Forthcoming papers

Abstract

The Hai River Basin (HRB) is a heavily irrigated region encompassing the North China Plain (NCP) in northeast China. In the last decades, continuous lowering of groundwater levels had been reported in the NCP. This study used data from the Gravity Recovery and Climate Experiment (GRACE) and in situ measurements to quantify recent changes in groundwater storage from 2003 to 2012. The signal from GRACE observations highlight a sharp decline in the deep subsurface water stores (deep unsaturated zone and groundwater systems) up to a rate of 17.0 ± 4.3 mm year^-1 between 2003 and 2012 over the HRB, equal to a volumetric loss of 5.5 ± 1.4 km³ year^-1. This result shows good consistency with in situ observations of groundwater hydraulic heads compiled from monitoring bores, and emphasizes GRACE’s ability to monitor large-scale groundwater storage variations. Results from GRACE also provide an independent assessment of the effectiveness of water saving programmes that have been implemented by the government so far. Our study indicates that groundwater overdrawal is still prevalent and the dominant factor for the persistent loss in groundwater storage over the HRB/NCP; the current groundwater consumption pattern is far beyond the natural recharge ability in groundwater system.

Editor D. Koutsoyiannis; Associate editor T. Wagener     

Lack of relationship between Al ages of chondrules and their mineralogical and chemical compositions

Previous studies have suggested the existence of a correlation between ²⁶Al relative crystallisation ages and mineralogical and bulk chemical compositions of ferromagnesian chondrules from the Bishunpur and Semarkona unequilibrated ordinary (0120 and 0150). However, because the precision in ²⁶Al ages was moderate, these correlations are questionable. Here, we report mineralogical and chemical compositions of 14 ferromagnesian chondrules from Semarkona for which precise ²⁶Al ages were previously obtained (Villeneuve et al., 2009). We find global correlation of ²⁶Al ages neither with bulk chemical composition of chondrules, nor with the different types of ferromagnesian chondrules, i.e. PO, POP and PP. This indicates that if some kind of correlations between chemical compositions of chondrules and their ages of formation exists, they do not exist at timescales that can be measured with the ²⁶Al-²⁶Mg systematics but presumably at much shorter timescales.     

Accurate Measurement of Rare Earth Elements by ICP‐MS after Ion‐Exchange Separation: Application to Ultra‐Depleted Samples

This study reports precise and accurate data for rare earth elements (REE) measured on eight geological reference materials, five enriched in REE (BE‐N, BHVO‐2, BR, BR‐24 and RGM‐1) and three very depleted in REE (BIR‐1, UB‐N and DTS‐2). Data were acquired by quadrupole ICP‐MS after isolation of the REE using an ion‐exchange chromatography procedure. All the measured REE abundances were similar within ≈ 5% (10% for the most REE‐depleted sample DTS‐2) to the high‐quality measurements previously published in the literature. We also show that by using an internal Tm spike, the reproducibility of the data was improved to ～ 1%. Applying this technique to the analysis of ultra‐depleted rock samples (sub ng g^?1), we show that significant improvements were obtained relative to the routine trace element measurement method. The chondrite‐normalised patterns were smooth instead of displaying irregularities. Although the classical method gives excellent results on REE‐rich samples, we believe that our technique improves the precision and accuracy of measurements for highly REE‐depleted rocks.     

The IWAS-ToolBox: Software coupling for an integrated water resources management

Numerical modeling of interacting flow and transport processes between different hydrological compartments, such as the atmosphere/land surface/vegetation/soil/groundwater systems, is essential for understanding the comprehensive processes, especially if quantity and quality of water resources are in acute danger, like e.g. in semi-arid areas and regions with environmental contaminations. The computational models used for system and scenario analysis in the framework of an integrated water resources management are rapidly developing instruments. In particular, advances in computational mathematics have revolutionized the variety and the nature of the problems that can be addressed by environmental scientists and engineers. It is certainly true that for each hydro-compartment, there exists many excellent simulation codes, but traditionally their development has been isolated within the different disciplines. A new generation of coupled tools based on the profound scientific background is needed for integrated modeling of hydrosystems. The objective of the IWAS-ToolBox is to develop innovative methods to combine and extend existing modeling software to address coupled processes in the hydrosphere, especially for the analysis of hydrological systems in sensitive regions. This involves, e.g. the provision of models for the prediction of water availability, water quality and/or the ecological situation under changing natural and socio-economic boundary conditions such as climate change, land use or population growth in the future.     

Contribution of interstitial OH groups to the incorporation of water in forsterite

Water incorporation in forsterite samples synthesized under low to medium silica-activity conditions mostly occurs via a substitutional mechanism in which a Si vacancy is compensated by four protons. Corresponding IR absorption spectra display a cluster of narrow and weakly anharmonic OH-stretching bands at wavenumbers above 3,500 cm^?1. However, this diagnostic spectrum is often superimposed to one broader absorption band, rarely two, displaying pronounced temperature-dependent properties and tentatively assigned to H atoms in interstitial position (Ingrin et al. in Phys Chem Miner 40:499–510, 2013). Here, we investigate the structural and vibrational properties of selected interstitial H-bearing defects in forsterite using a first-principles modeling approach. We show that the broad bands discussed by Ingrin et al. (Phys Chem Miner 40:499–510, 2013) are most likely related to interstitial OH groups in the vacant octahedral sites alternating with the M2 sites along the c axis of the forsterite structure. The corresponding OH defects lead to the formation of fivefold coordinated Si species. Their peculiar thermal properties stem from the vibrational phase relaxation due to the anharmonic coupling of the high-energy local OH-stretching mode with a low-energy vibrational mode. This “exchange mode” corresponds to the hindered longitudinal translation of the OH group. These results suggest that at high pressure, hydrogen incorporation in forsterite is dominated by coexisting interstitial OH groups and (4H)_Si defects.     

Two‐layer scree/snow‐avalanche triggered by rockfall (Eastern Alps): Significance for sedimentology of scree slopes

Rockfalls that trigger scree‐laden snow avalanches are common in mountain ranges, but the resulting avalanche development and its role in understanding the sedimentology of scree slopes are rarely described in detail. On Riepenwand (2774 m above sea‐level, Kalkkögel range, Alps), on 6 May 2011 a 5800 m³ rockfall of dolostone detached from the flank of a gorge in the upper part of the mountain. After first collapsing into the gorge, the fragmented rock mass fell down freely for 150 m onto a talus covered by coarse‐granular snow. Rockfall impact triggered a medium‐scale avalanche that developed: (i) a lower layer A of entrained, pure snow; and (ii) an upper layer B of clay‐sized to boulder‐sized fragments mixed with snow. This ‘two‐layer scree/snow avalanche’ halted in the distal slope segment of the talus. Boulders within layer B mainly came to rest in the distal part of the avalanche deposit. Fragments smaller than cobble‐size grade did not show obvious downslope segregation. With snowmelt, the rockfall fragments dispersed in layer B were concentrated to a clast‐supported veneer that was draped over the older talus surface upon slower melting of avalanche layer A. In the grain‐size fraction ≤16 mm, a mean of 5 wt% matrix (silt‐sized to clay‐sized grains) of the rockfall‐derived scree of layer B is similar to a mean matrix content of 7 wt% within stratified talus slopes of the Kalkkögel range. This similarity suggests that a major share of matrix – widespread in stratified talus – stems from rockfalls. The characteristics of the scree veneer as melt‐lag of a scree‐laden snow avalanche will be blurred with time. Fossil talus successions may contain a substantial proportion of scree carried down by snow avalanches. The formation of a distinct sedimentary facies of snow avalanche‐deposited scree is impeded by processes of redeposition and deposit modification on talus.     

The Herschel PACS photometer calibration

We present a flux calibration scheme for the PACS chopped point-source photometry observing mode based on the photometry of five stellar standard sources. This mode was used for science observations only early in the mission. Later, it was only used for pointing and flux calibration measurements. Its calibration turns this type of observation into fully validated data products in the Herschel Science Archive. Systematic differences in calibration with regard to the principal photometer observation mode, the scan map, are derived and amount to 5 ? 6 %. An empirical method to calibrate out an apparent response drift during the first 300 Operational Days is presented. The relative photometric calibration accuracy (repeatability) is as good as 1 % in the blue and green band and up to 5 % in the red band. Like for the scan map mode, inconsistencies among the stellar calibration models become visible and amount to 2 % for the five standard stars used. The absolute calibration accuracy is therefore mainly limited by the model uncertainty, which is 5 % for all three bands.     

Some methodological questions concerning advection measurements: a case study

A dataset from two campaigns conducted at the Vielsalm experimental site in Belgium was used as a basis for discussing some methodological problems and providing intermediate results on estimating CO₂ advection. The analysis focused on the horizontal [CO₂] gradient and on the vertical velocity w, the variables most affected by uncertainty. The sampling error for half-hourly horizontal [CO₂] gradients was estimated to be 1.3 μmol mol⁻¹. Despite this important random error for half-hour estimations of [CO₂], the mean horizontal [CO₂] gradients in advective conditions were shown to be representative at the ecosystem scale and to extend only to the lowest part of a drainage sub-layer, which developed in the trunk space. By contrast, under daytime conditions, this gradient was shown to be more sensitive to local source heterogeneities. The estimation of the short-term averaged vertical velocity ( was the greater source of error when computing advection terms. The traditional correction methods used to obtain are discussed and a (co)sine correction is tested to highlight the instrumental origin of the offset in w. A comparison of measurements by sonic anemometers placed close together above the canopy showed that the uncertainty on was 0.042 m s⁻¹, which is of the same order of magnitude as the velocity itself. In addition, as the drainage sub-layer is limited to the lowest part of the canopy, the representativeness of is questionable. An alternative computation using the divergence of the horizontal wind speed in the trunk space produced a estimation that was four times lower than the single-point measurement. However, this value gives a more realistic estimate of the vertical advection term and improves the CO₂ budget closure at the site.     

Polyhedral modelling of underground excavations

The use of key-block theory for the analysis of blocky rock mass structures in mining and civil engineering is well established. Such methods have traditionally been used to analyse the stability of rock blocks at free surfaces only. These methods have also been limited to the analysis of relatively few discontinuities, usually assumed to be infinitely persistent.