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  • Elsevier  (77,240)
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  • 2005-2009  (43,048)
  • 1990-1994  (24,068)
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  • 1
    Unknown
    Amsterdam ; Boston : Elsevier
    Keywords: Coal-fired furnaces. ; Coal-fired power plants. ; Coal.
    ISBN: 1-417-55267-0
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 289 (1992), S. 199-210 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
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  • 3
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Physics, Section B 342 (1990), S. 1-14 
    ISSN: 0550-3213
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
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  • 4
    ISSN: 0550-3213
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
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  • 5
    ISSN: 0550-3213
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Physics, Section B 403 (1993), S. 3-24 
    ISSN: 0550-3213
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
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  • 7
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Physics, Section B 421 (1994), S. 3-37 
    ISSN: 0550-3213
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
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  • 8
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Physics, Section B 386 (1992), S. 471-492 
    ISSN: 0550-3213
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Physics, Section B 418 (1994), S. 403-427 
    ISSN: 0550-3213
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Physics, Section B 373 (1992), S. 3-34 
    ISSN: 0550-3213
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 11
    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
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  • 12
    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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  • 13
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 274 (1992), S. 230-238 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
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  • 14
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 318 (1993), S. 249-262 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
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  • 15
    Publication Date: 2018-03-15
    Description: The behavioural and physical mechanisms involved in the tactics used by predators to catch their prey have been explored for a wide variety of vertebrate taxa but most studies have considered the viewpoints of predator and prey independently. We tackled this issue using an ecologically relevant predator–prey model: wolf spiders (Pardosa spp.) and wood crickets, Nemobius sylvestris. Crickets are particularly challenging prey to catch because their air-sensing systems enable them to detect small air movements caused by approaching predators. Using a high-speed video camera, we found that freely behaving spiders adopted either a fast or a slow velocity tactic to approach crickets. We then developed a device using a piston to simulate, as faithfully as possible, the spider's attack. The air flow generated by the piston was quantified by particle image velocimetry and then used to test the escape success of crickets at different attack velocities. Cricket escape success was lower for low and high piston velocities, matching the two tactics adopted by the spiders. Based on our results, we propose that the escape probability of prey after a given predator signal can be explained by the distance between the prey and the predator, the velocity of the predator and the strength of the signal. Both methodological and conceptual approaches presented in this study could provide useful methods to understand the biological and physical basis of predatory tactics in other animals.
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  • 16
    Publication Date: 2018-03-15
    Description: CO2 partial pressure in surface water was measured in the Northeast Atlantic and in the Hebride Shelf/North Sea area during a cruise with R.V. Poseidon in June 1991. A mean pCO2 of 303 μatm was found in the Atlantic between 50°N and 60°N. For an atmospheric CO2 content of 357.5 ppm(v) this corresponds to a partial pressure difference of −55 μatm. This supports the view that the subarctic Atlantic is a significant sink within the CO2 cycle between the ocean and the atmosphere. A comparison of our measurements with other data reveals that the pCO2 distribution changes significantly during May/June. This explained by seasonal warming, CO2 exchange with the atmosphere and biomass production. The contribution by each of these processes to the seasonal variations is calculated. It was found that during a plankton bloom the production of biomass is the dominating factor and may lower seawater pCO2 by almost 100 μatm. The shelf areas are charactrized by strong pCO2 gradients which are explained by water exchange with the Atlantic, temperature effects and biomass production.
    Type: Article , PeerReviewed
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  • 17
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    Elsevier
    In:  Marine Pollution Bulletin, 26 (3). pp. 152-155.
    Publication Date: 2018-03-22
    Description: Skin and hair samples of harbour seals (Phoca vitulina) found dead along the west coast of northern Germany in 1988 were analysed for total mercury, cadmium and lead. Cadmium and lead concentrations were below the detection limit in most skin samples. The mercury content of the hair (median: 23.1 μg g−1 wet wt) was several magnitudes higher than the mercury content of the skin (0.27 μg g−1 wet wt). Mercury concentrations in hair samples were significantly higher than lead concentrations (0.54 μg g−1 wet wt), which significantly exceeded cadmium levels (0.09 μg g−1 wet wt). Female seals revealed lower cadmium concentrations in the hair than male seals. Accumulations of metals with age were observed for cadmium and lead in hair samples and for mercury in skin samples of male seals. A connection between metal accumulation and pigmentation or rather moult was clearly recognizable.
    Type: Article , PeerReviewed
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  • 18
    Publication Date: 2018-03-07
    Description: Gas chromatography-mass spectrometry (GC-MS) analyses of organic concentrates from eastern Mediterranean surface water show that dissolved fossil fuel residues are dominated by unsubstituted aromatic hydrocarbons and heterocyclic aromatics and thus resemble products of incomplete combustion. Deviating from this interpretation, preferential photochemical oxidation of alkyl-substituted aromatics is suggested as the principal causative mechanism, although, especially near land-based sources. the influence of combustion-derived unsubstituted aromatics is not defined. Total concentrations of dissolved aromatics as determined by GC-FID (flame ionization detection) and GC-MS from a limited data subset were in reasonable agreement with UV fluorescence measurements of dissolved/dispersed oil residues. The same preponderance of unsubstituted aromatics over their alkyl derivatives was found in extracts of the particulate phase, but concentrations were small relative to alkanes and/or alkenes of recent marine biosynthetic origin. CPI (carbon preference index) values of higher molecular weight n-alkanes indicated varying contributions of plant waxes to the particulate hydrocarbon pool. CPI values of corresponding dissolved n-alkanes were found to be near unity, indicating fossil fuel origin. Despite differences in higher molecular weight n-alkane CPI values and the predominance of recent biosynthetic aliphatics, the similarity of dissolved and particulate aromatic fractions suggests limited adsorption by particles of fossil fuel derived hydrocarbons and heterocyclics.
    Type: Article , PeerReviewed
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  • 19
    Publication Date: 2018-03-22
    Description: Altimetric data from Geosat and some critical hydrographic measurements were used to estimate in real time the mesoscale physical oceanographic environment surrounding the Joint Global Ocean Flux Study (JGOFS) 1989 North Atlantic Bloom Experiment. Three cyclonic eddies, including an exceptionally large one, evolved and interacted over the 10 weeks of observations. Subsequent analysis of all available hydrographic data confirmed the real time estimates and provided further quantitative information concerning the mesoscale and submesoscale structure of the upper ocean. Remotely sensed indicators of near-surface chlorophyll content reveal significant biological variability on these wavelengths. The altimetric and hydrographic data have been assimilated into a dynamical model to produce optimal estimates of physical fields of interest as they evolve in time for use in physical and biological process studies
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  • 20
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    Elsevier
    In:  Marine Pollution Bulletin, 28 (7). pp. 413-416.
    Publication Date: 2018-04-09
    Description: As long as salinity in the Baltic Sea was high (as it was between 1948 and 1982) the depth range between 70 and 100 m suffered frequent anoxia. However, when salinity was low and when the position of the halocline was deep (as it was in the first half of the century) oxygen conditions were good and long-lived macrofauna occurred. Should the present trend to lower salinities continue (building bridges across the Belt Sea and reducing salt water inflow would be helpful) one can foresee a recolonization by macrofauna in the depth range 70–100 m.
    Type: Article , PeerReviewed
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  • 21
    Publication Date: 2018-06-15
    Description: The levels of four trace metals (Cd, Cu, Pb, and Zn) in the whole soft body and in different organs of the ocean quahog Arctica islandica were evaluated from four stations in Kiel Bay, Western Baltic. The relationships between the contents and concentrations of these metals and body size (weight and length) were also investigated. Double logarithmic plots of metal contents and concentrations against dry body weight and shell length, respectively, show straight-line relationships. The results indicate that smaller individuals have higher concentrations of Cu and Zn, two essential metals, while larger individuals have higher concentrations of Cd and Pb, two non-essential metals. The calculated regression slopes of metal content against dry-body weight revealed that Cd and Cu appear to be affected by maturation since two different slopes are observed for both metals before and after maturation. This was not obvious for Pb and Zn. Pooled slopes of metal content against dry-body weight for all animal sizes indicated that Cu and Zn have a one common slope of (0.82) and Cd and Pb another common one of (1.51). Plots of metal concentrations against shell length indicated also that Cu and Zn have one common slope of (−0.54) and Cd and Pb another one of (1.56). Moreover, it was possible to calculate one final slope of (1.53) for Cd and Pb from both content/weight and concentration/length plots. This indicates that A. islandica may have one metabolic strategy for the essential metals and another for the non-essential metals.
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  • 22
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    Elsevier
    In:  International Review of Cytology, 67 . pp. 171-214.
    Publication Date: 2018-10-29
    Description: This chapter discusses coral skeletogenesis, focusing on the morphology of the skeletogenic tissues. It reviews the light and electron microscope studies carried out in this regard, illustrating the example of the morphology of the skeletogenic tissues of the coral Pocillopora damicornis. A structural organic matrix is present in the adult skeleton of Pocillopora damicornis. One component of this structural matrix is present transiently at the growth surface of the skeleton. It consists of individual sheaths enveloping each forming aragonite crystal. These crystal sheaths, plus some small extracellular vesicles that are presumed to represent a precursor for the sheaths, are together implicated in the hypotheses for coral calcification. The hypotheses fall into the following three broad categories: (1) algal removal of possible inhibitory substances; (2) a general stimulatory effect of algal metabolism; and (3) algal contribution to a skeletal organic matrix.
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  • 23
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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.
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  • 24
    Publication Date: 2018-12-06
    Description: The once-contiguous North Atlantic craton (NAC) is crosscut by the Labrador Sea that opened during the Early Cenozoic after extensive Mesozoic continental rifting and removal of cratonic mantle. This large-scale structural change within the cratonic lithosphere was followed at about 150 Ma by the cessation of ultrapotassic and potassic-to-carbonatitic magma production, which had prevailed throughout much of the NAC history. At Aillik Bay, a sequence of olivine lamproites (1374.2 ± 4.2 Ma, 2σ), aillikites/carbonatites (590–555 Ma), and nephelinites (141.6 ± 1.0 Ma, 2σ) erupted through the southern NAC edge on the present-day Labrador Sea margin. Links between these alkaline magma types with diverse petrogeneses as a consequence of large-scale processes in the lithospheric mantle over a period of 1200 Myr are demonstrated utilizing their Sr–Nd–Hf–Pb isotope compositions. The Mesoproterozoic olivine lamproites are characterized by unradiogenic Nd (εNd(i) = − 8.4 to − 5.4), Hf (εHf(i) = − 11 to − 7.8), and Pb (206Pb/204Pb(i) = 14.2–14.8) but moderately radiogenic Sr isotope compositions (87Sr/86Sr(i) = 0.7047–0.7062) fingerprinting long-term enriched cratonic mantle, which must have reached to depths of more than 150 km at this time. In contrast, Neoproterozoic carbonate-rich aillikites and carbonatites have fairly radiogenic Nd (εNd(i) = 0.1–1.8), Hf (εHf(i) = − 0.9 to + 2.6), and Pb (206Pb/204Pb(i) = 17.5–18.8) but unradiogenic Sr isotope compositions (87Sr/86Sr(i) = 0.7033–0.7046) that point to the involvement of convective upper mantle material during melting. Simple binary mixing calculations coupled with the observation that carbonate-rich magmatism prevailed for over 30 Myr in the area imply a complex pattern of lithosphere–asthenosphere interaction at depths between ∼180 and 140 km. The Cretaceous nephelinites have slightly unradiogenic Nd (εNd(i) = − 4 to − 1.4), moderately radiogenic initial 87Sr/86Sr (0.7044–0.7062), but initial εHf (− 3.3 to + 1.4) similar to the aillikites and highly radiogenic Pb (206Pb/204Pb(i) = 19.1–20.2) isotope compositions. Their sodic mafic alkaline nature reflects partial melting at a higher level of the cratonic mantle tapping metasomatic components that had been introduced during the 〉 30 Myr of Neoproterozoic aillikite/carbonatite magmatism. The new 40Ar/39Ar age and Sr–Nd–Hf–Pb isotope data, along with petrological arguments, suggest that at least 30 km of the cratonic mantle beneath the southern NAC edge had been replaced by the hotter upwelling asthenosphere between ca. 550 Ma, when a thick diamond-bearing lithosphere was present, and 150 Ma. This lithospheric thinning presumably occurred shortly prior to Cretaceous continental rifting in response to enhanced plate-tectonic stresses focused at this zone of persistent lithospheric weakness. It appears, however, that the recurrent volatile-rich alkaline magmatism and associated mantle metasomatism played an important role in destroying the structural integrity of the cratonic mantle thereby aiding the subsequent lithosphere thinning.
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  • 25
    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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  • 26
    Publication Date: 2019-01-08
    Description: Numerical simulations of column collapse and pyroclastic density current (PDC) scenarios at Vesuvius were carried out using a transient 3D flow model based on multiphase transport laws. The model describes the dynamics of the collapse as well as the effects of the 3D topography of the volcano on PDC propagation. Source conditions refer to a medium-scale sub-Plinian event and consider a pressure-balanced jet. Simulation results provide new insights into the complex dynamics of these phenomena. In particular: 1) column collapse can be characterized by different regimes, from incipient collapse to partial or nearly total collapse, thus confirming the possibility of a transitional field of behaviour of the column characterized by the contemporaneous and/or intermittent occurrence of ash fallout and PDCs; 2) the collapse regime can be characterized by its fraction of eruptive mass reaching the ground and generating PDCs; 3) within the range of the investigated source conditions, the propagation and hazard potential of PDCs appear to be directly correlated with the flow-rate of the mass collapsing to the ground, rather than to the collapse height of the column (this finding is in contrast with predictions based on the energy-line concept, which simply correlates the PDC runout and kinetic energy with the collapse height of the column); 4) first-order values of hazard variables associated with PDCs (i.e., dynamic pressure, temperature, airborne ash concentration) can be derived from simulation results, thereby providing initial estimates for the quantification of damage scenarios; 5) for scenarios assuming a location of the central vent coinciding with that of the present Gran Cono, Mount Somma significantly influences the propagation of PDCs, largely reducing their propagation in the northern sector, and diverting mass toward the west and southeast, accentuating runouts and hazard variables for these sectors; 6) the 2D modelling approximation can force an artificial radial propagation of the PDCs since it ignores azimuthal flows produced by real topographies that therefore need to be simulated in fully 3D conditions.
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  • 27
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    Elsevier
    In:  Applied Energy, 41 (3). pp. 177-200.
    Publication Date: 2019-04-03
    Description: Nitrous oxide (N2O) is an important atmospheric trace gas. Changes in the concentration of N2O in the atmosphere have evoked considerable interest because of its role in (i) regulating stratospheric ozone levels, and (ii) contributing to the atmospheric greenhouse phenomenon. The global concentration of N2O in the atmosphere has been rising since the start of the Industrial Revolution, before which the concentration was almost constant at about 280–290 ppbv. In ad 1990, it reached about 310 ppbv and is rising at a rate of 0·5–1·1 ppbv (i.e. 0·2–0·3%) per year. In this paper, the history of N2O in the Earth's atmosphere, together with its latitudinal and altitudinal distributions, and seasonal oscillations, are described.
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  • 28
    Publication Date: 2018-03-14
    Description: Helium (RA = 3.0 to 5.6) and carbon (δ13C from −7.2 to −3.4‰) isotopic compositions, and relative CO2, CH4, N2, He and Ar contents of CO2-rich gases from Lakes Nyos and Monoun, Cameroon; Laacher See, Germany; Dieng Volcanic Plateau, Indonesia, and a well at Mt. Gambier, Australia, point to a common, essentially magmatic origin. Absorption of the original magmatic gases into deeply circulating groundwater and equilibration of the resulting solutions with crustal rock at temperatures of about 300°C fix CO2 and CH4 contents. On further rise, the solutions start to boil separating gas-rich vapors which, on encountering an impermeable barrier, may accumulate to form gas pockets with steadily increasing pressures. In the case of sufficiently high gas contents, the pressures may exceed lithostatic pressures leading to a blow-out or a “pneumatic” eruption (Dieng). Otherwise, gas may accumulate to form a stable pocket (Mt. Gambier). Minor leakage from such pockets may lead to surface discharges of CO2-rich gases as at Laacher See, re-absorption into shallow groundwater to the formation of the low-salinity, CO2-charged waters encountered at Lakes Nyos and Monoun. The occurrence of these high-CO2, low-temperature systems is likely to be favored in tectonically active regions, allowing deep, possibly mantle gases to rise, but with sufficiently low regional heat flows to prevent the establishment of large-scale geothermal activity.
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  • 29
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    Elsevier
    In:  Journal of Experimental Marine Biology and Ecology, 167 (1). pp. 91-108.
    Publication Date: 2019-03-13
    Description: A mechanistic account of skeletal density band formation in massive colonies of Porites is developed by linking observations from vital staining of growing skeletons with measurements of density band characteristics, dissepiment spacing and the depth to which skeleton was occupied by tissue. Three growth processes contribute to density band formation. First, addition of new skeleton at the outer surface of the colony. Second, thickening of existing skeleton through the depth of the tissue layer (tissue usually occupies skeleton formed over the last 4–13 months). Third, the density pattern is then modified by periodic and abrupt uplift of the lower margin of the tissue layer which occurs about every 30 days. Uplift is associated with formation of new dissepiments and produces a fine density band at the lower margin of the tissue layer. Less regular, fine bands are formed within the tissue layer probably as a result of variations in calcification at the colonial surface. X-radiography of skeletal slices compresses and combines the results of these mechanisms making it difficult to distinguish the contribution of individual mechanisms to the overall X-ray image. The relative importance of the three mechanisms — extension, thickening and tissue uplift — to overall skeletal growth may differ between individual colonies. Variability in the way the mechanisms operate and combine may account for widely differing reports of coral density banding.
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  • 30
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    Elsevier
    In:  Palaeogeography, Palaeoclimatology, Palaeoecology, 232 (2-4). pp. 408-428.
    Publication Date: 2019-05-10
    Description: Massive scleractinian corals secrete an aragonitic skeleton which incorporates a large array of chemical tracers. Corals present several advantages for palaeoclimate research: they grow continuously, and can live up to 1000 years; they are easy to date; and they can be sampled at high resolution (weekly to monthly resolution). Both live and fossil corals can be collected in the field. In the past two decades, significant efforts have been made to identify robust tracers of sea surface temperature (SST) and salinity (SSS) in corals. To date, Sr/Ca and δ18O are considered to be the most reliable SST tracers, although changes in seawater δ18O can significantly alter SST reconstructed from coralline δ18O. Because these variations in seawater δ18O can be linked to SSS changes, this initial problem can in fact be turned into an advantage and provide us with an SSS tracer. The SST component in the coral δ18O signal can either be evaluated through Sr/Ca measurements, or in some case simply filtered out. However, there is still much uncertainty concerning the exact mode of incorporation of trace elements and stable isotopes into the coral skeleton. The effects of growth rate, light intensity, feeding habits, pH and water chemistry are still poorly documented. A review of the strength and weaknesses of Sr/Ca and δ18O is presented, together with some examples of SST and SSS reconstructions. Other potential SST tracers are also reviewed. It is expected that the ability to grow corals in aquarium under controlled conditions, and that the development of sophisticated analytical techniques at the micrometric level should help us understand better the robustness of each tracers and the factors controlling their incorporation in coral aragonite.
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  • 31
    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
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  • 32
    Publication Date: 2014-04-15
    Description: Polynyas are common occurrences all around the Arctic and Antarctic. Coastal polynyas are generally highly productive, which can lead to substantial CO2 drawdown. Consequently, they are important sink regions for atmospheric CO2. Depending on the surface area, the timing, duration and other factors, large differences exist as to the importance of polynyas in a biogeochemical sense. In the Arctic, the North Water Polynya seems to be the most important one, while in the Antarctic the most important is the Ross Sea Polynya. Polynyas in the Arctic have been better investigated and therefore the important polynyas are described with some confidence as to accuracy and completeness. For the Antarctic, this only holds for the Ross Sea Polynya. For many other Antarctic polynyas, only incomplete information is available. This is true even for the large, well known Weddell Polynya of the 1970s, which represents one of the few open-ocean polynyas. Here its biogeochemical role is semi-quantitatively assessed by combining the physical data from the 1970s with the known distributions of biogeochemical properties from recent years. It is deduced that the Weddell Polynya was a significant one-time sink for anthropogenic CO2 and CFCs, with ensuing deep-sea sequestration. Notably, some coastal polynyas are instrumental in transferring anthropogenic CO2 from the ice-free shelves to the abyssal oceans.
    Repository Name: EPIC Alfred Wegener Institut
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  • 33
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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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  • 34
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    Elsevier
    In:  Earth and Planetary Science Letters, 251 (3-4). pp. 199-208.
    Publication Date: 2017-01-19
    Description: The historic record of large megathrust earthquakes suggests that the potential for great destructive events is much larger for Sumatra than Java. Bouguer gravity anomalies correlate well with the occurrence of large megathrust earthquakes in the Sunda subduction zone; negative anomalies mark segments characterized by larger earthquakes while positive anomalies indicate lower seismic potential. Thermal models and structural constraints derived from seismic and gravity data are used to explain the seismogenic behaviour in the Sunda subduction zone. With respect to Java, oblique subduction of young oceanic crust shifts the seismogenic coupling zone roughly 40 km trenchward offshore of northern Sumatra and increases the width of the locked megathrust. A prominent positive gravity anomaly offshore of Java is caused by a shallow mantle wedge underlying the forearc basin. A serpentinized mantle wedge would limit the width of the coupling zone off Java to only 30–40 km, compared to 〉 120 km offshore of Sumatra. Sumatra remains therefore the most vulnerable site for future megathrust earthquakes, while the shallow mantle wedge may limit the violence of rupture off Java.
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  • 35
    Publication Date: 2017-11-01
    Description: Ca isotope fractionation during inorganic calcite formation was experimentally studied by spontaneous precipitation at various precipitation rates (1.8 〈 log R 〈 4.4 μmol/m2/h) and temperatures (5, 25, and 40 °C) with traces of Sr using the CO2 diffusion technique. Results show that in analogy to Sr/Ca [see Tang J., Köhler S. J. and Dietzel M. (2008) Sr2+/Ca2+ and 44Ca/40Ca fractionation during inorganic calcite formation: I. Sr incorporation. Geochim. Cosmochim. Acta] the 44Ca/40Ca fractionation during calcite formation can be followed by the Surface Entrapment Model (SEMO). According to the SEMO calculations at isotopic equilibrium no fractionation occurs (i.e., the fractionation coefficient αcalcite-aq = (44Ca/40Ca)s/(44Ca/40Ca)aq = 1 and Δ44/40Cacalcite-aq = 0‰), whereas at disequilibrium 44Ca is fractionated in a primary surface layer (i.e., the surface entrapment factor of 44Ca, F44Ca 〈 1). As a crystal grows at disequilibrium, the surface-depleted 44Ca is entrapped into the newly formed crystal lattice. 44Ca depletion in calcite can be counteracted by ion diffusion within the surface region. Our experimental results show elevated 44Ca fractionation in calcite grown at high precipitation rates due to limited time for Ca isotope re-equilibration by ion diffusion. Elevated temperature results in an increase of 44Ca ion diffusion and less 44Ca fractionation in the surface region. Thus, it is predicted from the SEMO that an increase in temperature results in less 44Ca fractionation and the impact of precipitation rate on 44Ca fractionation is reduced. A highly significant positive linear relationship between absolute 44Ca/40Ca fractionation and the apparent Sr distribution coefficient during calcite formation according to the equation Δ44/40Cacalcite-aq=(−1.90±0.26)·logDSr−2.83±0.28is obtained from the experimental results at 5, 25, and 40 °C. Thus, Sr partitioning during calcite formation directly reflects Ca isotopic fractionation, independent of temperature, precipitation rate, and molar (Sr/Ca)aq ratio of the aqueous solution. If the (Sr/Ca)aq ratio is constant, Δ44/40Cacalcite-aq values can be directly followed by the Sr content of the precipitated calcite. A (Sr/Ca)aq ratio close to that of modern seawater yields the equation ... [View the MathML source]... Our experimental results indicate that neither precipitation rate nor temperature dominantly controls Ca isotope fractionation. However, Ca isotopes and Sr content of inorganic calcite comprise an excellent environmental multi-proxy in natural and applied systems.
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  • 36
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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.
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  • 37
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    Elsevier
    In:  Deep-Sea Research Part II-Topical Studies in Oceanography, 41 . pp. 307-324.
    Publication Date: 2016-10-10
    Description: Measurements of the chlorofluorocarbons (CFCs), F11 (CCl3F) and F12 (CCl2F2) were made during the Shelf Edge Exchange Processes II (SEEP-II) experiment in the Middle Atlantic Bight during 1988–1989. These compounds undergo large seasonal variations in surface water concentration as a result of temperature-induced solubility changes. Outgassing in summer produces vertical concentration gradients that can be exploited to estimate a cross-pycnocline vertical eddy-diffusivity suitable for biogeochemical flux calculations. Model results based on an exploratory study suggest an average Kz of 1 × 10−5 m2 s−1 for this region during the stratified period. CFCs have advantages over other budget approaches for studying mixing processes, including heat budgets, as there are no internal sources or sinks other than air-sea gas exchange. In order to exploit further the CFC budget of sub-pycnocline shelf waters, regular cruises through the summer months and characterization of CFC levels at the time of stratification are required.
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  • 38
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    Elsevier
    In:  Geochimica et Cosmochimica Acta, 71 (21). pp. 5135-5154.
    Publication Date: 2017-09-08
    Description: Porewater data from vent sites of the northeastern shelf off Sakhalin Island, Sea of Okhotsk, exhibit bottom-water concentrations down to a sediment depth of up to 300 cm. Below this depth, solute concentrations rapidly change due to methanogenesis and anaerobic methane oxidation (AMO). The profile shapes suggest an irrigation-like process that mixes on a meter scale. At these sites active gas emanation into the overlying water column and near-surface gas hydrates are commonly observed. We propose that methane gas bubbles rise through the soft surface sediments and cause mixing of the porewater. Mathematically, the bubble-induced irrigation can be described by eddy diffusion enhancing the diffusive transport of solutes by several orders of magnitude. A 3-D numerical transport-reaction model was developed to investigate the parameters defining the mixing process, such as bubble rise velocity, tube size, tube distribution in the sediment, and ebullition frequency. Model consistency with the field data requires eddy diffusivities ⩾1 × 105 cm2/a, tube densities of 〉4 tubes/m2 (equivalent to a tube spacing of 〈40 cm), active gas seepage for more than a few weeks or months, and moderate to low diagenetic reaction rates of solutes. The corresponding methane gas fluxes that are predicted from the results of the model realizations range from 1 × 103–5 × 105 L/(m2 a). Due to bubble mixing, solute fluxes in these sediments are increased by a factor of 3 and the maximum AMO rate by a factor of 7.
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  • 39
    Publication Date: 2017-08-03
    Description: Seven sediment cores were taken in the Sea of Okhotsk in a south-north transect along the slope of Sakhalin Island. The retrieved anoxic sediments and pore fluids were analyzed for particulate organic carbon (POC), total nitrogen, total sulfur, dissolved sulfate, sulfide, methane, ammonium, iodide, bromide, calcium, and total alkalinity. A novel method was developed to derive sedimentation rates from a steady-state nitrogen mass balance. Rates of organic matter degradation, sulfate reduction, methane turnover, and carbonate precipitation were derived from the data applying a steady-state transport-reaction model. A good fit to the data set was obtained using the following new rate law for organic matter degradation in anoxic sediments: View the MathML sourceRPOC=KCC(DIC)+C(CH4)+KC·kx·POC Turn MathJax on The rate of particulate organic carbon degradation (RPOC) was found to depend on the POC concentration, an age-dependent kinetic constant (kx) and the concentration of dissolved metabolites. Rates are inhibited at high dissolved inorganic carbon (DIC) and dissolved methane (CH4) concentrations. The best fit to the data was obtained applying an inhibition constant KC of 35 ± 5 mM. The modeling further showed that bromide and iodide are preferentially released during organic matter degradation in anoxic sediments. Carbonate precipitation is driven by the anaerobic oxidation of methane (AOM) and removes one third of the carbonate alkalinity generated via AOM. The new model of organic matter degradation was further tested and extended to simulate the accumulation of gas hydrates at Blake Ridge. A good fit to the available POC, total nitrogen, dissolved ammonium, bromide, iodide and sulfate data was obtained confirming that the new model can be used to simulate organic matter degradation and methane production over the entire hydrate stability zone (HSZ). The modeling revealed that most of the gas hydrates accumulating in Blake Ridge sediments are neither formed by organic matter degradation within the HSZ nor by dissolved methane transported to the surface by upward fluid flow but rather through the ascent of gas bubbles from deeper sediment layers. The model was further applied to predict rates of hydrate accumulation in Sakhalin slope sediments. It showed that only up to 0.3% of the pore space is occupied by gas hydrates formed via organic matter degradation within the HSZ. Gas bubble ascent may, however, significantly increase the total amount of hydrate in these deposits.
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  • 40
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    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 53 . pp. 869-893.
    Publication Date: 2016-11-01
    Description: This is a study about the spreading of newly formed deep waters following open ocean deep convection in the Northwestern Mediterranean Sea. The main results are from the SOFARGOS large scale float experiment initiated in 1994–1995. During the SOFARGOS project, CTD stations and Lagrangian observations of ocean currents were carried out in the Gulf of Lion from December 1994 to July 1995. Hydrological observations confirmed that deep water formation occurred very early during winter 1994–1995 (late December, early January) in conjunction with atmospheric cooling, deep convection penetrating down to 2000 m in the so-called Medoc area. Numerous eddies (both anticyclonic and cyclonic) drifted away from the convection area and advected newly formed deep waters far away from the source region. In particular, compact anticyclones appeared to be the most coherent (long-lived) eddies and capable of transporting newly formed Western Mediterranean Deep Waters several hundreds of kilometers away from the convection area. Characterized by an inner core of about 5 km in radius, these eddies are submesoscale features in the outer domain and appear as key elements of the open ocean convection processes. During their long journeys, these eddies interacted with larger scale features such as the Northern Boundary Current, the North Balearic Front, topographic Rossby waves, and Sardinian eddies. These interactions influenced the long-term behavior of the eddies (mean drift, composition) and represented an important part of (1) the spreading phase following deep convection and (2) the large scale thermohaline circulation
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  • 41
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    Elsevier
    In:  Earth and Planetary Science Letters, 236 (1-2). pp. 211-226.
    Publication Date: 2016-12-20
    Description: We have conducted a barometric study of basaltic lavas and mafic to ultramafic xenoliths from Cumbre Vieja volcano (La Palma) in order to reconstruct magma storage, plumbing and related intrusive island growth. The samples were collected both along the volcano's rift zone and from its subaerial and submarine flanks up to 30 km off the rift axis. Clinopyroxene–melt barometry of lavas yields a well-defined pressure range of 410–770 MPa (average 600 MPa) and shows no systematic variation with sample locality. This pressure range reflects a major fractionation level at ca. 15–26 km depth, within the uppermost mantle, where phenocrysts and melt last equilibrated. In contrast, microthermometry of CO2-dominated fluid inclusions in phenocrysts and xenoliths gives pressure estimates of 240 to 470 MPa (average 330 MPa), within the lower oceanic crust. These pressures are interpreted to reflect an underplating zone at 7–14 km depth where ascending magmas become ponded prior to eruption and where passing magmas temporarily stagnate during eruption. The underplating zone is inferred to extend to a radius of ca. 30 km at least, and its depth appears to increase slightly with distance to the rift axis. Our data thus show a remarkable pressure bimodality for long-term and short-term storage of magma that appears to be characteristic for Cumbre Vieja. By using a simple model based on the cumulative volume of material added to the crust, we have estimated uplift rates of 〉 0.5 m/ka due to underplating that occurs on the island scale. On a time-scale of some 10 ka, these uplift rates are of similar magnitude as global changes in sea-level. A second, more local mode of uplift and related faulting is caused by shallow intrusions into the volcanic edifice as is indicated by the highly irregular morphology of the Cumbre Vieja. We stress that intrusion-related uplift should be qualitatively considered when reconstructing the evolution of oceanic island volcanoes. Since most of the underplated material is inferred to consist of cumulate rocks being intimately mixed and juxtaposed with the lower oceanic crust and having similar densities, it is probably impossible to detect such an underplating zone seismically.
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  • 42
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    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 53 (10). pp. 1635-1657.
    Publication Date: 2016-11-01
    Description: Assemblage structures and distribution patterns of larval fishes and paralarval cephalopods were examined in September 1998 at Great Meteor Seamount, an isolated seamount located in the subtropical eastern North Atlantic. Early life stages of fish (n=18555) and cephalopods (n=1200) were collected at 23 stations with a multiple opening–closing net, in seven discrete depth strata from 290 m depth (close to the seamount plateau) to the surface. Oceanic species dominated in both taxonomic groups. A peak in diversity was observed at an intermediate depth, in the 100–150 m water layer. Direct and indirect gradient analyses showed distinct species assemblages in the upper and lower part of the water column, separated by approximately 150 m. The division was statistically significant, although a considerable overlap between species was also observed. Above the summit, vertical gaps were found in the distributions of the deeper assemblages, likely caused by increased predation pressure by benthopelagic fish. Horizontal distribution patterns of fish and cephalopods were similar and corresponded to the structure of closed circulation cells detected above the flanks and the flat plateau area. Fish assemblages were significantly different between the inner and outer seamount regime, which was approximately separated by the 1500 m depth contour. Differences in the taxonomic composition of cephalopods were less pronounced; for only one cephalopod species could a direct association with the seamount be assumed. The study indicates a significant retention potential at the seamount that facilitates local recruitment of resident stocks and generates self-sustainable populations isolated from the continental shelf and oceanic islands.
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  • 43
    Publication Date: 2017-08-03
    Description: Sediment core data from a site in the central Nordic seas suggest that during the mid-Pleistocene revolution (MPR) this region has experienced a systematic change in its overall oceanographic and climatic conditions. First distinct changes occur around 1 Ma and reveal the beginning of a shift in climate periodicity from stronger 41-ka cycles towards a dominant 100-ka cyclicity. Most pronounced are the changes at the study region between about 700 and 420 ka, when parallel to the evolution of large 100-ka cycles a distinct decrease in the input of magnetic particles is observed. Also, for this interval an intensification of glacial conditions is indicated by a marked increase in the accumulation rates of ice-rafted debris (IRD) during marine isotope stages 16 and 12. The observed mid-Pleistocene changes were likely due to a gradual shift from a more zonal behavior of the coupled ocean–atmosphere system at high northern latitudes prior to the MPR to more meridionality thereafter, a shift that affected both the patterns of ocean circulation and ice drift in the Nordic seas region. Accordingly, the subsequent MPR-related changes of these two climate parameters should be responsible for the decrease in the concentration of magnetic particles at the study site after 700 ka. With the mid-Pleistocene strengthening of the Nordic heat pump the mode of deep-water production and the flow of bottom currents changed at high northern latitudes, which led to an increased export of magnetic particles from basaltic source regions around Greenland and Iceland into the subpolar North Atlantic. Consequently, less magnetic material was deposited in the Nordic seas than before the MPR when water mass exchange between the Nordic seas and the North Atlantic was more restricted. In addition, the large Late-Pleistocene expansions of glacial ice caps on the eastern margin of the Nordic seas led to a major change in the composition of IRD material in the study area, with more material originating from the Scandinavian and Barents Sea shelf regions, which ultimately caused a dilution of the magnetic signal.
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  • 44
    Publication Date: 2018-07-19
    Description: The importance of grain size as a fundamental property controlling other physically derived properties is well known. Recent grain-size studies on periplatform sediments of the Caribbean and western north Atlantic have shown that grain-size variability is coupled with changes in carbonate platform productivity and export in response to Pleistocene–Holocene glacio-eustacy. These findings showed that periplatform sediments are dominated by fine-grained material during sea-level highstands and coarser material during sea-level lowstands. This paper addresses the question of grain-size patterns in periplatform settings and their relationship to glacio-eustacy. Furthermore, it considers whether these patterns are applicable to different types of margin settings (accretionary-erosional). Here, existing data (Pleistocene–Holocene) from the accretionary western leeward margin of Great Bahama Bank (ODP Leg 166) and new data from the erosional eastern windward margin (ODP Leg 101) are used. The results show that the grain-size patterns of both margins are controlled by late Neogene sea-level fluctuations. The accretionary leeward margin sediments indicate the same grain-size pattern as previously described in the literature. However, the erosional windward margin shows a reverse pattern, with coarser sediments in interglacials and finer deposits in glacials. This proposes that the leeward margin grain-size pattern is controlled by the productivity-export mode of the platform. This is indicated by the platform-top-derived fine muds, transported off-bank, to form a thick sediment wedge on the low-angled slope during interglacials. In contrast, on the windward margin, the sediment flux pattern is controlled by the impact of mass transport processes. This is indicated by the increased occurrence of turbidites during interglacials that might be more frequent at this time because the steep-angled erosional slope is less apt for the deposition of excess fine material. This material is eroded and/or bypasses the slopes and is redeposited in the periplatform basin setting.
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  • 45
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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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  • 46
    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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  • 47
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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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  • 48
    Publication Date: 2018-07-19
    Description: Our recent paper [McMurtry, G.M., Tappin, D.R., Sedwick, P.N., Wilkinson, I., Fietzke, J. and Sellwood, B., 2007a. Elevated marine deposits in Bermuda record a late Quaternary megatsunami. Sedimentary Geol. 200, 155–165.] critically re-examined elevated marine deposits in Bermuda, and concluded that their geological setting, sedimentary relations, micropetrography and microfaunal assemblages were inconsistent with sustained intertidal deposition. Instead, we hypothesized that these deposits were the result of a large tsunami that impacted the Bermuda island platform during the mid-Pleistocene. Hearty and Olson [Hearty, P.J., and Olson, S.L., in press. Mega-highstand or megatsunami? Discussion of McMurtry et al. “Elevated marine deposits in Bermuda record a late Quaternary megatsunami”: Sedimentary Geology, 200, 155–165, 2007 (Aug. 07). Sedimentary Geol. 200, 155–165.] in their response, attempt to refute our conclusions and claim the deposits to be the result of a +21 m eustatic sea level highstand during marine isotope stage (MIS) 11. In our reply we answer the issues raised by Hearty and Olson [Hearty, P.J., and Olson, S.L., in press. Mega-highstand or megatsunami? Discussion of McMurtry et al. “Elevated marine deposits in Bermuda record a late Quaternary megatsunami”: Sedimentary Geology, 200, 155–165, 2007 (Aug. 07). Sedimentary Geol. 200, 155–165.] and conclude that the Bermuda deposits do not provide unequivocal evidence of a prolonged + 21 m eustatic sea level highstand. Rather, the sediments are more likely the result of a past megatsunami in the North Atlantic basin.
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  • 49
    Publication Date: 2017-12-07
    Description: Boron and Pb isotopic compositions together with B–U–Th–Pb concentrations were determined for Pacific and Indian mantle-type mid-ocean ridge basalts (MORB) obtained from shallow drill holes near the Australian Antarctic Discordance (AAD). Boron contents in the altered samples range from 29.7 to 69.6 ppm and are extremely enriched relative to fresh MORB glass with 0.4–0.6 ppm B. Similarly the δ11B values range from 5.5‰ to 15.9‰ in the altered basalts and require interaction with a δ11B enriched fluid similar to seawater ∼ 39.5‰ and/or boron isotope fractionation during the formation of secondary clays. Positive correlations between B concentrations and other chemical indices of alteration such as H2O CO2, K2O, P2O5, U and 87Sr/86Sr indicate that B is progressively enriched in the basalts as they become more altered. Interestingly, δ11B shows the largest isotopic shift to + 16‰ in the least altered basalts, followed by a continual decrease to + 5–6‰ in the most altered basalts. These observations may indicate a change from an early seawater dominated fluid towards a sediment-dominated fluid as a result of an increase in sediment cover with increasing age of the seafloor. The progression from heavy δ11B towards lighter values with increasing degrees of alteration may also reflect increased formation of clay minerals (e.g., saponite). A comparison of 238U/204Pb and 206Pb/204Pb in fresh glass and variably altered basalt from Site 1160B shows extreme variations that are caused by secondary U enrichment during low temperature alteration. Modeling of the U–Pb isotope system confirms that some alteration events occurred early in the 21.5 m.y. history of these rocks, even though a significant second pulse of alteration happened at ∼ 12 Ma after formation of the crust. The U–Pb systematics of co-genetic basaltic glass and variably low temperature altered basaltic whole rocks are thus a potential tool to place age constraints on the timing of alteration and fluid flow in the ocean crust.
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  • 50
    facet.materialart.
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    Elsevier
    In:  Review of Palaeobotany and Palynology, 139 . pp. 151-169.
    Publication Date: 2016-09-14
    Description: Nineteen samples taken in the Upper Ordovician Kirkley Bank Formation at the recent Greenscoe section yielded a rich and moderately to well preserved chitinozoan assemblage, in spite of a high Conodont Colour Alteration Index. Within the assemblage, the Baltoscandian Fungochitina spinifera Biozone could be recognized, indicating a strong faunal exchange between the Baltica palaeocontinent and the Avalonian palaeomicrocontinent during the Late Ordovician. This biozone allowed a strong correlation with new chitinozoan biozonations in the Cautley district and Cross Fell Inlier, resulting in a late Onnian to early Cautleyan age for the Kirkley Bank Formation at Greenscoe.
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  • 51
    Publication Date: 2017-01-26
    Description: We present the first coral climate proxy data (Sr / Ca, δ18O, δ13C) from the Persian–Arabian Gulf using a Porites lutea coral collected offshore Kuwait. Both oxygen isotope- and Sr / Ca-ratios of the coral core investigated are statistically correlated with instrumental sea surface temperatures (SST) for the area from 1980–2002. However, the temperature calibration curve for Sr / Ca differs from other published curves in that its slope is much lower. The correlation coefficient between δ18Ocoral and instrumental SST is at the lower limit as compared to other sites. These differences most likely relate to insufficient data representation of cold winters and hot summers, and indicates that much higher sampling resolution is needed in marginal reef areas such as Kuwait with extreme environmental fluctuations, i.e., intra-annual SST-variation of 16–34 °C, as compared to low latitude locations with relatively low SST variation. Variations of carbon isotopes of the coral skeleton do not exhibit climate control, however, a negative excursion in 1991 might be attributed to the massive oil field fires of the II. Gulf War.
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  • 52
    Publication Date: 2016-12-21
    Description: ODP Leg 204, which drilled at Hydrate Ridge, provides unique insights into the fluid regime of an accretionary complex and delineates specific sub-seafloor pathways for fluid transport. Compaction and dewatering due to smectite–illite transition increase with distance from the toe of the accretionary prism and bring up fluids from deep within the accretionary complex to sampled depths (≤ 600 mbsf). These fluids have a distinctly non-radiogenic strontium isotope signature indicating reaction with the oceanic basement. Boron isotopes are also consistent with a deep fluid source that has been modified by desorption of heavy boron as clay minerals change from smectite to illite. One of three major horizons serves as conduit for the transport of mainly fluid. Our results enable us to evaluate fluid migration pathways that play important roles on massive gas hydrate accumulations and seepage of methane-rich fluids on southern Hydrate Ridge.
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  • 53
    facet.materialart.
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    Elsevier
    In:  Quaternary Science Reviews, 28 (5/6). pp. 433-448.
    Publication Date: 2019-01-23
    Description: The Storegga Slide, which occurred ∼8100 years ago, is one of the world's largest and best studied exposed submarine landslides. In this study we use novel geomorphometric techniques to constrain the submarine mass movements that have shaped the north-eastern Storegga Slide, understand the link between different forms of failure, and propose a revised development model for this region. According to this model, the north-eastern part of the Storegga Slide has developed in four major events. The first event (event 1) was triggered in water depths of 1500–2000 m. In this event, the surface sediments were removed by debris flows and turbidity currents, and deposited in the Norwegian Sea Basin. Loading of the seabed by sediments mobilised by the debris flows and turbidity currents resulted in the development of an evacuation structure. Loss of support associated with this evacuation structure, reactivation of old headwalls and seismic loading activated spreading in the failure surface of event 1 up to the main headwall (event 2). In some areas, spreading blocks have undergone high displacement and remoulding. Parts of the spreading morphology and the underlying sediment have been deformed or removed by numerous debris flows and turbidity currents (event 3). We suggest that the higher displacement and remoulding of the spreading blocks, and their removal by debris flows and turbidity currents, was influenced by increased pore pressures, possibly due to gas hydrate dissolution/dissociation or by lateral variability in the deposition of contourite drifts in palaoeslide scars. The fourth event entailed a large, blocky debris flow that caused localised compression and transpressive shearing in the southern part of the spreading area.
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  • 54
    Publication Date: 2017-08-03
    Description: The Dnepr paleo-delta area in the NW Black Sea is characterized by an abundant presence of methane seeps. During the expeditions of May–June 2003 and 2004 within the EU-funded CRIMEA project, detailed multibeam, seismic and hydro-acoustic water-column investigations were carried out to study the relation between the spatial distribution of methane seeps, sea-floor morphology and sub-surface structures. 2778 new methane seeps were detected on echosounding records in an area of 1540 km2. All seeps are located in the transition zone between the continental shelf and slope, in water depths of 66 to 825 m. The integration of the different geophysical datasets clearly indicates that methane seeps are not randomly distributed in this area, but are concentrated in specific locations. The depth limit for the majority of the detected seeps is 725 m water depth, which corresponds more or less with the stability limit for pure methane hydrate at the ambient bottom temperature (8.9 °C) in this part of the Black Sea. This suggests that, where gas hydrates are stable, they play the role of buffer for the upward migration of methane gas and thus prevent seepage of methane bubbles into the water column. Higher up on the margin, gas seeps are widespread, but accurate mapping illustrates that seeps occur preferentially in association with particular morphological and sub-surface features. On the shelf, the highest concentration of seeps is found in elongated depressions (pockmarks) above the margins of filled channels. On the continental slope where no pockmarks have been observed, seepage occurs along crests of sedimentary ridges. There, seepage is focussed by a parallel-stratified sediment cover that thins out towards the ridge crests. On the slope, seepage also appears in the vicinity of canyons (bottom, flanks and margins) or near the scarps of submarine landslides where mass-wasting breaches the fine-grained sediment cover that acts as a stratigraphic seal. The seismic data show the presence of a distinct “gas front,” which has been used to map the depth of the free gas within the sea-floor sediments. The depth of this gas front is variable and locally domes up to the sea floor. Where the gas front approaches the seafloor, gas bubbles were detected in the water column. A regional map of the sub-surface depth of the gas front emphasises this “gas front-versus-seep” relationship. The integration of all data sets indicates that the spatial distribution of methane seeps in the Dnepr paleo-delta is mainly controlled by the gas-hydrate stability zone as well as by stratigraphic and sedimentary factors.
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  • 55
    facet.materialart.
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    Elsevier
    In:  Geochimica et Cosmochimica Acta, 54 (12). pp. 3295-3313.
    Publication Date: 2018-03-08
    Description: The observed distribution of dissolved magnesium in the pore water of rapidly accumulating sediments shows significant deviations from the seawater value. We have shown that deviations during early diagenesis can be explained by reactions occurring at the surface of sediment particles. In anoxic pore water environments with high levels of dissolved total carbon dioxide the formation of Mg+2·CO3−2 complexes significantly reduces the concentration of the free Mg+2 ion. This decrease in the Mg+2 activity results in desorption of magnesium from the solid surfaces due to the re-equilibration of the adsorbed Mg+2 with the dissolved species. The effect of increasing carbonate complexation of Mg+2 in anoxic environments is initially compensated by the loss of sulfate, which is also a strong Mg+2 ligand. Therefore, significant changes in free Mg+2 concentration and thus in the magnesium desorption from solid surfaces by ligand competition for Mg+2 are more pronounced in sulfate-depleted systems undergoing methanogenesis. Such conditions are characteristic of most continental margin sediments. Another consequence of the decomposition of organic matter in hemipelagic sediments is the accumulation of high levels of ammonium ions which also displace Mg+2 from sediment-particle surfaces by ion exchange. These equilibria in the pore water-sediment systems can be described by empirical parameters, which were experimentally obtained. A computer model was used to determine the equilibrium conditions for solid-solution reactions as a function of changes in the pore-water composition in organicrich hemipelagic environments. This model includes complex formation, competition for Mg+2 between dissolved ligands and exchange sites and Mg+2NH+4 exchange reactions. The relative proportion of desorbed and displaced Mg+2 from the solid surface depends on the characteristics of the sediment and on the ΣCO2:NH+4 regenerative ratio in the pore waters. In sediments from Bransfield Strait, the Gulf of California, and the Peru margin, both release mechanisms for Mg+2—ligand competition and ion exchange with ammonium—were evaluated as part of the complex reaction system in order to explain the observed maxima in the dissolved magnesium profiles. Overlying the Mg+2 maxima, the Bransfield Strait and Gulf of California pore waters show minima in the dissolved magnesium concentration, concurrent with a measured increase in the cation exchange capacity (CEC) of the sediments. By including the observed CEC changes in the multi-component model we show that the negative anomaly in the dissolved Mg+2 profiles is a consequence of changes in the CEC of sediments during the very early stages of anoxic diagenesis.
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  • 56
    Publication Date: 2018-03-08
    Description: The 10Be records of four sediment cores forming a transect from the Norwegian Sea at 70°N (core 23059) via the Fram Strait (core 23235) to the Arctic Ocean at 86°N (cores 1533 and 1524) were measured at a high depth resolution. Although the material in all the cores was controlled by different sedimentological regimes, the 10Be records of these cores were superimposed by glacial/interglacial changes in the sedimentary environment. Core sections with high 10Be concentrations ( 〉 1 · 109 at/g) are related to interglacial stages and core sections with low10Be concentrations ( 〈 0.5 · 109 at/g) are related to glacial stages. Climatic transitions (e.g., Termination II, 5/6) are marked by drastic changes in the 10Be concentrations of up to one order of magnitude. The average 10Be concentrations for each climatic stage show an inverse relationship to their corresponding sedimentation rates, indicating that the 10Be records are the result of dilution with more or less terrigenous ice-rafted material. However, there are strong changes in the 10Be fluxes (e.g., Termination II) into the sediments which may also account for the observed oscillations. Most likely, both processes affected the 10Be records equally, amplifying the contrast between lower (glacials) and higher (interglacials) 10Be concentrations. The sharp contrast of high and low 10Be concentrations at climatic stage boundaries are an independent proxy for climatic and sedimentary change in the Nordic Seas and can be applied for stratigraphic dating (10Be stratigraphy) of sediment cores from the northern North Atlantic and the Arctic Ocean
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  • 57
    Publication Date: 2017-08-04
    Description: We use new swath bathymetry data acquired during the RV Sonne cruise GEOPECO and complement them with swath data from adjacent regions to analyse the morphotectonics of the Peruvian convergent margin. The Nazca plate is not covered with sediments and therefore has a rough surface along the entire Peruvian trench. The styles of roughness differ significantly along the margin with linear morphological features trending in various directions, most of them oblique to the trench and roughness magnitudes of a few to several hundred meters. The lower slope is locally very rough and at the verge of failure throughout the entire Peruvian margin, as a result of subduction erosion causing the lower slope to over-steepen. Using curvature attributes to quantitatively examine the morphology in the Yaquina and Mendaña areas revealed that the latter shows a larger local roughness both seaward and landward of the trench. However, the amplitude of morphological roughness is larger in the Yaquina area. We identified a 125 km2 large slump on the Lima middle slope. Morphometric dating suggests an age of 74500 years within 35 to 40% error. Estimated incision rates on the upper slope are between 0.1 and 0.3 mm per year suggesting that landscape evolution on the Peruvian submarine continental slope is similarly slow than that in the Atacama desert.
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  • 58
    Publication Date: 2016-06-15
    Description: The electron backscattering diffraction technique (EBSD) was used to analyze bulging recrystallization microstructures from naturally and experimentally deformed quartz aggregates, both of which are characterized by porphyroclasts with finely serrated grain boundaries and grain boundary bulges set in a matrix of very fine recrystallized grains. For the Tonale mylonites we investigated, a temperature range of 300–380 °C, 0.25 GPa confining pressure, a flow stress range of ~ 0.1–0.2 GPa, and a strain rate of ~ 10− 13 s− 1 were estimated. Experimental samples of Black Hills quartzite were analyzed, which had been deformed in axial compression at 700 °C, 1.2–1.5 GPa confining pressure, a flow stress of ~ 0.3–0.4 GPa, a strain rate of ~ 10− 6 s− 1, and to 44% to 73% axial shortening. Using orientation imaging we investigated the dynamic recrystallization microstructures and discuss which processes may contribute to their development. Our results suggest that several deformation processes are important for the dismantling of the porphyroclasts and the formation of recrystallized grains. Grain boundary bulges are not only formed by local grain boundary migration, but they also display a lattice misorientation indicative of subgrain rotation. Dynamic recrystallization affects especially the rims of host porphyroclasts with a hard orientation, i.e. with an orientation unsuitable for easy basal slip. In addition, Dauphiné twins within porphyroclasts are preferred sites for recrystallization. We interpret large misorientation angles in the experimental samples, which increase with increasing strain, as formed by the activity of fluid-assisted grain boundary sliding.
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  • 59
    Publication Date: 2017-06-21
    Description: Phases with massive abundances of Uvigerina species recorded in North Atlantic deep-sea cores were previously attributed to water mass properties or to extended high productivity during the last Glacial. We investigated the Uvigerina distribution in 53 sediment cores and 555 surface samples from the north-eastern Atlantic ranging from 308 to 708N and 1 to 4410 m water depth. Our results showed that Uvigerina pigmea dominated in late Pleistocene assemblages whereas Uvigerina peregrina and Uvigerina peregrina parva were common during the Holocene. Uvigerina pigmea lives today in the Gulf of Guinea and South Atlantic only (98N to 178S), but was present up to 548N during the Last Glacial Maximum. The species retreated north- and southwards during Termination I and disappeared in the north-eastern Atlantic off northern Portugal 6100 years ago. Uvigerina peregrina and U. peregrina parva spread out from isolated occurrences along the continental slope off western Iberia at the onset of Termination I. Uvigerina peregrina exhibited Recent abundance maxima at Goban Spur, Plateau des Landes, and the Iberian Margin. These areas are subjected to strong lateral advection by downslope transport and sediment focusing. The actual flux rate of particulate organic matter is locally raised by a factor of 4 to 5. Comparable flux rates were otherwise recorded at U. peregrina maxima under the NW-African coastal upwelling regime. The Recent distribution of U. pigmea and evidence from sediment cores show an organic carbon flux of 3.5 g C m-2 yr-1 as minimum for a sustainable population of this species. Alkenone, pigment and planktonic foraminiferal records from cores MD952039 and MD952040 revealed that a spring bloom dominated productivity dynamics and a balanced food particle composition of haptophyteae algae and diatoms were limiting environmental factors for U. pigmea during the Pleistocene. A widespread change from glacial to modern productivity characteristics during the last Deglaciation may have triggered the early Holocene disappearance of U. pigmea from the north-eastern Atlantic.
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  • 60
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    Elsevier
    In:  Progress in Oceanography, 65 . pp. 145-158.
    Publication Date: 2016-10-05
    Description: Despite their importance for the global oceanic nitrogen (N) cycle, estimates of N fluxes in the Arabian Sea remain in considerable uncertainty. In this report, we summarize current knowledge of important processes, including denitrification, N2 fixation and nitrous oxide emissions. Additionally, we discuss anthropogenic impacts on the N cycle in the region. Existing studies suggest that the Arabian Sea is a significant source of N2O, and a major sink for fixed-N mainly due to enhanced rates of denitrification that occur in suboxic portions of the water column in the Arabian Sea. Sedimentary denitrification is small compared to water column denitrification, and additions of fixed-N via N2 fixation also are small compared to pelagic denitrification. As a consequence, the fixed-N budget of the Arabian Sea is dominated by an advective supply from the south, and by the sink arising from pelagic denitrification. Although relatively small compared to the advective supply, inputs of fixed-N from runoff and from the atmosphere may have significant impacts on surface waters and on the coastal waters of western India, and these inputs are rising because of human activities. Overall, the Arabian Sea’s nitrogen cycle is likely to respond sensitively to climate change and, in turn, have an impact on climate via its N2O and denitrification components.
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  • 61
    Publication Date: 2017-07-24
    Description: TOPO-EUROPE addresses the 4-D topographic evolution of the orogens and intra-plate regions of Europe through a multidisciplinary approach linking geology, geophysics, geodesy and geotechnology. TOPO-EUROPE integrates monitoring, imaging, reconstruction and modelling of the interplay between processes controlling continental topography and related natural hazards. Until now, research on neotectonics and related topography development of orogens and intra-plate regions has received little attention. TOPO-EUROPE initiates a number of novel studies on the quantification of rates of vertical motions, related tectonically controlled river evolution and land subsidence in carefully selected natural laboratories in Europe. From orogen through platform to continental margin, these natural laboratories include the Alps/Carpathians–Pannonian Basin System, the West and Central European Platform, the Apennines–Aegean–Anatolian region, the Iberian Peninsula, the Scandinavian Continental Margin, the East-European Platform, and the Caucasus–Levant area. TOPO-EUROPE integrates European research facilities and know-how essential to advance the understanding of the role of topography in Environmental Earth System Dynamics. The principal objective of the network is twofold. Namely, to integrate national research programs into a common European network and, furthermore, to integrate activities among TOPO-EUROPE institutes and participants. Key objectives are to provide an interdisciplinary forum to share knowledge and information in the field of the neotectonic and topographic evolution of Europe, to promote and encourage multidisciplinary research on a truly European scale, to increase mobility of scientists and to train young scientists. This paper provides an overview of the state-of-the-art of continental topography research, and of the challenges to TOPO-EUROPE researchers in the targeted natural laboratories
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  • 62
    Publication Date: 2017-08-03
    Description: Several gas seeps and near-surface gas hydrate deposits have been identified in 850–900-m water depth on the continental slope offshore Batumi, Georgia (eastern Black Sea) using deep-towed high-resolution sidescan sonar data. The seeps are located on a ridge named Kobuleti Ridge separating two canyons: the Supsa canyon north of the ridge and the deeply incised central canyon south of it. The southern wall of this canyon shows signs for additional gas seeps. Gas seeps are shown by acoustic anomalies in the water column on raw sonar records and as high backscatter intensity areas on processed data. The seeps on Kobuleti Ridge are characterised by carbonate deposits at the centre and a much wider area where finely disseminated gas hydrates are present. Fractures of a NW–SE direction are present at the seep sites and are probably related to the formation and decomposition of gas. Individual sites of gas emission apparently exert their influence for a circular area of up to 40 m in diameter. Gas geochemistry from gravity cores shows high gas content and a mixture of biogenic and thermogenic gases together with the presence of gas hydrates. The seeps offshore Georgia are different from other known cold seeps in the Black Sea such as shallow water seeps of biogenic gas and deep water mud volcanoes. They are located in deep water within the zone of gas hydrate stability, lack significant relief and are characterised by active gas emission and the absence of mud volcanism.
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  • 63
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    Elsevier
    In:  Journal of Volcanology and Geothermal Research, 157 (1-3). pp. 9-33.
    Publication Date: 2017-07-25
    Description: The magmatic andesitic eruption of Arenal volcano on July 29–31, 1968, after centuries of dormancy, produced three new fissural craters (A, B and C) on its western flank and a multilayered pyroclastic deposit emplaced by complex transport mechanisms. The explosions were initially triggered by a volatile oversaturated (4–7 wt.% H2O) magma. Several lines of evidences suggest a small blast surge, where a wood-rich pyroclastic deposit was emplaced as a ground layer, followed by several units of coarse-grained (MdΦ between − 0.65 and − 5.40) tephra deposits (LU: lapilli units, DAU: double ash units). LU-1, -2, -3, DAU-1 and -2 consist of unconsolidated and well- to poorly sorted vesiculated bombs and lapilli of andesite, some blocks, ash and shredded wood. The individual units are possibly correlated with the major explosions of July 29. The thickness of the deposits decreases with the distance from the volcano from 5.6 m to a few centimeters. On average, 90% of the components are juvenile (10% dense andesite and 90% vesicular). These coarse-grained beds were deposited in rapid succession by a complex transport process, involving normal fallout, strong ballistic trajectories with a lateral hot (∼ 400 °C) blast surge (LU, equivalent to A1). Ballistic and coarse tephra sprayed in a narrow (85°) area within about 5.5 km from the lowest crater, and a high (ca. 10 km) eruption column dispersed airfall fine lapilli-ash 〉 100 km from the volcano. Ash-cloud forming explosions, producing thin pyroclastic surge and muddy phreatomagmatic fallout deposits (FLAU, equivalent to A2 and A3), closed the blast surge sequence. The successive explosions on July 30–31 mainly produced block and ash flows, and widely dispersed ash fall. The total volume of pyroclastic material is calculated as 25.8 ± 5.5 × 106 m3 (9.4 ± 2.0 × 106 m3 DRE). A model is proposed to explain the peculiarities of the formation, transportation and emplacement of the blast deposits. The intrusion of the presumed andesitic cryptodome possibly happened through an active thrust fault, favoring not only the formation of the lowest crater A, but also the low-angle explosive events. Prior to the eruption, several minerals were settling to the bottom of the magma chamber as is suggested by the increase of incompatible elements towards the bottom of the stratigraphic section. The major elements indicate that some crystal redistribution occurred and the maximum concentration of Al2O3, and Eu, and Sr support plagioclase enrichment in early phases of the eruption (top of LU-1 and DAU-1). From the about 20 recognized prehistoric and historic blast deposits in the world, approximately half were produced by sector collapse of the volcano and the other half by sudden decompression of cryptodomes or lava-dome collapses. The recent blasts (1888–1990s) elsewhere have an apparent recurrence of one event/decade, compared to just a dozen described for the previous 50 ka. Therefore, the adequate recognizers of the blast facies in the cone-building lithofacies, especially for small stratocones as described here, can help in understanding other historic and prehistoric cases, and their related hazards.
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  • 64
    Publication Date: 2017-11-01
    Description: A steady-state reaction-transport model is applied to sediments retrieved by gravity core from two stations (S10 and S13) in the Skagerrak to determine the main kinetic and thermodynamic controls on anaerobic oxidation of methane (AOM). The model considers an extended biomass-implicit reaction network for organic carbon degradation, which includes extracellular hydrolysis of macromolecular organic matter, fermentation, sulfate reduction, methanogenesis, AOM, acetogenesis and acetotrophy. Catabolic reaction rates are determined using a modified Monod rate expression that explicitly accounts for limitation by the in situ catabolic energy yields. The fraction of total sulfate reduction due to AOM in the sulfate–methane transition zone (SMTZ) at each site is calculated. The model provides an explanation for the methane tailing phenomenon which is observed here and in other marine sediments, whereby methane diffuses up from the SMTZ to the top of the core without being consumed. The tailing is due to bioenergetic limitation of AOM in the sulfate reduction zone, because the methane concentration is too low to engender favorable thermodynamic drive. AOM is also bioenergetically inhibited below the SMTZ at both sites because of high hydrogen concentrations (∼3–6 nM). The model results imply there is no straightforward relationship between pore water concentrations and the minimum catabolic energy needed to support life because of the highly coupled nature of the reaction network. Best model fits are obtained with a minimum energy for AOM of ∼11 kJ mol−1, which is within the range reported in the literature for anaerobic processes.
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  • 65
    Publication Date: 2017-10-12
    Description: Late Glacial to Holocene ice retreat was investigated along a 120 km long fjord system, reaching from Gran Campo Nevado (GCN) to Seno Skyring in the southernmost Andes (53°S). The aim was to improve the knowledge on regional and global control on glacier recession with special emphasis on latitudinal shifting of the westerlies. The timing of ice retreat was derived from peat and sediment cores, using mineralogical and chemical characteristics, and pollen as proxies. Stratigraphy was based on 14C-AMS ages and tephrochronology. The ice retreat of the Seno Skyring Glacier lobe is marked by an ice rafted debris layer which was formed around 18,300 to 17,500 cal. yr B.P. Subsequently, fast glacier retreat occurred until around 15,000 to 14,000 cal. yr B.P. during which around 84% of Skyring Glacier were lost. This fast recession was probably also triggered by an increase of the Equilibrium Line Altitude (ELA) from 200 to 300 m. Subsequently, the ice surface was lowered below the ELA in an area that previously made up more than 50% of the accumulation area. Much slower retreat and glacier fluctuations of limited extent in the fjord channel system northeast of GCN occurred between around 14,000 to 11,000 cal. yr B.P. during both the Antarctic Cold Reversal and the Younger Dryas. This slow down of retreat indicates a decline in the general warming trend and/or increased precipitation, due to a southward migration of the westerlies. After around 11,000 cal. yr B.P. pollen distribution shows evolved Magellanic Rainforest and similar climate as at present, which lasted throughout most of the Holocene. Only Late Neoglacial moraine systems were formed in the period 1220–1460 AD, and subsequently in the 1620s AD, and between 1870 and 1910 AD. The results indicate that the Gran Campo Nevado ice cap has reacted more sensitive and partly distinct to climate change, compared to the Patagonian Ice Field.
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  • 66
    Publication Date: 2017-12-11
    Description: The extraction of a deepwater radiogenic isotope signal from marine sediments is a powerful, though under-exploited, tool for the characterisation of past climates and modes of ocean circulation. The radiogenic and radioactive isotope compositions (Nd, Pb, Th) of ambient deepwater are stored in authigenic Fe–Mn oxyhydroxide coatings in marine sediments, but the unambiguous separation of the isotopic signal in this phase from other sedimentary components is difficult and measures are needed to ensure its seawater origin. Here the extracted Fe–Mn oxyhydroxide phase is investigated geochemically and isotopically in order to constrain the potential and the limitations of the reconstruction of deepwater radiogenic isotope compositions from marine sediments. Our results show that the isotope compositions of elements such as Sr and Os obtained from the Fe–Mn oxyhydroxide fraction are easily disturbed by detrital contributions originating from the extraction process, whereas the seawater isotope compositions of Nd, Pb and Th can be reliably extracted from marine sediments in the North Atlantic. The main reason is that the Nd, Pb and Th concentrations in the detrital phase of pelagic sediments are much lower than in the Fe–Mn oxyhydroxide fractions. This is reflected in Al/Nd, Al/Pb and Al/Th ratios of the Fe–Mn oxyhydroxide fractions, which are as low as or even lower than those of hydrogenetic ferromanganese crusts. Mass balance calculations illustrate that the use of the 87Sr/86Sr isotope composition to confirm the seawater origin of the extracted Nd, Pb and Th isotope signals is misleading. Even though the 87Sr/86Sr in the Fe–Mn oxyhydroxide fractions is often higher than the seawater Sr isotope composition, the corresponding detrital contribution does not translate into altered seawater Nd, Pb and Th isotope compositions due to mass balance constraints. Overall the rare earth element patterns, elemental ratios, as well as the mass balance calculations presented here highlight the potential of using authigenic Fe–Mn oxyhydroxide coatings as paleoceanographic archives for the analysis of past seawater Nd, Pb and Th isotope compositions.
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  • 67
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    Unknown
    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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  • 68
    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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  • 69
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    Unknown
    Elsevier
    In:  Journal of Marine Systems, 74 (Suppl.1). pp. 3-12.
    Publication Date: 2017-07-12
    Description: Upwelling is a typical phenomenon of the Baltic Sea. Because the Baltic Sea is a semi- enclosed basin, winds from favorable directions blowing predominately parallel to the coast cause upwelling leading to vertical displacement of the water body and mixing. During the thermal stratified period, upwelling can lead to a strong sea-surface temperature drop of more than 10 °C changing drastically the thermal balance and stability conditions at the sea-surface. Upwelling can play a key role in replenishing the euphotic zone with the nutritional components necessary for biological productivity when the surface layer is depleted of nutrients. Consequently, it has been found out that in such areas where upwelling lifts phosphorus-rich deep water to the surface, the N/P ratio becomes low which favors the blooming of nitrogen-fixing blue-green algae. The rapid temperature decrease during such events was recognized and documented a long time ago when temperature measurements became available. Thus, the study of the upwelling process has a long tradition. However, although the importance of upwelling has generally been accepted for the Baltic Sea, no general review of upwelling exists. The objective of this paper is a comprehensive review of the upwelling process, its dynamics and reflections to ecosystem processes in the Baltic Sea using all relevant literature which will help to close the gaps of present knowledge and some recommendations for future work are outlined accordingly.
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  • 70
    Publication Date: 2017-02-09
    Description: During segment-scale studies of the southern Mid-Atlantic Ridge (MAR), 7–12° S, we found evidence in the water column for high-temperature hydrothermal activity, off-axis, east of Ascension Island. Extensive water column and seafloor work using both standard CTD and deep submergence AUV and ROV deployments led to the discovery and sampling of the “Drachenschlund” (“Dragon Throat”) black smoker vent at 8°17.87′ S/13°30.45′ W in 2915 m water depth. The vent is flanked by several inactive chimney structures in a field we have named “Nibelungen”. The site is located 6 km south of a non-transform offset between two adjacent 2nd-order ridge-segments and 9 km east of the presently-active, northward-propagating A2 ridge-segment, on a prominent outward-facing fault scarp. Both vent-fluid compositions and host-rock analyses show this site to be an ultramafic-hosted system, the first of its kind to be found on the southern MAR. The thermal output of this single vent, based on plume rise-height information, is estimated to be 60 ± 15 MW. This value is high for a single “black smoker” vent but small for an entire field. The tectonic setting and low He content of the vent fluids imply that high-temperature off-axis venting at “Drachenschlund” is driven not by magmatic processes, as at the majority of on-axis hydrothermal systems, but by residual heat “mined” from the deeper lithosphere. Whether this heat is being extracted from high-temperature mantle peridotites or deep crustal cumulates formed at the “duelling” non-transfrom offset is unclear, in either case the Drachenschlund vent provides the first direct observations of how cooling of deeper parts of the lithosphere, at least at slow-spreading ridges, may be occurring.
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  • 71
    Publication Date: 2017-01-30
    Description: Future warming is predicted to shift the Earth system into a mode with progressive increase and vigour of extreme climate events possibly stimulating other mechanisms that invigorate global warming. This study provides new data and modelling investigating climatic consequences and biogeochemical feedbacks that happened in a warmer world not, vert, similar 112 Myr ago. Our study focuses on the Cretaceous Oceanic Anoxic Event (OAE) 1b and explores how the Earth system responded to a moderate not, vert, similar 25,000 yr lasting climate perturbation that is modelled to be less than 1 °C in global average temperature. Using a new chronological model for OAE 1b we present high-resolution elemental and bulk carbon isotope records from DSDP Site 545 from Mazagan Plateau off NW Africa and combine this information with a coupled atmosphere–land–ocean model. The simulations suggest that a perturbation at the onset of OAE 1b caused almost instantaneous warming of the atmosphere on the order of 0.3 °C followed by a longer (not, vert, similar 45,000 yr) period of not, vert, similar 0.8 °C cooling. The marine records from DSDP Site 545 support that these moderate swings in global climate had immediate consequences for African continental supply of mineral matter and nutrients (phosphorous), subsequent oxygen availability, and organic carbon burial in the eastern subtropical Atlantic, however, without turning the ocean anoxic. The match between modelling results and stratigraphic isotopic data support previous studies [summarized in Jenkyns, H.C., 2003. Evidence for rapid climate change in the Mesozoic–Palaeogene greenhouse world. The Royal Society, 361: 1885–1916.] in that methane emission from marine hydrates, albeit moderate in dimension, may have been the trigger for OAE 1b, though we can not finally rule out alternative mechanisms. Following the hydrate mechanism a total of 1.15 × 1018 g methane carbon (δ13C = − 60 ‰), equivalent to about 10% to the total modern gas hydrate inventory, generated the δ13Ccarb profile recorded in the section. Modelling suggests a combination of moderate-scale methane pulses supplemented by continuous methane emission at elevated levels over not, vert, similar 25,000 yr. The proposed mechanism, though difficult to finally confirm in the geological past, is arguably more likely to occur in a warmer world and apparently perturbs global climate and ocean chemistry almost instantaneously. This study shows that, once set-off, this mechanism can maintain Earth's climate in a perturbed mode over geological time leading to pronounced changes in regional climate.
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  • 72
    Publication Date: 2017-11-01
    Description: The free energy yield of microbial respiration reactions in anaerobic marine sediments must be sufficient to be conserved as biologically usable energy in the form of ATP. Anaerobic oxidation of methane (AOM) coupled to sulfate reduction (SRR) has a very low standard free energy yield of ΔG∘ = −33 kJ mol−1, but the in situ energy yield strongly depends on the concentrations of substrates and products in the pore water of the sediment. In this work ΔG for the AOM–SRR process was calculated from the pore water concentrations of methane, sulfate, sulfide, and dissolved inorganic carbon (DIC) in sediment cores from different sites of the European continental margin in order to determine the influence of thermodynamic regulation on the activity and distribution of microorganisms mediating AOM–SRR. In the zone of methane and sulfate coexistence, the methane-sulfate transition zone (SMTZ), the energy yield was rarely less than −20 kJ mol−1 and was mostly rather constant throughout this zone. The kinetic drive was highest at the lower part of the SMTZ, matching the occurrence of maximum AOM rates. The results show that the location of maximum AOM rates is determined by a combination of thermodynamic and kinetic drive, whereas the rate activity mainly depends on kinetic regulation.
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  • 73
    Publication Date: 2016-06-15
    Description: The southern Chilean convergent margin, between 50° and 57° S, is shaped by the interaction of the three main plates: Antarctic, South America and Scotia. North of 53° S, the convergence between Antarctic and South America plates is close to orthogonal to the continental margin strike. Here, the deformational style of the accretionary prism is mainly characterized by seaward-verging thrusts and locally by normal faults and fractures, a very limited lateral extension of prism, a very shallow dip (∼ 6°) décollement, and subduction of a thick and relatively undeformed trench sedimentary sequence. South of 53° S, convergence is oblique to the margin, locally, the trench sediments are proto-deformed by double vergence thrusting and the front of the prism grows through landward-verging thrusting. The décollement is sub-horizontal and deep, involving most of the sediment over the oceanic crust in the accretionary process, building a comparatively wide and thicker prism. A Bottom Simulating Reflector is present across the whole prism to the abyssal plan, suggesting the presence of gas in the sediments. The analysis of P- and S-wave velocity reflectivity sections, derived by amplitude versus offset technique (AVO), detailed velocity information and the velocity-derived sediment porosity have been integrated with the structural analysis of the accretionary prism of two selected pre-stack depth migrated seismic lines, aiming to explain the relation between fluid circulation and tectonics. Accretion along double vergence thrust faults may be associated with the presence of overpressured fluid, which decreases the effective shear stress coefficient along the main décollement and within the sediments, and modify the rheolgical properties of rocks. The presence of an adequate drainage network, represented by interconnected faults and fractures affecting the entire sedimentary sequence, can favour the escape of pore fluid toward the sea bottom, while, less permeable and not faulted sediments can favour fluid accumulations. Gravitational and tectonic dewatering, and stratigraphy could control the consolidation and the pore overpressure of sediments involved in subduction along the trench. The results of our analysis suggest the existence of a feedback between tectonic style and fluid circulation.
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  • 74