Mercury-binding proteins in the slipper limpet,Crepidula fornicata,exposed to increased soluble mercury

Crepidula fornicata were held in a flow-through bioassay system and exposed to sand-filtered seawater to which no soluble mercury (control) was added or to which either 5, 25, or 50 μg 1^?1 soluble Hg was added. At specific intervals during the 16-week experiment, a group of limpets was removed from each tank; one subgroup was exposed for 48 h to high concentrations of Hg, and another was analyzed for Hg-binding proteins by gelpermeation chromatography and spectrometry. Mortality from exposure to Hg in the 48-h acute toxicity tests was related to concentrations of Hg experienced both during the long-term exposure period and the 48-h exposure period. Chronic exposure to low levels of Hg resulted in increased amounts of total Hg in the whole body and in the low-molecular-weight Hg-binding proteins. No evidence was found for increased tolerance to Hg with preexposure.     

Diffusion of Sm,Sr, and Pb in fluorapatite

Diffusion coefficients for Sm, Sr, and Pb in fluorapatite at 900°–1250°C were obtained by measuring experimentally-induced diffusional uptake profiles of these elements in the margins of gem-quality apatite crystals. The crystals were immersed in synthetic melts enriched in the trace elements of interest and presaturated in apatite, and the resulting diffusion gradients were characterized by electron microprobe analysis. Except in the case of Pb, the diffusivities define good Arrhenius lines for the respective elements: D_Sm = 2.3 × 10^?6exp(?52,200/RT) D_Sr = 412 exp(?100,000/RT). (Diffusion perpendicular to and parallel to c is measurably different in the case of Sr; the Arrhenius equation given above is an average for the two directions). Results on Pb were erratic, probably because extremely Pb-rich melts were used for some of the experiments. Data believed to be reliable define the following Arrhenius line: D_Pb = 0.035 exp(?70,000/RT). Constraints based on closure of natural apatites with respect to Pb suggest that the experimental data can be extrapolated, with sizeable uncertainty, to temperatures as low as 550°C.When applied to the question of isotopic and trace-element equilibration of residual or entrained apatites with crustal melts, the measured diffusivities indicate that 0.05-cm crystals will rarely preserve the original Pb-isotope characteristics of the source; the same is not true, however, of Sr (and, under some conditions, the REE), which may be unaffected at crystal cores during typical melting events.     

Accommodation coefficient for trace gas uptake using deposition profile measurement in an annular reactor

A simple and inexpensive procedure is presented for the measurement of gaseous accommodation coefficients upon liquid or solid surfaces. The gas of interest is passed in laminar flow through an annular reactor and the profile of deposition is subsequently determined. The Cooney-Kim-Davies theoretical treatment of deposition in cylindrical systems is adapted to describe uptake on the walls of the annular reactor as a function of accommodation coefficient and diffusion coefficient. The accommodation coefficient () of ammonia on oxalic acid is determined in both cylindrical and annular systems and good agreement is found. Uptake of nitrogen dioxide on wet alkaline surfaces yields a value for of 2.5×10^–4, and on solely wet surfaces a value of 8.7×10^–5. Nitric and nitrous acids deposit to aqueous sodium carbonate/glycerol surfaces with values of of 1.5 × 10^–2 and 4.3×10^–3, respectively.     

Argon diffusion domains in K-feldspar I: microstructures in MH-10

Samples of MH-10, a K-feldspar thought to contain discrete diffusion domains for argon, have been examined by light and TEM microsopy to search for domain boudaries. We examined both unheated K-feldspar separates and samples heated in vacuum between 750 and 1150°C in order to characterize the initial microstructure as well as any changes resulting from laboratory heating. The MH-10 rock shows almost no evidence of plastic deformation, and the K-feldspar does not possess networks of dislocations which might define a subgrain structure derived from external stresses. Three classes of substructure are present in the K-feldspar, but only the third appears to have been affected by laboratory heating: (1) Cross-hatched extinction in light microscope is common but variably developed. TEM reveals almost no albite/pericline twinning but tweed microstructure is ubiquitous. (2) Turbid zones occur with about 5 volume % abundance. Micropores, <1 to 2m in diameter, characterize these regions, which often also contain bleds of albite, up to 40 m indiameter, TEM shows these turbid zones to be very complex with intricate twin and tweed structures at the sub-micron scale and numerous dislocation and strain features. (3) Albitic exsolution lamellae (<1 m thick, 20 m long and separated by 1 m) are rarely seen in the light microscope but TEM shows that 0.01 m thick by 0.2–1 m long lamellae, separated by 0.1 to 0.5 m, occur in about 20% of the sample. These lamellae are disk-shaped, have a semi-coherent or coherent relationship to the host K-feldspar, and seem to disappear upon heating to 750°C. Extensive diffusion studies have been conducted on HM-10, and the results analyzed in terms of distribution of sizes of diffusion domains. The preferred result of the analyses was a distribution consisting of three distinct sizes. The largest domain size identified in this way is approximately 50 to 100 m, and this corresponds to blocks of K-feldspar defined by the network of fractured/turbid zones. The smallest domain size inferred from diffusion analysis is 0.1 m which corresponds to the spacing between albite exsolution lamellae that may represent fast diffusion pathways. Alternatively, the modulated argon distribution accompanying the lamellar variation in feldspar composition may result in an overestimation of the initial diffusion coefficients. Even though a promising agreement exists between domain analyses based upon diffusional and microstructural analyses, at least two questions remain unanswered. Firstly, no clear candidate has been identified for a domain of intermediate size. Secondly, the diffusion analysis has been formulated with independent gas release from all domains, whereas the observed structures are likely to be nested (i.e., small domains exist inside bigger domains) with the network of semi-coherent lamellar boundaries having connectivity and permeability which can provide only a modest increase in argon diffusivity over bulk values.     

The Global Atmospheric Electrical Circuit and Climate

Evidence is emerging for physical links among clouds, global temperatures, the global atmospheric electrical circuit and cosmic ray ionisation. The global circuit extends throughout the atmosphere from the planetary surface to the lower layers of the ionosphere. Cosmic rays are the principal source of atmospheric ions away from the continental boundary layer: the ions formed permit a vertical conduction current to flow in the fair weather part of the global circuit. Through the (inverse) solar modulation of cosmic rays, the resulting columnar ionisation changes may allow the global circuit to convey a solar influence to meteorological phenomena of the lower atmosphere. Electrical effects on non-thunderstorm clouds have been proposed to occur via the ion-assisted formation of ultra-fine aerosol, which can grow to sizes able to act as cloud condensation nuclei, or through the increased ice nucleation capability of charged aerosols. Even small atmospheric electrical modulations on the aerosol size distribution can affect cloud properties and modify the radiative balance of the atmosphere, through changes communicated globally by the atmospheric electrical circuit. Despite a long history of work in related areas of geophysics, the direct and inverse relationships between the global circuit and global climate remain largely quantitatively unexplored. From reviewing atmospheric electrical measurements made over two centuries and possible paleoclimate proxies, global atmospheric electrical circuit variability should be expected on many timescales.     

Systematic analysis of K-feldspar Ar/Ar step heating results II: relevance of laboratory argon diffusion properties to nature

We examine a database containing the results of ⁴⁰Ar/³⁹Ar step-heating experiments performed on 194 basement K-feldspars to recover thermal history information. Qualitative examination of ⁴⁰Ar/³⁹Ar systematics reveals that about half of the K-feldspars examined are sufficiently well behaved to be suitable for thermal history analysis. Correlation algorithms are developed to quantitatively assess the degree to which age and ³⁹Ar release spectra are compatible with the same volume diffusion process. Upon applying these methods, we find that 65% of all samples yield correlation coefficients in excess of 0.8, whereas roughly 40% give values above 0.9. We further compare the observed correlation behavior with that predicted from the multidiffusion domain model and find good agreement for samples with correlation coefficients above 0.9. In contrast, hydrous phases unstable under in vacuo heating and K-feldspars with highly disturbed age spectra yield poorly correlated age and diffusion properties. The high degree of correlation exhibited by the majority of K-feldspars we have analyzed validates extrapolation of experimentally determined diffusion properties to conditions attending natural Ar loss within the crust. Despite this, a significant number of basement K-feldspars analyzed by the step-heating method yield ⁴⁰Ar/³⁹Ar systematics that are clearly problematic for thermal history analysis. We numerically explore the effects of low-temperature alteration of K-feldspar on thermochronological analysis and identify a range of conditions under which information is progressively lost. Finally, we demonstrate the insensitivity of thermal history calculations to detailed knowledge of the diffusion mechanism by introducing the heterogeneous diffusion model. We find that the multidiffusion domain approach can successfully recover imposed thermal histories from heterogeneous diffusion-type crystals and conclude that most details of the interpretive model employed are of secondary importance. The only requirement for recovering thermal histories from K-feldspar ⁴⁰Ar/³⁹Ar step-heating results is that argon loss proceeds by volume diffusion and that laboratory argon release adequately mimics the natural diffusion boundaries and mechanisms—a requirement implicitly met by those samples exhibiting high degrees of correlation.     

Species diversity of the genus <Emphasis Type="Italic">Skeletonema</Emphasis> (Bacillariophyceae) in the industrial harbor Dokai Bay,Japan

Seven Skeletonema species were identified at one station in the industrial harbor Dokai Bay, Japan, in October 2007 and then monthly from January 2008 to December 2009 by morphological scanning electron microscopy observations and molecular analyses of mainly the large subunit (LSU) rDNA. We refer to one species identified as S. dohrnii using LSU rDNA, but as S. marinoi using the small subunit (SSU) rDNA and consequently we use the term S. marinoi-dohrnii complex. This is the first time that S. ardens, S. costatum s.s., and S. pseudocostatum have been recorded in Japan and that S. menzelii and S. tropicum have been identified by molecular methods in Japan. The S. marinoi-dohrnii complex was isolated with high frequency all year-round, and S. japonicum was also isolated with high frequency but not so in summer. S. Tropicum was isolated from September to December, but S. ardens and S. costatum s.s. were isolated only when the water temperature exceeded 20°C. S. pseudocostatum bloomed just once, in summer, but S. menzelii was isolated in May and again in October. The continuous year-round occurrence of S. costatum s.l. in the bay is supported by the succession of these seven species. Six of the species, except S. menzelii, were important components of algal blooms in the bay. One to four species of Skeletonema were isolated every month. Monthly species diversity was higher when S. ardens, S. costatum s.s., and S. tropicum that are usually associated with tropical or subtropical waters, were isolated. In general, species diversity of the genus Skeletonema was very high in Dokai Bay.