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  • Other Sources  (4,812)
  • Articles (OceanRep)  (4,812)
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  • 1
    Publication Date: 2020-02-06
    Description: Highlights • The Fram Slide Complex has been active from late Miocene to late Pleistocene. • Local processes were critical for slope stability in the Fram Strait area. • Toe erosion caused by normal faulting may have led to retrogressive failure. • Low gradient contourite drifts might smooth and stabilize submarine slopes. • Low tsunami potential from the Fram Slide Complex could increase in the future. Abstract The best known submarine landslides on the glaciated NW European continental margins are those at the front of cross-shelf troughs, where the alternation of rapidly deposited glycogenic and hemi pelagic material generates sedimentary overpressure. Here, we investigate landslides in two areas built of contourite drifts bounded seaward by a ridge-transform junction. Seismic and bathymetric data from the Fram Slide Complex are compared with the tectonically similar Vastness area ~ 120 km to the south, to analyze the influence of local and regional processes on slope stability. These processes include tectonic activity, changes of climate and oceanography, gas hydrates and fluid migration systems, slope gradient, toe erosion and style of contourite deposition. Two areas within the Fram Slide Complex underwent different phases of slope failures, whereas there is no evidence at all for major slope failures in the Vastness area. The comparison cannot reveal the distinct reason for slope failure but demonstrates the strong impact of variation in the local controls on slope stability. The different failure chronologies suggest that toe erosion, which is dependent on the throw of normal faults, and the different thickness and geometry of contourite deposits can result in a critical slope morphology and exert pronounced effects on slope stability. These results highlight the limitations of regional hazard assessments and the need for multi-disciplinary investigations, as small differences in local controlling factors led to substantially different slope failure histories.
    Type: Article , PeerReviewed
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  • 2
    Publication Date: 2020-02-06
    Description: We used a new sedimentary record from a small kettle wetland to reconstruct the Late Glacial and Holocene vegetation and fire history of the Krutoberegovo-Ust Kamchatsk region in eastern Kamchatka Peninsula (Russia). Pollen and charcoal data suggest that the Late Glacial landscape was dominated by a relatively fire-prone Larix forest-tundra during the Greenland Interstadial complex (GI 1) and a subarctic steppe during the Younger Dryas (GS1). The onset of the Holocene is marked by the reappearance of trees (mainly Alnus incana) within a fern and shrub dominated landscape. The Holocene Thermal Maximum (HTM) features shifting vegetational communities dominated by Alnus shrubs, diverse forb species, and locally abundant aquatic plants. The HTM is further defined by the first appearance of stone birch forests (Betula ermanii) – Kamchatka's most abundant modern tree species. The Late Holocene is marked by shifts in forest dynamics and forest-graminoid ratio and the appearance of new non-arboreal taxa such as bayberry (Myrica) and meadow rue (Filipendula). Kamchatka is one of Earth's most active volcanic regions. During the Late Glacial and Holocene, Kamchatka's volcanoes spread large quantities of tephra over the study region. Thirty-four tephra falls have been identified at the site. The events represented by most of these tephra falls have not left evidence of major impacts on the vegetation although some of the thicker tephras caused expansion of grasses (Poaceae) and, at least in one case, forest die-out and increased fire activity.
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  • 3
    Publication Date: 2020-02-06
    Description: Highlights • Receiver functions from ocean-bottom seismometer stations reveal no significant crustal thickening in the surrounding of the Tristan da Cunha hot spot. • The mantle transition zone to the NW of Tristan da Cunha is thickened and cool. • The mantle transition zone is potentially thinned to the south/southwest of Tristan da Cunha. • A thickness of 60 to 75 km beneath Tristan da Cunha argues for a compositional control on the seismological lithosphere in the South Atlantic. Abstract The most prominent hotspot in the South Atlantic is Tristan da Cunha, which is widely considered to be underlain by a mantle plume. But the existence, location and size of this mantle plume have not been established due to the lack of regional geophysical observations. A passive seismic experiment using ocean bottom seismometers aims to investigate the lithosphere and upper mantle structure beneath the hotspot. Using the Ps receiver function method we calculate a thickness of 5 to 8 km for the oceanic crust at 17 ocean-bottom stations deployed around the islands. Within the errors of the method the thickness of the oceanic crust is very close to the global mean. The Tristan hotspot seems to have contributed little additional magmatic material or heat to the melting zone at the mid-oceanic ridge, which could be detected as thickened oceanic crust. Magmatic activity on the archipelago and surrounding seamounts seems to have only effected the crustal thickness locally. Furthermore, we imaged the mantle transition zone discontinuities by analysing receiver functions at the permanent seismological station TRIS and surrounding OBS stations. Our observations provide evidence for a thickened (cold) mantle transition zone west and northwest of the islands, which excludes the presence of a deep-reaching mantle plume. We have some indications of a thinned, hot mantle transition zone south of Tristan da Cunha inferred from sparse and noisy observations, which might indicate the location of a Tristan mantle plume at mid-mantle depths. Sp receiver functions image the base of lithosphere at about 60 to 75 km beneath the islands, which argues for a compositionally controlled seismological lithosphere-asthenosphere boundary beneath the study area.
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  • 4
    Publication Date: 2020-02-06
    Description: Highlights • Observations show that formation of sediment-laden sea ice occurs in coastal polynyas in winter. • Sea ice rafted sediments are a significant component of the Laptev Sea’s sediment budget. • No observational evidence for sediment entrainment into sea ice in mid-shelf polynyas at water depth greater than 20 m. Abstract Sea ice is an important vehicle for sediment transport in the Arctic Ocean. On the Laptev Sea shelf (Siberian Arctic) large volumes of sediment-laden sea ice are formed during freeze-up in autumn, then exported and transported across the Arctic Ocean into Fram Strait where it partly melts. The incorporated sediments are released, settle on the sea floor, and serve as a proxy for ice-transport in the Arctic Ocean on geological time scales. However, the formation process of sediment-laden ice in the source area has been scarcely observed. Sediment-laden ice was sampled during a helicopter-based expedition to the Laptev Sea in March/April 2012. Sedimentological, biogeochemical and biological studies on the ice core as well as in the water column give insights into the formation process and, in combination with oceanographic process studies, on matter fluxes beneath the sea ice. Based on satellite images and ice drift back-trajectories the sediments were likely incorporated into the sea ice during a mid-winter coastal polynya near one of the main outlets of the Lena River, which is supported by the presence of abundant freshwater diatoms typical for the Lena River phytoplankton, and subsequently transported about 80 km northwards onto the shelf. Assuming ice growth of 12 to 19 cm during this period and mean suspended matter content in the newly formed ice of 91.9 mg l-1 suggests that a minimum sediment load of 8.4x104 t might have been incorporated into sea ice. Extrapolating these sediment loads for the entire Lena Delta region suggests that at least 65% of the estimated sediment loads which are incorporated during freeze-up, and up to 10% of the annually exported sediment load may be incorporated during an event such as described in this paper.
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  • 5
    Publication Date: 2020-02-06
    Description: The recent volcanic eruptions of Eyjafjallajökull 2010 and Grímsvötn 2011 demonstrated the risks that mediumsized explosive Icelandic eruptions pose to the North Atlantic region. Using the Eyjafjallajökull 2010 eruption as a case study, we assess how traceable such eruptions are in the marine sedimentary record at medial distances from the source and investigate which factors have affected the particle transport to the marine sedimentary archive. During R/V Poseidon cruise 457, we recovered 13 box cores at 100–1600 m water depths and distances of 18–180 km southwest, south, and east of Iceland. Volcanic glass shards from the uppermost surface sediment were analyzed for their major element composition by electron microprobe and assigned to their eruptive source by geochemical fingerprinting. The predominantly basaltic particles are mostly derived from the Katla, Grímsvötn-Lakagígar, and Bárðarbunga-Veiðivötn volcanic systems. We also identified rhyolitic particles from the Askja 1875 and Öræfajökull 1362 eruptions. Only three out of almost 900 analyzed glass shards are derived from the recent Eyjafjallajökull 2010 eruption, suggesting that medium-sized eruptions are only poorly preserved in marine sediments located at medial distances southwest to east of Iceland. We conclude that the frequency of past medium-sized eruptions is likely higher than detectable in this archive.
    Type: Article , PeerReviewed
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  • 6
    Publication Date: 2020-02-06
    Description: Highlights: • Fungal infections represent an increasing threat to human health. • Fungal infections in plants are a worldwide problem to the agricultural industry. • Diverse antifungal compounds were isolated from different marine organisms. • The number of new antifungal marine natural products is rapidly developing. • Marine sponges and bacteria are the predominant sources for antifungal compounds. Abstract: Fungal diseases represent an increasing threat to human health worldwide which in some cases might be associated with substantial morbidity and mortality. However, only few antifungal drugs are currently available for the treatment of life-threatening fungal infections. Furthermore, plant diseases caused by fungal pathogens represent a worldwide economic problem for the agriculture industry. The marine environment continues to provide structurally diverse and biologically active secondary metabolites, several of which have inspired the development of new classes of therapeutic agents. Among these secondary metabolites, several compounds with noteworthy antifungal activities have been isolated from marine microorganisms, invertebrates, and algae. During the last fifteen years, around 65% of marine natural products possessing antifungal activities have been isolated from sponges and bacteria. This review gives an overview of natural products from diverse marine organisms that have shown in vitro and/or in vivo potential as antifungal agents, with their mechanism of action whenever applicable. The natural products literature is covered from January 2000 until June 2015, and we are reporting the chemical structures together with their biological activities, as well as the isolation source.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 7
    Publication Date: 2020-02-06
    Description: The active volcanic island Tristan da Cunha, located at the southwestern and youngest end of the Walvis Ridge - Tristan/Gough hotspot track, is believed to be the surface expression of a huge thermal mantle anomaly. While several criteria for the diagnosis of a classical hotspot track are met, the Tristan region also shows some peculiarities. Consequently it is vigorously debated if the active volcanism in this region is the expression of a deep mantle plume, or if it is caused by shallow plate tectonics and the interaction with the nearby Mid-Atlantic Ridge. Because of a lack of geophysical data in the study area, no model or assumption has been completely confirmed. We present the first amphibian P-wave finite-frequency travel time tomography of the Tristan da Cunha region, based on cross-correlated travel time residuals of teleseismic earthquakes recorded by 24 ocean-bottom seismometers. The data can be used to image a low velocity structure southwest of the island. The feature is cylindrical with a radius of ~ 100 km down to a depth of 250 km. We relate this structure to the origin of Tristan da Cunha and name it the Tristan conduit. Below 250 km the low velocity structure ramifies into narrow veins, each with a radius of ~ 50 km. Furthermore, we imaged a linkage between young seamounts southeast of Tristan da Cunha and the Tristan conduit.
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  • 8
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    Elsevier
    In:  Fisheries Research, 8 (1). pp. 35-44.
    Publication Date: 2017-01-10
    Description: In Moreton Bay, Queensland, the catch obtained using monofilament polyamide (PA) otter trawl-nets with multifilament polyethylene (PE) cod ends was compared with that obtained using multifilament PE trawl-nets of identical mesh opening (38 mm). Monofilament PA otter trawl-nets retained fewer small prawns ( 〈 24 mm carapace length) than conventional multifilament PE nets, but both nets caught similar quantities of larger prawns ( 〉 24 mm carapace length). The higher retention rate of small prawns by multifilament PE gear was reflected in the greater catch weights of Peraeus plebejus, Metapenaeus bennettae and Metapenaeopsis novaeguineae in those nets. Catch weights of larger prawn species such as Penaeus esculentus and Metapenaeus endeavouri did not differ between nets. Winter whiting (Sillago maculata) and squid (Loligo spp.) were trawled in similar abundance in both nets, although the monofilament retained fewer squid 〈 50 mm mantle length. More marketable ( 〉 15 cm carapace width) sand crabs (Portunus pelagicus) were caught in the monofilament net. There was not significant difference in the trash (noncommercial component) weight caught in both nets. Over the range of towing speeds tested (1.7–2.3 kn), use of monofilament nets significantly reduced total gear drag.
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  • 9
    Publication Date: 2020-02-06
    Description: Highlights: • Improved Claisen-Schmidt condensation using lithium hydroxide monohydrate in 1,4-dioxane. • Pyridylchalcones show good activity and selectivity against Trypanosoma brucei. • Pyridylchalcones show little activity against Leishmania donovani. • Promising leads in the development of novel compounds for the treatment of sleeping sickness. A library of novel pyridylchalcones were synthesised and screened against Trypanosoma brucei rhodesiense. Eight were shown to have good activity with the most potent 8 having an IC50 value of 0.29 μM. Cytotoxicity testing with human KB cells showed a good selectivity profile for this compound with a selectivity index of 47. Little activity was seen when the library was tested against Leishmania donovani. In conclusion, pyridylchalcones are promising leads in the development of novel compounds for the treatment of human African trypanosomiasis (HAT).
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  • 10
    Publication Date: 2020-07-31
    Description: Distribution and abundance of the horned octopus Eledone cirrhosa in the Tyrrhenian Sea are described on the basis of stratified-random bottom trawl surveys in spring and summer of the years 1985–1987. Specimens were caught between 25 and 630 m depth (higher densities between 50 and 200 m depth); mature males were found to prefer deeper bottoms than mature females. Young specimens occurred in spring samples from the Western Ligurian Sea and in summer samples from the Lower Tyrrhenian Sea, but were scarcely represented in the Higher Tyrrhenian Sea. Thus recruitment seems to be progressively delayed later in the season from north to south. The greatest abundance was recorded in the Higher Tyrrhenian Sea; wide seasonal variations of minimum stock biomass estimates have been observed and total biomass decreased from 1985 to 1987 in the surveyed areas.
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