<Superscript>10</Superscript>Be surface exposure dating of the last deglaciation in the Aare Valley,Switzerland

The combined Rhone and Aare Glaciers presumably reached their last glacial maximum (LGM) extent on the Swiss Plateau prior to 24 ka. Two well-preserved, less extensive moraine stades, the Gurten and Bern Stade, document the last deglaciation of the Aare Valley, yet age constraints are very scarce. In order to establish a more robust chronology for the glacial/deglacial history of the Aare Valley, we applied ¹⁰Be surface exposure dating on eleven boulders from the Gurten and Bern Stade. Several exposure ages are of Holocene age and likely document post-depositional processes, including boulder toppling and quarrying. The remaining exposure ages, however yield oldest ages of 20.7 ± 2.2 ka for the Gurten Stade and 19.0 ± 2.0 ka for the Bern Stade. Our results are in good agreement with published chronologies from other sites in the Alps.     

Aluminum coordination in metaaluminous and peralkaline silicate melts

Incremental amounts of Na₂O and K₂O added to immiscible melts in the MgO-CaO-TiO₂-Al₂O₃ SiO₂ system cause a decrease in critical temperature, phase separation and change in the pattern of Al₂O₃ partitioning. Al₂O₃, which is concentrated in the low SiO₂ immiscible melts in the alkali-free system, is increasingly partitioned into the high-SiO₂ immiscible melt as the alkali/aluminium ratio is increased. However, K₂O is more effective than Na₂O in stabilizing Al₂O₂ in the SiO₂-rich melt. The coordination changes occurring in the aluminosilicate melts upon the addition of the alkali oxides are described by CaAl₂O₄+2SiOK=2KAlO₂+SiOCaOSi where K (or Na) displaces Ca as the charge-balancing cation for the networkforming AlO₄ tetrahedra. The increased stability of the AlO₄ species in the highly polymerized SiO₂-rich melt and the consequent shrinkage of the miscibility gap is ascribed to positive configurational entropy and negative enthalpy changes associated with the formation of K, Na-AlO₄ species. Element partition systematics indicate that (Na, K)AlO₂ species favor the more polymerized, CaAl₂O₄ and TiO₂ species, the less polymerized silicate structure in the melt.     

Photoreactivation of Escherichia coli and Yersinia enterolytica after Irradiation with a 222 nm Excimer Lamp Compared to a 254 nm Low‐pressure Mercury Lamp

Photoreactivation of Escherichia coli ATCC 11229 and Yersinia enterolytica ATCC 4780 after irradiation with a 222 nm krypton‐chloride excimer lamp compared to a 254 nm mercury lamp was investigated under laboratory conditions. The bacteria samples were irradiated each with different doses of both wavelengths. After irradiation one sample of the bacteria was illuminated with fluorescent light, the other sample was stored in darkness to prevent photoreactivation. The inactivation curves were determined. Without photoreactivation, an irradiation of 69 J/m² at 254 nm was sufficient for a 4 log reduction for E. coli, and only 59 J/m² for Y. enterolytica. To get a 4 log reduction with following photoreactivation, 182 J/m² were necessary for E. coli and 180 J/m² for Y. enterolytica. After irradiation with the 222 nm excimer lamp the ratios were different. Without photoreactivation, an irradiation of 106 J/m² at 222 nm was sufficient for a 4 log reduction for E. coli and 88 J/m² for Y. enterolytica. With photoreactivation 161 J/m² were necessary for E. coli to get a 4 log reduction and 117 J/m² for Y. enterolytica. When the photoreactivation after irradiation is excluded, the mercury lamp with 254 nm clearly shows better results regarding inactivation. Whereas, when included, the excimer lamp with 222 nm wavelength obviously shows better results.     

Stromatolitic fabric of authigenic carbonate crusts: result of anaerobic methane oxidation at cold seeps in 4,850 m water depth

Methane seepage leads to Mg-calcite and aragonite precipitation at a depth of 4,850 m on the Aleutian accretionary margin. Stromatolitic and oncoid growth structures imply encrustation of microorganisms (microbial mats) in the host sediment with a unique growth direction downward into the sediment, forming crust-shaped lithologies. Biomarker investigations of the residue after carbonate dissolution show strong enrichments in crocetane and archaeol, which contain extremely low '¹³C values. This indicates the presence of methane-consuming archaea, and '¹³C values of -42 to -51‰ PDB indicate that methane is the carbon source for the carbonate crusts. Thus, it appears that stromatolitic encrustations of methanotrophic anaerobic archaea probably occurs in a consortium with sulphate-reducing bacteria and that carbonate precipitation proceeds downward into the sediment, where ascending cold fluids provide a methane source. Strontium and oxygen isotope analyses as well as ¹⁴C ages of the carbonates suggest that the fluids come from deep within the sediment and that carbonate precipitation began about 3,000 years ago.     

Production of lunar fragmental material by meteoroid impact

The rate of production of new fragmental lunar surface material is derived theoretically on the hypothesis that such material is excavated from a bedrock layer by meteoroid impacts. An overlaying regolith effectively shields the bedrock layer from small impacts, reducing the production rate of centimeter-sized and smaller blocks by a large factor. Logarithmic production rate curves for centimeter to meter-sized blocks are nonlinear for any regolith from centimeters to tens of meters in thickness, with small blocks relatively much less frequent for thicker (older) regoliths, suggesting the possibility of a statistical reverse bedding. Modest variations in the exponents of scaling laws for crater depth-diameter ratio and maximum block-diameter to crater diameter ratio are shown to have significant effects on the production rates. The production rate increases slowly with increasing size of the largest crater affecting the region.