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  • Elsevier  (490,604)
  • Essen : Verl. Glückauf
  • Krefeld : Geologischer Dienst Nordhein-Westfalen
  • 2005-2009  (490,607)
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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 294 (1992), S. 466-478 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 317 (1993), S. 474-484 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
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  • 3
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    Elsevier
    In:  Current Opinion in Chemical Biology, 13 (2). pp. 205-215.
    Publication Date: 2018-11-05
    Description: The biosynthesis of the microbial small molecule iron scavengers known as siderophores has been of interest since their discovery in the middle of the past century. Two main pathways for siderophore biosynthesis exist. One is directed by a large family of modular multienzymes called non-ribosomal peptide synthetases (NRPSs) while the other is NRPS independent. There has been a vast increase in our knowledge of siderophore biosynthesis over the past two decades and the enzymology of several NRPS-dependent pathways is now well-understood while dramatic recent progress has also been made in elucidating NRPS-independent pathways. As siderophores are virulence factors in many pathogenic microorganisms, genetic and biochemical knowledge of siderophore biosynthetic pathways can aid in the development of new antimicrobials as well as increasing our understanding of the natural machinery for the efficient assembly of structurally complex bioactive natural products.
    Type: Article , PeerReviewed
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  • 4
    Publication Date: 2018-12-06
    Description: Analysis of a well-dated peat core from Blue Cypress Marsh (BCM) provides a detailed record of natural and anthropogenic factors that controlled the geochemical cycles of a number of trace elements in Florida over the last five centuries. The trace elements were divided into "natural" and "anthropogenic" groups using concentration trends from the bottom to the top of the core. The "natural" group includes Li, Sc, Cr, Co, Ga, Ge, Zr, Nb, Cs, Ba, Hf, Y, Ta, Th, and REE (Rare Earth Elements). These elements show similar concentrations throughout the core, indicating that changes in human activities after European arrival in the "New World" did not affect their geochemical cycles. The "anthropogenic" group includes Pb, Cu, Zn, V, Sb, Sn, Bi, and Cd. Upcore enrichment of these elements indicates enhancement by anthropogenic activities. From the early 1500s to present, fluxes of the "anthropogenic" metals to the marsh increased significantly, with modern accumulation rates several-fold (e.g., V) to hundreds of times (e.g., Zn) greater than pre-colonial rates. The dominant input mechanism for trace elements from both groups to the marsh has been atmospheric deposition. Atmospheric input of a number of the elements, including the anthropogenic metals, was dominated by local sources during the last century. For several elements, long-distant transport may be important. For instance, REE and Nd isotopes provide evidence for long-range atmospheric transport dominated by Saharan dust. The greatest increase in flux of the "anthropogenic" metals occurred during the 20th century and was caused by changes in the chemical composition of atmospheric deposition entering the marsh. Increased atmospheric inputs were a consequence of several anthropogenic activities, including fossil fuel combustion (coal and oil), agricultural activities, and quarrying and mining operations. Pb and V exhibit similar trends, with peak accumulation rates in 1970. The principal anthropogenic source of V is oil combustion. The decline in V accumulation after 1970 in the BCM peat corresponds to the introduction of low-sulfur fuels and the change from heavy to distilled oils since the 1970s. After the 1920s, Pb distribution in the peat follows closely the history of alkyl lead consumption in the US, which peaked in the 1970s. Pb isotopes support this inference and furthermore, record changes in the ore sources used to produce leaded gasoline. Idaho ores dominated the peat Pb isotope record until the 1960s, followed by Pb from Mississippi Valley Type deposits from the 1960s to the 1980s. Enhanced fluxes of Cu, Zn, Cd, Sn, Sb, Bi, and to some extent Ni during the last century are likely also related to fossil fuel combustion. Local agricultural activities may also have influenced the geochemical cycles of Cu and Zn. The peat record shows enhanced U accumulation during the last century, possibly related to phosphate mining in western Florida. Sr isotopes in the peat core also reflect anthropogenic influence. The 87Sr/86Sr ratio decreases from natural background values in the basal part of the core to lower values in the upper part of the core. The Sr isotope shift is probably related to quarrying operations in Florida, and marks the first time an anthropogenic signal has been detected using the Sr isotope record in a peat core.
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  • 5
    Publication Date: 2017-10-09
    Description: Cosmogenic radionuclides in the one-million-year half-life range offer unique possibilities for age determinations in geophysics. In measurements where the radioactive decay is being utilized as a clock, uncertainties in age determinations may be reduced if the ratio of two radioisotopes with different half-lives can be used as a chronometer. In this work we investigate the atomic ratio of atmospheric 26Al (t1/2= 0.717 Ma) to 10Be (t1/2=1.386 Ma) measured with accelerator mass spectrometry (AMS), and its potential as a chronometer for dating old ice. The 26Al/10Be ratio decreases with an effective half-life of t1/2(26Al/10Be)= 1.49 Ma. For its application as a chronometer, the atmospheric 26Al/10Be ratio has to be well characterized. However, the properties of atmospheric 26Al have been understood only poorly so far. At the VERA AMS facility of the University of Vienna, a first systematic study of the global variations of the 26Al/10Be ratio in the atmosphere and in surface firn has been carried out, and pilot measurements of the 26Al/10Be ratio in deep Antarctic ice have been performed. Our results indicate that this ratio is globally constant to within 5% in the atmosphere and in surface firn with a mean value of 1.89×10−3. The data also suggest that non-atmospheric sources of 26Al, such as extraterrestrial, in situ produced or re-suspended 26Al, do not contribute significantly to the observed 26Al/10Beratio. In addition, atmospheric mixing seems to exert only aminor influence. In a first application of the method,26Al/10Be ratios were measured in chips collected in connection with the drilling of the lowest part of an ice core (2250 to 2760 m) in Dronning Maud Land,Antarctica. Surprisingly, variable 26Al/10Be ratios ranging between0.5 and up to 2 times the atmospheric ratio were found at different locations in this deep ice core. While the cause for the ratios higher than atmospheric remains unexplained so far, the ratios lower than atmospheric may be caused by radioactive decay, allowing a first dating attempt using the 26Al/10Be ratio. Thus, at an ice depthof 2760 m an approximate date of (6.7±2.6)×105years was established.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 6
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    Elsevier
    In:  Ocean Modelling, 26 (1-2). pp. 47-59.
    Publication Date: 2018-10-23
    Description: The effects of spatial variations of the thickness diffusivity (K) appropriate to the parameterisation of [Gent, P.R. and McWilliams, J.C., 1990. Isopycnal mixing in ocean circulation models. J. Phys. Oceanogr., 20, 150–155.] are assessed in a coarse resolution global ocean general circulation model. Simulations using three closures yielding different lateral and/or vertical variations in K are compared with a simulation using a constant value. Although the effects of changing K are in general small and all simulations remain biased compared to observations, we find systematic local sensitivities of the simulated circulation on K. In particular, increasing K near the surface in the tropical ocean lifts the depth of the equatorial thermocline, the strength of the Antarctic Circumpolar Current decreases while the subpolar and subtropical gyre transports in the North Atlantic increase by increasing K locally. We also find that the lateral and vertical structure of K given by a recently proposed closure reduces the negative temperature biases in the western North Atlantic by adjusting the pathways of the Gulf Stream and the North Atlantic Current to a more realistic position.
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  • 7
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    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 56 (9). pp. 1440-1448.
    Publication Date: 2016-11-01
    Description: The phytoplankton distribution off western Australia in the period from April to October is unique in that high biomass is generally associated with anticyclonic eddies and not with cyclonic eddies. As the western Australian region is oligotrophic this anomalous feature must be related to differing nutrient supply pathways to the surface mixed layer of cyclonic and anticyclonic eddies. A suite of modelled abiotic tracers suggests that cyclonic eddies are predominantly supplied by diapycnal processes that remain relatively weak until June–July, when they rapidly increase because of deepening surface mixed layers, which start to tap into the nutrient-replete waters below the euphotic zone. To the contrary, we find that anticyclonic eddies are predominantly supplied by injection of shelf waters, which carry elevated levels of inorganic nutrients and biomass. These injections start with the formation of the eddies in April–May, continue well into the austral winter and reach as far as several hundred kilometers offshore. The diapycnal supply of nutrients is suppressed in anticyclonic eddies since the injection of warm, low-salinity shelf waters delays the erosion of the density gradient at the base of the mixed layer. Our results are consistent with the observed seasonal cycles of chlorophyll a and observation of particulate organic matter export out of the surface mixed layer of an anticyclonic eddy in the region.
    Type: Article , PeerReviewed
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  • 8
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    Elsevier
    In:  Earth and Planetary Science Letters, 280 . pp. 118-127.
    Publication Date: 2017-02-10
    Description: The first full water column hafnium isotopic compositions of Atlantic seawater have been obtained at seven locations from the Labrador Sea to the Drake Passage. Despite subpicomolar concentrations in seawater, a precision of the Hf isotopic measurements of 〈03 epsilon(Hf) units was achieved. An overall epsilon(Hf) range between -3.1 in the Labrador Sea and +4.4 in Antarctic bottom water was determined, the distribution of which broadly reflects continental weathering inputs. Within particular water column profiles, significant differences of up to 4 epsilon(Hf) Units occur. Combined with Nd isotope data of the same samples, it is evident that the Hf isotopic composition of seawater is too radiogenic for a given Nd isotopic composition and that the largest difference between expected and measured Hf isotopic compositions in seawater occurs near the oldest continental crust in the Labrador Sea. This corroborates the previous proposition, which was mainly based on ferromanganese crust data, that the Hf isotopic composition of seawater is controlled by incongruent weathering of continental crust and possibly, to some extent, by hydrothermal contributions. Hafnium concentrations in the ocean do not increase along the deep ocean conveyer indicating an oceanic residence time of only a few hundred years, which is significantly shorter than previously assumed. The Hf isotopic composition of past seawater can therefore serve as a proxy for short distance, basin scale mixing processes and the regime and intensity of nearby continental weathering processes. (C) 2009 Elsevier B.V. All rights reserved
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  • 9
    Publication Date: 2016-11-01
    Description: A combination of 2-year-long mooring-based measurements and snapshot conductivity–temperature–depth (CTD) observations at the continental slope off Spitsbergen (81°30′N, 31°00′E) is used to demonstrate a significant hydrographic seasonal signal in Atlantic Water (AW) that propagates along the Eurasian continental slope in the Arctic Ocean. At the mooring position this seasonal signal dominates, contributing up to 50% of the total variance. Annual temperature maximum in the upper ocean (above 215 m) is reached in mid-November, when the ocean in the area is normally covered by ice. Distinct division into ‘summer’ (warmer and saltier) and ‘winter’ (colder and fresher) AW types is revealed there. Estimated temperature difference between the ‘summer’ and ‘winter’ waters is 1.2 °C, which implies that the range of seasonal heat content variations is of the same order of magnitude as the mean local AW heat content, suggesting an important role of seasonal changes in the intensity of the upward heat flux from AW. Although the current meter observations are only 1-year long, they hint at a persistent, highly barotropic current with little or no seasonal signal attached.
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  • 10
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    Elsevier
    In:  Environmental Modelling & Software, 24 . pp. 1012-1013.
    Publication Date: 2018-09-12
    Description: The presented software application allows GUI-based access to the bubble dissolution model presented by McGinnis et al. [McGinnis, D.F., Greinert, J., Artemov, Y., Beaubien, S.E., Wüest, A., 2006. The fate of rising methane bubbles in stratified waters: what fraction reaches the atmosphere? Journal of Geophysical Research 111, C09007. doi:http://dx.doi.org/10.1029/2005JC003183]. It quantifies the dissolution of gas bubbles (containing any combination of CH4, CO2, O2, N2, and Ar) in marine or lacustrine environments based on the initial bubble size, free gas composition and environmental parameters (temperature, salinity, and dissolved gas concentrations). The software enables scientists and engineers to evaluate bubble dynamics in a simple way on Windows® PCs
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  • 11
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    Elsevier
    In:  Comparative Biochemistry and Physiology A - Molecular and Integrative Physiology, 153 . pp. 278-283.
    Publication Date: 2017-12-11
    Description: It is still a matter of debate whether cephalopods can detect sound frequencies above 400 Hz. So far there is no proof for the detection of underwater sound above 400 Hz via a physiological approach. The controversy of whether cephalopods have a sound detection ability above 400 Hz was tested using the auditory brainstem response (ABR) approach, which has been successfully applied in fish, crustaceans, amphibians, reptiles and birds. Using ABR we found that auditory evoked potentials can be obtained in the frequency range 400 to 1500 Hz (Sepiotheutis lessoniana) and 400 to 1000 Hz (Octopus vulgaris), respectively. The thresholds of S. lessoniana were generally lower than those of O. vulgaris.
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  • 12
    Publication Date: 2017-08-04
    Description: We report on a multidisciplinary study of cold seeps explored in the Central Nile deep-sea fan of the Egyptian margin. Our approach combines in situ seafloor observation, geophysics, sedimentological data, measurement of bottom-water methane anomalies, pore-water and sediment geochemistry, and 230Th/U dating of authigenic carbonates. Two areas were investigated, which correspond to different sedimentary provinces. The lower slope, at ∼ 2100 m water depth, indicates deformation of sediments by gravitational processes, exhibiting slope-parallel elongated ridges and seafloor depressions. In contrast, the middle slope, at ∼ 1650 m water depth, exhibits a series of debris-flow deposits not remobilized by post-depositional gravity processes. Significant differences exist between fluid-escape structures from the two studied areas. At the lower slope, methane anomalies were detected in bottom-waters above the depressions, whereas the adjacent ridges show a frequent coverage of fractured carbonate pavements associated with chemosynthetic vent communities. Carbonate U/Th age dates (∼ 8 kyr BP), pore-water sulphate and solid phase sediment data suggest that seepage activity at those carbonate ridges has decreased over the recent past. In contrast, large (∼ 1 km2) carbonate-paved areas were discovered in the middle slope, with U/Th isotope evidence for ongoing carbonate precipitation during the Late Holocene (since ∼ 5 kyr BP at least). Our results suggest that fluid venting is closely related to sediment deformation in the Central Nile margin. It is proposed that slope instability leads to focused fluid flow in the lower slope and exposure of ‘fossil’ carbonate ridges, whereas pervasive diffuse flow prevails at the unfailed middle slope.
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  • 13
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    Elsevier
    In:  Earth and Planetary Science Letters, 280 (1/4). pp. 159-166.
    Publication Date: 2016-10-14
    Description: Various theoretical and numerical models have been proposed in order to explain joint formation and spacing in layered rock series. However, most of these models assume that the interfaces between the rock layers are perfectly welded, i.e. no slip occurs, and that all the layers are subjected to the same remote strain due to various processes (e.g. tectonic processes). Other factors may also induce extensional strain in rocks, e.g. phase transformations. However, such processes may induce different amounts of strain on the layers in a rock series leading to a strain mismatch between these layers. In this paper, we present a 1-D finite difference linear elastic model which allows joint formation within the middle layer in a three-layer rock series and is induced by a strain mismatch between the fractured, central layer and the surrounding matrix. Furthermore, the central layer in our model is not necessarily welded to the matrix layers and is allowed to slip along the interfaces between these layers if the shear strength of the material at the interface is reached. We find that the final fracture spacing to layer thickness ratio (S/Tf) in such layered systems is directly proportional to the ratio of the tensile and shear strength of the material. Changes in the material properties such as the shear modulus or Young's modulus do not affect these results. A natural analog of joint formation driven by phase transformations is found in the orthopyroxenite dykes of the Leka Ophiolite Complex (LOC), Norway. Joint formation in orthopyroxenite dykes results from serpentinization-driven expansion of the surrounding dunite matrix. Detailed field studies and measurements (583 sample points) yield S/Tf ratios between 0.1 and 1.0 with a mean value of 0.45 ± 0.20. We demonstrate that the strain mismatch-driven joint formation associated with interfacial slip explains the low S/Tf ratios obtained from field measurements and may also help us constrain rock strength.
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  • 14
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    Elsevier
    In:  Marine Pollution Bulletin, 58 . pp. 905-915.
    Publication Date: 2017-10-05
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  • 15
    Publication Date: 2017-08-08
    Description: The Masaya Caldera Complex has been the site of three highly explosive basaltic eruptions within the last six thousand years. A Plinian eruption ca. 2 ka ago formed the widespread deposits of the Masaya Triple Layer. We distinguish two facies within the Masaya Triple Layer from each other: La Concepción facies to the south and Managua facies to the northwest. These two facies were previously treated as two separated deposits (La Concepción Tephra and the Masaya Triple Layer of Pérez and Freundt, 2006) because of their distinct regional distribution and internal architectures. However, chemical compositions of bulk rock, matrix and inclusion glasses and mineral phases demonstrate that they are the product of a single basaltic magma batch. Additionally, a marker bed containing fluidal-shaped vesicular lapilli allowed us to make a plausible correlation between the two facies, also supported by consistent lateral changes in lithologic structure and composition, thickness and grain size. We distinguish 10 main subunits of the Masaya Triple Layer (I to X), with bulk volumes ranging between 0.02 and 0.22 km3, adding up to 0.86 km3 (0.4 km3 DRE) for the entire deposit. Distal deposits identified in two cores drilled offshore Nicaragua, at a distance of ∼ 170 km from the Masaya Caldera Complex, increase the total tephra volume to 3.4 km3 or ∼ 1.8 km3 DRE of erupted basaltic magma. Isopleth data of five major fallout subunits indicate mass discharges of 106 to 108 kg/s and eruption columns of 21 to 32 km height, affected by wind speeds of 〈 2 m/s to ∼ 20 m/s which increased during the course of the multi-episodic eruption. Magmatic Plinian events alternated with phreatoplinian eruptions and phreatomagmatic explosions generating surges that typically preceded breaks in activity. While single eruptive episodes lasted for few hours, the entire eruption probable lasted weeks to months. This is indicated by changes in atmospheric conditions and ash-layer surfaces that had become modified during the breaks in activity. The Masaya Triple Layer has allowed to reconstruct in detail how a basaltic Plinian eruption develops in terms of duration, episodicity, and variable access of external water to the conduit, with implications for volcanic hazard assessment.
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  • 16
    Publication Date: 2017-02-10
    Description: The Earth's mantle is chemically and isotopically heterogeneous, and a component of recycled oceanic crust is generally suspected in the convecting mantle [Hofmann and White, 1982. Mantle plumes from ancient oceanic crust. Earth Planet. Sci. Lett. 57, 421–436]. Indeed, the HIMU component (high µ = 238U/204Pb), one of four isotopically distinct end-members in the Earth's mantle, is generally attributed to relatively old (≥ 1–2 Ga) recycled oceanic crust in the form of eclogite/pyroxenite, e.g. [Zindler and Hart, 1986. Chemical geodynamics. Ann. Rev. Earth Planet. Sci. 14, 493–571]. Although the presence of the recycled component is generally supported by element and isotopic data, little is known about its physical state at mantle depths. Here we show that the concentrations of Ni, Mn and Ca in olivine from the Canarian shield stage lavas, which can be used to assess the physical nature of the source material (peridotite versus olivine-free pyroxenite) [Sobolev et al., 2007. The amount of recycled crust in sources of mantle-derived melts. Science 316, 412–417], correlate strongly with bulk rock Sr, Nd and Pb isotopic ratios. The most important result following from our data is that the enriched, HIMU-type (having higher 206Pb/204Pb than generally found in the other mantle end-members) signature of the Canarian hotspot magmas was not caused by a pyroxenite/eclogite constituent of the plume but appears to have been primarily hosted by peridotite. This implies that the old (older than ~ 1 Ga) ocean crust, which has more evolved radiogenic isotope compositions, was stirred into/reacted with the mantle so that there is not significant eclogite left, whereas younger recycled oceanic crust with depleted MORB isotopic signature (〈 1 Ga) can be preserved as eclogite, which when melted can generate reaction pyroxenite.
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  • 17
    Publication Date: 2017-09-27
    Description: Despite the particular scientific interest in the elements with high affinity to S and O2, but found in zero-valence state in nature, the origin of these native minerals has been little explored and remains obscure. Here we describe unique Sn–Pb droplets found in a closed analcime–calcite amygdale collected from a basaltic unit cropping out at Carsaig Bay (Isle of Mull, Inner Hebrides). The droplets consist of intimate intergrowths of nearly pure Sn0 and Pb0 domains in proportion 88:12 and are enveloped in a thin, brownish film of organic composition. The occurrence of the Sn–Pb droplets in a closed amygdale, their relationship with the host analcime + calcite and their Pb isotope composition (which does not match any known anthropogenic Pb source) rule out the possibility of anthropogenic contamination and support the natural origin of the Sn–Pb alloy. The variable isotope (Pb, Sr, Nd) compositions in different members of the host basaltic sequence suggest that a parent basaltic magma was modified by crustal assimilation and post-emplacement alteration processes. Considering all possible explanations, it appears that the most likely source of Pb for the Sn–Pb alloy is a discrete basaltic unit with an isotopic composition comparable to the Antrim basalts (Northern Ireland). The amygdale phases, on the other hand, show isotopic evidence for incorporation of elements from both local basaltic and sedimentary units. The apparent isotopic disequilibrium between Sn–Pb droplets and amygdale phases indicates a complex, multi-stage fluid evolution. The occurrence of Sn–Pb droplets in organic capsules suggests that the droplets and the enveloping organic substances are co-precipitates. This implies that the transportation and deposition of Sn and Pb might have occurred through organometallic compounds. We assume interaction of seawater fluids carrying metals leached from basaltic rocks with hydrocarbons from sedimentary units as a prerequisite for the formation of the organometallic complexes. The zeolites lining the basaltic vesicles might have destabilized the migrating organo-Sn and Pb compounds causing their breakdown and precipitation of Sn–Pb alloy.
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  • 18
    Publication Date: 2018-01-05
    Description: Salt tectonics and mud volcanism in the Latakia and Cyprus Basin, eastern Mediterranean, is investigated by means of swath sounding, reflection seismics and side-scan data as well as by camera and video sledge observations. Both basins are located east of Cyprus and are associated with the collision front between the African and Anatolian plate. The Pliocene–Quaternary sediment succession is underlain by up to 1 km thick Messinian evaporites. Both thick-skinned plate tectonic and thin-skinned salt tectonic control fluid dynamics and associated mud volcanism in the Latakia and Cyprus Basin as well as at the Troodos Latacia Culmination, which separates both basins. An end-member model is proposed which explains the presence of elongated topographic highs and trenches along the Troodos Larnaca Culmination and south of it by gravity gliding of the Messinian evaporites and associated fluid migration. Thin-skinned extension in the Troodos Larnaca Culmination and boudinage, respectively, facilitate fluid flow through and out of the evaporites. The fluid or mud flow dissolutes the salt layer and creates elongated trenches. Mud intrudes into the Pliocene–Quaternary sediments above the trenches. Consequently, the overburden is thickened and forms morphological ridges. South of the culmination the evaporites and overburden are folded due to thin-skinned shortening of the evaporites. In one instance fluid extrusion out of the evaporites is inferred from seismic data interpretation. The outflow caused a volume reduction and collapse of the evaporites. Mud volcanoes and fold anticlines align above deep-rooted transpressional fault systems which are associated with the African–Anatolian collision zone. The faults may act as conduits for rising fluids. In the western part of the survey area, where the Cyprus Arc strikes almost West–East and the collision occurred more frontal and stress was highest, mud volcanoes emerged. Further to the east, where the Cyprus Arc runs SW–NE and sinistral strike-slip has been proposed, fold anticlines evolved. Particular mud volcanoes and folds emerged prior to the deposition of the Messinian evaporites. The undisturbed upper Pleistocene sequences as well as the absence of significant mud outflow on the seafloor strongly suggest that the main fluid dynamic ceased.
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  • 19
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    Elsevier
    In:  Marine and Petroleum Geology, 26 . pp. 795-804.
    Publication Date: 2017-09-13
    Description: Heat flow anomalies provide critical information in active tectonic environments. The Gulf of Cadiz and adjacent areas are affected by the plate convergence between Africa and Europe, causing widespread deformation and faulting. Active thrust faults cause lateral movement and advection of heat that produces systematic variations in surface heat flow. In December 2003 new heat flow data were collected during the research vessel Sonne cruise SO175 in the Gulf of Cadiz over two sites of recent focused research activity: (i) the Gulf of Cadiz sedimentary prism and (ii) the Marques de Pombal escarpment. Both features have also been discussed as potential source areas of the Great Lisbon earthquake and tsunami of 1755. Background heat flow at the eastern terminus of the Horseshoe abyssal plain is about 52–59 mW/m2. Over the Gulf of Cadiz prism, heat flow decreases from ∼57 mW/m2 to unusually low values of 45 mW/m2 roughly 120 km eastward. Such low values and the heat flow trend are typical for active thrusting, supporting the idea of an east-dipping thrust fault. Slip rates are 10 ± 5 mm per year, assuming that the fault dips at 2°. A fault dipping at 5°, however, would result into slip rates of 1.5–5 mm per year, suggesting that subduction has largely ceased. Based on seismic data, the Marques de Pombal fault is interpreted as part of an active fault system located ∼100 km westward of Cape San Vincente. Heat flow over the fault is affected by refraction of heat caused by the 1 km high escarpment. Thermal models suggest that the slip rate along the fault must either be small or shear stresses acting on the fault are rather high. With respect to other fault zones, however, it is reasonable to assume that the fault's slip rate is small.
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  • 20
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    Elsevier
    In:  Earth and Planetary Science Letters, 288 (3-4). pp. 399-407.
    Publication Date: 2017-02-09
    Description: Newly pre-stack depth-migrated seismic images resolve the structural details of the western Java forearc and plate interface. The structural segmentation of the forearc into discrete mechanical domains correlates with distinct deformation styles. Approximately 2/3 of the trench sediment fill is detached and incorporated into frontal prism imbricates, while the floor sequence is underthrust beneath the décollement. Western Java, however, differs markedly from margins such as Nankai or Barbados, where a uniform, continuous décollement reflector has been imaged. In our study area, the plate interface reveals a spatially irregular, nonlinear pattern characterized by the morphological relief of subducted seamounts and thicker than average patches of underthrust sediment. The underthrust sediment is associated with a low velocity zone as determined from wide-angle data. Active underplating is not resolved, but likely contributes to the uplift of the large bivergent wedge that constitutes the forearc high. Our profile is located 100 km west of the 2006 Java tsunami earthquake. The heterogeneous décollement zone regulates the friction behavior of the shallow subduction environment where the earthquake occurred. The alternating pattern of enhanced frictional contact zones associated with oceanic basement relief and weak material patches of underthrust sediment influences seismic coupling and possibly contributed to the heterogeneous slip distribution. Our seismic images resolve a steeply dipping splay fault, which originates at the décollement and terminates at the sea floor and which potentially contributes to tsunami generation during co-seismic activity.
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  • 21
    Publication Date: 2017-12-12
    Description: The potential of solid waste originating from a recirculated fish culture system, i.e faecal material, uneaten food pellets and bacterial biofilms was examined as food source for the marine polychaete Nereis diversicolor. These polychaetes could be a valuable food for fish if they provide essential fatty acids to the fish. Therefore, we analysed the fatty acid profiles from feed and faecal materials, the sediment as well as the cultured organisms - fish and several batches of N diversicolor - from an integrated recirculating aquaculture system. The major fatty acids (saturated, monounsaturated and polyunsaturated) for all analysed fish feed, fish and faeces samples were C16:0, C18:1 and C22:6 (n - 3), accounting for 48% to 57% of the fatty acids in the samples. The major fatty acids within the sediment were C16:0. C18:1 and C18:3 (n - 3). accounting for 61% of the total fatty acids. The samples of N. diversicolor revealed C16:0. C18:1 and C20:5 (n - 3) as the major fatty acids. Combined, they accounted for 56% of the total fatty acids detected within the worm samples. The results indicate that a recycling or even an upgrade of excreted feed nutrients such as fatty acids, which were otherwise discharged, can be achieved through integrated aquaculture combining fish and worm culture. (C) 2009 Elsevier B.V. All rights reserved.
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  • 22
    Publication Date: 2017-01-23
    Description: The intensification of the Northern Hemisphere Glaciation (INHG) was a major event in the development of the current climate state, and as one of the most productive regions in the world's oceans, the behaviour of the Benguela Upwelling System (BUS) following the INHG is of wide interest. To investigate post-INHG changes in productivity and organic matter accumulation, total organic carbon and biomarker accumulation rates were determined for sediments from COP Site 1083 and compared to alkenone-derived sea surface temperatures and nitrogen isotopic compositions. These data indicate that the interval between 2.6 and 2.4 Ma was characterized by dramatic changes in upwelling intensity and organic carbon export on the northern edge of the modern BUS. The upwelling is reflected by significant changes in alkenone-derived SST estimates between glacial and interglacial intervals, with a total variability of 16 degrees C. The studied interval is also characterized by large changes in organic matter export as reflected by changes in TOC and biomarker accumulation rates, which show maxima during OIS 98 and during the transition from OIS 97 to 96. Intervals of elevated TOC are also characterized by elevated concentrations of sedimentary microbial biomarkers and lower %CaCO(3), suggesting that enhanced delivery of labile organic matter to the seafloor resulted in enhanced remineralisation with released CO(2) being consumed by CaCO(3) dissolution. However, in apparent contrast to recent Pleistocene sediments at the same site, organic matter export after the INHG was not solely driven by upwelling intensity. Of the three Pliocene glacial-interglacial cycles examined (OIS 101 to 96). each is unique with respect to the timing and magnitude of changes in organic matter accumulation. Each is also characterized by different algal assemblages as inferred from biomarker distributions, with OIS 97 and 96 particularly dominated by diatoms. We suggest that these differences reflect the important but evolving role of Southern Ocean waters in the Pliocene BUS: nutrient depletion of SO waters occurred during parts of Pliocene glacial intervals such that even intense upwelling did not persistently result in enhanced organic matter accumulation rates. (C) 2009 Elsevier B.V. All rights reserved.
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  • 23
    Publication Date: 2017-09-27
    Description: This study establishes for the first time the chronology and limnological history of Lake Amora (Dead Sea basin, Israel), whose deposits (the Amora Formation) comprise one of the longest exposed lacustrine records of the Pleistocene time. The Amora Formation consists of sequences of laminated primary aragonite and silty-detritus, Ca-sulfate minerals, halite and elastic units. This sedimentary sequence was uplifted and tilted by the rising Sedom salt diapir, exposing similar to 320 m of sediments on the eastern flanks of Mt. Sedom (the Arubotaim Cave (AC) section). The chronology of the AC section is based on U-disequilibrium dating ((230)Th-(234)U and (234)U-(238)U ages) combined with floating delta(18)O stratigraphy and paleomagnetic constraints. The determination of the (230)Th-(234)U ages required significant corrections to account for detrital Th and U. These corrections were performed on individual samples and on suites of samples from several stratigraphic horizons. The most reliable corrected ages were used to construct an age-elevation model that was further tuned to the oxygen isotope record of east Mediterranean foraminifers (based on the long-term similarity between the sea and lake oxygen isotope archives). The combined U-series-delta(18)O age-elevation model indicates that the (exposed) Amora sequence was deposited between similar to 740 and 70 ka, covering seven glacial-interglacial cycles (Marine Isotope Stages (MI5) 18 to 5). Taking the last glacial Lake Lisan and the Holocene Dead Sea lacustrine systems as analogs of the depositional-limnological environment of Lake Amora, the latter oscillated between wet (glacial) and more arid (interglacial) conditions, represented by sequences of primary evaporites (aragonite and gypsum that require enhanced supply of freshwater to the lakes) and elastic sediments, respectively. The lake evolved from a stage of rapid shifts between high and low-stand conditions during similar to 740 to 550 ka to a sabkha-like environment that existed (at the AC site) between 550 and 420 ka. This stage was terminated by a dry spell represented by massive halite deposition at 420 ka (MIS12-11). During MIS10-6 the lake fluctuated between lower and higher stands reaching its highest stand conditions at the late glacial MIS6, after which a significant lake level decline corresponds to the transition to the last interglacial (MISS) low-stand lake, represented by the uppermost part of the Formation. delta(18)O values in the primary aragonite range between 6.0 and -1.3 parts per thousand, shifting cyclically between glacial and interglacial intervals. The lowest 8180 values are observed during interglacial stages and may reflect short and intense humid episodes that intermittently interrupted the overall arid conditions. These humid episodes, expressed also by enhanced deposition of travertines and speleothems, seem to characterize the Negev Desert, and in contrast to the overall dominance of the Atlantic-Mediterranean system of rain patterns in the Dead Sea basin, some humid episodes during interglacials may be traced, to southern sources. (C) 2009 Elsevier Ltd. All rights reserved.
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  • 24
    Publication Date: 2012-10-22
    Description: The Mg- and Si-rich nature of the sub-cratonic lithospheric mantle (SCLM) beneath the Kaapvaal Craton indicates extensive melt depletion, followed by a Si-enrichment process. Six highly silica enriched peridotites from Kimberley containing high amounts of orthopyroxene (Opx) or garnet (Grt) that are locally concentrated in clots, were investigated to constrain the timing and nature of the Si-enrichment process. A clinopyroxene-bearing lherzolite containing an Opx-clot was studied to quantify the effects of recent metasomatism on the Si-enriched samples. Minerals from the lherzolite, together with Opx from harzburgites and Opx- and Grt-clots have Hf–Nd isotope ratios at the time of kimberlite eruption, 90 Ma, comparable to group I kimberlites and are close to trace element equilibrium with kimberlitic melts. This implies the xenoliths underwent major interaction with kimberlitic melts close to the time of kimberlite eruption. Harzburgites and mineral clots record equilibration pressures and temperatures of, respectively, between 3.5–4.3 GPa and 930–1060 °C. The garnets in Opx-clots have low Lu/Hf and εHf(t) −15, whereas garnets from Grt-clots have high Lu/Hf and εHf(t) +10. In contrast, Grt from both Grt- and Opx-clots have low Sm/Nd and εNd −10. The whole rock platinum group element (PGE) concentrations are an order of magnitude higher in the Grt-clot than the Opx-clot. Measured 187Os/188Os range from 0.1085 to 0.1222. The Grt-clot bearing sample yields Nd–Hf–Os isotope model ages that suggest formation in the Neoproterozoic (∼650 Ma). In contrast, an Opx-clot yields TRD ages of 2.8 Ga, which is interpreted as the time of formation of the host harzburgite. The Opx-clots and host harzburgites have comparable Lu–Hf isotope systematics that imply Opx growth at ∼1.3 Ga and hence their formation is not related to the Grt-clots. Garnets from Opx- and Grt-clots have elevated high-field strength element (HFSE) concentrations, and lack HFSE depletion relative to other trace elements with comparable degrees of incompatibility in the mantle (La/Nb 〈 0.5). In addition, calculated melts in equilibrium with Grt have strongly fractionated REE (Nd/Yb 〉 300) and HREE depletion (YbN 〈 0.1) suggesting equilibration with a hydrous melt that is more HREE depleted than a kimberlitic melt. Previous models that related Si-enrichment to subduction are inconsistent with the lack of HFSE depletion (La/Nb 〈 0.5). Therefore the favoured model for Opx- and Grt-clot formation is infiltration of a hydrous melt in a within plate geodynamical environment associated with volcanism in the Mid-proterozoic and Neoproterozoic, respectively. This implies that Si-enrichment of the Kaapvaal SCLM may be a consequence of numerous localised magmatic events rather than a single craton-wide process.
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  • 25
    Publication Date: 2014-01-27
    Description: A detailed investigation into the performance of two flow injection-chemiluminescence (FI-CL) manifolds (with and without a preconcentration column) for the determination of sub-nanomolar dissolved iron (Fe(II) + Fe(III)), following the reduction of Fe(III) by sulphite, in seawater is described. Kinetic experiments were conducted to examine the efficiency of reduction of inorganic Fe(III) with sulphite under different conditions and a rigorous study of the potential interference caused by other transition metals present in seawater was conducted. Using 100 μM concentrations of sulphite a reduction time of 4 h was sufficient to quantitatively reduce Fe(III) in seawater. Under optimal conditions, cobalt(II) and vanadium(IV)/(III) were the major positive interferences and strategies for their removal are reported. Specifically, cobalt(II) was masked by the addition of dimethylglyoxime to the luminol solution and vanadium(IV) was removed by passing the sample through an 8-hydroxyquinoline column in a low pH carrier stream. Manganese(II) also interfered by suppression of the CL response but this was not significant at typical open ocean concentrations. © 2009 Elsevier B.V. All rights reserved.
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  • 26
    Publication Date: 2015-01-27
    Description: The Gulf of Cadiz, off SW Iberia and the NW Moroccan margin, straddles the cryptic plate boundary between Africa and Eurasia, a region where the orogenic Alpine compressive deformation in the continental collision zone passes laterally to the west to strike-slip deformation. A set of new multibeam bathymetry, multi-channel and single-channel seismic data presented here image the main morphological features of tectonic origin of a significant part of the Gulf of Cadiz from the continental shelf to the abyssal plain. These morphotectonic features are shown to result from the reactivation of deeply rooted faults that changed their kinematics from the early Mesozoic rifting, through the Late Cretaceous–Paleogene collision, to the Pliocene–Quaternary thrusting and wrenching. The old faults control deep incised, more than 100 km long canyons and valleys. Several effects of neotectonics on deep water seabed are shown. These include: i) the complex morphology caused by wrenching on the 230 km long WNW–ESE faults that produced en echelon folds on the sediments; ii) the formation of up to 5 km wide crescent shaped scours at roughly 4 km water depth by reactivation of thrusts; iii) 10 km long creep folds on the continental slope; and iv) the formation of landslides on active fault escarpments. The present day deformation is partitioned on NE–SW thrusts and WNW–ESE to W–E strike-slip faults and is propagating northwards on N–S trending thrusts along the West Iberia Margin from 35.5°N to 38°N, which should be considered for seismic hazard.
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  • 27
    Publication Date: 2015-09-18
    Description: Particles sinking out of the euphotic zone are important vehicles of carbon export from the surface ocean. Most of the particles produce heavier aggregates by coagulating with each other before they sink. We implemented an aggregation model into the biogeochemical model of Regional Oceanic Modelling System (ROMS) to simulate the distribution of particles in the water column and their downward transport in the Northwest African upwelling region. Accompanying settling chamber, sediment trap and particle camera measurements provide data for model validation. In situ aggregate settling velocities measured by the settling chamber were around 55 m d(-1). Aggregate sizes recorded by the particle camera hardly exceeded I mm. The model is based on a continuous size spectrum of aggregates, characterised by the prognostic aggregate mass and aggregate number concentration. Phytoplankton and detritus make up the aggregation pool, which has an averaged, prognostic and size dependent sinking. Model experiments were performed with dense and porous approximations of aggregates with varying maximum aggregate size and stickiness as well as with the inclusion of a disaggregation term. Similar surface productivity in all experiments has been generated in order to find the best combination of parameters that produce measured deep water fluxes. Although the experiments failed to represent surface particle number spectra, in the deep water some of them gave very similar slope and spectrum range as the particle camera observations. Particle fluxes at the mesotrophic sediment trap site off Cape Blanc (CB) have been successfully reproduced by the porous experiment with disaggregation term when particle remineralisation rate was 0.2 d(-1). The aggregation-disaggregation model improves the prediction capability of the original biogeochemical model significantly by giving much better estimates of fluxes for both upper and lower trap. The results also point to the need for more studies to enhance our knowledge on particle decay and its variation and to the role that stickiness play in the distribution of vertical fluxes
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  • 28
    Publication Date: 2015-09-22
    Description: Planktic foraminiferal (PF) flux and faunal composition from three sediment trap time series of 2002–2004 in the northeastern Atlantic show pronounced year-to-year variations despite similar sea surface temperature (SST). The averaged fauna of the in 2002/2003 is dominated by the species Globigerinita glutinata, whereas in 2003/2004 the averaged fauna is dominated by Globigerinoides ruber. We show that PF species respond primarily to productivity, triggered by the seasonal dynamics of vertical stratification of the upper water column. Multivariate statistical analysis reveals three distinct species groups, linked to bulk particle flux, to chlorophyll concentrations and to summer/fall oligotrophy with high SST and stratification. We speculate that the distinct nutrition strategies of strictly asymbiontic, facultatively symbiontic, and symbiontic species may play a key role in explaining their abundances and temporal succession. Advection of water masses within the Azores Current and species expatriation result in a highly diverse PF assemblage. The Azores Frontal Zone may have influenced the trap site in 2002, indicated by subsurface water cooling, by highest PF flux and high flux of the deep-dwelling species Globorotalia scitula. Similarity analyses with core top samples from the global ocean including 746 sites from the Atlantic suggest that the trap faunas have only poor analogs in the surface sediments. These differences have to be taken into account when estimating past oceanic properties from sediment PF data in the eastern subtropical North Atlantic.
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  • 29
    Publication Date: 2015-09-25
    Description: In July 2007, phosphorus input by an upwelling event along the east coast of Gotland Island and the response of filamentous cyanobacteria were studied to determine whether introduced phosphorus can intensify cyanobacterial bloom formation in the eastern Gotland Basin. Surface temperature, nutrient concentrations, phytoplankton biomass and its stoichiometry, as well as phosphate uptake rates were determined in two transects between the coasts of Gotland and Latvia and in a short grid offshore of Gotland. In the upwelling area, surface temperatures of 11–12 °C and average dissolved inorganic phosphorus (DIP) concentrations of 0.26 μM were measured. Outside the upwelling, surface temperatures were higher (15.5–16.6 °C) and DIP supplies in the upper 10 m layer were exhausted. Nitrite and nitrate concentrations (0.01–0.22 μM) were very low within and outside the upwelling region. Abundances of filamentous cyanobacteria were highly reduced in the upwelling area, accounting for only 1.4–6.0% of the total phytoplankton biomass, in contrast to 18–20% outside the upwelling. The C:P ratio of filamentous cyanobacteria varied between 32.8 and 310 in the upwelling region, most likely due to the introduction of phosphorus-depleted organisms into the upwelling water. These organisms accumulate DIP in upwelling water and have lower C:P ratios as long as they remain in DIP-rich water. Thus, diazotrophic cyanobacteria benefit from phosphorus input directly in the upwelling region. Outside the upwelling region, the C:P ratios of filamentous cyanobacteria varied widely, between 240 and 463, whereas those of particulate material in the water ranged only between 96 and 224. To reduce their C:P ratio from 300 to 35, cyanobacteria in the upwelling region had to take up 0.05 mmol m−3 DIP, which is about 20% of the available DIP. Thus, a larger biomass of filamentous cyanobacteria may be able to benefit from a given DIP input. As determined from the DIP uptake rates measured in upwelling cells, the time needed to reduce the C:P ratio from 300 to 35 was too long to explain the huge bloom formations that typically occur in summer. However, phosphorus uptake rates increased significantly with increasing C:P ratios, allowing phosphorus accumulation within 4–5 days, a span of time suitable for bloom formation in July and August.
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  • 30
    Publication Date: 2015-08-06
    Description: The Middle Cambrian (~ 540 Ma) Gahcho Kué Kimberlite Field is situated about 275 km ENE of Yellowknife, NWT, Canada. The kimberlites were emplaced into 2.6 Ga Archean granitic rocks of the Yellowknife Supergroup. Four larger kimberlite bodies (5034, Tesla, Tuzo, and Hearne) as well as a number of smaller pipes and associated sheets occur in the field. In plan view, the Tuzo pipe has a circular outline at the surface, and it widens towards deeper levels. The pipe infill consists of several types of coherent and fragmental kimberlite facies. Coherent or apparent coherent (possibly welded) kimberlite facies dominate at depth, but also occur at shallow levels, as dikes intruded late in the eruptive sequence or individual coherent kimberlite clasts. The central and shallower portions of the pipe consist of several fragmental kimberlite varieties that are texturally classified as Tuffisitic Kimberlites. The definition, geometry and extent of the geological units are complex and zones controlled by vertical elements are most significant. The fluidal outlines of some of the coherent kimberlite clasts suggest that at least some are the product of disruption of magma that was in a semi-plastic state or even of welded material. Ragged clasts at low levels are inferred to form part of a complex peperite-like system that intrudes the base of the root zone. A variable, often high abundance of local wall-rock xenoliths between and within the kimberlite phases is observed, varying in size from sub-millimeter to several tens of meters. Wall-rock fragments are common at all locations within the pipe but are especially frequent in a domain with a belt-like geometry between 120 and 200 m depth in the pipe. Steeply outward-dipping bedded deposits made up of wall-rock fragments occur in deep levels of the pipe and are especially common under the downward-widening roof segments. The gradational contact relationships of these deposits with the surrounding kimberlite-bearing rocks as well as their location suggest that they formed more-or-less in situ. Different breccia facies inside the pipe suggest an origin by slumping, grain flows, rock fall or pyroclastic deposition. The shape and facies architecture of the Tuzo pipe suggests that the studied section of the pipe lies at a root zone–diatreme transitional structural level. Composite coherent kimberlite clasts imply that recycling processes were active over time, while reworked wall-rock rich deposits and ductily-deformed clasts of welded kimberlite point to the presence of temporary cavities in the root zone. The emplacement of the Tuzo pipe did not occur in a single, violent explosion, but involved repetitive volcanic explosions alternating with periods of relative quiescence. The observed features are typical of phreatomagmatic processes, which may include phases of less-explosive magmatic activity.
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  • 31
    Publication Date: 2015-11-18
    Description: Geophysical surveys and geological studies of gas hydrates in the western deep-water Ulleung Basin of the East Sea off the east coast of Korea have been carried out by the Korea Institute of Geoscience and Mineral Resources (KIGAM) since 2000. The work included a grid of 4782 km of 2D multi-channel seismic reflection lines and 11 piston cores 5–8 m long. In the piston cores, cracks generally parallel to bedding suggest significant in-situ gas. The cores showed high amounts of total organic carbon (TOC), and from the southern study area showed high residual hydrocarbon gas concentrations. The lack of higher hydrocarbons and the carbon isotope ratios indicate that the methane is primarily biogenic. The seismic data show areas of bottom-simulating reflectors (BSRs) that are associated with gas hydrates and underlying free gas. An important observation is the numerous seismic blanking zones up to 2 km across that probably reflect widespread fluid and gas venting and that are inferred to contain substantial gas hydrate. Some of the important results are: (1) BSRs are widespread, although most have low amplitudes; (2) increased P-wave velocities above some BSRs suggest distributed low to moderate concentration gas hydrate whereas a velocity decrease below the BSR suggests free gas; (3) the blanking zones are often associated with upbowing of sedimentary bedding reflectors in time sections that has been interpreted at least in part due to velocity pull-up produced by high-velocity gas hydrate. High gas hydrate concentrations are also inferred in several examples where high interval velocities are resolved within the blanking zones. Recently, gas hydrate recoveries by the piston coring and deep-drilling in 2007 support the interpretation of substantial gas hydrate in many of these structures.
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  • 32
    Publication Date: 2014-10-02
    Description: Trypanosomiasis and leishmaniasis pose major public health threats for many countries, particularly those in sub-Saharan Africa and South America. In the present study, we evaluated the in vitro antiprotozoal activity of three irregular, linear sesquiterpene lactones recently isolated from Greek Anthemis auriculata, namely anthecotulide (1), 4-hydroxyanthecotulide (2) and 4-acetoxyanthecotulide (3). Trypomastigote forms of Trypanosoma brucei rhodesiense and T. cruzi as well as axenic amastigotes of Leishmania donovani were used for testing. The cytotoxic potential of the compounds was also assessed against mammalian (rat) skeletal myoblasts (L6 cells). All compounds showed potent trypanocidal and leishmanicidal activity. 4-Hydroxyanthecotulide (2) appeared to be the most active compound against all parasites, particularly towards T. b. rhodesiense (IC50 0.56 μg/ml), whereas 4-acetoxyanthecotulide (3) was the least active. All three metabolites possessed toxicity on mammalian cells, which might limit their use as antiprotozoal agents.
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  • 33
    Publication Date: 2015-09-29
    Description: This article will review major features of the 'giant' Cape Blanc filament off Mauritania with regard to the transport of chlorophyll and organic carbon from the shelf to the open ocean. Within the filament, chlorophyll is transported about 400 km offshore. Modelled particle distributions along a zonal transect at 21 degrees N showed that particles with a sinking velocity of 5 m d(-1) are advected offshore by up to 600 km in subsurface particle clouds generally located between 400 m and 800 m water depth, forming an Intermediate Nepheloid Layer (INL). It corresponds to the depth of the oxygen minimum zone. Heavier particles with a sinking velocity of 30 m d(-1) are transported from the shelf within the Bottom Layer (BL) of more than 1000 m thickness, largely following the topography of the bottom slope. The particles advected within the BL contribute to the enhanced winter-spring mass fluxes collected at the open-ocean mesotrophic sediment trap site CB-13 (similar to 200 nm offshore), due to a long distance advection in deeper waters. The lateral contribution to the deep sediment trap in winter-spring is estimated to be 63% and 72% for organic carbon and total mass, respectively, whereas the lateral input for both components on an annual basis is estimated to be in the order of 15%. Biogenic opal increases almost fivefold from the upper to the lower mesotrophic CB-13 trap, also pointing to an additional source for biogenic silica from eutrophic coastal waters. Blooms obviously sink in smaller, probably mesoscale-sized patches with variable settling rates, depending on the type of aggregated particles and their ballast content. Generally, particle sinking rates are exceptionally high off NW Africa. Very high chlorophyll values and a large size of the Cape Blanc filament in 1998-1999 are also documented in enhanced total mass and organic carbon fluxes. An increasing trend in satellite chlorophyll concentrations and the size of the Cape Blanc filament between 1997 and 2008 as observed for other coastal upwelling areas is not documented
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  • 34
    Publication Date: 2017-07-21
    Description: The sediment temperature distribution at mud volcanoes provides insights into their activity and into the occurrence of gas hydrates. If ambient pressure and temperature conditions are close to the limits of the gas hydrate stability field, the sediment temperature distribution not only limits the occurrence of gas hydrates, but is itself influenced by heat production and consumption related to the formation and dissociation of gas hydrates. Located in the Sorokin Trough in the northern Black Sea, the Dvurechenskii mud volcano (DMV) was in the focus of detailed investigations during the M72/2 and M73/3a cruises of the German R/V Meteor and the ROV Quest 4000 m in February and March 2007. A large number of in-situ sediment temperature measurements were conducted from the ROV and with a sensor-equipped gravity corer. Gas hydrates were sampled in pressurized cores using a dynamic autoclave piston corer (DAPC). The thermal structure of the DMV suggests a regime of fluid flow at rates decreasing from the summit towards the edges of the mud volcano, accompanied by intermittent mud expulsion at the summit. Modeled gas hydrate dissociation temperatures reveal that the gas hydrates at the DMV are very close to the stability limits. Changes in heat flow due to variable seepage rates probably do not result in changes in sediment temperature but are compensated by gas hydrate dissociation and formation. (C) 2009 Elsevier Ltd. All rights reserved.
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  • 35
    Publication Date: 2017-02-10
    Description: We report new data on the major and trace element composition of melt inclusions in spinel phenocrysts (Mg# = 0.7-0.8, Cr/(Cr + Al) = 0.32-0.52, TiO2 = 0.06-0.60 wt.%) from Cretaceous MORB-like basalt (La/Yb = 0.94, Th/Nb = 0.055, Th/La = 0.041) in the Kamchatsky Mys ophiolites (Eastern Kamchatka). The melt inclusions preserved primitive melts (Mg# up to 0.72), which are remarkably depleted in incompatible trace elements compared to common MORBs. Numerous ultra-depleted inclusions from the studied sample have extraordinarily low Na2O (0.20-0.67 wt.%), TiO2 (0.16-0.5 wt.%), K (1.5-25 ppm), La (0.015-0.040 ppm), Zr (0.9-2 ppm), B (0.01-0.03 ppm), Ti/Zr = 300-1074, La/Yb = 0.008-0.075 and represent the most depleted melts known until now. The ultra-depleted melts from the Kamchatkan ophiolites are only comparable to a single melt inclusion from MORB of 9 degrees N Mid-Atlantic Ridge [Sobolev and Shimizu, Nature 363 (1993) 151-154] yet have higher FeO, CaO, heavy rare-earth element (Dy, Er, Yb) contents and lower Na2O and SiO2. These melts, possibly the last melt fractions produced in an upwelling mantle column, could represent the highest degrees (up to similar to 20%) of near-fractional melting of mantle with T-p >= 1400 degrees C, which started melting at similar to 75 km depth and continued to shallow depths of similar to 20 km. The presence of melts ranging in composition from ultra-depleted to compositions similar to Mauna Loa Volcano, Hawaii, high potential mantle temperature and association with rocks akin the Cretaceous Hawaiian tholeiites suggest that the trace element depleted melts preserved in spinel phenocrysts could have originated from extensive melting of a depleted component intrinsic to the Hawaiian plume or ambient upper mantle entrained and heated up at the plume margins. (C) 2009 Elsevier B.V. All rights reserved.
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  • 36
    Publication Date: 2017-09-27
    Description: We present major and trace element and Sr–Nd–Pb and U–Th–Pa–Ra isotope data for a small sample suite of primarily post-glacial, mildly alkalic volcanic rocks from the Snaefellsjökull central volcano situated off the main rift systems in western Iceland. The volcanic rocks are crystal-poor and range from olivine alkali basalt to trachyte and show tight correlations of major and trace elements that are explained by fractional crystallization involving removal of olivine, plagioclase, clinopyroxene, Fe–Ti oxide and apatite. Sr–Nd–Pb isotopes are practically invariant, consistent with derivation from the same source region. During fractionation from primitive basalt to evolved trachyte, (230Th/232Th), (230Th/238U) and (231Pa/235U) decrease progressively at broadly constant (238U/232Th). A continuous closed-system fractionation model that assumes constant initial (230Th/232Th) in the basaltic precursor melt indicates that hawaiite was derived from olivine basalt by not, vert, similar50% fractional crystallization within View the MathML source and trachyte by not, vert, similar80% fractionation within View the MathML source. An overrepresentation of evolved basalts and hawaiites with young inferred magma ages in the dataset is consistent with the parental precursor to these magmas intruded into the sub-volcanic magma plumbing system as a consequence of lithospheric rebound caused by deglaciation. Lavas affected by apatite removal have higher (231Pa/235U) than predicted for simple radioactive decay, suggesting apatite significantly fractionates U from Pa. The proposed fractionation model consistently explains our U-series data assuming View the MathML source and View the MathML source and View the MathML source. If applicable, these D values would indicate that the effect of apatite fractionation must be adequately considered when assessing differentiation time scales using (231Pa/235U) disequilibria data.
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  • 37
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    Elsevier
    In:  Palaeogeography Palaeoclimatology Palaeoecology, 278 (1/4). pp. 48-56.
    Publication Date: 2017-01-31
    Description: Until recently, the Arctic was assumed to be characterised by relatively warm conditions throughout the Early Cenozoic. However, recent investigations on deep-sea drilling cores from northern high latitudes, including the Arctic Ocean, give apparently contradicting results. Here we report the intermittent occurrence of certain temperature indicators in the Early Tertiary sedimentary sequence on Svalbard, which may represent the first direct northern high-latitude record of cold water temperatures for the early Cenozoic. Glendonites (calcite pseudomorphs after calcium carbonate hexahydrate) and erratics in otherwise fine-grained sediments require near-freezing temperatures and the presence of at least seasonal sea ice. This succession also contains coal seams and other warm climate indicators, but not on the same stratigraphical levels. These results imply the occurrence of cooling phases episodically during the warm background climate of the Paleocene and Eocene, suggesting that Arctic temperature variability was much greater than previously recognized.
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  • 38
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    Elsevier
    In:  Geochimica et Cosmochimica Acta, 73 . pp. 2645-2659.
    Publication Date: 2017-09-27
    Description: Nd concentration and isotope data have been obtained for the Canada, Amundsen, and Makarov Basins of the Arctic Ocean. A pattern of high Nd concentrations (up to 58 pM) at shallow depths is seen throughout the Arctic, and is distinct from that generally seen in other oceans where surface waters are relatively depleted. A range of isotopic variations across the Arctic and within individual depth profiles reflects the different sources of waters. The dominant source of water, and so Nd, is the Atlantic Ocean, with lesser contributions from the Pacific and Arctic Rivers. Radiogenic isotope Nd signatures (up to epsilon(Nd) = -6.5) can be traced in Pacific water flowing into the Canada Basin. Waters from rivers draining older terrains provide very unradiogenic Nd (down to epsilon(Nd) = -14.2) that can be traced in surface waters across much of the Eurasian Basin. A distinct feature of the Arctic is the general influence of the shelves on the Nd concentrations of waters flowing into the basins, either from the Pacific across the Chukchi Sea, or from across the extensive Siberian shelves. Water-shelf interaction results in an increase in Nd concentration without significant changes in salinity in essentially all waters in the Arctic, through processes that are not yet well understood. In estuarine regions other processes modify the Nd signal of freshwater components supplied into the Arctic Basin, and possibly also contribute to sedimentary Nd that may be subsequently involved in sediment-water interactions. Mixing relationships indicate that in estuaries, Nd is removed from major river waters to different degrees. Deep waters in the Arctic are higher in Nd than the inflowing Atlantic waters, apparently through enrichments of waters on the shelves that are involved in ventilating the deep basins. These enrichments generally have not resulted in major shifts in the isotopic compositions of the deep waters in the Makarov Basin (epsilon(Nd) similar to -10.5), but have created distinctive Nd isotope signatures that were found near the margin of the Canada Basin (with epsilon(Nd) similar to -9.0). The deep waters of the Amundsen Basin are also distinct from the Atlantic waters (with epsilon(Nd) = -12.3), indicating that there has been limited inflow from the adjacent Makarov Basin through the Lomonosov Ridge. (C) 2009 Elsevier Ltd. All rights reserved.
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  • 39
    Publication Date: 2017-02-09
    Description: Pressure solution is one of the main deformation mechanisms for lithify and stress release in the rocks from shallow subduction zones. We observed temperature-dependent pressure solution development in naturally deformed shale in Shimanto accretionary complex in southwest Japan. The pressure solution develops with shear-dominated or co-axial-dominated deformation. We evaluated apparent activation energy by applying the constitutive equation of pressure solution creep to the temperature-dependent relations. The activation energy of each deformation type was estimated as 18 kJ mol− 1 for shear-dominated and 45 kJ mol− 1 for co-axial-dominated shale. The energies enable us to speculate rate-limiting processes of pressure solution i.e. dissolution, diffusion and precipitation, by comparing the energies obtained in this study with energies had been measured by experiments. The lower activation energy estimated here was similar with that of diffusion. The similarity indicates that possible rate-limiting process of shale deformation in shallow subduction zone would be diffusion. The difference of energy between deformation types can be explained by distinctive grain boundary structure.
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  • 40
    Publication Date: 2017-09-27
    Description: We present the first comprehensive set of dissolved 10Be and 9Be concentrations in surface waters and vertical profiles of all major sub-basins of the Arctic Ocean, which are complemented by data from the major Arctic rivers Mackenzie, Lena, Yenisey and Ob. The results show that 10Be and 9Be concentrations in waters below 150 m depth are low and only vary within a factor of 2 throughout the Arctic Basin (350–750 atoms/g and 9–15 pmol/kg, respectively). In marked contrast, Be isotope compositions in the upper 150 m are highly variable and show systematic variations. Cosmogenic 10Be concentrations range from 150 to 1000 atoms/g and concentrations of terrigenous 9Be range from 7 to 65 pmol/kg, resulting in 10Be/9Be ratios (atom/atom) between 0.5 and 14 × 10−8. Inflowing Atlantic water masses in the Eurasian Basin are characterized by a 10Be/9Be signature of 7 × 10−8. The inflow of Pacific water masses across the Bering Strait is characterized by lower ratios of 2–3 × 10−8, which can be traced into the central Arctic Ocean, possibly as far as the Fram Strait. A comparison of the high dissolved surface 10Be and 9Be concentrations (corresponding to low 10Be/9Be signatures of ∼2 × 10−8) in the Eurasian Basin with hydrographic parameters and river data documents efficient and rapid transport of Be with Siberian river waters across the Siberian Arctic shelves into the central Arctic Basin, although significant loss and exchange of Be on the shelves occurs. In contrast, fresh surface waters from the Canada Basin also show high cosmogenic 10Be contents, but are not enriched in terrigenous 9Be (resulting in high 10Be/9Be signatures of up to 14 × 10−8). This is explained by a combination of efficient scavenging of Be in the Mackenzie River estuary and the shelves and additional supply of cosmogenic 10Be via atmospheric fallout and melting of old sea ice. The residence time of Be in the deep Arctic Ocean estimated from our data is 800 years and thus similar to the average Be residence time in the global ocean.
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  • 41
    Publication Date: 2017-07-28
    Description: During the Last Glacial Maximum much of North America was covered by the Laurentide ice sheet. Its melting during termination 1 led to systematic changes in proglacial lake formation, continental runoff, and possibly North Atlantic Meridional Overturning Circulation. The accompanying change in chemical weathering rates in the interior of North America throughout the deglaciation resulted in a pronounced change in seawater Pb isotope composition in the western North Atlantic Ocean. Here we present the first high-resolution records of seawater Pb isotope variations of North Atlantic Deep Water extracted from authigenic Fe–Mn oxyhydroxides in three sediment cores (51GGC, 1790 m depth; 31GGC, 3410 m depth; 12JPC, 4250 m depth) from the Blake Ridge off Florida. These data reveal a striking excursion from relatively unradiogenic 206Pb/204Pb as low as 18.93 towards highly radiogenic Pb isotope compositions that was initiated during the Bølling–Allerød interstadial and was most pronounced in both intermediate and deep waters during and after the Younger Dryas (206Pb/204Pb as high as 19.38 at 8.8 ka in 4250 m). This pattern is interpreted to be a direct function of increased inflow of continent-derived radiogenic Pb into the western North Atlantic, supplied through chemical weathering of North American rocks that had been eroded and freshly exposed during the preceding glacial cycle. These sediment-derived data are complemented by new laser ablation Pb isotope data from a ferromanganese crust from the Blake Plateau at 850 m water depth, which show only small glacial–interglacial Pb isotope variations of the Florida Current (206Pb/204Pb between 19.07 and 19.16). The lack of change in the Blake Plateau record at the same time as the radiogenic excursion in the deeper sediments supports a northern origin of the pulse of radiogenic Pb. After the Younger Dryas, the deep western North Atlantic has experienced a persistent highly radiogenic Pb supply that was most pronounced during the first half of the Holocene and still lasts until today.
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  • 42
    Publication Date: 2017-02-10
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  • 43
    Publication Date: 2016-06-15
    Description: Continental rifting at the Vøring Margin off mid-Norway was initiated during the earliest Eocene (~54 Ma), and large volumes of magmatic rocks were emplaced during and after continental breakup. In 2003, a marine survey collecting ocean bottom seismometer, single-channel re!ection, and magnetic data was conducted on the Norwegian Margin to constrain continental breakup and early sea!oor spreading processes. The pro"le described here crosses the northern part of the Vøring Plateau, and the crustal velocity model was constructed through a combination of ray-tracing and forward gravity modeling, the latter corrected for the thermal effects remaining from the sea!oor spreading. We found a maximum igneous crustal thickness of 18 km, decreasing to 6.5 km over the "rst ~6 M.y. after continental breakup. Both the volume and the duration of excess magmatism are about twice as large as that of the Møre Margin south of the East Jan Mayen Fracture Zone, which offsets the two margin segments by ~170 km. A similar reduction in magmatism occurs to the north over an along-margin distance of ~150 km to the Lofoten Margin, but without a margin offset. Both the geochemical data and the mean P-wave velocity indicate that there is active mantle upwelling combined with a moderate temperature increase during the earliest mantle melting at the Vøring Margin. The mean P-wave velocity versus crustal thickness also indicates that there is a transition from convection dominated to temperature dominated magma production ~2 M.y. after breakup. The magnetic data were used to derive plate half-spreading rates for the Northern Vøring Margin, which are very similar to that obtained at the Møre Margin. There is a strong correlation between magma productivity and early plate spreading rate, suggesting a common cause. A model for the breakup-related magmatism should be able to explain this correlation, but also the magma production peak at breakup, the along-margin magmatic segmentation, and the active mantle upwelling. Proposed end-member hypotheses comprise elevated uppermantle temperatures caused by a hot mantle plume, or edge-driven small-scale convection !uxing mantle rocks through the melt zone. Edge-driven convection does not easily explain these observations, but a mantle plume model in which buoyant plume material !ows laterally to pond in the rift-topography at the base of the lithosphere close to breakup time is promising: When the continents break apart, the hot and buoyant plume-material can !ow up into the rift zone from surrounding areas as the rift transits to drift, and the excess temperature of this material will then cause excess magmatism which dies off as the rift-restricted material is spent. The buoyancy of the plume-material may in addition cause active upwelling which can increase the melting furthermore, and also increase the force on the plate boundaries to enhance plate spreading rate. This conceptual model explains how both excess magmatism and spreading rate will be reduced similarly with time as the plume material is consumed by plate spreading, and thus correlate.
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  • 44
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    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 56 . pp. 1656-1674.
    Publication Date: 2016-11-01
    Description: The variability of two modes of Labrador Sea Water (LSW) (upper and deep Labrador Sea Water) and their respective spreading in the interior North Atlantic Ocean are investigated by means of repeated ship surveys carried out along the zonal WOCE line A2/AR19 located at 43–48°N (1993–2007) and along the GOOS line at about 48–51°N (1997–2002). Hydrographic section data are complemented by temperature, salinity, and velocity time series recorded by two moorings. They have been deployed at the western flank of the Mid-Atlantic Ridge (MAR) in the Newfoundland Basin during 1996–2004. The analysis of hydrographic anomalies at various longitudes points to a gradual eastward propagation of LSW-related signals, which happens on time scales of 3–6 years from the formation region towards the MAR. Interactions of the North Atlantic Current (NAC) with the Deep Western Boundary Current (DWBC) close to Flemish Cap point to the NAC being the main distributor of the different types of LSW into the interior of the Newfoundland Basin. Comparisons between the ship data and the mooring records revealed that the mooring sites are located in a region affected by highly variable flow. The mooring time series demonstrate an elevated level of variability with eddy activity and variability associated with the NAC considerably influencing the LSW signals in this region. Hydrographic data taken from Argo profiles from the vicinity of the mooring sites turned out to mimic quite well the temporal evolution captured by the moorings. There is some indication of occasional southward flow in the LSW layer near the MAR. If this can be considered as a hint to an interior LSW-route, it is at least of minor importance in comparison to the DWBC. It acts as an important supplier for the interior North Atlantic, distributing older and recently formed LSW modes southward along the MAR.
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  • 45
    Publication Date: 2017-07-19
    Description: The feeding behaviour of adults of the marine calanoid copepod Centropages hamatus was studied in laboratory experiments with ciliates and phytoplankton as food sources. The ingestion rate of algal (flagellates, diatoms) and ciliate prey (oligotrichs) as a function of prey concentration could be described by a Holling type III functional response. with close to zero ingestion rates at concentrations below 5 mu g Cl-1. In general, ingestion of ciliates was higher than ingestion of algae, and maximum feeding rates by adult males reached were half the feeding rates of adult females at prey concentrations exceeding 50 mu g Cl-1. When diatoms and ciliates were offered together C. hamatus (both sexes) fed exclusively on ciliates as long as they contributed with more than 5% to the mixture. This indicates the capability of active prey selection and switching between suspension feeding and ambush predation. Therefore, the feeding behaviour of adult C hamaths can be characterised as omnivorous with a preference for larger motile prey. This implies a trophic level above two, if there is a sufficient abundance of protozoan food available. (C) 2009 Elsevier B.V. All rights reserved.
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  • 46
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    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 56 (6). pp. 926-938.
    Publication Date: 2016-11-01
    Description: Labrador Sea convection was most intense and reached the greatest depths in the early 1990s, followed by weaker, shallower, and more variable convection after 1995. The Simple Ocean Data Assimilation (SODA) version 2.0.2/2.0.4 assimilation model is used to explore convective activity in the North Atlantic Ocean for the period from 1992 to 2007. Hydrographic conditions, which are relatively well observed during this period, are used to compare modeled and observed winter mixed-layer depths and water mass anomalies in relation to Deep Western Boundary Current transports and meridional overturning circulation (MOC) changes at the exit of the subpolar basin. The assimilation differs markedly from local observations in the March mixed-layer depth, which represents deep convection and water mass transformation. However, mean MOC rates at the exit of the subpolar gyre, forced by stratification in the mid-latitudes, are similar to estimates based on observations and show no significant decrease during the 1992–2007 period. SODA reproduces the deep Labrador Sea Water formation in the western North Atlantic without any clear indication of significant formation in the Irminger Sea while the lighter upper Labrador Sea Water density range is reached in the Irminger Sea in the 1990s, in agreement with existing assumptions of deep convection in the Irminger Sea and also supported by computed lag correlations with the Labrador Sea. Deep Water transformation mainly takes place in the eastern North Atlantic. The introduction of CFC-11 into the SODA model as a tracer reproduces the mean and multiyear variations of observed distributions.
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  • 47
    Publication Date: 2017-08-08
    Description: Nicaragua comprises seven historically active volcanoes (Cosigüina, San Cristobal, Telica, Cerro Negro, Momotombo, Masaya, and Concepcion), five of which are in a state of continuous degassing. Published measurements of the atmospheric dispersion of continuous emissions from Nicaraguan volcanoes, the chemical and aerosol microphysical modifications of the released gases and aerosols, and related acid deposition and impacts on the environment cover only short periods of time. We applied a three-dimensional atmosphere-chemistry/aerosol numerical model over Central America focussing on Nicaraguan volcanic emissions for month long simulation periods during the dry and wet seasons of 2003. The model is able to reproduce observed monthly precipitation and wind speed throughout the year 2003. Model results for near surface SO2 concentrations and SO2 dry deposition fluxes around Masaya volcano are in very good agreement with field measurements. During the dry season, oxidation of SO2 to sulphate plays only a minor role downwind of the Nicaraguan volcanoes and over the Pacific Ocean, whereas SO2 released from Arenal and Poas in Costa Rica is oxidised to sulphate much faster and closer to the volcanoes due to higher humidity and cloud water availability. During the wet season, more variable wind conditions lead to reduced dispersion of SO2 over the Pacific Ocean and increased dispersion inland. The availability of liquid water in the atmosphere favours sulphate formation close to the Nicaraguan volcanoes via aqueous phase oxidation and represents another limitation for the dispersion of SO2. Strong precipitation removes sulphate quickly from the atmosphere by wet deposition. Atmospheric SO2 concentrations and in particular dry deposition close to the volcanoes show a pronounced diurnal cycle.
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  • 48
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    Elsevier
    In:  Progress in Oceanography, 83 . pp. 143-150.
    Publication Date: 2016-10-04
    Description: The coastal upwelling off Mauritania and its connection with the oxygen minimum zone (OMZ) in the tropical Atlantic is investigated in an eddy-resolving general circulation model. Two main supply routes for the upwelling are identified. First a southern eastward pathway crossing 23 degrees W between 3 degrees N and 10 degrees N related to the equatorial zonal current system supplies up to 50% of the water upwelled in winter, and about 30% in summer. Second, another eastward pathway crossing 23 degrees W further north between 28 degrees N and 38 degrees N supplies 35% of the upwelled water in spring compared to 25% during the rest of the year. Most of the water of the northern pathway is entrained into the mixed layer already before reaching the upwelling region. Only the southern pathway contributes not recently ventilated waters to the upwelling. The connection with the OMZ is very weak, only about 1% of the upwelling waters originate here. On the other hand, if water from the OMZ reaches the surface mixed layer within 6 years, this mostly (71%) happens in the upwelling region
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  • 49
    Publication Date: 2017-09-27
    Description: We critically evaluate the applicability of Ca-isotope ratios in planktonic foraminifers as proxy for past sea surface temperatures (SST) and isotope composition of paleo-seawater (δ44Casw) reconstructions. Previous studies have shown discrepancies regarding the temperature sensitivity of Ca isotope fractionation in foraminifers of more than one order of magnitude. We present new data from the planktonic foraminifer species Orbulina universa, Globigerinoides sacculifer and Neogloboquadrina pachyderma (sinistral) from culture experiments, multinet deployments and coretop samples. Specimens of G. sacculifer cultured at low salinities (33–34.5) show predominantly no major temperature dependent Ca isotope fractionation, in contrast to previous individuals cultured at higher salinities of 34.5–36. The new data of O. universa are consistent with previously published results, revealing a small but significant temperature sensitivity. Calcium isotope fractionation in tests of N. pachyderma shows a significant variation with temperature, which is not uniform over the total investigated temperature range (−1.6 °C to +10 °C), possibly reflecting the influence of additional controlling factors besides temperature. Controlled dissolution experiments in the laboratory indicate that the Ca-isotope composition of G. sacculifer and N. pachyderma is relatively insensitive to partial dissolution of their tests. Calcium isotope ratios in the planktonic foraminifers G. sacculifer and N. pachyderma (s) reveal a complex Ca isotope fractionation behaviour, which is not yet fully understood. Additional validation studies are crucial to enhance the basic understanding of the calcium isotope systematics in planktic foraminifer shells, and the potential for applying Ca-isotope ratios as proxies for seawater temperature and the oceanic Ca budget.
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  • 50
    Publication Date: 2017-08-04
    Description: Studying the morphology and subsurface geometry of mud volcanoes provides insights into their activity. This paper describes the internal structure of the Håkon Mosby mud volcano (HMMV) in the southwestern Barents Sea and presents a conceptual model of its evolution. The lack of a mud edifice and the profuse gas flares suggest that in the recent past the mud volcano evolution was predominantly controlled by venting of gas-rich fluids and free gas. However, the analysis of high-resolution single-channel seismic (SCS) data reveals for the first time the existence of a pseudo-mud chamber at the top of the 3 km deep central conduit. It was once created at the seabed and is now a buried expression that acts as mud chamber. The pseudo-mud chamber is situated approximately 300 m below the seafloor, directly above the 330 ka Bear Island Slide (BIS) scar reflection and below glacigenic debris flow deposits that constitute the sediment on top. The sediment profiler data indicates a younger mud deposit above the debris flows, which points to a reactivation of the mud volcano. The reactivation was most likely triggered by the contrast in density between the gas-rich mud chamber and the high-density debris flow deposits. Three stages, i.e. initiation, sealing and reactivation, and a second active period define the evolution of this young mud volcano. Both, the morphology and size of the conduit as well as in-situ temperature gradients point towards a focused and rapid fluid flow.
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  • 51
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    Elsevier
    In:  Geochimica et Cosmochimica Acta, 73 . pp. 91-101.
    Publication Date: 2017-09-27
    Description: The first Hf isotope data for seawater are reported for a series of stations in the Northwestern Pacific and define a range from epsilon(Hf) = 3.5 +/- 1.4 to 8.6 +/- 1.6. Most samples have values within error of the average of epsilon(Hf) = 5.9, but significant variations are found in intermediate waters at a depth of 600 m, as well as in deep waters. The Nd and Hf isotope compositions of the deep waters fall within the range of values found for surfaces of hydrogenetic ferromanganese crusts in the region, confirming that Hf in the Fe-Mn crusts has been derived from the overlying water column, which thus provide an archive of past seawater compositions. Although the seawater samples are generally close to the global epsilon(Nd)-epsilon(Hf) correlation obtained from ferromanganese crusts, there are significant deviations from this correlation indicating that there is some additional decoupling between Nd and Hf isotope signals, most likely caused by local water mass mixing and differences in residence times. This is not resolved in the crust samples, which integrate seawater signals over 10(4) years. The combined use of these two isotope systems in seawater therefore provides an additional dimension for tracing water masses in the oceans. Studies of the distribution of oceanic Hf isotope compositions that have been confined to deep water and boundary waters, as recorded in seafloor ferromanganese crusts, can now be extended and aimed at characterising the entire present-day water column. Average Hf concentrations measured in this study are somewhat lower than previously reported, suggesting a shorter residence time for Hf in the global oceans, although the uncertainty in the extent of Hf removal from the water column during estuarine mixing as well as a lack of data on hydrothermal and dust inputs remains a limit on how well the residence time can be defined. (C) 2008 Elsevier Ltd. All rights reserved.
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  • 52
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    Elsevier
    In:  Journal of Volcanology and Geothermal Research, 186 (3/4). pp. 361-378.
    Publication Date: 2017-08-08
    Description: A model of diatreme evolution in a shallow marine setting is based on a multi-disciplinary analysis of diatremes in the Iblean Mountains (Sicily). The approach includes stratigraphic, volcanological, structural, petrologic and compositional data. We invoke a complex interplay of internal (rapid ascent and pyroclastic fragmentation of a volatile (CO2)-rich nephelinitic magma at depth) and external factors. These comprise hydroclastic explosions due to near-surface interaction of the rising particle/volatile mixture with seawater and water-saturated lime mud. Other external factors contributing to diatreme formation include regional and local tectonics (graben formation in pull-apart motion) combined with lateral pipe enlargement by bedrock-spalling and radial block subsidence into the diatreme pipe. We suggest that fragmentation of volatile-rich magma due to internal eruption forcing was fundamental in the formation of the Iblean shallow marine diatremes. Internal and external factors may act to a variable degree, however, during diatreme evolution in general.
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  • 53
    Publication Date: 2017-08-22
    Description: The dissolution of in-situ generated methane hydrate in undersaturated, synthetic seawater (S = 35) was investigated in a series of laboratory-based experiments at P-/T-conditions within the hydrate stability field. A controlled flow field was generated across the smooth hydrate surface to test if, in addition to thermodynamic variables, the dissolution rate is influenced by changing hydrodynamic conditions. The dissolution rate was found to be strongly dependent on the friction velocity, showing that hydrate dissolution in undersaturated seawater is a diffusion-controlled process. The experimental data was used to obtain diffusional mass transfer coefficients kd, which were found to correlate linearly with the friction velocity, u★. The resulting kd/u★-correlation allows predicting the flux of methane from natural gas hydrate exposures at the sediment/seawater interface into the bulk water for a variety of natural P, T and flow conditions. It also is a tool for estimating the rate of hydrate regrowth at locations where natural hydrate outcrops at the seafloor persist in contact with undersaturated seawater
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  • 54
    Publication Date: 2016-10-04
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  • 55
    Publication Date: 2017-08-04
    Description: Newly acquired bathymetric and seismic reflection data have revealed mass-transport deposits (MTDs) on the northeastern Cretan margin in the active Hellenic subduction zone. These include a stack of two submarine landslides within the Malia Basin with a total volume of approximately 4.6 km(3) covering an area of about 135 km(2). These two MTDs have different geometry, internal deformations and transport structures. The older and stratigraphic lower MTD is interpreted as a debrite that fills a large part of the Malia Basin, while the second, younger MTD, with an age of at least 12.6 cal. ka B.P., indicate a thick, lens-shaped, partially translational landslide. This MTD comprises multiple slide masses with internal structure varying from highly deformed to nearly undeformed. The reconstructed source area of the older MTD is located in the westernmost Malia Basin. The source area of the younger MTD is identified in multiple headwalls at the slope-basin-transition in 450 m water depth. Numerous faults with an orientation almost parallel to the southwest-northeast-trending basin axis occur along the northern and southern boundaries of the Malia Basin and have caused a partial steepening of the slope-basin-transition. The possible triggers for slope failure and mass-wasting include (i) seismicity and (ii) movement of the uplifting island of Crete from neotectonics of the Hellenic subduction zone, and (iii) slip of clay-mineral-rich or ash-bearing layers during fluid involvement. (c) 2009 Elsevier B.V. All rights reserved.
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  • 56
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    Elsevier
    In:  Deep-Sea Research Part II-Topical Studies in Oceanography, 56 . pp. 1868-1983.
    Publication Date: 2016-10-13
    Description: Analysis of the temporal and spatial variability of biological processes and identification of the main variables that drive the dynamic regime of marine ecosystems is complex. Correlation between physical variables and long-term changes in ecosystems has routinely been identified, but the specific mechanisms involved remain often unclear. Reasons for this could be various: the ecosystem can be very sensitive to the seasonal timing of the anomalous physical forcing; the ecosystem can be contemporaneously influenced by many physical variables and the ecosystem can generate intrinsic variability on climate time scales. Marine ecosystems are influenced by a variety of physical factors, e.g., light, temperature, transport, turbulence. Temperature has a fundamental forcing function in biology, with direct influences on rate processes of organisms and on the distribution of mobile species that have preferred temperature ranges. Light and transport also affect the physiology and distribution of marine organisms. Small-scale turbulence determines encounter between larval fish and their prey and additionally influences the probability of successful pursuit and ingestion. The impact of physical forcing variations on biological processes is studied through long-term observations, process studies, laboratory experiments, retrospective analysis of existing data sets and modelling. This manuscript reviews the diversity of physical influences on biological processes, marine organisms and ecosystems and their variety of responses to physical forcing with special emphasis on the dynamics of zooplankton and fish stocks.
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  • 57
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    Elsevier
    In:  Geochimica et Cosmochimica Acta, 73 (13). A285-A285.
    Publication Date: 2012-07-05
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  • 58
    Publication Date: 2017-08-04
    Description: Detailed exploration with remotely operated and autonomous deep submergence vehicles has revealed, at 9 degrees 33'S, the presence of the southernmost active hydrothermal field known so far on the Mid-Atlantic Ridge. The size of the hydrothermal field, which we have named "Lilliput", is about 1000 m x 250 m. It lies in a water depth of 1500 m on a ridge segment (Segment A3) with considerably thickened crust of 11 km. Four relatively small diffuse vent sites occur on a large young (estimated 〈100 years old) lava flow, partly covering the flow with hydrothermal Fe-oxide/hydroxide sediments. Based on homogeneous major element compositions of ca. 25 lava samples, this flow covers an area of at least 5 km x 0.6 km. The lava flow erupted from a series of parallel fissures at the western edge of the flow and a volcanic ridge consisting of up to 30 m high pillow mounds. The volcanic ridge probably represents the surface expression of an underlying dike which fed the flow. Several drained lava pond structures were observed within the flow but only one shows hydrothermal activity. The hydrothermal venting and precipitation of abundant Fe-oxyhydroxides appear to be related to the young diking and eruption event and the four different hydrothermally active sites of the Lilliput field lie along and almost equidistant from the eastern flank of the supposed dike. Although a hydrothermal plume some 500 m above the seafloor was found in two consecutive years (2005 and 2006), no high-temperature venting associated with Lilliput has been found. in agreement with findings at other ridges with thick crust such as Reykjanes. High magma supply rate and frequent diking and eruption events may lead to hot hydrothermal vents being rare in slow-spreading segments with thick crust whereas diffuse venting is abundant. Interestingly, the fauna at the Lilliput vents largely consists of small and apparently juvenile mussels (Bathymodiolus sp.) and did not show any signs of growth during the four years of continuing observations possibly reflecting pulsing hydrothermal activity.
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  • 59
    Publication Date: 2017-12-07
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  • 60
    facet.materialart.
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    Elsevier
    In:  Remote Sensing of Environment, 113 (9). pp. 1853-1867.
    Publication Date: 2019-01-23
    Description: A new Bitemporal Mineral Dust Index (BMDI) is derived from Meteosat Second Generation (MSG) infrared observations over land at two different time slots per day. This daily dust index is evaluated with AErosol RObotic NETwork (AERONET) surface observations, MODerate resolution Imaging Spectro-radiometer (MODIS) “Deep Blue” Aerosol Optical Depth (AOD) and Ozone Monitoring Instrument (OMI) Aerosol Index, showing a good capability of the BMDI for dust detection and dust load estimation over land and also over deserts. BMDI dust detection is shown to be limited in scenes with high atmospheric humidity as e.g. coastal regions. In particular the insensitivity of BMDI to biomass burning aerosol is shown, leading to the possibility of remote sensing of mineral dust also in regions with large contributions of biomass burning aerosol to the total column aerosol concentrations. Time series of mineral dust as inferred from BMDI for the year 2006 are presented for four regions over the Sahara. These time series show strong (and different) annual cycles of dust load for all four regions. Especially the strong episodic character of atmospheric dust in the main source regions can be inferred from BMDI observations.
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  • 61
    Publication Date: 2017-10-12
    Description: Neogene marine sediments can be dated via decay of the cosmogenic radionuclide Be-10. Two cores from the Alpha and Mendeleev Ridges in the Arctic Ocean have been analyzed for seawater-derived beryllium (Be) isotopes in order to date the sediments and to calculate sedimentation rates. The decrease of Be-10 concentration in the cores was used to calculate first order sedimentation rates. To eliminate the dilution effect of beryllium caused by short-term changes in sedimentation rate and grain size, the Be-10 concentrations were normalized to the terrigenous stable isotope Be-9 determined in the same sample aliquot. The measured Be-10 concentrations yield low average sedimentation rates for the Alpha and Mendeleev Ridges of 2.3 mm ka(-1) and 2.7 mm ka(-1), respectively. Sedimentation rates calculated from the Be-10/Be-9 ratios result in similarly low values, ranging from 0.2 to 6.8 mm ka(-1) for the Alpha Ridge core and from 1.9 to 6.9 mm ka(-1) for the Mendeleev Ridge core. However, amino acid racemization dating for the past 150 ka of a core adjacent to the Mendeleev Ridge core studied here indicates significantly higher sedimentation rates than calculated from the downcore decrease of Be-10 and Be-10/Be-9. If such higher rates also prevailed at the locations of our cores, for which there is biostratigraphic evidence, either the supply of Be-10 was much lower than assumed or that of Be-9 was much higher. This could imply that the signature of the deep waters in this part of the Arctic Ocean compared to today was largely different for most of the past approximately one million years with a significantly lower Be-10/Be-9 ratio. Our study also addresses the variability of beryllium isotopes in sediment cores across the Arctic Ocean through a comparison of previously published results. Calculated Be-10 fluxes reveal low values in the Amerasian Basin and highest values in the Eurasian Basin, near the Fram. Strait. The decrease of Be isotopes in the two studied Amerasian Basin cores may thus have been caused by environmental factors such as significantly reduced inflow of Atlantic waters in the past, reduced input of Be-10 and/or increased input of Be-9 from the shelves, combined with a more efficient sea ice shielding in this part of the Arctic Ocean. (C) 2009 Elsevier B.V. All rights reserved.
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  • 62
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    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 56 . pp. 2216-2234.
    Publication Date: 2016-11-01
    Description: Cold-water coral ecosystems building cold-water carbonate mounds occur worldwide and are especially developed along the European margin, from northern Norway to the Gulf of Cadiz. A remarkable mound province is documented southwest of Ireland along the Porcupine and Rockall Banks. In this area carbonate mounds are formed in water depths between 500 and 1200 m and are often densely settled by cold-water coral ecosystems offering many ecological niches for benthic foraminifera. We investigated total (unstained) benthic foraminiferal assemblages from surface sediments (0–1 cm, 〉63 μm size fraction) of this region with the aim to trace their distribution patterns and to test if they can be used as bioindicators for facies characterization in different parts of carbonate mound systems. Our quantitative data were further statistically treated with non-metric multidimensional scaling (nMDS) based on Bray–Curtis similarity matrix to highlight community patterns that were not readily apparent. Our results indicate that different benthic foraminiferal assemblages characterize different facies along cold-water carbonate mounds and are related to the environmental conditions and available substrates. The following facies can be described: (1) the Off-Mound Facies is dominated by uvigerinids and other infaunal species; (2) the Dropstone Facies is characterized by infaunal Globocassidulina subglobosa and attached-epifaunal Cibicidoides sp.; (3) the Dead Coral Facies is characterised by epifaunal species (e.g., Planulina ariminensis, Hanzawaia boueana) and infaunal species (Spiroplectinella wrightii, Angulogerina angulosa, Epistominella vitrea); (4) the Living Coral Facies includes both infaunal and epifaunal species, but is dominated by the epifaunal Discanomalina coronata; and (5) the Sandwave Facies contains high abundances of epifaunal species including D. coronata. Based on this distribution, we propose D. coronata, as an indicator species to identify active mounds and/or living cold-water coral ecosystems. Our results also emphasise the importance of studying the small size fractions that yield many infaunal species. A causal link exists between distribution patterns of benthic foraminifera and cold-water coral facies, thus providing an independent tool to identify and describe the different facies in this setting.
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  • 63
    facet.materialart.
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    Elsevier
    In:  Geochimica et Cosmochimica Acta, 73 . pp. 3218-3233.
    Publication Date: 2017-09-27
    Description: The first isotopic compositions of dissolved hafnium in seawater from across the Arctic Ocean are reported. Most samples from the four sub-basins of the Arctic Ocean have values within error of an average of epsilon(Hf) = +0.8. Combined Hf-Nd isotope compositions do not fall on the well-established positive correlation for mantle and crustal rocks. Instead, Arctic waters have Hf that is more radiogenic than that typically found in rocks with similar Nd isotope compositions, a feature previously found in ferromanganese crusts and waters from the Pacific Ocean. Arctic seawater samples generally fall on the lower part of the ferromanganese crust array, reflecting influences of inputs from Arctic rivers and interactions of shelf waters with underlying sediments. Arctic rivers have much higher Hf concentrations (7-30 pM) than Arctic seawater (0.36-4.2 pM). Water from the Mackenzie River has the least radiogenic Hf, with epsilon(Hf) = -7.1 +/- 1.7, and plots furthest away from the ferromanganese crust array, while waters from the Ob, Yenisey, and Lena Rivers have values that are indistinguishable from most Arctic waters. In the Amundsen, Makarov, and Canada basins, Hf concentrations are highest at the surface and lowest in the deeper waters, reflecting the influences of riverine inputs and of waters that have flowed over the extensive Siberian continental shelves and have Nd and Hf characteristics that reflect water-sediment interactions. This is in contrast to the relatively low near surface Hf concentrations reported for locations elsewhere. The Pacific water layer in the Canada Basin exhibits the highest value of epsilon(Hf) = +6.8 +/- 1.8, reflecting the Hf isotopic composition of waters entering the Arctic from the Pacific Ocean. Mixing relationships indicate that a substantial fraction of the Hf in the Mackenzie River is lost during estuarine mixing; the behaviour of Hf from other rivers is less constrained. (C) 2009 Elsevier Ltd. All rights reserved.
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  • 64
    Publication Date: 2017-08-04
    Description: Continental shelves represent areas of highest economical and ecological importance. Nevertheless, these sedimentary systems remainpoorly understood due to a complex interplay of various factors and processeswhich results in highly individual construction schemes. Previous studies of sedimentary shelf systems have mainly focused on a limited number of cores, retrieved from Holocene fine-grained depocentres. As such, the relation between shelf architecture and sedimentary history remains largely obscure. Here,we present newdata fromthe NW Iberian shelf comprising shallow-seismic profiles, a large number of sediment cores, and an extended set of radiocarbon dates to reveal the Late Quaternary evolution of a low-accumulation shelf system in detail. OntheNWIberian shelf, threemain seismic units are identified. These overly a prominent erosional unconformity on top of the basement. The lowermost Unit 1 is composed of maximal 75-m thick, Late Tertiary to Pleistocene deposits. The youngest sediments of this unit are related to the last glacial sea-level fall. Unit 2 was controlled by the deglacial sea-level rise and shows a maximumthickness of 15 m. Finally, Unit 3 comprises deposits related to the late stage of sea-level rise and the modern sea-level highstand with a thickness of 4 m in mid-shelf position. Two pronounced seismic reflectors separate these main units from each other. Their origin is related to (1) exposure and ravinement processes during lower sea level, and (2) to reworking and re-deposition of coarse sediments during subsequent sea-level rise. According to the sediment core ground-truthing, sediments of the Late Tertiary to Pleistocene unit predominantly display homogenous fine sands with exceptional occurrences of palaeosols that indicate an ancient exposure surface. Fine sands which were deposited in the run of the last sea-level rise show a time-transgressive retrogradational development. The seismic reflectors, bounding the individual units, appear in the cores as 0.1 to 1-m thick deposits consisting either of shell gravels or siliceous coarse sands with gravels. The modern sea-level highstand stage is characterised by zonal deposition of mud forming a mud belt in mid-shelf position, and sediment starvation on outer shelf zones. Radiocarbon ages indicate that this mud beltwas the main depocentre for river-supplied fine material on the NWIberian shelf at least over the past 5.32 ka BP. The initial onset of this depocentre is proposed to be related to a shift in the balance between rate of sea-level rise and amount of terrigenous sediment supply. Various other stratigraphical shelf reconstructions reveal analogies in architecturewhich indicate that timing and shaping of the individual units on low-accumulation shelves is fundamentally controlled by eustatic sea-level changes. Other factors of local importance such as differential elevation of the basement and the presence of morphological barriers formed by rocky outcrops on the seafloor have additionally modifying influence on the sedimentary processes.
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  • 65
    facet.materialart.
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    Elsevier
    In:  Journal of Experimental Marine Biology and Ecology, 372 . pp. 75-81.
    Publication Date: 2017-07-11
    Description: The small sepiolid cephalopod Rossia moelleri Steenstrup, 1856 transfers sperm by implantation of spermatangia into female tissue. Although this is a common sperm transfer and storage strategy in cephalopods, the mechanism behind implantation of spermatangia is poorly understood. In the lab, we artificially induced the spermatophoric reaction and spermatangia implanted into female tissue. The force necessary to penetrate the mantle was measured using a needle attached to a force transducer. Taking diameter and bluntness factor into account, this force was estimated to be 0.3 N. Analysis of the spermatophoric reaction showed that the maximum force (1.12 μN–9.36 μN) produced as a result of acceleration (1.57–3.59 mm/s2) of the forward moving sperm mass (2.6–7 mg) was insufficient to be solely responsible for the penetration of the spermatangia into tissue. Scanning electron microscopy revealed no structures that could have facilitated the implantation of the spermatangium. Histological sections of the implanted spermatangium visualized the cement body being orally secreted from the spermatangium, probably facilitating the implantation either by lysis of the surrounding tissue or by acting as a lubricant during implantation. This study shows that the autonomous implantation process of spermatangia of R. moelleri does not have a purely mechanical basis but necessitates an additional, probably chemical mechanism or a combination of these two.
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  • 66
    facet.materialart.
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    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 56 . pp. 1615-1632.
    Publication Date: 2016-11-01
    Description: A comprehensive analysis of velocity data from subsurface floats in the northwestern tropical Atlantic at two depth layers is presented: one representing the Antarctic Intermediate Water (AAIW, pressure range 600–1050 dbar), the other the upper North Atlantic Deep Water (uNADW, pressure range 1200–2050 dbar). New data from three independent research programs are combined with previously available data to achieve blanket coverage in space for the AAIW layer, while coverage in the uNADW remains more intermittent. Results from the AAIW mainly confirm previous studies on the mean flow, namely the equatorial zonal and the boundary currents, but clarify details on pathways, mostly by virtue of the spatial data coverage that sets float observations apart from e.g. shipborne or mooring observations. Mean transports in each of five zonal equatorial current bands is found to be between 2.7 and 4.5 Sv. Pathways carrying AAIW northward beyond the North Brazil Undercurrent are clearly visible in the mean velocity field, in particular a northward transport of 3.7 Sv across 16°N between the Antilles islands and the Mid-Atlantic Ridge. New maps of Lagrangian eddy kinetic energy and integral time scales are presented to quantify mesoscale activity. For the uNADW, mean flow and mesoscale properties are discussed as data availability allows. Trajectories in the uNADW east of the Lesser Antilles reveal interactions between the Deep Western Boundary Current (DWBC) and the basin interior, which can explain recent hydrographic observations of changes in composition of DWBC water along its southward flow.
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  • 67
    Publication Date: 2014-01-27
    Description: This paper presents the results of an inter-comparison exercise undertaken to test the reliability and performance of a voltammetric in situ profiling system (VIP system) and carried out by partners based in Italy, Sweden, Switzerland and the UK. The VIP system was designed to allow in situ simultaneous monitoring of the dynamic fractions (i.e. the maximum potentially bioavailable fractions) of Cu(II), Pb(II) and Cd(II) in natural waters at a frequency of 2-3 analyses h - 1. The four participating groups used the VIP systems under laboratory conditions to determine dissolved concentrations of Cu, Pb and Cd in river, estuarine and coastal water reference materials (SLRS-3/4, SLEW-2/3 and CASS3/4, respectively). The accuracy of the VIP method was comparable to that of established methodologies, including inductively coupled plasma mass spectrometry and voltammetric methods using mercury-electrodes. The VIP systems were also applied to determine the dynamic fractions of the target analytes in freshly collected samples ex situ, as well as in situ in contrasting European marine waters. There was good agreement between the concentrations of the dynamic metal fractions determined in laboratory analyses, and observed during the simultaneous deployment of up to five VIP instruments for periods of several hours in coastal waters. The simultaneous in situ deployment of two VIP instruments in an estuary showed a consistent analytical performance over several days of continuous operation. The results of this inter-comparison exercise show that the VIP system is a reliable submersible probe for accurate, sensitive and high resolution in situ monitoring of dissolved metal fractions in the picomolar (Cd, Pb) and nanomolar (Cu) concentration ranges. © 2009 Elsevier B.V. All rights reserved.
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  • 68
    Publication Date: 2015-01-27
    Description: New high-resolution multi-beam bathymetry data allowed the recognition of several bathymetric lineaments (ca. 100 km long, trending WNW–ESE) in seafloor sediments of the Gulf of Cadiz, offshore SW Iberia. The interpretation of multi-channel (MCS) profiles crosscutting these lineaments showed that they are controlled by underlying deep seated faults, which have endured a polyphase reactivation history. To get insights on the Recent tectonic evolution of these structures, we performed two sets of analogue modelling experiments, assuming: 1) right-lateral strike-slip basement faulting and coupled passive shearing affecting an overlying soft cover; and 2) low-angle transpressive deformation along a narrow shear band overlying the fault. Our results show a good correlation between the experimentally obtained structural patterns and the natural morphotectonic lineaments, allowing the use of some of the observed natural features as strain gauges. Based on this, we conclude that the study lineaments correspond to the bathymetric expression of ongoing dextral wrenching reactivation of WNW–ESE pre-existing faults, and we estimate the age of this tectonic reactivation as being ca. 1.8 Ma (i.e. form late Pliocene to Present day). These characteristics agree with the most recent kinematic models derived from geodetic observations, indicating that Present day convergence between Nubia and Iberia is subparallel to the newly identified lineaments and occurs at a 4 mm/yr rate.
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  • 69
    Publication Date: 2018-03-09
    Description: Distributions of dissolved vitamin B12 and total dissolved Co were measured to gain an understanding of the cycling of these interdependent micronutrients in six marine settings including; an upwelling location, a semi-enclosed bay, two urban coastal systems, and two open ocean locations. Along the coast of Baja California, Mexico, concentrations of B12 and dissolved Co varied from 0.2 to 11 pM and 180 to 990 pM, respectively. At a nearby upwelling station, vitamin B12 and Co concentrations ranged from 0.3 to 7.0 pM and 22 to 145 pM, and concentrations did not correlate with upwelling intensity. Concentrations of B12 were highest within Todos Santos Bay, a semi-enclosed bay off the coast of Baja California, Mexico, during a dinoflagellate bloom, ranging from 2 to 61 pM, while Co concentrations varied between 61 and 194 pM. In the anthropogenically impacted Long Island Sound, NY, U.S.A., B12 levels were between 0.1 and 23 pM and Co concentrations varied from 60 to 1900 pM. However, anthropogenic inputs were not evident in B12 levels in the San Pedro Basin, located outside Los Angeles, Ca, U.S.A., where concentrations of B12 were 0.2–1.8 pM, approximating observed open ocean B12 concentrations. In the Southern Ocean and North Atlantic Ocean, B12 levels were 0.4–4 pM and 0.2–2 pM, respectively. Total Co concentrations in the Southern Ocean and North Atlantic tended to be low; measuring 26–59 pM and 15–80 pM, respectively. These low Co concentrations may limit B12 synthesis and its availability to B12-requiring phytoplankton because the total dissolved Co pool is not necessarily entirely bioavailable.
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  • 70
    Publication Date: 2018-03-09
    Description: Prompted by recent data analyses suggesting that the flux of particulate organic carbon sinking into deep waters is determined by fluxes of mineral ballasts, we undertook a study of the relationships among organic matter (OM), calcium carbonate, opal, lithogenic material, and excess aluminum fluxes as part of the MedFlux project. We measured fluxes of particulate components during Spring and Summer of 2003, and Spring of 2005, using a swimmer-excluding sediment trap design capable of measuring fluxes both in a time-series (TS) mode and in a configuration for obtaining particle settling velocity (SV) profiles. On the basis of these studies, we suggest that distinct OM–ballast associations observed in particles sinking at a depth of ∼200 m imply that the mechanistic basis of the organic matter–ballast association is set in the upper water column above the Twilight Zone, and that the importance of different ballast types follows the seasonal succession of phytoplankton. As in other studies, carbonate appears to enhance the flux of organic matter over opal. Particles must be at least half organic matter before their settling velocity is affected by ballast concentration. This lack of change in ballast composition with SV in particles with 〈40% OM content suggests that particle SV reaches a maximum because of the increasing importance of inertial drag. Relative amounts of OM and opal decrease with depth due to decomposition and dissolution; carbonates and lithogenic material contribute about the same amount to total mass, or increase slightly, throughout the water column. The high proportion of excess Al cannot be explained by its incorporation into diatom opal or reverse weathering, so Al is most likely adsorbed to particulate oxides. On shorter time scales, dust appears to increase particle flux through its role in aggregation rather than by nutrient inputs enhancing productivity. We suggest that the role of dust as a catalyst in particle formation may be a central mechanism in flux formation in this region, particularly when zooplankton fecal pellet production is low.
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