europe and their correlation with regional precipitation rates over the Rhine basin. Two different climate model ensemble outputs are explored: ESSENCE and CMIP5. The results of the CP-method are then compared to observations and uncorrected model outputs. Results from a simple bias correction based on a delta factor (NoCP-method) are also used for comparison. For both summer and winter, the CP-method offers a statistically significant improvement of precipitation statistics for subsets of data dominated by particular circulation regimes, demonstrating the circulation-dependence of the precipitation bias. Uncorrected, CP and NoCP corrected model outputs were used as forcing to a hydrological model to simulate river discharges. The CP-method leads to a larger improvement in simulated discharge in the Alpine area in winter than in summer due to a stronger dependence of Rhine precipitation on atmospheric circulation in winter. However, the NoCP-method, in comparison to the CP-method, improves the discharge estimations over the entire Rhine basin.     

Determining sea level change in the German Bight

Regional mean sea level changes in the German Bight are considered. Index time series derived from 15 tide gauge records are analysed. Two different methods for constructing the index time series are used. The first method uses arithmetic means based on all available data for each time step. The second method uses empirical orthogonal functions. Both methods produce rather similar results for the time period 1924–2008. For this period, we estimate that regional mean sea level increased at rates between 1.64 and 1.74 mm/year with a 90% confidence range of 0.28 mm/year in each case. Before 1924, only data from a few tide gauges are available with the longest record in Cuxhaven ranging back till 1843. Data from these tide gauges, in particular from Cuxhaven, thus receive increasingly more weight when earlier years are considered. It is therefore analysed to what extent data from Cuxhaven are representative for the regional sea level changes in the German Bight. While this cannot be clarified before 1924, it is found that this is not the case from 1924 onwards when changes in Cuxhaven can be compared to that derived from a larger data set. Furthermore, decadal variability was found to be substantial with relatively high values towards the end of the analysis period. However, these values are not unusual when compared to earlier periods.     

Characterization of sediments in an abandoned mining area; a case study of Mansfeld region,Germany

The distribution of selected heavy metals, including some radionuclides, metalloids and non-metals was determined in stream sediments in a region influenced by abandoned copper mining and ore processing activities. A considerable amount of the ore processing waste with a very complex composition and highly elevated concentrations of zinc, sulfur, lead, copper, arsenic, and a lot of other elements in the range between 100 and 1,000 mg/kg (Sb, Mn, Ni, Cr, Cd, Hg, and Ag) was piled up on mine dumps. The dispersion of the pollutants originating from this source and their environmental impact were investigated. Both, sediments and original waste material were studied to indicate the pathways and the mobilization behavior of different pollutants. For this purpose, the process of the elution of pollutants by application of different fractionation schemes was studied. The capabilities of different analytical techniques are shown for the analysis of solid samples (X-ray fluorescence spectrometry, Gamma-spectrometry) and liquid ones (ICP-atomic emission spectrometry, ICP-mass spectrometry and different techniques of atomic absorption). Additionally, the coupling of ion chromatography and ICP-MS detection was used to study the distribution of arsenic species in the sediment cores of a lake which acts as a natural sink for the region.     

Late Cretaceous porphyry Cu and epithermal Cu–Au association in the Southern Panagyurishte District,Bulgaria: the paired Vlaykov Vruh and Elshitsa deposits

Vlaykov Vruh–Elshitsa represents the best example of paired porphyry Cu and epithermal Cu–Au deposits within the Late Cretaceous Apuseni–Banat–Timok–Srednogorie magmatic and metallogenic belt of Eastern Europe. The two deposits are part of the NW trending Panagyurishte magmato-tectonic corridor of central Bulgaria. The deposits were formed along the SW flank of the Elshitsa volcano-intrusive complex and are spatially associated with N110-120-trending hypabyssal and subvolcanic bodies of granodioritic composition. At Elshitsa, more than ten lenticular to columnar massive ore bodies are discordant with respect to the host rock and are structurally controlled. A particular feature of the mineralization is the overprinting of an early stage high-sulfidation mineral assemblage (pyrite ± enargite ± covellite ± goldfieldite) by an intermediate-sulfidation paragenesis with a characteristic Cu–Bi–Te–Pb–Zn signature forming the main economic parts of the ore bodies. The two stages of mineralization produced two compositionally different types of ores—massive pyrite and copper–pyrite bodies. Vlaykov Vruh shares features with typical porphyry Cu systems. Their common geological and structural setting, ore-forming processes, and paragenesis, as well as the observed alteration and geochemical lateral and vertical zonation, allow us to interpret the Elshitsa and Vlaykov Vruh deposits as the deep part of a high-sulfidation epithermal system and its spatially and genetically related porphyry Cu counterpart, respectively. The magmatic–hydrothermal system at Vlaykov Vruh–Elshitsa produced much smaller deposits than similar complexes in the northern part of the Panagyurishte district (Chelopech, Elatsite, Assarel). Magma chemistry and isotopic signature are some of the main differences between the northern and southern parts of the district. Major and trace element geochemistry of the Elshitsa magmatic complex are indicative for the medium- to high-K calc-alkaline character of the magmas. ⁸⁷Sr/⁸⁶Sr_(i) ratios of igneous rocks in the range of 0.70464 to 0.70612 and ¹⁴³Nd/¹⁴⁴Nd_(i) ratios in the range of 0.51241 to 0.51255 indicate mixed crustal–mantle components of the magmas dominated by mantellic signatures. The epsilon Hf composition of magmatic zircons (+6.2 to +9.6) also suggests mixed mantellic–crustal sources of the magmas. However, Pb isotopic signatures of whole rocks (²⁰⁶Pb/²⁰⁴Pb = 18.13–18.64, ²⁰⁷Pb/²⁰⁴Pb = 15.58–15.64, and ²⁰⁸Pb/²⁰⁴Pb = 37.69–38.56) along with common inheritance component detected in magmatic zircons also imply assimilation processes of pre-Variscan and Variscan basement at various scales. U–Pb zircon and rutile dating allowed determination of the timing of porphyry ore formation at Vlaykov Vruh (85.6 ± 0.9 Ma), which immediately followed the crystallization of the subvolcanic dacitic bodies at Elshitsa (86.11 ± 0.23 Ma) and the Elshitsa granite (86.62 ± 0.02 Ma). Strontium isotope analyses of hydrothermal sulfates and carbonates (⁸⁷Sr/⁸⁶Sr = 0.70581–0.70729) suggest large-scale interaction between mineralizing fluids and basement lithologies at Elshitsa–Vlaykov Vruh. Lead isotope compositions of hydrothermal sulfides (²⁰⁶Pb/²⁰⁴Pb = 18.432–18.534, ²⁰⁷Pb/²⁰⁴Pb = 15.608–15.647, and ²⁰⁸Pb/²⁰⁴Pb = 37.497–38.630) allow attribution of ore-formation in the porphyry and epithermal deposits in the Southern Panagyurishte district to a single metallogenic event with a common source of metals.     

Petrographic,fluid inclusion and isotopic study of the Dikulushi Cu–Ag deposit,Katanga (D.R.C.): implications for exploration

The Dikulushi Cu–Ag vein-type deposit is located on the Kundelungu Plateau, in the southeastern part of the Democratic Republic of Congo (D.R.C.). The Kundelungu Plateau is situated to the north of the Lufilian Arc that hosts the world-class stratiform Cu–Co deposits of the Central African Copperbelt. A combined petrographic, fluid inclusion and stable isotope study revealed that the mineralisation at Dikulushi developed during two spatially and temporally distinct mineralising episodes. An early Cu–Pb–Zn–Fe mineralisation took place during the Lufilian Orogeny in a zone of crosscutting EW- and NE-oriented faults and consists of a sequence of sulphides that precipitated from moderate-temperature, saline H₂O–NaCl–CaCl₂-rich fluids. These fluids interacted extensively with the country rocks. Sulphur was probably derived from thermochemical reduction of Neoproterozoic seawater sulphate. Undeformed, post-orogenic Cu–Ag mineralisation remobilised the upper part of the Cu–Pb–Zn–Fe mineralisation in an oxidising environment along reactivated and newly formed NE-oriented faults in the eastern part of the deposit. This mineralisation is dominated by massive Ag-rich chalcocite that precipitated from low-temperature H₂O–NaCl–KCl fluids, generated by mixing of moderate- and low-saline fluids. The same evolution in mineralisation assemblages and types of mineralising fluids is observed in three other Cu deposits on the Kundelungu Plateau. Therefore, the recognition of two distinct types of (vein-type) mineralisation in the study area has a profound impact on the exploration in the Kundelungu Plateau region. The identification of a Cu–Ag type mineralisation at the surface could imply the presence of a Cu–Pb–Zn–Fe mineralisation at depth.