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  • Other Sources  (823)
  • Elsevier  (810)
  • Annual Reviews
  • International Union of Crystallography (IUCr)
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  • 2020-2022  (50)
  • 2005-2009  (665)
  • 1985-1989  (75)
  • 1980-1984  (33)
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Year
  • 1
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    Elsevier
    In:  Signal Processing, Tokyo, Elsevier, vol. 8, no. 1, pp. 401-413, pp. L16603
    Publication Date: 1985
    Keywords: Spectrum ; Maximum likelihood
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  • 2
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 14 B, pp. 225, (ISBN 3-7643-7011-4)
    Publication Date: 1984
    Keywords: Applied geophysics ; seismic Migration ; Seismics (controlled source seismology) ; Acoustics
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  • 3
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 3, pp. 6322, (ISBN 0-521-79203-7)
    Publication Date: 1989
    Keywords: Textbook of physics ; Textbook of geophysics ; Stress ; Boundary Element Method
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  • 4
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    Elsevier
    In:  New York, Elsevier, vol. 138, no. 2, pp. 125-169, (ISBN 0-7923-5034-0)
    Publication Date: 1987
    Keywords: Borehole geophys. ; Textbook of geophysics
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  • 5
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    Elsevier
    In:  Amsterdam, 652 pp., Elsevier, vol. 39, no. XVI:, pp. 227-235, (0-444-51955-6)
    Publication Date: 1989
    Keywords: Borehole geophys. ; Textbook of geophysics ; Dual Induction Latero log
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  • 6
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    Elsevier
    In:  Amsterdam, Elsevier, vol. Developments in Petroleum Science vol. 15B, no. Publ. No. 12, pp. 9, (ISBN: 0-12-636380-3)
    Publication Date: 1986
    Keywords: Borehole geophys. ; Textbook of geophysics ; Tectonics ; Geol. aspects ; GFZ ; RUB ; GMG ; 3.45.8 ; UniL ; IfGuG ; in ; Französisch
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  • 7
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    Elsevier
    In:  Amsterdam, Elsevier, vol. Developments in Petroleum Science vol. 15A, no. Publ. No. 12, pp. 9, (ISBN: 0-12-636380-3)
    Publication Date: 1984
    Keywords: Borehole geophys. ; Textbook of geophysics ; GFZ ; RUB ; GMG ; 3.45.8 ; UniL ; IfGuG ; in ; Französisch
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  • 8
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 26, no. ALEX(01)-FR-77-01, AFTAC Contract F08606-76-C-0025, pp. 329, (ISBN: 0-08-043649-8)
    Publication Date: 1987
    Keywords: Seismology ; Seismics (controlled source seismology) ; Applied geophysics ; Layers
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  • 9
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    Elsevier
    In:  Amsterdam, 253 pp., Elsevier, vol. 10, no. 1, pp. 1-40, (ISBN: 3-540-23712-7)
    Publication Date: 1983
    Keywords: Textbook of geophysics ; Acoustics ; Seismics (controlled source seismology) ; Waves ; Wave propagation
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  • 10
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    Elsevier
    In:  Bull., Open-File Rept., Ground Motion and Engineering Seismology, Amsterdam, Elsevier, vol. 14, no. 86-425, pp. 231-241, (ISBN 0080419208)
    Publication Date: 1987
    Keywords: Seismology ; Strong motions
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  • 11
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    Elsevier
    In:  Bull., Open-File Rept., The Origin of Arcs, Amsterdam, Elsevier, vol. 65, no. 1, pp. 63-78, (ISBN 0080419208)
    Publication Date: 1986
    Keywords: Tectonics ; Geol. aspects ; Fault zone ; Plate tectonics
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  • 12
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    Elsevier
    In:  Advances in Geophysics, ed.: Renata Dmowska, Warszawa, Elsevier, vol. 47, no. 7, pp. 65-111, pp. L21303, (ISBN: 0-12-018847-3)
    Publication Date: 2005
    Keywords: Fault zone ; Rock mechanics ; Friction ; Fracture ; Physical properties of rocks ; geometry
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  • 13
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    Elsevier
    In:  Advances in Geophysics, ed.: Renata Dmowska, Heidelberg, Elsevier, vol. 47, no. 8, pp. 1-64, pp. 1516, (ISBN: 0-12-018847-3)
    Publication Date: 2005
    Keywords: Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Subduction zone ; USA
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  • 14
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 12, pp. 225, (ISBN 3-7643-7011-4)
    Publication Date: 1985
    Keywords: Textbook of geophysics ; Seismics (controlled source seismology) ; seismic Migration ; Acoustics ; Wave propagation ; Waves
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  • 15
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 6, no. 16, pp. 220, (ISBN: 3540148477)
    Publication Date: 1989
    Keywords: Fracture ; Rock mechanics ; Elasticity
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  • 16
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 81A and 81B, no. 22, pp. 65-70, (1405101733, 336 p.)
    Publication Date: 1984
    Keywords: Textbook of geophysics ; Earth model, also for more shallow analyses !
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  • 17
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    Elsevier
    In:  Amsterdam, 566+XIII pp., Elsevier, vol. 65, no. ALEX(01)-FR-77-01, AFTAC Contract F08606-76-C-0025, pp. 95-104, (ISBN: 0-08-044051-7)
    Publication Date: 1986
    Keywords: Elasticity theory of dislocations ; Textbook of geophysics ; Dislocation
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  • 18
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    Elsevier
    In:  Amsterdam, 613 pp., Elsevier, vol. 52, no. ALEX(01)-FR-77-01, AFTAC Contract F08606-76-C-0025, pp. 95-104, (ISBN: 0-08-044051-7)
    Publication Date: 1987
    Keywords: Inversion ; Textbook of mathematics ; Textbook of geophysics
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  • 19
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 65, no. ALEX(01)-FR-77-01, AFTAC Contract F08606-76-C-0025, pp. 95-104, (ISBN: 0-08-044051-7)
    Publication Date: 1989
    Keywords: Textbook of geophysics ; Gravimetry, Gravitation ; Crustal deformation (cf. Earthquake precursor: deformation or strain)
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  • 20
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    Elsevier
    In:  Bull., Polar Proj. OP-O3A4, Signal Processing II: Theories and Applications, Bath, Elsevier, vol. 186, no. XVI:, pp. 689-692, (ISBN: 3-540-23712-7)
    Publication Date: 1983
    Keywords: Seismology ; Seismic arrays ; Spectrum ; Broad-band ; Data analysis / ~ processing ; f-k-Analysis ; Schuessler ; Schussler
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  • 21
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    Elsevier
    In:  Bull., Polar Proj. OP-O3A4, Signal Processing II: Theories and Applications, Leiden, Elsevier, vol. 11, no. XVI:, pp. 673-680, (ISBN: 3-540-23712-7)
    Publication Date: 1983
    Keywords: Seismology ; Seismics (controlled source seismology) ; Filter- ; Data analysis / ~ processing ; Schuessler ; Schussler
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  • 22
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    Elsevier
    In:  Bull., Polar Proj. OP-O3A4, Computer-aided Seismic Analysis and Discrimination, London, Elsevier, vol. 16, no. 4, pp. 97-109, (ISBN 0080419208)
    Publication Date: 1981
    Keywords: Group veloc. ; Velocity analysis
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  • 23
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    Elsevier
    In:  Amsterdam, I-VII + 329 pp., Elsevier, vol. 1, no. Publ. No. 12, pp. 127, (ISBN 3-540-44363-0)
    Publication Date: 1980
    Keywords: Geothermics ; application ; and ; prospection ; Earthquake hazard ; nuclear ; power ; plants ; Earthquake risk ; solar ; Energy (of earthquakes) ; pollution ; FROTH ; pp. ; 1-81, ; 279-288
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  • 24
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 20, no. Publ. No. 12, pp. 23-40, (ISBN 3935922167)
    Publication Date: 1986
    Keywords: Textbook of geophysics ; Data analysis / ~ processing ; Elasticity
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  • 25
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 2, no. 1, pp. 1-40, (ISBN 3-7643-6675-3)
    Publication Date: 1989
    Keywords: Textbook of geophysics ; Seismics (controlled source seismology) ; Applied geophysics ; Data analysis / ~ processing
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  • 26
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    Elsevier
    In:  Bull., Polar Proj. OP-O3A4, Fractals in Physics, Amsterdam, Elsevier, vol. 24, no. 4, pp. 177-180, (ISBN 0080419208)
    Publication Date: 1986
    Keywords: Fracture ; FractureT
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  • 27
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    Elsevier
    In:  Bull., Polar Proj. OP-O3A4, The Origin of Arcs, Amsterdam, Elsevier, vol. 13, no. Subvol. a, pp. 93-113, (ISBN 0080419208)
    Publication Date: 1986
    Keywords: CRUST ; earth mantle ; Plate tectonics ; Muller
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  • 28
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    Elsevier
    In:  Amsterdam, Elsevier
    Publication Date: 1980
    Keywords: Seismology ; Seismics (controlled source seismology) ; Wave propagation ; Waves ; Textbook of geophysics
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  • 29
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 1, pp. 225, (ISBN 3-7643-7011-4)
    Publication Date: 1987
    Keywords: Textbook of geophysics ; Applied geophysics ; Seismics (controlled source seismology)
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  • 30
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    Elsevier
    In:  Amsterdam, 652 pp., Elsevier, vol. 39, no. XVI:, pp. 227-235, (0-444-51955-6)
    Publication Date: 2005
    Keywords: Seismics (controlled source seismology) ; Applied geophysics ; Wave propagation ; plane ; spherical ; and ; cylindrical ; Waves ; in ; isotropic ; and ; transversely ; isotropic ; solids, ; liquid-solid ; models, ; and ; media ; with ; cylindrical ; inclusions ; (boreholes) ; Textbook of geophysics
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  • 31
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 16, no. 22, pp. 662-664, (ISBN 0-470-87000-1 (HB), ISBN 0-470-87001-X (PB))
    Publication Date: 1987
    Keywords: Surface waves ; Seismology ; Textbook of geophysics ; Wave propagation
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  • 32
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 16, no. 1, pp. 662-664, (ISBN 0-470-87000-1 (HB), ISBN 0-470-87001-X (PB))
    Publication Date: 1988
    Keywords: Textbook of geology ; Tectonics ; Fault zone ; Stress ; Fracture ; Engineering geophys.
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  • 33
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    Elsevier
    In:  Bull., Open-File Rept., Continuum Theories in Solid Earth Physics, Amsterdam, 566+XIII pp., Elsevier, vol. 186, no. 16, pp. 18-186, (ISBN 0080419208)
    Publication Date: 1986
    Keywords: Elasticity theory of dislocations ; Dislocation ; Review article
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  • 34
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    Elsevier
    In:  Bull., Open-File Rept., Signal Processing II: Theories and Applications, Orlando, Elsevier, vol. 37, no. 16, pp. 681-684, (ISBN 1-86239-165-3, vi + 330 pp.)
    Publication Date: 1983
    Keywords: Detectors ; Seismic arrays ; Seismology ; Schuessler ; Schussler
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  • 35
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    Elsevier
    In:  Professional Paper, Open-File Rept., Thermodynamics of Point Defects and the Relation with Bulk Properties, New York, Elsevier, vol. 1, no. 16, pp. 410-412, 417-420, (ISBN 0080419208)
    Publication Date: 1986
    Keywords: Geomagnetics ; Earthquake precursor: prediction research ; Earthquake precursor: magnetic ; Geoelectrics ; Physical properties of rocks
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  • 36
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    Elsevier
    In:  Fisheries Research, 8 (1). pp. 35-44.
    Publication Date: 2017-01-10
    Description: In Moreton Bay, Queensland, the catch obtained using monofilament polyamide (PA) otter trawl-nets with multifilament polyethylene (PE) cod ends was compared with that obtained using multifilament PE trawl-nets of identical mesh opening (38 mm). Monofilament PA otter trawl-nets retained fewer small prawns ( 〈 24 mm carapace length) than conventional multifilament PE nets, but both nets caught similar quantities of larger prawns ( 〉 24 mm carapace length). The higher retention rate of small prawns by multifilament PE gear was reflected in the greater catch weights of Peraeus plebejus, Metapenaeus bennettae and Metapenaeopsis novaeguineae in those nets. Catch weights of larger prawn species such as Penaeus esculentus and Metapenaeus endeavouri did not differ between nets. Winter whiting (Sillago maculata) and squid (Loligo spp.) were trawled in similar abundance in both nets, although the monofilament retained fewer squid 〈 50 mm mantle length. More marketable ( 〉 15 cm carapace width) sand crabs (Portunus pelagicus) were caught in the monofilament net. There was not significant difference in the trash (noncommercial component) weight caught in both nets. Over the range of towing speeds tested (1.7–2.3 kn), use of monofilament nets significantly reduced total gear drag.
    Type: Article , PeerReviewed
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  • 37
    Publication Date: 2020-05-14
    Description: The volcanic arc of the Hellenic subduction zone with its four volcanic centers is of major relevance when evaluating the seismovolcanic hazard for the Aegean region. We present results from a 22-station temporary seismic network (CYCNET) in the central Hellenic Volcanic Arc (HVA). CYCNET recordings allow to analyze the level and spatio-temporal evolution of microseismic activity in this region for the first time. A total of 2175 events recorded between September 2002 and July 2004 are analyzed using statistical methods, cluster analysis and relative relocation techniques. We identify distinct regions with significantly varying spatiotemporal behavior of microseismicity. A large portion of the seismic activity within the upper crust is associated with the presence of islands representing horst structures that were generated during the major Oligocene extensional phase. In contrast, the central part of the Cyclades metamorphic core complex remains aseismic considering our magnitude threshold of 1.8 except one spot where events occur swarm-like and with highly similar waveforms. The highest activity in the study area was identified along the SW–NE striking Santorini–Amorgos zone. Within this zone the submarine Columbo volcano exhibits strong temporal variations of seismic activity on a high background level. This activity is interpreted to be directly linked to the magma reservoir and therein the migration of magma and fluids towards the surface. NE of Columbo where no volcanic activity has yet been reported we observe a similar seismicity pattern with small-scaled activity spots that might represent local pathways of upward migrating fluids or even developing volcanic activity within this zone of crustal weakness. In contrast, the Santorini and Milos volcanic complexes do not show significant temporal variations and low to moderate background activity, respectively. Relating our results to the distribution of historical earthquakes and the GPS-derived horizontal velocity field we conclude that the Santorini–Amorgos zone is presently in the state of right-lateral transtension reflecting a major structural boundary of the volcanic arc subdividing it into a seismically and volcanically quiet western and an active eastern part.
    Type: Article , PeerReviewed
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  • 38
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    Elsevier
    In:  Organic Geochemistry, 39 (8). pp. 1000-1006.
    Publication Date: 2017-06-26
    Description: The anaerobic oxidation of methane (AOM), by converting methane to bicarbonate which is then precipitated as extensive carbonate crusts, is an important methane sink in the Earth’s ocean systems. Here we employ a multidisciplinary approach to investigate the role of microorganisms in carbonate precipitation using biomarker analysis, scanning electron microscopy (SEM) and X-ray diffraction. We examined two microbial mats from the Black Sea and found that one comprised carbonate in both aragonite and Mg calcite forms and most likely ANME-1 archaea, whereas the other contained only Mg calcite and most likely ANME-2 archaea. We conclude, as have others, that the different microbial communities could impart different influences on carbonate mineralogy and morphology. Although further research is needed, this is a contribution to our understanding of those relationships, which could prove critical in the interpretation of ancient sedimentary deposits.
    Type: Article , PeerReviewed
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  • 39
    Publication Date: 2017-06-27
    Description: There is growing concern about the transfer of methane originating from water bodies to the atmosphere. Methane from sediments can reach the atmosphere directly via bubbles or indirectly via vertical turbulent transport. This work quantifies methane gas bubble dissolution using a combination of bubble modeling and acoustic observations of rising bubbles to determine what fraction of the methane transported by bubbles will reach the atmosphere. The bubble model predicts the evolving bubble size, gas composition, and rise distance and is suitable for almost all aquatic environments. The model was validated using methane and argon bubble dissolution measurements obtained from the literature for deep, oxic, saline water with excellent results. Methane bubbles from within the hydrate stability zone (typically below 500 m water depth in the ocean) are believed to form an outer hydrate rim. To explain the subsequent slow dissolution, a model calibration was performed using bubble dissolution data from the literature measured within the hydrate stability zone. The calibrated model explains the impressively tall flares (〉1300 m) observed in the hydrate stability zone of the Black Sea. This study suggests that only a small amount of methane reaches the surface at active seep sites in the Black Sea, and this only from very shallow water areas (〈100 m). Clearly, the Black Sea and the ocean are rather effective barriers against the transfer of bubble methane to the atmosphere, although substantial amounts of methane may reach the surface in shallow lakes and reservoirs.
    Type: Article , PeerReviewed
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  • 40
    Publication Date: 2018-03-07
    Description: Structure-based inhibitor design has led to the discovery of a number of potent inhibitors of glycogen phosphorylase b (GPb), N-acyl derivatives of β-d-glucopyranosylamine, that bind at the catalytic site of the enzyme. The first good inhibitor in this class of compounds, N-acetyl-β-d-glucopyranosylamine (NAG) (Ki = 32 μM), has been previously characterized by biochemical, biological and crystallographic experiments at 2.3 Å resolution. Bioisosteric replacement of the acetyl group by trifluoroacetyl group resulted in an inhibitor, N-trifluoroacetyl-β-d-glucopyranosylamine (NFAG), with a Ki = 75 μM. To elucidate the structural basis of its reduced potency, we determined the ligand structure in complex with GPb at 1.8 Å resolution. To compare the binding mode of N-trifluoroacetyl derivative with that of the lead molecule, we also determined the structure of GPb–NAG complex at a higher resolution (1.9 Å). NFAG can be accommodated in the catalytic site of T-state GPb at approximately the same position as that of NAG and stabilize the T-state conformation of the 280s loop by making several favourable contacts to Asn284 of this loop. The difference observed in the Ki values of the two analogues can be interpreted in terms of subtle conformational changes of protein residues and shifts of water molecules in the vicinity of the catalytic site, variations in van der Waals interaction, and desolvation effects.
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  • 41
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    Elsevier
    In:  Advances in Parasitology, 68 . pp. 111-137.
    Publication Date: 2020-04-23
    Type: Article , PeerReviewed
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  • 42
    Publication Date: 2020-07-28
    Description: Carbohydrates on parasite surfaces have been shown to play an important role in host–parasite coevolution, mediating host non-self recognition and parasite camouflage. Parasites that switch hosts can change their surface molecules to remain undetected by the diverse immune systems of their different hosts. However, the question of individual variation in surface sugar composition and its relation to infectivity, virulence, immune evasion and growth of a parasite in its different hosts is as yet largely unexplored. We studied such fitness consequences of variation in surface sugars in a sympatric host–parasite system consisting of the cestode Schistocephalus solidus and its intermediate hosts, a copepod and the three-spined stickleback. Using lectins to analyse the sugar composition, we show that the tapeworm changes its surface according to the invertebrate or vertebrate host. Importantly, sugar composition seems to be genetically variable, as shown by differences among tapeworm sibships. These differences are related to variation in parasite fitness in its second intermediate host, i.e. infectivity and growth. Surface sugar composition may thus be a proximate correlate of the evolutionarily relevant variability in infectivity and virulence of parasites in different hosts.
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  • 43
    Publication Date: 2017-04-06
    Description: We employ a combined interpretation of Hydrosweep swath bathymetry and high resolution multi-channel seismic reflection data to investigate the development of Cap Timiris Canyon, a newly discovered submarine canyon offshore Mauritania. The dominantly V-shaped and deeply entrenched canyon exhibits many fluvial features including dendritic and meander patterns, cut-off loops and terraces, and is presently incising. Distal meander patterns, confined within a narrow fault-controlled corridor, show several stages of evolution, the latest of which is dominated by a down-system meander-loop migration. Terraces exhibit a variety of internal structures suggesting they originated through different processes including sliding/slumping, uplift-induced incision and lateral accretion. We ascribe canyon origin to an ancient river system in the adjacent presently arid Sahara Desert that breached the shelf during a Plio/Pleistocene sea level lowstand and delivered sediment directly into the slope area. Our data suggest that the initial invading unchannelised sheet of sand-rich turbidity flows initiated canyon formation by gradually mobilising along linear seafloor depressions and fault-controlled zones of weakness. We propose that the development of canyon morphology and structure was influenced by the stages of active flow of the coupling river system, and hence could act as a proxy for understanding the paleo-climatic evolution of a ‘green’ Sahara since Plio/Pleistocene times.
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  • 44
    Publication Date: 2020-07-15
    Description: Chemical disparities at the interface between subducting oceanic crustal rocks and the harzburgitic mantle lead to the formation of reaction zones in the mantle above the subducting slabs composed of hybrid rocks that may carry exotic trace-element patterns and isotopic signatures. Subsequent burial of these metasomatised rocks as part of the progressively subducted slab could deliver trace elements and volatiles to the source region of arc magma. A natural laboratory to study reactions at the slab–mantle interface maybe found in exhumed high-pressure mélanges, where sedimentary, mafic and ultramafic lithologies are juxtaposed and metamorphosed at high-P/T conditions. A mélange zone of that type is found in northern Syros, where metasomatic reaction zones (“blackwalls”) formed on a metre scale at the contact of metasedimentary blueschists and serpentinite. Five different zones within such a contact display the assemblages (I) glaucophane+garnet+phengite+epidote, (II) glaucophane+epidote+chlorite, (III) chlorite+epidote+omphacite±albite (IV) chlorite±titanite±rutile±apatite and (V) serpentine+chromite. Accessory phases, such as apatite, allanite, rutile, titanite, tourmaline, zircon and monazite are abundant in zones II to IV. The observed succession of assemblages together with whole-rock major and trace-element compositions reflect the two dominant processes that are thought to have operated along the lithological contact: (A) diffusion of chemical components driven by the compositional contrast of the juxtaposed rocks, and (B) flux of hydrous fluids along the contact, which depleted (e.g., LILE, SiO2) or enriched (e.g., B, LREE) certain elements in various zones. Thermodynamic modelling is able to closely predict the succession of mineral assemblages as they are expected from diffusion of Mg and Ca across the contact zone. Employed to various P–T conditions and different juxtaposed rock types, this type of modelling could be used to access and evaluate larger portions of the subduction system. Our results support existing models that suggest that mixing and redistribution of major and trace elements in subduction zones may be related to the formation of hybrid rocks in mélange zones
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  • 45
    Publication Date: 2017-06-27
    Description: In several fields of cell biology, correlative microscopy is applied to compare the structure of objects at high resolution under the electron microscope with low resolution light microscopy images of the same sample. It is, however, difficult to prepare samples and marker systems that are applicable for both microscopic techniques for the same specimen at the same time. In our studies, we used microbial mats from Cold Seep communities for a simple and rapid correlative microscopy method. The mats consist of bacterial and archaeal microorganisms, coupling reverse methanogenesis to the reduction of sulfate. The reverse methanogenic pathway also generates carbonates that precipitate inside the mat and may be the main reason for the formation of a microbial reef. The mat shows highly differentiated aggregates of various organisms, tightly interconnected by extracellular polysaccharides. In order to investigate the role of EPS as adhesive mucilage for the biofilm and as a precipitation matrix for carbonate minerals, samples were embedded in a hydrophilic resin (Lowicryl K4 M). Sections were suitable for light as well as electron microscopy in combination with lectins, either labeled with a fluorescent marker or with colloidal gold. This allows lectin mapping at low resolution for light microscopy in direct comparison with a highly resolved electron microscopic image.
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  • 46
    Publication Date: 2017-06-27
    Description: Samples collected from the shelf-edge wedge using surface grab samples and the Jago submersible constrain the KwaZulu-Natal shelf-edge wedge to a late Pliocene age on the basis of the absence of Gephyrocapsa oceanica s.l. and Discoaster brouweri, and the presence of Calcidiscus macintyrei. This correlates with proposed Tertiary sea-level curves for southern Africa and indicates relative sea-level fall during the late Pliocene coupled with hinterland uplift. Exposed failure scarps in the upper portions of submarine canyons yield sediment samples of early Pleistocene ages, indicating the uppermost age of deposition of clinoform topsets exposed in the scarp walls. Partially consolidated, interbedded silty and sandy deposits of similar age outcrop in the thalweg of Leven canyon at a depth of 150 m. These sediments provide an upper age limit of the shelf-edge wedge of early Pleistocene, giving a sedimentation rate of this wedge of 162–309 m/Ma. The distribution of widespread basal-most Pleistocene sediments on the upper slope indicates that these sediments escaped major reworking during sea-level falls associated with Pleistocene glaciations and remain as relict upper slope veneers. The absence of more recent sediments suggests that this area has been a zone of sediment bypass or starvation since the early Pleistocene. Areas where younger sediments mantle deposits of early Pleistocene ages represent areas of offshore bedload parting, re-distributing younger Holocene sediment offshore and downslope.
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  • 47
    Publication Date: 2018-03-09
    Description: Prompted by recent data analyses suggesting that the flux of particulate organic carbon sinking into deep waters is determined by fluxes of mineral ballasts, we undertook a study of the relationships among organic matter (OM), calcium carbonate, opal, lithogenic material, and excess aluminum fluxes as part of the MedFlux project. We measured fluxes of particulate components during Spring and Summer of 2003, and Spring of 2005, using a swimmer-excluding sediment trap design capable of measuring fluxes both in a time-series (TS) mode and in a configuration for obtaining particle settling velocity (SV) profiles. On the basis of these studies, we suggest that distinct OM–ballast associations observed in particles sinking at a depth of ∼200 m imply that the mechanistic basis of the organic matter–ballast association is set in the upper water column above the Twilight Zone, and that the importance of different ballast types follows the seasonal succession of phytoplankton. As in other studies, carbonate appears to enhance the flux of organic matter over opal. Particles must be at least half organic matter before their settling velocity is affected by ballast concentration. This lack of change in ballast composition with SV in particles with 〈40% OM content suggests that particle SV reaches a maximum because of the increasing importance of inertial drag. Relative amounts of OM and opal decrease with depth due to decomposition and dissolution; carbonates and lithogenic material contribute about the same amount to total mass, or increase slightly, throughout the water column. The high proportion of excess Al cannot be explained by its incorporation into diatom opal or reverse weathering, so Al is most likely adsorbed to particulate oxides. On shorter time scales, dust appears to increase particle flux through its role in aggregation rather than by nutrient inputs enhancing productivity. We suggest that the role of dust as a catalyst in particle formation may be a central mechanism in flux formation in this region, particularly when zooplankton fecal pellet production is low.
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  • 48
    Publication Date: 2020-08-12
    Description: The four naturally-occurring radium isotopes (223Ra, 224Ra, 226Ra and 228Ra) were used to estimate the submarine groundwater discharge (SGD) in the Isola La Cura marsh area in the northern Venice Lagoon (Italy). By determining the radium contributors to the study area (river, coastal ocean and sediments) the radium excess in the lagoon water was quantified through a mass balance model. This radium excess is attributed to a submarine groundwater discharge source and represents the most important input of radium. Possible endmembers were considered from analysis of groundwater samples (subtidal and marsh piezometers, marsh wells and seepage meters) that were enriched in Ra by one to two orders of magnitude relative to surface waters. In particular, a permeable layer at 80 cm depth in the surrounding marsh is considered to be representative of the most likely SGD source, although similar radium activities were measured in other subtidal porewater samples collected in the Isola La Cura area. The estimated SGD flux to the study area ranged from 1 · 109 to 6 · 109 L·d− 1, the same order of magnitude as the overall riverine input to the lagoon (3 · 109 L·d− 1). A major fraction of this SGD flux is likely recirculated seawater, as evidenced by the endmember salinity. The water residence time of 2 days was estimated by both using the shortest-lived radium isotope and estimating the volume of water exchanged between the lagoon and the open sea during a tidal cycle (tidal prism approach). This SGD flux could be used to estimate the input of other chemical species (metals, nutrients, etc.) via SGD which might affect the Venice Lagoon ecosystem.
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  • 49
    Publication Date: 2020-08-12
    Description: There is increasing evidence that submarine groundwater discharge (SGD) in many areas represents a major source of dissolved chemical constituents to the coastal ocean. In Great South Bay, NY, previous studies have shown that the discharge of nutrients with SGD may cause harmful algal blooms. This study estimates SGD to Great South Bay during August 2006 by performing a mass balance for each of the dissolved Ra isotopes (224Ra, 223Ra, 228Ra, 226Ra). The budget indicates a major unknown source (between 30 and 60% of the total input) of Ra to the bay. This imbalance can be resolved by a flux of Ra-enriched groundwater on the order of 3.5–4.5 × 109 L d− 1, depending on the Ra isotope. The Ra-estimated SGD rates compare well with those previously estimated by models of flow that decreases exponentially away from shore. Compared to previous reports of fresh groundwater discharge to the bay, the Ra-estimated discharge must comprise approximately 90% recirculated seawater. The good agreement between Ra- and model-estimated flow rates indicates that the primary SGD endmember may be best sampled at shallow depths in the sediments a short distance bayward of the low tide line.
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  • 50
    Publication Date: 2018-03-09
    Description: Seasonal (Spring and Summer 2002) concentrations of dissolved (〈0.22 μm) trace metals (Ag, Al, Co, Cu, Mn, Ni, Pb), inorganic nutrients (NO3, PO4, Si), and DOC were determined in groundwater samples from 5 wells aligned along a 30 m shore-normal transect in West Neck Bay, Long Island, NY. Results show that significant, systematic changes in groundwater trace metal and nutrient composition occur along the flowpath from land to sea. While conservative mixing between West Neck Bay water and the groundwaters explains the behavior of Si and DOC, non-conservative inputs for Co and Ni were observed (concentration increases of 10- and 2-fold, respectively) and removal of PO4 and NO3 (decreases to about half) along the transport pathway. Groundwater-associated chemical fluxes from the aquifer to the embayment calculated for constituents not exhibiting conservative behavior can vary by orders of magnitude depending on sampling location and season (e.g. Co, 3.4 × 102– 8.2 × 103 μmol d−1). Using measured values from different wells as being representative of the true groundwater endmember chemical composition also results in calculation of very different fluxes (e.g., Cu, 6.3 × 103 μmol d−1 (inland, freshwater well) vs. 2.1 × 105 μmol d−1(seaward well, S = 17 ppt)). This study suggests that seasonal variability and chemical changes occurring within the subterranean estuary must be taken into account when determining the groundwater flux of dissolved trace metals and nutrients to the coastal ocean.
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  • 51
    Publication Date: 2018-03-09
    Description: A mass balance for the naturally-occurring radium isotopes (224Ra, 223Ra, 228Ra, and 226Ra) in Jamaica Bay, NY, was conducted by directly estimating the individual Ra contributions of wastewater discharge, diffusion from fine-grained subtidal sediments, water percolation through marshes, desorption from resuspended particles, and water exchange at the inlet. The mass balance revealed a major unknown source term accounting for 19–71% of the total Ra input, which could only be resolved by invoking a source from submarine groundwater. Shallow (〈 2 m depth) groundwater from permeable sediments in Jamaica Bay was brackish and enriched in Ra relative to surface bay waters by over two orders of magnitude. To balance Ra fluxes, a submarine groundwater input of 0.8 × 109–9.0 × 109 L d− 1 was required. This flux was similar for all four isotopes, with individual estimates varying by less than a factor of 2. Our calculated groundwater flux was 6- to 70-fold higher than the fresh groundwater discharge to the bay estimated by hydrological methods, but closely matched direct flow rates measured with seepage meters. This suggests that a substantial portion of the discharge consisted of recirculated seawater. The magnitude of submarine groundwater discharge varied seasonally, in the order: summer 〉 autumn 〉 spring. Chemical analyses suggest that the recirculated seawater component of submarine groundwater delivers as much dissolved nitrogen to the bay as the fresh groundwater flux.
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  • 52
    Publication Date: 2018-03-09
    Description: Distributions of dissolved vitamin B12 and total dissolved Co were measured to gain an understanding of the cycling of these interdependent micronutrients in six marine settings including; an upwelling location, a semi-enclosed bay, two urban coastal systems, and two open ocean locations. Along the coast of Baja California, Mexico, concentrations of B12 and dissolved Co varied from 0.2 to 11 pM and 180 to 990 pM, respectively. At a nearby upwelling station, vitamin B12 and Co concentrations ranged from 0.3 to 7.0 pM and 22 to 145 pM, and concentrations did not correlate with upwelling intensity. Concentrations of B12 were highest within Todos Santos Bay, a semi-enclosed bay off the coast of Baja California, Mexico, during a dinoflagellate bloom, ranging from 2 to 61 pM, while Co concentrations varied between 61 and 194 pM. In the anthropogenically impacted Long Island Sound, NY, U.S.A., B12 levels were between 0.1 and 23 pM and Co concentrations varied from 60 to 1900 pM. However, anthropogenic inputs were not evident in B12 levels in the San Pedro Basin, located outside Los Angeles, Ca, U.S.A., where concentrations of B12 were 0.2–1.8 pM, approximating observed open ocean B12 concentrations. In the Southern Ocean and North Atlantic Ocean, B12 levels were 0.4–4 pM and 0.2–2 pM, respectively. Total Co concentrations in the Southern Ocean and North Atlantic tended to be low; measuring 26–59 pM and 15–80 pM, respectively. These low Co concentrations may limit B12 synthesis and its availability to B12-requiring phytoplankton because the total dissolved Co pool is not necessarily entirely bioavailable.
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  • 53
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    Elsevier
    In:  Tectonophysics, 405 (1-4). pp. 121-140.
    Publication Date: 2019-04-29
    Description: The Hawaiian–Emperor Seamount chain records the motion of the Pacific Plate relative to the Hawaiian mantle hotspot for ~80 m.y. A notable feature of the chain is the pronounced bend at its middle. This bend had been widely credited to a change in plate motion, but recent research suggests a change in hotspot motion as an alternative. Existing paleomagnetic data from the Emperor Chain suggest that the hotspot moved south during the Late Cretaceous and Early Tertiary, but reached its current latitude by the age of the bend. Thus, data from area of the bend are important for understanding changes in plume latitude. In this study, we analyze the magnetic anomalies of five seamounts (Annei, Daikakuji-W, Daikakuji- E, Abbott, and Colahan) in the region of the bend. These particular seamounts were chosen because they have been recently surveyed to collect multibeam bathymetry and magnetic data positioned with GPS navigation. Inversions of the magnetic and bathymetric data were performed to determine the mean magnetization of each seamount and from these results, paleomagnetic poles and paleolatitudes were calculated. Three of the five seamounts have reversed magnetic polarities (two are normal) and four contain a small volume of magnetic polarity opposite to the main body, consistent with formation during the Early Cenozoic, a time of geomagnetic field reversals. Although magnetization inhomogene ties can degrade the accuracy of paleomagnetic poles calculated from such models, the seamounts give results consistent with one another and with other Pacific paleomagnetic data of approximately the same age. Seamount paleolatitudes range from 13.7 to 23.7, with an average of 19.4F7.4 (2j). These values are indistinguishable from the present-day paleolatitude of the Hawaiian hotspot. Together with other paleomagnetic and geologic evidence, these data imply that the Hawaiian hotspot has moved little in latitude during the past ~45 m.y.
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  • 54
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    Elsevier
    In:  Cretaceous Research, 29 (5-6). pp. 725-753.
    Publication Date: 2018-02-07
    Description: The Cretaceous is a special episode in the history of the Earth named for a unique rock type, chalk. Chalk is similar to modern deep-sea calcareous ooze and its deposition in epicontinental seas occurred as these areas became an integral part of the ocean. The shelf-break fronts that today separate inshore from open-ocean waters cannot have existed during the Late Cretaceous probably because the higher sea level brought the base of the wind-mixed Ekman layer above the sea floor on the continental margins. A second peculiarity of the Cretaceous is its warm equable climate. Tropical and polar temperatures were warmer than today. Meridional and ocean-continent temperature gradients were lower. The warmer climate was a reflection of higher atmospheric levels of greenhouse gasses, CO2 and possibly CH4, reinforced by higher water vapor content in response to the warmer temperatures. Most of the additional energy involved in the meridional heat transport system was transported as latent heat of vaporization of H20 by the atmosphere. Poleward heat transport may have been as much as 1 Petawatt (20%) greater than it is today. C3 plants provided for more efficient energy transport into the interior of the continents. Circulation of the Cretaceous ocean may have been very different from that of today. It is impossible for large areas of the modern ocean to become anoxic, but episodes of local anoxia occurred during the earlier Cretaceous and became regional to global during the middle of the Cretaceous. The present ocean structure depends on constant wind systems, which in turn depend on stability of the atmospheric pressure systems forced by polar ice. During most of the Cretaceous the polar regions were ice free. Without polar ice there were seasonal reversals of the high-latitude atmospheric pressure systems, resulting in disruption of the mid- and high latitude wind systems. Without constant mid-latitude westerly winds, there would be no subtropical and polar fronts in the ocean, no well-developed ocean pycnocline, and no tropical subtropical gyres dominating ocean circulation. Instead the ocean circulation would be accomplished through mesoscale eddies which could carry warmth to the polar regions. Greater knowledge and understanding of the Cretaceous is critical for learning how the climate system operates when one or both polar regions are ice free.
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  • 55
  • 56
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    Elsevier
    In:  Animal Behaviour, 28 (4). pp. 1123-1126.
    Publication Date: 2017-02-01
    Description: Pairs of individually recognizable male Octopus vulgaris were observed in a large seawater tank containing two suitable homes (brick pots or plastic buckets). None of the animals established exclusive occupancy of one home and for much of the time both animals were associated together at the same site. Usually one of the two homes was preferred and its occupant was most likely to be the larger animal, or the earlier resident if they were of equal size. Large animals were observed to take food forcefully from smaller octopus. An arm alignment interaction is described which, it is suggested, may be a means by which two octopuses establish their relative sizes.
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  • 57
    Publication Date: 2020-07-30
    Description: The South Aegean Active Volcanic Arc consists of a chain of five volcanic centers, the most active of which is the Santorini Volcano. A local radio-linked seismological network is installed on the island consisting of five permanent and four temporary stations. The temporary stations have been in operation periodically during the period 1994–1996 and two of them were installed on adjacent islands. All stations are equipped with vertical-component short period seismometers. During the period 1994–2002 a significant number of earthquakes has been recorded, with local (duration) magnitudes, MD, up to 5.0 and focal depths varying between 0 km and 35 km. Two clusters of epicenters have been located in the broader area of the Santorini Volcano. The first cluster is located in the caldera of the volcano and is associated with the volcanic process in the Kameni Island. The second (larger) cluster is located near the northern edge of the Santorini Island at the Kolumbo Reef and is connected with the volcanic process at this reef. These clusters can be appropriately associated with the two main tectonic features (faults) in the area under study. The first one (N60°E direction) corresponds to the continuation of the Amorgos fault in the area, while the secondary tectonic line (EW direction) is probably related with the southern edge of a submarine graben, which is located between the islands Amorgos and Santorini. Using the data set of the best-located earthquakes, recorded during the period 1994–2002, an attempt has been made to derive an appropriate equivalent 1 –D earth model for the area under study, in order to improve the accuracy of the determined hypocenters, as well as to obtain a preliminary knowledge of the volcano structure.
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  • 58
    Publication Date: 2017-07-10
    Description: A total of 131 current meter records of between 6 and 24 month duration are analysed to describe the deep flow field of the eastern North Atlantic from 19° to 54°N and from the Continental Slope to the Mid Atlantic Ridge. Mean flows are weak and may be statistically indeterminate in some records and locations, but appear to indicate cyclonic circulations around the Iberia and Porcupine abyssal plains with a generally southward flow along the Mid Atlantic ridge and a deep northward slope current (where measurements exist) along the eastern boundary. The deepest inflow to the north-eastern basin that has been identified to date takes place through the Discovery Gap of 〉4,700 m sill-depth at 37° 25′N 15° 45′W in the Azores-Portugal ridge. South of that ridge, observations are sparse and no systematic circulation is yet evident. These observations are discussed in relation to recent geostrophic estimates of the deep circulation.
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  • 59
    Publication Date: 2018-03-02
    Description: Sediments on high Arctic shelves result from modern processes and the effect of former glaciations. Based on data from the northern Barents Sea, an area with input from large and numerous surging glaciers, we define two principal zones with different environmental regimes and corresponding sedimentary facies: (1) a glacier-proximal zone influenced by grounding-line processes and the immediately adjacent areas affected by glacial sediment input, and (2) a glacier-distal, sea-ice and current-controlled zone, which also includes a wide sediment-starved region dominated by biogenic carbonate accumulation. Characteristic of the glacier-proximal zone are glacial surges which affect sedimentation rates and leave a diagnostic pattern of sea-floor morphologies. Extensive ice gouging causes a homogeneous sediment texture. In the glacier-distal zone, fine-grained mud supplied from sea ice and infrequent coarser material deposited from icebergs is reworked by modern oceanographic processes. On shallow banks, in 30–50 m of water, carbonates accumulate from a prolific bottom fauna formed in response to extensive reworking and nutrient supply.
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  • 60
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    Elsevier
    In:  Journal of Colloid and Interface Science, 76 (2). pp. 541-556.
    Publication Date: 2016-11-30
    Description: A general method for simulating aerosol size distribution dynamics is developed. The method, based on dividing the particle size domain into sections and dealing only with one integral quantity in each section (e.g., number, surface area, or volume), has the advantages that the integral quantity is conserved within the computational domain and coagulations between all particle sizes are properly accounted for. To demonstrate the simplicity and accuracy of the method for a practical problem, the evolution of a power plant plume aerosol undergoing coagulation is simulated.
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  • 61
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    Elsevier
    In:  In: Scallops: Biology, Ecology and Aquaculture. Developments in aquaculture and fisheries science, 35 . Elsevier, Amsterdam, pp. 493-520. 2. Ed. ISBN 978-0-444-50482-1
    Publication Date: 2016-12-12
    Type: Book chapter , NonPeerReviewed
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  • 62
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    Elsevier
    In:  Quaternary Science Reviews, 4 (4). pp. 215-278.
    Publication Date: 2020-06-04
    Description: Molluscan fossils collected from shallow water marine sediment across NW Europe and nearby Arctic regions have been analysed for the extent of isoleucine epimerization (DL ratio) in indigenous protein residues. The DL ratios confirm that essentially all ‘classical’ Eemian sites from NW Europe are of the same age, and are correlative with the type locality near Amersfoort in the Netherlands; shells from interglacial marine sediment beneath the type Weichselian till in Poland also correlate with the type Eemian site. DL ratios in Holsteinian marine shells (0.29) are substantially higher than in their Eemian counterparts (0.17); ‘Late Cromerian’ shells yield even higher ratios (0.46). DL ratios in late glacial shells (0.06) and Middle Weichselian shells (0.09) permit differentiation from modern (0.01) and last interglacial material. Based on the position of the Matuyama-Brunhes boundary and the differences in DL ratios, the Eemian must correlate with isotope substage 5e, whereas the Holsteinian is most likely substage 7c, possibly stage 9 but certainly younger than stage 11. Intra-Saalian warm periods may be terrestrial equivalents of the younger substages of stage 7. Extensive pre-Eemian marine sediments along the SW coast of Denmark previously correlated with the Holsteinian are shown to be of ‘Late Cromerian’ age. The underlying till there is the first widespread evidence of a pre-Elsterian till in NW Europe. DL ratios in molluscs from last interglacial sites along the Arctic coast of the USSR, the Arctic Islands and eastern Greenland are substantially lower than in their European counterparts due to their low thermal histories. The combined mid- and high-latitude data are used to develop a predictive model for the expected DL ratio in any of several moderate epimerization-rate taxa for last interglacial sites with mean temperatures between −20 and +15°C. Not all sites could be unambiguously assigned to an established interglacial. The Fjøsanger (Norway) and Margareteberg (Sweden) sites previously thought to be Eemian, yield DL ratios higher than in secure nearby Eemian material. It is yet unresolved whether these are aberrant sites or if they predate the last interglacial. In situ shoreline deposits encountered in borings in SW Belgium and in exposures on the Belgium coastal plain contain molluscs that yield DL ratios intermediate between secure Eemian and Late Weichselian ratios, raising the possibility that a late stage 5 high-sea-level event attained near-modern levels in the southern North Sea basin. Resolution of these uncertainties is the focus of future work.
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  • 63
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    Elsevier
    In:  Earth and Planetary Science Letters, 231 (1-2). pp. 53-72.
    Publication Date: 2017-05-02
    Description: We derive an estimate for the chemical composition of the depleted MORB mantle (DMM), the source reservoir to mid-ocean ridge basalts (MORBs), which represents at least 30% the mass of the whole silicate Earth. A database for the chemical and physical properties of abyssal peridotites has become robust and complete enough to truly access a reference DMM. Using trace element depletion trends from the abyssal peridotites, it is possible to construct a large part of DMM’s trace element pattern. Splicing this information with isotopic constraints (Sr–Nd–Pb–Hf) and canonical ratios (Ce/Pb, Nb/Ta, Nb/U, Ba/Rb, H2O/Ce, CO2/Nb and Cl/K), we can extend abundance estimates to all the incompatible elements including volatile content. The resulting trace element pattern for average DMM constrains parental MORB to be generated by 6% aggregated fractional melting, consistent with recent models for hydrous melting of the mantle [P.D. Asimow, J.E. Dixon, C.H. Langmuir, A hydrous melting and fractionation model for mid-ocean ridge basalts: application to the Mid-Atlantic Ridge near the Azores, Geochem. Geophys. Geosyst. 5 (2004) 10.1029/2003GC000568]. We show that DMM is roughly balanced by the continental crust and better balanced upon inclusion of ocean island basalt source and oceanic crust components. Compared to the primitive mantle, DMM has been depleted by 2–3% melt extraction and has only 15% the radiogenic heat production.
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  • 64
    Publication Date: 2017-06-28
    Description: Numerous methane-emitting bottom features, such as seeps, methane clathrate hydrates (clathrates), and mud volcanoes, have been identified recently in the Black Sea. The fluxes of methane from these sources averaged over large spatial scales are unknown. Here we take advantage of the fact that the Black Sea is a semi-enclosed basin with restricted deep water circulation to establish first-order estimates of basin-wide fluxes of methane from these sources to the water column and atmosphere. First, we measured the natural radiocarbon content of methane (14C–CH4) dissolved in the water column and emitted from seeps. The 14C–CH4 results showed that the dominant source of methane to the water column is emitted from seeps and a smaller source is diagenetically produced in relatively modern sediments. The 14C–CH4 results were then used to partition a basin-wide total methane budget; this analysis estimated the basin-wide flux of methane from seeps and clathrates to the water column to be 3.60 to 4.28 Tg yr− 1. Second, a geochemical box model was used to calculate possible distributions of methane inputs from seeps and clathrates as well as provide additional estimates of the basin-wide flux of methane from seeps and clathrates to the water column (4.95 to 5.65 Tg yr− 1).
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  • 65
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    Elsevier
    In:  Palaeogeography Palaeoclimatology Palaeoecology, 227 (1-3). pp. 31-47.
    Publication Date: 2017-06-30
    Description: Carbonates recovered from anoxic waters between 235 and 1555 m depth in the northwestern Black Sea were analyzed for lipid biomarkers and stable carbon isotopic compositions. In addition, a methane-seep-related microbial mat and a sample of surface sediment recovered from a non-seep site were studied for comparison. High concentrations of strongly 13C-depleted lipids attributed to bacteria and archaea mediating the anaerobic oxidation of methane (AOM) were found in all samples except for the sediment. Differences of the dominant AOM-performing communities between the carbonates indicated by specific lipid patterns appear to be caused by the respective biogeochemical settings. High proportions of ANME-2 consortia are found at sites of assumingly high partial pressures of methane while ANME-1 associations dominate at locations of moderate methane supply. In the sedimentary concretion, a complex mixture of biomarkers for terrestrial and planktonic organisms was found. Different molecular structures along with strong variations in the stable carbon isotopic compositions (δ13C = − 20.2‰ to − 94.3‰) allow for an estimation of the proportions of tetraether-bound biphytanes derived from planktonic Crenarchaeota and methanotrophic Euryarchaeota. Our data imply that the shape of AOM-derived carbonate precipitates in Black Sea environments is crucially influenced by the respective methane supply. Active AOM-driven chimney-like bioherms, similar to those previously observed on the Ukrainian shelf, might also develop in the deep euxinic zone at 1555 m water depths.
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  • 66
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    Elsevier
    In:  Elsevier, Amsterdam, 294 pp. ISBN 0-444-42471-7
    Publication Date: 2019-08-28
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  • 67
    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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  • 68
    Publication Date: 2017-11-08
    Description: Marine geophysical surveys employing Seabeam, multi- and single-channel seismic reflection, gravity and magnetic instruments were conducted at two locations along the continental slope of the Peru Trench during the Seaperc cruise of the R/V “Jean Charcot” in July 1986. These areas are centered around 5°30′S and 9°30′S off the coastal towns of Paita and Chimbote respectively. These data indicate that (1) the continental slope off Peru consists of three distinct morpho-structural domains (from west to east are the lower, middle and upper slopes) instead of just two as previously reported; (2) the middle slope has the characteristics of a zone of tectonic collapse at the front of a gently flexured upper slope; (3) the upper half of the lower slope appears to represent the product of mass wasting; (4) thrusting at the foot of the margin produces a continuous morphologic feature representing a deformation front where the products of mass-wasting are overprinted by a compressional tectonic fabric; (5) a change in the tectonic regime from tensional to compressional occurs at the mid-slope-lower slope boundary, the accretionary prism being restricted to the very base of the lower slope in the Paita area. The Andean margin off Peru is an “extensional active margin” or a “collapsing active margin” developing a subordinated accretionary complex induced by massive collapse of the middle slope area.
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  • 69
    Publication Date: 2017-08-22
    Description: The dissolution of in-situ generated methane hydrate in undersaturated, synthetic seawater (S = 35) was investigated in a series of laboratory-based experiments at P-/T-conditions within the hydrate stability field. A controlled flow field was generated across the smooth hydrate surface to test if, in addition to thermodynamic variables, the dissolution rate is influenced by changing hydrodynamic conditions. The dissolution rate was found to be strongly dependent on the friction velocity, showing that hydrate dissolution in undersaturated seawater is a diffusion-controlled process. The experimental data was used to obtain diffusional mass transfer coefficients kd, which were found to correlate linearly with the friction velocity, u★. The resulting kd/u★-correlation allows predicting the flux of methane from natural gas hydrate exposures at the sediment/seawater interface into the bulk water for a variety of natural P, T and flow conditions. It also is a tool for estimating the rate of hydrate regrowth at locations where natural hydrate outcrops at the seafloor persist in contact with undersaturated seawater
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  • 70
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    Elsevier
    In:  Geochimica et Cosmochimica Acta, 73 . pp. 2645-2659.
    Publication Date: 2017-09-27
    Description: Nd concentration and isotope data have been obtained for the Canada, Amundsen, and Makarov Basins of the Arctic Ocean. A pattern of high Nd concentrations (up to 58 pM) at shallow depths is seen throughout the Arctic, and is distinct from that generally seen in other oceans where surface waters are relatively depleted. A range of isotopic variations across the Arctic and within individual depth profiles reflects the different sources of waters. The dominant source of water, and so Nd, is the Atlantic Ocean, with lesser contributions from the Pacific and Arctic Rivers. Radiogenic isotope Nd signatures (up to epsilon(Nd) = -6.5) can be traced in Pacific water flowing into the Canada Basin. Waters from rivers draining older terrains provide very unradiogenic Nd (down to epsilon(Nd) = -14.2) that can be traced in surface waters across much of the Eurasian Basin. A distinct feature of the Arctic is the general influence of the shelves on the Nd concentrations of waters flowing into the basins, either from the Pacific across the Chukchi Sea, or from across the extensive Siberian shelves. Water-shelf interaction results in an increase in Nd concentration without significant changes in salinity in essentially all waters in the Arctic, through processes that are not yet well understood. In estuarine regions other processes modify the Nd signal of freshwater components supplied into the Arctic Basin, and possibly also contribute to sedimentary Nd that may be subsequently involved in sediment-water interactions. Mixing relationships indicate that in estuaries, Nd is removed from major river waters to different degrees. Deep waters in the Arctic are higher in Nd than the inflowing Atlantic waters, apparently through enrichments of waters on the shelves that are involved in ventilating the deep basins. These enrichments generally have not resulted in major shifts in the isotopic compositions of the deep waters in the Makarov Basin (epsilon(Nd) similar to -10.5), but have created distinctive Nd isotope signatures that were found near the margin of the Canada Basin (with epsilon(Nd) similar to -9.0). The deep waters of the Amundsen Basin are also distinct from the Atlantic waters (with epsilon(Nd) = -12.3), indicating that there has been limited inflow from the adjacent Makarov Basin through the Lomonosov Ridge. (C) 2009 Elsevier Ltd. All rights reserved.
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  • 71
    Publication Date: 2019-09-23
    Description: The Upper Rhine Graben has two Plio-Quaternary depocentres usually interpreted as resulting from tectonic reactivation. The southern basin, near Freiburg im Breisgau (Germany), contains up to 250 m of sediments. Beneath the younger alluvial deposits related to the current drainage system, a former river network deeply entrenched in the substratum reveals a very low regional base level of early Pleistocene age. The offset of channels at faults allows us to infer a Pleistocene reactivation of the syn-rift fault pattern and the estimation of slip rates. Maximum vertical movements along the faults have not exceeded 0.1 mm/yr since the middle Pleistocene. Current activity is concentrated along the westernmost faults. Morphologic markers indicate late Pleistocene reactivation of the Rhine River fault, and geophysical prospecting suggests a near-surface offset of young sedimentary deposits. The size of the fault segments potentially reactivated suggests that earthquakes with magnitude larger than Mw=6.3Mw=6.3 could be expected in the area with a return interval of about 8000 years. Extrapolated to the duration of the Plio-Pleistocene, the strain rate estimates reveal that the tectonic forcing may account for only one-third to one-half of the whole thickness of the Plio-Pleistocene sediments of the basin fill. Thus other processes must be invoked to understand the growth of the Plio-Pleistocene basin. Especially the piracy of the Rhine River to the north during the early Pleistocene could explain these effects.
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  • 72
    Publication Date: 2017-10-05
    Description: A liquid chromatograph/mass spectrometry (LC/MS) method was developed for the simultaneous quantitation of seven compounds (safflor yellow A, puerarin, daidzein, ginsenosides (Rg(1), Rb(1), Rd), and notoginsenoside R(1)) in rat plasma samples with sufficient sensitivity to facilitate analysis of samples collected after an intravenous injection of Naodesheng. The plasma samples were subjected to protein precipitation with acetone, and analyzed using negative atmospheric pressure chemical ionization mass spectrometry in selected ion monitoring (SIM) mode with baicalin as an internal standard. Good linearity for all the seven compounds was observed. The intra- and inter-day precision of analysis was 〈15.0% for each compound, and the accuracy ranged from 90.0% to 109.0%. This quantitation method was successfully applied to a pharmacokinetic study of following intravenous injection of rats with Naodesheng
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  • 73
    Publication Date: 2018-10-02
    Description: European eel (Anguilla anguilla) elvers were intraperitoneally injected with different doses of 3,3′,4,4′-tetrachlorobiyphenyl (PCB77) to examine and characterize the inductive effect of coplanar PCBs on CYP1A1 gene expression in liver and gills by using a semi-quantitative RT-PCR analysis. The influence of PCB77 injection on transcription activity of the housekeeping gene glyceraldehyde-3-phosphate-dehydrogenase (GAPDH) was tested to determine its suitability as a reference gene for further quantitative gene expression analyses. Our results clearly indicate a significant dose-dependent increase in CYP1A1 gene expression in the gills of European eel, while in liver tissues a significant elevation in CYP1A1 gene expression was only detectable at highest contamination rates, indicating the potential of CYP1A1 differential gene expression analysis in gills as a biomarker for PCB contamination in eels. PCB77 contamination did not affect GAPDH transcription in gills but, at highest doses, resulted in a significant elevation in liver, speaking against GAPDH as a reference housekeeping gene after PCB exposure.
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  • 74
    Publication Date: 2017-09-08
    Description: Calcium isotope fractionation was measured on skeletal aragonite and calcite from different marine biota and on inorganic calcite. Precipitation temperatures ranged from 0 to 28°C. Calcium isotope fractionation shows a temperature dependence in accordance with previous observations: 1000 · ln(αcc) = −1.4 + 0.021 · T (°C) for calcite and 1000 · ln(αar) = −1.9 + 0.017 · T (°C) for aragonite. Within uncertainty the temperature slopes are identical for the two polymorphs. However, at all temperatures calcium isotopes are more fractionated in aragonite than in calcite. The offset in δ44/40Ca is about 0.6‰. The underlying mechanism for this offset may be related to the different coordination numbers and bond strengths of the calcium ions in calcite and aragonite crystals, or to different Ca reaction behavior at the solid-liquid interface. Recently, the observed temperature dependence of the Ca isotope fractionation was explained quantitatively by the temperature control on precipitation rates of calcium carbonates in an experimental setting (Lemarchand et al., 2004). We show that this mechanism can in principle also be applied to CaCO3 precipitation in natural environments in normal marine settings. Following this model, Ca isotope fractionation in marine Ca carbonates is primarily controlled by precipitation rates. On the other hand the larger Ca isotope fractionation of aragonite compared to calcite can not be explained by different precipitation rates. The rate control model of Ca isotope fractionation predicts a strong dependence of the Ca isotopic composition of carbonates on ambient CO32− concentration. While this model is in general accordance with our observations in marine carbonates, cultured specimens of the planktic foraminifer Orbulina universa show no dependence of Ca-isotope fractionation on the ambient CO32− concentration. The latter observation implies that the carbonate chemistry in the calcifying vesicles of the foraminifer is independent from the ambient carbonate ion concentration of the surrounding water.
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  • 75
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    Elsevier
    In:  Marine Policy, 33 . pp. 180-181.
    Publication Date: 2017-10-10
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  • 76
    Publication Date: 2019-09-23
    Description: δ18O values of nine tropical–subtropical planktonic foraminiferal species with different preferential habitat depths collected from 62 core–top samples along an east–west transect across the tropical Atlantic/Caribbean were used to test the applicability of interspecific δ18O gradients for reconstructions of tropical upper ocean stratification. In general, the δ18O difference (Δδ18O) between intermediate- and shallow-dwelling species decreases, and Δδ18O between deep and intermediate dwellers increases with increasing thermocline depth towards the west. The statistical significance of regional differences in Δδ18O highlights Δδ18O between the intermediate dwellers (in particular Globorotalia scitula and Globorotalia tumida) and the shallow dweller Globigerinoides ruber pink, as well as Δδ18O between the deep dwellers Globorotalia crassaformis or Globorotalia truncatulinoides dextral and intermediate dwellers as most sensitive to changes in tropical Atlantic thermocline depth. Based on the observed regional variations in interspecific Δδ18O, we propose a multispecies stratification index “STRAtrop” = (δ18Ointermediate − δ18Oshallow) / (δ18Odeep − δ18Oshallow) for the tropical ocean. Statistically significant differences in STRAtrop values between the E-Atlantic and the Caribbean suggest that this index may be a useful tool to monitor variations in tropical upper ocean stratification in the geological record.
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  • 77
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    Elsevier
    In:  Quaternary Science Reviews, 6 (3-4). pp. 231-243.
    Publication Date: 2016-04-08
    Description: Piston cores from fiords, shelf troughs, and the deep-sea off eastern Baffin Island, N.W.T., Canada, have been sampled for texture and detrital carbonate in the 〈2 mm fraction. The sediments consist primarily of silty clays usually containing 〈5% sand. Estimates are made for sediment accumulation (kg/m**2/ka) over the last ca. 10 ka. Three sets, of two cores each, lie on a fiord-shelf transect and thus define variations in sediment accumulation gradients. These continental margin data are compared with cruder estimates of Holocene sediment accumulation at three sites farther offshore in Baffin Bay, Davis Strait and the northern Labrador Sea. Minimum accumulation in a 2 ka interval was 200 kg/m2 with a maximum estimate of 8,800 kg/m2. Detrital carbonate accumulation varies between 0 and 1,300 kg/m**2. Median accumulation for a typical fiord-shelf-deep-sea transect over the last 10 ka have been 10,340, 3493 and 820 kg/m**2. At DSDP Leg, site 645 in central Baffin Bay, the sedimentation rate ranged between 40 and 130 m/Ma (ca. 400 and 1200 kg/m**2/2ka); that is, comparable with the Late Quaternary input into Baffin Bay.
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  • 78
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    Elsevier
    In:  Journal of Experimental Marine Biology and Ecology, 75 (2). pp. 171-190.
    Publication Date: 2016-04-25
    Description: The exchange of inorganic nutrients; ammonium, nitrate and reactive phosphate between burrows of the infaunal polychaete Nereis virens Sars and the overlying water was assessed using V-shaped sediment cores. Exchange was determined by monitoring ventilation current and nutrient concentration of in- and excurrent water. Ammonium supply appeared independent of overlying water concentrations, showing a constant release of 0.5 μmol·h−1 (for a 2-g individual + burrow system) at concentrations from 2 to 87 μM. Of this release ≈40% originated from worm excretion, and the rest from microbial mineralization. Nitrate and phosphate exchange appeared very sensitive to overlying water concentrations, having equilibrium (zero flux) at 10–15 and 3 μM, respectively. Below these concentrations nitrate showed a slight release (due to nitrification), whereas phosphate was released at a rate of 3.2 × 10−2 μmol·h−1 at 1 μM (mineralization and desorption). Above equilibrium they both were removed during water passage through worm burrows, reaching 0.4 μmol·h−1 for nitrate at 107 μM (nitrate reduction) and 3.7 × 10−2 μmol·h−1 for phosphate at 5.6 μM (adsorption processes). The burrow system apparently acted as a buffer for phosphate and, to some degree, nitrate in the overlying water. At the study site (Norsminde Fjord estuary) nereid burrows were estimated to increase the sediment-water interface 150%. About 17% of the water column was cycled through the sediment by Nereis each day. The worm + burrow system was estimated to release 95 μmol· m−2·h−1 ammonium to the overlying water, which was ≈76–90% of the total release of ammonium from the sediment (30–36% was worm excretion).
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  • 79
    Publication Date: 2017-12-11
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  • 80
    Publication Date: 2016-04-08
    Description: Clay- and silt-size mineral assemblages are described from eight piston cores from the fiords and shelf on the western margin of Baffin Bay, Arctic Canada. Radiocarbon dates indicate that all the cores extend back in time to the last local glacial/interglacial transition (i.e. 8–10 ka); four extend back to between 10 and 12 ka, and HU77-021-156, located on the Southeast Baffin Island shelf, includes the entire late Foxe glacial stage. Silt- and clay-size particles constitute ca 40 and 55%, respectively, by weight of the bulk sediment. The clay-size fraction is dominated by mica; feldspars and quartz are the main constituents of the silt fraction. The fiord sediments are mainly composed of local mineralogies, but on the shelf, and at times in the fiords, exotic mineral species occur. The most important of these are detrital carbonates, derived from erosion of the Paleozoic basins in Arctic Canada and/or northwest Greenland. Both calcite and dolomite occur; calcite is the major carbonate mineral in the “southern” cores, whereas dolomite is the most abundant in cores north of 66°N. Higher inputs of carbonate species occur during regional deglaciation, 7–10 ka, and during the last 5 ka (probably reflecting increased iceberg production from northwest Greenland). Thus variations in the precentages of the carbonate minerals indicate significant shifts in Late Quaternary glacial-sediment source areas and oceanographic regimes.
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  • 81
    Publication Date: 2016-04-08
    Description: Acoustic basement lies at an average of between 6.0 and 6.5 sec two-way time below sea level in the southern Rockall Trough and northern Porcupine Abyssal Plain. The overlying sedimentary succession reaches maximum thicknesses of at least 4.0 sec, and can be divided by 3 regionally-developed seismic reflecting horizons, which are used as a framework to establish an acoustic stratigraphy for the area by selecting three “type” seismic sections. These reflectors are named, in ascending order, Shackleton, Charcot and Challenger. The area is crossed by E—W basement high structures, the Clare Lineament (which may be an easterly extension of the Charlie Gibbs Fracture Zone), that separates the Porcupine Abyssal Plain from the eastern part of southern Rockall Trough. Under the latter, the post-Shackleton acoustic sequence is thickened, as if dammed to the north of the Clare Lineament, whilst a further thickening, above reflector Charcot, occurs along a NE—SW line somewhat farther north into the southern Rockall Trough. This can also be related to shallow-lying acoustic basement features. Pre-Shackleton sediments overlie a very irregular basement topography. The acoustic characters of the various sediment packages are described and it is speculated that major changes in the sedimentary environments took place across reflectors Shackleton and Challenger, the latter probably establishing the modern bottom current circulation patterns. No ages can be unequivocally assigned to the main reflectors, but previously published data suggest a late Eocene—Oligocene age for Challenger. Possible lavas or sills are identified in the succession between reflectors Shackleton and Charcot.
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  • 82
    Publication Date: 2016-04-08
    Description: Isopach asymmetry, and sediment component changes in DSDP cores from the SE Atlantic (Orange Basin) support the hypothesis of major drainage system changes in SW Africa during late Cretaceous—Cenozoic time. This involved alternations in the use of the 28°S (modern Orange River) and 31°S (modern Olifants River) exit points across the western escarpment by rivers carrying run-off from the Upper Orange/Vaal catchment areas, as well as radical re-organizations of internal drainage geometry. It is postulated that during late Cretaceous times the 28°S exit was used, with the Middle Orange River following a course in the interior well to the south (up to 150 km) of its modern channel. Sediment discharge rates from this river were relatively high (at least 10 × 106 m3 yr−1), and resulted in rapid advancement of the continental margin sediment prism west of the mouth by large-scale slumping. The Palaeogene Orange/Vaal river exit was via the 31°S escarpment crossing, and during the later part of this period, the Cape Canyon was cut across the continental shelf and slope. A significant reduction in sediment discharge (to 2.0 × 106 m3 yr−1) suggests that the Lower Tertiary climate for SW Africa was drier than that of late Cretaceous times. However, aridity did not commence until late Miocene times, when the Orange/Vaal discharge had switched back to the 28°S exit. Modern sediment discharge rates (6.5 × 106 m3 yr−1) are relatively high and reflect soil erosion caused by agricultural activity. The two major alterations in exit point of the Orange/Vaal (late Cretaceous—early Tertiary, and late Oligocene—early Miocene) are related to periods of low sea level, which promoted river capture adjacent to the western escarpment. An additional factor in the first course change may have been the disruption of the Middle Orange channel by late Cretaceous igneous intrusions. Less important internal reorganizations of the drainage system are postulated in late Miocene—Pleistocene times. Economic implications for offshore diamond distribution are briefly mentioned.
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  • 83
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    Elsevier
    In:  Marine Geology, 87 (2-4). pp. 323-328.
    Publication Date: 2016-04-11
    Description: Changes in composition of modern benthic ostracod faunas across the continental margin of southwestern Africa occur at boundaries between and within major water masses: a Mixed Layer-Antarctic Intermediate Water (AAIW) boundary at 200 m, an AAIW salinity minimum zone at 650 m, an AAIW bathyal thermocline at 1000 m, and the AAIW/North Atlantic Deep Water (NADW) boundary at 1500 m. In addition, two population changes occur within the NADW at 1.8–2.0 km and 2.0–3.0 km. The Antarctic Bottom Water assemblage is sparse and poorly preserved.
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  • 84
    Publication Date: 2016-04-12
    Description: Large Neogene slumps have affected over 260,000 km2 of the outer continental margin and adjacent Cape Basin off southwestern Africa. Individual structures cover areas up to 68,700 km2 and proximally are commonly composed of huge rotated sediment blocks up to 450 m thick and several kilometers across. Seismic shocks, possibly in conjunction with lower-slope undercutting by bottom-current erosion, are suggested as possible trigger mechanisms for these features which are all thought to be post-Pliocene (possibly Pleistocene) in age. Older slumps are also recognized along the margin and four cycles of sedimentation/slumping are identified: early Upper Cretaceous (I); late Upper Cretaceous (II); Palaeogene (III); and Neogene (IV). In the main part of the Orange Basin depocentre (west of Childs Bank) the Cretaceous slump styles are thought to represent Mississippi delta-type down-slope sediment cascades (with reverse faulting and mud diapirism) over 1 km thick which resulted from very rapid dumping of terrigenous material from the Orange River. Cainozoic slumps show a different tectonic style and locus and this is thought to reflect a change in sedimentation patterns which resulted from lower terrigenous input onto the margin, higher biogenic/authigenic sedimentation, and slowed crustal subsidence. A connection possibly exists between low sea level stands and the Cainozoic episodes of slumping.
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  • 85
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    Elsevier
    In:  Methods in Cell Biology, 88 . pp. 59-82.
    Publication Date: 2016-05-09
    Description: This chapter describes a range of quantitative tools that can be applied to ultrathin sections of biological material. The transmission electron microscopy quantitative estimations are generally made on images taken of ultrathin sections, but the very first concern of any well designed study is the origin of these images. The distribution of gold labeling over an array of cellular structures displayed in ultrathin sections can be estimated in two main ways. A major use of profile data on ultrathin sections is in assessing gold particle labeling of cell components. The ultrathin sections are exposed to antibodies localized using particles of colloidal gold, and because the section presents the components to the gold labeling system it is crucial to follow the sampling scheme already outlined. This ensures an unbiased sample of cell components is contained in the sections and can gain access to the gold labeling system. Colloidal gold is particulate and can be quantified as a signal that represents the underlying component, and the two principal readouts of interest to cell biologists are the distribution and concentration of gold labeling. New methods have been developed to evaluate labeling distributions and labeling intensities by statistical means.
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  • 86
    Publication Date: 2015-01-22
    Description: An 1180-cm long core recovered from Lake Lyadhej-To (68°15′ N, 65°45′ E, 150 m a.s.l.) at the NW rim of the Polar Urals Mountains reflects the Holocene environmental history from ca. 11,000 cal. yr BP. Pollen assemblages from the diamicton (ca. 11,000–10,700 cal. yr BP) are dominated by Pre-Quaternary spores and redeposited Pinaceae pollen, pointing to a high terrestrial input. Turbid and nutrient-poor conditions existed in the lake ca. 10,700–10,550 cal. yr BP. The chironomid-inferred reconstructions suggest that mean July temperature increased rapidly from 10.0 to 11.8 °C during this period. Sparse, treeless vegetation dominated on the disturbed and denuded soils in the catchment area. A distinct dominance of planktonic diatoms ca. 10,500–8800 cal. yr BP points to the lowest lake-ice coverage, the longest growing season and the highest bioproductivity during the lake history. Birch forest with some shrub alder grew around the lake reflecting the warmest climate conditions during the Holocene. Mean July temperature was likely 11–13 °C and annual precipitation—400–500 mm. The period ca. 8800–5500 cal. yr BP is characterized by a gradual deterioration of environmental conditions in the lake and lake catchment. The pollen- and chironomid-inferred temperatures reflect a warm period (ca. 6500–6000 cal. BP) with a mean July temperature at least 1–2 °C higher than today. Birch forests disappeared from the lake vicinity after 6000 cal. yr BP. The vegetation in the Lyadhej-To region became similar to the modern one. Shrub (Betula nana, Salix) and herb tundra have dominated the lake catchment since ca. 5500 cal. yr BP. All proxies suggest rather harsh environmental conditions. Diatom assemblages reflect relatively short growing seasons and a longer persistence of lake-ice ca. 5500–2500 cal. yr BP. Pollen-based climate reconstructions suggest significant cooling between ca. 5500 and 3500 cal. yr BP with a mean July temperature 8–10 °C and annual precipitation—300–400 mm. The bioproductivity in the lake remained low after 2500 cal. yr BP, but biogeochemical proxies reflect a higher terrestrial influx. Changes in the diatom content may indicate warmer water temperatures and a reduced ice cover on the lake. However, chironomid-based reconstructions reflect a period with minimal temperatures during the lake history.
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  • 87
    Publication Date: 2017-08-09
    Description: This study was performed to investigate gas formation and gas saturation conditions related to acoustic turbidity in shallow (∼40 m deep) marine basins. The Arkona Basin, Baltic Sea, with its organic-rich fine-grained surface sediment provides an ideal “Natural Laboratory” to characterise free gas using seismic, geoacoustic, and geochemical methods. The area of acoustic turbidity covers about 1500 km2 of the central Arkona Basin, corresponding to areas where organic-rich post-glacial sediments exceed 4–6 m in thickness. The highest concentration of pore water methane (7660 μmol L−1), found in areas of high acoustic turbidity, was near the calculated lower limit of methane solubility for the measured in situ temperature, salinity, and pressure. Pore water methane concentration decreased to near 4 μmol L−1 in areas outside of the zone of high acoustic turbidity. Stable carbon (−70.7‰ to −92.3‰ PDB) and hydrogen (−124‰ to −185‰ SMOW) isotope values of methane indicate that methane is predominantly formed by microbial CO2 reduction in Arkona Basin surface sediments and rules out significant contributions of other sources.
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  • 88
    Publication Date: 2017-08-09
    Description: Hydrous CaMg-carbonate was synthesized at temperatures of 40 degrees, 60 degrees and 80 degrees C in the laboratory. This material has very similar mineralogical characteristics to natural disordered dolomite from the Coorong region in South Australia. Besides the dolomite variable amounts of amorphous carbonate are present in all samples. The oxygen isotope compositions of synthesized bulk carbonate samples (e.g., amorphous carbonate plus dolomite) plot significantly lower than the Northrop and Clayton (1966) dolomite-water equilibrium. Fractionated degassing of the samples, however, revealed relatively low oxygen isotope values for fast-reacting (using 100% H3PO4) amorphous carbonate. In contrast, slow-reacting dolomite has more positive oxygen isotope values, and calculated carbonate-water oxygen isotope fractionation values are close to strongest known dolomite-water oxygen isotope fractionation published earlier on. Variations of reaction/stabilization temperatures during synthesis gave evidence for dolomite formation from hypersaline solutions by a dissolution/reprecipitation process. It is likely that amorphous carbonate has been a problem in defining the dolomite-water fractionation in the past. Moreover, dolomite-associated amorphous carbonate contents probably led to incorrect speculations about lower oxygen isotope fractionation in a so-called protodolomite-water system. Copyright (c) 2005 Elsevier Ltd.
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  • 89
    Publication Date: 2019-09-23
    Description: The skill of numerical Lagrangian drifter trajectories in three numerical models is assessed by comparing these numerically obtained paths to the trajectories of drifting buoys in the real ocean. The skill assessment is performed using the two-sample Kolmogorov-Smirnov statistical test. To demonstrate the assessment procedure, it is applied to three different models of the Agulhas region. The test can either be performed using crossing positions of one-dimensional sections in order to test model performance in specific locations, or using the total two-dimensional data set of trajectories. The test yields four quantities: a binary decision of model skill, a confidence level which can be used as a measure of goodness-of-fit of the model, a test statistic which can be used to determine the sensitivity of the confidence level, and cumulative distribution functions that aid in the qualitative analysis. The ordering of models by their confidence levels is the same as the ordering based on the qualitative analysis, which suggests that the method is suited for model validation. Only one of the three models, a 1/10 degree two-way nested regional ocean model, might have skill in the Agulhas region. The other two models, a 1/2 degree global model and a 1/8 degree assimilative model, might have skill only on some sections in the region.
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  • 90
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    Elsevier
    In:  Sedimentary Geology, 175 . pp. 3-8.
    Publication Date: 2018-07-19
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  • 91
    Publication Date: 2016-10-05
    Description: Centropages typicus is one of the most common, abundant and best studied calanoid copepods in neritic waters of the Mediterranean Sea, which means it can provide useful information about the long-term dynamics of the Mediterranean epipelagic ecosystem. This paper presents the first comparative overview of the seasonal and long-term variability of C. typicus in different Mediterranean regions. This review is based on quantitative information from the published literature and novel data from five ongoing zooplankton time-series carried out in the Mallorca Island (Balearic Sea), the Bay of Villefranche (Ligurian Sea), the Gulf of Naples (Tyrrhenian Sea), the Gulf of Trieste (North Adriatic Sea), and the Saronikos Gulf (Aegean Sea). In most Mediterranean regions, C. typicus has a perennial occurrence, with peaks of abundance that reflect the succession of different generations. Throughout the Mediterranean, the annual cycle of C. typicus is characterized by minima in winter and major peaks in April–June, which is earlier than those observed in European Atlantic waters, where the peaks are more frequently recorded in summer and fall. In the regions investigated, the annual cycle shows remarkable similarities in terms of timing, but notable differences in the peak height; populations are far more abundant in coastal north-western regions and less abundant in the eastern basin. In the long-term, changes in C. typicus phenology observed in the Bay of Villefranche and in the Gulf of Naples are related to the North Atlantic Oscillation (NAO) index. In these two regions, the species responds to climate forcing similarly in terms of average seasonal patterns (bi-modal patterns in years of positive NAO, unimodal patterns in years of negative NAO) but oppositely in terms of quantity, indicating different influence of the NAO on the two regions. At decadal scales, C. typicus populations show high interannual variability with marked geographical differences. In some areas, the patterns are clearly characterized by alternate phases of higher and lower annual abundances, at higher frequency (mainly 1–2 years) in the Gulf of Naples, and lower frequency in the Saronikos Gulf (mainly 4–5 years) and in the Gulf of Trieste (mainly 5–6 years). Synchronous phases of increasing or decreasing abundance are discernable only for a few sites and short periods, for example from 1998 to 2000 in the Gulf of Naples, Gulf of Trieste and Saronikos Gulf. The regional differences observed in the long-term patterns of C. typicus populations suggest that the temporal dynamics of this species are significantly more affected by local conditions than by any possible common driving force acting at basin scale through teleconnections.
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  • 92
    Publication Date: 2017-12-11
    Description: The study of interfacial properties in the marine environment is important for the understanding of air-sea gas exchange processes, especially with respect to the behaviour of entrained air bubbles. Seawater contains surfactant material, much of which is thought to origin from the exudation of dissolved organic material (DOM) by phytoplankton. This study aims at investigating the influence of different phytoplankton species on the surface shear viscosity of an air-water interface. Measurements of surface shear viscosity were carried out with the ISR1 interfacial shear rheometer. Surface shear viscosities of stock cultures of Phaeocystis sp., Thalassiosira rotula, Thalassiosira punctigera and Nitzschia closterium as well as of F/2 nutrient medium and seawater were measured. The surface shear viscosity of N. closterium was investigated during different stages of its growth as well as for an unfiltered stock culture sample and its filtrate. Results reveal that the influence of phytoplankton on the surface shear viscosity is species specific. An increase in surface shear viscosity occurred for the N. closterium stock culture only. The remaining cultures showed similar behaviour to F/2 nutrient medium. The increase of surface shear viscosity during the growth of N. closterium occurred mainly during the exponential growth phase. The increases in surface shear viscosity depend on the presence of phytoplankton cells in the sample. The formation of compact mechanical structures at the air-water interface originating from the aggregation of DOM released by N. closterium as a cause for the observed increases in surface shear viscosity is discussed.
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  • 93
    Publication Date: 2017-12-05
    Description: Seven new fungal polyketides possessing linear pentaene structures ending in cyclic moieties were isolated from the mycelium extract of a marine sponge-derived Penicillium rugulosum. Feeding of C-13-labeled acetate and L-methionine was used to verify the polyketide origin of prugosene A1. It could also be shown that prugosenes B1 and C1 were formed from prugosene A1 by hydrolysis and decarboxylation of its oxabicyclo[2.2.1]heptane unit.
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  • 94
    Publication Date: 2019-09-23
    Description: Live (Rose Bengal stained) benthic foraminifera were investigated in surface sediment samples from the Okhotsk Sea to reveal the relationship between faunal characteristics and environmental parameters. Live benthic foraminifera were quantified in the size fraction 〉 125 µm in the upper 8 cm of replicate sediment cores, recovered with a multicorer at five stations along the Sakhalin margin, and at three stations on the southwestern Kamchatka slope. The stations are from water depths between 625 to 1752 m, located close or within the present Okhotsk Sea oxygen minimum zone, with oxygen levels between 0.3 and 1.5 ml l- 1. At the high-productivity and ice-free Kamchatka stations, live benthic foraminifera are characterized by maximal standing stocks (about 1700-3700 individuals per 50 cm2), strong dominance of calcareous species (up to 87-91% of total live faunas), and maximal habitat depths (down to 5.2-6.7 cm depth). Vertical distributions of total faunal abundances exhibit a clear subsurface maximum in sediments. At the Sakhalin stations, which are seasonally ice-covered and less productive, live benthic foraminifera show lower standing stocks (about 200-1100 individuals per 50 cm2), lower abundance of calcareous species (10-64% of total live faunas), and shallower habitat depths (down to 2.5-5.4 cm depth). Faunal vertical distributions are characterized by maximum in the uppermost surface sediments. It is suggested that 1) lower and strongly seasonal organic matter flux, caused by the seasonal sea ice cover and seasonal upwelling, 2) lower bottom water oxygenation (0.3-1.1 ml l- 1), and 3) more pronounced influence of carbonate undersaturated bottom water along the Sakhalin margin are the main factors responsible for the observed faunal differences. According to species downcore distributions and average living depths, common calcareous species were identified as preferentially shallow, intermediate and deep infaunal. Foraminiferal microhabitat occupation correlates with the organic matter flux and the depth of the oxygenated layer in sediments.
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  • 95
    Publication Date: 2017-02-09
    Description: Three ferromanganese crusts from the northeast, northwest and central Atlantic were re-dated using osmium (Os) isotope stratigraphy and yield ages from middle Miocene to the present. The three Os isotope records do not show evidence for growth hiatuses. The reconstructed Os isotope-based growth rates for the sections older than 10 Ma are higher than those determined previously by the combined beryllium isotope (10Be/9Be) and cobalt (Co) constant-flux methods, which results in a decrease in the maximum age of each crust. This re-dating does not lead to significant changes to the interpretation of previously determined radiogenic isotope neodymium, lead (Nd, Pb) time series because the variability of these isotopes was very small in the records of the three crusts prior to 10 Ma. The Os isotope record of the central Atlantic crust shows a pronounced minimum during the middle Miocene between 15 and 12 Ma, similar to a minimum previously observed in two ferromanganese crusts from the central Pacific. For the other two Atlantic crusts, the Os isotope records and their calibration to the global seawater curve for the middle Miocene are either more uncertain or too short and thus do not allow for a reliable identification of an isotopic minimum. Similar to pronounced minima reported previously for the Cretaceous/Tertiary and Eocene/Oligocene boundaries, possible interpretations for the newly identified middle Miocene Os isotope minimum include changes in weathering intensity and/or a meteorite impact coinciding with the formation of the Nördlinger Ries Crater. It is suggested that the eruption and weathering of the Columbia River flood basalts provided a significant amount of the unradiogenic Os required to produce the middle Miocene minimum.
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  • 96
    Publication Date: 2017-09-27
    Description: We critically evaluate the applicability of Ca-isotope ratios in planktonic foraminifers as proxy for past sea surface temperatures (SST) and isotope composition of paleo-seawater (δ44Casw) reconstructions. Previous studies have shown discrepancies regarding the temperature sensitivity of Ca isotope fractionation in foraminifers of more than one order of magnitude. We present new data from the planktonic foraminifer species Orbulina universa, Globigerinoides sacculifer and Neogloboquadrina pachyderma (sinistral) from culture experiments, multinet deployments and coretop samples. Specimens of G. sacculifer cultured at low salinities (33–34.5) show predominantly no major temperature dependent Ca isotope fractionation, in contrast to previous individuals cultured at higher salinities of 34.5–36. The new data of O. universa are consistent with previously published results, revealing a small but significant temperature sensitivity. Calcium isotope fractionation in tests of N. pachyderma shows a significant variation with temperature, which is not uniform over the total investigated temperature range (−1.6 °C to +10 °C), possibly reflecting the influence of additional controlling factors besides temperature. Controlled dissolution experiments in the laboratory indicate that the Ca-isotope composition of G. sacculifer and N. pachyderma is relatively insensitive to partial dissolution of their tests. Calcium isotope ratios in the planktonic foraminifers G. sacculifer and N. pachyderma (s) reveal a complex Ca isotope fractionation behaviour, which is not yet fully understood. Additional validation studies are crucial to enhance the basic understanding of the calcium isotope systematics in planktic foraminifer shells, and the potential for applying Ca-isotope ratios as proxies for seawater temperature and the oceanic Ca budget.
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  • 97
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    Elsevier
    In:  Geochimica et Cosmochimica Acta, 73 . pp. 3218-3233.
    Publication Date: 2017-09-27
    Description: The first isotopic compositions of dissolved hafnium in seawater from across the Arctic Ocean are reported. Most samples from the four sub-basins of the Arctic Ocean have values within error of an average of epsilon(Hf) = +0.8. Combined Hf-Nd isotope compositions do not fall on the well-established positive correlation for mantle and crustal rocks. Instead, Arctic waters have Hf that is more radiogenic than that typically found in rocks with similar Nd isotope compositions, a feature previously found in ferromanganese crusts and waters from the Pacific Ocean. Arctic seawater samples generally fall on the lower part of the ferromanganese crust array, reflecting influences of inputs from Arctic rivers and interactions of shelf waters with underlying sediments. Arctic rivers have much higher Hf concentrations (7-30 pM) than Arctic seawater (0.36-4.2 pM). Water from the Mackenzie River has the least radiogenic Hf, with epsilon(Hf) = -7.1 +/- 1.7, and plots furthest away from the ferromanganese crust array, while waters from the Ob, Yenisey, and Lena Rivers have values that are indistinguishable from most Arctic waters. In the Amundsen, Makarov, and Canada basins, Hf concentrations are highest at the surface and lowest in the deeper waters, reflecting the influences of riverine inputs and of waters that have flowed over the extensive Siberian continental shelves and have Nd and Hf characteristics that reflect water-sediment interactions. This is in contrast to the relatively low near surface Hf concentrations reported for locations elsewhere. The Pacific water layer in the Canada Basin exhibits the highest value of epsilon(Hf) = +6.8 +/- 1.8, reflecting the Hf isotopic composition of waters entering the Arctic from the Pacific Ocean. Mixing relationships indicate that a substantial fraction of the Hf in the Mackenzie River is lost during estuarine mixing; the behaviour of Hf from other rivers is less constrained. (C) 2009 Elsevier Ltd. All rights reserved.
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  • 98
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    National Academy of Sciences
    In:  PNAS Proceedings of the National Academy of Sciences of the United States of America, 104 (9). pp. 3037-3042.
    Publication Date: 2019-09-23
    Description: Increased knowledge of the present global carbon cycle is important for our ability to understand and to predict the future carbon cycle and global climate. Approximately half of the anthropogenic carbon released to the atmosphere from fossil fuel burning is stored in the ocean, although distribution and regional fluxes of the ocean sink are debated. Estimates of anthropogenic carbon (C ant) in the oceans remain prone to error arising from (i) a need to estimate preindustrial reference concentrations of carbon for different oceanic regions, and (ii) differing behavior of transient ocean tracers used to infer C ant. We introduce an empirical approach to estimate C ant that circumvents both problems by using measurement of the decadal change of ocean carbon concentrations and the exponential nature of the atmospheric C ant increase. In contrast to prior approaches, the results are independent of tracer data but are shown to be qualitatively and quantitatively consistent with tracer-derived estimates. The approach reveals more C ant in the deep ocean than prior studies; with possible implications for future carbon uptake and deep ocean carbonate dissolution. Our results suggest that this approachs applied on the unprecedented global data archive provides a means of estimating the C ant for large parts of the world's ocean.
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  • 99
    Publication Date: 2017-01-09
    Description: In this study we show how substantial gains towards the goals of ecosystem-based fisheries management (EBFM) can be achieved by different single-species management. We show that fishing has much less impact on stocks if fish are caught after they have reached the size (Lopt) where growth rate and cohort biomass are maximum. To demonstrate our point we compare the impact of three fishing scenarios on 9 stocks from the North Sea and the Baltic. Scenario (1) is the current fishing regime, scenario (2) is a new management regime proposed by the European Commission, aiming for maximum sustainable yield obtained from all stocks, and scenario (3) is set so that it achieves the same yield as scenario (2), albeit with fishing on sizes beyond Lopt. Results show that scenarios (2) and (3) are significant improvements compared to current fishing practice. However, scenario (3) consistently shows least impact on the stocks, with seven-fold higher biomass of demersal fishes and an age structure similar to an unfished stock. This allows juveniles and adults to better fulfil their ecological roles, a major step towards the goals of ecosystem-based fisheries management. We give examples where scenario (3) is practiced in successful fisheries. We present a new interpretation of the relative yield per recruit isopleth diagram with indication of a new target area for fisheries operating within the context of EBFM. We present a new expression of the relative biomass per recruit isopleth diagram, which supports our analysis. We conclude that size matters for precautionary and ecosystem-based fisheries management and present a list of additional advantages associated with fishing at Lopt.
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  • 100
    facet.materialart.
    Unknown
    National Academy of Sciences
    In:  PNAS Proceedings of the National Academy of Sciences of the United States of America, 106 . pp. 20602-20609.
    Publication Date: 2019-09-23
    Description: Throughout Earth's history, the oceans have played a dominant role in the climate system through the storage and transport of heat and the exchange of water and climate-relevant gases with the atmosphere. The ocean's heat capacity is ≈1,000 times larger than that of the atmosphere, its content of reactive carbon more than 60 times larger. Through a variety of physical, chemical, and biological processes, the ocean acts as a driver of climate variability on time scales ranging from seasonal to interannual to decadal to glacial–interglacial. The same processes will also be involved in future responses of the ocean to global change. Here we assess the responses of the seawater carbonate system and of the ocean's physical and biological carbon pumps to (i) ocean warming and the associated changes in vertical mixing and overturning circulation, and (ii) ocean acidification and carbonation. Our analysis underscores that many of these responses have the potential for significant feedback to the climate system. Because several of the underlying processes are interlinked and nonlinear, the sign and magnitude of the ocean's carbon cycle feedback to climate change is yet unknown. Understanding these processes and their sensitivities to global change will be crucial to our ability to project future climate change.
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