Sulphur source and genesis of polymetallic sulphide occurrences of the Ofoten district in the Central–North Norwegian Caledonides: evidence from sulphur isotopic studies

Fourteen stratiform, stratabound and vein-type sulphide occurrences in the Upper Allochthon of the Central–North Norwegian Caledonides have been studied for their sulphur, oxygen and hydrogen isotope composition. Depositional ages of host rocks to the stratabound and stratiform sulphide occurrences range from 590 to 640?Ma. The sulphides and their host rocks have been affected by polyphase deformation and metamorphism with a peak temperature of 650?°C dated to 432?Ma. A total of 104 sulphide and 2 barite samples were analysed for δ³⁴S, 16 whole-rock and quartz samples for δ¹⁸O and 12 samples of muscovite for δD. The overall δ³⁴S values range from ?14 to +31‰ with the majority of sampled sulphides lying within a range of +4 to +15‰. In most cases δ³⁴S within each hand specimen behaves in accordance with the equilibrium fractionation sequence, δ³⁴S_gn<δ³⁴S_cp<δ³⁴S_sph<δ³⁴S_py. A systematic increase in δ³⁴S from the vein sulphides (?8‰) through schist/amphibolite-hosted (+6‰) and schist-hosted (+7 to +12‰) to dolomite-hosted (+12 to +31‰) occurrences is documented. The δ³⁴S averages of the stratiform schist-hosted sulphides are 17 to 22‰ lower than in the penecontemporaneous seawater sulphate. The Bjørkåsen (+4 to +6‰) occurrence is a volcanogenic massive sulphide (VMS) transitional to sedimentary massive sulphide (SMS), exhalative, massive, pyritic deposit of Cu–Zn–Pb sulphides formed by fluids which obtained H₂S via high-temperature reduction of seawater sulphate by oxidation of Fe²⁺ during the convective circulation of seawater through underlying rock sequences. The Raudvatn, volcanic-hosted, disseminated Cu sulphides (+6 to +8‰) obtained sulphur via a similar process. The Balsnes, stratiform, ‘black schist’-hosted, pyrite–pyrrhotite occurrence (?6 to ?14‰) is represented by typical diagenetic sulphides precipitated via bacteriogenic reduction of coeval (ca. 600?Ma) seawater sulphate (+25 to +35‰) in a system open to sulphate supply. The δ³⁴S values of the Djupvik–Skårnesdalen (+7 to +12‰), Hammerfjell (+5 to 11‰), Kaldådalen (+10 to +12‰) and Njallavarre (+7 to +8‰) stratiform, schist-hosted, massive and disseminated Zn–Pb (±Cu) sulphide occurrences, as well as the stratabound, quartzite-hosted, Au-bearing arsenopyrite occurrence at Langvatnet (+7 to +11‰), suggest that thermochemically reduced connate seawater sulphate was a principal sulphur source. The Sinklien and Tårstad, stratabound, dolomite- and dolomite collapse breccia-hosted, Zn (±Cu–Pb) sulphides are marked by the highest enrichment in ³⁴S (+20 to +31‰). The occurrences ?are?assigned to the Mississippi-Valley-type deposits.?High δ³⁴S values require reduction/replacement of contemporaneous (ca. 590?Ma) evaporitic sulphate (+23 to +34‰) with C_org-rich fluids in a closed system. The Melkedalen (+12 to +15‰), stratabound, fault-controlled, Cu–Zn sulphide deposit is hosted by the ca. 595?Ma dolomitised Melkedalen marble. The deposit is composed of several generations of ore minerals which formed by replacement of host dolomite. Polyphase hydrothermal fluids were introduced during several reactivation episodes of the fault zone. The positive δ³⁴S values with a very limited fractionation (<3‰) are indicative of the sulphide-sulphur generated through abiological, thermochemical reduction of seawater sulphate by organic material. The vein-type Cu (±Au–W) occurrences at Baugefjell, Bugtedalen and Baugevatn (?8 to ?4‰) are of hydrothermal origin and obtained their sulphur from igneous sources with a possible incorporation of sedimentary/diagenetic sulphides. In a broad sense, all the stratiform/stratabound, sediment-hosted, sulphide occurrences studied formed by epigenetic fluids within two probable scenarios which may be applicable separately or interactively: (1) expulsion of hot metal-bearing connate waters from deeper parts of sedimentary basins prior to nappe translation (late diagenetic/catagenetic/epigenetic fluids) or (2) tectonically driven expulsion in the course of nappe translation (early metamorphic fluids). A combination of (1) and (2) is favoured for the stratabound, fault-controlled, Melkedalen and Langvatnet occurrences, whereas the rest are considered to have formed within option (1). The sulphides and their host rocks were transported from unknown distances and thrust on to the Fennoscandian Shield during the course of the Caledonian orogeny. The displaced/allochthonous nature of the Ofoten Cu–Pb–Zn ‘metallogenetic province’ would explain the enigmatically high concentration of small-scale Cu–Pb–Zn deposits that occur only in this particular area of the Norwegian Caledonides.     

Interaction between water flow and oxygen deficiency on growth in the infaunal brittle star Amphiura filiformis (Echinodermata: Ophiuroidea)

Interactions between ‘oxygen concentration’ (normoxia: >80% oxygen saturation, and hypoxia: 18% oxygen saturation) and ‘water flow velocity’ (low: 0.1 cm s⁻¹, and moderate: 0.5 cm s⁻¹) were studied on growth rates in the brittle star Amphiura filiformis in a flow-through aquaria system. Effects of ‘sublethal predation’ on growth rates were investigated as ‘number of amputated arms’ (1 and 3 arms) and ‘amputation of the disk’. A significant interaction between oxygen concentration and water flow velocity was observed in mean arm regeneration rate, but in both flow velocities higher mean arm regeneration rates were observed in normoxia compared to hypoxia. In hypoxia a positive response in arm regeneration rate was observed in moderate flow compared to low flow velocity. In normoxia, however, no response to flow velocity was observed. The latter observation indicates that Amphiura filiformis is able to maintain the ventilation of the burrow at low flow velocities, but in low oxygen concentrations hydrodynamic forces seem to affect growth. A significant interaction between oxygen concentration and disk amputation was observed in both arm and disk regeneration rates, indicating that the disk is the major organ for gas exchange in this species. The number of arms amputated, however, did not affect mean arm regeneration rate. The results obtained in this study suggest that the secondary production in subtidal infaunal populations could be negatively affected by low oxygen concentrations and that this response is even more negative in combination with low flow velocities in the near-bottom water.     

A spatial comparison of four satellite derived 1 km global land cover datasets

Global change issues are high on the current international political agenda. A variety of global protocols and conventions have been established aimed at mitigating global environmental risks. A system for monitoring, evaluation and compliance of these international agreements is needed, with each component requiring comprehensive analytical work based on consistent datasets. Consequently, scientists and policymakers have put faith in earth observation data for improved global analysis. Land cover provides in many aspects the foundation for environmental monitoring [FAO, 2002a. Proceedings of the FAO/UNEP Expert Consultation on Strategies for Global Land Cover Mapping and Monitoring. FAO, Rome, Italy, 38 pp.]. Despite the significance of land cover as an environmental variable, our knowledge of land cover and its dynamics is poor [Foody, G.M., 2002. Status of land cover classification accuracy assessment. Rem. Sens. Environ. 80, 185–201]. This study compares four satellite derived 1 km land cover datasets freely available from the internet and in wide use among the scientific community. Our analysis shows that while these datasets have in many cases reasonable agreement at a global level in terms of total area and general spatial pattern, there is limited agreement on the spatial distribution of the individual land classes. If global datasets are used at a continental or regional level, agreement in many cases decreases significantly. Reasons for these differences are many—ranging from the classes and thresholds applied, time of data collection, sensor type, classification techniques, use of in situ data, etc., and make comparison difficult. Results of studies based on global land cover datasets are likely influenced by the dataset chosen. Scientists and policymakers should be made aware of the inherent limitations in using current global land cover datasets, and would be wise to utilise multiple datasets for comparison.     

Radiative decay data for highly excited Zr i levels

Radiative lifetimes of 17 excited levels in Zr  i , in the energy interval 29 000–40 974 cm⁻¹, have been investigated using the time-resolved laser-induced fluorescence method. The levels belong to the 4d²5s5p, 4d³5p and 4d5s²5p electronic configurations and were excited in a single-step process from either the ground term, 4d²5s² a ³F, or from the low-lying 4d²5s² a ³P and a ⁵F terms. For three levels, we confirm previous measurements while for 14 of the levels the lifetimes have been measured for the first time. The experimental results are compared to theoretical calculations performed with a multiconfiguration relativistic Hartree–Fock method including core-polarization effects. Theoretical transition probabilities of astrophysical interest, scaled by the experimental lifetimes, for the depopulating channels of the investigated levels are also presented.     

Influence of IMF draping direction and crustal magnetic field location on Martian ion beams

Data from the Ion Mass Analyzer (IMA) sensor of the ASPERA-3 instrument suite onboard Mars Express and data from the Magnetometer/Electron Reflectometer (MAG/ER) on Mars Global Surveyor have been analyzed to determine whether ion beam events (IBEs) are correlated with the direction of the draped interplanetary magnetic field (IMF) or the proximity of strong crustal magnetic fields to the subsolar point. We examined 150 IBEs and found that they are organized by IMF draping direction. However, no clear dependence on the subsolar longitude of the strongest magnetic anomaly is evident, making it uncertain whether crustal magnetic fields have an effect on the formation of the beams. We also examined data from the IMA sensor of the ASPERA-4 instrument suite on Venus Express and found that IBEs are observed at Venus as well, which indicates the morphology of the Martian and Venusian magnetotails are similar.     

Multi-technique comparison of troposphere zenith delays and gradients during CONT08

CONT08 was a 15 days campaign of continuous Very Long Baseline Interferometry (VLBI) sessions during the second half of August 2008 carried out by the International VLBI Service for Geodesy and Astrometry (IVS). In this study, VLBI estimates of troposphere zenith total delays (ZTD) and gradients during CONT08 were compared with those derived from observations with the Global Positioning System (GPS), Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), and water vapor radiometers (WVR) co-located with the VLBI radio telescopes. Similar geophysical models were used for the analysis of the space geodetic data, whereas the parameterization for the least-squares adjustment of the space geodetic techniques was optimized for each technique. In addition to space geodetic techniques and WVR, ZTD and gradients from numerical weather models (NWM) were used from the European Centre for Medium-Range Weather Forecasts (ECMWF) (all sites), the Japan Meteorological Agency (JMA) and Cloud Resolving Storm Simulator (CReSS) (Tsukuba), and the High Resolution Limited Area Model (HIRLAM) (European sites). Biases, standard deviations, and correlation coefficients were computed between the troposphere estimates of the various techniques for all eleven CONT08 co-located sites. ZTD from space geodetic techniques generally agree at the sub-centimetre level during CONT08, and??as expected??the best agreement is found for intra-technique comparisons: between the Vienna VLBI Software and the combined IVS solutions as well as between the Center for Orbit Determination (CODE) solution and an IGS PPP time series; both intra-technique comparisons are with standard deviations of about 3?C6?mm. The best inter space geodetic technique agreement of ZTD during CONT08 is found between the combined IVS and the IGS solutions with a mean standard deviation of about 6?mm over all sites, whereas the agreement with numerical weather models is between 6 and 20?mm. The standard deviations are generally larger at low latitude sites because of higher humidity, and the latter is also the reason why the standard deviations are larger at northern hemisphere stations during CONT08 in comparison to CONT02 which was observed in October 2002. The assessment of the troposphere gradients from the different techniques is not as clear because of different time intervals, different estimation properties, or different observables. However, the best inter-technique agreement is found between the IVS combined gradients and the GPS solutions with standard deviations between 0.2 and 0.7?mm.     

Ellipsoidal area mean gravity anomalies — precise computation of gravity anomaly reference fields for remove-compute-restore geoid determination

Gravity anomaly reference fields, required e.g. in remove-compute-restore (RCR) geoid computation, are obtained from global geopotential models (GGM) through harmonic synthesis. Usually, the gravity anomalies are computed as point values or area mean values in spherical approximation, or point values in ellipsoidal approximation. The present study proposes a method for computation of area mean gravity anomalies in ellipsoidal approximation (‘ellipsoidal area means’) by applying a simple ellipsoidal correction to area means in spherical approximation. Ellipsoidal area means offer better consistency with GGM quasigeoid heights. The method is numerically validated with ellipsoidal area mean gravity derived from very fine grids of gravity point values in ellipsoidal approximation. Signal strengths of (i) the ellipsoidal effect (i.e., difference ellipsoidal vs. spherical approximation), (ii) the area mean effect (i.e., difference area mean vs. point gravity) and (iii) the ellipsoidal area mean effect (i.e., differences between ellipsoidal area means and point gravity in spherical approximation) are investigated in test areas in New Zealand and the Himalaya mountains. The impact of both the area mean and the ellipsoidal effect on quasigeoid heights is in the order of several centimetres. The proposed new gravity data type not only allows more accurate RCR-based geoid computation, but may also be of some value for the GGM validation using terrestrial gravity anomalies that are available as area mean values.     

Simulating the Carbon Cycling of Northern Peatlands Using a Land Surface Scheme Coupled to a Wetland Carbon Model (CLASS3W-MWM)

Northern peatlands store approximately one-third of the terrestrial soil carbon (C), although they cover only 3% of the global land mass. Northern peatlands can be subdivided into bogs and fens based on their hydrology and biogeochemistry. Peatland hydrology and biogeochemistry are tightly coupled to climate and, therefore, may be very sensitive to climate variability and change. To address the fate of the large peatland soil C storage under a future changed climate, a peatland C model, the McGill Wetland Model (MWM), was coupled to a land surface climate model (the wetland version of the Canadian Land Surface Scheme, CLASS3W), referred as CLASS3W-MWM. We evaluated the CLASS3W-MWM for a bog (Mer Bleue, located at 45.41°N, 75.48°W, in eastern Canada) and a poor fen (Degerö Stormyr, located at 64°11′N, 19°33′E, in northern Sweden).

CLASS3W-MWM captured the magnitude and direction of the present day C cycling very well for both bogs and fens. Moreover, the seasonal and interannual variability were reproduced reasonably well. Root mean square errors (RMSE) were <0.65 and the degree of agreements (d*) were >0.8 for the components of net ecosystem production (NEP) for both the Mer Bleue bog and the Degerö Stormyr fen. The performance of the coupled model for both bog and fen is similar to that of the stand-alone MWM driven by observed weather rather than simulated surface and soil climate. This modelling study suggests that northern peatlands are hydrologically and thermally conservative ecosystems. It was also shown that C cycling for bogs and fens was more sensitive to changes in air temperature than precipitation. Changes in temperature within the Intergovernmental Panel on Climate Change (IPCC) projected range switch the peatlands from a present-day C sink to a source, but projected changes in precipitation still maintain the peatlands as a C sink, although to a somewhat lesser degree. Increase in atmospheric CO₂ concentration enhances C sequestration for both bogs and fens. Our sensitivity analysis suggests that northern peatlands respond to changes in temperature, precipitation and doubled CO₂ concentration in a highly non-linear way. The sensitivity of C cycling in northern peatlands with respect to changes in air temperature, precipitation and the concentration of atmospheric CO₂ together is not a simple addition or subtraction of the sensitivity of the individual changes. Therefore, the sensitivity of a combination of changes in temperature, precipitation and doubled CO₂ concentration is very different from the sensitivity of peatlands to each environmental variable on their own. Our sensitivity analysis suggests that fens have a narrower tolerance to climate changes than bogs.

RÉSUMÉ [Traduit par la rédaction] Les tourbières du Nord renferment approximativement le tiers du carbone se trouvant dans le sol terrestre, même si elles ne couvrent que 3% des terres du globe. On peut subdiviser les tourbières du Nord en tourbières hautes et en tourbières basses selon leur hydrologie et leur biogéochimie. L'hydrologie et la biogéochimie des tourbières sont intimement liées au climat et peuvent donc être très sensibles à la variabilité et au changement climatique. Pour étudier comment évoluera le stockage du carbone dans les grands terrains tourbeux sous un climat futur modifié, nous avons couplé un modèle de carbone de tourbière, le McGill Wetland Model (MWM), à un modèle climatique de surface terrestre (la version terres humides du CLASS3W canadien), c'est-à-dire le CLASS3W–MWM. Nous avons évalué le CLASS3W–MWM pour une tourbière haute (Mer Bleue, situé à 45,41°N, 75,48°O, dans l'est du Canada) et pour une tourbière basse ombrotrophe (Degerö Stormyr, situé à 64°11′N, 19°33′E, dans le nord de la Suède).

Le CLASS3W–MWM a très bien capturé la grandeur et la direction du recyclage actuel du carbone, tant pour les tourbières hautes que pour les tourbières basses. De plus, la variabilité saisonnière et interannuelle a été raisonnablement bien reproduire. Les écarts-types étaient <0,65 et les degrés de concordance (d*) étaient >0,8 pour les composantes de la production nette de l’écosystème tant pour la tourbière haute Mer Bleue que pour la tourbière basse Degerö Stormyr. La performance du modèle couplé pour la tourbière haute et la tourbière basse est semblable à celle du MWM autonome piloté par des conditions observées plutôt que par un climat simulé de la surface et du sol. Cette étude par modèle suggère que les tourbières du Nord sont des écosystèmes hydrologiquement et thermiquement conservatifs. Il a aussi été démontré que le recyclage du carbone pour les tourbières hautes et basses était plus sensible aux changements dans la température de l'air que dans les précipitations. Des changements de température de l'ordre de ceux projetés par le Groupe d'experts intergouvernemental sur l’évolution du climat (GIEC) font que les actuels puits de carbone que constituent les tourbières se transforment en sources, mais les changements projetés dans les précipitations maintiennent encore les tourbières comme des puits de carbone, quoique dans une moindre mesure. L'accroissement de la concentration du CO₂ atmosphérique améliore la séquestration du carbone à la fois pour les tourbières hautes et les tourbières basses. Notre analyse de sensibilité suggère que les tourbières du Nord réagissent aux changements dans la température et les précipitations et à une concentration doublée de CO₂ d'une façon fort peu linéaire. La sensibilité du recyclage du carbone dans les tourbières du Nord par rapport aux changements dans la température de l'air, les précipitations et la concentration du CO₂ atmosphérique ensemble n'est pas une simple addition ou soustraction de la sensibilité aux changements individuels. Par conséquent, la sensibilité à une combinaison de changements dans la température et les précipitations et à une concentration doublée de CO₂ est très différente de la sensibilité des tourbières à chaque variable environnementale prise seule. Notre analyse de sensibilité suggère que les tourbières basses ont une plus faible tolérance aux changements climatiques que les tourbières hautes.