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  • 101
    Publication Date: 2019-01-29
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 102
    Publication Date: 2019-01-30
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 103
    Publication Date: 2019-01-30
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 104
    Publication Date: 2019-01-30
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 105
    Publication Date: 2019-01-30
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 106
    Publication Date: 2019-01-29
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  • 107
    Publication Date: 2019-01-30
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 108
    Publication Date: 2019-01-30
    Description: Globally, marine subtidal hard-substrate habitats provide important ecological functions to a variety of sessile and mobile taxa. The southern North Sea is a marine environment with relatively low amounts of hard-substrate areas. Surveys with high taxonomic resolution on the associated hard-substrate epifauna, e.g. by diving observations, are challenging in this region because of strong tidal currents and considerable water depths. Therefore, the characteristics and functions of hard-substrate habitats in the North Sea remain poorly understood. The goal of this study was to extend the knowledge on sessile taxa assemblages in four hard-substrate areas within the German Bight (SE North Sea) using underwater video observations as a straight-forward and visual method to obtain and process detailed data on seafloor characteristics. Still images from drift videos were analyzed to determine the epifaunal assemblages attached to the stones on a presence/absence scale. A subsample of cobbles, boulders and large boulders was further investigated to derive quantitative data on the colonized area for each taxon and stone size. The four areas showed significant differences in sessile taxa richness, with higher numbers of sessile taxa in the deeper far-shore areas than in the shallower nearshore areas, despite a generally high similarity in the sessile animal taxa spectrum. Within the areas, cobbles were mainly dominated by short-lived taxa (〈 5 years) like Spirobranchus triqueter and ascidians, while boulder-sized stones were largely colonized by long-lived taxa (〉 5 years) like Metridium dianthus, Flustra foliacea and Alcyonium digitatum. Most of the stones were typically covered by epifauna by more than 50%. The differences in the sessile taxa spectrum between the areas were interpreted as a consequence of reduced abiotic stress and higher habitat complexity in the far-shore areas. The dominance of short-lived taxa on cobbles, in comparison to long-lived taxa on boulder-sized stones, possibly reflects the frequency of disturbance and the competitiveness of these taxa.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 109
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    PANGAEA
    Publication Date: 2019-01-30
    Description: The purpose of this list of digital platforms is to facilitate the research of scientific data (articles, books, conferences, websites, indexers, etc.) by students of all undergraduate levels. The interface of platforms have similarities and because of this, low degree of difficulty of use. I emphasize that the key to an excellent literature search on digital platforms is to choose the right "keyword".
    Repository Name: EPIC Alfred Wegener Institut
    Type: PANGAEA Documentation , NonPeerReviewed
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  • 110
    Publication Date: 2019-01-30
    Description: Continuing losses of multi-year sea ice (MYI) across the Arctic are causing first-year sea ice (FYI) to dominate the Arctic ice pack. Melting FYI provides a strong seasonal pulse of dissolved organic matter (DOM) into surface waters; however, the biological impact of this DOM input is unknown. Here we show that DOM additions cause important and contrasting changes in under-ice bacterioplankton abundance, production and species composition. Utilization of DOM was influenced by molecular size, with 10–100 kDa and 〉100 kDa DOM fractions promoting rapid growth of particular taxa, while uptake of sulfur and nitrogen-rich low molecular weight organic compounds shifted bacterial community composition. These results demonstrate the ecological impacts of DOM released from melting FYI, with wide-ranging consequences for the cycling of organic matter across regions of the Arctic Ocean transitioning from multi-year to seasonal sea ice as the climate continues to warm.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 111
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    In:  Persoonia - Molecular Phylogeny and Evolution of Fungi (1878-9080) vol.42 (2019) p.36
    Publication Date: 2018-08-17
    Description: Phylogenetic analyses of a combined DNA data matrix containing nuclear small and large subunits (nSSU, nLSU) and mitochondrial small subunit (mtSSU) ribosomal RNA and the largest and second largest subunits of the RNA polymerase II (rpb1, rpb2) of representative Pezizomycotina revealed that the enigmatic genera Xylobotryum and Cirrosporium form an isolated, highly supported phylogenetic lineage within Leotiomyceta. Acknowledging their morphological and phylogenetic distinctness, we describe the new class Xylobotryomycetes, containing the new order Xylobotryales with the two new families Xylobotryaceae and Cirrosporiaceae. The two currently accepted species of Xylobotryum, X. andinum and X. portentosum, are described and illustrated by light and scanning electron microscopy. The generic type species X. andinum is epitypified with a recent collection for which a culture and sequence data are available. Acknowledging the phylogenetic distinctness of Candelariomycetidae from Lecanoromycetes revealed in previous and the current phylogenetic analyses, the new class Candelariomycetes is proposed.
    Keywords: Ascomycota ; Dothideomycetes ; Eurotiomycetes ; five new taxa ; multigene phylogenetic analyses ; pyrenomycetes ; Sordariomycetes
    Repository Name: National Museum of Natural History, Netherlands
    Type: Article / Letter to the editor
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  • 112
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    In:  Persoonia - Molecular Phylogeny and Evolution of Fungi (1878-9080) vol.42 (2019) p.1
    Publication Date: 2018-08-17
    Description: Colletotrichum species are plant pathogens, saprobes, and endophytes on a range of economically important hosts. However, the species occurring on pear remain largely unresolved. To determine the morphology, phylogeny and biology of Colletotrichum species associated with Pyrus plants, a total of 295 samples were collected from cultivated pear species (including P. pyrifolia, P. bretschneideri, and P. communis) from seven major pearcultivation provinces in China. The pear leaves and fruits affected by anthracnose were sampled and subjected to fungus isolation, resulting in a total of 488 Colletotrichum isolates. Phylogenetic analyses based on six loci (ACT, TUB2, CAL, CHS-1, GAPDH, and ITS) coupled with morphology of 90 representative isolates revealed that they belong to 10 known Colletotrichum species, including C. aenigma, C. citricola, C. conoides, C. fioriniae, C. fructicola, C. gloeosporioides, C. karstii, C. plurivorum, C. siamense, C. wuxiense, and two novel species, described here as C. jinshuiense and C. pyrifoliae. Of these, C. fructicola was the most dominant, occurring on P. pyrifolia and P. bretschneideri in all surveyed provinces except in Shandong, where C. siamense was dominant. In contrast, only C. siamense and C. fioriniae were isolated from P. communis, with the former being dominant. In order to prove Koch’s postulates, pathogenicity tests on pear leaves and fruits revealed a broad diversity in pathogenicity and aggressiveness among the species and isolates, of which C. citricola, C. jinshuiense, C. pyrifoliae, and C. conoides appeared to be organ-specific on either leaves or fruits. This study also represents the first reports of C. citricola, C. conoides, C. karstii, C. plurivorum, C. siamense, and C. wuxiense causing anthracnose on pear.
    Keywords: Colletotrichum ; multi-gene phylogeny ; pathogenicity ; Pyrus
    Repository Name: National Museum of Natural History, Netherlands
    Type: Article / Letter to the editor
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  • 113
    Publication Date: 2018-08-27
    Description: In many lichen-forming fungi, molecular phylogenetic analyses lead to the discovery of cryptic species within traditional morphospecies. However, in some cases, molecular sequence data also questions the separation of phenotypically characterised species. Here we apply an integrative taxonomy approach ‒ including morphological, chemical, molecular, and distributional characters ‒ to re-assess species boundaries in a traditionally speciose group of hair lichens, Bryoria sect. Implexae. We sampled multilocus sequence and microsatellite data from 142 specimens from a broad intercontinental distribution. Molecular data included DNA sequences of the standard fungal markers ITS, IGS, GAPDH, two newly tested loci (FRBi15 and FRBi16), and SSR frequencies from 18 microsatellite markers. Datasets were analysed with Bayesian and maximum likelihood phylogenetic reconstruction, phenogram reconstruction, STRUCTURE Bayesian clustering, principal coordinate analysis, haplotype network, and several different species delimitation analyses (ABGD, PTP, GMYC, and DISSECT). Additionally, past population demography and divergence times are estimated. The different approaches to species recognition do not support the monophyly of the 11 currently accepted morphospecies, and rather suggest the reduction of these to four phylogenetic species. Moreover, three of these are relatively recent in origin and cryptic, including phenotypically and chemically variable specimens. Issues regarding the integration of an evolutionary perspective into taxonomic conclusions in species complexes, which have undergone recent diversification, are discussed. The four accepted species, all epitypified by sequenced material, are Bryoria fuscescens, B. glabra, B. kockiana, and B. pseudofuscescens. Ten species rank names are reduced to synonymy. In the absence of molecular data, they can be recorded as the B. fuscescens complex. Intraspecific phenotype plasticity and factors affecting the speciation of different morphospecies in this group of Bryoria are outlined.
    Keywords: chemotypes ; cryptic species ; haplotypes ; incomplete lineage sorting ; integrative taxonomy ; microsatellites ; speciation ; species concepts
    Repository Name: National Museum of Natural History, Netherlands
    Type: Article / Letter to the editor
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  • 114
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    In:  Persoonia - Molecular Phylogeny and Evolution of Fungi (1878-9080) vol.42 (2019) p.50
    Publication Date: 2018-08-31
    Description: Ips typographus (Coleoptera, Scolytinae) is a spruce-infesting bark beetle that occurs throughout Europe and Asia. The beetle can cause considerable damage, especially when colonized trees are stressed and beetle populations increase. Although some studies have shown that populations of I. typographus in Europe, China and Japan are genetically distinct, these populations are biologically similar, including a strong association with ophiostomatoid fungi. To date, only two Leptographium spp. have been reported from the beetle in China, while 40 species have been reported from Europe and 13 from Japan. The aims of this study were to identify the ophiostomatoid fungal associates of I. typographus in north-eastern China, and to determine whether the fungal assemblages reflect the different geographical populations of the beetle. Field surveys in Jilin and Heilongjiang provinces yielded a total of 1 046 fungal isolates from 145 beetles and 178 galleries. Isolates were grouped based on morphology and representatives of each group were identified using DNA sequences of the ribosomal LSU, ITS, β-tubulin, calmodulin and elongation factor 1-α gene regions. A total of 23 species of ophiostomatoid fungi were identified, including 12 previously described species and 11 novel species, all of which are described here. The dominant species were Ophiostoma bicolor, Leptographium taigense and Grosmannia piceiperda D, representing 40.5 %, 27.8 % and 17.8 % of the isolates, respectively. Comparisons of species from China, Europe and Japan are complicated by the fact that some of the European and all the Japanese species were identified based only on morphology. However, assuming that those identifications are correct, five species were shared between Europe, Japan and China, two species were shared between China and Japan, five between Europe and China, and two between Europe and Japan. Consequently, Ips typographus populations in these different geographic areas have different fungal assemblages, suggesting that the majority of these beetle-associations are promiscuous. The results also suggested that the symbionts of the bark beetle do not reflect the population structures of the beetle. The use of fungal symbiont assemblages to infer population structures and invasion history of its vectors should thus be interpreted with circumspection.
    Keywords: 11 new taxa ; Ophiostomatales ; Microascales ; vector ; Scolytinae
    Repository Name: National Museum of Natural History, Netherlands
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  • 115
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    Springer International Publishing
    In:  Fission-Track Thermochronology and its Application to Geology | Springer Textbooks in Earth Sciences, Geography and Environment
    Publication Date: 2018-09-04
    Description: The geomorphologic evolution of orogens has been a subject of revived interest and accelerated development over the past few decades, thanks to both the increasing availability of high-resolution data and computing power and the realisation that orogenic topography plays a central role in coupling deep-earth and surface processes. Low-temperature thermochronology takes a central place in this revived interest, as it allows us to link quantitative geomorphology to the spatial and temporal patterns of exhumation. In particular, rock cooling rates over million-year timescales derived from thermochronological data have been used to reconstruct rock exhumation histories, to detect km-scale relief changes, and to document lateral shifts in relief. In this chapter, we review how classic approaches of determining exhumation histories have contributed to our understanding of landscape evolution, and we highlight novel approaches to quantifying relief changes that have been developed over the last decade. We discuss how patterns of exhumation in laterally accreting orogens are recorded by low-temperature thermochronology, and how such data can be applied to infer temporal variations in exhumation rates, providing indirect constraints on topographic development. We subsequently review recent studies aimed at quantifying relief development and modification associated with river incision, glacial modifications of landscapes, and shifts in the position of range divides. We also point out how interpretations of some datasets are non-unique, emphasizing the importance of understanding the full range of processes that may influence landscape morphology and how each may affect spatial patterns of thermochronologic ages.
    Language: English
    Type: http://purl.org/eprint/type/BookItem
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  • 116
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    Springer
    In:  Karst Water Environment : Advances in Research, Management and Policy | The Handbook of Environmental Chemistry
    Publication Date: 2018-09-11
    Description: Examination of microbial communities within karst aquifers is an important aspect of determining the quality of the drinking water obtained from groundwater. While past work has been based on culture-based assays, a more complete view of the microbial community within karst aquifers can be achieved using molecular approaches based on DNA sequencing. Due to a reduced cell number when compared to surface environments, collecting sufficient microbial cells for analysis in karst aquifers can be problematic. In addition to issues of cell density, particulates due to the geologic location, technological limitations of equipment that can be hand-carried and work for extended periods underground, and even the physical access to some of these subsurface sites, all contribute to making examination of the microbiology in karst aquifers a challenge. This chapter highlights some of the approaches we have used to successfully isolate microbial cells for DNA extraction from an aquifer accessed in a remote cave location. The methods we developed can aid other researchers to evaluate the microbiology of similar isolated karst aquifers.
    Language: English
    Type: http://purl.org/eprint/type/BookItem
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  • 117
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    Elsevier
    In:  In: Encyclopedia of Ecology. , ed. by Fath, B. D. Elsevier, Oxford, UK, pp. 108-115. 2. ed. ISBN 978-0-444-63768-0
    Publication Date: 2018-10-16
    Type: Book chapter , NonPeerReviewed
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  • 118
    Publication Date: 2018-10-23
    Description: Highlights • New 40Ar/39Ar dates from SW Pacific and Zealandia igneous rocks form the basis of a revised tectonic model. • Intraplate lavas erupted onto continental, LIP and oceanic crust from 99 to 78 Ma. • Spreading ridges and transforms adjusted themselves around a collided Hikurangi Plateau. • Kinematically stable Pacific-Antarctic spreading became established from c. 84 Ma. • Osbourn Trough Sea floor spreading possibly ceased at c. 79 Ma. Abstract New 40Ar/39Ar ages of igneous rocks clarify the nature, timing and rates of movement of the oceanic Pacific, Phoenix, Farallon and Hikurangi plates against Gondwana and Zealandia in the Late Cretaceous. With some qualifications, cessation of spreading at the Osbourn Trough is dated c. 79 Ma, i.e. 30–20 m.y. later than 110–100 Ma Hikurangi Plateau-Gondwana collision. Oceanic crust of pre-84 Ma is confirmed to be present at the eastern end of the Chatham Rise, and a 99–78 Ma intraplate lava province erupted across juxtaposed Zealandia, Hikurangi Plateau and oceanic crust. We propose a new regional tectonic model in which a mechanically jammed Hikurangi Plateau resulted in the dynamic propagation of small, kinematically misaligned short-length 110–84 Ma spreading centres and long-offset fracture zones. It is only from c. 84 Ma that geometrically stable spreading became localized at what is now the Pacific-Antarctic Ridge, as Zealandia started to split from Gondwana.
    Type: Article , PeerReviewed
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  • 119
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    Taylor & Francis Group
    In:  The Anthropocene Debate and Political Science | Routledge Research in Global Environmental Governance
    Publication Date: 2018-10-23
    Language: English
    Type: http://purl.org/eprint/type/BookItem
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  • 120
    Publication Date: 2018-10-26
    Description: After Rock-Eval & TOC screening and heterogeneity evaluation on 91 Palaeogene source rock samples from a well drilled in the Austrian Molasse Basin, ten shale samples were selected for detailed investigations by means of pyrolysis-gas chromatography, bulk kinetics and biomarker identification and quantification. Afterwards, 2-D biplots based on principal component analysis were applied to unravel the palaeo-environmental control on the development of petroleum source rocks. All samples are immature source rocks with good petroleum generation potentials. The redox environment during deposition was generally reducing, and palaeosalinity is suggested to be the main factor causing the differences in organic carbon contents among the samples. The hydrogen index values, the gas generation preferences and the aromaticity of the products are controlled by both depositional environment and precursors, and the product of a salinity indicator (MTTC) and the oleanane index is introduced as predictive proxy to evaluate these features. The maturity indicator (Tmax) is revealed as dominated by the stability of the kerogen structure which is controlled by the proportion of organic sulphur compounds in the kerogen. The global Eocene-Oligocene climate change from a greenhouse to an icehouse world is suggested to play an important role in changing the palaeoenvironment and further in influencing the development of petroleum source rocks by triggering upwelling, increasing the palaeo-sea water salinity and decreasing the deposition of carbonate-minerals. The chemometric method suggested here acts as a powerful tool in identifying the controlling factors for the petroleum generation potential among many variables, and can be applied more widely in petroleum geology when multi-parameters are involved to get quick and meaningful correlations.
    Language: English
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 121
    Publication Date: 2018-10-29
    Description: There is increasing evidence that abrupt vegetation shifts and large-scale erosive phases occurred in Central Africa during the third millennium before present. Debate exists as to whether these events were caused by climate change and/or intensifying human activities related to the Bantu expansion. In this study, we report on a multi-proxy investigation of a sediment core (KZR-23) recovered from the Congo submarine canyon. Our aim was to reconstruct climate, erosion and vegetation patterns in the Congo Basin for the last 10,000yrs, with a particular emphasis on the late Holocene period. Samples of modern riverine suspended particulates were also analyzedto characterize sediment source geochemical signatures from across the Congo watershed. We find that a sudden increase of bulk sediment aluminium-to-potassium (Al/K) ratios and initial radiocarbon ages of bulk organic matter occurred after 2,200yrs ago, coincident with a pollen-inferred vegetation change suggesting forest retreat and development of savannas. Although hydrogen isotope compositions of plant waxes (δDwax) do not reveal a substantial hydroclimate shift during this period, neodymium isotopes and rare earth elements in detrital fractions indicate provenance changes for the sediment exported from the Congo Basin at that time, hence suggesting a reorganization of spatial rainfall patterns across Central Africa during this event. Taken together, these findings provide evidence for changing landscapes in Central Africa from about 2,200yrs ago, associated with synchronous events of vegetation changes and enhanced erosion of pre-aged and highly weathered soils. These events coincided remarkably well with the arrival of Iron Age communities into the rainforest, as inferred from comparison to regional archaeological syntheses. While the human impact on the environment remains difficult to quantify at the scale of the vast Congo Basin, we tentatively propose that strengthening of El Niño-Southern Oscillation (ENSO) variability at that time played a key role in triggering the observed environmental changes, and possibly acted as a driver for the eastward migration of Bantu-speaking peoples across Central Africa.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 122
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    In:  CASI
    Publication Date: 2018-10-17
    Description: NASA has developed and commercialized high temperature coatings and bearings for extreme conditions. These technologies are now under consideration by industry for automotive applications such as turbochargers, fuel cell compressors and exhaust gas path mechanism applications. In this presentation, a review of Oil-Free technologies and their current state-of-development is introduced. Key NASA contributions to the field as documented by patents, research papers and technology demonstrations is also presented.
    Keywords: Mechanical Engineering
    Type: GRC-E-DAA-TN50940 , Schaeffler International Bearing Meeting; 25 Jan. 2018; Herzogenaurach; Germany
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  • 123
    Publication Date: 2018-11-02
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  • 124
    Publication Date: 2018-10-30
    Description: Highlights • New 40Ar/39Ar age and geochemical (major, trace element, Sr-Nd-Pb-Hf isotope) data are presented from the Walvis Ridge, belonging to the Tristan-Gough hotspot track in the South Atlantic. • The entire Tristan-Gough hotspot system, including Walvis Ridge, display a spatially continuous age progression. • The Gough-type component is the dominant geochemical flavor of the Tristan-Gough plume and has also been identified in the Discovery and Shona hotspot systems. • The geochemical heterogeneity in the South Atlantic DUPAL region can be reproduced by mixing of Gough-type enriched mantle with continental crust and a FOZO/PREMA-like component. • The HIMU-type alkalic lavas on the Walvis Ridge and older part of Shona hotspot track are ∼30 Ma younger in age than the EMI-type primarily tholeiitic basement lavas at a given locality. Abstract Long-lived spatial geochemical zonation of the Tristan-Gough and Discovery hotspot tracks and temporal variations from EMI-type basement to HIMU-type late-stage volcanism at the Walvis Ridge and Shona hotspot tracks point to a complex evolution and multiple source areas for the South Atlantic hotspots. Here we report 40Ar/39Ar age and geochemical (major and trace element, Sr-Nd-Pb-Hf isotope) data for samples from 16 new sites on the Walvis Ridge. This aseismic ridge is the oldest submarine expression of the Tristan-Gough mantle plume and represents the initial reference locality of the EMI end member in the South Atlantic Ocean. The EMI-type lavas display an excellent age progressive trend of ∼31 mm/a along the entire Tristan-Gough hotspot track, indicating constant plate motion over a relatively stationary melt anomaly over the last ∼115 Ma. The Gough-type EMI composition of the Tristan-Gough hotspot track is the dominant composition on the 〉70 Ma part of the Walvis Ridge, the Etendeka and Parana flood basalts, and along the Gough sub-track, extending from DSDP Site 525A on the SW Walvis Ridge to Gough Island, whereas Tristan-type EMI dominates on the Tristan Track, extending from DSDP Sites 527 and 528 to Tristan da Cunha Island. Gough-type EMI is also the dominant composition of the northern Discovery and Shona hotspot tracks, suggesting that these hotspots tap a common source reservoir. The continuous EMI-type supply over ≥132 Ma, coupled with high 3He/4He (〉10 RA), points to a deep-seated reservoir for this mantle material. The Tristan and Southern Discovery EMI-type flavors can be reproduced by mixing of the Gough-type component with (1) FOZO/PREMA to produce Tristan-type lavas, and (2) marine sediments or upper continental crust to generate the Southern Discovery-type composition. South Atlantic hotspots with EMI-type compositions overlie the margin (1 % ∂Vs velocity contour) of the African Large Low Shear Velocity Province (LLSVP), which may promote the emergence of geochemical “zonation”. The St. Helena HIMU-type volcanism, however, is located above internal portions of the LLSVP, possibly reflecting a layered LLSVP.
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  • 125
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    Elsevier
    In:  Journal of Petroleum Science and Engineering, 172 . pp. 855-877.
    Publication Date: 2018-10-29
    Description: Gas hydrates are crystalline ice-like structures formed from water and gas molecules at high pressure and low temperature conditions. They are considered as near-future energy resources. Recently, there have been many drilling activities in gas hydrates in both permafrost regions (mainly Mallik wells, Canada; Ignik Sikumi #1 well, Alaska; Mount Elbert #1, Alaska) and marine sediments (the wells drilled in Gulf of Mexico and India drilling expeditions). In this study, it is aimed to evaluate and analyze logging-while drilling data (LWD) and other drilling data of these drilling activities. Initially, all drilling parameters (i.e. rate of penetration, weight on bit, torques, mud logs, etc.) of these wells were collected and drawn to see the change in parameters with depths. In order to indicate the changes in drilling parameters in the sediments containing gas hydrates, gas hydrate saturations were estimated from resistivity logs and NMR logs in this study. High resistivity log values and methane peaks in drilling fluid were good indicators of gas hydrate existence. During the drilling of permafrost formations and gas hydrates deposited in coarse sands as pore filling, the rate of penetration generally decreased. Differently, there was not almost any change in the rate of penetration during the drilling of fracture-filling gas hydrates within silts/clay in India. Borehole enlargements (washouts) were commonly seen in the wells drilled in marine sediments (Gulf of Mexico and Indian expeditions). However, this effect was minimum during the drilling of the wells in permafrost regions. This difference is due to the loose sediments in marine environment. Furthermore, gamma and density logs were seriously affected by washouts, mainly in marine sediments. It was observed that pore-filling gas hydrates affect the rate of penetration and keep the sediments stable because well collapses mainly occurred in the sediments without any gas hydrates. However, the temperature of drilling fluid should be close to the temperature of gas hydrate zones to reduce the effect of drilling on gas hydrate dissociation for the wells both in permafrost and marine sediments. In Gulf Mexico and Indian drilling expeditions, riser and wellhead equipment were not used. However, the usage of surface casing might decrease the risk of borehole collapses due to very loose sediments close to sea floor. Another important outcome of this study is that the pressure gradient follows hydrostatic pressure gradients according to the pressure analysis within gas hydrate stability zones of marine sediments. Finally, the analyses of drilling parameters revealed that drilling through gas hydrate bearing strata is not as risky as it might have been considered. The key is hidden in appropriate drilling design.
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  • 126
    Publication Date: 2018-10-29
    Description: Highlights • Thermodynamic and kinetic influences of NaCl on HFC-125a hydrate were investigated. • NaCl enrichment in the unconverted solution resulted in a lower conversion. • The presence of NaCl had little effect on the ΔH of HFC-125a hydrate. • The hydrate dissociation was retarded due to the formation of NaCl⋅2H2O. In this study, HFC-125a was selected as a hydrate-forming guest for gas hydrate-based desalination. The thermodynamic and kinetic effects of NaCl on HFC-125a hydrates were investigated with a primary focus on phase equilibria, gas uptake, dissociation enthalpy, and dissociation behavior. The equilibrium curve of HFC-125a hydrate shifted to higher pressure regions at any given temperature depending on the concentration of NaCl. The presence of NaCl also reduced the gas uptake and conversion to hydrates, because of the enrichment of NaCl in the solution during gas-hydrate formation. Even though NaCl did not affect the dissociation enthalpy of the HFC-125a hydrate, the thermograms obtained using a high-pressure micro-differential scanning calorimeter (HP μ-DSC) demonstrated that HFC-125a + NaCl hydrates started to dissociate at lower temperatures due to NaCl in unconverted solutions. Rietveld refinement of powder X-ray diffraction (PXRD) patterns indicated that the HFC-125a hydrate (sII) was transformed into Ih as it dissociated. The dissociation of HFC-125a + NaCl hydrates was retarded and completely ended at higher temperatures compared to the pure HFC-125a hydrate by the sodium chloride dihydrate (NaCl⋅2H2O). Overall, these results could facilitate a better understanding of HFC-125a hydrates in the presence of NaCl; further, they might also be useful in the design and operation of hydrate-based desalination plants using HFC-125a.
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  • 127
    Publication Date: 2018-11-08
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 128
    Publication Date: 2018-11-09
    Description: Multiple toxic and bioactive compounds produced by Alexandrium spp. cause adverse effects on bivalves, but these effects are frequently difficult to attribute to a single compound class. To disentangle the effect of neurotoxic vs lytic secondary metabolites, we exposed blue mussels to either a paralytic shellfish toxin (PST) producing Alexandrium spp. strain, or to an exclusively lytic compound (LC) producing strain, or a strain containing both compound classes, to evaluate the time dependent effects after 3 and 7 days of feeding. Tested parameters comprised signs of paralysis, feeding activity, and immune cell integrity (hemocyte numbers and viability; lysosomal membrane destabilization) and function (ROS production). Both compound classes caused paralysis and immune impairment. The only effect attributable exclusively to PST was increased phagocytic activity after 3 days and impaired feeding activity after 7 days, which curtailed toxin accumulation in digestive glands. Paralysis signals and lysosomal membrane destabilization were more closely, but not exclusively, matched with LC exposure. Effects on circulating hemocyte integrity and immune related functions were mostly transient or remain stable within 7 days; except for increased lysosomal labialization and decreased extracellular ROS production when mussels were exposed to the toxin combination. M. edulis displays adaptive fitness traits to survive and maintain immune capacity upon prolonged exposure to environmentally relevant concentrations of PST and/or LC producing Alexandrium strains.
    Repository Name: EPIC Alfred Wegener Institut
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  • 129
    Publication Date: 2018-11-06
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 130
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    Elsevier
    In:  Multiple stressors in river ecosystems. Status, impacts and prospects for the future
    Publication Date: 2018-11-07
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  • 131
    Publication Date: 2018-11-12
    Description: We present a transport-reaction model (TRACTION) specifically designed to account for non-ideal transport effects in the presence of thermodynamic (e.g. salinity or temperature) gradients. The model relies on the most fundamental concept of solute diffusion, which states that the chemical potential gradient (Maxwell’s model) rather than the concentration gradient (Fick’s law) is the driving force for diffusion. In turn, this requires accounting for species interactions by applying Pitzer’s method to derive species chemical potentials and Onsager coefficients instead of using the classical diffusion coefficients. Electrical imbalances arising from varying diffusive fluxes in multicomponent systems, like seawater, are avoided by applying an electrostatic gradient as an additional transport contribution. We apply the model to pore water data derived from the seawater mixing zone at the submarine Mercator mud volcano in the Gulf of Cadiz. Two features are particularly striking at this site: (i) Ascending halite-saturated fluids create strong salinity (NaCl) gradients in the seawater mixing zone that result in marked chemical activity, and thus chemical potential gradients. The model predicts strong transport-driven deviations from the mixing profile derived from the commonly used Fick’s diffusion model, and is capable of matching well with the profile shapes observed in the pore water concentration data. Even better agreement to the observed data is achieved when ion pairs are transported separately. (ii) The formation of authigenic gypsum (several wt%) occurs in the surface sediments, which is typically restricted to evaporitic surface processes. Very little is known about the gypsum paragenesis in the subseafloor and we first present possible controls on gypsum solubility, such as pressure, temperature, and salinity (pTS), as well as the common ion and ion pairing effects. Due to leaching of deep diapiric salt, rising fluids of the MMV are saturated with respect to gypsum (as well as celestite and barite). Several processes that could drive these fluids towards gypsum supersaturation and hence precipitation were postulated and numerically quantified. In line with the varied morphology of the observed gypsum crystals, gypsum paragenesis at the MMV is likely a combination of two temperature-related processes. Gypsum solubility increases with increasing temperature, especially in strong electrolyte solutions and the first mechanism involves the cooling of saturated fluids along the geothermal gradient during their ascent. Secondly, local temperature changes, i.e. cooling during the transition from MMV activity towards dormancy results in the cyclic build-up of gypsum. The model showed that the interpretation of field data can be majorly misguided when ignoring non-ideal effects in extreme diagenetic settings. While at first glance the pore water profiles at the Mercator mud volcano would indicate strong reactive influences in the seawater mixing zone, our model shows that the observed species distributions are in fact primarily transport-controlled. The model results for SO4 are particularly intriguing, as SO4 is shown to diffuse into the sediment along its increasing (!) concentration gradient. Also, a pronounced gypsum saturation peak can be observed in the seawater mixing zone. This peak is not related to the dissolution of gypsum but is simply a result of the non-ideal transport forces acting on the activity profile of SO4 and Ca profiles.
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  • 132
    Publication Date: 2018-11-14
    Description: This study contributes to the understanding of long- and short-term determinants of cooperation among water users. We experimentally investigate the potential of water users’ self-governance in enhancing their contributions to a common pool as opposed to external regulation. Our focus is on the irrigated areas of Kazakhstan and Uzbekistan. Due to their Soviet past, these countries have a reputation for low bottom-up cooperation potential. Based on the different pre-Soviet irrigation traditions of the two study sites, we assess the effectiveness of short-term incentives compared to long term cultural factors of cooperation. History might matter, but we find it does not predetermine the success of current water decentralization in ancient as compared to relatively recently established irrigation sites. Our study reveals that external regulation, in fact, decreases farmers’ cooperation, whereas face-to-face communication increases it. This finding calls into question the top-down approach prevalent in current water policies of the region. Moreover, it suggests the viability of endogenous cooperation and hence encourages the implementation of truly self-governed water management policies in Central Asia. However, the substantial heterogeneity in individual contributions apparent at the village level also signals a warning that one-size-fits-all approaches to local cooperation are unlikely to succeed.
    Keywords: ddc:330 ; Water-management ; Self-governance ; Field experiment ; Cultural determinants ; Central Asia
    Repository Name: EconStor: OA server of the German National Library of Economics - Leibniz Information Centre for Economics
    Language: English
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  • 133
    Publication Date: 2018-11-13
    Description: Among the most derived calanoid copepod superfamily Clausocalanoidea about half of the genera belong to the so-called “Bradfordian” families that are defined by the presence of sensory setae at the maxilla and maxilliped. Many of these “Bradfordian” taxa are insufficiently well described, because their taxonomy is complicated and phylogenetic relationships are not completely resolved. We therefore aimed to unravel their phylogenetic relationships using molecular multi-gene analyses. We conducted molecular multi-gene analysis on 26 species from 15 genera representing all seven “Bradfordian” families using five gene fragments, the nuclear ribosomal 18S, 28S and internal transcribed spacer 2 DNA, and mitochondrial cytochrome c oxidase subunit I and cytochrome b. The monophyly of “Bradfordians” as one lineage in the superfamily Clausocalanoidea was supported by Maximum Likelihood and Bayesian Inference multi-gene analyses. Except for the support of species belonging to the same genus and specimens belonging to the same species, no phylogenetic relationships among genera and families were supported. The impossibility of resolving phylogenetic relationships among “Bradfordian” genera and families may be due to the young age or fast radiation of “Bradfordians” within the mostly derived calanoid superfamily Clausocalanoidea. Therefore, mutation rates might be not sufficient to track phylogenetic relationships. Evidence on phylogenetic relationships between genera and families remain unresolved after implementing integrated morphological and molecular taxonomic approaches.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 134
    Publication Date: 2018-11-20
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 135
    Publication Date: 2018-11-20
    Description: Atlantic cod (Gadus morhua) is an important recreational and commercial fisheries target species in the Northern hemisphere. Release rates are high in the recreational fishery due to regulatory and voluntary catch-and-release practice. Although post-release mortality of cod is relatively low, there is potential for further reductions. The most effective way to reduce post-release mortality is to minimize the catch of sublegal fish or non-target species and to reduce hooking injuries by using more selective fishing methods. This study investigated the influence of the lure/bait type on: (1) size of fish, (2) catch and harvest, (3) proportion of bycatch, (4) hooking location, and (5) injury (bleeding) in the western Baltic Sea recreational cod fishery. Data were collected via random onboard sampling of 35 charter vessel angling trips (778 anglers) and during two supplementary studies in the western Baltic Sea. Overall, the median total length was significantly higher for cod caught on artificial lures (39 cm) than for cod caught on natural bait (28 cm), leading to a 43% higher proportion of sublegal (〈38 cm) cod for bait than for lure. Median catch-per-unit-efforts (number of captured cod per angling hour) did not differ significantly between lure and bait angling (both: 0.49 cod per hour), whereas the median harvest-per-unit-effort (number of captured cod ≥ minimum landing size (38 cm) per angling hour) was significantly higher for lure (0.24 cod ≥38 cm per hour) than for bait angling (0.06 cod ≥38 cm per hour). The incidence of deep hooking and severe bleeding was significantly higher for bait angling. Furthermore, bait angling significantly increased bycatch of other species dominated by whiting (Merlangius merlangus) and European flounder (Platichthys flesus). Cod anglers can reduce the catch of sublegal cod and non-target species and minimize hooking injuries of released fish by using lures instead of bait in the western Baltic Sea. Thus, voluntary terminal gear recommendations may be an effective tool for anglers and managers to increase selectivity in recreational cod fisheries.
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  • 136
    Publication Date: 2018-11-19
    Description: The present study is based on a series of two-dimensional simple shear numerical simulations of two-phase non-linear viscous materials used to investigate the mechanical behaviour of two-phase aggregates representing partially molten rocks. These simulations couple viscoplastic deformation with dynamic recrystallisation (DRX). The aim of these simulations is to investigate the competition between deformation and recrystallisation, and how they affect the mechanical behaviour and resulting microstructures of the deforming material. We systematically vary the melt to solid rock ratio, the dihedral angle of melt and the ratio of DRX vs. deformation. The results show that the amount of DRX and the dihedral angle have a first-order impact on the bulk rheology and the melt distribution in the aggregate. The numerical results allow defining two regimes, depending on the relative contribution of deformation and DRX: (1) a deformation-dominated regime at high strain rates (i.e., with a low ratio of recrystallisation vs. viscoplastic deformation) and (2) a recrystallisation-dominated regime at low strain rates (i.e., with a high ratio of recrystallisation vs. viscoplastic deformation). The first case results in systems bearing large connected melt pockets whose viscous flow controls the deformation of the aggregate, while disconnected smaller melt pockets develop in models where dynamic recrystallisation dominates. The results of this study allow us to better understand the development of connected melt pockets, which may focus melt flow. The distribution of the melt phase plays a key role in the formation of larger-scale melt-enriched shear bands, which in turn has a direct influence on large-scale convective mantle flow.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 137
    Publication Date: 2018-11-21
    Description: Non-classical nonlinear elasticity in micro-inhomogeneous materials such as rocks and cracked or granular materials leads to a number of phenomena ranging from hysteresis and memory to a transient response of elastic properties to perturbations in dynamic or quasi-static experiments. Dynamic acousto-elastic testing (DAET) provides very detailed observations of some of these phenomena that are still not fully understood in terms of their physical origin. We suggest that the observations of non-classical nonlinear elasticity can be related to the physics of friction. We propose a conceptual model for the nonlinear elasticity based on friction of internal interfaces and the process of contact aging that leads to an increase of friction with increasing contact time. The central element of the model is the continuous interplay between (1) softening that occurs as small-scale damage due to shear motion of internal contacts and (2) stiffening (healing) as a thermally activated process of establishing connections across the contact at the current strain state. Chemical bonds, mineral fibres or capillary bridges are the most likely candidates for the physical nature of these connections. Our model qualitatively describes dynamic softening, hysteresis, slow dynamics and the shape of DAET loops including the absence of cusps and the loop orientation that leads to a stiffening at both maxima and minima of the dynamic strain
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  • 138
    Publication Date: 2018-11-27
    Description: The neodymium isotope proxy has become a valuable tool for the reconstruction of past ocean water mass provenance and mixing. For its accurate application, knowledge about the origin and preservation of Nd in sedimentary archives is crucial. Recently, concerns have emerged regarding the applicability of neodymium isotopes as a conservative palaeo water mass tracer, given potential Nd fluxes from sediments into bottom waters (Abbott et al., 2015a) and inferred relabelling of ocean waters by settling detrital material (Roberts and Piotrowski, 2015). Consequently, a decoupling of water mass provenance and proxy variations may arise. We investigate the mobility of Nd around extreme detrital sedimentation events such as glacial ice rafting pulses and turbidite deposition in the Northeast Atlantic. The constructed records from sediment leachates span extreme Nd isotope variations including volcanic (εNd ∼ 0) and Laurentian (εNd ∼ −27) sources. We find that Nd was released into pore waters from reactive detritus inside some detrital layers during early diagenesis, thereby overprinting any archived bottom water Nd signature and precluding the reconstruction of past water mass provenance during the affected time intervals. However, we do not observe any definite indication of diffusive vertical migration of Nd into adjacent layers. Furthermore, bottom water Nd isotope signatures were not modified to a measurable degree by any potential benthic flux of Nd during the deposition of these detrital sediment layers. Consequently, the Nd isotope composition of the pelagic glacial Northeast Atlantic water masses were resilient to such episodic large detrital fluxes. Apart from extreme local sedimentation events, we confirm the presence of detritally overprinted deep waters north of 47°N during the peak glacial from comparison of Northeast Atlantic depth transects. We furthermore suggest that the sensitivity of deep waters to this overprinting effect increased during periods of reduced Atlantic Meridional Overturning Circulation and elevated ice rafting. Overall, our study demonstrates that a thorough evaluation of the proportion of Nd originating from physical water mass advection versus in situ chemical inputs is crucial for the reliable application of Nd isotopes as a water mass tracer.
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  • 139
    Publication Date: 2018-11-27
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  • 140
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    Springer
    In:  Natural Gas Engines: For Transportation and Power Generation | Energy, Environment, and Sustainability
    Publication Date: 2018-11-29
    Description: Lean-burn natural gas engines can be used to reduce exhaust emissions significantly. However, as the mixture is leaned out, the occurrence of extinction and incomplete combustion increases, resulting in poor performance and stability, as well as elevated levels of unburned hydrocarbon (UHC) and nitrogen oxides (NOx) emissions. The partially stratified charge (PSC) method can be used to mitigate these issues, while extending the lean misfire limit (LML) beyond its equivalent, homogeneous level. In this chapter, the PSC ignition and combustion processes are examined following a comprehensive experimental and numerical approach. Experiments are conducted in an idealized PSC configuration, using a constant volume combustion chamber (CVCC), to identify the principle enabling mechanisms of the PSC methodology. Engine tests conducted in a single-cylinder research engine (SCRE) demonstrate the feasibility of various PSC implementations in improving performance and emission characteristics in real-world settings. Complementary numerical analyses for the CVCC are obtained through large eddy simulations (LES), while Reynolds-averaged Navier–Stokes (RANS) simulations are conducted for SCRE with reduced chemical kinetics. The corresponding simulated results provide additional insights in characterizing the effect of fuel stratification on flame kernel maturation and flame propagation, the interplay between chemistry and turbulence at different overall air–fuel ratios, as well as formation of major pollutant species.
    Language: English
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  • 141
    Publication Date: 2018-11-29
    Description: This paper investigates the interplay between the German incentive regulation and renewable capacity integration. A comprehensive review of the current incentive regulation scheme and its 2016 amendment is first presented. Then, results of ten representative interviews with large-scale distribution system operators are analyzed. Firstly, all necessary grid integration measures could so far be implemented. Secondly, creating proper incentives for intelligent operating equipment to partly substitute conventional grid expansion remains a challenge. Thirdly, the new curtailment regulation of 2016 is welcome, but will not become a substitute for grid expansion as long as renewable integration rates are high. Moreover, the discussions on further improvements to the incentive regulation scheme reveal a distribution conflict between grid operators and grid users.
    Language: English
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  • 142
    Publication Date: 2018-11-28
    Description: Life cycle and reproduction of Calanus hyperboreus were studied during a year of record low ice cover in the southeastern Beaufort Sea. Stages CIV, adult females and CV dominated the overwintering population, suggesting a 2- to 3-year life cycle. Within two spring-summer months in the upper water column females filled their energy reserves before initiating their downward seasonal migration. From February to March, vigorous reproduction (20–65 eggs f−1 d−1) delivered numerous eggs (29 000 eggs m−2) at depth and nauplii N1-N3 (17 000 ind. m−2) in the water column. However, CI copepodite recruitment in May, coincident with the phytoplankton bloom, was modest in Amundsen Gulf compared to sites outside the gulf. Consequently, C. hyperboreus abundance and biomass stagnated throughout summer in Amundsen Gulf. As a mismatch between the first-feeding stages and food was unlikely under the favourable feeding conditions of April-May 2008, predation on the egg and larval stages in late winter presumably limited subsequent recruitment and population growth. Particularly abundant in Amundsen Gulf, the copepods Metridia longa and C. glacialis were likely important consumers of C. hyperboreus eggs and nauplii. With the ongoing climate-driven lengthening of the ice-free season, intensification of top-down control of C. hyperboreus recruitment by thriving populations of mesopelagic omnivores and carnivores like M. longa may counteract the potential benefits of increased primary production over the Arctic shelves margins for this key prey of pelagic fish, seabirds and the bowhead whale.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 143
    Publication Date: 2018-11-28
    Description: Protodunes emerge from a flat sand bed at the upwind margin of White Sands Dune Field, and, over several hundred meters, transition into fully developed dunes. Here, we investigate spatial and temporal changes in topography across this transition from 2007 to 2016 using lidar-derived topography, structure-from-motion-derived topography, and RTK GPS. We characterize the deposits present in 2015 using ground penetrating radar. Symmetric protodunes give way downwind to an asymmetric protodune at the transition to slipface development. Between 2007 and 2016, protodune amplitude increased from 0.2 m to 4.0 m, migration rate increased from 3.2 m/yr to 6.1 m/yr, and wavelength increased from 76 m to 122 m. Ground-penetrating radar surveys show strata between flat and 15° make up the stratigraphic architecture of the protodunes. Strata increase in steepness commensurate with an increase in amplitude. Decimeter accumulations of low-angle strata associated with initial protodune stages give way to 4 m of accumulation composed of sets up to 1 m thick prior to slipface development. Topsets present in the thickest sets indicate near critical angles of bedform climb. Growth and slipface development occur by aerodynamic sand trapping and protodune merging. Changes in asymmetry erase initial slipfaces prior to permanent slipface development, after which efficient sand trapping and scour promotes the transition to a dune across 20 m in 5 years. Protodune stratification has hallmarks of sandsheet stratification and can be appreciated within the greater suite of processes that create low-angle eolian stratification found in modern and ancient environments.
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  • 144
    Publication Date: 2018-11-29
    Description: Germany’s ambition to promote sustainable energy globally, on the basis of its own “Energiewende,” has led to the development of a multi-faceted international energy transition policy with various activities and an agenda to promote renewables and energy efficiency abroad. While domestic energy policy developments in Germany have received substantial attention in research and public debate, this is still less true for the country’s international energy transition policy. With the new German government’s program now having taken shape and implementation starting, it is time to assess the foundations and likely direction of and the most relevant challenges for Germany’s efforts to promote sustainable energy internationally. This perspective article takes a look at the aspects shaping Germany’s outreach to partner countries outside the EU to promote sustainable energy and addresses open questions related to its agenda. Germany’s international energy transition policy builds on a longstanding track record, but in order to maintain credibility and visibility in leadership for sustainable energy, two key challenges remain: setbacks in domestic climate mitigation efforts are putting into question claims for climate leadership and struggles to expand the Energiewende beyond the electricity sector require a new spin to international collaboration efforts, more and more directed toward bidirectional exchange and mutual learning.
    Language: English
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  • 145
    Publication Date: 2018-12-04
    Description: Phylogenetic and taxonomic studies on the brown-rot fungi Postia and related genera, are carried out. Phylogenies of these fungi are reconstructed with multiple loci DNA sequences including the internal transcribed spacer regions (ITS), the large subunit (nLSU) and the small subunit (nSSU) of nuclear ribosomal RNA gene, the small subunit of mitochondrial rRNA gene (mtSSU), the translation elongation factor 1-α gene (TEF1), the largest subunit of RNA polymerase II (RPB1) and the second subunit of RNA polymerase II (RPB2). Ten distinct clades of Postia s.lat. are recognized. Four new genera, Amaropostia, Calcipostia, Cystidiopostia and Fuscopostia, are established, and nine new species, Amaropostia hainanensis, Cyanosporus fusiformis, C. microporus, C. mongolicus, C. piceicola, C. subhirsutus, C. tricolor, C. ungulatus and Postia sublowei, are identified. Illustrated descriptions of the new genera and species are presented. Identification keys to Postia and related genera, as well as keys to the species of each genus, are provided.
    Keywords: Fomitopsidaceae ; multi-marker analyses ; Oligoporus ; phylogeny ; taxonomy ; Tyromyces ; wood-inhabiting fungi
    Repository Name: National Museum of Natural History, Netherlands
    Type: Article / Letter to the editor
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  • 146
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    Elsevier
    In:  Earth and Planetary Science Letters, 506 . pp. 381-387.
    Publication Date: 2018-12-04
    Description: Highlights • A small fraction of corrugated detachment fault surfaces is eventually exposed at the seafloor. • Seafloor slopes indicate effective friction of ∼0.2 on shallow part of detachments. • Moderate-offset detachment faults may be largely blanketed by hanging wall material. • Seafloor-shaping processes profoundly alter the morphology of oceanic core complexes. Abstract While oceanic detachment faults have been proposed to account for the accretion of ∼40% of new seafloor in the North Atlantic ocean, clear exposures of large-offset, often-corrugated fault surfaces remain scarce and spatially limited. To help resolve this paradox, we examine the conditions under which detachment fault growth may or may not lead to extensive exposure of corrugated fault planes at the seafloor. Using high-resolution bathymetry from four detachment faults at the northern Mid-Atlantic Ridge, we investigate the rafting of hanging wall-derived debris over emerging fault scarps, which can lead to covering shallow-dipping corrugated fault surfaces. We model this process using critical taper theory, and infer low effective friction coefficients (∼0.2) on the shallowest portion of detachment faults. A corollary to this result is that detachments emerging from the seafloor at angles 〈13° are more likely to become blanketed under an apron of hanging wall material. We generalize these findings as a simple model for the progressive exposure and flexural rotation of detachment footwalls, which accounts for the continued action of seafloor-shaping processes. Our model suggests that many moderate-offset, hidden detachment faults may exist along slow mid-ocean ridges, and do not feature an exposed fault surface.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 147
    Publication Date: 2018-12-04
    Description: Highlights • Increased glacial sedimentation rates do not generate sufficient overpressure to trigger a landslide. • Simulated overpressures for different sedimentation scenarios do not significantly differ. • A glacimarine layer underneath rapidly-deposited sediments is important for overpressure build-up. • An earthquake of M6.9 or larger at a short distance from the Tampen Slide headwall could have triggered the Tampen Slide. Abstract Trough mouth fans are environments characterized by high sediment supply during glacial stages and the occurrence of large-scale instabilities. The geological record indicates that several of these environments have failed repeatedly resulting in large submarine landslides. The roles of sedimentation rate, weak layers, glacial loading and unloading as well as seismic activity on triggering megaslides in trough-mouth-fan systems is still unclear. A better understanding of the preconditioning factors, triggers and consequences of these landslides is crucial due to the hazard they pose to coastal communities and offshore industries. In this paper, we focus on the North Sea Trough Mouth Fan, which is the result of massive glacial sediment input delivered to the shelf edge through the Norwegian Channel, southeast Nordic Seas margin. The Tampen Slide, one of several large paleo-landslides that have happened within the North Sea Trough Mouth Fan, took place at c. 130 ka (end of MIS 6), and removed an estimated 1800 km3 of sediment. Here, we use boundary conditions from the Tampen Slide and 2D Finite Element Modeling (Abaqus software from Simulia) to evaluate the effects of variations in sedimentation rates as well as sediment properties on the generation of excess pore pressure, fluid flow, and slope stability along the axis of the trough-mouth-fan system. The model domain, 40 km in length and 2 km in height, is dominated by glacigenic debris flows and glacimarine sediment deposits. We use geotechnical data measured on samples of glacigenic and glacimarine sediment deposits from the nearby Ormen Lange gas field area to constrain the model. We evaluate the stability of the slope under various scenarios, including constant sediment loading, episodic changes in sedimentation rates and abrupt pulses in sediment delivery for a 61 kyr period (MIS 6). The models show that increased sedimentation rates during glacial stages do not generate sufficient excess pore pressure to set off a landslide. Furthermore, the simulated overpressures for the different sedimentation scenarios do not significantly differ at the end of the model runs. The results also highlight the importance of a basal glacimarine sediment layer underneath the rapidly-deposited sediments for the build-up of overpressure. Consequently, this glacimarine sediment layer has the inherited potential to act as a weak layer facilitating instability. However, as overpressure due to sediment deposition alone does not result in slope failure, we couple the preconditioned slope with earthquake ground shaking. Based on attenuation models, an earthquake of approximately M6.9 or larger at a short distance from the Tampen Slide headwall could have triggered the landslide. Therefore, we suggest glacial sedimentation and a glacimarine sediment layer to represent preconditioning factors, and seismic shaking as the final trigger mechanism for the Tampen Slide, i.e. similar to the situation that lead to the development of the Storegga Slide in the same area.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 148
    Publication Date: 2018-12-04
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 149
    Publication Date: 2018-12-04
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 150
    Publication Date: 2018-12-04
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 151
    Publication Date: 2018-12-04
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  • 152
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    Elsevier
    In:  Geochimica et Cosmochimica Acta, 245 . pp. 406-425.
    Publication Date: 2018-12-06
    Description: Stable isotopes (15,14N, 18,16O) of dissolved inorganic nitrogen (N) were measured in sediment porewaters and benthic flux chambers across the Peruvian oxygen minimum zone (OMZ) from 74 to 1000 m water depth. Sediments at all locations were net consumers of bottom water NO3−. In waters shallower than 400 m, this sink was largely attributed to dissimilatory nitrate reduction to ammonium (DNRA) by filamentous nitrate-storing bacteria (Marithioploca and Beggiatoa) and to denitrification by foraminifera. The apparent N isotope effect of benthic NO3− loss (15εapp) was 7.4 ± 0.7‰ at microbial mat sites and 2.5 ± 0.9‰ at the lower fringe of the OMZ (400 m) where foraminifera were abundant. The OMZ sediments were a source of 15N-enriched NO2− (28.9 to 65.5‰) and NH4+ (19.4–20.5‰) to the bottom water. Model simulations generally support a previous hypothesis attributing the 15NH4+ enrichment to a coupling between DNRA and anammox (termed DAX) using biologically-stored NO3− from Marithioploca and NH4+ from the porewater. The model predicts that 40% of NO3− that is actively transported into the sediment by Marithioploca is reduced to N2 by this pathway. DAX enhances N2 fluxes by a factor of 2–3 and accounts for 70% of fixed N loss to N2. Moreover, because most of the ambient porewater NH4+ is generated by DNRA, up to two-thirds of biologically-transported NO3− could end up being lost to N2. This challenges the premise that Marithioploca-dominated sediments tend to conserve fixed N. By limiting the flux of 15NH4+ back to the ocean, DAX also tends to decrease benthic N fractionation. Tracking the fate of NH4+ once it leaves the sediment is critical for understanding how the benthos contributes to N isotope signals in the water column.
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  • 153
    Publication Date: 2018-12-03
    Description: The chapter presents a review of sea ice properties in relation to sub-seasonal to seasonal (S2S) predictions in the Arctic and the Antarctic. After a concise presentation of the main processes governing sea ice physics, the spatial distribution, seasonal cycle, and variability of sea ice in both poles are described. Using a variety of observations and model reconstructions of the four recent decades, the memory of the main descriptors of the sea ice state is quantified. In both the Arctic and the Antarctic, persistence of the sea ice areal properties emerges as the primarily source of sea ice sub-seasonal predictability, with strong dependence on season. Further memory can be obtained from reemergence mechanisms, implying processes internal to sea ice and coupling with the atmosphere and the ocean. In addition, lessons from modeling studies are addressed in terms of potential sea ice predictability and actual predictive skill. Finally, the chapter provides an overview of our understanding of the possible role of sea ice as a source of S2S atmospheric predictability, both in the polar regions and beyond.
    Repository Name: EPIC Alfred Wegener Institut
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  • 154
    Publication Date: 2018-12-07
    Description: This study presents new high resolution sedimentary δ15N records from piston cores collected within and outside the present-day eastern south Pacific oxygen minimum zone along a latitudinal transect from 3.5°S to 15°S. Radiocarbon dating of foraminifera and organic matter show that the cores cover the Holocene and the last deglaciation with high sedimentation rate allowing interpretations at millennial to centennial timescale. High δ15N values, reaching 10‰ and large amplitude changes, with a magnitude of ~4‰, are observed in the southern part of the studied area during the last 18 ka BP. In contrast, the northern Peruvian cores located on the edge of the OMZ show low δ15N values varying from 4 to 6‰ with amplitude of only 1‰, during the same time period. δ15N values decrease in all the studied cores from the last deglaciation to the early Holocene (17 to 8.5 ka BP) and reach a minimum value during the mid-Holocene. The δ15N variations are attributed to microbial N-loss to N2, e.g. denitrification and/or anammox, and the characteristic 15N-enriched signal that is recorded in the underlying sediments under suboxic to anoxic conditions where denitrifiers thrive. Surprisingly, δ15N values from cores located within the OMZ show similar values as the more northern cores located outside the OMZ between 5 and 8.5 ka BP. This minimum is not related to local changes in export production, reconstructed from sedimentary organic carbon, total nitrogen and bromine, but appears to be controlled by changes in the ventilation of the area. The low δ15N values recorded between 8.5 and 5 ka BP are well correlated with more arid conditions developed along the Peruvian margin and an increase of the sea surface temperature gradient along the Peruvian margin and between the West and East Pacific along the equator, implying an intensification of the Hadley circulation and climatic conditions similar to La Niña-like state. Consequently, these mid-Holocene conditions led to greater ventilation of subsurface waters that deepened the Peruvian oxycline then revealing similar conditions as observed today in the northern part of the study area.
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  • 155
    Publication Date: 2018-12-10
    Repository Name: EPIC Alfred Wegener Institut
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  • 156
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    In:  In: Oceanographic and Biological Aspects of the Red Sea. , ed. by Rasul, N. M. A. and Stewart, I. C. F. Springer Oceanography Series . Springer, Cham, pp. 185-194.
    Publication Date: 2018-12-11
    Description: The deep-sea brines of the Red Sea are unusual extreme environments and form characteristically steep gradients across the brine-seawater interfaces. Due to their unusual nature and unique combination of physical-chemical conditions these interfaces provide an interesting source of new findings in the fields of geochemistry, geology, microbiology, biotechnology, virology, and general biology. The current chapter summarizes recent and new results in the study of geochemistry and life at the interfaces of brine-filled deeps of the Red Sea.
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  • 157
    Publication Date: 2018-12-11
    Description: Hydrate dissociation equilibrium conditions for the mixture of carbon dioxide (CO2), nitrogen (N2), and water (H2O) are measured in the temperature range of 274.15–280.15 K. The relative molar composition of carbon dioxide in the feed gas mixture varies between 0.05 and 0.25 which is the interesting range of composition when it comes to production of methane, and sequestration of carbon dioxide, from methane hydrate reservoirs. A thermodynamic model is presented based on the classical van der Waals and Platteeuw (vdW-P) solid solution theory for the hydrate phase combined with the Equation of State (EoS) for combustion gas and combustion gas-like mixtures (CG-EoS). The results of this model are compared to the dissociation data measured here, along with all available data from the experimental literature. The predicted results from two thermodynamic software programs, CSMGem, and Multiflash (which use Peng-Robinson (PR) and Cubic Plus Association (CPA) EoSs respectively), are also statistically evaluated. A Clausius-Clapeyron type equation was used to derive the enthalpy of dissociation at 279.15 K, and the values were found to converge for mixtures containing 0.1–0.25 mol fraction of carbon dioxide.
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  • 158
    Publication Date: 2018-12-10
    Description: Highlights • Seafloor geomorphology was important in the structuring of abyssal megafauna. • Differences in megafaunal community ecology were found between all landscape types. • Lower megafauna density & diversity in a bathymetric valley than flat and ridge areas. • Large samples, collected by AUV, were required to make robust ecological conclusions. The potential for imminent polymetallic nodule mining in the Clarion Clipperton Fracture Zone (CCZ) has attracted considerable scientific and public attention. This concern stems from both the extremely large seafloor areas that may be impacted by mining, and the very limited knowledge of the fauna and ecology of this region. The environmental factors regulating seafloor ecology are still very poorly understood. In this study, we focus on megafaunal ecology in the proposed conservation zone ‘Area of Particular Environmental Interest 6′ (study area centred 17°16′N, 122°55′W). We employ bathymetric data to objectively define three landscape types in the area (a level bottom Flat, an elevated Ridge, a depressed Trough; water depth 3950–4250 m) that are characteristic of the wider CCZ. We use direct seabed sampling to characterise the sedimentary environment in each landscape, detecting no statistically significant differences in particle size distributions or organic matter content. Additional seafloor characteristics and data on both the metazoan and xenophyophore components of the megafauna were derived by extensive photographic survey from an autonomous underwater vehicle. Image data revealed that there were statistically significant differences in seafloor cover by nodules and in the occurrence of other hard substrata habitat between landscapes. Statistically significant differences in megafauna standing stock, functional structuring, diversity, and faunal composition were detected between landscapes. The Flat and Ridge areas exhibited a significantly higher standing stock and a distinct assemblage composition compared to the Trough. Geomorphological variations, presumably regulating local bottom water flows and the occurrence of nodule and xenophyophore test substrata, between study areas may be the mechanism driving these assemblage differences. We also used these data to assess the influence of sampling unit size on the estimation of ecological parameters. We discuss these results in the contexts of regional benthic ecology and the appropriate management of potential mining activities in the CCZ and elsewhere in the deep ocean.
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  • 159
    Publication Date: 2018-12-11
    Description: The initial opening of the Africa-Antarctica Corridor, in the heart of Gondwana, is still enigmatic due to missing information on the origin of major crustal features and the exact timing of the onset of the first oceanic crust in the Jurassic. Therefore, in 2014, new ship-borne magnetic data were systematically acquired in the northern Mozambique Basin and across Beira High, which we merged with all accessible magnetic data in the Mozambique Basin. Herein, distinct magnetic lineations are observed, which allow a refined identification of a whole set of Jurassic magnetic spreading anomalies, constraining the timing of the onset of oceanization, beginning at M38n.2n (164.1 Ma). In combination with high-resolution potential field data from the conjugate Antarctic margin, well-expressed fracture zones can be traced throughout the Africa-Antarctica Corridor and allow the precise rotation of Antarctica back to Africa. The initial fit depicts striking continuations of onshore tectonic features across the plate boundaries taking onshore aeromagnetic data of both margins into account. Within a tight Gondwana fit, the Beira High can be restored along the major sinistral Namama-Orvin Shear Zone of the East African-Antarctic Orogen. The Beira High represents a continental block, which was detached from Antarctica, by 157 Ma at the latest. Simultaneously, the Antarctic plate cleared the area of the MCP. However, the crustal nature of the southern MCP remains ambiguous. The Northern Natal Valley and the Mozambique Ridge consist of thick oceanic crust, being emplaced between M26r-M18n (157.1–144 Ma) and M18n-M6n (144–131.7 Ma), respectively. About the half of this crust was won from the Antarctic plate by a series of southwards directed ridge jumps to the northern boundary of the Explora Wedge. A refined kinematic break-up model constrained by the most extensive magnetic dataset is presented describing consistently the initial opening of the Africa-Antarctica Corridor and the Somali Basin.
    Repository Name: EPIC Alfred Wegener Institut
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  • 160
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    In:  In: Geological Setting, Palaeoenvironment and Archaeology of the Red Sea. , ed. by Rasul, N. M. A. and Stewart, I. C. F. Springer, Cham, pp. 37-52.
    Publication Date: 2018-12-14
    Description: Continental rifting and ocean basin formation can be observed at the present day in the Red Sea, which is used as the modern analogue for the formation of mid-ocean ridges. Competing theories for how spreading begins—either by quasi-instantaneous formation of a whole spreading segment or by initiation of spreading at multiple discrete “nodes” separated by thinned continental lithosphere—have been put forward based, until recently, on the observations that many seafloor features and geophysical anomalies (gravity, magnetics) along the axis of the Red Sea appeared anomalous compared to ancient and modern examples of ocean basins in other parts of the world. The latest research shows, however, that most of the differences between the Red Sea Rift (RSR) and other (ultra)slow-spreading mid-ocean ridges can be related to its relatively young age and the presence and movement of giant submarine salt flows that blanket large portions of the rift valley. In addition, the geophysical data that was previously used to support the presence of continental crust between the axial basins with outcropping oceanic crust (formerly named “spreading nodes”) can be equally well explained by processes related to the sedimentary blanketing and hydrothermal alteration. The observed spreading nodes are not separated from one another by tectonic boundaries but rather represent “windows” onto a continuous spreading axis which is locally inundated and masked by massive slumping of sediments or evaporites from the rift flanks. Volcanic and tectonic morphologies are comparable to those observed along slow and ultra-slow spreading ridges elsewhere and regional systematics of volcanic occurrences are related to variations in volcanic activity and mantle heat flow. Melt-salt interaction due to salt flows, that locally cover the active spreading segments, and the absence of large detachment faults as a result of the nearby Afar plume are unique features of the RSR. The differences and anomalies seen in the Red Sea still may be applicable to all young oceanic rifts, associated with plumes and/or evaporites, which makes the Red Sea a unique but highly relevant type example for the initiation of slow rifting and seafloor spreading and one of the most interesting targets for future ocean research.
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  • 161
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    In:  In: Geological Setting, Palaeoenvironment and Archaeology of the Red Sea. , ed. by Rasul, N. M. A. and Stewart, I. C. F. Springer, Cham, pp. 221-232.
    Publication Date: 2018-12-14
    Description: Hydrothermal circulation at mid-ocean ridges and assimilation of hydrothermally altered crust or hydrothermal fluids by rising magma can be traced by measuring chlorine (Cl) excess in erupted lavas. The Red Sea Rift provides a unique opportunity to study assimilation of hydrothermally altered crust at an ultra-slow spreading ridge (maximum 1.6 cm yr−1 full spreading rate) by Cl, due to its saline seawater (40–42‰, cf. 35‰ in open ocean water), the presence of (hot) brine pools (up to 270‰ salinity and 68 °C) and the thick evaporite sequences that flank the young rift. Absolute chlorine concentrations (up to 1300 ppm) and Cl concentrations relative to minor or trace elements of similar mantle incompatibility (e.g., K, Nb) are much higher in Red Sea basalts than in basalts from average slow spreading ridges. Mantle Cl/Nb concentrations can be used to calculate the Cl-excess, above the magmatic Cl, that is present in the samples. Homogeneous within-sample Cl concentrations, high Cl/H2O, the decoupling of Cl-excess from other trace elements and its independence of the presence of highly saline seafloor brines at the site of eruption indicate that Cl is not enriched at the seafloor. Instead we find basaltic Cl-excess to be spatially closely correlated with evidence of hydrothermal activity, suggesting that deeper assimilation of hydrothermal Cl is the dominant Cl-enrichment process. A proximity of samples to both evaporite outcrops and bathymetric signs of volcanism on the seafloor enhance Cl-excess in basalts. The basaltic Cl-excess can be used as a tracer together with new bathymetric maps as well as indications of hydrothermal venting (hot brine pools, metalliferous Hydrothermal circulation at mid-ocean ridges and assimilation of hydrothermally altered crust or hydrothermal fluids by rising magma can be traced by measuring chlorine (Cl) excess in erupted lavas. The Red Sea Rift provides a unique opportunity to study assimilation of hydrothermally altered crust at an ultra-slow spreading ridge (maximum 1.6 cm yr−1 full spreading rate) by Cl, due to its saline seawater (40–42‰, cf. 35‰ in open ocean water), the presence of (hot) brine pools (up to 270‰ salinity and 68 °C) and the thick evaporite sequences that flank the young rift. Absolute chlorine concentrations (up to 1300 ppm) and Cl concentrations relative to minor or trace elements of similar mantle incompatibility (e.g., K, Nb) are much higher in Red Sea basalts than in basalts from average slow spreading ridges. Mantle Cl/Nb concentrations can be used to calculate the Cl-excess, above the magmatic Cl, that is present in the samples. Homogeneous within-sample Cl concentrations, high Cl/H2O, the decoupling of Cl-excess from other trace elements and its independence of the presence of highly saline seafloor brines at the site of eruption indicate that Cl is not enriched at the seafloor. Instead we find basaltic Cl-excess to be spatially closely correlated with evidence of hydrothermal activity, suggesting that deeper assimilation of hydrothermal Cl is the dominant Cl-enrichment process. A proximity of samples to both evaporite outcrops and bathymetric signs of volcanism on the seafloor enhance Cl-excess in basalts. The basaltic Cl-excess can be used as a tracer together with new bathymetric maps as well as indications of hydrothermal venting (hot brine pools, metalliferous sediments) to predict where hydrothermal venting or now inactive hydrothermal vent fields can be expected. Sites of particular interest for future hydrothermal research are the Mabahiss Deep, the Thetis-HadarbaHatiba Deeps and Shagara-Aswad-Erba Deeps (especially their large axial domes), and Poseidon Deep. Older hydrothermal vent fields may be present at the Nereus and Suakin Deeps. These sites significantly increase the potential of hydrothermal vent field prospection in the Red Sea.
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  • 162
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    In:  In: Oceanographic and Biological Aspects of the Red Sea. , ed. by Rasul, N. M. A. and Stewart, I. C. F. Springer, Cham, Switzerland, pp. 401-418. ISBN 978-3-319-99416-1
    Publication Date: 2018-12-14
    Description: Coral reefs in the Red Sea belong to the most diverse and productive reef ecosystems worldwide, although they are exposed to strong seasonal variability, high temperature, and high salinity. These factors are considered stressful for coral reef biota and challenge reef growth in other oceans, but coral reefs in the Red Sea thrive despite these challenges. In the central Red Sea high temperatures, high salinities, and low dissolved oxygen on the one hand reflect conditions that are predicted for ‘future oceans’ under global warming. On the other hand, alkalinity and other carbonate chemistry parameters are considered favourable for coral growth. In coral reefs of the central Red Sea, temperature and salinity follow a seasonal cycle, while chlorophyll and inorganic nutrients mostly vary spatially, and dissolved oxygen and pH fluctuate on the scale of hours to days. Within these strong environmental gradients micro- and macroscopic reef communities are dynamic and demonstrate plasticity and acclimatisation potential. Epilithic biofilm communities of bacteria and algae, crucial for the recruitment of reef-builders, undergo seasonal community shifts that are mainly driven by changes in temperature, salinity, and dissolved oxygen. These variables are predicted to change with the progression of global environmental change and suggest an immediate effect of climate change on the microbial community composition of biofilms. Corals are so-called holobionts and associate with a variety of microbial organisms that fulfill important functions in coral health and productivity. For instance, coral-associated bacterial communities are more specific and less diverse than those of marine biofilms, and in many coral species in the central Red Sea they are dominated by bacteria from the genus Endozoicomonas. Generally, coral microbiomes align with ecological differences between reef sites. They are similar at sites where these corals are abundant and successful. Coral microbiomes reveal a measurable footprint of anthropogenic influence at polluted sites. Coral-associated communities of endosymbiotic dinoflagellates in central Red Sea corals are dominated by Symbiodinium from clade C. Some corals harbour the same specific symbiont with a high physiological plasticity throughout their distribution range, while others maintain a more flexible association with varying symbionts of high physiological specificity over depths, seasons, or reef locations. The coral-Symbiodinium endosymbiosis drives calcification of the coral skeleton, which is a key process that provides maintenance and formation of the reef framework. Calcification rates and reef growth are not higher than in other coral reef regions, despite the beneficial carbonate chemistry in the central Red Sea. This may be related to the comparatively high temperatures, as indicated by reduced summer calcification and long-term slowing of growth rates that correlate with ocean warming trends. Indeed, thermal limits of abundant coral species in the central Red Sea may have been exceeded, as evidenced by repeated mass bleaching events during previous years. Recent comprehensive baseline data from central Red Sea reefs allow for insight into coral reef functioning and for quantification of the impacts of environmental change in the region.
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  • 163
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    In:  Springer Oceanography Book series . Springer, Cham, Switzerland, 550 pp. ISBN 978-3-319-99417-8
    Publication Date: 2018-12-14
    Description: This book includes invited contributions presenting the latest research on the oceanography and environment of the Red Sea. In addition to covering topics relevant to research in the region and providing insights into marine science for non-experts, it is also of interest to those involved in the management of coastal zones and encourages further research on the Red Sea
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  • 164
    Publication Date: 2018-12-14
    Description: Highlights • Northern Hispaniola Margin is studied with new high-resolution bathymetry and vintage seismic data. • Northern Hispaniola Deformed Belt forms an active N-verging fold-and-thrust imbricate system. • Gravity failures are frequent features in the Northern Hispaniola Margin and Bahamas Banks slope. • Oblique collision accelerates the Bahamas Carbonate Province collapse and retreat. • New observations help the assessment of tsunami hazards in the Northern Caribbean region. Abstract The northern margin of Hispaniola records the oblique collision/underthrusting of the Bahamas Carbonate Province with the island-arc. Due to the collision, northern Hispaniola has suffered several natural disasters caused by major earthquakes and tsunamis, such as the historic earthquake of 1842, the tsunami caused by earthquake-driven slumping in 1918 in the Mona Passage, the seismic crisis of 1943–1953 with five events of M 〉 7.0 or the seismic crisis of 2003 with a main shock of M6.3 and a large aftershock of M5.3. Using new swath multibeam bathymetry data and vintage single- and multi-channel seismic profiles, we have performed a regional scale analysis and interpretation of the shallow surface and active processes along the northern margin of the Dominican Republic. We have identified three morphostructural provinces: a) the Bahamas Banks, b) the Hispaniola Trench and c) the Insular Margin, which are divided into two tectonic domains, the Collision Domain and Underthrusting Domain. The southern slope of the Bahamas Carbonate Province shows a very irregular morphology produced by active erosive processes and normal dip-slip faulting, evidence of an extensional tectonic regime and margin collapse. This collapse is of major extent in the Oblique Collision Domain where there are erosive and fault escarpments with higher dip-slip fault throws. The Hispaniola Trench, is formed by the Caicos and Hispaniola basins in the underthrusting domain, and by the Santisima Trinidad and Navidad basins in the Oblique Collision Domain. They have a flat seafloor with a sedimentary filling of variable thickness consisting of horizontal or sub-horizontal turbiditic levels. The turbiditic fill mostly proceeds from the island arc through wide channels and canyons, which transports sediment from the shelf and upper slope. The Insular Margin comprises the Insular Shelf and the Insular Slope. The active processes are generated on the Insular Slope where the Northern Hispaniola Deformed Belt is developed. This Deformed Belt shows a very irregular morphology, with a WNW-ESE trending N verging imbricate thrust-and fold system. This system is the result of the adjustment of the oblique collision/underthrusting between the North American plate and the Caribbean plate. In the Oblique Underthrusting Domain the along-strike development of the imbricate system is highly variable forming salients and recesses. This variability is due to along-strike changes in the sediment thickness of the Hispaniola Trench, as well as to the variable topography of the underthrusting Bahamas Carbonate Province. In the Oblique Collision Domain, the morphology of the Insular Slope and the development of the Deformed Belt deeply change. The imbricate system is barely inferred and lies upslope. These changes are due to the active collision of Bahamas Carbonate Province with the Insular Margin where the spurs are indented against the Insular Margin. Throughout the entire area studied, gravitational instabilities have been observed, especially on the Insular Margin and to a lesser extent on the southern slope of the Bahamas Carbonate Province. These instabilities are a direct consequence of the active underthrusting/collision process. We have mapped large individual slumps north of Puerto Plata in the Oblique Underthrusting Domain and zones of major slumps in the Oblique Collision Domain. These evidences of active processes must be considered as near-field sources in future studies on the assessment of tsunami hazards in the region.
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  • 165
    Publication Date: 2018-12-10
    Description: In Nepal, majority of households still burn solid fuels in inefficient cook stoves inside poorly ventilated kitchens, which results in very high levels of indoor pollutants, including black carbon (BC). Previous studies have not yet reported BC concentrations in typical kitchen configurations in rural Nepal. In this study, fine particulate matter (PM) and BC concentrations were monitored continuously inside two types of kitchens (separated from and attached to the main house) under actual cooking practices. Prior to monitoring of pollutants, a field survey was conducted to gain insight into the types of kitchens, cook stoves and fuels used. Indoor PM and BC concentrations were monitored using biomass fuels in traditional cook stoves (TC) and improved cook stoves (ICS). Clear diurnal variations of the pollutants were observed in both kitchens, with the highest concentrations during cooking times. BC and PM concentrations during cooking and non-cooking periods demonstrated clear reductions in the concentrations during non-cooking periods. It was observed that the concentrations rose steeply during the first half hour of cooking, then decreased slightly and finally leveled off to the non-cooking period concentrations. 24-hour average indoor PM concentrations in both kitchens frequently exceeded Nepal's indoor air quality standards and the WHO PM2.5 guidelines, by a factor of ~8 to ~28. We found that the specific type of ICS used in this study, a commonly used ICS in Nepal and other developing countries might help in PM emission reductions but not necessarily BC emission reduction.
    Language: English
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  • 166
    Publication Date: 2018-12-10
    Description: Based on diatom, aquatic pollen and non-pollen palynomorph (NPP), lake sediment microfacies, and X-ray fluorescence (XRF) analyses we define three main phases of lake basin development including a marshy phase (ca. 16,600–9400 cal. yr BP), lagoon phase (ca. 9400–5900 cal. yr BP) and freshwater lake phase (since ca. 5900 cal. yr BP). Marine influence on the lake system linked to global sea-level rise and the Holocene marine transgression reached a maximum between ca. 8000 and 6000 cal. yr BP. An increase of Aulacoseira subarctica at 5530 cal. yr BP marks the end of the Holocene Thermal Optimum (i.e. onset of Middle Holocene cooling) in the study region. Our results further suggest that freshwater Lake Kushu had a significant effect on the initial habitation of Rebun Island by sedentary hunter-gatherer populations. The reconstructed onset of stable freshwater conditions (ca. 5100 cal. yr BP) coincided with the appearance of the earliest permanent settlements during the Middle Jomon culture phase (ca. 5000–4000 cal. yr BP). On the other hand, there is evidence for human-induced changes in the limnological conditions. This includes enhanced sediment and nutrient input into Lake Kushu resulting in high eutrophication levels that caused strongly reduced diatom productivity and enhanced green algae growth, which can be attributed to human activities apparently associated with the Okhotsk (ca. 1450–950 cal. yr BP) and Classic Ainu (ca. 350–100 cal. yr BP) culture periods.
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  • 167
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    In:  Journal of Structural Geology
    Publication Date: 2018-12-10
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  • 168
    Publication Date: 2018-12-10
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  • 169
    Publication Date: 2018-12-10
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  • 170
    Publication Date: 2018-12-11
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  • 171
    Publication Date: 2018-12-11
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  • 172
    Publication Date: 2018-12-12
    Description: Highlights The increase in volcanic activity after the last glacial maximum observed on Iceland has led to one of the most fascinating hypothesis in science in the last decades: that deglaciation may force volcanism. We: - Re-analyzed four longer tephra records with the same statistical method and demonstrated that all contain the ∼41 kyr and ∼100 kyr Millankovitch periodicities. - The frequency spectra of the tephra and δ18O records are significantly correlated supporting the hypothesis that orbital-driven global climate changes interact with the volcanic eruption frequency regionally and globally. - However, the simultaneous analysis of the four best-characterized tephra records shows that correlations and associated time lags suffer from a number of uncertainties including the nature and quality of tephra time series, a wide range in geographic latitudes and geological settings, as well as applied statistical methods Therefore more precise tephra time series (preservation and age optimized) from different regions (glaciated versus non-glaciated) and geological settings (island arcs, continental arcs, intraplate) are needed together with standardized statistical analysis to decipher the impact of these factors on a global perspective of how climate may control volcanism. Abstract The increase in volcanic activity after the last glacial maximum observed on Iceland has led to one of the most fascinating hypothesis in science in the last decades: that deglaciation may force volcanism. Consequently, tephrostratigraphic records of sufficient length that cover multiple glacial cycles have been used to test whether such relationships hold systematically through the Quaternary. Here we review such tephra records that have been linked with climate proxy records such as δ18O in marine sediments, which is a measure of sea-level change and which is thought to be orbitally forced, as it exhibits the characteristic Milankovitch periodicities of precession (∼23 kyr), obliquity (∼41 kyr) and eccentricity (∼100 kyr). Statistical analyses have identified these periodicities also in long tephra records from different latitudes and geotectonic settings, as well as in compiled semi-global records. These studies detect Milankovitch periods in their tephra record, and also a phase shift relative to the δ18O record in such that periods of increased eruption frequencies coincide with the deglaciation period at the glacial/interglacial transition when ice and water loads on the lithosphere change most rapidly. However, there are also disparities in results and interpretations, which may be attributable to the different methods of analysis applied by the studies. We have therefore re-analyzed the four best-characterized tephra records by the same methods. We distinguish between analysis in the frequency domain, a novel approach, and analysis in the time domain, which has been used in previous studies. Analysis in the frequency domain identifies harmonic frequencies that arise from the binary nature of the tephra records and complicate the identification of primary frequencies. However, we show that all four records show spectral density peaks near the main Milankovitch periodicities of 41 and 100 kyr, and that they produce meaningful and significant statistical correlations with each other and the global δ18O record but not with random time series. Although the time-domain correlations with δ18O roughly confirm phase shifts implying peak volcanism during deglaciation, correlation coefficients arising from very noisy records are generally too low for precise constraints on the relative timing. These deficiencies presently hamper the recognition of the physical mechanisms through which global climate changes affect volcanism at both, high-latitude glaciated regions and low-latitude non-glaciated regions.
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  • 173
    Publication Date: 2018-12-12
    Type: inbook