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Geochemistry of fluid phases and sediments: relevance to hydrothermal circulation in Middle Valley, ODP Legs 139 and 169
No full textGeochemical and isotopic studies of pore fluids and solid phases recovered from the Dead Dog and Bent Hill hydrothermal sites in Middle Valley (Ocean Drilling Program Leg 169) have been compared with similar data obtained previously from these sites during Ocean Drilling Program Leg 139. Although generally the hydrothermal systems reflect non-steady state conditions, the data allow an assessment of the history of the hydrothermal processes. Sediment K/Al ratios as well as the distribution of anhydrite in the sediments suggest that the Dead Dog hydrothermal field has been, and still is, active. In contrast, similar data in the Bent Hill hydrothermal field indicate a waning of hydrothermal activity. Pore fluid and hydrothermal vent data in the Dead Dog hydrothermal field are similar in nature to the data collected during ODP Leg 139. In the area of the Bent Hill sulfide deposit, however, the pore water data indicate that recent wholesale flushing of the sediment column with relatively unaltered seawater has obliterated a previous record of hydrothermal activity in the pore fluids. Data from the deepest part of Hole 1035A in the Bent Hill locality show the presence of hydrothermal fluids at greater depths in this area. This suggests the origin of the hydrothermal fluids found to be emanating from Hole 1035F, which constitutes one of the first man made hydrothermal vents in the Middle Valley hydrothermal system. Similarly, CORKed Hole 858G, because of seal failures, has acted as a hydrothermal vent, with sulfide deposits forming inside the CORK
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Distributions of polychlorinated biphenyls (PCB's), hydrocarbons and fatty acids among sedimentary organic matter fractions
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Molecular biomarker hydrocarbons as discriminant indicators of environmental pollution - characterization and sources
Get PDFSaccharides in atmospheric particulate and sedimentary organic matter : status overview and future perspectives
Get PDFSaccharides are omnipresent compounds in terrestrial and marine ecosystems. Since the 2000s, their role in
environmental and geochemical studies has significantly increased, but only anhydrosaccharides (mainly levoglucosan)
have been reviewed. Here we present the wider knowledge about saccharides in organic matter of
aerosols, bottom sediments, soils, dust, and sedimentary rocks. The main purpose here is to characterize the
possible sources of saccharides, as well as sacharol formation, seasonal variability, and the possible applications
in environmental and paleoenvironmental interpretations. Different saccharide sources were designated,
including biomass burning, and particulate matter such as pollen, spores, lichen, and fungi, as well as polysaccharide
decomposition as possible inputs of monosaccharides. The main focus was on the most common
saccharides encountered in environmental samples and sedimentary rocks. These are the mono- and disaccharides
glucose, fructose, sucrose, and trehalose, and sacharols arabitol and mannitol. The anhydrosaccharides
levoglucosan, mannosan, and galactosan were evaluated as ancient wildfire indicators and
industrialization tracers found in lacustrine sediments starting from Pleistocene to contemporary deposits.
However, other anhydrosaccharides like xylosan and arabinosan were also found as products of fossil wood
burning. These anhydrosaccharides have the potential to be further tracers of hemicellulose burning. Additional
recommendations are proposed for future research, including environmental and paleoenvironmental topics that
need to be addressed
Hydrothermal alteration of organic matter at spreading centers
No full textAlteration of organic matter, mainly amino acids, at sub-seafloor hydrothermal conditions has been investigated by performing laboratory experiments and by studying deep-sea sediments from hydrothermally active areas on the northern Juan de Fuca Ridge, northeast Pacific Ocean.Quaternary sediments from Middle Valley and the eastern flank of the Juan de Fuca Ridge recovered during the Ocean Drilling Program Legs 139 and 168 have been analyzed for total hydrolyzable amino acid concentrations, individual amino acid abundances and stereochemistry in order to evaluate the effects of hydrothermal stress on the decomposition of sedimentary amino acids. In near surface sediments, amino acids account for up to 3.3% of the total organic carbon content and up to 12% of the total nitrogen content. The non-protein amino acid b-alanine and g-aminobutyric acid become increasingly abundant with depth in low temperature holes (Leg 168) as a result of enzymatic decarboxylation of aspartic acid and glutamic acid, respectively. The decomposition of amino acid in high temperature holes (Leg 139) is enhanced with depth and the amino acid patterns indicates that most amino acids are incorporated into geopolymers and that condensation results in increased stability of some amino acids.The effects of low temperature hydrothermal activity on microbially mediated organic matter diagenesis were studied by comparing depth concentration profiles of interstitial sulfate and methane of Holes 1023A, 1024B, 1025B and 1028A, ODP Leg 168. Diffusional exchange between sulfate-rich basement fluids and pore-waters increases the interstitial sulfate concentrations with depth below local sulfate minima caused by bacterial sulfate reduction. The effects of diffusional processes on pore-water chemistry in the sediment column is reflected by the inhibition of methane production and is largely dependent on sediment thickness.The decomposition of alanine, leucine, aspartic acid and serine in aqueous solutions was studied at 200oC and 50 bar with the purpose of evaluating the effect dissolved oxygen on decomposition rates. The redox buffering mineral assemblage pyrite-pyrrhotite-magnetite was used to constrain the oxygen fugacity to geologically realistic values. Comparisons between results obtained from buffered and nonbuffered runs show that the decomposition is faster for most amino acids but serine in nonbuffered experiments.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Wax Lipids from Leaf Surfaces of Some Common plants of Malaysia
Get PDFEpicuticular wax lipids from leaves of some common plant species found in the Klang Valley, Malaysia were extracted into dichloromethane for analysis. Extracts were separated into hydrocarbon, carboxylic acid, ketone and alcohol
fractions. The fractions after derivatization were then subjected to gas chromatographic (GC) and gas chromatography-mass spectrometric (GC-M5) analyses. The wax yield was highest for Mestta ferrea while the lowest yield was obtained from Eugenia gran dis. In most species studied the m~or n-alkane was found to be hentriacontane (C31 ), followed by tritriacontane (C,,) and nonacosane (C",) , respectively. The n-alkanes exhibit a saw-tooth pattern
which is characteristic of a biogenic origin. A strong even-to-odd carbon number predominance is observed for both the n-alkanoic acids and 1)alkanols.
Only traces of mainly B-sitosterol were detected in some of the species. The triterpenoids and triterpenes were mostly found in the wax of Mesua ferrea with «- and p-boswellic acids as the major components and minor amounts of «- and p-amyrin. Other biomarkers identified were «and
p-amyrones, friedelin, friedelanol, friedelane, olean-12-ene, taraxerene, squalene, dihydronyctanthic acid, dihydroroburic acid and dihydrocanaric acid. This study has shown that the distribution of n-alkanes is a function of the ambient temperature
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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