Flood seasonality across Scandinavia—Evidence of a shifting hydrograph?

Fluvial flood events have substantial impacts on humans, both socially and economically, as well as on ecosystems (e.g., hydroecology and pollutant transport). Concurrent with climate change, the seasonality of flooding in cold environments is expected to shift from a snowmelt‐dominated to a rainfall‐dominated flow regime. This would have profound impacts on water management strategies, that is, flood risk mitigation, drinking water supply, and hydro power. In addition, cold climate hydrological systems exhibit complex interactions with catchment properties and large‐scale climate fluctuations making the manifestation of changes difficult to detect and predict. Understanding a possible change in flood seasonality and defining related key drivers therefore is essential to mitigate risk and to keep management strategies viable under a changing climate. This study explores changes in flood seasonality across near‐natural catchments in Scandinavia using circular statistics and trend tests. Results indicate strong seasonality in flooding for snowmelt‐dominated catchments with a single peak occurring in spring and early summer (March through June), whereas flood peaks are more equally distributed throughout the year for catchments located close to the Atlantic coast and in the south of the study area. Flood seasonality has changed over the past century seen as decreasing trends in summer maximum daily flows and increasing winter and spring maximum daily flows with 5–35% of the catchments showing significant changes at the 5% significance level. Seasonal mean daily flows corroborate those findings with higher percentages (5–60%) of the catchments showing statistically significant changes. Alterations in annual flood occurrence also point towards a shift in flow regime from snowmelt‐dominated to rainfall‐dominated with consistent changes towards earlier timing of the flood peak (significant for 25% of the catchments). Regionally consistent patterns suggest a first‐order climate control as well as a local second‐order catchment control, which causes inter‐seasonal variability in the streamflow response.     

Short-term environmental variability in cold-water coral habitat at Viosca Knoll,Gulf of Mexico

The Lophelia pertusa community at Viosca Knoll (VK826) is the most extensive found to date in the Gulf of Mexico. As part of a multi-disciplinary study, the physical setting of this area was described using benthic landers, CTD transects and remotely operated vehicle observations. The site was broadly characterised into three main habitats: (1) dense coral cover that resembles biogenic reef complexes, (2) areas of sediment, and (3) authigenic carbonate blocks with sparse coral and chemosynthetic communities. The coral communities were dominated by L. pertusa but also contained numerous solitary coral species. Over areas that contained L. pertusa, the environmental conditions recorded were similar to those associated with communities in the north-eastern Atlantic, with temperature (8.5–10.6 °C) and salinity (～35) falling within the known species niche for L. pertusa. However, dissolved oxygen concentrations (2.7–2.8 ml l^?1) and density (σ_Θ, 27.1–27.2 kg m^?3) were lower and mass fluxes from sediment trap data appeared much higher (4002–4192 mg m^?2 d^?1). Yet, this species still appears to thrive in this region, suggesting that L. pertusa may not be as limited by lower dissolved oxygen concentrations as previously thought. The VK826 site experienced sustained eastward water flow of 10–30 cm s^?1 over the 5-day measurement period but was also subjected to significant short-term variability in current velocity and direction. In addition, two processes were observed that caused variability in salinity and temperature; the first was consistent with internal waves that caused temperature variations of 0.8 °C over 5–11 h periods. The second was high-frequency variability (20–30 min periods) in temperature recorded only at the ALBEX site. A further pattern observed over the coral habitat was the presence of a 24 h diel vertical migration of zooplankton that may form part of a food chain that eventually reaches the corals. The majority of detailed studies concerning local environmental conditions in L. pertusa habitats have been conducted within the north-eastern Atlantic, limiting most knowledge of the niche of this species to a single part of an ocean basin. Data presented here show that the corals at VK826 are subjected to similar conditions in temperature, salinity, and flow velocity as their counterparts in the north-east Atlantic, although values for dissolved oxygen and density (sigma-theta: σ_Θ) are different. Our data also highlight novel observations of short-term environmental variability in cold-water coral habitat.     

Evaluation of biotite-garnet geothermometers: application to the English River subprovince,Ontario

In recent years, there have been numerous calibrations of the biotite-garnet Fe-Mg exchange geothermometer. The Eastern Lac Seul region of the English River subprovince, Ontario, provides an excellent field area in which to compare these calibrations.Trend surface analysis using the temperatures obtained from garnet cores and matrix biotites-showed almost identical trends in the eastern Lac Seul region regardless of the calibration used. The absolute temperatures and the precision of each calibration do, however, show large variation. Geothermometers based solely on lnK_D were found to give more precise results than the calibrations that attempt to incorporate non-Fe-Mg components. The Perchuk and Lavrent'eva (1983) thermometer yields the most precise and accurate results. If a sufficient number of samples are collected over a region, it can be used to estimate metamorphic temperature trends to ±30° C. Metamorphism and migmatization of the English River subprovince occurred during the Kenoran orogeny, 2.68 b.y. ago. Our results show that a thermal anticline has been preserved, with temperatures of 600° C at the north and south contacts with Uchi and Wabigoon Greenstone belts, increasing to 725 °C at the center of the subprovince. A garnet-cordierite in isograd occurs at 650° C and an orthopyroxene in isogradat 700° C.     

The control of maturity and kerogen type on quantitative analytical pyrolysis data

Quantitative pyrolysis-gas chromatography has been performed on 96 kerogen samples isolated from 17 wells on the Norwegian Continental shelf. Petrographic and bulk geochemical measurements were also performed on the samples, and a combined data set of 117 variables for each sample was analysed using principal components analysis (PCA). This approach provides an objective and reproducible means of kerogen characterisation, which can be easily automated. In addition to objective kerogen characterisation and facile visualisation of facies and maturity related chemical trends, the method has the potential to allow objective prediction of key geochemical parameters such as maturity level from pyrogram data.     

Chemical models of vitrinite reflectance evolution

A global kinetic model of vitrinite reflectance evolution is developed to illustrate a new approach to vitrinite reflectance modelling. The method utilizes quantitative pyrolysisgas Chromatographic data from isolated vitrinite kerogens to derive the concentrations of structurally specific moieties (alkylphenol precursors) in vitrinite kerogens as a function of rank. This data set is used to calibrate a gaussian distributed activation energy model for phenol-precursor loss from vitrinites using published burial histories. Phenol yield is then correlated with vitrinite reflectance. The predictive vitrinite reflectance model based on this phenol system is tested against a well from the US Gulf Coast area, the results being compared with a Lopatin model of the same well. This type of vitrinite reflectance model is numerically compatible with current generation kinetic models of hydrocarbon production from source rock kerogens, and has a better heating rate independence than Lopatin's method.

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Zusammenfassung Um eine neue Annäherung an das Modellieren der Vitrinit-Reflexion zu demonstrieren, wurde ein global-kinetisches Modell der Entwicklung der Vitrinit-Reflexion erstellt. Die Methode verwendet Daten von quantitativer Pyrolyse-Gas Chromatographie isolierten Vitrinitkerogens, um die Konzentration von strukturspezifischen Moieten (Alkylophenol-Vorläufer) in Vitrinitkerogen als Funktion der Reihenfolge zu erhalten. Verwendet werden diese Daten, um ein nach Gauss verteiltes Aktivierungsenergiemodell zu kalibrieren, das mit Hilfe von veröffentlichten Ablagerungsgeschichten den Phenol-Vorläuferverlust von Vitriniten beschreibt. Die Phenol-Ausbeute wird dann mit der Vitrinit-Reflexion korreliert. Das auf dem Phenolsystem basierende Vitrinit-Reflexionsmodell wird in einem Test einem Bohrloch an der amerikanischen Golfküste gegenübergestellt. Die Ergebnisse werden mit dem Lopatinmodell des selben Bohrlochs verglichen. Diese Art eines Vitrinit-Reflexionsmodells ist numerisch wettbewerbsfähig mit der heutigen Generation kinetischer Modelle der Kohlenwasserstofferzeugung aus Trägergesteinskerogenen. Außerdem ist seine Unabhängigkeit von der Erhitzungsrate größer als mit der Lopatin-Methode.

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Résumé L'auteur présente un modèle cinétique global de l'évaluation du pouvoir réflecteur de la vitrinite, afin d'illuster une approche nouvelle dans la modélisation de ce pourvoir réflecteur. Cette méthode utilise des données quantitatives fournies par la pyrolyse combinée à la Chromatographie en phase gazeuse et relatives à des kérogènes de vitrinite. A partir de ces données, on exprime les concentrations des fractions à structure spécifique dans les kérogènes vitrinitiques en fonction du degré d'évolution. A partir de cet ensemble de données, on établit un modèle de l'énergie d'activation selon une distribution gaussienne, applicable à la perte de phénol-précurseur dans les vitrinites, en se référant à cet effet aux déroulements historiques de l'enfouissement fournis par la littérature. La production de phénol est alors mise en relation avec le pourvoir réflecteur de la vitrinite. Le modèle du pouvoir réflecteur prévisible, basé sur ce système des phénols a été contrôlé dans un forage de la côte du golfe du Mexique (USA), et les résultats comparés à ceux du modèle de Lopatin appliqué au même forage. Le modèle présenté est numériquement compatible avec les modèles cinétiques habituels qui rendent compte de la production d'hydrocarbure à partir des kérogènes des roches-mères; il présente une meilleure indépendance que la méthode de Lopatin par rapport au taux d'échauffement.

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Inversion for seismic anisotropy using genetic algorithms1

A general inversion scheme based on a genetic algorithm is developed to invert seismic observations for anisotropic parameters. The technique is applied to the inversion of shear-wave observations from two azimuthal VSP data sets from the Conoco test site in Oklahoma. Horizontal polarizations and time-delays are inverted for hexagonal and orthorhombic symmetries. The model solutions are consistent with previous studies using trial and error matching of full waveform synthetics. The shear-wave splitting observations suggest the presence of a shear-wave line singularity and are consistent with a dipping fracture system which is known to exist at the test site. Application of the inversion scheme prior to full waveform modelling demonstrates that a considerable saving in time is possible whilst retaining the same degree of accuracy.     

Structural control and origin of volcanism in the Taupo volcanic zone,New Zealand

Taupor volcanic zone (TVZ) is the currently active volcanic arc and back-arc basin of the Taupo-Hikurangi arc-trench system, North Island, New Zealand. The volcanic arc is best developed at the southern (Tongariro volcanic centre) end of the TVZ, while on the eastern side of the TVZ it is represented mainly by dacite volcanoes, and in the Bay of Plenty andesite/dacite volcanoes occur on either side of the Whakatane graben. The back-arc basin is best developed in the central part of the TVZ and comprises bimodal rhyolite and high-alumina basalt volcanism. Widespread ignimbrite eruptions have occurred from this area in the past 0.6 Ma. Normal faults occur in both arc and back-arc basin. They are generally steeply dipping (>40°) and strike between 040° and 080°. In the back-arc basin, fault zones are en echelon and have the same trend as alignments of rhyolite domes and basalt vents. Open fissures have formed during historic earthquakes along some of the faults, and geodetic measurements on the north side of Lake Taupo suggest extension of 14±4 mm/year. In the Bay of Plenty and M_L=6.3 earthquake occurred on 2 March 1987. Modelling of known structure in the area together with data derived from this earthquake suggests block faulting with faults dipping 45°±10° NW and a similar dip is suggested by seismic profiling of faults offshore of the Bay of Plenty where extension is estimated to be 5±2 mm/year. To the east of the TVZ, the North Island shear belt (NISB) is a zone of reverse-dextral, strike-slip faults, the surface expression of which terminates at the eastern end of the TVZ. On the opposite side of the TVZ in the offshore western Bay of Plenty and on line with the NISB is the Mayor Island fault belt. If the two fault belts were once continuous, as seems likely, strike-slip faults probably extend through the basement of the TVZ. When extension associated with the arc and back-arc basin is combined with these strike-slip faults, the resulting transtension provides a suitable tectonic environment for caldera formation and voluminous ignimbrite eruptions in the back-arc basin. The types of volcano in the TVZ are considered to be related to the source of magma and overlying crustal structure. Lavas of the arc are probably formed by a multistage process involving (1) subsolidus slab dehydration, (2) anatexis of the mantle wedge, (3) fractionation and minor crustal assimilation and (4) magma mixing. High-alumina basalts of the back-arc basin may be derived by partial melting of peridotite at the top of the mantle wedge, while rhyolitic magmas are thought to come from partial melting of lavas and subvolcanic reservoirs associated with the southern end of the Coromandel volcanic zone. Extreme thinning associated with transtension in the back-arc basin will favour the eruption of large-volume, gas-rich ignimbrites accompanied by caldera formation.     

Composition,oxygen isotope geochemistry and origin of smectite in the metalliferous sediments of the Bauer Deep,southeast Pacific

The sediments of the Bauer Deep, an open ocean basin situated on the northwest Nazca Plate in the southeast Pacific, constitute a regional metalliferous deposit dominated by authigenic smectite.Two 2-metre long cores from the Bauer Deep were examined to investigate the nature and origin of the smectite.Infra-red and Mossbauer spectroscopy and wet chemical analysis (LiBO₂ fusion) of isolated smectite, indicate the mineral is a Mg-rich, Al-rich nontronite. Oxygen isotopic compositions for isolated smectite are uniform and translate to a non-hydrothermal temperature of formation of about 3°C. SEM observations show an abundance of well-preserved biogenic opal in surface and near surface sediment but postburial dissolution and transformation of this phase to smectite is evident at depth.Smectite formation is the result of interaction between iron oxyhydroxide, ponded in the Bauer Deep following a hydrothermal origin at the adjacent East Pacific Rise, and biogenic opal. A reaction mechanism is proposed.Regional factors control smectite formation. In particular, formation is inhibited in areas of CaCO₃ accumulation (topographic elevations) but favoured in areas of oxyhydroxide and opal ponding (topographic depressions).     

Distribution and mode of occurrence of zinc and lead in glacial soils

The distribution and mode of occurrence of zinc and lead have been examined in glacial soils developed over a complex Precambrian marble-paragneiss terrain in the Adirondack Mountains of New York. Based on distribution within the soil profiles, zinc is enriched in the B₁ horizon of soils sampled over marble and lead is generally enriched in the A horizon, particularly in soils developed over paragneiss. Contrast is calculated using

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, where is the mean of n_A anomalous and n_B background samples, and S_p is the pooled standard deviation) for zinc, lead and cold-extractable heavy metals in soils sampled over marble and paragneiss. The t-values indicate that the B₁, soil horizon is the most suitable for sampling on a regular basis, even though lead is most concentrated in the A horizon.The distribution of zinc and lead among exchangeable, organic, iron-manganese oxide, clay, silt and sand fractions of B₁ horizons from two anomalous and one background soil indicates that both zinc and lead are tied up principally in iron and manganese oxides. The anomalous samples exhibit zinc enrichment in the Fe-oxide digestion and high Mn/Fe ratios for the Mn-oxide digestion (as well as the total analysis). In terms of total contribution to the sample, significant proportions of zinc in the clastic fraction can be attributed to zinc substitution into clays plus the ineffective removal of Fe-oxides by the ammonium oxalate extraction procedure. Lead, on the other hand, occurs in significant concentrations in clay, silt and sand as well as Fe- and Mn-oxides, probably as a trace constituent in feldspars or adsorbed onto clay surfaces.