The Eldgjá eruption: timing,long-range impacts and influence on the Christianisation of Iceland

The Eldgjá lava flood is considered Iceland’s largest volcanic eruption of the Common Era. While it is well established that it occurred after the Settlement of Iceland (circa 874 CE), the date of this great event has remained uncertain. This has hampered investigation of the eruption’s impacts, if any, on climate and society. Here, we use high-temporal resolution glaciochemical records from Greenland to show that the eruption began in spring 939 CE and continued, at least episodically, until at least autumn 940 CE. Contemporary chronicles identify the spread of a remarkable haze in 939 CE, and tree ring-based reconstructions reveal pronounced northern hemisphere summer cooling in 940 CE, consistent with the eruption’s high yield of sulphur to the atmosphere. Consecutive severe winters and privations may also be associated with climatic effects of the volcanic aerosol veil. Iceland’s formal conversion to Christianity dates to 999/1000 CE, within two generations or so of the Eldgjá eruption. The end of the pagan pantheon is foretold in Iceland’s renowned medieval poem, V?luspá (‘the prophecy of the seeress’). Several lines of the poem describe dramatic eruptive activity and attendant meteorological effects in an allusion to the fiery terminus of the pagan gods. We suggest that they draw on first-hand experiences of the Eldgjá eruption and that this retrospection of harrowing volcanic events in the poem was intentional, with the purpose of stimulating Iceland’s Christianisation over the latter half of the tenth century.     

Bonding of methyl mercury to reduced sulfur groups in soil and stream organic matter as determined by x-ray absorption spectroscopy and binding affinity studies

We combined synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy and binding affinity studies to determine the coordination, geometry, and strength of methyl mercury, CH₃Hg (II), bonding in soil and stream organic matter. Samples of organic soil (OS), potentially soluble organic substances (PSOS) from the soil, and organic substances from a stream (SOS) draining the soil were taken along a short “hydrological transect.” We determined the sum of concentrations of highly reduced organic S groups (designated Org-S_RED), such as thiol (RSH), disulfane (RSSH), sulfide (RSR), and disulfide (RSSR), using sulfur K-edge XANES. Org-S_RED varied between 27% and 64% of total S in our samples. Hg L_III-edge EXAFS analysis were determined on samples added CH₃Hg (II) to yield CH₃Hg (II)/Org-S_RED ratios in the range 0.01-1.62. At low ratios, Hg was associated to one C atom (the methyl group) at an average distance of 2.03 ± 0.02 Å and to one S atom at an average distance of 2.34 ± 0.03 Å, in the first coordination shell. At calculated CH₃Hg(II)/Org-S_RED ratios above 0.37 in OS, 0.32 in PSOS, and 0.24 in SOS, the organic S sites were saturated by CH₃Hg⁺, and O (and/or N) atoms were found in the first coordination shell of Hg at an average distance of 2.09 ± 0.01 Å. Based on the assumption that RSH (and possibly RSSH) groups take part in the complexation of CH₃Hg⁺, whereas RSSR and RSR groups do not, approximately 17% of total organic S consisted of RSH (+ RSSH) functionalities in the organic soil. Corresponding figures for samples PSOS and SOS were 14% and 9%, respectively. Competitive complexation of CH₃Hg⁺ by halide ions was used to determine the average binding strength of native concentrations of CH₃Hg (II) in the OS sample. Using data for Org-S_RED, calculated surface complexation constants were in the range from 10^16.3 to 10^16.7 for a model RSH site having an acidity constant of mercaptoacetic acid. These values compare favorably with identically defined stability constants (log K₁) for the binding of methyl mercury to thiol groups in well-defined organic compounds.     

Climate Variability-Observations, Reconstructions, and Model Simulations for the Atlantic-European and Alpine Region from 1500-2100 AD

A detailed analysis is undertaken of the Atlantic-European climate using data from 500-year-long proxy-based climate reconstructions, a long climate simulation with perpetual 1990 forcing, as well as two global and one regional climate change scenarios. The observed and simulated interannual variability and teleconnectivity are compared and interpreted in order to improve the understanding of natural climate variability on interannual to decadal time scales for the late Holocene. The focus is set on the Atlantic-European and Alpine regions during the winter and summer seasons, using temperature, precipitation, and 500 hPa geopotential height fields. The climate reconstruction shows pronounced interdecadal variations that appear to “lock” the atmospheric circulation in quasi-steady long-term patterns over multi-decadal periods controlling at least part of the temperature and precipitation variability. Different circulation patterns are persistent over several decades for the period 1500 to 1900. The 500-year-long simulation with perpetual 1990 forcing shows some substantial differences, with a more unsteady teleconnectivity behaviour. Two global scenario simulations indicate a transition towards more stable teleconnectivity for the next 100 years. Time series of reconstructed and simulated temperature and precipitation over the Alpine region show comparatively small changes in interannual variability within the time frame considered, with the exception of the summer season, where a substantial increase in interannual variability is simulated by regional climate models.     

Coral bleaching and habitat effects on colonisation of reef fish assemblages: An experimental study

Degradation and mortality of corals is increasing worldwide and is expected to have significant effects on coral reef fish; hence studies on these effects are essential. In the present study, a field experiment was set up within Mafia Island Marine Park in Tanzania (East Africa) to examine the effects of bleaching and habitat structure on colonisation of coral reef fish assemblages. Live and bleached staghorn coral Acropora formosa was transplanted onto plots in a site dominated by sand and rubble, and the experimental design comprised of three treatments: live coral, bleached coral and eroded coral rubble. There was an immediate increase (within 24 h) in fish abundance and diversity in the two treatments with standing corals. Overall, live and bleached coral plots showed similar effects, but differed from the eroded coral plots which had a much lower abundance and diversity of fish. In general, fish species diversity changed with time over the study period while fish abundance did not. Multivariate analyses showed that while there were differences in fish assemblage structure between standing corals and the eroded coral treatment, there was neither a difference between live and bleached coral treatments nor any temporal effects on fish assemblage structure. Our findings suggest that physical structure and complexity of habitat have stronger effects on colonisation of reef fish assemblages than changes in coral health (such as bleaching) which do not affect coral structure. This may have important implications for appropriate coral reef management.     

Reworked Middle Jurassic sandstones as a marker for Upper Cretaceous basin inversion in Central Europe—a case study for the U–Pb detrital zircon record of the Upper Cretaceous Schmilka section and their implication for the sedimentary cover of the Lausitz Block (Saxony,Germany)

International Journal of Earth Sciences - The Saxonian–Bohemian Cretaceous Basin (Elbsandsteingebirge, E Germany and Czech Republic, Elbtal Group) comprises Upper Cretaceous sedimentary rocks...     

Storm surges in the Western Baltic Sea: the present and a possible future

Globally-coupled climate models are generally capable of reproducing the observed trends in the globally averaged atmospheric temperature or mean sea level. However, the global models do not perform as well on regional/local scales. Here, we present results from four 100-year ocean model experiments for the Western Baltic Sea. In order to simulate storm surges in this region, we have used the General Estuarine Transport Model (GETM) as a high-resolution local model (spatial resolution ≈ 1?km), nested into a regional atmospheric and regional oceanic model in a fully baroclinic downscaling approach. The downscaling is based on the global model ECHAM5/MPI-OM. The projections are imbedded into two greenhouse-gas emission scenarios, A1B and B1, for the period 2000–2100, each with two realisations. Two control runs from 1960 to 2000 are used for validation. We use this modelling system to statistically reproduce the present distribution of surge extremes. The usage of the high-resolution local model leads to an improvement in surge heights of at least 10% compared to the driving model. To quantify uncertainties associated with climate projections, we investigate the impact of enhanced wind velocities and changes in mean sea levels. The analysis revealed a linear dependence of surge height and mean sea level, although the slope parameter is spatially varying. Furthermore, the modelling system is used to project possible changes within the next century. The results show that the sea level rise has greater potential to increase surge levels than does increased wind speed. The simulations further indicate that the changes in storm surge height in the scenarios can be consistently explained by the increase in mean sea level and variation in wind speed.     

Influence of the boundary layer height on the global air–sea surface fluxes

Results from large-eddy simulations and field measurements have previously shown that the velocity field is influenced by the boundary layer height, z _i , during close to neutral, slightly unstable, atmospheric stratification. During such conditions the non-dimensional wind profile, φ _m , has been found to be a function of both z/L and z _i /L. At constant z/L, φ _m decreases with decreasing boundary layer height. Since φ _m is directly related to the parameterizations of the air–sea surface fluxes, these results will have an influence when calculating the surface fluxes in weather and climate models. The global impact of this was estimated using re-analysis data from 1979 to 2001 and bulk parameterizations. The results show that the sum of the global latent and sensible mean heat fluxes increase by 0.77 W m⁻² or about 1% and the mean surface stress increase by 1.4 mN m⁻² or 1.8% when including the effects of the boundary layer height in the parameterizations. However, some regions show a larger response. The greatest impact is found over the tropical oceans between 30°S and 30°N. In this region the boundary layer height influences the non-dimensional wind profile during extended periods of time. In the mid Indian Ocean this results in an increase of the mean annual heat fluxes by 2.0 W m⁻² and an increase of the mean annual surface stress by 2.6 mN m⁻².     

Turbulence characteristics in a near neutrally stratified urban atmosphere

Turbulence measurements from the city of Uppsala, Sweden, are analysed. Measurements were taken at two sites: one in the central area, ca. 6 m above roof level, the average building height being ca. 15 m; the other at ca. 8 and 50 m above the ground on a tower situated 100 m downwind of a sharp discontinuity between the densely built-up urban area and flat grass-covered land. The average stability was close to neutral, the range being -0.2 < z/L < 0.2. The main emphasis of the study is on the non-dimensional standard deviations of the velocity components _i /u _*t and on the corresponding non-dimensional energy spectra, u _*t being a local velocity scale defined as _i /( _l is the local momentum flux). Comparison with results obtained from surface-layer measurements at ideal sites (with u _*, being the ordinary friction velocity) shows good general agreement. The most complete agreement is found for the tower 50 m measurements, a result which is notable as this measurement point is found to be within a distinctly transitional zone between the urban and post-urban boundary layers. The results from the central city measurement point are also fairly close to the ideal results, the deviations found being small in view of the fact that the site is probably inside the layer in which the roughness elements (the buildings) have direct influence. The measurements at the tower 8 m level show certain distinct deviations from ideal results: all three _i /u _*l , are higher by ca. 10%, the excessive energy being found at the low frequency end of the spectrum. Arguments are presented for this feature to be due to a spectral lag effect.     

Multiple sources for mineralizing fluids in the Charmitan gold(-tungsten) mineralization (Uzbekistan)

Mineral assemblages present within the Charmitan gold(-tungsten) quartz-vein mineralization have been investigated for their cathodoluminescence behaviour, chemical composition and noble gas isotope systematics. This inventory of methods allows for the first time a systematic reconstruction of the paragenetic relationships of quartz, scheelite, sulphides and native gold within the gold mineralization at Charmitan and provides the basis to utilise noble gas data in the discussion of sources and evolution of ore-forming fluids. The vein quartz is classified into four generations based on microscopic and cathodoluminescence investigations. Quartz I shows intense brittle deformation as associated scheelite I. Undeformed scheelite II overgrows scheelite I and has lower light rare earth element and higher intermediate rare earth element contents as well as higher strontium concentrations. Scheelite II is associated with the economic gold mineralization and formed during re-crystallisation and re-precipitation of material which was partly re-mobilised from early scheelite I during infiltration of gold-bearing fluids. Early stage native gold inclusions are often associated with stage 2 sulphides, scheelite II and bismuth tellurides and contain Ag (3.6–24.4 wt.%), Hg (≤1.0 wt.%) and Bi (≤0.2 wt.%). Later stage electrum grains occur in association with stage 3 sulphides and sulphosalts and contain Hg (<0.8 wt.%) and elevated Sb concentrations (up to 3.0 wt.%). Noble gas isotope data (³He/⁴He: 0.2-0.4 Ra) for hydrothermal ore fluids trapped in the gold-related sulphides and sulphosalts (stage 2 pyrite and arsenopyrite; stage 3 pyrite, sphalerite, galena and lead sulphosalts) suggest that diverse fluid sources were involved in the formation of the Charmitan gold deposit. These data are indicative of a small, but significant input of fluids from external, deep-seated (mantle and possibly lower crust) sources. A decrease in the input of mantle helium and an increasing role of crustal helium from early to later stages of the mineralization is suggested by the measured ³He/⁴He and ⁴⁰Ar*/⁴He ratios. Sulphides from ore veins in meta-sedimentary rocks contain higher portions of meteoric fluids than those in intrusive rock types as indicated by their lower ³He/³⁶Ar ratios. The ³He/³⁶Ar ratios in the meta-sedimentary rocks agree well with ratios typical of gold mineralizations in the Tien Shan gold province completely hosted by meta-sedimentary sequences, indicating intense fluid-wall rock interaction.