Complete remagnetization of some Permian dykes from western Norway induced during burial/uplift

Stable paleomagnetic directions in four basaltic dykes and in some associated Caledonian metamorphic rocks define high-latitude, Mesozoic paleomagnetic pole positions which are not compatible with the K---Ar age of 250 My determined for the dykes. A monotonic increase of 40% occurs in the potassium content of samples taken across a dyke 32 cm wide. This is accompanied by only a 1–2% variation in the K---Ar age of the samples, suggesting the absence of any significant level of initial argon. Titanomagnetite grains having bulk compositions around x = 0.6 have suffered extensive low-temperature alteration, forming assemblages of ferri-rutile granules in a matrix of pure magnetite. The complete remagnetisation of both the dykes and the associated country rocks is probably an expression of a VRM acquired at elevated temperatures (150–500°C) at the emplacement depth of the dykes. A stable remanent magnetisation was locked-in during uplift of the area, probably related to the Kimmerian basin development in the adjacent North Sea and the epeirogenic uplift of western Fennoscandia.     

Oxygen consumption rate of shrimp exposed to crude oil extract

The shallow water shrimp Palaemon adspersus was exposed to 200, 100 and 0 ppb WSF of crude oil for 14 days after which the oxygen consumption rate was measured in a closed chamber with an electrode. Previous work has shown a changed oxygen consumption rate in animals exposed to WSF in concentrations 100 to 1000 times the concentrations used in the present experiments. The oxygen consumption rate was also significantly increased by the low concentrations used in the present work.Although the oxygen consumption rate was significantly increased, as an effect of WSF-pollution, the method is very time-consuming.     

Abundance and distribution of gold,palladium and iridium in some spinel and garnet lherzolites: implications for the nature and origin of precious metal-rich intergranular components in the upper mantle

The abundance and distribution of Au, Pd, Ir, Cu, Co and Cr has been determined in mantle-derived spinel lherzolite xenoliths in basanites from Mt Porndon (Victoria, Australia) and Kilbourne Hole (New Mexico, U.S.A.) and in garnet lherzolites from the Matsoku and Thaba Putsoa kimberlites (Lesotho). Minerals in the lherzolites concentrate Au, Pd and Ir in the following sequence of increasing platinum group element (PGE) content; garnet, olivine, orthopyroxene, clinopyroxene, spinel. and demonstrate that there exists a real crystallochemical control on the distribution of PGE. Whole rock PGE abundances calculated from the modal mineralogy are less than actually determined and indicate that the bulk of the PGE (60–80%) occur in a sulphide-rich intergranular component. A metasomatic origin for this component is considered to be unlikely and it is proposed that it represents an immiscible sulphide melt which has been retained in the mantle after extraction of a sulphur saturated basic partial melt. This component may in the case of garnet lherzolites have been modified by metasomatic events in the mantle leading to Au depletion and rare earth element addition. Spinel lherzolites are relatively homogeneous at a given locality but differ in their PGE content regionally. The weighted average abundances of PGE in a spinel lherzolite upper mantle are 0.6 ppb. Au, 4.0 ppb Pd. 3.6 ppb Ir. Garnet lherzolites are very heterogeneous and insufficient data is available to allow calculation of geochemically meaningful averages. Spinel lherzolite-basalt based pyrolite contains 0.9 ppb Au, 4.3 ppb Pd, 3.0 ppb Ir, and indicates that the mantle contains an apparent excess of Au over a calculated abundance based upon the siderophilic equilibrium distribution of Au between core and mantle. This excess is considered to be due to failure to consider the chalcophilic nature of Au in the mantle and not to the addition of a meteoritic component to a mantle equilibrated with the core.     

Two-dimensional simulations of surface deformation caused by slab detachment

Detachment of the deeper part of subducted lithosphere causes changes in a subduction zone system which may be observed on the Earth's surface. Constraints on the expected magnitudes of these surface effects can aid in the interpretation of geological observations near convergent plate margins where detachment is expected. In this study, we quantify surface deformation caused by detachment of subducted lithosphere. We determine the range of displacement magnitudes which can be associated with slab detachment using numerical models. The lithospheric plates in our models have an effective elastic thickness, which provides an upper bound for rapid processes, like slab detachment, to the surface deformation of lithosphere with a more realistic rheology. The surface topography which develops during subduction is compared with the topography shortly after detachment is imposed. Subduction with a non-migrating trench system followed by detachment leads to a maximum surface uplift of 2–6 km, while this may be higher for the case of roll-back preceding detachment. In the latter situation, the back-arc basin may experience a phase of compression after detachment. Within the context of our elastic model, the surface uplift resulting from slab detachment is sensitive to the depth of detachment, a change in friction on the subduction fault during detachment and viscous stresses generated by sinking of the detached part of the slab. Overall, surface uplift of these magnitudes is not diagnostic of slab detachment since variations during ongoing subduction may result in similar vertical surface displacements.     

Arias Intensity Assessment of Liquefaction Test Sites on the East Side of San Francisco Bay Affected by the Loma Prieta,California, Earthquake of 17 October 1989

Uncompacted artificial-fill deposits on the east side of San Francisco Bay suffered severe levels of soil liquefaction during the Loma Prieta earthquake of 17 October 1989. Damaged areas included maritime-port facilities, office buildings, and shoreline transportation arteries, ranging from 65 to 85 km from the north end of the Loma Prieta rupture zone. Typical of all these sites, which represent occurrences of liquefaction-induced damage farthest from the rupture zone, are low cone penetration test and Standard Penetration Test resistances in zones of cohesionless silty and sandy hydraulic fill, and underlying soft cohesive Holocene and Pleistocene sediment that strongly amplified ground motions. Postearthquake investigations at five study sites using standard penetration tests and cone penetration tests provide a basis for evaluation of the Arias intensity-based methodology for assessment of liquefaction susceptibility.     

Atmospheric input of nitrogen into the North Sea: ANICE project overview

The aim of the atmospheric nitrogen inputs into the coastal ecosystem (ANICE) project is to improve transport–chemistry models that estimate nitrogen deposition to the sea. To achieve this, experimental and modelling work is being conducted which aims to improve understanding of the processes involved in the chemical transformation, transport and deposition of atmospheric nitrogen compounds. Of particular emphasis within ANICE is the influence of coastal zone processes. Both short episodes with high deposition and chronic nitrogen inputs are considered in the project. The improved transport–chemistry models will be used to assess the atmospheric inputs of nitrogen compounds into the European regional seas (the North Sea is studied as a prototype) and evaluate the impact of various emission reduction strategies on the atmospheric nitrogen loads. Assessment of the impact of atmospheric nitrogen on coastal ecosystems will be based on comparisons of phytoplankton nitrogen requirements, other external nitrogen inputs to the ANICE area of interest and the direct nitrogen fluxes provided by ANICE. Selected results from both the experimental and modelling components are presented here. The experimental results show the large spatial and temporal variability in the concentrations of gaseous nitrogen compounds, and their influences on fluxes. Model calculations show the strong variation of both concentrations and gradients of nitric acid at fetches of up to 25 km. Aerosol concentrations also show high temporal variability and experimental evidence for the reaction between nitric acid and sea salt aerosol is provided by size-segregated aerosol composition measured at both sides of the North Sea. In several occasions throughout the experimental period, air mass back trajectory analysis showed connected flow between the two sampling sites (the Weybourne Atmospheric Observatory on the North Norfolk coast of the UK and Meetpost Noordwijk, a research tower at 9 km off the Dutch coast). Results from the METRAS/SEMA mesoscale chemistry transport model system for one of these cases are presented. Measurements of aerosol and rain chemical composition, using equipment mounted on a commercial ferry, show variations in composition across the North Sea. These measurements have been compared to results obtained with the transport–chemistry model ACDEP which calculates the atmospheric inputs into the whole North Sea area. Finally, the results will be made available for the assessment of the impact of atmospheric nitrogen on coastal ecosystems.     

Urban and suburban storm water runoff as a source of polycyclic aromatic hydrocarbons (PAHs) to Massachusetts estuarine and coastal environments

Urban and suburban storm water runoff from ten locations in eastern Massachusetts was analyzed for 39 polycyclic aromatic hydrocarbons (PAHs) compounds. Similar profiles in PAH composition were observed for groups of samples and appear to reflect land use. The largest group includes, urban storm water from areas with a mix of industrial, commercial, and residential use. Fluoranthene, phenanthrene, pyrene, chrysene, and benzo (b) fluoranthene were the predominant compounds in this group, but lighter molecular weight PAHs were also present. Sources of PAHs to storm water include a combination of petroleum and combustion. The profile of PAH compounds in local atmospheric deposition was similar to urban storm water, but differed in several of the predominant compounds. PAHs in storm water could increase the levels of these compounds in nearshore sediments and may be the most important source of high molecular weight PAHs to these environments.     

Characteristics of turnover of carbonyl sulfide in four different soils

Release and uptake of carbonyl sulfide (OCS) were measured at 25°C in samples of three forest soils (BL, BW, PBE) and one soil from a rape field (RA). The soil samples were flushed with a constant flow of either air (oxic conditions) or nitrogen (anoxic conditions) containing defined concentrations of OCS. A cryogenic trapping technique with liquid argon (-186 °C) was used to collect gas samples for analysis in a gas chromatograph equipped with a flame-photometric detector. The dependence of net OCS fluxes between soil and atmosphere could be described by a simple model of simultaneous OCS production and OCS uptake. By using this model, production rates (P), uptake rate constants (k) and compensation concentrations (m _c ) of OCS could be determined as function of the soil type and the incubation conditions. Under oxic conditions, OCS production (P) and uptake were observed in all soils tested. However, the compensation concentrations (<166 ng l^-1; 1 ng OCS l^-1=0.41 ppbv) that were calculated from the model were high relative to the ambient OCS concentration (ca. 0.5 ppbv). The production rates (0.16–1.9 ng h^-1 g^-1 dw) that were actually measured when flushing the soil samples with air containing zero OCS were smaller than those (17–114 ng h^-1 g^-1 dw) calculated from the model. This observation was explained by two different concepts: one assuming the existence of a threshold concentration (m _t ) below which OCS was no longer consumed in the soil; the other assuming the existence of two different OCS consumption processes, of which only the process active at elevated OCS concentrations was covered by the experiments. The latter concept allowed the estimation of OCS compensation concentrations that were partially low enough to allow the uptake of atmospheric OCS by soil. Both OCS production and uptake in PBE soil were dependent on soil temperature (optimum 20 °C) indicating a microbial process. However, both production and consumption of OCS were not consistently inhibited by sterilization of the soil, suggesting that they were not exclusively due to microbiological processes. Under anoxic conditions, OCS was also produced, but was not consumed except in one soil (RA). Production of OCS in the soils was stimulated after addition of thiocyanate, but not thiourea, thiosulfate, thioglycolate, tetrathionate, sulfate, elemental sulfur, cysteine and methionine.     

Observations of gravity waves in the upper and lower stratosphere by lidar and ozonesondes

Lidar observations of Rayleigh backscatter and temperature profiles measured by ozonesondes have been used to investigate gravity waves in the upper and lower stratosphere, respectively, over Aberystwyth (52.4°N, 4.1°W). Both data sets have been used to investigate the vertical wavenumber spectrum of the wave field at high wavenumbers. Similar analytic techniques applied to each data set enable direct comparison of the spectra. The possibility of laminar structures generated by differential advection contaminating gravity-wave fields deduced from temperature and/or density measurement is discussed and the behaviour of the wave-field mean potential energy reveals a seasonal cycle throughout the stratosphere with a late winter maximum and a summer minimum.