1,721,124 research outputs found
Expedition 390/393 Scientific Prospectus addendum: South Atlantic Transect
No full textThe South Atlantic Transect (SAT) is a multidisciplinary scientific ocean drilling project that will recover complete sedimentary sections and the upper ~250 m of the underlying oceanic crust along a slow/intermediate spreading rate Mid-Atlantic Ridge crustal flow line at ~31°S. These cores were originally scheduled to be collected during International Ocean Discovery Program (IODP) Expeditions 390 and 393 in October–December 2020 and April–June 2021, respectively. In 2020 and 2021, the global COVID-19 pandemic resulted in the postponement of several IODP expeditions, including Expeditions 390 and 393, chiefly because science parties were unable to travel to the R/V JOIDES Resolution. In response, the ship was used to conduct preparatory work for the postponed expeditions that did not require a science party aboard but could be carried out by the ship’s crew and a team of technicians from the JOIDES Resolution Science Operator. Two of these expeditions (390C and 395E) were in service of the SAT drilling project, to reduce the operational risks and expedite basement drilling during the rescheduled Expeditions 390 and 393. Expeditions 390C and 395E visited five of the six primary SAT sites and successfully cored a single advanced piston corer/extended core barrel hole penetrating the entire sediment section and <10 m into the underlying basalt before installing a reentry system in a second hole at each site visited. Given these accomplishments, the operations plans for the rescheduled Expeditions 390 and 393 have been revised
Phylogeny and Predicted Functional Capabilities of a Sulfur-Oxidizing and Denitrifying Clade of Bacteroidetes from Sulfidic Environments
Full text linkEnvironments rich in sulfur compounds (sulfidic) are common in the ocean, and the ability to gain energy (dissimilatory) from sulfur redox reactions is widespread in bacteria. The Sulfiphilic Bacteroidetes (SB), have been found exclusively in sulfidic environments, but little is known about their metabolic potential and membership. The ability to perform dissimilatory sulfur redox would make them unique among Bacteroidetes, which are primarily known as heterotrophs that specialize in degrading complex organic molecules. Using 16S rRNA phylogeny and analysis of single amplified genomes (SAGs) from Saanich Inlet, a seasonally hypoxic basin, we elucidate the global distribution and potential metabolic capabilities of the SB clade.
Phylogenetic analysis revealed that this clade was monophyletic and had a global distribution. It is hypothesized this clade combines heterotrophic amino acid and sugar uptake with denitrification and respiratory sulfur oxidation/polysulfide reduction. Putative genes for sulfur oxidation via polysulfide reductase (psr) were found in the combined genome, and phylogenetic analysis confirmed these genes were likely to be psrABC. A denitrification pathway was present and complete save for the absence of a gene catalyzing reduction of NO to N2O. The SB clade possesses the potential to grow by degrading a variety of polysaccharides and peptides, and possesses both aerobic respiratory and anaerobic fermentation pathways, including the TCA cycle, acetogenesis and ethanol fermentation. The presence of aerobic and anaerobic metabolic pathways makes the clade suited to environments experiencing periodic oxygen depletion. The inferred metabolic capabilities of the SB clade taken with their wide range suggest they are potentially important players in global nitrogen and sulfur cycling
Expedition 395E Preliminary Report: Complete South Atlantic Transect Reentry Systems
No full textInternational Ocean Discovery Program (IODP) Expeditions 390C and 395E were implemented in response to the global COVID-19 pandemic and occupied sites proposed for the postponed Expeditions 390 and 393, South Atlantic Transect 1 and 2. Expedition 395E completed most of the preparatory work that Expedition 390C did not have time to complete. The overall objective of Expeditions 390C and 395E was to core one hole at each of the South Atlantic Transect sites with the advanced piston corer/extended core barrel (APC/XCB) system to basement for gas safety monitoring and to install a reentry system with casing through the sediment to a few meters into basement in a second hole.Expedition 395E started in Cape Town, South Africa, and ended in Reykjavík, Iceland, after 20 days of on-site operations. We cored to basement at two new sites, U1560 and U1561, and completed reentry systems at three sites, U1556, U1557, and U1560. These operations will expedite basement drilling during the rescheduled Expeditions 390 and 393.Hole U1560A (Proposed Site SATL-25A) lies in ~15.2 Ma crust and is composed of carbonate-rich sediments to 120 meters below seafloor (mbsf) and 2.5 m of underlying basalt. A reentry system was deployed in Hole U1560B to 122.0 mbsf. We then moved to the sites at the western end of the transect on ~61 Ma crust. In Hole U1557D, 10¾ inch casing was deployed to 571.6 mbsf to deepen the 16 inch casing that was deployed during Expedition 390C, and in Hole U1556B, a reentry system was deployed to 284.2 mbsf. The remaining operations time was insufficient to install a reentry system at the originally planned site, Proposed Site SATL-33B. Instead, we cored Hole U1561A (Proposed Site SATL-55A) to 47 mbsf. It is composed of red clay and carbonate ooze overlying 3 m of basalt.The six primary sites of the South Atlantic Transect lie perpendicular to the Mid-Atlantic Ridge on the South American plate, overlying crust ranging in age from 7 to 61 Ma. Basement coring will increase our understanding of how crustal alteration progresses over time across the flanks of a slow/intermediate-spreading ridge and how microorganisms survive in deep subsurface environments. Sediment will be used in paleoceanographic and microbiological studies.</p
Expedition 390C Preliminary Report: South Atlantic Transect Reentry Systems
No full textInternational Ocean Discovery Program (IODP) Expedition 390C was implemented in response to the global COVID-19 pandemic and occupied sites proposed for the postponed Expeditions 390 and 393. The objectives for Expedition 390C were to core one hole at each site with the advanced piston corer/extended core barrel (APC/XCB) system to basement for gas safety monitoring and to install a reentry system with casing through the sediment to between ~5 m above basement and <5 m into basement in a second hole. These operations will expedite basement drilling during the rescheduled South Atlantic Transect Expeditions 390 and 393. The six primary sites for those expeditions form a transect perpendicular to the Mid-Atlantic Ridge on the South American plate, overlying crust ranging in age from 7 to 61 Ma. Basement coring will increase our understanding of how crustal alteration progresses over time across the flanks of a slow/intermediate spreading ridge and how microorganisms survive in deep subsurface environments. Sediment will be used in paleoceanographic and microbiological studies. Expedition 390C started in Kristiansand, Norway, and ended in Cape Town, South Africa, after 31 days of operations. We cored a single APC/XCB sediment hole to the contact with hard rock material at four of the six sites and successfully installed reentry systems with casing at three. Two failed attempts at drilling in casing and a reentry system into hard rock at Site U1558 indicate that the Dril-Quip reentry cones and running tools are incompatible with use in hard rock because the release mechanism does not work when the casing string weight cannot be fully removed from the running tool. Therefore, at Sites U1558 and U1559, casing was installed to ~10 m above basement. Site U1557 has a thick sediment cover (564 m) and will require multiple casing strings to reach basement; a single 16” casing string was installed to 60 meters below seafloor at this site, and later expeditions will extend casing.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Characterization of Marine Biogenic Atmospheric Ice Nucleating Particles
No full textAerosol may act as ice nucleating particles (INPs) that catalyze the formation of ice containing clouds at temperatures above the homogeneous nucleation threshold (-38 ��C). Aerosol enriched in organic matter may be derived from phytoplankton primary production in marine environments or soil and plant fragments in terrestrial environments. Biogenic aerosol plays an impactful, but poorly constrained, role in ecosystems, biogeochemical processes, and the Earth���s climate system. This dissertation focuses on understanding the ice nucleation efficiency of globally abundant biomolecules and marine phytoplankton. A marine coccolithophore (Emiliania huxleyi) and coccolithovirus (EhV-207) were used as a model system during exponential growth and viral lysis in a marine aerosol reference tank (MART). Viral interactions with E. huxleyi did not enhance the production of efficient INPs. The mean freezing temperatures of sea spray aerosol (SSA) during viral production and lysis were statistically lower (range of -26.9 to -29.6 ��C) compared to pre-viral infection and phytoplankton growth (range of -25.9 to -28.3 ��C). The results during active growth of E. huxleyi contrast with previous results of SSA from other phytoplankton species (Thalassiosira weissflogii and Synechococcus elongatus), which had the highest ice nucleation efficiency during fast growth rates. Therefore, differences in chemical composition and physical characteristics may play a role in determining the ice nucleation efficiency of organic matter. To better understand the chemical composition of biogenic INPs, molecules including amino acids, nucleic acids, a peptide, and proteins present in a range of environments were investigated, with immersion mode freezing temperatures ranging from -19 to -26 ��C. The globally abundant protein, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), was an extremely efficient INP (-7.9 ��C) at high concentration (> 10^-1 mg ml^-1) and present in ambient continental aerosol with up to 2 x 10^-6 ice nucleation active sites per L of air. The ice nucleation efficiency of RuBisCO is potentially controlled by changes in concentration and subsequent aggregation, with a broad range in nucleation temperatures (onset of -6.8 ��C and complete freezing at -31.6 ��C). However, I demonstrated that proteins are not a universal source of efficient biogenic INPs. Four additional chemically and structurally diverse proteins were weakly effective INPs, irrespective of molecular weight or degree of aggregation. Although a wide range of biogenic material contribute to ice nucleation, only select proteins have shown to have high catalytic efficiency for ice formation over global distributions. Therefore, the chemical composition and molecular-level mechanisms contributing to highly efficient biogenic INPs is important to understand for predictive climate modeling in the future
Variations on the Author
Full text link“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
Full text linkWe 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
Hydrocarbon Degradation Potential in Free-Living and Micro-Aggregate Bacterial Structures in the Waters of the Gulf of Mexico
Full text linkCrude oil is a heterogenous complex mixture composed of hydrocarbons with different structures, bioavailability, and chemical properties. Due to the various components of crude oil, it is crucial to understand how and when hydrocarbon-degrading microbial communities respond to each crude oil component during degradation. Here, I used culture-independent DNA analytical approaches to monitor structural and functional changes in natural marine microbial communities from northwest Gulf of Mexico over weeks to months after exposure to added oil and chemically dispersed oil in two different experiments, one using mesopelagic waters and the other using coastal surface waters.
The first experiment, described in Chapter II, is an investigation of the impact of crude oil or dispersed oil exposure in different concentrations on mesopelagic microbial community abundance and composition as examined via microscopy and 16S rRNA amplicon analysis and biodegradation of oil, assessed via hydrocarbon chemistry. The second experiment, presented in Chapters III and IV, simulated an oil spill in coastal waters. Metagenomics was used to determine taxonomic and functional profiles of free-living and oil-droplet associated (BOMA) microbial communities analyzed based on comparing their Metagenome-Assembled Genomes (MAGs).
The work presented in Chapter II showed that the concentration of spilled oil substantially affects the microbial response more than the presence of dispersant - higher concentrations of oil, regardless of the presence of dispersant, resulted in higher concentrations of BOMA and similar microbial communities. In addition, the relative abundance of the most abundant putative hydrocarbon degrader detected, Marinobacter, was not influenced by dispersant when oil was present. Data in Chapter III showed that the selective pressure of hydrocarbons led to the enrichment of certain species that are metabolically adapted to hydrocarbon degradation, shifting the microbial communities into more specialized taxa, and changing the overall community structure, which offers more niches to occupy. The microbial community structure of free-living and BOMA size fractions was different, especially between control and Oiled treatments. At the end of the experiment, overall reduced biodiversity was observed, which indicates enhanced hydrocarbon degradation. In Chapter IV, the results suggested that BOMA contains exclusive genes that weren���t detected in Free-living Oiled microbial communities. This includes genes encoding chemotaxis and heavy metal transport, suggesting that the microorganisms living in micro-aggregate communities appear to be more specialized. While genes involved in aromatic hydrocarbon degradation pathways were detected more frequently in free-living microbial metagenomes, indicating that the Free-living fraction is more proficient in overall hydrocarbon degradation
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