Sulfur isotope fractionation during bacterial sulfate reduction in organic-rich sediments

Isotope fractionation during sulfate reduction by natural populations of sulfate-reducing bacteria was investigated in the cyanobacterial microbial mats of Solar Lake, Sinai and the sediments of Logten Lagoon sulfuretum, Denmark. Fractionation was measured at different sediment depths, sulfate concentrations, and incubation temperatures. Rates of sulfate reduction varied between 0.1 and 37 micromoles cm-3 d-1, with the highest rates among the highest ever reported from natural sediments. The depletion of 34S during dissimilatory sulfate reduction ranged from 16% to 42%, with the largest 34S-depletions associated with the lowest rates of sulfate reduction and the lowest 34S-depletions with the highest rates. However, at high sulfate reduction rates (>10 micromoles cm-3 d-1) the lowest fractionation was 20% independent of the rates. Overall, there was a similarity between the fractionation obtained by the natural populations of sulfate reducers and previous measurements from pure cultures. This was somewhat surprising given the extremely high rates of sulfate reduction in the experiments. Our results are explained if we conclude that the fractionation was mainly controlled by the specific rate of sulfate reduction (mass cell-1 time-1) and not by the absolute rate (mass volume-1 time-1). Sedimentary sulfides (mainly FeS2) were on average 40% depleted in 34S compared to seawater sulfate. This amount of depletion was more than could be explained by the isotopic fractionations that we measured during bacterial sulfate reduction. Therefore, additional processes contributing to the fractionation of sulfur isotopes in the sediments are indicated. From both Solar Lake and Logten Lagoon we were able to enrich cultures of elemental sulfur-disproportionating bacteria. We suggest that isotope fractionation accompanying elemental sulfur disproportionation contributes to the 34S depletion of sedimentary sulfides at our study sites.     

The Ms = 6.2, June 15, 1995 Aigion earthquake (Greece): evidence for low angle normal faulting in the Corinth rift

We present the results of a multidisciplinary study of the M_s = 6.2, 1995, June 15, Aigion earthquake (Gulf of Corinth, Greece). In order to constrain the rupture geometry, we used all available data from seismology (local, regional and teleseismic records of the mainshock and of aftershocks), geodesy (GPS and SAR interferometry), and tectonics. Part of these data were obtained during a postseismic field study consisting of the surveying of 24 GPS points, the temporary installation of 20 digital seismometers, and a detailed field investigation for surface fault break. The Aigion fault was the only fault onland which showed detectable breaks (< 4 cm). We relocated the mainshock hypocenter at 10 km in depth, 38 ° 21.7 N, 22 ° 12.0 E, about 15 km NNE to the damaged city of Aigion. The modeling of teleseismic P and SH waves provides a seismic moment M_o = 3.4 10¹⁸ N.m, a well constrained focal mechanism (strike 277 °, dip 33 °, rake – 77°), at a centroidal depth of 7.2 km, consistent with the NEIC and the revised Harvard determinations. It thus involved almost pure normal faulting in agreement with the tectonics of the Gulf. The horizontal GPS displacements corrected for the opening of the gulf (1.5 cm/year) show a well-resolved 7 cm northward motion above the hypocenter, which eliminates the possibility of a steep, south-dipping fault plane. Fitting the S-wave polarization at SERG, 10 km from the epicenter, with a 33° northward dipping plane implies a hypocentral depth greater than 10 km. The north dipping fault plane provides a poor fit to the GPS data at the southern points when a homogeneous elastic half-space is considered: the best fit geodetic model is obtained for a fault shallower by 2 km, assuming the same dip. We show with a two-dimensional model that this depth difference is probably due to the distorting effect of the shallow, low-rigidity sediments of the gulf and of its edges. The best-fit fault model, with dimensions 9 km E–W and 15 km along dip, and a 0.87 m uniform slip, fits InSAR data covering the time of the earthquake. The fault is located about 10 km east-northeast to the Aigion fault, whose surface breaks thus appears as secondary features. The rupture lasted 4 to 5 s, propagating southward and upward on a fault probably outcropping offshore, near the southern edge of the gulf. In the shallowest 4 km, the slip – if any – has not exceeded about 30 cm. This geometry implies a large directivity effect in Aigion, in agreement with the accelerogram aig which shows a short duration (2 s) and a large amplitude (0.5 g) of the direct S acceleration. This unusual low-angle normal faulting may have been favoured by a low-friction, high pore pressure fault zone, or by a rotation of the stress directions due to the possible dip towards the south of the brittle-ductile transition zone. This fault cannot be responsible for the long term topography of the rift, which is controlled by larger normal faults with larger dip angles, implying either a seldom, or a more recently started activity of such low angle faults in the central part of the rift.     

A fast response,open path,infrared hygrometer,using a semiconductor source

Investigations were carried out as to the feasibility of using a semiconductor source in the design of a new rapid response, open-path hygrometer. A single-beam instrument was constructed employing an infrared light emitting diode (LED) as a source instead of the usual high energy, wideband filament. The spectral emission envelope encompassed the 1.87 m water absorption band. Electronic modulation and thermoelectrical cooling of the diode eliminated the conventional chopper wheel and stabilized the peak wavelength emission. Path length was 200 mm. Over a water vapour concentration range of 0–16 g m^–3, absorption varied by 2% in a linear fashion. At 10 Hz, the noise level was 0.1 g m^–3 rms. Hygrometer resolution and stability are constrained by the detector noise level, the small source emission in the absorption band and low frequency drift in the optical filter. Despite these problems, the new instrument showed comparable performance characteristics to a commercial Lyman- hygrometer. Latent heat fluxes measured with both instruments and a Kaijo-Denki, 3-D sonic anemometer agreed to within 4% over a range 0–350 W m^–2. Further improvements in performance can be anticipated with advances in detector and LED technology.     

A multifractal analysis of lidar measured water vapour

Accurate and fast-response measurements of space-time observations of specific humidity were made above a drying land surface at the University of California at Davis, using the Los Alamos water Raman-lidar. In an attempt to quantify the space-time intermittency features of turbulent flows in the lower atmosphere, a multifractal analysis of these water vapour measurements was performed. The structure of the specific humidity, (x, t), was analyzed quantifying a scalar gradient measure both in time and space, for all possible one-dimensional cuts, i.e. and . The results confirm the multifractal nature of this scalar gradient measure (a type of scalar dissipation rate) and show that humidity measurements at fixed times (x) are more intermittent (e.g. have less entropy dimension) than those at fixed locations in space (t). Similar multifractal behaviour of the spatial data, with and without a transformation from the observed wind velocities, supports the validity of Taylor's hypothesis for the studied fields.     

Optical anisotropy of zoned magnetites due to form birefringence

Summary Five polished samples of zoned magnetites from skarn deposits showed optical anisotropy effects under the ore microscope, though X-ray powder diffraction investigations indicated cubic magnetite. Using high magnification ore microscopy (oil immersion lenses, monochromatic light), extremely fine zones with slightly different reflectivity were observed. Scanning electron microscopy (SEM) of etched samples confirmed zones with a thickness between a few m and 100 nm. EDX analyses showed differences in the composition of these zones, ranging from almost pure magnetite to contents of CaO, MgO, A1₂O₃, SiO₂ up to 4 wt.% in total. Thus, the extremely thin, parallel zones of magnetite, with slightly different compositions and different optical constants (reflectivity, absorption, refraction), obviously lead to optical anisotropy due to form birefringence.

---

Optische anisotropie zonarer Magnetite aufgrund von formdoppelbrechung

Zusammenfassung Fünf Anschliffe von zonar gebauten Magnetiten aus Skarn-Lagerstätten zeigten unter dem Erzmikroskop optische Anisotropie-Erscheinungen, obwohl Röntgen-Pulverauf-nahmen kubischen Magnetit ergaben. Mittels hochauflösender Erzmikroskopie (Öl-Immersion, monochromatisches Licht) wurden extrem feine Zonierungen mit etwas unterschiedlichem Reflexionsvermögen beobachtet. Rasterelektronenmikroskopie (SEM) von angeätzten Proben bestätigte eine Zonendicke zwischen einigen Yin und 100 nm. EDX Analysen zeigten Unterschiede in der Zusammensetzung dieser Zonen, die von fast reinem Magnetit bis zu CaO-, MgO-, A1₂O_3-, SiO₂-Gehalten von insgesamt 4 Gew.% reichen. Offensichtlich fiihren die extrem diinnen, parallelen Zonierungen mit unterschiedlicher Zusammensetzung, und folglich unterschiedlichen optischen Konstanten (Reflexion, Absorption, Lichtbrechung) zu optischer Anisotropie durch Formdoppelbrechung.

     

Chemical composition of hard- and softrock groundwaters from central Norway with special consideration of fluoride and Norwegian drinking water limits

Groundwaters from crystalline and metamorphic rocks (hardrocks) and from Quaternary deposits, i.e., alluvial and glacial deposits (softrocks) from the counties of Nord-Trøndelag and Sør-Trøndelag were analyzed for major and minor elements and ions including fluoride. The median concentration of F^– in water from the hardrock aquifers is 0.28 mg/l (14.7 eq/l) in contrast to water from softrock aquifers in which it is found to be 0.05 mg/1 (2.6 eq/l). More importantly, ca. 15% of the locations where water was abstracted from hardrock wells contain 1.5 mg/l (78.9 eq/l) F^– or more. Thus, 15% of all hardrock wells returned F^– results that are at or above the maximum recommended value for drinking water. Of the softrock wells, none are above 1 mg/l. Geologists would normally expect higher F^–contents in groundwaters derived from acid rocks, e.g., in granitic or gneissic areas. When comparing the host lithology with the observed F^–contents, however, no clear relationship between F^– content and lithology is visible. The highest observed F^– values actually occur in gneissic host rocks. However, wells drilled in amphibolites/greenstones, mica schists, calcareous rocks, and sedimentary rocks all returned some analytical results above 1.5 mg/l F^–. These results suggest that all hardrock wells drilled should be tested for F^– and the users informed about the results and advised to take any necessary precautions. When applying the recently proposed Norwegian drinking water limits to our data, 51% of all softrock well waters and 56% of all hardrock well waters are unfit for consumption without prior treatment, although we analyzed only for about half of the proposed elements/parameters. This result seriously questions the concept of fixed action levels—many of them with totally unproven health implications—for so many parameters/elements for hardrock groundwaters.     

The role of women in environmental management: an overview of the rural Cameroonian situation

Rural Cameroonian women interact with the environment through their numerous daily chores, and so produce in each Cameroonian ecological zone specific problems which with time can no longer be managed. In cutting down and burning the vegetation so as to create farms, in fetching water, fuel wood and so on in order to satisfy the needs of each household, the Cameroonian rural woman is pushed into a situation where she devastates and accelerates environmental degradation.In any ecological, climatic, ethnic or cultural zone, in which she finds herself, she sets in motion the continuous natural resource consumption process. Unfortunately, she has no firm authority over the land, credit and decision-making where she can come in, interact and check some of these negative consequences. The men have also been identified as accomplices in this environmental degradation process since they push the women into taking much from the environment so as to satisfy men and general domestic needs.Since the rural Cameroonian women constitute a potential partner (56,6%) of the rural production force, this paper highlights the problems created in each zone with the view of awakening public opinion, and creating an awareness of the magnitude in each zone. Some proposals, through the discussion methodology are envisaged. This, through compensatory measures, exchanges in take and give, and in farm community actions to uphold any positive checks. When all these are properly focused and the women's right to land, credit, training and decision-making recognised, they can be brought to the forefront as partners in the better management of the environment.     

Estimation for partially observed Markov processes

Many stochastic process models for environmental data sets assume a process of relatively simple structure which is in some sense partially observed. That is, there is an underlying process (X_n, n 0) or (X_t, t 0) for which the parameters are of interest and physically meaningful, and an observable process (Y_n, n 0) or (Y_t, t 0) which depends on the X process but not otherwise on those parameters. Examples are wide ranging: the Y process may be the X process with missing observations; the Y process may be the X process observed with a noise component; the X process might constitute a random environment for the Y process, as with hidden Markov models; the Y process might be a lower dimensional function or reduction of the X process. In principle, maximum likelihood estimation for the X process parameters can be carried out by some form of the EM algorithm applied to the Y process data. In the paper we review some current methods for exact and approximate maximum likelihood estimation. We illustrate some of the issues by considering how to estimate the parameters of a stochastic Nash cascade model for runoff. In the case of k reservoirs, the outputs of these reservoirs form a k dimensional vector Markov process, of which only the kth coordinate process is observed, usually at a discrete sample of time points.     

Geochemical Evidence for Subduction Fluxes, Mantle Melting and Fractional Crystallization Beneath the South Sandwich Island Arc

The volcanoes of the South Sandwich island arc follow threedistinct series: low-K tholeiitic (followed by Zavodovski, Candlemas,Vindication, Montagu and Bristol), tholeiitic (followed by Visokoi,Saunders and Bellinghausen) and calcalkaline (followed by Leskov,Freehand and part of Cook and Thule). Flux calculations indicatethat the percentage contribution of the subduction componentto the mantle source of all three series varies from undetectable(e.g. Zr) through small (e.g. Nd=20%) and moderate (e.g. La,Ce, Sr=50–80%) to dominant (e.g. Pb, K, Ba, Rb, Cs >90%)with little change along the arc. Isotope systematics (Pb, Nd,Sr) show that this subduction component obtains a greater contributionfrom altered oceanic crust than from pelagic sediment. Elementsfor which the subduction contribution is small show that themantle is already depleted relative to N-MORB mantle (equivalentto loss of an 2•5% melt fraction) before melting beneaththe arc. After addition of the subduction component, dynamicmelting of this depleted mantle then causes the variations inK that distinguish the three series. The estimated degree ofpartial melting (20%) is slightly greater than that beneathocean ridges, though geothermometry suggests that the primarymagma temperature (1225C) is similar to that of primary MORB.About half of the melting may be attributed to volatile addition,and half to decompression. Dynamic melting involving three-dimensional,two-phase flow may be needed to explain fully the inter-islandvariations. KEY WORDS: geochemistry; petrology; fluxes; melting; subduction ^*Corresponding author