Spatial Patterns and Structure of the Mountain Birch Tree-Limit in the Southern Swedish Scandes – A Regional Perspective

Altitudinal tree- and forest-limits of mountain birch ( Betula pubescens Ehrh. ssp. tortuosa (Ledeb.) Nyman) were measured (m a.s.l.) on 229 sites forming a regional network of sites intended for long-term monitoring. Regional and local topographical variables used for correlations with the recorded elevations included slope aspect, inclination, morphology, snow depth and shortest distance to the sea. No relationship between past human utilization of natural resources and the vertical extension (width) and position of the tree-limit ecotone was found and thus the ecotone is regarded as natural. It is concluded that tree- and forest-limit altitudes are regionally controlled by macroclimate, and correlate negatively with the degree of maritimity. On a more local scale, snow conditions, and microtopography, are important for tree- and forest-limit altitudinal position. The ecotone is wider in snow accumulation areas than in deflation areas, and tree- and forest-limit altitudes are generally higher on slopes with a varied micro-topography than on flat slopes. Slope aspect and inclination are also important, and the highest tree- and forest-limit altitudes are generally found on steep, SE-W-facing slopes. Tree height at the tree-limit is independent of the analysed topographical parameters and fairly constant at 2.7 m, suggesting a strong common environmental control. Many of the results presented in this paper are confirmations of the results of earlier, small-scale investigations or of surveys lacking statistically treated data.     

Palaeoclimatic studies in South Shetland Islands,Antarctica, based on numerous stratigraphic variables in lake sediments

The hitherto longest found lake sediment sequence on Byers Peninsula, Livingston Island, South Shetland Islands, was analysed with respect to lithology, chronology, diatoms, Pediastrum, pollen and spores, mosses, mineralogy, and sediment chemistry. During the ca. 5000 year long development the sediments were influenced by frequent tephra fall-outs. This volcanic impact played a major role in the lake's history during two periods, 4700–4600 and 2800–2500 BP, but was of importance during the lake's entire history with considerable influence on many of the palaeoenvironmentally significant indicators. The large and complex data set was analysed and zonated with different types of multivariate analysis. This resulted in a subdivision of the sequence into 8 time periods and 21 variables. Redundancy analysis (RDA) of this data set, both without and with the tephra periods, and with 4–6 of the variables as explanatory environmental variables, reveal that climatic/environmental signals are detectable. The palaeoclimatic picture that emerged out of the tephra noise suggests that the first 100 years were characterized by mild, humid conditions. This was followed by a less mild and humid climate until ca. 4000 BP when a gradual warming seems to have started, coupled with increased humidity. These mild and humid conditions seem to have reached an optimum slightly after 3000 BP. At ca. 2500 BP a distinct climatic deterioration occurred with colder and drier conditions and long seasons with ice cover. This arid, cold phase probably reached its optimum conditions at ca. 1500 BP, when slightly warmer conditions might have prevailed for a while. Except for the modern sample with rather mild climate, the last 1400 years seem to have been fairly arid and cold, and the effects of the frequent volcanic activity during this period is only vaguely seen in the records.     

A comparison of chironomid biostratigraphy from Lake Vuolep Njakajaure with vegetation, lake-level, and climate changes in Abisko National Park, Sweden

Chironomid remains from the sediment of Lake Vuolep Njakajaure reflect limnological conditions resulting from changing climate and vegetation throughout the Holocene, but do not strictly follow accepted climate trends or the vegetation history based on regional pollen and macrofossil analyses. Chironomid community changes appear to be influenced by organic nutrient input from the surrounding catchment vegetation and lake hydrology, both of which are indirectly responding to some combination of climate change, hypolimnetic oxygen concentration, and changes in basin morphology. The chironomid-based quantitative mean July air-temperature reconstruction differs from other regional quantitative records; this discrepancy is likely related to limnological conditions particular to Lake Vuolep Njakajaure. Comparison of a northern Swedish temperature transfer function and one from western Canada reveals differences in the mean July air-temperature optima of several common taxa, suggesting that the existing conservative estimates of Holocene climate change in northern Sweden may be underestimated due to the limited temperature gradient captured by the Swedish training set.     

Uncertainty in drought monitoring by the Standardized Precipitation Index: the case study of the Abruzzo region (central Italy)

As shown by several authors, drought monitoring by the Standardized Precipitation Index (SPI) presents some uncertainties, mainly dependent on the choice of the probability distribution used to describe the cumulative precipitation and on the characteristics (e.g., length and variability) of the dataset. In this paper, the uncertainty related to SPI estimates has been quantified and analyzed with regards to the case study of the Abruzzo region (Central Italy), by using monthly precipitation recorded at 75 stations during the period 1951–2009. First, a set of distributions suitable to describe the cumulative precipitation at the 3-, 6-, and 12-month time scales was identified by using L-moments ratio diagrams. The goodness-of-fit was evaluated by applying the Kolmogorov–Smirnov test, and the Normality test on the derived SPI series. Then the confidence intervals of SPI have been calculated by applying a bootstrap procedure. The size of the confidence intervals has been considered as a measure of uncertainty, and its dependence on several factors such as the distribution type, the time scale, the record length, and the season has been examined. Results show that the distributions Pearson type III (PE3), Weibull (WEI), Generalized Normal (GNO), Generalized Extreme Value (GEV), and Gamma (GA2) are all suitable to describe the cumulative precipitation, with a slightly better performance of the PE3 and GNO distributions. As expected, the uncertainty increases as the record length and time scale decrease. The leading source of uncertainty is the record length while the effects due to seasonality and time scale are negligible. Two-parameter distributions make it possible to obtain confidence intervals of SPI (particularly for extreme values) narrower than those obtained by three-parameter distributions. Nevertheless, due to a poorer goodness of fit, two-parameter distributions can provide less reliable estimates of the precipitation probability. In any event, independently of the type of distribution, the SPI estimates corresponding to extreme precipitation values are always characterized by a relevant uncertainty. This is due to the explosion of the probability variability that occurs when precipitation values approach the tails of the supposed distribution.     

Analysis of drought in the region of Abruzzo (Central Italy) by the Standardized Precipitation Index

The paper presents a comprehensive analysis of drought phenomena in the Region of Abruzzo (Central Italy) using the Standardized Precipitation Index (SPI) computed at different time scales (3, 6, 12, 24 months). The study is based on monthly precipitation data collected from 1951 to 2009 at 69 climatic stations uniformly distributed over the region. According to the trend analysis, most stations are characterized by increments in both drought severity and variability, particularly at the longer time scales. A principal component analysis applied to SPI time series enabled to identify two main patterns: the first more correlated to the coastal areas, the second more correlated to the inland, mountainous areas. However, the spatial patterns become less defined as the time scale increases, making more uncertain the definition of homogenous areas to be used in drought management plans. In most cases, the identified drought patterns have similar negative overall tendencies, but different trend directions in some sub-periods. In particular, the first drought pattern is clearly characterized by a trend reversal (from decreasing to increasing) during the last decade. This temporal evolution, consistent with that observed by large-scale analyses in the corresponding (or near) grid points, was not detected for the second pattern, which is probably influenced by local topographic and/or orographic factors. The results confirm the complexity of drought phenomenon in a typical Mediterranean region and the necessity of high-resolution datasets to capture its temporal and spatial variability.     

Sediment contamination in floodplains and alluvial terraces as an historical record of gold exploitation in the Carmo River basin,Southeast Quadrilátero Ferrífero,Minas Gerais,Brazil

This paper describes the geochemistry of sediment samples placed in floodplains and alluvial terraces downstream from gold mines in the Carmo River basin, Quadrilátero Ferrífero, Minas Gerais, Brazil. The geochemistry signature Na₂O, K₂O, SiO₂, CaO, MgO, Al₂O₃, Fe₂O₃, TiO₂, P₂O₅, Mn, As, Cu, Zn, Ba, Ni, Cr, S, Co were analyzed in different facies from stratigraphic profiles. As, Cu, Zn, and Mn anomalies are mainly associated with the clayed facies deposited in floodplains and oxbow lakes, and with coarse‐sediment facies deposited in the channel. The facies were accumulated by the gold exploitation activity in the region. The contamination of As, Cu, and Zn was controlled by minerals such as iron oxides and hydroxides (hematite, magnetite, and mainly goethite), manganese oxides, and sulfide‐rich minerals. The As‐bearing sediments of the region characterize one of the most As contaminated area of Brazil. Their main source is associated with gold exploration in the last three centuries.     

A lunar cryptomare dome near Mee H and Drebbel F

In this study, we examine the lunar mare dome Mee 1 situated near the craters Mee H and Drebbel F in a region showing evidence of ancient (pre-Orientale) mare volcanism and cryptomare deposits. Regional stratigraphic relations indicate that Mee 1 was formed prior to the Orientale impact at the beginning of the Imbrian period. Based on a combined photoclinometry and shape from shading technique applied to telescopic CCD images of the dome acquired under oblique illumination, we determined a diameter of Mee 1 of 25 km, a height of 250 m, a flank slope of 1.15^°, and a volume of . Based on rheologic modelling of the dome and a viscoelastic model of the feeder dike, we obtained a magma viscosity of , an effusion rate of , a duration of the effusion process of 1.6 years, a magma rise speed of , a width of the feeder dike of 32 m, and a horizontal dike length of 144 km. A comparison of Mee 1 with domes with similar morphometric properties, which are located near Milichius and inside the crater Petavius, reveals strong similarities with respect to the viscosity of the dome-forming magma and the feeder dike geometry, while the effusion rate and magma rise speed of Mee 1 are somewhat higher. The pronounced morphometric differences between Mee 1 and a smaller dome situated close to the crater Doppelmayer and characterised by a similar magma viscosity suggest that the growth of that dome was limited by exhaustion of the magma reservoir, while Mee 1 and the other larger domes display morphometric properties presumably coming closer to the cooling limit. The comparison of the ancient dome Mee 1 with the younger (Eratosthenian) edifices near Milichius and Doppelmayer suggests that the conditions in the upper mantle and the crust favoured high eruption volumes, effusion rates, and magma rise speeds, implying the occurrence of large magma reservoirs preventing the limitation of dome growth by magma exhaustion. On the other hand, we observe similar general morphometric, rheologic, and feeder dike characteristics and, thus, conclude that the formation conditions of lunar mare domes did not change fundamentally during the Imbrian period.