Rare earth element partitioning between titanite and silicate melts: Henry’s law revisited

We present detailed experimental results on the partitioning of rare earth elements (REE) between titanite and a range of different silicate melts. Our results show that Henry’s law of trace element partitioning depends on bulk composition, the available partners for heterovalent substitution, crystal composition, and melt composition. We illustrate that the partition coefficients for Sm depend very strongly on the bulk concentration of Sm in the system. The substitution mechanism, by which rare earth elements are incorporated into the crystal structure, plays an important role for trace element partitioning and also for the onset of Henry’s law. Our data show that there are clear differences between substitution mechanisms of major elements compared to elements which are present only as traces. Our experiments also clearly show that the onset of Henry’s law depends on the concentrations of the sum of all trace elements which are incorporated into the crystal by the same substitution mechanism. For geochemical modelling of magmatic processes involving titanite, and indeed other accessory phases, it is of crucial importance to first evaluate whether the REE, and other trace elements, are present as traces or as major elements, only then appropriate D values may be chosen.     

Synthesis and Preliminary Characterisation of New Silicate, Phosphate and Titanite Reference Glasses

Eleven synthetic silicate and phosphate glasses were prepared to serve as reference materials for in situ microanalysis of clinopyroxenes, apatite and titanite, and other phosphate and titanite phases. Analytical results using different micro-analytical techniques showed that the glass fragments were homogeneous in major and trace elements down to the micrometre scale. Trace element determinations using inductively coupled plasma-mass spectrometry (ICP-MS), multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS), laser-ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) and secondary ionisation mass spectrometry (SIMS) showed good agreement for most elements (Li, Be, B, Cs, Rb, Ba, Sr, Ga, Pb, U, Th, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Er, Tm, Yb, Lu, Zr, Hf, Ta, Nb) studied and provide provisional recommended values.     

Dated Paleontological cave sites of Central Europe from Late Middle Pleistocene to early Upper Pleistocene (OIS 5 to OIS 8)

Caves are terrestrial depositories that preserve a large variety of organic and inorganic remains. These may contain important Quaternary climatic and ecological information. Most of the faunal remains, however, cannot be linked to any Interglacial or Glacial period exclusively. Reliable dating of such remains is therefore required. Experience has, however, shown that ESR dating of speleothems or ²³⁰Th/U dating of bones are of disputable value. Only TIMS-²³⁰Th/U dating of speleothems appears to yield reliable ages. Dating the bottom and top of speleothem layers permit assigning Pleistocene faunal remains to the OIS chronology if the deposition of the speleothems and the faunal remains are clearly correlated. Care must be taken to consider the depositional situation of each site before interpreting any age dates. In this paper we present an overview of all numerically dated paleontological cave sites in Central Europe between OIS 5 and OIS 8. A total of 25 strata were dated from 13 sites, most of them deposited during OIS 5; the rest belonging to OIS 6 and 7. Numerically dated paleontological sites older than OIS 8 are not known.     

Towards Adaptive Grids for Atmospheric Boundary-Layer Simulations

We present a proof-of-concept for the adaptive mesh refinement method applied to atmospheric boundary-layer simulations. Such a method may form an attractive alternative to static grids for studies on atmospheric flows that have a high degree of scale separation in space and/or time. Examples include the diurnal cycle and a convective boundary layer capped by a strong inversion. For such cases, large-eddy simulations using regular grids often have to rely on a subgrid-scale closure for the most challenging regions in the spatial and/or temporal domain. Here we analyze a flow configuration that describes the growth and subsequent decay of a convective boundary layer using direct numerical simulation (DNS). We validate the obtained results and benchmark the performance of the adaptive solver against two runs using fixed regular grids. It appears that the adaptive-mesh algorithm is able to coarsen and refine the grid dynamically whilst maintaining an accurate solution. In particular, during the initial growth of the convective boundary layer a high resolution is required compared to the subsequent stage of decaying turbulence. More specifically, the number of grid cells varies by two orders of magnitude over the course of the simulation. For this specific DNS case, the adaptive solver was not yet more efficient than the more traditional solver that is dedicated to these types of flows. However, the overall analysis shows that the method has a clear potential for numerical investigations of the most challenging atmospheric cases.     

On the variability of the surface environment response to synoptic forcing over complex terrain: a multivariate data analysis approach

Synoptic climatology relates the atmospheric circulation with the surface environment. The aim of this study is to examine the variability of the surface meteorological patterns, which are developing under different synoptic scale categories over a suburban area with complex topography. Multivariate Data Analysis techniques were performed to a data set with surface meteorological elements. Three principal components related to the thermodynamic status of the surface environment and the two components of the wind speed were found. The variability of the surface flows was related with atmospheric circulation categories by applying Correspondence Analysis. Similar surface thermodynamic fields develop under cyclonic categories, which are contrasted with the anti-cyclonic category. A strong, steady wind flow characterized by high shear values develops under the cyclonic Closed Low and the anticyclonic H–L categories, in contrast to the variable weak flow under the anticyclonic Open Anticyclone category.     

ATR-FTIR spectroscopic study of the adsorption of desferrioxamine B and aerobactin to the surface of lepidocrocite (γ-FeOOH)

The adsorption of two model siderophores, desferrioxamine B (DFOB) and aerobactin, to lepidocrocite (γ-FeOOH) was investigated by attenuated total reflection infrared spectroscopy (ATR-FTIR). The adsorption of DFOB was investigated between pH 4.0 and 10.6. The spectra of adsorbed DFOB indicated that two to three hydroxamic acid groups of adsorbed DFOB were deprotonated in the pH range 4.0-8.2. Deprotonation of hydroxamic acid groups of adsorbed DFOB at pH values well below the first acid dissociation constant of solution DFOB species (pK_a = 8.3) and well below the point of zero charge of lepidocrocite (pH_PZC = 7.4) suggested that the surface speciation at the lower end of this pH range (pH 4) is dominated by a surface DFOB species with inner-sphere coordination of two to three hydroxamic acids groups to the surface. Maximum adsorption of DFOB occurred at approximately pH 8.6, close to the first pK_a value of the hydroxamic acid groups, and decreased at lower and higher pH values.The spectra of adsorbed aerobactin in the pH range 3-9 indicated at least three different surface species. Due to the small spectral contributions of the hydroxamic acid groups of aerobactin, the interactions of these functional groups with the surface could not be resolved. At high pH, the spectral similarity of adsorbed aerobactin with free aerobactin deprotonated at the carboxylic acid groups indicated outer-sphere complexation of the carboxylate groups. With decreasing pH, a significant peak shift of the asymmetric carboxylate stretch vibration was observed. This finding suggested that the (lateral) carboxylic acid groups are coordinated to the surface either as inner-sphere complexes or as outer-sphere complexes that are strongly stabilized at the surface by hydrogen bonding at low pH.