Variations in the natural abundance of 15N in estuarine suspended particulate matter: A specific indicator of biological processing

In this study, the ¹⁴N:¹⁵N ratio of suspended particulate material collected from the Tamar river estuary, south-west England, is described. Three populations of particles, distinguishable by their ¹⁵N content, were observed. This investigation has shown that populations of estuarine particles are generated by biological transformations in situ and that the ¹⁵N content of estuarine particles does not merely reflect hydrodynamic mixing of the freshwater and seawater source particulate material.     

Gravitational wave radiation from the coalescence of white dwarfs

We compute the emission of gravitational radiation from the merging of a close white dwarf binary system. This is done for a wide range of masses and compositions of the white dwarfs, ranging from mergers involving two He white dwarfs, through mergers in which two CO white dwarfs coalesce, to mergers in which a massive ONe white dwarf is involved. In doing so we follow the evolution of the binary system using a smoothed particle hydrodynamics code. Even though the coalescence process of the white dwarfs involves considerable masses, moving at relatively high velocities with a high degree of asymmetry we find that the signature of the merger is not very strong. In fact, the most prominent feature of the coalescence is that in a relatively small time-scale (of the order of the period of the last stable orbit, typically a few minutes) the sources stop emitting gravitational waves. We also discuss the possible implications of our calculations for the detection of the coalescence within the framework of future space-borne interferometers like LISA.     

Initial interpretation of Titan plasma interaction as observed by the Cassini plasma spectrometer: Comparisons with Voyager 1

The Cassini plasma spectrometer (CAPS) instrument made measurements of Titan's plasma environment when the Cassini Orbiter flew through the moon's plasma wake October 26, 2004 (flyby TA). Initial CAPS ion and electron measurements from this encounter will be compared with measurements made by the Voyager 1 plasma science instrument (PLS). The comparisons will be used to evaluate previous interpretations and predictions of the Titan plasma environment that have been made using PLS measurements. The plasma wake trajectories of flyby TA and Voyager 1 are similar because they occurred when Titan was near Saturn's local noon. These similarities make possible direct, meaningful comparisons between the various plasma wake measurements. They lead to the following: (A) The light and heavy ions, H⁺and N⁺/O⁺, were observed by PLS in Saturn's magnetosphere in the vicinity of Titan while the higher mass resolution of CAPS yielded H⁺ and H₂⁺as the light constituents and O⁺/CH₄⁺ as the heavy ions. (B) Finite gyroradius effects were apparent in PLS and CAPS measurements of ambient O⁺ ions as a result of their absorption by Titan's extended atmosphere. (C) The principal pickup ions inferred from both PLS and CAPS measurements are H⁺, H₂⁺, N⁺, CH₄⁺ and N₂⁺. (D) The inference that heavy pickup ions, observed by PLS, were in narrow beam distributions was empirically established by the CAPS measurements. (E) Slowing down of the ambient plasma due to pickup ion mass loading was observed by both instruments on the anti-Saturn side of Titan. (F) Strong mass loading just outside the ionotail by a heavy ion such as N₂⁺ is apparent in PLS and CAPS measurements. (G) Except for the expected differences due to the differing trajectories, the magnitudes and structures of the electron densities and temperatures observed by both instruments are similar. The high-energy electron bite-out observed by PLS in the magnetotail is consistent with that observed by CAPS.     

Acoustic oceanography by remote sensing

Ocean dynamical processes exist over a wide range of temporal and spatial scales. Remotely stationed acoustic devices are being used to "sense" the interior of the oceans at previously unattainable scales. The method is similar to computer-aided tomography (CAT) scans of the brain, but the measurement difficulties are far more severe. The results of a demonstration experiment are reviewed and some directions for acoustic oceanography are discussed.     

Coma Morphology of Three Non-periodic Comets

The coma morphology and short-term evolution was investigated of three non-periodic comets in retrograde orbits, C/2001 Q4 (NEAT), C/2002 T7 (LINEAR), and C/2003 K4 (LINEAR). All three comets display distinct coma features, which were very different from one comet to the next and remained rather constant in shape during the observational period. A single, broad feature perpendicular to the sun-tail direction dominated the coma of C/2003 K4 in all used filters (B,V,R,I), whereas the coma of Comet C/2002 T7 exhibited different features in blue and red filters. C/2001 Q4 showed rather complex coma morphology with clear short-term variability in coma brightness. Therefore, these non-periodic comets neither show a featureless coma nor any similarities of the features detected. The overall distribution of coma material was investigated from the shape of radial coma profiles averaged around the comet nucleus. For C/2001 Q4 and C/2002 T7, the slopes fitted to the linear part of these profiles are flatter in the blue than in the red, which can be explained by the presence of coma gas. For C/2003 K4 no such difference is indicated in the May observations (r = 2.3 AU), while in July (r = 1.7 AU) the profiles in the B-filter are flatter than in V, R, and I, hence gas contamination was relevant at least in the B filter. The R and I filter images were used to determine approximate Afρ values of each comet as a function of time.     

A reinterpretation of the crustal N‐isotope record: evidence for a 15N‐enriched Archean atmosphere?

A new compilation of N‐isotope and abundance data for metasedimentary rocks, and hyrdothermal micas that proxy for bulk crust, show systematic patterns. (1) δ¹⁵N values of kerogen in Precambrian cherts are more negative relative to siliciclastic counterparts, probably due to a mantle hydrothermal component. (2) There is a secular trend from average δ¹⁵N 15.3 ± 1.8‰ in Archean shales, through intermediate values in the Proterozoic, to Phanerozoic counterparts where δ¹⁵N averages +3.5‰. (3) Hydrothermal micas in metamorphic hydrothermal systems of Palaeozoic and Mesozoic age that proxy for crust have δ¹⁵N within the range of contemporaneous sedimentary rocks. (4) Hydrothermal micas track the secular trend of δ¹⁵N for kerogen from 2.7 Ga to the Phanerozoic. (5) Within Precambrian datasets δ¹⁵N does not increase with decreasing N content; accordingly, high δ¹⁵N values cannot stem either from metamorphism or form Rayleigh fractionation. (6) Previous studies show isotopic shifts during metamorphism are only +1 to +3‰ up to amphibolite facies. Values of 10–24‰ are attributed to a high δ¹⁵N Archean atmosphere, a residual signature of CI carbonaceous chondrites where δ¹⁵N is +30‰ to + 42‰.     

Deep-ocean piezometer probe technology for geotechnical investigations

Two single-sensor piezometer probes, 8 mm in diameter, were developed for deep-ocean geotechnical investigations. These probes were tested in a hyperbaric chamber pressurized to 55 MPa (8000 psi). Testing was performed for a period of five weeks under high hydrostatic pressure with the probes inserted in reconstituted illitic marine sediment. Small differential pore-water pressures were generated in response to both mechanically and thermally generated forcing functions. During deep-ocean simulated pressure tests, the sensors exhibited excellent sensitivity and stability. These developments in piezometer-probe technology provide a quantitative means of assessing important geotechnical parameters of fine-grained seabed deposits.     

Deforestation and leaching of nitrogen as nitrates into underground water in intertropical zones: The example of Côte d'lvoire

High nitrate contents (up to 200 mgl) have been observed in wells drilled into fractured aquifers lying beneath layers of weathered and decayed rock in the humid tropics where annual rainfall is over 1000 mm and where there is no notable pollution. The source of the nitrates is linked mainly with localized deforestation by man.     

Dissolution and depletion of ferromagnesian minerals from Holocene tephra layers in an acid bog,New Zealand,and implications for tephra correlation

This study examines the depletion of ferromagnesian silicate minerals from a sequence of thin, distal, mainly rhyolitic tephra layers of Holocene age preserved in an acid peat bog (Kopouatai), North Island, New Zealand. The rate of such depletion has been fast, as indicated by the complete loss of biotite from one tephra layer (Kaharoa Tephra), in which it is normally dominant, in only ca. 770 yr. Chemical dissolution is advocated as the likely cause for the depletion, with amphiboles and other mineral grains commonly showing etch pits, microcaves, and other characteristic surface solution features. Theoretical thermodynamic and kinetic models show a marked increase in the rate of dissolution of all ferromagnesian minerals under conditions of low pH (< 4), but that where silica concentrations in solution are high the relative proportions of minerals remaining are unaffected. However, where concentrations of dissolved silica are low, as in most bog environments, the relative proportions of ferromagnesian minerals are affected as well as absolute amounts being decreased. Amphiboles are depleted relative to pyroxenes, consistent with kinetic studies. The results show that the identification and correlation of tephras on the basis of relative abundances of ferromagnesian minerals alone may be unreliable, and emphasise the need to use multiple criteria in such studies.