Aqueous–solid solution thermodynamic model of U(VI) uptake in C–S–H phases

Reliable thermodynamic models assessing the interaction of radionuclides with cementitious materials are important in connection with long-term predictions of the safe disposal of radioactive waste in cement-based repositories. In this study, a geochemical model of U(VI) interaction with calcium silicate hydrates (C–S–H phases), the main component of hardened cement paste (HCP), has been developed. Uranium(VI) sorption isotherms on C–S–H phases of different Ca:Si ratios (C:S) and structural data from spectroscopic studies provided the indispensable set of experimental data required for the model development. This information suggested that U(VI) is neither adsorbed nor incorporated in the Ca–O octahedral layers of the C–S–H structure, but rather is located in the interlayer, similar to Ca²⁺ and other cations. With a view to the high recrystallisation rates and the cryptocrystalline ‘gel-like’ structure of the C–S–H phases, these observations indicated a U(VI) uptake driven by the formation of a solid solution.     

Limnologische Beiträge zur Glazialgeologie

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Preparation and characterization of antibacterial silver/vermiculites and silver/montmorillonites

The reason for the preparation and characterization of the novel antibacterial silver/vermiculites (Ag/V) together with the silver/montmorillonites (Ag/M) was that the information on the vermiculite structure change and stability of Ag/V in water as well as its effect on bacteria are sporadic. The vermiculite (V), (Si_3.02Al_0.98)^IV (Mg_2.27Al_0.12Ti_0.07)^VI O₁₀(OH)₂ Ca_0.09Na_0.21K_0.50 from West China and montmorillonite (M), (Si_3.96Al_0.04)^IV (Al_1.20Mg_0.42Ti_0.02)^VI O₁₀ (OH)₂Ca_0.15Na_0.14K_0.08 from Ivan?ice (Czech Republic), fraction <0.4 μm were the starting clay materials for sample preparation. The samples V1 and M1 were prepared via reaction of the V and M with the 0.01 mol L⁻¹ AgNO₃ aqueous solution. The samples V2 and M2 were treated with the aqueous solution of AgNO₃ for two times. The cation exchange and reduced metallic silver on M1 and V1 evoked the specific surface area (SSA) diminution, the mean particle-size diameter extension and appearance of micropores with radius (<0.4 nm). Repeated silver cation exchange in M2 and V2 reduced particle size, increased slightly SSA and micropores with radius of 0.4-0.5 nm. Samples Ag/V and Ag/M showed higher content of pores with radius 0.5-1.0 nm than original V and M. The Ag concentration was found higher in Ag/V than in Ag/M and higher in repeatedly treated samples: 0.9 wt.% Ag in V1, 1.4 wt.% Ag in V2, 0.6 wt.% Ag in M1 and 1.0 wt.% Ag in M2. Vermiculite structure consisting of the hydrated interstratified phases and the mica-like phase changed to the cation-one-zero layer hydrate interstratification structure in V1 and to the random of two-one layer hydrate interstratifications in V2. Infrared and Mössbauer spectroscopy revealed no changes in the structure of the clay minerals that could be related directly to the sorption and crystallization of silver. Transmission electron microscopy showed that the silver nanoparticles size distribution was much narrower for the samples Ag/M than for Ag/V. The mean size of the Ag particles was between 40 and 50 nm. Although the Ag nanoparticles did not adhere sufficiently at the clay minerals surface and migrated moderately into water, all samples under study were approved to be effective inhibitors of the bacterial growth persisting for the whole testing period of 6 days. Silver/vermiculite was antimicrobial more efficient against Klebsiella pneumoniae and Pseudomonas aeruginosa than silver/montmorillonite.     

Future changes in daily summer temperature variability: driving processes and role for temperature extremes

Anthropogenic greenhouse gas emissions are expected to lead to more frequent and intense summer temperature extremes, not only due to the mean warming itself, but also due to changes in temperature variability. To test this hypothesis, we analyse daily output of ten PRUDENCE regional climate model scenarios over Europe for the 2071–2100 period. The models project more frequent temperature extremes particularly over the Mediterranean and the transitional climate zone (TCZ, between the Mediterranean to the south and the Baltic Sea to the north). The projected warming of the uppermost percentiles of daily summer temperatures is found to be largest over France (in the region of maximum variability increase) rather than the Mediterranean (where the mean warming is largest). The underlying changes in temperature variability may arise from changes in (1) interannual temperature variability, (2) intraseasonal variability, and (3) the seasonal cycle. We present a methodology to decompose the total daily variability into these three components. Over France and depending upon the model, the total daily summer temperature variability is projected to significantly increase by 20–40% as a result of increases in all three components: interannual variability (30–95%), seasonal variability (35–105%), and intraseasonal variability (10–30%). Variability changes in northern and southern Europe are substantially smaller. Over France and parts of the TCZ, the models simulate a progressive warming within the summer season (corresponding to an increase in seasonal variability), with the projected temperature change in August exceeding that in June by 2–3 K. Thus, the most distinct warming is superimposed upon the maximum of the current seasonal cycle, leading to a higher intensity of extremes and an extension of the summer period (enabling extreme temperatures and heat waves even in September). The processes driving the variability changes are different for the three components but generally relate to enhanced land–atmosphere coupling and/or increased variability of surface net radiation, accompanied by a strong reduction of cloudiness, atmospheric circulation changes and a progressive depletion of soil moisture within the summer season. The relative contribution of these processes differs substantially between models.     

Rain and dewdrops on titan based on in situ imaging

The Descent Imager/Spectral Radiometer (DISR) of the Huygens probe was in an excellent position to view aspects of rain as it descended through Titan's atmosphere. Rain may play an important part of the methane cycle on Titan, similar to the water cycle on Earth, but rain has only been indirectly inferred in previous studies. DISR detected two dark atmospheric layers at 11 and 21 km altitude, which can be explained by a local increase in aerosol size by about 5-10%. These size variations are far smaller than those in rain clouds, where droplets grow some 1000-fold. No image revealed a rainbow, which implies that the optical depth of raindrops was less than ∼0.0002/km. This upper limit excludes rain and constrains drizzle to extremely small rates of less than 0.0001 mm/h. However, a constant drizzle of that rate over several years would clear the troposphere of aerosols faster than it can be replenished by stratospheric aerosols. Hence, either the average yearly drizzle rate near the equator was even less (<0.1 mm/yr), or the observed aerosols came from somewhere else. The implied dry environment is consistent with ground-based imaging showing a lack of low-latitude clouds during the years before the Huygens descent. Features imaged on Titan's surface after landing, which might be interpreted as raindrop splashes, were not real, except for one case. This feature was a dewdrop falling from the outermost baffle of the DISR instrument. It can be explained by warm, methane-moist air rising along the bottom of the probe and condensing onto the cold baffle.     

Stratigraphic and geochemical evidence for the depositional environment of the early archaean isua supracrustal belt,southern west greenland

The highly deformed c. 3800 Ma Isua supracrustal belt is a fragment of a more extensive Early Archaean sedimentary and volcanic succession intruded by and tectonically intercalated with tonalitic and granitic Amftsoq gneisses in the period 3800-3600 Ma. The supracrustal rocks recrystallised under amphibolite facies conditions between 3800 and 3600 Ma, in the Late Archaean and locally at c. 1800 Ma. Layered sequences of rock of sedimentary and probable volcanic origin form over 50% of the belt. Bodies of high MgAl basic rocks and ultramafic rocks were intruded into the layered sequences prior to isoclinal folding and intrusion of Amitsoq gneisses. The layered rocks which are < 1 km thick are divided into two sequences, that are in faulted contact with each other. The way-up of these sequences has been determined from facing-directions of locally-preserved graded layering in felsic metasediments at several localities. The overall upwards change in sedimentary succession is interpreted as showing change from dominantly basic to dominantly felsic volcanism which provided the major clastic component of the sediments. Clastic sedimentation took place against a background of chemical sedimentation, shown by interlayers of banded iron formation, metachert and calc-silicate rocks throughout the sequences. The felsic rocks locally preserve graded bedding and possible conglomerate structures, indicating deposition from turbidite flows and possibly as debris flows. Nodules in the felsic rocks contain structures interpreted as fiammé. There is an irregular enrichment in K₂O/Na₂O in many of the felsic rocks at constant SiO₂ and Al₂O₃ content, interpreted as owing to alteration of original andesitic to dacitic volcanic rocks. Banded iron formations locally contain conglomeratic structures suggesting sedimentary reworking, possibly under shallow water conditions. Lithological and geochemical characters of the clastic components of the supracrustal sequences are consistent with derivation from felsic and basic volcanic rocks and do not require a continental source.     

Colouration Phenomena of Mediterranean Blennies (Pisces,Blenniidae)

Abstract. The blennies of the Mediterranean Sea were observed in nature by snorkeling and SCUBA diving. Particular attention was paid to their changeable basic patterns and colouring alternations as effected by ecological and ethological factors. Additionally, the tendency for colour change was tested in differently coloured tanks. These experiments failed to demonstrate the striking adaptations seen in the natural environment, except for a remarkable reaction to black and white. The summary of all known reports is supported by colour illustrations; the problems of the colouring alternations are discussed.     

Atmospheric deposition of cadmium in the northeastern USA

Lake sediment cores, dated by ²¹⁰Pb, were collected from Spectacle Pond (SP), Massachusetts, and Side Pistol Lake (SPL) and Sargent Mountain Pond (SMP), Maine, USA. SP is a kettle seepage lake in granitic sand and gravel. SMP is a drainage pond on granite with little soil in the small watershed. SPL is a drainage lake in granitic till. The three cores were analyzed for total Cd. For SP and SMP, maximum concentrations of 1.7 and 3.9 mg/kg, four and eight times background concentrations, respectively, occur in the late 1960s. Accumulation rates reach maximum values concurrently with concentration and are 0.054 and 0.016 μg/cm²/a, more than 10 times background. Concentration and accumulation rate age relationships in SMP and SP are similar for background values, timing and magnitude of increase to peak values, and the decrease nearly to background values since about 1975. The chemical response to decreased atmospheric deposition lags in SPL sediment. Kettle-like lakes more clearly indicate changes in atmospheric deposition than drainage lakes.     

On the natural variability of the pre-industrial European climate

We suggest that climate variability in Europe for the “pre-industrial” period 1500–1900 is fundamentally a consequence of internal fluctuations of the climate system. This is because a model simulation, using fixed pre-industrial forcing, in several important aspects is consistent with recent observational reconstructions at high temporal resolution. This includes extreme warm and cold seasonal events as well as different measures of the decadal to multi-decadal variance. Significant trends of 50-year duration can be seen in the model simulation. While the global temperature is highly correlated with ENSO (El Nino- Southern Oscillation), European seasonal temperature is only weakly correlated with the global temperature broadly consistent with data from ERA-40 reanalyses. Seasonal temperature anomalies of the European land area are largely controlled by the position of the North Atlantic storm tracks. We believe the result is highly relevant for the interpretation of past observational records suggesting that the effect of external forcing appears to be of secondary importance. That variations in the solar irradiation could have been a credible cause of climate variations during the last centuries, as suggested in some previous studies, is presumably due to the fact that the models used in these studies may have underestimated the internal variability of the climate. The general interpretation from this study is that the past climate is just one of many possible realizations and thus in many respects not reproducible in its time evolution with a general circulation model but only reproducible in a statistical sense.