Quantifying the error of 2D bulk chondrule analyses using a computer model to simulate chondrules (SIMCHON)

Bulk chondrule compositions are important to many questions in cosmochemistry, however, the number of available bulk chondrule data sets is still small. A main reason for this is the difficulties of determining bulk chondrule compositions. A commonly used technique is to obtain 2D bulk chondrule compositions from meteorite sections. This technique has an error that we quantify here for the first time using a mathematical model of a chondrule called SIMCHON. The theoretically calculated errors are compared to errors that we determined from serial sectioning of eight Efremovka chondrules. The errors obtained from both approaches are in excellent agreement, proving that our mathematical model produces reliable errors that can be assigned to 2D bulk chondrule compositions. These errors allow a much better interpretation of 2D bulk chondrule data. We provide a table that contains typical errors for 2D bulk compositions of porphyritic chondrules. The errors are in the range of ±<1–30 relative‐%. This should be acceptable for many problems in cosmochemistry. The effect of a chemical layering inside chondrules and the occurrence of a rim around them, as well as the occurrence of opaque and other accessory phases have been studied. A spreadsheet is provided that enables the calculation of errors for any desired chondrule mineral composition. BO chondrules have a negligible error, but it is impossible to provide reasonable error estimates for BO chondrules with an igneous rim. Radial pyroxene chondrules have negligible errors.     

The water content of CM carbonaceous chondrite falls and finds,and their susceptibility to terrestrial contamination

CM carbonaceous chondrites can be used to constrain the abundance and H isotopic composition of water and OH in C-complex asteroids. Previous measurements of the water/OH content of the CMs are at the higher end of the compositional range of asteroids as determined by remote sensing. One possible explanation is that the indigenous water/OH content of meteorites has been overestimated due to contamination during their time on Earth. Here we have sought to better understand the magnitude and rate of terrestrial contamination through quantifying the concentration and H isotopic composition of telluric and indigenous water in CM falls by stepwise pyrolysis. These measurements have been integrated with published pyrolysis data from CM falls and finds. Once exposed to Earth's atmosphere CM falls are contaminated rapidly, with some acquiring weight percent concentrations of water within days. The amount of water added does not progressively increase with time because CM falls have a similar range of adsorbed water contents to finds. Instead, the petrologic types of CMs strongly influence the amount of terrestrial water that they can acquire. This relationship is probably controlled by mineralogical and/or petrophysical properties of the meteorites that affect their hygroscopicity. Irrespective of the quantity of water that a sample adsorbs or its terrestrial age, there is minimal exchange of H in indigenous phyllosilicates with the terrestrial environment. The falls and finds discussed here contain 1.9–10.5 wt% indigenous water (average 7.0 wt%) that is consistent with recent measurements of C-complex asteroids including Bennu.     

Tree-ring reconstructed rainfall variability in Zimbabwe

We present the first tree-ring reconstruction of rainfall in tropical Africa using a 200-year regional chronology based on samples of Pterocarpus angolensis from Zimbabwe. The regional chronology is significantly correlated with summer rainfall (November–February) from 1901 to 1948, and the derived reconstruction explains 46% of the instrumental rainfall variance during this period. The reconstruction is well correlated with indices of the El Niño-southern oscillation (ENSO), and national maize yields. An aridity trend in instrumental rainfall beginning in about 1960 is partially reproduced in the reconstruction, and similar trends are evident in the nineteenth century. A decadal-scale drought reconstructed from 1882 to 1896 matches the most severe sustained drought during the instrumental period (1989–1995), and is confirmed in part by documentary evidence. An even more severe drought is indicated from 1859 to 1868 in both the tree-ring and documentary data, but its true magnitude is uncertain. A 6-year wet period at the turn of the nineteenth century (1897–1902) exceeds any wet episode during the instrumental era. The reconstruction exhibits spectral power at ENSO, decadal and multi-decadal frequencies. Composite analysis of global sea surface temperature during unusually wet and dry years also suggests a linkage between reconstructed rainfall and ENSO.     

Investigating the impact of initial soil moisture conditions on total infiltration by using an adapted double-ring infiltrometer

ABSTRACT

This study presents an adaptation of the double-ring infiltrometer (DRI) device, which allows several infiltration experiments to be conducted at the same location. Hence, it becomes possible to use the DRI method to investigate infiltration behaviour under different initial soil moisture conditions. The main feature is the splitting of the inner ring into two parts. While the lower part remains in the soil throughout the investigation period, the upper part is attached to the lower one just before the infiltration experiment. This method was applied to eight test sites in an Alpine catchment, covering different land-use/cover types. The results demonstrated the applicability of the adapted system and showed correlations between total water infiltration and initial soil moisture conditions on pastures, independent of the underlying soil type. In contrast, no correlation was found at forest sites or wetlands. Thus, the study emphasizes the importance of paying special attention to the impact of initial soil moisture conditions on the infiltration—and consequently the runoff behaviour—at managed areas. Given the differences in the total infiltrated water of between 30 and 1306 mm, consideration of the interplay between initial soil moisture conditions, land-use/cover type, and soil properties in rainfall–runoff models is a prerequisite to predict runoff production accurately.

EDITOR Z.W. Kundzewicz; ASSOCIATE EDITOR not assigned     

Impacts of deforestation and afforestation in the Mediterranean region as simulated by the MPI atmospheric GCM

For two reasons it is important to study the sensitivity of the global climate to changes in the vegetation cover over land. First, in the real world, changes in the vegetation cover may have regional and global implications. Second, in numerical simulations, the sensitivity of the simulated climate may depend on the specific parameterization schemes employed in the model and on the model's large-scale systematic errors. The Max-Planck-Institute's global general circulation model ECHAM4 has been used to study the sensitivity of the local and global climate during a full annual cycle to deforestation and afforestation in the Mediterranean region. The deforestation represents an extreme desertification scenario for this region. The changes in the afforestation experiment are based on the pattern of the vegetation cover 2000 years before present when the climate in the Mediterranean was more humid. The comparison of the deforestation integration to the control shows a slight cooling at the surface and reduced precipitation during the summer as a result of less evapotranspiration of plants and less evaporation from the assumption of eroded soils. There is no significant signal during the winter season due to the stronger influence of the mid-latitude baroclinic disturbances. In general, the results of the afforestation experiment are opposite to those of the deforestation case. A significant response was found in the vicinity of grid points where the land surface characteristics were modified. The response in the Sahara in the afforestation experiment is in agreement with the results from other general circulation model studies.     

Die grünen Werfener Schichten von Mitterberg (Salzburg)

Zusammenfassung Auf Grund ihrer stratigraphischen Stellung und petrographischen Übereinstimmung werden die grünen Quarzite als Werfener Schichten erkannt. Teile davon stellen vollkommen ausgelaugtes Haselgebirge vor. Die regional-tektonische Bedeutung dieser Gesteine wird dadurch gegeben, daß sie auch innerhalb der Grauwackenzone auftreten.Mit 1 Textabbildung.     

Analysing the interaction between emission trading and renewable electricity support in TIMES

As the number of instruments applied in the area of energy and climate policy is rising, the issue of policy interaction needs to be explored further. This article analyses the interdependencies between the EU Emissions Trading Scheme (EU ETS) and the German feed-in tariffs (FITs) for renewable electricity in a quantitative manner using a bottom-up energy system model. Flexible modelling approaches are presented for both instruments, with which all impacts on the energy system can be evaluated endogenously. It is shown that national climate policy measures can have an effect on the supranational emissions trading system by increasing emission reduction in the German electricity sector by up to 79 MtCO₂ in 2030. As a result, emission certificate prices decline by between 1.9 €/tCO₂ and 6.1 €/tCO₂ and the burden sharing between participating countries changes, but no additional emission reduction is achieved at the European level. This also implies, however, that the cost efficiency of such a cap-and-trade system is distorted, with additional costs of the FIT system of up to €320 billion compared with lower costs for ETS emission certificates of between €44 billion and €57 billion (cumulated over the period 2013–2020).

Policy relevance

In order to fulfil ambitious emission reduction targets a large variety of climate policy instruments are being implemented in Europe. While some, like the EU ETS, directly address CO₂ emissions, others aim to promote specific low-carbon technologies. The quantitative analysis of the interactions between the EU ETS and the German FIT scheme for renewable sources in electricity generation presented in this article helps to understand the importance of such interaction effects. Even though justifications can be found for the implementation of both types of instrument, the impact of the widespread use of support mechanisms for renewable electricity in Europe needs to be taken into account when fixing the reduction targets for the EU ETS in order to ensure a credible long-term investment signal.     

Die 2. Konferenz der Baltischen Ozeanographen

Ohne Zusammenfassung