Dendrochronology for the last 1400 years in eastern Tibet

Twentyfour tree-ring chronologies of various tree-species(Picea, Abies, Larix, Juniperus) from sites near the upper timberline in eastern Tibet were established, the longest one dating back to 620 A.D. A new classification of pointer intervals is presented, distinguishing between different kinds of signatures in a tree-ring series and amount of growth change in relation to the previous year. The various types of signatures can be related to meteorological events like cold winters and summers, summer drought or to recreation reactions after years of reduced growth. The distribution pattern and type of pointer intervals combined with ring width variation enables the detection of periods of favourable or unfavourable growth conditions with regard to climate history. Based on far-distance correlations and signature analysis regions of similar tree-growth are mapped out.     

Urbanization and vulnerable urban groups in Gaborone/Botswana

This article examines two factors which are of major importance for urban poverty groups in Botswana: the costs the urban poor have to pay for housing, and the role assets like cattle and land play as safety elements in the urban livelihood system.     

Changing predictability of Indian monsoon rainfall anomalies?

The predictability of Indian summer monsoon rainfall from pre-season circulation indices is explored from observations during 1939–91. The predictand is the all-India average of June–September precipitation NIR, and the precursors examined are the latitude position of the 500 mb ridge along 75°E in April (L), the pressure tendency April minus January at Darwin (DPT), March-April-May temperature at six stations in west central India (T6), the sea surface temperature (SST) anomaly in the northeastern Arabian Sea in May (ASM), SST anomaly in the Arabian Sea in January (ANJ), northern hemisphere temperature anomaly in January–February (NHT), and Eurasian snow cover in January (SNOW). Monsoon rainfall tends to be enhanced with a more northerly ridge position, small Darwin pressure tendency, warmer pre-season conditions, and reduced winter snow cover. However, relationships have varied considerably over the past half-century, with the strongest associations during 1950–80, and a drastic weakening in the 1980s. Four prediction models were constructed based on stepwise multiple regression, using as predictors combinations of L, DPT, T6, ASM, and NHT, with 1939–68 as “dependent” dataset, or training period, and 1969–91 as “independent” dataset or verification period. For the 1969–80 portion of the verification period calculated and observed NIR values agreed closely, with the models explaining 74–79% of the variance. By contrast, after 1980 predictions deteriorated drastically, with the explained variance for the 1969–89 time span dropping to 25–31%. The monsoon rainfall of 1990 and 1991 turned out to be again highly predictable from models based on stepwise multiple regression and linear discriminant analysis and using as input L + DPT or L + DPT + NHT, and with this encouragement an experimental real-time forecast was issued of the 1992 monsoon rainfall. These results underline the need for investigations into decadal-scale changes in the general circulation setting and raise concern for the continued success of seasonal forecasting.     

Untersuchungen über die Beeinflussung der planktischen Photosynthese durch anorganische Metallsalze im eutrophen Alpnachersee und der mesotrophen Horwer Bucht

The effects on phytoplankton photosynthesis of inorganic metal salts HgCl₂, CuSO₄, Cd(NO₃)₂, ZnCl₂ and Pb(NO₃)₂ were studied over monthly intervals. In experiments with individual metals, phytoplankton photosynthesis was not adversely affected if the concentration increase above background levels did not exceed 10^?9 mole Hg/l, 5·10^?9 mole Cu/l, 2·10^?8 mole Cd/l, 5·10^?8 mole Zn/l and 2·10^?7 mole Pb/l, respectively. However when the concentration was increased by 5·10^?10 mole Hg/l+5·10^?9 mole Cu/l+5·10^?9 mole Cd/l+5·10^?8 mole Zn/l+5·10^?8 mole Pb/l photosynthesis was significantly reduced, due to a synergetic effect of the combined metals. The influence of phytoplankton density, pH-value concentration of calcium, dissolved organic nitrogen and allochthonous debris on heavy metal toxicity was investigated. Changes in phytoplankton composition are believed to the main reason for the seasonal variation in the toxic effects of heavy metals.     

A room-temperature phase transition in maximum microcline. Absorption in the far infrared (10–200 cm−1) in the temperature range 110–300 K

The far infrared powder absorption spectra (10–200 cm^?1) for a maximum microcline sample (obtained by ion-exchange from Amelia albite) and for a natural maximum microcline were measured at steps of 10 K on lowering and raising the temperature between 300 and 110 K. Of the absorption bands at 97.5, 113.5, 137.5, 148, and 157 cm^?1 occurring at room temperature, those at 157 and eventually 148 cm^?1 showed evidence of a phase transition and only that at 157 cm^?1 showed hysteresis. The transition occurs at 245±5 K on lowering the temperature and the low-temperature form can be superheated to 300 K in the case of the ion-exchange sample. Oriented thin sections parallel to (001) and (010) were also measured to 110 K as a function of the direction of the electric vector E, but could not be unambiguously interpreted. Though the effect is very slight it is tentatively proposed that the phase transition (already characterized by calorimetry and lattice parameters) involves changes in K-O and T-O-T bonds.     

26Al and rare gases in Allende,Bereba and Juvinas: implications for production rates

The ²⁶Al, light rare gas and major and minor element contents of Al-rich and poor samples separated from Allende. Bereba and Junivas have been measured. The production rate of ²¹Ne from Al (²¹P_Al) is $\text{(1.9 ± 0.6) ×}{}^{21}\text{P}{}_{\mathrm{Si}}$ and ${}^{\mathrm{<mtext>22</mtext><mtext>21</mtext>}}\text{P}{}_{\mathrm{Al}}\text{= 1.4 ± 0.4.}$ The ³He, ²¹Ne and ³⁸Ar exposure ages of the eucritic pyroxenes agree suggesting complete cosmogenic gas retention. The eucritic feldspars have lost virtually all ³He and most radiogenic ⁴He. The equation ²⁶Al = 0.42 ± 0.41 Mg + 2.74 ± 0.21 Si + 4.92 ± 0.51 Al + 1.33 S + 0.24 Ca + 0.03 Fe reproduces within 15% our ²⁶Al measurements and the average values measured in ordinary chondrites without recourse to unusual cosmic-ray effects.     

Two modified smoky quartz centers in natural citrine

Electron paramagnetic resonance (EPR) measurements on natural citrine and greenish-yellow quartz revealed the presence of several localized hole centers adjacent to an aluminium impurity. The g tensors and their principal axes directions were determined for the two most prominent centers. The g-tensor variations and ²⁷Al hyperfine splittings are roughly half as large as for the well-known smoky quartz centers. Optical and infrared absorption, thermal stability and thermoluminescence were also studied. In these citrine centers an additional defect must be present in the immediate neighborhood of the hole, but the exact nature of this defect is still unknown.     

An improved oxygen method for measuring primary production in lakes

The accuracy of the Winkler technique for measuring dissolved oxygen was increased to 0.002–0.005 mg O₂/l with a photometric endpoint detection method. This precision is valuable for accurate measurements of primary production only if an oxygen release on illuminating dark adapted samples and the instability of the oxygen concentration of undersaturated water are taken into account. This work was supported by the ‘Swiss National Science Foundation’.     

On the standardization of measurements of the anisotropy of magnetic susceptibility

The magnetic anisotropy of several artificially constructed samples has been measured with different types of instruments in several laboratories. Susceptibility bridge determinations have given consistent results, but the magnitude of the anisotropy determined by the Digico anisotropy delineator is incorrect. For future measurements with this instrument it is necessary to make either a simple calibration change or to make a minor change in the associated computer program. A set of equations for correcting the old published data is given.