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  • Elsevier  (136,775)
  • American Chemical Society  (42,918)
  • 2015-2019  (179,693)
  • 2015  (179,693)
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  • 1
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    Acidithrix ferrooxidans gen. nov., sp. nov.; a filamentous and obligately heterotrophic, acidophilic member of the Actinobacteria that catalyzes dissimilatory oxido-reduction of iron (2015)
    Elsevier
    Details
    Publication Date: 2023-11-16
    Description: A novel acidophilic member of the phylum Actinobacteria was isolated from an acidic stream draining an abandoned copper mine in north Wales. The isolate (PY-F3) was demonstrated to be a heterotroph that catalyzed the oxidation of ferrous iron (but not of sulfur or hydrogen) under aerobic conditions, and the reduction of ferric iron under micro-aerobic and anaerobic conditions. PY-F3 formed long entangled filaments of cells (〉50 μm long) during active growth phases, though these degenerated into smaller fragments and single cells in late stationary phase. Although isolate PY-F3 was not observed to grow below pH 2.0 and 10 °C, harvested biomass was found to oxidize ferrous iron at relatively fast rates at pH 1.5 and 5 °C. Phylogenetic analysis, based on comparisons of 16S rRNA gene sequences, showed that isolate PY-F3 has 91–93% gene similarity to those of the four classified genera and species of acidophilic Actinobacteria, and therefore is a representative of a novel genus. The binomial Acidithrix ferrooxidans is proposed for this new species, with PY-F3 as the designated type strain (=DSM 28176T, =JCM 19728T).
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  • 2
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    Upwelling velocity and ventilation in the Mauritanian upwelling system estimated by CFC-12 and SF6 observations (2015)
    Elsevier
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    Publication Date: 2023-11-08
    Description: Transient tracer data (CFC-12 and SF6) from three oceanographic field campaigns to the Mauritanian Upwelling area conducted during winter, spring and summer from 2005 to 2007 is presented. The transient tracers are used to constrain a possible solution to the transient time distribution (TTD) along 18°N and to quantify the mean ages in vertical sections perpendicular to the coast. We found that an Inverse Gaussian distribution where the ratio of the moments δ and Γ equals 1.2 is a possible solution (δ/Γ=1.2) of the TTD. The transient tracers further show considerable under-saturation in the mixed layer during the winter and spring cruises that can only be maintained by mixing or upwelling by tracer-poor water from below the mixed layer. We use dissipation data from microstructure measurements and the tracer depth distribution to quantify the flux of tracers to the mixed layer by vertical diffusivity and wind data from the ship to quantify the air-sea flux. We then use the magnitude of the under-saturation in the mixed layer to estimate the advective upwelling velocity which is the balance the first two processes, in a steady state assumption. We find that the upwelling velocities range from less than 1 to 5.6×10-5ms-1 (〈0.8-4.8md-1), with generally higher values close to the coast, but with comparable upwelling velocities during spring and winter. During the summer cruise the transient tracers were close to equilibrium with the atmosphere, suggesting no upwelling. We have shown the use of CFC-12 and SF6 transient tracer data for calculating upwelling velocity, and found an overall uncertainty of roughly ±50%.
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  • 3
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    Quantifying effects of UV-B, temperature, and pH on eDNA degradation in aquatic microcosms (2015)
    Elsevier
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    Publication Date: 2023-06-28
    Description: Environmental DNA (eDNA) degradation is a primary mechanism limiting the detection of rare species using eDNA techniques. To better understand the environmental drivers of eDNA degradation, we conducted a laboratory experiment to quantify degradation rates. We held bullfrog (Lithobates catesbeianus) tadpoles in microcosms, then removed the tadpoles and assigned the microcosms to three levels each of temperature, ultraviolet B (UV-B) radiation, and pH in a full factorial design. We collected water samples from each microcosm at six time steps (0 to 58 days). In all microcosms, most degradation occurred in the first three to 10 days of the experiment, but eDNA remained detectable after 58 days in some treatments. Degradation rates were lowest under cold temperatures (5 °C), low UV-B levels, and alkaline conditions. Higher degradation rates were associated with factors that contribute to favorable environments for microbial growth (higher temperatures, neutral pH, moderately high UV-B), indicating that the effects of these factors may be biologically mediated. The results of this experiment indicate that aquatic habitats that are colder, more protected from solar radiation, and more alkaline are likely to hold detectable amounts of eDNA longer than those that are warmer, sunnier, and neutral or acidic. These results can be used to facilitate better characterization of environmental conditions that reduce eDNA persistence, improved design of temporal sampling intervals and inference, and more robust detection of aquatic species with eDNA methods.
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  • 4
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    Disparities in glacial advection of Southern Ocean Intermediate Water to the South Pacific Gyre (2015)
    Elsevier
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    Publication Date: 2023-01-23
    Description: Highlights • Surface Mg/Ca-temperatures and salinities show comparable glacial conditions. • Subsurface Mg/Ca-temperatures suggest that LGM is ∼3 to ∼2 °C colder than MIS 6. • Relative to Holocene, subsurface salinities suggest fresher LGM and saltier MIS 6 • Thermal gradients suggest stratified LGM and well-mixed MIS 6 water column. • Contrasting glacial scenarios suggest variable formation and advection of SOIWs. Abstract The Intermediate Waters formed in the Southern Ocean are critical for ventilating the thermocline in the Southern Hemisphere Gyres and transporting climatic signals from high to low latitudes on glacial-interglacial time-scales. Despite the importance of the Southern Ocean Intermediate Waters (SOIWs), information on past changes in SOIWs formation is fragmentary, and its impact on the South Pacific Gyre (SPG)'s thermocline largely unknown. Here, we present a 200 kyr record of paired Mg/Ca ratios and stable oxygen isotope from surface and deep dwelling planktonic foraminifera, from the SPG. On average, the Globigerina bulloides Mg/Ca-derived sea surface temperatures show similar conditions during the LGM and Marine Isotope Stage (MIS) 6 (9.4 °C versus 9.8 °C). In contrast, the subsurface temperatures derived from the Mg/Ca values of Globorotalia inflata and Globorotalia truncatulinoides suggest that LGM is ∼3 to ∼2  °C colder than MIS 6. Furthermore, at subsurface depths the reconstructed δ18Osw-ivc record (proxy for relative local salinity changes) suggests opposite glacial conditions, with slightly saltier-than-Holocene waters during MIS 6, and fresher-than-Holocene waters during LGM. Contrasting glacial scenarios, plausibly due to changes in the presence of SOIWs at the study site, suggest variable formation and/or advection of SOIWs to the SPG during different glacial stages. The variability in SOIWs is probably driven by the changes in the intensity of the Southern Westerly Winds.
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  • 5
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    Derivation of an observation-based map of North African dust emission (2015)
    Elsevier
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    Publication Date: 2023-01-03
    Description: Highlights: • North African dust emission and emission frequency from six models are examined. • There is a power law relationship between emission and emission event frequency. • The lognormal distribution of surface winds gives rise to this power law relation. • Annual North Africa dust emission is estimated via satellite retrievals of emission frequency. • We estimate that 82% of all North Africa dust emission is between 15° and 20°N. Abstract: Changes in the emission, transport and deposition of aeolian dust have profound effects on regional climate, so that characterizing the lifecycle of dust in observations and improving the representation of dust in global climate models is necessary. A fundamental aspect of characterizing the dust cycle is quantifying surface dust fluxes, yet no spatially explicit estimates of this flux exist for the World’s major source regions. Here we present a novel technique for creating a map of the annual mean emitted dust flux for North Africa based on retrievals of dust storm frequency from the Meteosat Second Generation Spinning Enhanced Visible and InfraRed Imager (SEVIRI) and the relationship between dust storm frequency and emitted mass flux derived from the output of five models that simulate dust. Our results suggest that 64 (±16)% of all dust emitted from North Africa is from the Bodélé depression, and that 13 (±3)% of the North African dust flux is from a depression lying in the lee of the Aïr and Hoggar Mountains, making this area the second most important region of emission within North Africa.
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  • 6
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    Evaluating machine learning and statistical prediction techniques for landslide susceptibility modeling (2015)
    Elsevier
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    Publication Date: 2022-09-23
    Description: Highlights • We modeled landslide susceptibility with statistical and machine learning techniques. • We evaluate performance, predictor importance, and visual appearance of susceptibility maps. • Differences in model prediction performance were for the majority non-significant. • Consequently, landslide modelers may consider selecting modeling techniques based on additional practical criteria. Statistical and now machine learning prediction methods have been gaining popularity in the field of landslide susceptibility modeling. Particularly, these data driven approaches show promise when tackling the challenge of mapping landslide prone areas for large regions, which may not have sufficient geotechnical data to conduct physically-based methods. Currently, there is no best method for empirical susceptibility modeling. Therefore, this study presents a comparison of traditional statistical and novel machine learning models applied for regional scale landslide susceptibility modeling. These methods were evaluated by spatial k-fold cross-validation estimation of the predictive performance, assessment of variable importance for gaining insights into model behavior and by the appearance of the prediction (i.e. susceptibility) map. The modeling techniques applied were logistic regression (GLM), generalized additive models (GAM), weights of evidence (WOE), the support vector machine (SVM), random forest classification (RF), and bootstrap aggregated classification trees (bundling) with penalized discriminant analysis (BPLDA). These modeling methods were tested for three areas in the province of Lower Austria, Austria. The areas are characterized by different geological and morphological settings. Random forest and bundling classification techniques had the overall best predictive performances. However, the performances of all modeling techniques were for the majority not significantly different from each other; depending on the areas of interest, the overall median estimated area under the receiver operating characteristic curve (AUROC) differences ranged from 2.9 to 8.9 percentage points. The overall median estimated true positive rate (TPR) measured at a 10% false positive rate (FPR) differences ranged from 11 to 15pp. The relative importance of each predictor was generally different between the modeling methods. However, slope angle, surface roughness and plan curvature were consistently highly ranked variables. The prediction methods that create splits in the predictors (RF, BPLDA and WOE) resulted in heterogeneous prediction maps full of spatial artifacts. In contrast, the GAM, GLM and SVM produced smooth prediction surfaces. Overall, it is suggested that the framework of this model evaluation approach can be applied to assist in selection of a suitable landslide susceptibility modeling technique.
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  • 7
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    Diatom silicon isotopes as a proxy for silicic acid utilisation : a Southern Ocean core top calibration (2015)
    Elsevier
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    Publication Date: 2022-05-26
    Description: © The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geochimica et Cosmochimica Acta 96 (2012): 174-192, doi:10.1016/j.gca.2012.08.002.
    Description: Despite a growing body of work that uses diatom δ30Si to reconstruct past changes in silicic acid utilisation, few studies have focused on calibrating core top data with modern oceanographic conditions. In this study, a microfiltration technique is used to divide Southern Ocean core top silica into narrow size ranges, separating components such as radiolaria, sponge spicules and clay minerals from diatoms. Silicon isotope analysis of these components demonstrates that inclusion of small amounts of non-diatom material can significantly offset the measured from the true diatom δ30Si. Once the correct size fraction is selected (generally 2–20 μm), diatom δ30Si shows a strong negative correlation with surface water silicic acid concentration (R2 = 0.92), highly supportive of the qualitative use of diatom δ30Si as a proxy for silicic acid utilisation. The core top diatom δ30Si matches well with mixed layer filtered diatom δ30Si from published in situ studies, suggesting little to no effect of either dissolution on export through the water column, or early diagenesis, on diatom δ30Si in sediments from the Southern Ocean. However, the core top diatom δ30Si shows a poor fit to simple Rayleigh or steady state models of the Southern Ocean when a single source term is used. The data can instead be described by these models only when variations in the initial conditions of upwelled silicic acid concentration and δ30Si are taken into account, a caveat which may introduce some error into quantitative reconstructions of past silicic acid utilisation from diatom δ30Si.
    Description: The Oxford isotope geochemistry lab is supported by an ERC grant to Halliday. This work was carried out as part of Natural Environmental Research Council (NERC) Grant NE/F005296/1, and Antarctic Peninsula core tops collected thanks to the Antarctic Funding Initiative Grant AFI4-02.
    Repository Name: Woods Hole Open Access Server
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  • 8
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    Genealogical analyses of multiple loci of litostomatean ciliates (Protista, Ciliophora, Litostomatea) (2015)
    Elsevier
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    Publication Date: 2022-05-26
    Description: © The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Molecular Phylogenetics and Evolution 66 (2012): 397-411, doi:10.1016/j.ympev.2012.06.024.
    Description: The class Litostomatea is a highly diverse ciliate taxon comprising hundreds of free-living and endocommensal species. However, their traditional morphology-based classification conflicts with 18S rRNA gene phylogenies indicating (1) a deep bifurcation of the Litostomatea into Rhynchostomatia and Haptoria + Trichostomatia, and (2) body polarization and simplification of the oral apparatus as main evolutionary trends in the Litostomatea. To test whether 18S rRNA molecules provide a suitable proxy for litostomatean evolutionary history, we used eighteen new ITS1-5.8S rRNA-ITS2 region sequences from various free-living litostomatean orders. These single- and multiple-locus analyses are in agreement with previous 18S rRNA gene phylogenies, supporting that both 18S rRNA gene and ITS region sequences are effective tools for resolving phylogenetic relationships among the litostomateans. Despite insertions, deletions and mutational saturations in the ITS region, the present study shows that ITS1 and ITS2 molecules can be used to infer phylogenetic relationships not only at species level but also at higher taxonomic ranks when their secondary structure information is utilized to aid alignment.
    Description: Financial support was provided by the Austrian Science Foundation (FWF Projects P-19699-B17 and P-20360-B17 to Wilhelm Foissner), the Slovak Scientific Grant Agency (VEGA Project 1/0600/11 to Peter Vd’ačný), and US NSF Grants (Projects MCB-0348341 and DEB-0816840 to Slava S. Epstein).
    Keywords: Body polarization ; ITS1-5.8S rRNA-ITS2 region sequences ; Motif ; Oral simplification ; Secondary structure
    Repository Name: Woods Hole Open Access Server
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  • 9
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    Comparison of the physical and geotechnical properties of gas-hydrate-bearing sediments from offshore India and other gas-hydrate-reservoir systems (2015)
    Elsevier
    Details
    Publication Date: 2022-05-26
    Description: This paper is not subject to U.S. copyright. The definitive version was published in Marine and Petroleum Geology 58A (2014): 139-167, doi:10.1016/j.marpetgeo.2014.07.024.
    Description: The sediment characteristics of hydrate-bearing reservoirs profoundly affect the formation, distribution, and morphology of gas hydrate. The presence and type of gas, porewater chemistry, fluid migration, and subbottom temperature may govern the hydrate formation process, but it is the host sediment that commonly dictates final hydrate habit, and whether hydrate may be economically developed. In this paper, the physical properties of hydrate-bearing regions offshore eastern India (Krishna-Godavari and Mahanadi Basins) and the Andaman Islands, determined from Expedition NGHP-01 cores, are compared to each other, well logs, and published results of other hydrate reservoirs. Properties from the hydrate-free Kerala-Konkan basin off the west coast of India are also presented. Coarser-grained reservoirs (permafrost-related and marine) may contain high gas-hydrate-pore saturations, while finer-grained reservoirs may contain low-saturation disseminated or more complex gas-hydrates, including nodules, layers, and high-angle planar and rotational veins. However, even in these fine-grained sediments, gas hydrate preferentially forms in coarser sediment or fractures, when present. The presence of hydrate in conjunction with other geologic processes may be responsible for sediment porosity being nearly uniform for almost 500 m off the Andaman Islands. Properties of individual NGHP-01 wells and regional trends are discussed in detail. However, comparison of marine and permafrost-related Arctic reservoirs provides insight into the inter-relationships and common traits between physical properties and the morphology of gas-hydrate reservoirs regardless of location. Extrapolation of properties from one location to another also enhances our understanding of gas-hydrate reservoir systems. Grain size and porosity effects on permeability are critical, both locally to trap gas and regionally to provide fluid flow to hydrate reservoirs. Index properties corroborate more advanced consolidation and triaxial strength test results and can be used for predicting behavior in other NGHP-01 regions. Pseudo-overconsolidation is present near the seafloor and is underlain by underconsolidation at depth at some NGHP-01 locations.
    Description: This work was supported by the Coastal and Marine Geology, and Energy Programs of the U.S. Geological Survey. Partial support for this research was provided by Interagency Agreement DE-FE0002911 between the USGS Gas Hydrates Project and the U.S. Department of Energy's Methane Hydrates R&D Program.
    Keywords: Physical properties ; Gas hydrate ; Porosity ; Atterberg limits ; Consolidation ; Permeability ; Shear strength ; Scanning electron microscopy
    Repository Name: Woods Hole Open Access Server
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  • 10
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    Seabirds, gyres and global trends in plastic pollution (2015)
    Elsevier
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    Publication Date: 2022-05-26
    Description: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Environmental Pollution 203 (2015): 89-96, doi:10.1016/j.envpol.2015.02.034.
    Description: Fulmars are effective biological indicators of the abundance of floating plastic marine debris. Long-term data reveal high plastic abundance in the southern North Sea, gradually decreasing to the north at increasing distance from population centres, with lowest levels in high-arctic waters. Since the 1980s, pre-production plastic pellets in North Sea fulmars have decreased by ∼75%, while user plastics varied without a strong overall change. Similar trends were found in net-collected floating plastic debris in the North Atlantic subtropical gyre, with a ∼75% decrease in plastic pellets and no obvious trend in user plastic. The decreases in pellets suggest that changes in litter input are rapidly visible in the environment not only close to presumed sources, but also far from land. Floating plastic debris is rapidly “lost” from the ocean surface to other as-yet undetermined sinks in the marine environment.
    Description: This paper had its origin in the Marine Debris working group convened by the National Center for Ecological Analysis and Synthesis (NCEAS), University of California, Santa Barbara, with support from Ocean Conservancy.
    Keywords: Fulmarus glacialis ; Plastic ingestion ; Marine debris ; North Atlantic subtropical gyre ; Industrial plastic pellets
    Repository Name: Woods Hole Open Access Server
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