Cosmic ray exposure and pre‐atmospheric size of the Gebel Kamil iron meteorite

Cosmogenic He, Ne, and Ar as well as the radionuclides ¹⁰Be, ²⁶Al, ³⁶Cl, ⁴¹Ca, ⁵³Mn, and ⁶⁰Fe have been determined on samples from the Gebel Kamil ungrouped Ni‐rich iron meteorite by noble gas mass spectrometry and accelerator mass spectrometry (AMS), respectively. The meteorite is associated with the Kamil crater in southern Egypt, which is about 45 m in diameter. Samples originate from an individual large fragment (“Individual”) as well as from shrapnel. Concentrations of all cosmogenic nuclides—stable and radioactive—are lower by a factor 3–4 in the shrapnel samples than in the Individual. Assuming negligible ³⁶Cl decay during terrestrial residence (indicated by the young crater age <5000 years; Folco et al. 2011 ), data are consistent with a simple exposure history and a ³⁶Cl‐³⁶Ar cosmic ray exposure age (CRE) of approximately (366 ± 18) Ma (systematic errors not included). Both noble gases and radionuclides point to a pre‐atmospheric radius >85 cm, i.e., a pre‐atmospheric mass >20 tons, with a preferred radius of 115–120 cm (50–60 tons). The analyzed samples came from a depth of approximately 20 cm (Individual) and approximately 50–80 cm (shrapnel). The size of the Gebel Kamil meteoroid determined in this work is close to estimates based on impact cratering models combined with expectations for ablation during passage through the atmosphere (Folco et al. 2010 , 2011 ).     

Solar activity and the variations of the geomagnetic Kp-index

A careful correlation analysis is made between various types of solar activity as observed at photospheric levels and the daily variations of the geomagnetic K_p-index which, in turn, is a measure of the solar wind speed. We find that in no case does a significant enough correlation exist to pin-point a physical relation between some aspect of photospheric activity and the solar wind speed. It is concluded that the physical processes that do determine the wind speed occur at coronal heights.     

Strukturuntersuchung an einer basaltischen Hornblende von Černošin, ČSR

Inhalt Die basaltische Hornblende von ernoin, SR, wird optisch, chemisch und röntgenographisch untersucht.Die Besetzung einzelner Positionen mehrerer Hornblenden wird durch Auszählen der Elektronen aus den Fourierprojektionen kontrolliert.Mit einer Textabbildung     

Impacts of recent climate change on wheat production systems in Western Australia

The wheatbelt of Western Australia shows a distinct Mediterranean climate with most of the rainfall occurring in the winter months. The main factor limiting plant production in this region is rainfall. Due to clearing of native vegetation, dryland salinity is a major problem in south-west Australia. Since the mid 1970s the region has experienced a significant decrease in winter rainfall. Across nine sites, growing season rainfall (May to October) decreased by an average of 11% and the sum of rainfall in June and July (June + July) decreased by 20%. We used the ASPIM-Nwheat model in combination with historic climate data to study the impact of recent climate change on the hydrology and production of wheat based farming systems by comparing results for before and after 1975. Despite the large decline in rainfall, simulated yields based on the actual weather data did not fall. At the same time, simulated drainage decreased by up to 95% which will significantly reduce the spread of dryland salinity. These results were due to the rainfall changes mainly occurring in June and July, a period when rainfall often exceeds crop demand and large amounts of water are usually lost by deep drainage. The findings will have significant implications for estimates of future climate change impacts in this region with changes in rainfall causing non-proportional impacts on production and hydrological aspects, such as deep drainage and waterlogging, where proportionality is often presumed.     

Rapid and cyclic aeolian deposition during the Last Glacial in European loess: a high-resolution record from Nussloch, Germany

This paper reports the results of an investigation of the Weichselian Upper Pleniglacial loess sequences of Nussloch (Rhine Valley, Germany) based on stratigraphy, palaeopedology, sedimentology, palynology, malacology and geochemistry (δ¹³C), supported by radiocarbon, TL and OSL dating. Grain-size and magnetic susceptibility records are taken at 5 cm intervals from the Upper Pleniglacial (UPG) loess. The data indicate cyclic variations in loess deposition between ca 34 and 17 ka, when the sedimentation rate is especially high (1.0–1.2 m per ka for more than 10 m). The grain-size index (GSI: ratio of coarse silt versus fine silt and clay) shows variations, which are assumed to be an indirect measurement of wind intensity. The sedimentation rate, interpreted from the profiles, indicates high values in loess (Loess events LE-1 to LE-7) and low or negligible values in tundra gley horizons G1 to G8. OSL ages from the loess and ¹⁴C dates from organic matter in the loess show that loess deposition was rapid but was interrupted by shorter periods of reduced aeolian sedimentation. Comparison between the data from Nussloch and other European sequences demonstrates a progressive coarsening of the loess deposits between ca 30 and 22 ka. This coarsening trend ends with a short but major grain-size decrease and is followed by an increase to a new maximum at 20 ± 2 ka (“W” shape). Correlation between the loess GSI and the Greenland ice-core dust records, suggests a global connection between North Atlantic and Western European global atmospheric circulation and wind regimes. In addition, the typical Upper Pleniglacial loess deposition begins at ca 30–31 ka, close to Heinrich event (HE) 3, and the main period of loess sedimentation at about 25 ± 2 ka is coeval to HE 2. Correlation of magnetic susceptibility and grain-size records shows that the periods, characterised by high GSI, coincide with an increase in the amount of ferromagnetic minerals reworked from the Rhine alluvial plain. They suggest enhancement in the frequency of the storms from N–NW. These results are integrated within a palaeogeographical model of dust transport and deposition in Western Europe for the Weichselian Upper Pleniglacial (or Late Pleniglacial).     

Die Untersuchungsergebnisse an Gesteinsdeformationen (Petrotektonik)

Ohne Zusammenfassung     

Geologische Untersuchungen in der Gegend von Bobbio im Nordapennin.

Ohne Zusammenfassung     

Evaluation of spatial and temporal characteristics of GNSS-derived ZTD estimates in Nigeria

Theoretical and Applied Climatology - This study presents an in-depth analysis to comprehend the spatial and temporal variability of zenith tropospheric delay (ZTD) over Nigeria during the period...     

3‐D hydrodynamic simulations of the solar chromosphere

We present first results of three‐dimensional numerical simulations of the non‐magnetic solar chromosphere, computed with the radiation hydrodynamics code CO⁵BOLD. Acoustic waves which are excited at the top of the convection zone propagate upwards into the chromosphere where the waves steepen into shocks. The interaction of the waves leads to the formation of complex structures which evolve on short time scales. Consequently, the model chromosphere is highly dynamical, inhomogeneous, and thermally bifurcated.     

How Different Analysis and Interpolation Methods Affect the Accuracy of Ice Surface Elevation Changes Inferred from Satellite Altimetry

Satellite altimetry has been widely used to determine surface elevation changes in polar ice sheets. The original height measurements are irregularly distributed in space and time. Gridded surface elevation changes are commonly derived by repeat altimetry analysis (RAA) and subsequent spatial interpolation of height change estimates. This article assesses how methodological choices related to those two steps affect the accuracy of surface elevation changes, and how well this accuracy is represented by formal uncertainties. In a simulation environment resembling CryoSat-2 measurements acquired over a region in northeast Greenland between December 2010 and January 2014, different local topography modeling approaches and different cell sizes for RAA, and four interpolation approaches are tested. Among the simulated cases, the choice of either favorable or unfavorable RAA affects the accuracy of results by about a factor of 6, and the different accuracy levels are propagated into the results of interpolation. For RAA, correcting local topography by an external digital elevation model (DEM) is best, if a very precise DEM is available, which is not always the case. Yet the best DEM-independent local topography correction (nine-parameter model within a 3,000 m diameter cell) is comparable to the use of a perfect DEM, which exactly represents the ice sheet topography, on the same cell size. Interpolation by heterogeneous measurement-error-filtered kriging is significantly more accurate (on the order of 50% error reduction) than interpolation methods, which do not account for heterogeneous errors.