Transport of dissolved organic carbon in streams of differing physiographic characteristics

Transport of dissolved organic carbon (DOC) in four river systems in different physiographic regions of the United States was related to link magnitude by a power function, log Y = ?0.84 + 1.24 log X. Multiple linear regression indicated that discharge, watershed area, and link magnitude explained almost all variation in DOC transport. For purposes of ecosystem comparison, link magnitude appeared superior to other classification systems, such as stream order.In two of the river systems, the largest fraction of DOC was transported in the spring. A third has a winter transport maximum; the last had bimodal spring and fall maxima.Streams transporting similar total amounts of DOC may vary widely in DOC concentration (mg. 1^?1). Particulate organic matter concentration was not simply related to that of DOC.Ranges and means of DOC concentration, mean DOC: POC ratios, annual load of transported DOC as well as annual watershed DOC output were tabulated for 45 streams and rivers, representing a broad range of stream systems and physiographic regions. Mean DOC concentration for these 45 waterways ranged from 0.7 to 28 mg. 1^?1. The very low DOC values are found in undisturbed streams; many of the higher values are associated with larger streams influenced by human activities. Most DOC outputs fell within the range 0.21–5.42 metric tons. km^?2.yr^?1; mean DOC:POC ranged between 0.09 and 70.A comparison was made among several biomes of the ratio of experted DOC to watershed gross and net primary production. DOC, while playing a major role in aquatic ecosystem organic budgets, appears to be of little significance in the nutrient balance of watersheds.     

Self-reversal explanation for the Laschamp/Olby geomagnetic field excursion

The reversed natural remanent magnetisation (NRM) of the volcanic features at Laschamp and Olby (Chaîne des Puys, Auvergne, France) is commonly believed to document the youngest excursion of the geomagnetic field during the present Brunhes epoch. Recent radiometric dating determines the age of these lavas to be 35000–45000 y. Continuous thermal demagnetisation indicates that under laboratory conditions the NRM of many Olby samples undergoes complete or partial self-reversal; to a lesser extent this is also true for the Laschamp material. Thus self-reversal may be another possible explanation of the reversed NRM directions. Magnetic, optical and microprobe analyses suggest that the self-reversal mechanism is based upon magnetostatic interaction between differently oxidised titanomagnetite phases.     

Biogeochemistry and bacteriology of ferrous iron oxidation in geothermal habitats

A survey of hot, acid springs in Yellowstone Park has shown that high concentrations of ferrous and ferric iron are often present. Total ionic iron concentrations in different springs ranged from less than 1 ppm to greater than 200 ppm, and up to 50% of the ionic iron was in the ferrous form. Some of these springs also have high concentrations of reduced sulfur species (S^2? and S⁰). Significant populations of the bacterium Sulfolobus, acidocaldarius, an autotrophic organism able to live and oxidize sulfur compounds at low pH and high temperature, were present in most of these springs. The role of this organism in the oxidation of ferrous iron was investigated by incubating natural samples of water and assaying for disappearance of ferrous iron. Controls in which bacterial activity was inhibited by addition of 10% NaCl were also run. Bacterial oxidation of ferrous iron occurred in most but not all of the spring waters. The temperature optimum for oxidation varied from spring to spring, but significant oxidation occurred at temperatures of 80–85°C, but not at 90°C. Thus, 85–90°C is the upper temperature at which bacterial iron oxidation occurs; a similar upper limit has previously been reported for sulfur oxidation in the same kinds of springs. The steady-state concentrations of ferrous and ferric iron are determined by the rate at which these ions move into the spring pools with the ground water (flow rate), by the rate at which ferric iron is reduced to the ferrous state by sulfide, and by the rate of bacterial oxidation. The bacterial oxidation rate is faster than the flow rate, so that the rate of reduction of ferric iron is probably the rate-controlling reaction. In several springs, no decrease in ferrous iron occurred, even though high bacterial populations were present. It was shown that in these springs, ferrous iron oxidation occurred but the ferric iron formed was reduced back to the ferrous state again. These springs were all high in suspended sediment and the reductant was shown to be present in the sediment. X-ray diffraction revealed that the sediment contained three major ingredients, elemental sulfur, natroalunite, and quartz. Chemical analyses showed a small amount of sulfide, too little to reduce the ferric iron. Elemental sulfur itself did not reduce ferric iron but when elemental sulfur was removed from the sediment by CS₂ extraction, the activity of the sediment was abolished. It is hypothesized that the sulfide present in the sediment (possibly bound to natroalunite) reacts with elemental sulfur to form a reductant for ferric iron. The results show that bacteria can have a profound influence on the ferrous/ferric ratios of geothermal systems, but that temperature and mineral composition of the water may significantly influence the overall result.     

The Blosseville Coast basalts of East Greenland: Their occurrence,composition and temporal variations

In the system CaO-MgO-A1₂O₃-SiO₂ the tie lines connecting anorthite with other phases are sequentially broken down with increasing pressure according to the following univariant reactions: anorthite+ enstatite_ss+sillimanite pyrope-grossular_ss+quartz (3), anorthite+enstatite_ss pyrope-grossular_ss+diopside_ss+quartz (2), anorthite+pyrope-grossular_ss+ quartz diopside_ss+kyanite (4) and anorthite+diopside_ss grossular-pyrope_ss +kyanite+quartz (8). At 1,200 ° C these reactions occur at 14.5± 0.5, 15.5±0.5, 19.5±0.5 and 26.4±1 kilobar and have positive slopes (dP/dT) of 1±0.5, 2.8±0.5, 13.3±0.5 and 24±2bars/°C respectively. An invariant point involving kyanite rather than sillimanite, occurs at 850 °C±25 °C and 14.5±0.5kbar at the intersection of reactions (3), (2) and (4). Reaction(4) exhibits significant curvature with an increase in dP/dT from 13.3±0.5 to 18.5± 0.5 bars/°C between 1,050° and 850° C. The pressure at which the complete grossular-pyrope join is stable with quartz is estimated at 41 ± 1 kbar at 1,200 ° C. The pressure at which garnet appears according to reaction (2) is lowered by 5 kbar for a composition with anorthite and orthopyroxene (En_0.5Fs_0.5). Enstatite and plagioclase (An_0.5Ab_0.5) first produce garnet at 2 kbar higher pressure than enstatite and pure anorthite (reaction (2)). The calcium content of garnet in various divariant assemblages is relatively insensitive to temperature but very sensitive to pressure, it is therefore a useful geobarometer. At metamorphic temperatures of 700–850 °C pressures of 8–10 kbar are required for the formation of quartz-bearing garnet granulites containing calcic plagioclase and with (Mg/Mg+Fe) bulk = 0.5.     

The solar hafnium abundance

The solar Hf abundance is determined using nine Hf ii lines in the photospheric spectrum. The transition probabilities were obtained from lifetime measurements performed by the beam-foil technique. The abundance derived from synthetic spectrum calculations is A(Hf) = 0.88 ± 0.08 in the logarithmic A(H) = 12.00 scale.     

Fluorophores in the Arabian Sea and their relationship to hydrographic conditions

 Water mass distributions, upwelling and filament formation are of complex significance for biological and chemical processes. Temperature and salinity are routinely used to characterize these hydrographic conditions. In situ profiles and sample analyses from the cruise So119 of RV Sonne in May 1997 into the Arabian Sea indicate that optical parameters such as the fluorescence of phytoplankton pigments, gelbstoff and proteins reflect hydrographic processes as well, and are useful to describe and explain biochemical processes. The dependence of bio-optical parameters to DOC and chlorophyll a concentrations is examined. While the relation between extracted chlorophyll and chlorophyll fluorescence is quite reasonable, DOC and gelbstoff fluorescence do not show a functional dependency. This is mainly due to sunlight-induced degradation of fluorophores in the surface layer. Enhanced gelbstoff signals in intermediate and deep waters are related to Persian Gulf Water. The optical data reveal a relation between the depth of the chlorophyll maximum, the depth of 1% surface light and the geographical latitude. In the context of remote sensing of phytoplankton biomass from ocean colour images, the depth of the chlorophyll maximum is a crucial parameter. Thus, the revealed dependency on latitude is useful for the evaluation of primary production with satellite remote sensing. Received: 22 May 2002 / Accepted: 18 February 2003 Responsible Editor: Andreas Oschlies Acknowledgements. This work was supported by a grant from the Federal Minister of Education and Technology, Bonn, within the framework of the JGOFS Arabian Sea program. We are grateful to the captain and the crew of RV Sonne for their support. Special thanks are given to the chief scientist of the cruise, Pr. V. Ittekkot, for helpful discussions. We are indebted to Mr. Rüdiger Heuermann and Mr. Nils Bürckel for their participation in the cruise and their support in the data analysis.     

Multiple-mineral inclusions in diamonds from the Snap Lake/King Lake kimberlite dike, Slave craton, Canada: a trace-element perspective

Multiple inclusions of minerals in diamonds from the Snap Lake/King Lake kimberlites of the southeastern Slave craton in Canada have been analyzed for trace elements to elucidate the petrogenetic history of these inclusions, and of their host diamonds. As observed worldwide, the harzburgitic-garnet diamond inclusions (DIs) possess sinusoidal REE patterns that indicate an early depletion event, followed by metasomatism by LREE-enriched, HREE-depleted fluids. Furthermore, these fluids appear to contain appreciable concentrations of LILE and HFSE, based on the increasing abundances of these elements in the olivine inclusion that occurs at the outer portion of a diamond compared to that near the core. The compositions of these fluids are probably a mixture of hydrous-silicic melt, carbonatitic melt, and brine, similar to the compositions of micro-inclusions in diamonds reported by Navon et al. (2003). Comparison between the compositions of majoritic and normal harzburgitic garnets shows that the former are more depleted in terms of major/minor elements (higher Cr#) but significantly more enriched in the REE (up to 10×). This characteristic may indicate the higher susceptibility for metasomatic enrichment of previously more depleted garnets. Garnets of eclogitic paragenesis show strong LREE-depleted patterns, whereas the coexisting omphacite inclusion has relatively flat light- and middle-REE but depleted HREE. Whole-rock reconstruction from coexisting garnet and omphacite inclusions indicates that the protolith of these inclusions was probably the extrusive section of an oceanic crust, subducted beneath the Slave craton.     

Nature of diamonds in Yakutian eclogites: views from eclogite tomography and mineral inclusions in diamonds

We have performed dissections of two diamondiferous eclogites (UX-1 and U33/1) from the Udachnaya kimberlite, Yakutia in order to understand the nature of diamond formation and the relationship between the diamonds, their mineral inclusions, and host eclogite minerals. Diamonds were carefully recovered from each xenolith, based upon high-resolution X-ray tomography images and three-dimensional models. The nature and physical properties of minerals, in direct contact with diamonds, were investigated at the time of diamond extraction. Polished sections of the eclogites were made, containing the mould areas of the diamonds, to further investigate the chemical compositions of the host minerals and the phases that were in contact with diamonds. Major- and minor-element compositions of silicate and sulfide mineral inclusions in diamonds show variations among each other, and from those in the host eclogites. Oxygen isotope compositions of one garnet and five clinopyroxene inclusions in diamonds from another Udachnaya eclogite (U51) span the entire range recorded for eclogite xenoliths from Udachnaya. In addition, the reported compositions of almost all clinopyroxene inclusions in U51 diamonds exhibit positive Eu anomaly. This feature, together with the oxygen isotopic characteristics, is consistent with the well-established hypothesis of subduction origin for Udachnaya eclogite xenoliths. It is intuitive to expect that all eclogite xenoliths in a particular kimberlite should have common heritage, at least with respect to their included diamonds. However, the variation in the composition of multiple inclusions within diamonds, and among diamonds, from the same eclogite indicates the involvement of complex processes in diamond genesis, at least in the eclogite xenoliths from Yakutia that we have studied.     

Sensitivity analysis of seismic hazard for the northwestern portion of the state of Gujarat, India

We test the sensitivity of seismic hazard to three fault source models for the northwestern portion of Gujarat, India. The models incorporate different characteristic earthquake magnitudes on three faults with individual recurrence intervals of either 800 or 1600 years. These recurrence intervals imply that large earthquakes occur on one of these faults every 266–533 years, similar to the rate of historic large earthquakes in this region during the past two centuries and for earthquakes in intraplate environments like the New Madrid region in the central United States. If one assumes a recurrence interval of 800 years for large earthquakes on each of three local faults, the peak ground accelerations (PGA; horizontal) and 1-Hz spectral acceleration ground motions (5% damping) are greater than 1 g over a broad region for a 2% probability of exceedance in 50 years' hazard level. These probabilistic PGAs at this hazard level are similar to median deterministic ground motions. The PGAs for 10% in 50 years' hazard level are considerably lower, generally ranging between 0.2 g and 0.7 g across northwestern Gujarat. Ground motions calculated from our models that consider fault interevent times of 800 years are considerably higher than other published models even though they imply similar recurrence intervals. These higher ground motions are mainly caused by the application of intraplate attenuation relations, which account for less severe attenuation of seismic waves when compared to the crustal interplate relations used in these previous studies. For sites in Bhuj and Ahmedabad, magnitude (M) 7 3/4 earthquakes contribute most to the PGA and the 0.2- and 1-s spectral acceleration ground motion maps at the two considered hazard levels.