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  • 2015-2019  (1,854,196)
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  • 1
    Call number: Z 06.0500
    Type of Medium: Journal available for loan
    Pages: 30 cm
    ISSN: 1824-7741
    Former Title: Vorgänger Geologisch-paläontologische Mitteilungen, Innsbruck
    Language: German , English
    Note: Ersch. unregelmäßig , Beiträge teilweise in Englisch
    Branch Library: GFZ Library
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  • 2
    Call number: MOP 19538/1d-6d
    Type of Medium: Monograph available for loan
    Pages: 111 S.
    ISSN: 0486-2287
    Language: Russian
    Note: In kyrill. Schr.
    Location: MOP - must be ordered
    Branch Library: GFZ Library
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  • 3
    Monograph available for loan
    Monograph available for loan
    [Edgecumbe, N.Z.] : A. Muller
    Call number: M 15.89146
    Description / Table of Contents: An account of the results of the 2 March 1987 earthquake in the eastern Bay of Plenty and the aftermath's effects on the people and places on the Rangitaiki Plains
    Type of Medium: Monograph available for loan
    Pages: 223 S., , Ill.
    Language: English
    Branch Library: GFZ Library
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  • 4
    Monograph available for loan
    Monograph available for loan
    Garmisch-Partenkirchen : Institut für atmosphärische Umweltforschung der Fraunhofer- Gesellschaft
    Call number: MOP 44829 / Mitte
    Type of Medium: Monograph available for loan
    Pages: 25 S. , graph. Darst.
    Language: English
    Location: MOP - must be ordered
    Branch Library: GFZ Library
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  • 5
    Call number: S 90.0066(162,1)
    In: Geologisches Jahrbuch / A
    Type of Medium: Series available for loan
    Pages: 261 Seiten , Ill., 1 DVD-ROM (12 cm) und 1 Tafel-Beil. ([2] S.)
    ISBN: 9783510968534
    Series Statement: Geologisches Jahrbuch 162
    Classification: A.2.8.
    Language: German
    Location: Lower compact magazine
    Branch Library: GFZ Library
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  • 6
    Monograph non-lending collection
    Monograph non-lending collection
    Leiden : Nijhoff ; 1.2009 -
    Call number: IASS 17.92082
    Type of Medium: Monograph non-lending collection
    ISSN: 1876-8814
    Language: English
    Branch Library: IASS Library
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  • 7
    Monograph available for loan
    Monograph available for loan
    Madrid : Secc
    Call number: PIK N 456-17-90913
    Type of Medium: Monograph available for loan
    Pages: 536 Seiten
    Series Statement: Ministerio de Transportes Turismo Y Comunicaciones : Publicación Serie A 114
    Parallel Title: 1,1=6; 2,1=13 von Publicaciones / D / Ministerio del Aire, Subsecretaria de Aviación Civil, Servicio Meteorológico Nacional
    Language: Spanish
    Branch Library: PIK Library
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  • 8
    Call number: PIK N 453-17-91096
    Type of Medium: Monograph available for loan
    Pages: 50 Seiten , Illustrationen, Diagramme
    Language: German
    Branch Library: PIK Library
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  • 9
    Monograph available for loan
    Monograph available for loan
    Bonn : Helmholtz Association ; 2006-
    Associated volumes
    Call number: 3/S 07.0034(2016)
    In: Annual report
    Type of Medium: Monograph available for loan
    Pages: 51 Seiten
    ISSN: 1865-6439 , 1865-6447
    Parallel Title: Erscheint auch als Annual report ... / Helmholtz Association of German Research Centres
    Language: English
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  • 10
    Call number: M 18.91571
    Type of Medium: Monograph available for loan
    Pages: 134 Seiten
    ISSN: 2363-7196
    Series Statement: Global tectonics and metallogeny : special issue Vol. 10/2-4
    Classification: A.3.4.
    Parallel Title: Erscheint auch als Global tectonics and metallogeny
    Language: English
    Location: Upper compact magazine
    Branch Library: GFZ Library
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  • 11
    Call number: AWI G6-19-92375
    In: Berichte / Christian-Albrechts-Universität zu Kiel, Institut für Geowissenschaften, Nr. 9
    Type of Medium: Monograph available for loan
    Pages: 278 Seiten , Illustrationen
    ISSN: 0175-9302
    Series Statement: Berichte / Christian-Albrechts-Universität zu Kiel, Institut für Geowissenschaften 9
    Language: German
    Note: Zugleich: Dissertation, Christian-Albrechts-Universität zu Kiel, 1999 , INHALTSVERZEICHNIS 1. Einleitung 1.1 Kenntnisstand und offene Fragen 1.2 Fragestellung und Ziele dieser Arbeit 2. Umweltbedingungen in den Arbeitsgebieten 2.1 Hydrographie, Eisverhältnisse und NAO 2.2 Zur Variation von Wassertiefe und Breite der Dänemarkstraße und zur Vereisung Islands während des letzten Glazials 3. Methoden 3.1 Auswahl der Kernstationen 3.2 Probennahme und Analysen (Übersicht) 3.3 Zur Rekonstruktion von Paläobedingungen im Oberflächenwasser Zur Aussage stabiler Isotopenverhältnisse in planktischen Foraminiferen Zur Messung stabiler Isotopenverhältnisse Zur Massenspektrometrie Zur Rekonstruktion von Oberflächentemperaturen Alkane und Alkohole als Maß für Staubeintrag Eistranspmtiertes Material und vulkanische Aschen 3.4 Zur Rekonstruktion von Paläobedingungen im Zwischen-/ Tiefenwasser Häufigkeit von Cibicides- und anderen benthischen Arten (inkl. Taxonomie) Stabile Isotopenverhältnisse in benthischen Foraminiferen 3.5 AMS 14C-Datierungen Probenreinigung 3. 6 Hauptelementanalysen von vulkanischen Asche-Leithorizonten 3. 7 Geomagnetische Meßgrößen und magnetische Suszeptibiltät 3.8 Techniken zur Spektralanalyse 4. Methodische Ergebnisse 4.1 Zum Einfluß der Probenreinigung auf δ18O-/ δ13C-Werte 4.2 Probleme bei der langfristigen Reproduzierbarkeit von δ18O-Zeitreihen 4.3 Einfluß der Korngröße und Artendefinition planktischer Foraminiferen auf SST-Rekonstruktionen in hohen Breiten 4.4 Vergleich der stabilen Isotopenwerte von Cibicides lobatulus und Cibicidoides wuellerstorfi 5. Stratigraphische Grundlagen und Tiefenprofile der Klimasignale 5.1 Stratigraphische Korrelation zwischen parallel-gekernten GKG- und SL-/KL-Profilen 5.2 Flanktische δ18O-/ δ13C-Kurven, 14C-Alter und biostratigraphische Fixpunkte Westliches Islandbecken Kern PS2644 Kern PS2646 Kern PS2647 Kern 23351 Vøring-Plateau Kern 23071 Kern 23074 5.3 Benthische δ18O-/ δ13C-Werte in Kern PS2644 5.4 Siliziklastische Sedimentkomponenten: Eistransportiertes Material Westliches Islandbecken Kern PS2644 Kern PS2646 Kern PS2647 Vøring-Plateau Kern 23071 Kern 23074 5.5 Vulkanische Glasscherben in Kern PS2644: Wind- und Eiseintrag 5.6 Geochemie und Alter einzelner Tephralagen als Leithorizonte Westliches Islandbecken Kern PS2644 Kern PS2646 Kern PS2647 Vøring-Plateau Kern 23071 Kern 23074 5.7 Magnetische Suszeptibilität in den Kernen PS2644, PS2646 und PS2647 Kern PS2644 Kern PS2646 und PS2647 5.8 Geomagnetische Feldintensität und Richtungsänderungen in Kern PS2644 5.9 Variation von Planktonfauna und -flora Westliches Islandbecken: Kern PS2644 Kern PS2646 und PS2647 Vøring-Plateau: Kern 23071 und 23074 5.10 Benthische Foraminiferen in Kern PS2644 6. Entwicklung von Temperatur und Salzgehalt nördlich der Dänemark-Straße 6.1 Variation der Oberflächentemperatur nach Planktonforaminiferen 6.2 Variation der Oberflächentemperatur nach Uk37 6.3 Variation der Oberflächensalinität 7. Die Feinstratigraphie von Kern PS2644 als Basis für eine Eichung der 14C-Altersskala 22 - 55 ka 7.1 Korrelation zwischen den Klimasignalen in Kern PS2644 und der GISP2-Klimakurve zum Kalibrieren der 14C-Alter und Erstellen eines Altersmodells Tephrachronologische Marker Korrelationsparameter und -regeln Sonderfälle/ Probleme bei der Korrelation 7.2 Alters-stratigraphische Korrelation der Klimakurven von Kern 23071 und 23074 7.3 Variation der Altersanomalien zwischen 20 und 55 14C-ka 7.4 Variabilität des planktischen 14C-Reservoiralters in Schmelzwasserbeeinflußten Seegebieten Variation der planktischen 14C-Alter unmittelbar an der Basis von Heinrich-Ereignis 4 Unterschiede zwischen planktischen und benthischen 14C-Altern in der westlichen Islandsee. Zur Erklärung der inversen Altersdifferenzen 7.5 Differenz zwischen 14C- und Kalenderalter: Zeitliche Variation unter Einfluß des Erdmagnetfeldes - Modell und Befund 7.6 Sedimentationsraten der Kerne 23071, 23074 und PS2644 nach dem GISP2-Altersmodell Vøring-Plateau: Kerne 23071 und 23074 Südwest-Islandsee: Kern PS2644 8. Klimaoszillationen im Europäischen Nordmeer in der Zeit und Frequenzdomäne 8.1 "Der Einzelzyklus" in den Klimakurven von Kern PS2644 8.2 Zur Veränderlichkeit der Warm- und Kaltextreme sowie Zyklenlänge Besonderheiten in der Zyklenlänge Variation der Kalt-(Stadiale) Variation der Interstadiale 8.3 Periodizitäten der Klimasignale im Frequenzband der D.-Oe.-Zyklen. Der D.-Oe.-Zyklus von 1470 J., seine Multiplen und harmonischen Schwingungen Weitere Frequenzen: 1000-1150 Jahre- und 490- 510 Jahre-Zyklizitäten Höhere Frequenzen im Bereich von Jahrhunderten und Dekaden 8.4 Phasenbeziehungen und (örtliche) Steuemngsmechanismen der Dansgaard-Oeschger-Zyklen 9. Schlußfolgerungen Danksagung Literaturverzeichnis Anhang
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  • 12
    Call number: IASS 15.89494
    Type of Medium: Monograph available for loan
    Pages: Losebl.-Ausg.
    Edition: Stand: Oktober 2010
    ISBN: 9783768501828
    Language: German
    Branch Library: IASS Library
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  • 13
    Monograph available for loan
    Monograph available for loan
    London : Penguin Books
    Type of Medium: Monograph available for loan
    ISBN: 9780141985206
    Language: English
    Branch Library: IASS Library
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  • 14
    Call number: M 92.0634
    Type of Medium: Monograph available for loan
    ISBN: 9054100605
    Language: English
    Branch Library: GFZ Library
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  • 15
    Call number: (DE-599)GBV03709842X
    Type of Medium: Monograph available for loan
    Language: German
    Location: MOP - must be ordered
    Branch Library: GFZ Library
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  • 16
    Monograph available for loan
    Monograph available for loan
    Leningrad : Gidrometeorolog. Izd.
    Call number: MOP 33767
    Type of Medium: Monograph available for loan
    Pages: 663 S.
    Language: Russian
    Note: In kyrill. Schr., russ.
    Location: MOP - must be ordered
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  • 17
    Journal available for loan
    Journal available for loan
    München : Altop-Verlag ; 2007 -
    Call number: Z 19.92410
    Type of Medium: Journal available for loan
    Pages: 30 cm
    ISSN: 1865-4266
    Former Title: Vorg. Nachhaltiges Wirtschaften in Deutschland
    Language: German
    Note: Ungezählte Beil. ab 2010: Special , Erscheint jährlich 4x
    Branch Library: IASS Library
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  • 18
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 294 (1992), S. 466-478 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 19
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 317 (1993), S. 474-484 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 20
    Publication Date: 2019-03-28
    Description: Beside its global effects, climate change is manifested in many regionally pronounced features mainly resulting from changes in the oceanic and atmospheric circulation. Here we investigate the influence of the North Atlantic SST on shaping the winter-time response to global warming. Our results are based on a long-term climate projection with the Max Planck Institute Earth System Model (MPI-ESM) to investigate the influence of North Atlantic sea surface temperature pattern changes on shaping the atmospheric climate change signal. In sensitivity experiments with the model’s atmospheric component we decompose the response into components controlled by the local SST structure and components controlled by global/remote changes. MPI-ESM simulates a global warming response in SST similar to other climate models: there is a warming minimum—or ”warming hole”—in the subpolar North Atlantic, and the sharp SST gradients associated with the Gulf Stream and the North Atlantic Current shift northward by a few a degrees. Over the warming hole, global warming causes a relatively weak increase in rainfall. Beyond this, our experiments show more localized effects, likely resulting from future SST gradient changes in the North Atlantic. This includes a significant precipitation decrease to the south of the Gulf Stream despite increased underlying SSTs. Since this region is characterised by a strong band of precipitation in the current climate, this is contrary to the usual case that wet regions become wetter and dry regions become drier in a warmer climate. A moisture budget analysis identifies a complex interplay of various processes in the region of modified SST gradients: reduced surface winds cause a decrease in evaporation; and thermodynamic, modified atmospheric eddy transports, and coastal processes cause a change in the moisture convergence. The changes in the the North Atlantic storm track are mainly controlled by the non-regional changes in the forcing. The impact of the local SST pattern changes on regions outside the North Atlantic is small in our setup.
    Type: Article , PeerReviewed
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  • 21
    Publication Date: 2018-11-12
    Description: We present a transport-reaction model (TRACTION) specifically designed to account for non-ideal transport effects in the presence of thermodynamic (e.g. salinity or temperature) gradients. The model relies on the most fundamental concept of solute diffusion, which states that the chemical potential gradient (Maxwell’s model) rather than the concentration gradient (Fick’s law) is the driving force for diffusion. In turn, this requires accounting for species interactions by applying Pitzer’s method to derive species chemical potentials and Onsager coefficients instead of using the classical diffusion coefficients. Electrical imbalances arising from varying diffusive fluxes in multicomponent systems, like seawater, are avoided by applying an electrostatic gradient as an additional transport contribution. We apply the model to pore water data derived from the seawater mixing zone at the submarine Mercator mud volcano in the Gulf of Cadiz. Two features are particularly striking at this site: (i) Ascending halite-saturated fluids create strong salinity (NaCl) gradients in the seawater mixing zone that result in marked chemical activity, and thus chemical potential gradients. The model predicts strong transport-driven deviations from the mixing profile derived from the commonly used Fick’s diffusion model, and is capable of matching well with the profile shapes observed in the pore water concentration data. Even better agreement to the observed data is achieved when ion pairs are transported separately. (ii) The formation of authigenic gypsum (several wt%) occurs in the surface sediments, which is typically restricted to evaporitic surface processes. Very little is known about the gypsum paragenesis in the subseafloor and we first present possible controls on gypsum solubility, such as pressure, temperature, and salinity (pTS), as well as the common ion and ion pairing effects. Due to leaching of deep diapiric salt, rising fluids of the MMV are saturated with respect to gypsum (as well as celestite and barite). Several processes that could drive these fluids towards gypsum supersaturation and hence precipitation were postulated and numerically quantified. In line with the varied morphology of the observed gypsum crystals, gypsum paragenesis at the MMV is likely a combination of two temperature-related processes. Gypsum solubility increases with increasing temperature, especially in strong electrolyte solutions and the first mechanism involves the cooling of saturated fluids along the geothermal gradient during their ascent. Secondly, local temperature changes, i.e. cooling during the transition from MMV activity towards dormancy results in the cyclic build-up of gypsum. The model showed that the interpretation of field data can be majorly misguided when ignoring non-ideal effects in extreme diagenetic settings. While at first glance the pore water profiles at the Mercator mud volcano would indicate strong reactive influences in the seawater mixing zone, our model shows that the observed species distributions are in fact primarily transport-controlled. The model results for SO4 are particularly intriguing, as SO4 is shown to diffuse into the sediment along its increasing (!) concentration gradient. Also, a pronounced gypsum saturation peak can be observed in the seawater mixing zone. This peak is not related to the dissolution of gypsum but is simply a result of the non-ideal transport forces acting on the activity profile of SO4 and Ca profiles.
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  • 22
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    Elsevier
    In:  In: Encyclopedia of Ecology. , ed. by Fath, B. D. Elsevier, Oxford, UK, pp. 108-115. 2. ed. ISBN 978-0-444-63768-0
    Publication Date: 2018-10-16
    Type: Book chapter , NonPeerReviewed
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  • 23
    Publication Date: 2018-10-30
    Description: Highlights • New 40Ar/39Ar age and geochemical (major, trace element, Sr-Nd-Pb-Hf isotope) data are presented from the Walvis Ridge, belonging to the Tristan-Gough hotspot track in the South Atlantic. • The entire Tristan-Gough hotspot system, including Walvis Ridge, display a spatially continuous age progression. • The Gough-type component is the dominant geochemical flavor of the Tristan-Gough plume and has also been identified in the Discovery and Shona hotspot systems. • The geochemical heterogeneity in the South Atlantic DUPAL region can be reproduced by mixing of Gough-type enriched mantle with continental crust and a FOZO/PREMA-like component. • The HIMU-type alkalic lavas on the Walvis Ridge and older part of Shona hotspot track are ∼30 Ma younger in age than the EMI-type primarily tholeiitic basement lavas at a given locality. Abstract Long-lived spatial geochemical zonation of the Tristan-Gough and Discovery hotspot tracks and temporal variations from EMI-type basement to HIMU-type late-stage volcanism at the Walvis Ridge and Shona hotspot tracks point to a complex evolution and multiple source areas for the South Atlantic hotspots. Here we report 40Ar/39Ar age and geochemical (major and trace element, Sr-Nd-Pb-Hf isotope) data for samples from 16 new sites on the Walvis Ridge. This aseismic ridge is the oldest submarine expression of the Tristan-Gough mantle plume and represents the initial reference locality of the EMI end member in the South Atlantic Ocean. The EMI-type lavas display an excellent age progressive trend of ∼31 mm/a along the entire Tristan-Gough hotspot track, indicating constant plate motion over a relatively stationary melt anomaly over the last ∼115 Ma. The Gough-type EMI composition of the Tristan-Gough hotspot track is the dominant composition on the 〉70 Ma part of the Walvis Ridge, the Etendeka and Parana flood basalts, and along the Gough sub-track, extending from DSDP Site 525A on the SW Walvis Ridge to Gough Island, whereas Tristan-type EMI dominates on the Tristan Track, extending from DSDP Sites 527 and 528 to Tristan da Cunha Island. Gough-type EMI is also the dominant composition of the northern Discovery and Shona hotspot tracks, suggesting that these hotspots tap a common source reservoir. The continuous EMI-type supply over ≥132 Ma, coupled with high 3He/4He (〉10 RA), points to a deep-seated reservoir for this mantle material. The Tristan and Southern Discovery EMI-type flavors can be reproduced by mixing of the Gough-type component with (1) FOZO/PREMA to produce Tristan-type lavas, and (2) marine sediments or upper continental crust to generate the Southern Discovery-type composition. South Atlantic hotspots with EMI-type compositions overlie the margin (1 % ∂Vs velocity contour) of the African Large Low Shear Velocity Province (LLSVP), which may promote the emergence of geochemical “zonation”. The St. Helena HIMU-type volcanism, however, is located above internal portions of the LLSVP, possibly reflecting a layered LLSVP.
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  • 24
    Publication Date: 2018-12-14
    Description: Highlights • Northern Hispaniola Margin is studied with new high-resolution bathymetry and vintage seismic data. • Northern Hispaniola Deformed Belt forms an active N-verging fold-and-thrust imbricate system. • Gravity failures are frequent features in the Northern Hispaniola Margin and Bahamas Banks slope. • Oblique collision accelerates the Bahamas Carbonate Province collapse and retreat. • New observations help the assessment of tsunami hazards in the Northern Caribbean region. Abstract The northern margin of Hispaniola records the oblique collision/underthrusting of the Bahamas Carbonate Province with the island-arc. Due to the collision, northern Hispaniola has suffered several natural disasters caused by major earthquakes and tsunamis, such as the historic earthquake of 1842, the tsunami caused by earthquake-driven slumping in 1918 in the Mona Passage, the seismic crisis of 1943–1953 with five events of M 〉 7.0 or the seismic crisis of 2003 with a main shock of M6.3 and a large aftershock of M5.3. Using new swath multibeam bathymetry data and vintage single- and multi-channel seismic profiles, we have performed a regional scale analysis and interpretation of the shallow surface and active processes along the northern margin of the Dominican Republic. We have identified three morphostructural provinces: a) the Bahamas Banks, b) the Hispaniola Trench and c) the Insular Margin, which are divided into two tectonic domains, the Collision Domain and Underthrusting Domain. The southern slope of the Bahamas Carbonate Province shows a very irregular morphology produced by active erosive processes and normal dip-slip faulting, evidence of an extensional tectonic regime and margin collapse. This collapse is of major extent in the Oblique Collision Domain where there are erosive and fault escarpments with higher dip-slip fault throws. The Hispaniola Trench, is formed by the Caicos and Hispaniola basins in the underthrusting domain, and by the Santisima Trinidad and Navidad basins in the Oblique Collision Domain. They have a flat seafloor with a sedimentary filling of variable thickness consisting of horizontal or sub-horizontal turbiditic levels. The turbiditic fill mostly proceeds from the island arc through wide channels and canyons, which transports sediment from the shelf and upper slope. The Insular Margin comprises the Insular Shelf and the Insular Slope. The active processes are generated on the Insular Slope where the Northern Hispaniola Deformed Belt is developed. This Deformed Belt shows a very irregular morphology, with a WNW-ESE trending N verging imbricate thrust-and fold system. This system is the result of the adjustment of the oblique collision/underthrusting between the North American plate and the Caribbean plate. In the Oblique Underthrusting Domain the along-strike development of the imbricate system is highly variable forming salients and recesses. This variability is due to along-strike changes in the sediment thickness of the Hispaniola Trench, as well as to the variable topography of the underthrusting Bahamas Carbonate Province. In the Oblique Collision Domain, the morphology of the Insular Slope and the development of the Deformed Belt deeply change. The imbricate system is barely inferred and lies upslope. These changes are due to the active collision of Bahamas Carbonate Province with the Insular Margin where the spurs are indented against the Insular Margin. Throughout the entire area studied, gravitational instabilities have been observed, especially on the Insular Margin and to a lesser extent on the southern slope of the Bahamas Carbonate Province. These instabilities are a direct consequence of the active underthrusting/collision process. We have mapped large individual slumps north of Puerto Plata in the Oblique Underthrusting Domain and zones of major slumps in the Oblique Collision Domain. These evidences of active processes must be considered as near-field sources in future studies on the assessment of tsunami hazards in the region.
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  • 25
    Publication Date: 2019-04-12
    Description: This study investigates the Lesser Antilles fore-arc at the latitude of Guadeloupe Archipelago and evidences that La Désirade Island, the eastermost island of the forearc, displays a staircase coastal sequence including four uplifted marine terraces and an upper reefal platform with mean shoreline angle elevations ranging from 10 to 210 m above sea level (asl). The platform paleobathymetry is constraint by a detailed analysis of the sediments. We propose a revised morphostratigraphy for this coastal sequence including 5 paleo-shorelines based on six U/Th dating from aragonitic corals from the three lowest terraces combined with paleobathymetric analysis of the fossil corals present in the upper platform. Terrace and upper platform carving of construction periods occurred during Marine Isotopic Stages MIS 5e, MIS 9, and during the intervals MIS 15–17, MIS 19–25 and MIS 31–49 (upper coral reef platform). Our results evidence a bulk decreasing uplift rate since early Calabrian to Present-Day, clearly documented since 310 ka (MIS 9) (from 0.14 to 0.19 to ca 0 mm/y). Our data are consistent with first the transient influence of the subducting oceanic Tiburon ridge during Calabrian, then with other parametres of the subduction zone since late Calabrian to Present-Day (dip of the slab, basal erosion of the upper plate, inherited structures …)
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  • 26
    Publication Date: 2019-03-14
    Description: Holocene fringing reef development around Bora Bora is controlled by variations in accommodation space (as a function of sea-level and antecedent topography) and exposure to waves and currents. Subsidence ranged from 0 to 0·11 m kyr−1, and did not create significant accommodation space. A windward fringing reef started to grow 8·7 kyr bp, retrograded towards the coast over a Pleistocene fringing reef until ca 6·0 kyr bp, and then prograded towards the lagoon after sea-level had reached its present level. The retrograding portion of the reef is dominated by corals, calcareous algae and microbialite frameworks; the prograding portion is largely detrital. The reef is up to 13·5 m thick and accreted vertically with an average rate of 3·12 m kyr−1. Lateral growth amounts to 13·3 m kyr−1. Reef corals are dominated by an inner Pocillopora assemblage and an outer Acropora assemblage. Both assemblages comprise thick crusts of coralline algae. Palaeobathymetry suggests deposition in 0 to 10 m depth. An underlying Pleistocene fringing reef formed during the sea-level highstand of Marine Isotope Stage 5e, and is also characterized by the occurrence of corals, coralline algal crusts and microbialites. A previously investigated, leeward fringing reef started to form contemporaneously (8·78 kyr bp), but is thicker (up to 20 m) and solely prograded throughout the Holocene. A shallow Pocillopora assemblage and a deeper water Montipora assemblage were identified, but detrital facies dominate. At the Holocene reef base, only basalt was recovered. The Holocene windward–leeward differences are a consequence of less accommodation space on the eastern island side that eventually led to a more complex reef architecture. As a result of higher rates of exposure and flushing, the reef framework on the windward island side is more abundant and experienced stronger cementation. In the Pleistocene, the environmental conditions on the leeward island side were presumably unfavourable for fringing reef growth.
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  • 27
    Publication Date: 2019-01-24
    Description: Northeast Atlantic marine ecosystems such as the Bay of Biscay, Celtic Sea, English Channel, Subpolar Gyre region, Icelandic waters and North Sea as well as the Mediterranean Sea show concomitant ‘regime shift’-like changes around the mid-1990s, which involved all biota of the pelagial: phytoplankton, zooplankton, pelagic fish assemblages, demersal fish assemblages and top predators. These shifts were caused by complex ocean-atmosphere interactions initiating large-scale changes in the strength and direction of the current systems, that move water masses around the North Atlantic, and involved the North Atlantic Oscillation (NAO), the Atlantic Meridional Overturning Circulation (AMOC), and the subpolar gyre (SPG). The contractions and expansions of the SPG and fluctuations of the Atlantic Multidecadal Oscillation (AMO) play a key role in these complex processes. Small pelagic fish population trends were the sentinels of these changes in the mid-1990s in the ecosystems under investigation.
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  • 28
    Publication Date: 2018-11-20
    Description: Atlantic cod (Gadus morhua) is an important recreational and commercial fisheries target species in the Northern hemisphere. Release rates are high in the recreational fishery due to regulatory and voluntary catch-and-release practice. Although post-release mortality of cod is relatively low, there is potential for further reductions. The most effective way to reduce post-release mortality is to minimize the catch of sublegal fish or non-target species and to reduce hooking injuries by using more selective fishing methods. This study investigated the influence of the lure/bait type on: (1) size of fish, (2) catch and harvest, (3) proportion of bycatch, (4) hooking location, and (5) injury (bleeding) in the western Baltic Sea recreational cod fishery. Data were collected via random onboard sampling of 35 charter vessel angling trips (778 anglers) and during two supplementary studies in the western Baltic Sea. Overall, the median total length was significantly higher for cod caught on artificial lures (39 cm) than for cod caught on natural bait (28 cm), leading to a 43% higher proportion of sublegal (〈38 cm) cod for bait than for lure. Median catch-per-unit-efforts (number of captured cod per angling hour) did not differ significantly between lure and bait angling (both: 0.49 cod per hour), whereas the median harvest-per-unit-effort (number of captured cod ≥ minimum landing size (38 cm) per angling hour) was significantly higher for lure (0.24 cod ≥38 cm per hour) than for bait angling (0.06 cod ≥38 cm per hour). The incidence of deep hooking and severe bleeding was significantly higher for bait angling. Furthermore, bait angling significantly increased bycatch of other species dominated by whiting (Merlangius merlangus) and European flounder (Platichthys flesus). Cod anglers can reduce the catch of sublegal cod and non-target species and minimize hooking injuries of released fish by using lures instead of bait in the western Baltic Sea. Thus, voluntary terminal gear recommendations may be an effective tool for anglers and managers to increase selectivity in recreational cod fisheries.
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  • 29
    Publication Date: 2018-11-28
    Description: Protodunes emerge from a flat sand bed at the upwind margin of White Sands Dune Field, and, over several hundred meters, transition into fully developed dunes. Here, we investigate spatial and temporal changes in topography across this transition from 2007 to 2016 using lidar-derived topography, structure-from-motion-derived topography, and RTK GPS. We characterize the deposits present in 2015 using ground penetrating radar. Symmetric protodunes give way downwind to an asymmetric protodune at the transition to slipface development. Between 2007 and 2016, protodune amplitude increased from 0.2 m to 4.0 m, migration rate increased from 3.2 m/yr to 6.1 m/yr, and wavelength increased from 76 m to 122 m. Ground-penetrating radar surveys show strata between flat and 15° make up the stratigraphic architecture of the protodunes. Strata increase in steepness commensurate with an increase in amplitude. Decimeter accumulations of low-angle strata associated with initial protodune stages give way to 4 m of accumulation composed of sets up to 1 m thick prior to slipface development. Topsets present in the thickest sets indicate near critical angles of bedform climb. Growth and slipface development occur by aerodynamic sand trapping and protodune merging. Changes in asymmetry erase initial slipfaces prior to permanent slipface development, after which efficient sand trapping and scour promotes the transition to a dune across 20 m in 5 years. Protodune stratification has hallmarks of sandsheet stratification and can be appreciated within the greater suite of processes that create low-angle eolian stratification found in modern and ancient environments.
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  • 30
    Publication Date: 2018-12-04
    Description: Highlights • Increased glacial sedimentation rates do not generate sufficient overpressure to trigger a landslide. • Simulated overpressures for different sedimentation scenarios do not significantly differ. • A glacimarine layer underneath rapidly-deposited sediments is important for overpressure build-up. • An earthquake of M6.9 or larger at a short distance from the Tampen Slide headwall could have triggered the Tampen Slide. Abstract Trough mouth fans are environments characterized by high sediment supply during glacial stages and the occurrence of large-scale instabilities. The geological record indicates that several of these environments have failed repeatedly resulting in large submarine landslides. The roles of sedimentation rate, weak layers, glacial loading and unloading as well as seismic activity on triggering megaslides in trough-mouth-fan systems is still unclear. A better understanding of the preconditioning factors, triggers and consequences of these landslides is crucial due to the hazard they pose to coastal communities and offshore industries. In this paper, we focus on the North Sea Trough Mouth Fan, which is the result of massive glacial sediment input delivered to the shelf edge through the Norwegian Channel, southeast Nordic Seas margin. The Tampen Slide, one of several large paleo-landslides that have happened within the North Sea Trough Mouth Fan, took place at c. 130 ka (end of MIS 6), and removed an estimated 1800 km3 of sediment. Here, we use boundary conditions from the Tampen Slide and 2D Finite Element Modeling (Abaqus software from Simulia) to evaluate the effects of variations in sedimentation rates as well as sediment properties on the generation of excess pore pressure, fluid flow, and slope stability along the axis of the trough-mouth-fan system. The model domain, 40 km in length and 2 km in height, is dominated by glacigenic debris flows and glacimarine sediment deposits. We use geotechnical data measured on samples of glacigenic and glacimarine sediment deposits from the nearby Ormen Lange gas field area to constrain the model. We evaluate the stability of the slope under various scenarios, including constant sediment loading, episodic changes in sedimentation rates and abrupt pulses in sediment delivery for a 61 kyr period (MIS 6). The models show that increased sedimentation rates during glacial stages do not generate sufficient excess pore pressure to set off a landslide. Furthermore, the simulated overpressures for the different sedimentation scenarios do not significantly differ at the end of the model runs. The results also highlight the importance of a basal glacimarine sediment layer underneath the rapidly-deposited sediments for the build-up of overpressure. Consequently, this glacimarine sediment layer has the inherited potential to act as a weak layer facilitating instability. However, as overpressure due to sediment deposition alone does not result in slope failure, we couple the preconditioned slope with earthquake ground shaking. Based on attenuation models, an earthquake of approximately M6.9 or larger at a short distance from the Tampen Slide headwall could have triggered the landslide. Therefore, we suggest glacial sedimentation and a glacimarine sediment layer to represent preconditioning factors, and seismic shaking as the final trigger mechanism for the Tampen Slide, i.e. similar to the situation that lead to the development of the Storegga Slide in the same area.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 31
    Publication Date: 2018-11-27
    Description: The neodymium isotope proxy has become a valuable tool for the reconstruction of past ocean water mass provenance and mixing. For its accurate application, knowledge about the origin and preservation of Nd in sedimentary archives is crucial. Recently, concerns have emerged regarding the applicability of neodymium isotopes as a conservative palaeo water mass tracer, given potential Nd fluxes from sediments into bottom waters (Abbott et al., 2015a) and inferred relabelling of ocean waters by settling detrital material (Roberts and Piotrowski, 2015). Consequently, a decoupling of water mass provenance and proxy variations may arise. We investigate the mobility of Nd around extreme detrital sedimentation events such as glacial ice rafting pulses and turbidite deposition in the Northeast Atlantic. The constructed records from sediment leachates span extreme Nd isotope variations including volcanic (εNd ∼ 0) and Laurentian (εNd ∼ −27) sources. We find that Nd was released into pore waters from reactive detritus inside some detrital layers during early diagenesis, thereby overprinting any archived bottom water Nd signature and precluding the reconstruction of past water mass provenance during the affected time intervals. However, we do not observe any definite indication of diffusive vertical migration of Nd into adjacent layers. Furthermore, bottom water Nd isotope signatures were not modified to a measurable degree by any potential benthic flux of Nd during the deposition of these detrital sediment layers. Consequently, the Nd isotope composition of the pelagic glacial Northeast Atlantic water masses were resilient to such episodic large detrital fluxes. Apart from extreme local sedimentation events, we confirm the presence of detritally overprinted deep waters north of 47°N during the peak glacial from comparison of Northeast Atlantic depth transects. We furthermore suggest that the sensitivity of deep waters to this overprinting effect increased during periods of reduced Atlantic Meridional Overturning Circulation and elevated ice rafting. Overall, our study demonstrates that a thorough evaluation of the proportion of Nd originating from physical water mass advection versus in situ chemical inputs is crucial for the reliable application of Nd isotopes as a water mass tracer.
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  • 32
    Publication Date: 2019-02-28
    Description: To resolve historical misinterpretations of species descriptions and to comprehend the morphological diversity together with the distribution of Ulva compressa Linnaeus in northern Germany, a morphological and molecular study was undertaken of recently collected specimens and herbarium vouchers. Phylogenetic analyses from sequences of the plastid encoded tufA gene confirmed that U. compressa is abundant along the German Baltic Sea and North Sea coasts. We were able to genetically confirm the presence of U. compressa in the Baltic Sea below salinities of 15 PSU. However, we detected morphologies agreeing with the attached and branched tubular type material only in the North Sea, while U. compressa on Baltic Sea coasts indiscriminately exhibited a very distinct morphology of sheet-like thalli that were always unattached, with the exception of one collection site. Drifting forms were also frequently detected in the Wadden Sea, but not on the island of Helgoland. The tufA sequences of attached and tubular forms of U. compressa from the German Wadden Sea were identical to the drifting sheets found in the Wadden and Baltic Seas and the sequence divergence was extremely small at ≤0.9%. The proliferating, blade-like thalli of U. compressa appear as a nuisance ecotype that is able to form massive accumulations associated with oxygen depletion. Mass accumulations were observed to cause severe damage and increased mortality of habitat forming Zostera and Ruppia populations.
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  • 33
    Publication Date: 2019-03-08
    Description: As one of the most abundant and ubiquitous representatives of marine and brackish coastal macrophytobenthos communities, the genus Ulva is not only an important primary producer but also of ecological and morphogenetic interest to many scientists. Ulva mutabilis became an important model organism to study morphogenesis and mutualistic interactions of macroalgae and microorganisms. Here, we report that our collections of Ulva compressa Linnaeus (1753) from Germany are conspecific with the type strains of the model organism U. mutabilis Føyn (1958), which were originally collected at Olhão on the south coast of Portugal and have from that time on been maintained in culture as gametophytic and parthenogenetic lab strains. Different approaches were used to test conspecificity: (i) comparisons of vegetative and reproductive features of cultured material of U. mutabilis and German U. compressa demonstrated a shared morphological pattern; (ii) gametes of U. compressa and U. mutabilis successfully mated and developed into fertile sporophytic first‐generation offspring; (iii) molecular phylogenetics and species delimitation analyses based on the Generalized Mixed Yule‐Coalescent method showed that U. mutabilis isolates (sl‐G[mt+]) and (wt‐G[mt‐]) and U. compressa belong to a unique Molecular Operational Taxonomic Unit. According to these findings, there is sufficient evidence that U. mutabilis and U. compressa should be regarded as conspecific.
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  • 34
    facet.materialart.
    Unknown
    Springer
    In:  In: Oceanographic and Biological Aspects of the Red Sea. , ed. by Rasul, N. M. A. and Stewart, I. C. F. Springer, Cham, Switzerland, pp. 401-418. ISBN 978-3-319-99416-1
    Publication Date: 2018-12-14
    Description: Coral reefs in the Red Sea belong to the most diverse and productive reef ecosystems worldwide, although they are exposed to strong seasonal variability, high temperature, and high salinity. These factors are considered stressful for coral reef biota and challenge reef growth in other oceans, but coral reefs in the Red Sea thrive despite these challenges. In the central Red Sea high temperatures, high salinities, and low dissolved oxygen on the one hand reflect conditions that are predicted for ‘future oceans’ under global warming. On the other hand, alkalinity and other carbonate chemistry parameters are considered favourable for coral growth. In coral reefs of the central Red Sea, temperature and salinity follow a seasonal cycle, while chlorophyll and inorganic nutrients mostly vary spatially, and dissolved oxygen and pH fluctuate on the scale of hours to days. Within these strong environmental gradients micro- and macroscopic reef communities are dynamic and demonstrate plasticity and acclimatisation potential. Epilithic biofilm communities of bacteria and algae, crucial for the recruitment of reef-builders, undergo seasonal community shifts that are mainly driven by changes in temperature, salinity, and dissolved oxygen. These variables are predicted to change with the progression of global environmental change and suggest an immediate effect of climate change on the microbial community composition of biofilms. Corals are so-called holobionts and associate with a variety of microbial organisms that fulfill important functions in coral health and productivity. For instance, coral-associated bacterial communities are more specific and less diverse than those of marine biofilms, and in many coral species in the central Red Sea they are dominated by bacteria from the genus Endozoicomonas. Generally, coral microbiomes align with ecological differences between reef sites. They are similar at sites where these corals are abundant and successful. Coral microbiomes reveal a measurable footprint of anthropogenic influence at polluted sites. Coral-associated communities of endosymbiotic dinoflagellates in central Red Sea corals are dominated by Symbiodinium from clade C. Some corals harbour the same specific symbiont with a high physiological plasticity throughout their distribution range, while others maintain a more flexible association with varying symbionts of high physiological specificity over depths, seasons, or reef locations. The coral-Symbiodinium endosymbiosis drives calcification of the coral skeleton, which is a key process that provides maintenance and formation of the reef framework. Calcification rates and reef growth are not higher than in other coral reef regions, despite the beneficial carbonate chemistry in the central Red Sea. This may be related to the comparatively high temperatures, as indicated by reduced summer calcification and long-term slowing of growth rates that correlate with ocean warming trends. Indeed, thermal limits of abundant coral species in the central Red Sea may have been exceeded, as evidenced by repeated mass bleaching events during previous years. Recent comprehensive baseline data from central Red Sea reefs allow for insight into coral reef functioning and for quantification of the impacts of environmental change in the region.
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  • 35
    Publication Date: 2019-01-08
    Description: Stable isotope compositions of methane (δ13C and δD) and of short-chain alkanes are commonly used to trace the origin and fate of carbon in the continental crust. In continental sedimentary systems, methane is typically produced through thermogenic cracking of organic matter and/or through microbial methanogenesis. However, secondary processes such as mixing, migration or biodegradation can alter the original isotopic and composition of the gas, making the identification and the quantification of primary sources challenging. The recently resolved methane 'clumped' isotopologues Δ13CH3D and Δ12CH2D2 are unique indicators of whether methane is at thermodynamic isotopic equilibrium or not, thereby providing insights into formation temperatures and/or into kinetic processes controlling methane generation processes, including microbial methanogenesis. In this study, we report the first systematic use of methane Δ13CH3D and Δ12CH2D2 in the context of continental sedimentary basins. We investigated sedimentary formations from the Southwest Ontario and Michigan Basins, where the presence of both microbial and thermogenic methane was previously proposed. Methane from the Silurian strata coexist with highly saline brines, and clumped isotopologues exhibit large offsets from thermodynamic equilibrium, with Δ12CH2D2 values as low as -23‰. Together with conventional δ13C and δD values, the variability in Δ13CH3D and Δ12CH2D2 to first order reflects a mixing relationship between near-equilibrated thermogenic methane similar to gases from deeper Cambrian and Middle Ordovician units, and a source characterized by a substantial departure from equilibrium that could be associated with microbial methanogenesis. In contrast, methane from the Devonian-age Antrim Shale, associated with less saline porewaters, reveals Δ13CH3D and Δ12CH2D2 values that are approaching low temperature thermodynamic equilibrium. While microbial methanogenesis remains an important contributor to the methane budget in the Antrim Shale, it is suggested that Anaerobic Oxidation of Methane (AOM) could contribute to reprocessing methane isotopologues, yielding Δ13CH3D and Δ12CH2D2 signatures approaching thermodynamic equilibrium.
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  • 36
    Publication Date: 2019-01-07
    Description: Highlights • The youngest known (2 Ma) volcanically-active subduction system. • Exceptionally diverse range of magma compositions coeval and spatially juxtaposed. • Mixing of an upwelling asthenospheric mantle melt and a slab melt. • Modern example of an immature subduction system building its proto forearc. • Modern analog of the environment where SSZ ophiolites lithosphere forms. Abstract The development of ideas leading to a greater understanding of subduction initiation is limited by the scarcity of present-day examples. Furthermore, the few examples identified so far unfortunately provide few insights into the nature of magmatism at the inception of subduction. Here we report new observations from the Matthew and Hunter (M&H) subduction zone, a very young subduction zone located in the South-West Pacific. Tectonics of the area show it is younger than 2 Ma, making the M&H the youngest known volcanically-active subduction system and hence providing unique insights into the earliest stages of subduction initiation. Volcanism in this area comprises an exceptionally diverse range of contemporaneously erupting magma compositions which are spatially juxtaposed. Pb isotopic compositions and abundance of LILE and REE strongly suggest melting of upwelling asthenospheric mantle (Indian MORB) and subducted oceanic crust (Pacific MORB of the South Fiji Basin) and the mixing of these two components. Volcanism occurs much closer to the trench compared to volcanism in more mature subduction zones. We demonstrate that the M&H subduction zone is a modern example of an immature subduction system at the stage of pre-arc, near-trench magmatism. It is not yet building an arc but what we propose to call a Subduction Initiation Terrane (SITER). Today, the proto-forearc of the M&H subduction zone is a collage of these SITERs, coeval back-arc domains and remnants of pre-existing terranes including old Vitiaz Arc crust. The M&H area represents a modern analog of a Supra Subduction Zone setting where potentially a majority of ophiolites have formed their crustal and lithospheric components. Present-day magmatism in the M&H area therefore provides clues to understanding unforeseen distribution of contrasted magmatic rock types in fossil forearcs, whether they are at the front of mature subduction zones or in ophiolites.
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  • 37
    Publication Date: 2019-01-09
    Description: Highlights • Continental margin-scale spatial variability in C values among grain size fractions is presented. • Two different hydrodynamic modes influencing in 14C heterogeneity are identified. • A new index (H14 index) is defined to describe overall 14C heterogeneity within marine surface sedimentary OC. Abstract The deposition and long-term burial of sedimentary organic matter (OM) on continental margins comprises a fundamental component of the global carbon cycle. A key unknown in interpretation of carbon isotope records of sedimentary OM is the extent to which OM accumulating in continental shelf and slope sediments is influenced by dispersal and redistribution processes. Here, we present results from an extensive survey of organic carbon (OC) characteristics of grain size fractions (ranging from 〈20 to 250 μm) retrieved from Chinese marginal sea surface sediments in order to assess the extent to which the abundance and isotope composition of OM in shallow shelf seas is influenced by hydrodynamic processes. Our findings show that contrasting relationships exist between 14C contents of OC and grain size in surface sediments associated with two different hydrodynamic modes, suggesting that transport pathways and mechanisms imparted by the different hydrodynamic conditions exert a strong influence on 14C contents of OM in continental shelf sediments. In deeper regions and erosional areas, we infer that bedload transport exerts the strongest influence on (decreases) OC 14C contents of the coarser fraction, while resuspension processes induce OC 14C depletion of intermediate grain size fractions in shallow inner-shelf settings. We use the inter-fraction spread in 14C values, defined here as 14H , to argue that the hydrodynamic processes amplify overall 14C heterogeneity within corresponding bulk sediment samples. The magnitude and footprint of this heterogeneity carries implications for our understanding of carbon cycling in shallow marginal seas.
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  • 38
    Publication Date: 2019-01-14
    Description: The Earth’s ocean floor deforms continuously under the influence of plate tectonic processes. In recent years, the development of deep-sea instruments using acoustic direct-path ranging allows observations of ocean floor deformation with unprecedented spatial and temporal resolution. Due to rapid technological progress, acoustic ranging emerged as a central research field to monitor seafloor deformation. Here we review recent developments and the progress of direct-path ranging applications. We discuss the methodology and examine the effects of the oceanographic environment on the measurement precision. Comparing the resolution of previous deployments, we find that the baseline uncertainty increases linearly with baseline length, at least for distances up to 3 km, but with different linear relations for each deployment. Measurements of displacement at millimeter-level precision across normal, thrust or strike-slip faults are discussed to evaluate the influence of dedicated network designs appropriate for the discrete fault geometries. Furthermore, tectonically quiet areas, such as flanks of coastal or ocean island volcanoes and passive continental margins pose substantial hazards that often lack in-situ monitoring and are therefore a significant target for the application of seafloor geodetic techniques.
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  • 39
    Publication Date: 2019-01-10
    Description: Ice sheets are currently ignored in global methane budgets1,2. Although ice sheets have been proposed to contain large reserves of methane that may contribute to a rise in atmospheric methane concentration if released during periods of rapid ice retreat3,4, no data exist on the current methane footprint of ice sheets. Here we find that subglacially produced methane is rapidly driven to the ice margin by the efficient drainage system of a subglacial catchment of the Greenland ice sheet. We report the continuous export of methane-supersaturated waters (CH4(aq)) from the ice-sheet bed during the melt season. Pulses of high CH4(aq) concentration coincide with supraglacially forced subglacial flushing events, confirming a subglacial source and highlighting the influence of melt on methane export. Sustained methane fluxes over the melt season are indicative of subglacial methane reserves that exceed methane export, with an estimated 6.3 tonnes (discharge-weighted mean; range from 2.4 to 11 tonnes) of CH4(aq) transported laterally from the ice-sheet bed. Stable-isotope analyses reveal a microbial origin for methane, probably from a mixture of inorganic and ancient organic carbon buried beneath the ice. We show that subglacial hydrology is crucial for controlling methane fluxes from the ice sheet, with efficient drainage limiting the extent of methane oxidation5 to about 17 per cent of methane exported. Atmospheric evasion is the main methane sink once runoff reaches the ice margin, with estimated diffusive fluxes (4.4 to 28 millimoles of CH4 per square metre per day) rivalling that of major world rivers6. Overall, our results indicate that ice sheets overlie extensive, biologically active methanogenic wetlands and that high rates of methane export to the atmosphere can occur via efficient subglacial drainage pathways. Our findings suggest that such environments have been previously underappreciated and should be considered in Earth’s methane budget.
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  • 40
    Publication Date: 2019-02-22
    Description: The role of accessory minerals in the incongruent release of Hf and Pb during continental weathering and its implications for the generation of distinct seawater isotope compositions is subject of debate. While it has been suggested that radiogenic Hf and Pb isotope signatures released during the dissolution of rocks are controlled by the relative abundances of minerals with distinct isotope compositions and differences in their resistance to dissolution there has not been a comprehensive experimental investigation of these processes to date. We carried out systematic sequential leaching experiments on fresh and partly weathered granitic rock samples as well as separated zircons from the Central Aar Granite in Switzerland. Combined with major and rare earth element concentrations our new quantitative experimental data reveal systematic preferential release of radiogenic Nd, Hf and Pb isotopes primarily controlled by dissolution characteristics of the host rock's easily dissolvable accessory and major minerals, in particular apatite and sphene, during weak chemical weathering. Moreover, Pb isotope signatures of incipient weathering conditions, contrary to expectations, indicate initial congruent release of Pb from freshly exposed mineral surfaces that becomes subsequently incongruent. During more advanced chemical weathering stages, as well as enhanced physical weathering conditions, the dissolution of major minerals (i.e. feldspars) becomes dominant for Nd and Pb isotope signatures, whereas Hf isotopes are still dominated by contributions from highly radiogenic accessories. Additional leaching experiments of zircon separates were performed to test the specific role of zircons for Hf isotope compositions of riverine runoff. It is demonstrated that zircon is more efficiently dissolved when physical weathering is enhanced. This increased Hf release originating from partial dissolution of zircons, however, is quantitatively not sufficient to explain less radiogenic Hf isotope signatures in seawater during episodes of enhanced mechanical erosion alone. Moreover, the observed addition of Hf from the more congruent dissolution of the zircon-free fractions of the parent rock due to enhanced physical weathering indicate that these minerals also play an important role in controlling Hf isotope signatures released under deglacial conditions.
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  • 41
    Publication Date: 2019-01-07
    Description: Highlights: • Designing spawning closures requires consideration of the mechanisms through which the closures can affect the fish stocks. • Small area closures may have unintended negative effects to the stocks due to fishing effort reallocation. • Closures covering most of the stock distribution are more robust to gaps in biological knowledge than small area closures. Abstract: Fisheries management measures often include spatio-temporal closures during the spawning period of the fish with an overarching aim of improving the stock status. The different mechanisms how a spawning closure potentially can influence the stock are often not explicitly considered when designing such closures. In this paper, we review and synthesize the available data and knowledge on potential effects of the implemented spawning closures on cod in the Baltic Sea. The Baltic cod example represents a relatively data rich case, which allows demonstrating how a closure might affect different parameters of stock status via different mechanisms, including potential unintended negative effects. We conclude that designing relatively small area closures appropriately is highly complex and data demanding, and may involve tradeoffs between positive and negative impacts on the stock. Seasonal closures covering most of the stock distribution during the spawning time are more robust to data limitations, and less likely to be counterproductive if suboptimally designed.
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  • 42
    facet.materialart.
    Unknown
    Nature Publishing Group
    In:  Nature Geoscience, 12 . pp. 84-86.
    Publication Date: 2019-01-29
    Description: Atmospheric levels of chloroform, an ozone-depleting substance not part of the Montreal Protocol, have risen. The increase may be attributable to industrial emissions in Eastern China
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  • 43
    facet.materialart.
    Unknown
    Copernicus Publications (EGU)
    In:  Ocean Science Discussions . pp. 1-43.
    Publication Date: 2019-01-17
    Description: he characteristics of the main water masses in the Atlantic Ocean are investigated and defined as Source Water Types (SWTs) from their formation area by six key properties based on the GLODAPv2 observational data. These include both conservative (potential temperature and salinity) and non-conservative (oxygen, silicate, phosphate and nitrate) variables. For this we divided the Atlantic Ocean into four vertical layers by distinct potential densities in the shallow and intermediate water column, and additionally by concentration of silicate in the deep waters. The SWTs in the upper/central water layer originates from subduction during winter and are defined as central waters, formed in four distinct areas; East North Atlantic Central water (ENACW), West North Atlantic Central Water (WNACW), East South Atlantic Central Water (ESACW) and West South Atlantic Central Water (WSACW). Below the upper/central layer the intermediate layer consist of three main SWTs; Antarctic Intermediate Water (AAIW), Subarctic Intermediate Water (SAIW) and Mediterranean Overflow Water (MOW). The North Atlantic Deep Water (NADW) is the dominating SWT in the deep and overflow layer, and is divided into upper and lower NADW based on the different origins and properties. The origin of both the upper and lower NADW is the Labrador Sea Water (LSW), the Iceland–Scotland Overflow Water (ISOW) and Denmark Strait Overflow Water (DSOW). Antarctic Bottom Water (AABW) is the only natural SWT in the bottom layer and this SWT is redefined as North East Atlantic Bottom Water (NEABW) in the north of equator due to the change of key properties, especial silicate. Similar with NADW, two additional SWTS, Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW), are defined in the Weddell Sea in order to understand the origin of AABW. The definition of water masses in biogeochemical space is useful for, in particular, chemical and biological oceanography to understand the origin and mixing history of water samples.
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  • 44
    Publication Date: 2019-01-17
    Description: We present a new near-global coupled biogeochemical ocean-circulation model configuration. The configuration features a horizontal discretization with a grid spacing of less than 11km in the Southern Ocean and gradually coarsens in meridional direction to more than 200km at 64°N where the model is bounded by a solid wall. The underlying code framework is GFDL's Modular Ocean Model coupled to the Biology Light Iron Nutrients and Gasses (BLING) ecosystem model of Galbraith et al. (2010). The configuration is cutting-edge in that it features both a relatively equilibrated oceanic carbon inventory and a realistic representation of eddy kinetic energy – a combination that has, to-date, been precluded by prohibitive computational cost. Results from a simulation with climatological forcing and a sensitivity experiment with increasing winds suggest that the configuration is suited to explore Southern Ocean Carbon uptake dynamics on decadal timescales. Further, the fidelity of simulated bottom water temperatures off and on the Antarctic Shelf suggest that the configuration may be used to provide boundary conditions to ice-sheet models. The configuration is dubbed MOMSO a Modular Ocean Model Southern Ocean configuration.
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  • 45
    Publication Date: 2019-02-20
    Description: Metal-sulfides are wide-spread in marine benthic habitats. At deep-sea hydrothermal vents, they occur as massive sulfide chimneys formed by mineral precipitation upon mixing of reduced vent fluids with cold oxygenated sea water. Although microorganisms inhabiting actively venting chimneys and utilizing compounds supplied by the venting fluids are well studied, only little is known about microorganisms inhabiting inactive chimneys. In this study, we combined 16S rRNA gene-based community profiling of sulfide chimneys from the Manus Basin (SW Pacific) with radiometric dating, metagenome (n = 4) and metaproteome (n = 1) analyses. Our results shed light on potential lifestyles of yet poorly characterized bacterial clades colonizing inactive chimneys. These include sulfate-reducing Nitrospirae and sulfide-oxidizing Gammaproteobacteria dominating most of the inactive chimney communities. Our phylogenetic analysis attributed the gammaproteobacterial clades to the recently described Woeseiaceae family and the SSr-clade found in marine sediments around the world. Metaproteomic data identified these Gammaproteobacteria as autotrophic sulfide-oxidizers potentially facilitating metal-sulfide dissolution via extracellular electron transfer. Considering the wide distribution of these gammaproteobacterial clades in marine environments such as hydrothermal vents and sediments, microbially accelerated neutrophilic mineral oxidation might be a globally relevant process in benthic element cycling and a considerable energy source for carbon fixation in marine benthic habitats
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  • 46
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    Elsevier
    In:  Geochimica et Cosmochimica Acta, 246 . pp. 213-233.
    Publication Date: 2019-02-08
    Description: The development of weathering profiles shapes Earth’s surface and regulates its climate via chemical weathering. Hence, it is essential to be able to determine the age of weathering profiles and quantify how fast they form. Uranium-series isotopes allow for such quantification. However, isotope compositions are generally measured in bulk regolith, which represents a complex mixture of mineral and organic phases of different origins that can impact the reliability of the information derived from U-series isotopes. Thus, in this study, we assess whether sequential extraction and mineral separation could provide more reliable estimates of weathering ages and rates. We focus on a granitic profile developed under temperate climate in southeastern Australia, a tectonically quiescent environment. Regolith production rates have been independently estimated in the region using cosmogenic isotopes. As expected, the mineralogy and geochemistry of the bulk regolith show that biotite and feldspar are the main phases lost during weathering, progressively replaced by clay minerals. There is no evidence for significant input of element from external sources, such as via aerosol deposition. While sequential extraction does not seem to affect major mineral phases and element concentrations, it is suspected of producing artificial radioactive disequilibrium. Biotite separates show very large accumulation of U and Th, which increases with decreasing depth. Regolith production rates and mineral dissolution rates calculated with weathering rates estimated using the bulk saprolite and quartz separate compositions yield values comparable to independent estimates. Conversely, weathering ages derived from the compositions of saprolite leached experimentally or biotite separates underestimate regolith production rates and mineral dissolution rates. Thus, sequential extraction or biotite separation are not recommended methods to derive reliable rates of regolith production and mineral dissolution. Despite the potential complexity of the composition of bulk regolith, the use of regolith without any pre-treatment seems to yield satisfying estimates of regolith production and mineral dissolution rates. The composition of quartz separates yields rates similar to those derived from bulk compositions. This provides an alternative method, potentially allowing reliable results to be obtained from a single mineral phase rather than a complex mixture of weathering products.
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  • 47
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    Copernicus Publications (EGU)
    In:  Ocean Science Discussions . pp. 1-32.
    Publication Date: 2019-01-17
    Description: The distribution of the main water masses in the Atlantic Ocean are investigated with the Optimal Multi-Parameter (OMP) method. The properties of the main water masses in the Atlantic Ocean are described in a companion article; here these definitions are used to map out the general distribution of those water masses. Six key properties, including conservative (potential temperature and salinity) and non-conservative (oxygen, silicate, phosphate and nitrate), are incorporated into the OMP analysis to determine the contribution of the water masses in the Atlantic Ocean based on the GLODAP v2 observational data. To facilitate the analysis the Atlantic Ocean is divided into four vertical layers based on potential density. Due to the high seasonal variability in the mixed layer, this layer is excluded from the analysis. Central waters are the main water masses in the upper/central layer, generally featuring high potential temperature and salinity and low nutrient concentrations and are easily distinguished from the intermediate water masses. In the intermediate layer, the Antarctic Intermediate Water (AAIW) from the south can be detected to ~30°N, whereas the Subarctic Intermediate Water (SAIW), having similarly low salinity to the AAIW flows from the north. Mediterranean Overflow Water (MOW) flows from the Strait of Gibraltar as a high salinity water. NADW dominates the deep and overflow layer both in the North and South Atlantic. In the bottom layer, AABW is the only natural water mass with high silicate signature spreading from the Antarctic to the North Atlantic. Due to the change of water mass properties, in this work we renamed to North East Antarctic Bottom Water NEABW north of the equator. Similarly, the distributions of Labrador Sea Water (LSW), Iceland Scotland Overflow Water (ISOW), and Denmark Strait Overflow Water (DSOW) forms upper and lower portion of NADW, respectively roughly south of the Grand Banks between ~50 and 66°N. In the far south the distributions of Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW) are of significance to understand the formation of the AABW.
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  • 48
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    Alfred-Wegener-Institut
    In:  Alfred-Wegener-Institut, List auf Sylt, Germany, 2 pp.
    Publication Date: 2019-02-04
    Description: Wochenbericht AL519-1 (28.01.-03.02.2019) [Alkor]
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  • 49
    Publication Date: 2019-02-14
    Description: Extratropical volcanic eruptions are commonly thought to be less effective at driving large-scale surface cooling than tropical eruptions. However, recent minor extratropical eruptions have produced a measurable climate impact, and proxy records suggest that the most extreme Northern Hemisphere cold period of the Common Era was initiated by an extratropical eruption in 536 CE. Using ice-core-derived volcanic stratospheric sulfur injections and Northern Hemisphere summer temperature reconstructions from tree rings, we show here that in proportion to their estimated stratospheric sulfur injection, extratropical explosive eruptions since 750 CE have produced stronger hemispheric cooling than tropical eruptions. Stratospheric aerosol simulations demonstrate that for eruptions with a sulfur injection magnitude and height equal to that of the 1991 Mount Pinatubo eruption, extratropical eruptions produce time-integrated radiative forcing anomalies over the Northern Hemisphere extratropics up to 80% greater than tropical eruptions, as decreases in aerosol lifetime are overwhelmed by the enhanced radiative impact associated with the relative confinement of aerosol to a single hemisphere. The model results are consistent with the temperature reconstructions, and elucidate how the radiative forcing produced by extratropical eruptions is strongly dependent on the eruption season and sulfur injection height within the stratosphere.
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  • 50
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    Copernicus Publications (EGU)
    In:  Atmospheric Chemistry and Physics, 19 (3). pp. 1819-1834.
    Publication Date: 2019-02-22
    Description: Eddy covariance measurements show gas transfer velocity suppression at medium to high wind speed. A wind-wave interaction described by the transformed Reynolds number is used to characterize environmental conditions favoring this suppression. We take the transformed Reynolds number parameterization to review the two most cited wind speed gas transfer velocity parameterizations: Nightingale et al. (2000) and Wanninkhof (1992, 2014). We propose an algorithm to adjust k values for the effect of gas transfer suppression and validate it with two directly measured dimethyl sulfide (DMS) gas transfer velocity data sets that experienced gas transfer suppression. We also show that the data set used in the Nightingale 2000 parameterization experienced gas transfer suppression. A compensation of the suppression effect leads to an average increase of 22% in the k vs. u relationship. Performing the same correction for Wanninkhof 2014 leads to an increase of 9.85 %. Additionally, we applied our gas transfer suppression algorithm to global air-sea flux climatologies of CO2 and DMS. The global application of gas transfer suppression leads to a decrease of 11% in DMS outgassing. We expect the magnitude of Reynolds suppression on any global air-sea gas exchange to be about 10%
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  • 51
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    In:  , 2 pp.
    Publication Date: 2019-02-27
    Description: 18/2/2019-24/2/2019
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  • 52
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    In:  , 2 pp.
    Publication Date: 2019-02-25
    Description: 17.-25.02.2019
    Type: Report , NonPeerReviewed
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  • 53
    Publication Date: 2019-02-27
    Description: Predictive species distribution models are mostly based on statistical dependence between environmental and distributional data and therefore may fail to account for physiological limits and biological interactions that are fundamental when modelling species distributions under future climate conditions. Here, we developed a state-of-the-art method integrating biological theory with survey and experimental data in a way that allows us to explicitly model both physical tolerance limits of species and inherent natural variability in regional conditions and thereby improve the reliability of species distribution predictions under future climate conditions. By using a macroalga-herbivore association (Fucus vesiculosus - Idotea balthica) as a case study, we illustrated how salinity reduction and temperature increase under future climate conditions may significantly reduce the occurrence and biomass of these important coastal species. Moreover, we showed that the reduction of herbivore occurrence is linked to reduction of their host macroalgae. Spatial predictive modelling and experimental biology have been traditionally seen as separate fields but stronger interlinkages between these disciplines can improve species distribution projections under climate change. Experiments enable qualitative prior knowledge to be defined and identify cause-effect relationships, and thereby better foresee alterations in ecosystem structure and functioning under future climate conditions that are not necessarily seen in projections based on non-causal statistical relationships alone.
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  • 54
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    AtlantOS
    In:  AtlantOS Deliverable, D8.10 . AtlantOS, 11 pp.
    Publication Date: 2019-03-11
    Description: This task will use outputs from the Copernicus Marine Environment Monitoring Service (CMEMS) to develop a system for ship routing hazard mapping. Starting from knowledge of the environmental fields affecting vessel seakeeping, the system will estimate hazard and cost associated to known routes in the Atlantic Ocean. The system will employ model analysis or reanalysis of sea state (wave height, period, and direction), hydrodynamics (near surface ocean currents), and meteorological (wind) models. The system will produce an objective route hazard assessment, based on UNIBO experience in hazard mapping and probabilistic approaches. The investigated routes will be selected based on the most relevant ones, according to the AIS (Automatic Information System) density maps. In particular, the existing CMCC ship routing code (VISIR) will be first of all validated through inter-­comparison with analytical benchmarks and other published models. VISIR’s functionalities will then be extended for optimizing the operational costs (bunker) of large ocean-­going vessels sailing along routes compliant with IMO safety recommendations. The same approach will be extended to computation of vessel operational costs along the route. This information will build up a database, queried by the end-­user through a graphical interface for visualizing customized maps of route hazard and cost for user provided parameters [D8.10]. The fitness of AtlantOS for ship routing will be analyzed with a dedicated report [D8.14].
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  • 55
    Publication Date: 2019-04-16
    Description: Atmospheric deposition can be an important source of nutrients and trace metals to oligotrophic alpine lakes, affecting their biogeochemistry. We measured trace metal concentrations and lead (Pb) isotope ratios in lake water, river water, ground water, and aerosol total suspended particles (TSP), as well as nutrient (NO 3 − , NH 4 + , PO 4 3− ) concentrations in TSP in the Tahoe Basin. The contribution of TSP deposition to the lake trace metal budget was assessed. Our results show seasonality in TSP and associated trace metal concentrations with higher concentrations during Oct – April. However, trace metal solubilities are higher during May – Sept, resulting in a higher contribution of soluble trace metals to the lake water. The source of most of the trace metals in TSP in the Lake Tahoe Basin is mineral dust; however, Zn, Cu, and Cd also have an anthropogenic origin. Among major nutrients, NO 3 − concentrations are slightly higher during Oct – April, while NH 4 + and soluble reactive phosphorus (SRP) are higher during May – Sept. The distributions of trace metal concentrations and Pb isotopic ratios are homogenous throughout the lake water column, suggesting that the residence time of the trace metals in the lake is longer than the lake water mixing time. The contribution of atmospheric TSP deposition to the upper 20 m of lake water trace metal inventory is low, ranging from 0.03% for V to 5.7% for Mn. A triple-isotopes plot of Pb indicates that riverine and groundwater inputs are the major Pb sources, but aerosols still contribute some Pb to the lake. This article is part of a special issue entitled: Conway GEOTRACES - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.
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  • 56
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    In:  [Poster] In: 79. Annual meeting of the German Geophysical Society (DGG), 04.-07.03.2019, Braunschweig, Germany .
    Publication Date: 2019-04-12
    Description: OBS data are exposed to additional noise sources like tilt and compliance. We show that the data can be enhanced prior to the usage of standardised land seismology techniques, such as ambient noise tomography. We do this by estimating group velocities before and after enhancing the signal. This project is part of AlpArray and aims to improve the understanding of the proposed subduction polarity change between the Alpine and Apennine subduction.
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  • 57
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    In:  , 2 pp.
    Publication Date: 2019-03-18
    Description: Dritter Wochenbericht der FS Poseidon Expedition POS 533 - AIMAC Atmosphäre-Ozean-Inseln-Biogeochemische Wechselwirkungen in den Makaronesischen Archipelen der Kap Verden, der Kanaren und Madeira (11.03.-17.03.2019) Mindelo (Kap Verden) - Las Palmas (Gran Canaria) - Funchal (Madeira) - Las Palmas
    Type: Report , NonPeerReviewed
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  • 58
    Publication Date: 2019-03-27
    Type: Thesis , NonPeerReviewed
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  • 59
    Publication Date: 2019-04-04
    Description: We quantify the oceanic sink for anthropogenic carbon dioxide (CO 2 ) over the period 1994 to 2007 by using observations from the global repeat hydrography program and contrasting them to observations from the 1990s. Using a linear regression–based method, we find a global increase in the anthropogenic CO 2 inventory of 34 ± 4 petagrams of carbon (Pg C) between 1994 and 2007. This is equivalent to an average uptake rate of 2.6 ± 0.3 Pg C year −1 and represents 31 ± 4% of the global anthropogenic CO 2 emissions over this period. Although this global ocean sink estimate is consistent with the expectation of the ocean uptake having increased in proportion to the rise in atmospheric CO 2 , substantial regional differences in storage rate are found, likely owing to climate variability–driven changes in ocean circulation.
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  • 60
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    Senckenberg am Meer
    In:  Senckenberg am Meer, Wilhelmshaven, Germany, 2 pp.
    Publication Date: 2019-04-01
    Description: (24.03. – 31.03.2019)
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  • 61
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    Society of Economic Geologists
    In:  Economic Geology, 114 (2). pp. 397-400.
    Publication Date: 2019-04-09
    Description: The transport and deposition of gold from colloidal suspensions in hydrothermal fluids has been a persistent theme in ore deposits research. Studies of active geothermal systems show that a complete model of gold transport must include both dissolved and particulate forms. However, samples of the hydrothermal fluids are commonly spiked with aqua regia after collection in order to put any solids back into solution, thus preventing a quantitative assessment of the particle load. Although attempts have been made to filter the solids, gold nanoparticles (Au NPs) will mostly pass the 0.2-µm filters that are in common use, and a simple technique for analyzing suspended particles in the liquids has been lacking. In this study, we demonstrate how time-resolved acquisition of mass 197 in a conventional inductively coupled plasma-mass spectrometer (ICP-MS) can be used to detect and measure Au NPs in the filtered liquids, with an example of well-characterized fluids from the Reykjanes geothermal field on Iceland. The technique allows for precise monitoring of the solution as it is introduced into the plasma with the capability of identifying individual particles carried in suspension. Results show that Au particles passing the 0.2-µm filters are abundant in the studied samples, and measurements of the individual particles can be used to determine their size. The experiment highlights the potential of emerging ICP-MS techniques, including very fast data acquisition and multielement analysis of single particles in timeof-flight mode, for characterization of NPs in hydrothermal fluids.
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  • 62
    Publication Date: 2019-04-02
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  • 63
    Publication Date: 2019-03-28
    Description: Highlights • Geochronology and provenance analysis from the Cosinas and Machiques Basins show a new tectono-sedimentological evolution. • Multiproxy analysis are required to understand tectono-sedimentological evolution in extensional basins. • Paleogeographic evolution shows a closer connection between Maya and Guajira blocks since the early Jurassic. Abstract Jurassic extensional basins developed along the northwestern margin of South America during the break-up of Pangea. Presently, these basins are dispersed in several tectonic blocks of the northern Andes and Mexico, hindering reconstruction of western equatorial Pangea before break-up. This is the case of the Cosinas Basin (Guajira block) and the Machiques Basin (Perijá Range), in northern Colombia, which are filled by Jurassic sedimentary and volcano-sedimentary successions. Autochthonous and para-autochthonous hypotheses on the origin of this basins have been proposed. The purpose of this research is to document the sedimentological evolution, depositional age (Sr-isotope + U-Pb geochronology), sediment provenance and paleogeography of the Cosinas and Machiques basins in order to constrain whether these basins formed within a single extensional margin or they formed as extensional basins in different tectonic blocks. Volcanic detrital zircon U-Pb ages documented in La Quinta Formation in the Machiques Basin and at the base of Rancho Grande Formation in the Cosinas Basin suggest that extensional basins were active in Early Jurassic time. However, a significant difference exists in their subsequent history. Whereas in the Machiques Basin dominates the accumulation of Lower and Middle Jurassic volcanoclastic deposits with abrupt lateral thickness changes, accumulation in the Cosinas Basin is dominantly of siliciclastic strata, with the record of two major marine incursions in Late Jurassic time. Integration of provenance results indicates that the Santander Massif supplied sediments to the Machiques Basin. In contrast, Middle to Upper Jurassic sandstones of the Cosinas Basin document unroofing of basement blocks that include metamorphic, sedimentary and plutonic rocks from the Guajira and Maya blocks. The similarity in age and composition of pre-Jurassic rocks in northwestern South America and the so-called peri-Gondwana blocks in the Mexican subcontinent (i.e., Maya and Oaxaquia blocks) challenge the use of detrital zircon population as an indicator of the autochthonous or para-autochthonous origin of the Guajira block. Large uncertainty of paleomagnetic results, and the lack of constraints for the time magnetization acquisition preclude estimating paleolatitudes for the Guajira block in Jurassic time but support previous interpretation of ca. 70°-90° clockwise rotation of the Guajira block relative to stable South America craton. Our preferred paleogeography considers that the Cosinas and Machiques basins were close to each other along the western continental margin of Pangea during the onset of extension in Early Jurassic time. The change from continental to marine depositional environments in Middle to Late Jurassic time along the Cosinas Basin, which have not been identified in the Machiques Basin or other autochthonous Jurassic basins in northwestern South America, allow us to propose that these blocks were separated during the Callovian - Tithonian interval, with the Cosinas Basin remaining closer to a conjugate Mexican margin, that we interpret as the Maya block. Collision of the Guajira block with the South American margin occurred near the Jurassic-Cretaceous boundary, as documented by deformation of Jurassic units previous to deposition of Berriasian strata in the Guajira block.
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  • 64
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    Pleiades Publishing, Springer
    In:  Lithology and Mineral Resources, 54 (2). pp. 79-92.
    Publication Date: 2019-04-02
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  • 65
    Publication Date: 2019-04-03
    Description: Sediments were sampled at nine stations on a transect across a 7–10 m thick Holocene mud layer in Aarhus Bay, Denmark, to investigate the linkages between CH4 dynamics and the rate and depth distribution of organic matter degradation. High-resolution sulfate reduction rates determined by tracer experiments (35S-SRR) decreased by several orders of magnitude down through the mud layer. The rates showed a power law dependency on sediment age: SRR (nmol cm−3 d−1) = 106.18 × Age−2.17. The rate data were used to independently quantify enhanced SO42− transport by bioirrigation. Field data (SO42–, TCO2, T13CO2, NH4+ and CH4 concentrations) could be simulated with a reaction-transport model using the derived bioirrigation rates and assuming that the power law was continuous into the methanogenic sediments below the sulfate-methane transition zone (SMTZ). The model predicted an increase in anaerobic organic carbon mineralization rates across the transect from 2410 to 3540 nmol C cm−2 d−1 caused by an increase in the sediment accumulation rate. Although methanogenesis accounted for only ∼1% of carbon mineralization, a large relative increase in methanogenesis along the transect led to a considerable shallowing of the SMTZ from 428 to 257 cm. Methane gas bubbles appeared once a threshold in the sedimentation accumulation rate was surpassed. The 35S-measured SRR data indicated active sulfate reduction throughout the SO42− zone whereas quasi-linear SO42− gradients over the same zone indicated insignificant sulfate reduction. This apparent inconsistency, observed at all stations, was reconciled by considering the transport of SO42− into the sediment by bioirrigation, which accounted for 94 ± 2% of the total SO42− flux across the sediment-water interface. The SRR determined from the quasi-linear SO42− gradients were two orders of magnitude lower than measured rates. We conclude that models solely based on SO42− concentration gradients will not capture high SRRs at the top of the sulfate reduction zone if they do not properly account for (i) SO42− influx by bioirrigation, and/or (ii) the continuity of organic matter reactivity with sediment depth or age.
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  • 66
    Publication Date: 2019-04-02
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  • 67
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    In:  , 2 pp.
    Publication Date: 2019-04-01
    Description: TRR181 Cruise Poseidon 533/2 25. March - 1. April 2019 1. Weekly report!
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  • 68
    Publication Date: 2019-04-03
    Description: Highlights • Novel approach to constrain past export production using Ba isotopes. • Ba isotopes improve reliability of the Ba accumulation productivity proxy. • Higher productivity during PETM recovery contributed to rapid carbon sequestration. Abstract The Paleocene–Eocene thermal maximum (PETM; ∼56 Ma) was a transient global warming event associated with a huge perturbation to the global carbon cycle. Changes in marine biological productivity may have contributed to the rapid recovery from this climate change event, by driving the burial of inorganic and organic carbon. Disagreement between proxy reconstructions, however, makes the response of biological productivity to climatic changes experienced during the PETM uncertain. Accumulation of non-detrital barium (Ba) in marine sediments is a commonly used proxy for export production. This proxy however can be compromised by artifacts resulting from dilution and changes in barite preservation, issues that have been debated for its application to sediments deposited during the PETM. Here we present a new approach to address these limitations, by combining non-detrital Ba accumulation with Ba isotope data for marine PETM sediments. Observed positive correlation between these variables is consistent with their control by local changes in export production. These results help resolve previous discrepancies between productivity reconstructions, and indicate export production at sites in the Southern Ocean and South Atlantic decreased or remained unchanged following the PETM onset, followed by an increase to maximum values in the PETM recovery period. This increase in export production coincides with elevated carbonate accumulation rates, representing an important mode of carbon sequestration. These new constraints therefore support the idea that increased production and export of calcifying nannoplankton, perhaps driven by changes in ocean stratification and/or terrestrial runoff, played an important role in rapid recovery from the PETM. This work also demonstrates the utility of sedimentary Ba isotope compositions for understanding past changes in the marine carbon cycle.
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  • 69
    Publication Date: 2019-04-03
    Description: Highlights • Exposure ages that constrain ice sheet thickness collated from an online database. • Thinning rates are reconstructed from 23 sites across Antarctica. • Palaeo-thinning rates are comparable to modern observations. • Wide-spread thinning during the Holocene, but after Meltwater Pulse 1A. Abstract Constraining Antarctic ice sheet evolution provides a way to validate numerical ice sheet models that aid predictions of sea-level rise. In this paper we collate cosmogenic exposure ages from exposed nunataks in Antarctica that have been used, or have the potential to be used, to constrain rates of thinning of the Antarctic Ice Sheets since the Last Glacial Maximum. We undertake quality control of the data and adopt a Bayesian approach to outlier detection. Past thinning rates are modelled by Monte Carlo linear regression analysis. We present thinning rates from 23 sites across Antarctica. The resulting data set is the first Antarctic-wide collation of past ice sheet thinning rates and provides an empirical starting point for future model-data comparisons. Palaeo-thinning rates are spatially variable with high rates appearing to correlate to areas of contemporary rapid changes. On centennial timescales past thinning rates are comparable to modern day observations implying that modern day thinning has the potential to persist for centuries in numerous parts of Antarctica. The onset of abrupt thinning from all sites post-dates Meltwater Pulse 1A suggesting that its source region(s) are distal to areas where exposure age constraints on ice surface geometry exist.
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