Meteoric fluid‐rock interaction in Variscan shear zones

Variscan shear zones in the Armorican Massif represent sites of strong fluid‐rock interaction. The hydrogen isotope composition of muscovite (δD_Ms) from syntectonic leucogranite allows to determine the source of fluids that infiltrated the footwall of three detachment zones and the South Armorican Shear Zone. Using temperatures of hydrogen isotope exchange estimated from microstructural data, we calculate the hydrogen isotope ratios of water (δD_water) present within the shear zones during high‐temperature deformation. A ~40‰ difference in δD_water values from deep to shallow crustal level reveals a mixing relationship between deep crustal fluids with higher δD values that range from ?34 to ?33‰, and meteoric fluids with δD values as low as ?74‰ in the upper part of detachment footwalls.     

Comparison of atmospheric aerosol backscattering and air mass back trajectories

Summary Atmospheric backscattering from aerosol particulates has been measured over the Atlantic at 10.6 μm wavelength with an airborne, coherent heterodyne, lidar, and corresponding air mass back trajectories have been calculated. These back trajectories (usually extended up to 10 days prior to the backscatter measurement) have shown very diverse origins for the air parcels at different altitudes. In many cases it has been possible to attribute the observed levels of scattering to these origins over oceanic, arctic, continental, industrial etc. regions. This is illustrated by 6 flight records: out of Ascension Island in the South Atlantic; over the Azores in the mid North Atlantic; over the UK and the North Sea; and in the Arctic along 71° North. In each of these regions the profiles of backscatter versus altitude show highly variable features; remarkably different origins for air masses at different altitudes are evident from the corresponding back trajectory analyses. It is thus possible for the first time to present probable explanations for the different levels of scattering observed at different altitudes. Received July 14, 2000 Revised May 14, 2001     

Oxidation state and electronic configuration determination of copper in tetrahedrite group minerals by L-edge X-ray absorption spectroscopy

L-edge X-ray absorption spectroscopy employing a synchrotron radiation source has been used to study the electronic structure and valency of Cu in the chemically and structurally complex tetrahedrite group of minerals. Mechanical mixtures of Cu²⁺O and Cu⁺FeS₂ were used to estimate the relative cross sections of Cu²⁺ and Cu⁺; the absorption of Cu²⁺ at 931 eV is 25 times greater than that of Cu⁺ at 945 eV. Using this calibration, Cu²⁺/Cu ratios were found to vary from 0.00 to 0.054 in the tetrahedrite samples studied; the highest proportion of Cu²⁺ occurs in synthetic tetrahedrites with a composition close to Cu₁₂Sb₄S₁₃. This study reveals the utility of the technique for determining the valence state of copper in complex minerals, allowing the crystal chemistry to be more fully characterised.     

A simulation model of how life history strategies mediate pollution effects on fish populations

Pollution effects on fish populations were estimated with a simulation model, using Leslie matrices. Results from changing only first-year survival rate (S_o) have already been published (Schaaf et al. 1987). This paper explores the effects of perturbing both S_o and the adult survival rate (S_i) for 12 spatial-temporal stocks. Most stocks examined are more sensitive to permanent change in S_i than to changes in S_o. The relative importance of these two rates in determining the population growth rate (λ) depends upon the age distribution of the expected lifetime egg production of age i females (V_i). In turn, the vector V_i, as measured by its mean and standard deviation, is shown to vary among geographic or temporal stocks of a single species. Hence, we quantify the impact on population size of destroying a fixed percentage of habitat, relative to where and when it occurs (i.e., relative impact on S_i and S_o). For example, destroying 1% of the Atlantic menhaden habitat would reduce λ by 0.8% and the population by 8.0% in 10 yr, if the impact affected only adults (e.g., offshore in winter). If the 1% habitat destruction all occurred in the estuaries, affecting juveniles as well, λ would be reduced by almost 5%, and in 10 yr drive the population down to 58% of its former equilibrium. We show that knowledge of the mean and variance of the age distribution of V_i permits prediction of relative sensitivity among species to pollution. Within species, this knowledge of V_i permits comparison of the effects of impacting different life stages and at different times and places.     

Ecology of estuarine bacteria capable of causing human disease: A review

Certain bacteria indigenous to estuaries are capable of acting as opportunistic pathogens of humans. While it is sometimes difficult to prove that a given bacterium is a bona fide inhabitant of the estuary from which it was isolated, it is even more difficult to describe the niche of that bacterial species. This statement applies to all estuarine bacteria, including opportunistic human pathogens. On the other hand, much has been learned about the pathogenic attributes of bacteria that cause human disease, including genetic control mechanisms for virulence factors. The focus of this review is to put into perspective current knowledge of the ecology of those estuarine bacteria that can inhabit both estuaries and humans. Particular attention is paid to those attributes that allow these bacteria to exist in and move between estuaries and the human body. Genera covered includeAcinetobacter, Aeromonas, Clostridium, Enterobacter, Flavobacterium, Klebsiella, Legionella, Listeria, Plesiomonas, Pseudomonas, andVibrio, and the conclusion reached is that much remains to be learned about the estuarine ecology of these important bacteria.     

Electronic structures of sulfide minerals — Theory and experiment

The sulfide minerals exhibit a rich diversity in sturctural chemistry and in electrical, magnetic and other physical properties. Models based on molecular orbital theory and incorporating some elements of band theory can be developed to describe the diverse valence electron behavior in these minerals. Qualitative models can be proposed on the basis of observed properties, and the models can be tested and refined using experimental data from X-ray emission and X-ray photoelectron spectroscopy and quantum mechanical calculations performed on cluster units which form the basic building blocks of the crystals. This approach to chemical bonding in sulfide minerals is illustrated for binary non-transition metal sulfides (ZnS, CdS, HgS, PbS), binary transition metal sulfides (FeS₂, CoS₂, NiS₂, CuS₂ ZnS₂) and more complex sulfides (CuFeS₂, Cu₂S, Ag₂S, CuS, Co₃S₄, CuCo₂S₄, Fe₃S₄). The relationship between qualitative and quantitative theories is reviewed with reference to the pyrite-marcasite-arsenopyrite-loellingite series of minerals. Application of the models to understanding structure-determining principles, relative stabilities, solid solution limits and properties such as color, reflectance and hardness are discussed.     

An automatic data processing system for storage and manipulation of life history,catch, and angler effort data

Responding to a need created by voluminous collections of fish life history, catch and angler effort information, a computerized information management system was developed at the National Marine Fisheries Service laboratory in Beaufort, N.C. for use on an IBM Model 360/65 Computing System. The management system incorporates sequential data storage on disks, analytic programs written in IBM FORTRAN IV, and editing/updating programs written in American National Standard COBOL. The file creation procedure utilizes single or multiple card entry records to generate a single master record. Analytic programs generate arrays displaying fish weights and simple statistics, length-frequency distributions, catch curves, back-calculated fish lengths per annulus, back-calculated length frequency distributions, percentages sexually mature, reproductive condition, age at sexual maturity (using gonad index), occurrence and abundance.     

Recent Rapid Regional Climate Warming on the Antarctic Peninsula

The Intergovernmental Panel on Climate Change (IPCC) confirmed that mean global warming was 0.6 ± 0.2 °C during the 20th century and cited anthropogenic increases in greenhouse gases as the likely cause of temperature rise in the last 50 years. But this mean value conceals the substantial complexity of observed climate change, which is seasonally- and diurnally-biased, decadally-variable and geographically patchy. In particular, over the last 50 years three high-latitude areas have undergone recent rapid regional (RRR) warming, which was substantially more rapid than the global mean. However, each RRR warming occupies a different climatic regime and may have an entirely different underlying cause. We discuss the significance of RRR warming in one area, the Antarctic Peninsula. Here warming was much more rapid than in the rest of Antarctica where it was not significantly different to the global mean. We highlight climate proxies that appear to show that RRR warming on the Antarctic Peninsula is unprecedented over the last two millennia, and so unlikely to be a natural mode of variability. So while the station records do not indicate a ubiquitous polar amplification of global warming, the RRR warming on the Antarctic Peninsula might be a regional amplification of such warming. This, however, remains unproven since we cannot yet be sure what mechanism leads to such an amplification. We discuss several possible candidate mechanisms: changing oceanographic or changing atmospheric circulation, or a regional air-sea-ice feedback amplifying greenhouse warming. We can show that atmospheric warming and reduction in sea-ice duration coincide in a small area on the west of the Antarctic Peninsula, but here we cannot yet distinguish cause and effect. Thus for the present we cannot determine which process is the probable cause of RRR warming on the Antarctic Peninsula and until the mechanism initiating and sustaining the RRR warming is understood, and is convincingly reproduced in climate models, we lack a sound basis for predicting climate change in this region over the coming century.