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  • 1
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    Kluwer
    In:  Dordrecht, 396 pp., Kluwer, vol. 138, no. 2, pp. 527-553, (ISBN: 1-4020-1179-2)
    Publikationsdatum: 2003
    Schlagwort(e): Earthquake risk ; Earthquake hazard ; interdisciplinary ; Textbook of geophysics ; Textbook of geology
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  • 2
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    Kluwer
    In:  Dordrecht, 552 pp., Kluwer, vol. 19, no. 22, pp. 662-664, (ISBN 1-4020-1244-6)
    Publikationsdatum: 2003
    Schlagwort(e): Tsunami(s) ; Oceanography ; Earthquake hazard ; land ; slides ; submarine ; coast
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  • 3
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    Kluwer
    In:  Dordrecht, 348 pp., Kluwer, vol. 20, no. Publ. No. 12, pp. 81-89, (ISBN 1-4020-1729-4)
    Publikationsdatum: 2003
    Schlagwort(e): GFZ ; M04.0014 ; 000266148 ; Textbook of geophysics ; Statistical investigations ; Artificial intelligence (AI) ; Seismics (controlled source seismology) ; Borehole geophys. ; Applied geophysics ; Electromagnetic methods/phenomena ; Seismology
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  • 4
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    Kluwer
    In:  Dordrecht, 388 pp., Kluwer, vol. 26, no. Publ. No. 12, pp. 95-104, (ISBN: 1-4020-1592-5)
    Publikationsdatum: 2003
    Beschreibung: Data assimilation is the combination of information from observations and models of a particular physical system in order to get the best possible estimate of the state of that system. The technique has wide applications across a range of earth sciences, a major application being the production of operational weather forecasts. Others include oceanography, atmospheric chemistry, climate studies, and hydrology. Data Assimilation for the Earth System is a comprehensive survey of both the theory of data assimilation and its application in a range of earth system sciences. Data assimilation is a key technique in the analysis of remote sensing observations and is thus particularly useful for those analysing the wealth of measurements from recent research satellites. This book is suitable for postgraduate students and those working on the application of data assimilation in meteorology, oceanography and other earth sciences.
    Schlagwort(e): Modelling ; Data analysis / ~ processing ; Textbook of geophysics ; Textbook of geology ; TBMeteorology
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  • 5
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    Kluwer
    In:  Dordrecht, 368 pp., Kluwer, vol. 70, pp. 71-83, (ISBN: 1-4020-0821-X)
    Publikationsdatum: 2003
    Beschreibung: Preface. 1. Introduction; B. Boots, et al. Part I: Statistical models of spatial systems. Section A: Spatial statistics. 2. Geographic patterns of urban residential development; J. Lee. 3. Using local statistics for boundary characterization; B. Boots. 4. Local spatial interaction modelling based on the geographically weighted regression approach; T. Nakaya. Section B: Space-time analysis. 5. Understanding activity scheduling and rescheduling behaviour: theory and numerical illustration; Chang-Hyeon Joh, et al. 6. Geographical model of a self-organizing megalopolis with time-space convergence; I. Mizuno. 7. Epidemic modelling of HIV/AIDS transfers between eastern and western Europe; P. Smith, R. Thomas. Part II: Computational methods. Section A: Simulation models. 8. A spatial microsimulation model for social policy evaluation; D. Ballas, et al. 9. Analysis of the effect of land use patterns on the anthropogenic energy discharged from air conditioning and hot water supply using a modified CSU mesoscale model; T. Watanabe, et al. 10. Generalized Thuenen and Thuenen-Ricardo models for Asian land use; K. Konagaya. Section B: GIS models. 11. Balancing consensus and conflict with a GIS-based multi-participant, multi-criteria decision support tool; R. D. Feick, G. B. Hall. 12. Grid-based population distribution estimates from historical Japanese topographical maps using GIS: Y. Arai, S. Koike. 13. GIS modelling for rain-induced debris-flow hazards in a small watershed; S. Zhao, T. Tamura. Section C: The internet. 14. A geographical interpretation of cyberspace: preliminary analysis on the scaling tendency of information spaces; N. Shiode. 15. On modelling internet transactions as a time-dependent random walk: an application of the retail aggregate space-time trip (RASTT) model; R. G. V. Baker. 16. Development of disaster information network system in the Asian region: internet GIS for disaster information management; Y. Ogawa, et al. 17. Geographical conceptualization of cyberplaces; M. Takeyama.
    Schlagwort(e): Modelling ; Data analysis / ~ processing ; Textbook of geophysics ; Textbook of geology ; TBMeteorology
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  • 6
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    Kluwer
    In:  Dordrecht, 616 pp., Kluwer, vol. 4, no. Subvol. b, pp. 220, (ISBN: 0-7923-5686-1)
    Publikationsdatum: 2003
    Schlagwort(e): Textbook of geology ; geography ; GIS ; Global Positioning System ; pollution ; remote ; sensing ; Deep seismic sounding (espec. cont. crust) ; decision ; support ; system ; internet ; GSDI ; European ; CZM
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  • 7
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    Kluwer
    In:  Dordrecht, 356 pp., Kluwer, vol. 22, no. 1, pp. 799-804, (ISBN 1-4020-1777-4 (hb) and ISBN 1-4020-1778-2 (pb))
    Publikationsdatum: 2003
    Schlagwort(e): Textbook of geophysics ; Seismology ; Seismicity ; Earthquake hazard ; Source ; Earthquake risk ; Earthquake engineering, engineering seismology ; Earthquake precursor: prediction research ; Greece ; Turkey
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  • 8
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    Kluwer
    In:  Dordrecht, 460 pp., Kluwer, vol. 17, pp. 225, (ISBN 1-4020-1408-2)
    Publikationsdatum: 2003
    Beschreibung: Foreword. How to climb the gravity wall; R. Rummel. I: Precise orbit determination and gravity field modelling. Strategies for precise orbit determination of low earth orbiters using the Global Positioning System; U. Hugentobler, G. Beutler. Aiming at a 1 cm orbit for low earth orbiters: reduced-dynamic and kinematic precise orbit determination; P. N. A. M. Visser, J. van den Ijssel. Space-wise, time-wise, torus and Rosborough representations in gravity field modelling; N. Sneeuw. Gravity field recovery from GRACE: unique aspects of the high precision inter-satellite data and analysis methods; G. Balmino. Global gravity field recovery using solely Global Positioning System tracking and accelerometer data from CHAMP; C. Reigber, et al. The processing of band-limited measurements: filtering techniques in the least squares context and in the presence of data gaps; W.-D. Schuh. II: Solid earth physics. Long wavelength sea level and solis surface perturbations driven by polar ice mass variations: fingerprinting Greenland and Antarctic ice sheet flux; M. E. Tamisiea, et al. Benefits from GOCE within solid earth geophysics; A. M. Marotta. The potential of GOCE in constraining the structure of the crust and lithosphere from post-glacial rebound; L. L. A. Vermeersen. Deep and shallow solid-earth structures reconstructed with sequential integrated inversion (SII) of seismic and gravity data; R. Tondi, et al. Present-day sea level change: observations and causes; A. Cazenave, et al. III: Ocean circulation. Global ocean data assimilation and geoid measurements; C. Wunsch, D. Stammer. Resolution needed for an adequate determination of the mean ocean circulation from altimetry and an improved geoid; C. Le Provost, M. Bremond. Error characteristics estimated from CHAMP, GRACE and GOCE derived geoids and from satellite altimetry derived mean dynamic topography; E. J. O. Schrama. Estimating the high-resolution mean sea-surface velocity field by combined use of altimeter and drifter data for geoid model improvement; S. Imawaki, et al. Combined use of altimetry and in situ gravity data for coastal dynamics studies; K. Haines, et al. Feasibility and contribution to ocean circulation studies of ocean bottom pressure determination; C. W. Hughes, V. Stepanov. Impact of geoid improvement on ocean mass and heat transport estimates; P. Le Grand. How operational oceanography can benefit from dynamic topography estimates as derived from altimetry and improved geoid; P. Y. Le Traon, et al. IV: Geodesy. Remarks on the role of height datum in altimetry-gravity boundary-value problems; F. Sacerdote, F. Sanso. Ocean tides in GRACE monthly averaged gravity fields; P. Knudsen. Tidal models in a new era of satellite gravimetry; R. D. Ray, et al. The elusive stationary geoid; M. Vermeer. Geodetic methods for calibration of GRACE and GOCE; J. Bouman, R. Koop. V: Sea level. Benefits of GRACE and GOCE to sea level studies; P. Woodworth, J. M. Gregory. What might GRACE contribute to studies of post glacial rebound? J. Wahr, I. Velicogna. Measuring the distribution of ocean mass using GRACE; R. S. Nerem, et al. Monitoring changes in continental water storage with GRACE; S. Swenson, J. Wahr. VI: Future concepts. Attitude and drag control: an application to the GOCE satellite; E. Canuto, et al. On superconductive gravity gradiometry in space; S. Zarembinski. Satellite-satellite laser links for future gravity missions; P. L. Bender et al. Possible future use of laser gravity gradiometers; P. L. Bender, et al. MICROSCOPE instrument development lessons for GOCE; P. Touboul. Needs and tools for future gravity measuring missions; M. Aguirre-Martinez, N. Sneeuw. VII: Closing session. GOCE: first earth explorer core mission; M. R. Drinkwater, et al. Earth gravity field from space from senors to earth sciences: closing remarks; G. Beutler.
    Schlagwort(e): Textbook of geodesy ; Earth tides ; Least-squares ; Data analysis / ~ processing ; Geodesy ; Rheology ; Inelastic ; Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Gravimetry, Gravitation ; Modelling
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  • 9
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    Kluwer
    In:  Dordrecht, 352 pp., Kluwer, vol. 4, no. 1, pp. 1-40, (ISBN: 1-4020-1348-5 hb, ISBN: 1-4020-1349-3 pb)
    Publikationsdatum: 2003
    Schlagwort(e): Tsunami(s) ; Textbook of geophysics ; Textbook of geology ; Yalciner
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  • 10
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    Kluwer
    In:  Professional Paper, Geophysical Applications of Artificial Neural Networks and Fuzzy Logic, Dordrecht, Kluwer, vol. 4, no. 16, pp. 287-304, (ISBN 1-4020-1729-4)
    Publikationsdatum: 2003
    Schlagwort(e): Statistical investigations ; Artificial intelligence (AI) ; Seismology ; Detectors ; Polarization ; NOISE ; Discrimination ; automatic ; picking
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  • 11
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    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 108 (B4). p. 2182.
    Publikationsdatum: 2018-04-11
    Beschreibung: Methane clathrate hydrate (structure I) is found to be very strong, based on laboratory triaxial deformation experiments we have carried out on samples of synthetic, high‐purity, polycrystalline material. Samples were deformed in compressional creep tests (i.e., constant applied stress, σ), at conditions of confining pressure P = 50 and 100 MPa, strain rate 4.5 × 10−8 ≤ equation image ≤ 4.3 × 10−4 s−1, temperature 260 ≤ T ≤ 287 K, and internal methane pressure 10 ≤ PCH4 ≤ 15 MPa. At steady state, typically reached in a few percent strain, methane hydrate exhibited strength that was far higher than expected on the basis of published work. In terms of the standard high‐temperature creep law, equation image = Aσne−(E*+PV*)/RT the rheology is described by the constants A = 108.55 MPa−n s−1, n = 2.2, E* = 90,000 J mol−1, and V* = 19 cm3 mol−1. For comparison, at temperatures just below the ice point, methane hydrate at a given strain rate is over 20 times stronger than ice, and the contrast increases at lower temperatures. The possible occurrence of syntectonic dissociation of methane hydrate to methane plus free water in these experiments suggests that the high strength measured here may be only a lower bound. On Earth, high strength in hydrate‐bearing formations implies higher energy release upon decomposition and subsequent failure. In the outer solar system, if Titan has a 100‐km‐thick near‐surface layer of high‐strength, low‐thermal conductivity methane hydrate as has been suggested, its interior is likely to be considerably warmer than previously expected.
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  • 12
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    AGU (American Geophysical Union)
    In:  In: Inside the Subduction Factory. , ed. by Eiler, J. Geophysical Monograph, 138 . AGU (American Geophysical Union), Boulder, pp. 153-174.
    Publikationsdatum: 2017-03-01
    Beschreibung: Most Central American volcanoes occur in an impressive volcanic front that trends parallel to the strike of the subducting Cocos Plate. The volcanic front is a chain, made of right-stepping, linear segments, 100 to 300 Km in length. Volcanoes cluster into centers, whose spacing is random but averages about 27 Km. These closely spaced, easily accessible volcanic centers allow mapping of geochemical variations along the volcanic front. Abundant back-arc volcanoes in southeast Guatemala and central Honduras allow two cross-arc transects. Several element and isotope ratios (e.g. BalLa, Uffh, B/La, IOBe/9Be, 87Sr/86Sr) that are thought to signal subducted marine sediments or altered MORB consistently define a chevron pattern along the arc, with its maximum in Nicaragua. BalLa, a particularly sensitive signal, is 130 at the maximum in Nicaragua but decreases out on the limbs to 40 in Guatemala and 20 in Costa Rica, which is just above the nominal mantle value of 15. This high amplitude regional variation, roughly symmetrical about Nicaragua, contrasts with the near constancy, or small gradient, in several plate tectonic parameters such as convergence rate, age of the subducting Cocos Plate, and thickness and type of subducted sediment. The large geochemical changes over relatively short distances make Central America an important margin for seeking the tectonic causes of geochemical variations; the regional variation has both a high amplitude and structure, including flat areas and gradients. The geochemical database continues to improve and is already adequate to compare to tectonic models with length scales of 100 Km or longer.
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  • 13
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    AGU (American Geophysical Union)
    In:  , ed. by Hurrell, J. W., Kushnir, Y., Ottersen, G. and Visbeck, M. Geophysical Monograph Series, 134 . AGU (American Geophysical Union), Washington, DC, 279 pp.
    Publikationsdatum: 2012-03-13
    Materialart: Book , PeerReviewed
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  • 14
    Publikationsdatum: 2016-09-07
    Beschreibung: Oceanic ecosystems altered by interdecadal climate variability may provide a feedback to the physical climate by phytoplankton affecting heat fluxes into the upper ocean and dimethylsulfide fluxes into the atmosphere
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  • 15
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 33 . pp. 1990-1999.
    Publikationsdatum: 2018-04-10
    Beschreibung: Intrinsic oscillations of stable geophysical surface frontal currents of the unsteady, nonlinear, reduced-gravity shallow-water equations on an f plane are investigated analytically and numerically. For frictional (Rayleigh) currents characterized by linear horizontal velocity components and parabolic cross sections, the primitive equations are reduced to a set of coupled nonlinear ordinary differential equations. In the inviscid case, two periodic analytical solutions of the nonlinear problem describing 1) the inertially reversing horizontal displacement of a surface frontal current having a fixed parabolic cross section and 2) the cross-front pulsation of a coastal current emerging from a motionless surface frontal layer are presented. In a linear and in a weakly nonlinear context, analytical expressions for field oscillations and their frequency shift relative to the inertial frequency are presented. For the fully nonlinear problem, solutions referring to a surface frontal coastal current are obtained analytically and numerically. These solutions show that the currents oscillate always superinertially, the frequency and the amplitude of their oscillations depending on the magnitude of the initial disturbance and on the squared current Rossby number. In a linear framework, it is shown that disturbances superimposed on the surface frontal current are standing waves within the bounded region, the frequencies of which are inertial/superinertial for the first mode/higher modes. In the same frame, a zeroth mode, which could be interpreted as the superposition of an inertial wave on a background vorticity field, would formally yield subinertial frequencies. For surface frontal currents affected by Rayleigh friction, it is shown that the magnitude of the mean current decays according to a power law and that the oscillations decay faster, because this decay follows an exponential law. Implications of the intrinsic oscillations and of their rapid dissipation for the near-inertial motion in an active ambient ocean are discussed.
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  • 16
    Publikationsdatum: 2017-02-14
    Beschreibung: The southern central Chilean margin at the site of the largest historically recorded earthquake in the Valdivia region, in 1960 (Mw = 9.5), is part of the 5000-km-long active subduction system whose geodynamic evolution is controversially debated and poorly understood. Covering the area between 36° and 40°S, the oceanic crust is segmented by prominent fracture zones. The offshore forearc and its onshore continuation show a complex image with segments of varying geophysical character, and several fault systems active during the past 24 m.y. In autumn 2001, the project SPOC was organized to study the Subduction Processes Off Chile, with a focus on the seismogenic coupling zone and the forearc. The acquired seismic data crossing the Chilean subduction system were gathered in a combined offshore-onshore survey and provide new insights into the lithospheric structure and evolution of active margins with insignificant frontal accretion.
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  • 17
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    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 4 (7).
    Publikationsdatum: 2018-01-31
    Beschreibung: [1] Very rare, halogen-rich andesite melt inclusions (HRA) in bytownitic plagioclase phenocrysts (An89–90) from tephra fallout of the Izu arc volcanic front (Izu VF) provide new insights into the processes of fluid release from slab trenchward to the volcanic front in a cool subduction zone. These HRA are markedly enriched in Cl, F and Li - by factors of up to 8 (Cl, F) and 1.5 (Li) - but indistinguishable with respect to the fluid-mobile large-ion lithophile elements (LILE; K, Sr, Rb, Cs, Ba, Pb, U), rare earths (REE) or high field strength elements (HFSE) from the low-K tholeiitic magmas of the Izu VF. We suggest that the chemical signature of the HRA reflects the presence of a fluid in the mantle source that originated from the serpentinized mantle peridotite above the metacrust. This “wedge serpentinite” presumably formed by fluid infiltration beneath the forearc and was subsequently down-dragged with the slab to arc front depths. The combined evidence from the Izu VF (∼110 km above slab) and the outer forearc serpentinite seamounts (∼25 to 30 km above slab) suggests that the slab flux of B and Cl is highest beneath the forearc, and decreases with increasing slab depths. In contrast, the slab flux of Li is minor beneath the forearc, but increases with depth. Fluorine may behave similarly to Li, whereas the fluid-mobile LILE appear to be largely retained in the slab trenchward from the Izu VF. Consequently, the chemical signatures of both Izu trench sediments and basaltic rocks appear preserved until arc front depths.
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  • 18
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 33 . pp. 431-435.
    Publikationsdatum: 2018-04-10
    Beschreibung: Aspects of the dynamics of warm-core eddies evolving in a deep ocean are investigated using the results of laboratory experiments and numerical simulations. The vortices, produced experimentally in a system brought to solid body rotation by rapidly lifting a bottomless cylinder containing freshwater immersed in a salty ambient fluid, show clearly the presence of inertial oscillations: deepenings and contractions, shoalings and expansions, alternate during an exact inertial period. These pulsations, though predicted analytically and simulated numerically, had never been measured before for surface eddies having aspect ratios, as well as Rossby and Burger numbers, typical of geophysical warm-core eddies. The spatial structure of the vortex radial and tangential velocity components is analyzed using the experimental results and numerical simulations carried out by means of a layered, nonlinear, reduced-gravity frontal model. It is found that, while the dependence of the vortex radial velocity on the vortex radius evolves toward linearity as time elapses, different spatial structures seem to be possible for the vortex tangential velocity dependence. This behavior, which strongly differs from the “pulson” dynamics, is instead consistent with recently found analytical solutions of the nonlinear, reduced-gravity shallow-water equations describing the dynamics of warm-core eddies on an f plane.
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  • 19
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    AGU (American Geophysical Union)
    In:  Tectonics, 22 (6). p. 1072.
    Publikationsdatum: 2017-06-28
    Beschreibung: The convergent Sunda margin off Indonesia displays all geological features characteristic of an accretion-dominated subduction zone. A combined interpretation of prestack depth-migrated seismic reflection data and velocity information gained from refraction studies is supplemented by high-resolution bathymetric data and for the first time allows the exact mapping of backstop regimes. Initially, the outer high evolved as material was pushed against a static rigid arc framework backstop underlying a forearc basin. Increasing material strength of the outer high due to lithification formed a dynamic backstop, which controls accretion today. An out-of-sequence thrust marks the transition from the recent active frontal accretionary prism to the outer high and may be traced in the seismic and bathymetric data over the whole extent of the study area. The existence of a static as well as a dynamic backstop controls the forearc geometry and is associated with the segmentation of the forearc, which is observed in regimes of frontal as well as of oblique subduction. Mass balance calculations, which account for porosity changes and metamorphism, indicate a subduction history dominated by accretionary processes since the late Eocene. Accretion is associated with the low values of basal friction inferred for the Sunda margin. Structural investigations of conjugate fault planes indicate a very weak basal detachment. Effective stress analyses reveal that intrinsically weak material causes the high strength ratio of the detachment to the overlying sediments, whereas overpressuring within the frontal accretionary prism is negligible.
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  • 20
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    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Atmospheres, 108 (D19). Art.No. 4599.
    Publikationsdatum: 2018-02-06
    Beschreibung: Simplified representations of spatially inhomogeneous (three-dimensional (3-D)) clouds in radiative transfer models provide systematic errors when calculating solar broadband radiative fluxes. An example is the neglect of horizontal photon transports as it is the case for the independent column approximation (ICA). The present work tries to quantify and interpret these errors on the basis of a large set of 3-D mixed phase cloud scenarios with 3-D varying extinction coefficients, scattering phase functions, and single-scattering albedos. The cloud cases result from a mesoscale atmospheric circulation model with detailed cloud microphysics. Domain-averaged cloud radiative fluxes are calculated by means of a Monte Carlo radiative transfer model. Depending on cloud type and solar zenith angle (SZA) the differences between 3-D and ICA results range from +20 W m−2 to −30 W m−2 for the upward reflected fluxes and from +10 W m−2 to −7 W m−2 for the absorbed fluxes. The mean (averaged over all cloud realizations) errors of the ICA-based upward fluxes vary between 5 W m−2 overestimation at 15°SZA and 6 W m−2 underestimation at 75°SZA. The ICA underestimates the absorbed flux by ∼1–2 W m−2 for most SZA except for 75°. It is found that neglecting the horizontal variability of the absorption and scattering properties of the cloud hydrometeors leads to a general underestimation of solar broadband absorption by as much as 15 W m−2 with average values between 4 W m−2 at small SZA and 1 W m−2 at large SZA.
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  • 21
    Publikationsdatum: 2018-01-31
    Beschreibung: Between 1996 and 1998, a concerted effort was made to study the deep open ocean convection in the Labrador Sea. Both in situ observations and numerical models were employed with close collaboration between the researchers in the fields of physical oceanography, boundary layer meteorology, and climate. A multitude of different methods were used to observe the state of ocean and atmosphere and determine the exchange between them over the experiment's period. The Labrador Sea Deep Convection Experiment data collection aims to assemble the observational data sets in order to facilitate the exchange and collaboration between the various projects and new projects for an overall synthesis. A common file format and a browsable inventory have been used so as to simplify the access to the data.
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  • 22
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 33 (1). pp. 75-87.
    Publikationsdatum: 2018-04-11
    Beschreibung: Two large-scale free-drifting isobaric-floats experiments, “SOFARGOS”/Marine Science and Technology Programme, phase 2 (MAST2) and Mass Transfer and Ecosystem Response (MATER)/MAST3, undertaken in 1994–95 in the northwestern Mediterranean Sea and in 1997–98 in the Algerian Basin, respectively, have revealed for the first time that Western Mediterranean Deep Water, newly formed by deep convection in the Gulf of Lion (the so-called Medoc site), can be advected several hundreds of kilometers away from the formation area by anticyclonic submesoscale coherent vortices (SCVs). This behavior implies that SCVs participate actively in the large-scale thermohaline circulation and deep ventilation of the western Mediterranean Sea. These SCVs are characterized by small radius (5 km), very low potential vorticity, high aspect ratio (0.1), and extended lifetime (〉0.5 yr).
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  • 23
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    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 30 (7). p. 1314.
    Publikationsdatum: 2018-02-20
    Beschreibung: Current hydrographic data can provide snapshots but no continuous timeseries of the meridional overturning circulation (MOC). Using output from two eddy-permitting numerical ocean models we test the feasibility of a monitoring system for the MOC in the North Atlantic. The results suggest that a relatively simple arrangement, using moorings placed across a longitude-depth section and the zonal wind stress, is able to capture most of the MOC strength and vertical structure as a function of time. Being closely related to the transport of energy to the North Atlantic, measuring the MOC would open the prospect of having continuous information about a key element of northern hemisphere climate.
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  • 24
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    AGU (American Geophysical Union)
    In:  Paleoceanography, 18 (2). p. 1030.
    Publikationsdatum: 2017-05-10
    Beschreibung: GLAMAP 2000 presents new reconstructions of the Atlantic's sea surface temperatures (SST) at the Last Glacial Maximum (LGM), defined at both 21,500–18,000 years B.P. (“Last Isotope Maximum”) and 23,000–19,000 years B.P. (maximum glacial sea level low stand and orbital minimum of solar insolation; EPILOG working group; see Mix et al. [2001]). These reconstructions use 275 sediment cores between the North Pole and 60°S with carefully defined chronostratigraphies. Four categories of core quality are distinguished. More than 100 core sections provide a glacial record with subcentennial- to multicentennial-scale resolution. SST estimates are based on a new set of almost 1000 reference samples of modern planktic foraminifera and on improved transfer-function techniques to deduce SST from census counts of microfossils, including radiolarians and diatoms. New proxies also serve to deduce sea ice boundaries. The GLAMAP 2000 SST patterns differ significantly in crucial regions from the CLIMAP [1981] reconstruction and thus are important in providing updated boundary conditions to initiate and validate computational models for climate prediction.
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  • 25
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    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 30 (6). GRL-1298.
    Publikationsdatum: 2015-03-06
    Beschreibung: This study has been motivated by reports of extraordinary change in the Arctic Ocean observed in recent decades. Most of these observations are based on synoptic measurements, while evaluation of anomalies requires an understanding of the underlying long-term variability. Historical climatologies give reference means, and while these datasets are a reliable source of the mean Atlantic Layer temperature, they significantly underestimate variability. Using historical data, we calculated statistical parameters for selected Arctic Ocean regions. They demonstrate a high level of Atlantic Layer temperature variability in the Nansen Basin and sea-surface salinity fluctuations on the Siberian shelf and the Amundsen Basin. These estimates suggest strong limitations on our ability to define amplitudes of anomalies by comparing recent synoptic measurements with climatologies, especially for regions characterized by strong variability.
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  • 26
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    AGU (American Geophysical Union)
    In:  In: Methane Hydrates in Quaternary Climate Change: The Clathrate Gun Hypothesis. AGU (American Geophysical Union), Washington, DC, pp. 1-9. ISBN 0-87590-296-0
    Publikationsdatum: 2015-09-09
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  • 27
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 33 (7). pp. 1351-1364.
    Publikationsdatum: 2019-04-29
    Beschreibung: Bulk properties of the Denmark Strait overflow (DSO) plume observed in velocity and hydrography surveys undertaken in 1997 and 1998 are described. Despite the presence of considerable short-term variability, it is found that the pathway and evolution of the plume density anomaly are remarkably steady. Bottom stress measurements show that the pathway of the plume core matches well with a rate of descent controlled by friction. The estimated entrainment rate diagnosed from the rate of plume dilution with distance shows a marked increase in entrainment at approximately 125 km from the sill, leading to a net dilution consistent with previous reports of a doubling of overflow transport measured by current meter arrays. The entrainment rate increase is likely related to the increased topographic slopes in the region, compounded by a decrease in interface stratification as the plume is diluted and enters a denser background.
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  • 28
    Publikationsdatum: 2015-01-26
    Beschreibung: The results of the first protozoological study in terms of paleoecology of long-term sediments and buried soils formed in the cryolite zone of northeastern Siberia are discussed. The data on testaceans (Protozoa: Testacea) inhabiting various sites of Bykovsky Peninsula, Laptev Sea coast near estuary of Lena, within the last 53 000 years (Late Pleistocene and Holocene) are presented.
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  • 29
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    AGU (American Geophysical Union)
    In:  In: Methane Hydrates in Quaternary Climate Change: The Clathrate Gun Hypothesis. AGU (American Geophysical Union), Washington, DC, pp. 105-107. ISBN 0-87590-296-0
    Publikationsdatum: 2015-09-09
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  • 30
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    AGU (American Geophysical Union)
    In:  In: Explosive Subaqueous Volcanism. , ed. by White, J. D. L., Smellie, J. L. and Clague, D. A. AGU (American Geophysical Union), Washington, USA, pp. 167-178.
    Publikationsdatum: 2015-08-11
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  • 31
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    AMS (American Meteorological Society)
    In:  Journal of Atmospheric and Oceanic Technology, 20 (5). pp. 742-751.
    Publikationsdatum: 2020-08-04
    Beschreibung: A new shipboard current profiler, a 75-kHz ocean surveyor, was operationally used during two research cruises in the tropical Atlantic and the subpolar North Atlantic, respectively. Here, a report is presented on the first experience with this instrument in two very different current regimes, in the Tropics with large vertical shears, and in the subpolar regime with mainly barotropic flow. The ocean surveyor continuously measured currents in the upper ocean from near the surface to about 500–700-m depth. The measurement range showed a dependence on the regional and temporal variations of scattering particles and on the intensity of swell and wind waves. Statistical comparisons are performed with on-station lowered acoustic Doppler current profiler (LADCP) profiles and underway measurements by classic shipboard acoustic Doppler current profiler (ADCP) measurements. Accuracy estimates for hourly averaged ocean surveyor currents result in errors of about 1 cm s–1 for on-station data and of 2–4 cm s–1 for underway measurements, depending on the regional abundance of scatterers and on the weather conditions encountered.
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  • 32
    Publikationsdatum: 2018-01-30
    Beschreibung: [1] We report results of magnetic data from the Nazca Plate and of geochemical (major element and Sr-Nd-Pb-isotope) analyses of rocks dredged from the Galápagos hot spot tracks (Cocos, Carnegie, Malpelo and Coiba Ridges and adjacent seamounts) in the Central East Pacific. Magnetic anomalies indicate that the Malpelo and Carnegie Ridges were once attached and that seafloor spreading separated the two ridges between 14.5 Ma and 9.5 Ma. The variations in Sr-Nd-Pb isotopic composition show that three of the mantle components currently observed at the Galápagos (Central, Southern, and Eastern) existed in the hot spot for at least 20 m.y., whereas the Northern Galápagos mantle component has been present for at least ∼15 Ma. Our data are consistent with the existence of a compositionally zoned/striped Galápagos plume since ∼20 Ma. Combined constraints from the morphology of the hot spot tracks, the magnetic record, and the isotope geochemistry of the rock samples provide new insights into the hot spot-ridge geometry and interaction of the Galápagos hot spot with the Cocos-Nazca spreading center (CNS) over the past 20 m.y. At 19.5 Ma a ridge jump moved the spreading axis to the northern edge of the hot spot. Between 19.5 and 14.5 Ma, the spreading axis was located above the center of the hot spot. At 14.5 Ma, a new ridge jump moved the spreading axis to the south, splitting the paleo-Carnegie Ridge into the present Carnegie and Malpelo Ridges. The repeated ridge jumps reflect capture of the northwardly drifting spreading center by the Galápagos hot spot. At 11–12 Ma an offset of the spreading axis lay above the plume center. Spreading between the Carnegie and Malpelo Ridges continued until 9.5 Ma.
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  • 33
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    AMS (American Meteorological Society)
    In:  Journal of the Atmospheric Sciences, 60 . pp. 152-165.
    Publikationsdatum: 2018-04-16
    Beschreibung: A new mechanism is proposed that explains two key features of the observed El Niño–Southern Oscillation (ENSO) phenomenon—its irregularity and decadal amplitude changes. Using a low-order ENSO model, the authors show that the nonlinearities in the tropical heat budget can lead to bursting behavior characterized by decadal occurrences of strong El Niño events. La Niña events are not affected, a feature that is also seen in ENSO observations. One key result of this analysis is that decadal variability in the Tropics can be generated without invoking extratropical processes or stochastic forcing. The El Niño bursting behavior simulated by the low-order ENSO model can be understood in terms of the concept of homoclinic and heteroclinic connections. It is shown that this new model for ENSO amplitude modulations and irregularity, although difficult to prove, might explain some features of ENSO dynamics seen in more complex climate models and the observations.
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  • 34
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    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 4 (4). p. 9003.
    Publikationsdatum: 2018-01-31
    Beschreibung: [1] The Franciscan Complex (Coast Ranges and Diablo Range, California) and the Western Baja Terrane (WBT; Baja California, Mexico) were metamorphosed along high-P/T paths like those experienced in many active subduction zones, recording peak conditions up to ∼1 GPa and 300°C. Franciscan and WBT metasedimentary rocks are similar in lithology and geochemistry to clastic sediments outboard of many subduction zones. These metamorphic suites provide evidence regarding devolatilization history experienced by subducting sediments, information that is needed to mass-balance the inputs of materials into subduction zones with their respective outputs. Analyzed samples have lower total volatile contents than their likely protoliths. Little variation in LOI among similar lithologies at differing metamorphic grades, suggests that loss of structurally bound water occurred during early clay-mineral transformations. Finely disseminated carbonate is present in the lowest-grade rocks, but absent in all higher-grade rocks. δ13CVPDB of reduced-C is uniform in the lower-grade Franciscan samples (mean = −25.1‰, 1σ = 0.4‰), but varies in higher-grade rocks (−28.8 to −21.9‰). This likely reflects a combination of devolatilization and C-isotope exchange, between organic and carbonate reservoirs. Nitrogen concentration ranges from 102 to 891 ppm, with δ15Nair of +0.1 to +3.0‰ (n = 35); this organic-like δ15N probably represents an efficient transfer of N from decaying organic matter to reacting clay minerals. The lowest-grade rocks in the Coastal Belt have elevated carbonate contents and correlated N-δ15N variations, and exhibit the most uniform δ13C and C/N, all consistent with these rocks having experienced less devolatilization. Most fluid-mobile trace elements are present at concentrations indistinguishable from protoliths. Suggesting that, despite apparent loss of much clay-bound H2O and CO2 from diagenetic cements (combined, 〈5–10 wt. %), most fluid-mobile trace elements are retained to depths of up to ∼40 km. Organic-like δ15N, lower than that of many seafloor sediments, is consistent with some loss of adsorbed N (perhaps as NO3−) during early stages of diagenesis. The efficient entrainment of fluid-mobile elements to depths of at least 40 km in these relatively cool subduction zone settings lends credence to models invoking transfer of these elements to the subarc mantle.
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  • 35
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    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 30 . pp. 2169-2172.
    Publikationsdatum: 2018-02-20
    Beschreibung: The sea surface temperatures (SSTs) of the tropical Indian Ocean show a pronounced warming since the 1950s. We have analyzed the impact of this warming on Sahelian rainfall and on the North Atlantic Oscillation (NAO) by conducting ensemble experiments with an atmospheric general circulation model. Additionally, we investigate the impact of the other two tropical oceans on these two climate parameters. Our results suggest that the warming trend in the Indian Ocean played a crucial role for the drying trend over the West Sahel from the 1950s to 1990s and may also have contributed to the strengthening of the NAO during the most recent decades.
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  • 36
    Publikationsdatum: 2017-05-10
    Beschreibung: On the basis of 52 sediment cores, analyzed and dated at high resolution, the paleoceanography and climate of the Last Glacial Maximum (LGM) were reconstructed in detail for the Fram Strait and the eastern and central Arctic Ocean. Sediment composition and stable isotope data suggest three distinct paleoenvironments: (1) a productive region in the eastern to central Fram Strait and along the northern Barents Sea continental margin characterized by Atlantic Water advection, frequent open water conditions, and occasional local meltwater supply and iceberg calving from the Barents Sea Ice Sheet; (2) an intermediate region in the southwestern Eurasian Basin (up to 84–85°N) and the western Fram Strait characterized by subsurface Atlantic Water advection and recirculation, a moderately high planktic productivity, and a perennial ice cover that breaks up only occasionally; and (3) a central Arctic region (north of 85°N in the Eurasian Basin) characterized by a low-salinity surface water layer and a thick ice cover that strongly reduces bioproduction and bulk sedimentation rates. Although the total inflow of Atlantic Water into the Arctic Ocean may have been reduced during the LGM, its impact on ice coverage and halocline structure in the Fram Strait and southwestern Eurasian Basin was strong.
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  • 37
    Publikationsdatum: 2018-01-30
    Beschreibung: [1] We report Hf isotope compositions of 79 lavas that record the early (∼5–95 Ma) history of the Galápagos plume volcanism. These include lavas from the Caribbean Large Igneous Province (CLIP; ∼95–70 Ma), the accreted Galápagos paleo-hot spot track terranes (54–65 Ma) of Costa Rica (Quepos, Osa and Burica igneous complexes), and the Galápagos hot spot tracks (〈20 Ma) located on the Pacific seafloor (Cocos, Carnegie, Malpelo, and Coiba Ridges and associated seamounts). These samples have previously been well characterized in terms of major and trace elements, Sr-Nd-Pb isotopes and Ar/Ar ages. As a result of the relative immobility of the high field strength and rare earth elements during syn- and post-emplacement hydrothermal activity and low-temperature alteration, combined Lu-Hf and Sm-Nd isotope systematics, when used in conjunction with Pb isotopes, provide a particular powerful tool, for evaluating the source compositions of ancient and submarine lavas. The combined Nd-Hf isotope data suggest that three of the isotopically distinct source components found today in the Galápagos Islands (the Floreana-like southern component, the Fernandina-like central component, and the depleted Genovesa-like eastern component) were present in the CLIP already by 95–70 Ma. The fourth Pinta-like northern component is first recorded at about 83–85 Ma by volcanism taking place during the transition from the plume head/CLIP to plume tail stage and has then been present in the hot spot track continuously thereafter. The identification of the unique northern and southern Galápagos Plume Hf-Nd-Pb isotope source signatures within the CLIP and the oldest hot spot track lavas provides direct evidence that the CLIP represents the plume head stage of the Galápagos hot spot. Hafnium isotopes are consistent with the possibility that two types of sediment components may have contributed to the Hf, Nd and Pb isotope compositions of the Galápagos plume lavas. One component, characterized by Δ207Pb/204Pb ≈ 0 and high positive ΔεHf has an isotope signature indicative of relatively recently recycled pelagic sediment, a signature typical of the southern Galápagos island Floreana. The other component has an EM like isotopic composition resembling modern seafloor sediments with positive Δ207Pb/204Pb and lower ΔεHf, a signature typical of the northern Galápagos island Pinta.
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  • 38
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 33 . pp. 2307-2319.
    Publikationsdatum: 2018-04-10
    Beschreibung: Processes that influence the volume and heat transport across the Greenland–Scotland Ridge system are investigated in a numerical model with ° horizontal resolution. The focus is on the sensitivity of cross-ridge transports and the reaction of the subpolar North Atlantic Ocean circulation to changes in wind stress and buoyancy forcing on seasonal to interannual timescales. A general relation between changes in wind stress or cross-ridge density contrasts and the overturning transport of Greenland–Iceland–Norwegian Seas source water is established from a series of idealized experiments. The relation is used subsequently to interpret changes in an experiment over the years 1992–97 with realistic forcing. On seasonal and interannual timescales there is a clear correlation between heat flux and wind stress curl variability. The realistic model suggests a steady decrease in the strength of the cyclonic subpolar gyre of the North Atlantic with a corresponding decrease in heat transport during the 1990s
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  • 39
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    AMS (American Meteorological Society)
    In:  Journal of Climate, 16 (15). pp. 2569-2585.
    Publikationsdatum: 2020-08-04
    Beschreibung: The role of mean and stochastic freshwater forcing on the generation of millennial-scale climate variability in the North Atlantic is studied using a low-order coupled atmosphere–ocean–sea ice model. It is shown that millennial-scale oscillations can be excited stochastically, when the North Atlantic Ocean is fresh enough. This finding is used in order to interpret the aftermath of massive iceberg surges (Heinrich events) in the glacial North Atlantic, which are characterized by an excitation of Dansgaard–Oeschger events. Based on model results, it is hypothesized that Heinrich events trigger Dansgaard–Oeschger cycles and that furthermore the occurrence of Heinrich events is dependent on the accumulated climatic effect of a series of Dansgaard–Oeschger events. This scenario leads to a coupled ocean–ice sheet oscillation that shares many similarities with the Bond cycle. Further sensitivity experiments reveal that the timescale of the oscillations can be decomposed into stochastic, linear, and nonlinear deterministic components. A schematic bifurcation diagram is used to compare theoretical results with paleoclimatic data.
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  • 40
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    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 17 (1). pp. 1005-1024.
    Publikationsdatum: 2018-03-16
    Beschreibung: Temporal trends in oceanic dissolved inorganic carbon (DIC) and δ13C-DIC were reconstructed along five isopycnals in the upper 1000 m of the North Atlantic Ocean using a back-calculation approach. The mean anthropogenic DIC increase was 1.21 ± 0.07 μmol kg−1 yr−1 and the mean 13C decrease was −0.026 ± 0.002‰ yr−1, both in good agreement with the results from previous studies. The observed δ13C-DIC perturbation ratio is −0.024 ± 0.003‰ (μmol kg−1)−1. Our results indicate that the North Atlantic is able to maintain equilibrium with the anthropogenic perturbation for DIC and follows it with decadal time lag for δ13C. A CFC-calibrated one-dimensional isopycnal advection-diffusion model is used to evaluate temporal DIC and δ13C trends and perturbation ratios of the reconstructions. We investigate the time history of the air-sea CO2 and 13C disequilibria in the North Atlantic and discuss the importance of physical and biological processes in maintaining them. We find evidence that the North Atlantic Ocean is characterized by enhanced uptake of anthropogenic CO2. Also, we use the model to examine how the time rate of change of δ13C depends on changes in the temporal evolution of δ13C in the atmosphere. The model evolution explains the curious result that the time rate of change of surface water δ13C in the North Atlantic Ocean can exceed that observed concurrently in the atmosphere. Finally we introduce a powerful way of estimating the global air-sea pCO2 disequilibrium based on the oceanic δ13C-DIC perturbation ratio.
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  • 41
    Publikationsdatum: 2019-09-23
    Beschreibung: Erosional convergent margins, where material is removed from the base of the upper plate and subducted on the lower plate, are fundamental features of the Circum Pacific. The erosional Middle America Trench convergent Pacific margin, remarkable for its broad diversity of dynamic environments, is a natural laboratory for studying convergent margin processes and seismogenesis. These environments include a shallow and deep trench axis, shallow-to-steep-dipping plate interfaces, abnormally hot-to-cold subducting plate temperatures, and a subducting plate with smooth morphology bordering basement ridges and seamounts. The subducting topography accelerates erosion and localizes seismicity.
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  • 42
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    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 30 (15). Nr. 1781.
    Publikationsdatum: 2018-02-20
    Beschreibung: It is shown that the Arctic averaged wintertime temperature variability during the 20th century can be essentially described by two orthogonal modes. These modes were identified by an Empirical Orthogonal Function (EOF) decomposition of the 1892-1999 surface wintertime air temperature anomalies (40degreesN-80degreesN) using a gridded dataset covering high Arctic. The first mode (1st leading EOF) is related to the NAO and has a major contribution to Arctic warming during the last 30 years. The second one (3rd leading EOF) dominates the SAT variability prior to 1970. A correlation between the corresponding principal component PC3 and the Arctic SAT anomalies is 0.79. This mode has the largest amplitudes in the Kara-Barents Seas and Baffin Bay and exhibits no direct link to the large-scale atmospheric circulation variability, in contrast to the other leading EOFs. We suggest that the existence of this mode is caused by long-term sea ice variations presumably due to Atlantic inflow variability
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  • 43
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    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 17 (2). p. 1052.
    Publikationsdatum: 2016-06-15
    Beschreibung: Three scenarios have been proposed to explain the 20-ppm post-8000 BP rise in atmospheric CO2 content. Indermühle et al. [1999] call on a climate-induced decrease in terrestrial biomass. W. F. Ruddiman (personal communication, 2002) calls on an anthropogenically induced decrease in terrestrial biomass. Broecker et al. [2001] suggest instead that this rise in CO2 was a response to a CaCO3 preservation event induced by an early Holocene increase in terrestrial biomass. The biomass decline hypothesis not only rests on shaky 13C data, but also requires an unreasonably large decrease in biomass (195 ± 40 GtC). While evidence for a decrease in deep sea carbonate ion concentration over the last 8000 years reconstructed from CaCO3 size index and foraminifera shell weight measurements appears to support the idea that the CO2 rise was caused by a change in the inventory of terrestrial biomass, the decrease appears to be too large to be explained solely in this way. Regardless, the CO3= decline cannot be used to distinguish between the late Holocene biomass decrease and early Holocene biomass increase scenarios. Only when a convincing 13C record for atmospheric CO2 has been generated will it be possible to make this distinction.
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  • 44
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    AGU (American Geophysical Union)
    In:  In: The North Atlantic Oscillation: climatic significance and environmental impact. , ed. by Hurrell, J. W., Kushnir, Y., Ottersen, G. and Visbeck, M. Geophysical Monograph Series, 134 . AGU (American Geophysical Union), Washington, DC, pp. 1-36.
    Publikationsdatum: 2020-03-26
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  • 45
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    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 17 (1). p. 1023.
    Publikationsdatum: 2018-02-27
    Beschreibung: Bromoform (CHBr3) is the largest single source of atmospheric organic bromine and therefore of importance as a source of reactive halogens to the troposphere and lower stratosphere. The sea-to-air flux, originating with macroalgal and planktonic sources, is the main source for atmospheric bromoform. We review bromoform's contribution to atmospheric chemistry, its atmospheric and oceanic distributions and its oceanic sources and sinks. We have reassessed oceanic emissions, based on published aqueous and airborne concentration data, global climatological parameters, and information concerning coastal and biogenic sources. The goals are to attempt an estimate of the global source strength and partly to identify key regions that require further investigation. The sea-to-air flux is spatially and temporally variable with tropical, subtropical and shelf waters identified as potentially important source regions. We obtain an annual global flux of bromoform of ∼10 Gmol Br yr−1 (3–22 Gmol Br yr−1). This estimate is associated with significant uncertainty, arising from data precision and coverage, choice of air-sea exchange parameterizations and model assumptions. Anthropogenic sources of ∼0.3 (to 1.1) Gmol Br yr−1 (as CHBr3) can be locally significant, but are globally negligible. Our estimate of the global oceanic source is three to four times higher than recent estimates based on the modeling of atmospheric sinks. The reasons for this discrepancy could lie with the limited regional and temporal data available and the broad assumptions that underlie our flux calculations. Alternatively, atmospheric sink calculations, often made on the basis of background CHBr3 levels, may neglect the influence of strong but highly localized sources (e.g., from some coastal and shelf regions). The strongly variable and poorly characterized source of CHBr3, together with its short atmospheric lifetime, complicates model-based estimation of the distribution of reactive Br resulting from its atmospheric degradation. An integrated program of marine and atmospheric observations, atmospheric modeling and mechanistic studies of oceanic bromoform production is required to better constrain present and future Br delivery to the atmosphere.
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  • 46
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    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 17 (3). p. 1084.
    Publikationsdatum: 2018-03-15
    Beschreibung: A new model for the marine cycles of particulate organic carbon (POC), oxygen, nitrate, and phosphorus has been developed and applied to explore the controls and constraints on marine productivity and nutrient inventories. The coupled benthic-pelagic model uses a new approach for the simulation of the reactive phosphorus turnover (Preac corresponding to the sum of organic P, authigenic P, and adsorbed phosphate) in marine sediments. The simulated POC/Preac burial ratio in shelf, slope and rise, and deep-sea sediments increases under strongly reducing conditions in agreement with field observation. The model runs revealed that the spread of anoxia in bottom waters may enhance the productivity of the global ocean by one order of magnitude if sufficient nitrate is provided by N2-fixation. Thus anoxic bottom waters promote eutrophic conditions and vice versa. Additional model runs showed that the productivity and nutrient inventory of the glacial ocean were probably enhanced due to the falling sea level. Marine regression induced a narrowing of the depositional areas on the continental shelves and thereby an increase in the fraction of POC exported to the deep ocean. The accelerated POC delivery, in turn, decreased the oxygen contents of the deep water and thus favored the release of phosphate from deep-sea and rise sediments. Enhanced recycling of phosphate at the seafloor promoted further POC export in a positive feedback loop.
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  • 47
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    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 30 (6). p. 1296.
    Publikationsdatum: 2018-02-20
    Beschreibung: The island of Tenerife is composed of three Miocene shields, which are centered by the Cañadas volcano since the Pliocene. Tenerife sits on more than 2 km thick oceanic sediments. Quaternary volcanism of the Cañadas series and giant landslides were principally confined to triaxial rift zones. The mechanism of triaxial rifting, however, has remained unclear. Physical analog models show that these rift zones may have formed by gravity-driven lateral escape of island segments, induced by loading of the deformable substratum. For experiments scaled to Tenerife, three adjacent sand cones were mounted onto viscous PDMS substratum. Gravitational spreading caused circumferential expansion of each cone, until a large edifice (Cañadas) was constructed in their center. The older cones now acted each as a buttress; radial fractures were overprinted by fractional spreading of the Cañadas edifice. This resulted in formation of three main extensional zones, resembling the triaxial rifting configuration of Tenerife.
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  • 48
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    Unbekannt
    AMS (American Meteorological Society)
    In:  Journal of Climate, 16 . pp. 2717-2734.
    Publikationsdatum: 2018-07-24
    Beschreibung: Synoptic-scale variability in the air–sea turbulent fluxes in the areas of midlatitudinal western boundary currents is analyzed. In the Gulf Stream area, ocean–atmosphere fluxes on synoptic time- and space scales are clearly coordinated with the propagating synoptic-scale atmospheric transients. The statistical analysis of 6-hourly resolution sea level pressure and surface turbulent fluxes from the NCEP–NCAR reanalysis for the period from 1948 to 2000 in the area of strong sea surface temperature gradients in the Gulf Stream gives strong proof for the association between the propagating cyclones and synoptic patterns of surface turbulent fluxes. It is shown that sea–air interaction in this area is controlled by the sharpness of surface temperature gradients in the ocean and by the intensity of the advection of the air masses in different parts of cyclones during the cold-air and warm-air outbreaks. A simple parameter based on the joint consideration of the characteristics of sea surface temperature and sea level pressure fields is used to characterize the synoptic variability of air–sea turbulent fluxes. The effectiveness of the relationship between surface temperature and surface pressure on one side and air–sea flux anomalies on the other vary from year to year in phase with variability in the frequencies of deep atmospheric cyclones in the Gulf Stream area. The limits of applicability of the approach, its sensitivity to higher-resolution sea surface temperature data, and the possibility of its further applications are discussed.
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  • 49
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    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 30 (15). 1793,.
    Publikationsdatum: 2018-02-20
    Beschreibung: The response of the Arctic Ocean sea ice system to Northern Annular Mode-like wind forcing has been investigated using an ocean/sea ice general circulation model coupled to an atmospheric boundary layer model. A series of idealized experiments was performed to investigate the Arctic Ocean's response to idealized winter wind anomalies on interannual to multi-decadal time scales. The sea ice response of the model consists of a rapid change of ice movements leading to widespread variation in sea ice thickness and concentration. In most areas the response is largely independent of the forcing frequency with only a slight increase towards longer periods. Only the Greenland Sea exhibited a change in sign of sea ice concentration anomalies at about 20 years period which appears to be caused by slow adjustment of the oceanic circulation.
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  • 50
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    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 4 (2). p. 1018.
    Publikationsdatum: 2018-01-31
    Beschreibung: [1] New and published analyses of major element oxides (SiO2, TiO2, Al2O3, FeO*, MnO, MgO, CaO, K2O, Na2O and P2O5) from the central Izu Bonin and Mariana arcs (IBM) were compiled in order to investigate the evolution of the IBM in terms of major elements since arc inception at ∼49 million years ago. The database comprises ∼3500 volcanic glasses of distal tephra fallout and ∼500 lava samples, ranging from the Quaternary to mid-Eocene in age. The data were corrected to 4 wt% MgO in order to display the highly resolved temporal trends. These trends show that the IBM major elements have always been “arc-like” and clearly distinct from N-MORB. Significant temporal variations of some major element oxides are apparent. The largest variations are displayed by K4.0. The data support a model wherein the K2O variability is caused by the addition of slab component with strongly differing K2O contents to a fairly depleted subarc mantle; variable extents of melting, or mantle heterogeneity, appear to play a negligible role. The other major element oxides are controlled by the composition and processes of the subarc mantle wedge. The transition from the boninitic and tholeiitic magmatism of the Eocene and Oligocene to the exclusively tholeiitic magmatism of the Neogene IBM is proposed to reflect a change in the composition of the subarc mantle wedge. The early boninitic magmas originate from an ultra-depleted subarc mantle, that is residual to either the melting of E-MORB mantle, or of subcontinental lithospheric mantle. During the Eocene and Oligocene, this residual mantle is gradually replaced by Indian MORB mantle advected from the backarc regions. The Indian MORB mantle is more radiogenic in Nd isotope ratios but also more fertile with respect to major and trace elements. Therefore the Neogene tholeiites have higher Al2O3 and TiO2 contents and lower mg# numbers at given SiO2 content. After the subarc mantle replacement was complete in the late Oligocene or early Miocene, the Neogene IBM entered a “steady state” that is characterized by the continuous advection of Indian MORB mantle from the reararc, which is fluxed by fluids and melt components from slab. The thickness of the IBM crust must have grown with time, but any effects of crustal thickening on the major element chemistry of the IBM magmas appear to be minor relative to the compositional changes that are related to source composition. Therefore next to the processes of melting, the composition of the mantle sources must play a major role in creating substantiative heterogeneities in the major element chemistry of the arc crust.
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  • 51
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    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 108 (C3). p. 3092.
    Publikationsdatum: 2019-04-04
    Beschreibung: A first step for improving the climatological state of high‐resolution general circulation models by means of data assimilation is presented. A method developed for the assimilation of statistical characteristics into chaotic ocean models is applied to assimilate SSH variability from TOPEX/POSEIDON and ERS1 in association with temperature and salinity from the World Ocean Atlas 1997 in order to estimate the underlying mean circulation. The method requires a parameterization of SSH variability which derives from the approach of Green and Stone. By estimating initial conditions for temperature and salinity, a mean state is achieved which, although not fully consistent with the altimetric and climatological data, is markedly improved on time scales of one year in comparison to the control run. The assimilation of SSH variability data introduces complementary information about the main frontal structures consistent with climatological observations. The state is however not an equilibrium state and returns back to the first guess quasi‐equilibrium state for longer integration periods.
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  • 52
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    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 108 (C6). p. 3181.
    Publikationsdatum: 2019-04-29
    Beschreibung: We report on a combined modeling and observational effort to understand the Denmark Strait Overflow (DSO). Four cruises over the course of 3 years mapped hydrographic properties and velocity fields with high spatial resolution. The observations reveal the mean path of the dense water, as well as the presence of strong barotropic flows, energetic variability, and strong bottom friction and entrainment. A regional sigma coordinate numerical model of interbasin exchange using realistic bottom topography and an overflow forced only by an upstream reservoir of dense fluid is compared with the observations and used to further investigate these processes. The model successfully reproduces the volume transport of dense water at the sill, as well as the 1000-m descent of the dense water in the first 200 km from the sill and the intense eddies generated at 1–3 day intervals. Hydraulic control of the mean flow is indicated by a region supercritical to long gravity waves in the dense layer located approximately 100 km downstream of the sill in both model and observations. In addition, despite the differences in surface forcing, both model and observations exhibit similar transitions from mostly barotropic flow at the sill to a bottom-trapped baroclinic flow downstream, indicating the dominant role of the overflow in determining the full water column dynamics.
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  • 53
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    AGU (American Geophysical Union)
    In:  Geophysical Research Letters (30).
    Publikationsdatum: 2018-02-20
    Beschreibung: We present evidence showing that the nonlinear dynamic heating (NDH) in the tropical Pacific ocean heat budget is essential in the generation of intense El Niño events as well as the observed asymmetry between El Niño (warm) and La Niña (cold) events. The increase in NDH associated with the enhanced El Niño activity had an influence on the recent tropical Pacific warming trend and it might provide a positive feedback mechanism for climate change in the tropical Pacific.
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  • 54
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    Kluwer
    In:  Journal of Radionanalytical and Nuclear Chemistry, 256 (3). pp. 473-480.
    Publikationsdatum: 2019-09-23
    Beschreibung: A new method is presented for rapid and selective enrichment of radium in natural samples using 225Ra as a chemical yield tracer. The new technique allows a complete separation of the target nuclide from the sample matrix with high separation factors for thorium and uranium. The use of EmporeÔ Radium Rad Disks combines the easy handling of column chromatography with the high selectivity and rapid extraction kinetics of solvent extraction chromatography. Following this new chemical approach, eluates are obtained which are well suited for a-spectrometric analysis of Ra, Th and U.
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  • 55
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    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 108 (C5). p. 3159.
    Publikationsdatum: 2018-04-18
    Beschreibung: A series of numerical experiments with models of the Atlantic Ocean is analyzed with respect to the uptake of CFC‐11 and its export from the subpolar gyre with the North Atlantic Deep Water. We discuss the influence of parameterizations for air‐sea gas exchange and subgrid‐scale processes on the rate of CFC‐11 that enters the North Atlantic Ocean and its dependence on horizontal grid spacing in models from medium (4/3°) to eddy‐permitting (1/3°) horizontal resolution. Model results are compared with observational estimates of tracer inventories in order to evaluate to what degree the simulations capture realistic CFC distributions. While higher resolution is needed to model details of the CFC distribution, for example, in the Deep Western Boundary Current, the medium resolution models are able to simulate quantitatively satisfying CFC inventories in different water masses. Nevertheless, the inventories derived from the medium‐resolution experiments show a critical dependence on details of the parameterization of the mixing effect of mesoscale eddies and on the representation of bottom boundary layer processes. The numerical representation of eddy activity turns out to be of crucial importance in order to obtain modeled CFC inventories in agreement with observed values, which can be achieved either by carefully choosing the mixing parameterization or by applying higher horizontal resolution. The ratio of CFC‐11 being exported southward from the subpolar North Atlantic to the total CFC‐11 inventory in NADW does not vary significantly over the suite of model experiments.
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  • 56
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    Unbekannt
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 30 (12). p. 1614.
    Publikationsdatum: 2018-02-20
    Beschreibung: Shear-wave splitting parameters (fast polarization direction and delay time) are determined using data from LA RISTRA (Colorado pLAteau RIo Grande Rift/Great Plains Seismic TRAnsect), a deployment of broadband seismometers extending from the Great Plains, across the Rio Grande Rift and the Jemez Lineament, to the Colorado Plateau. Results show that the fast polarization directions are sub-parallel to North American absolute plate motion. The largest deviations from the plate motion are observed within the western edge of the Great Plains and in the interior of the Colorado Plateau where lithospheric anisotropy may be significant. Delay times range from 0.8 to 1.8 seconds with an average value of 1.4 seconds; the largest values are along the Jemez Lineament and the Rio Grande Rift which are underlain by an uppermost mantle low velocity zone extending to depths of ∼200 km. The anisotropy beneath the central part of LA RISTRA shows a remarkably consistent pattern with a mean fast direction of 40° ± 6°. Seismic anisotropy can be explained by differential horizontal motion between the North American lithosphere and westerly to southwesterly flow of the asthenospheric mantle. The approximately N-S fast direction found beneath western Texas is similar to that observed beneath the southern rift and may reflect a different dynamic regime.
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  • 57
    Publikationsdatum: 2018-02-20
    Beschreibung: The seasonal and interannual variation in the lower mesospheric subtropical jet (LMSJ) and their dependence on the 11-year solar cycle are studied by comparing observational data with simulations by two general circulation models. In the model simulations, a strengthening of the LMSJs is found in both hemispheres during the winter under the solar maximum condition, similar to the observation. However the model responses are substantially smaller except for one case in the southern hemisphere. It is also found that the stronger LMSJ due to an enhanced solar forcing appears during the period which follows an increasing period of interannual variation. Analysis of the observed seasonal march of the LMSJ in each year shows two different regimes of behavior. For a successful simulation, the model should realistically reproduce the observed interannual variability as well as the climatological mean.
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  • 58
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    AGU (American Geophysical Union)
    In:  Paleoceanography, 18 (2). p. 1047.
    Publikationsdatum: 2016-09-02
    Beschreibung: [1] Using 150 core top samples, we developed a conservative but fairly robust new measure to reconstruct past changes in (maximum) seasonal sea ice distribution in the northern North Atlantic, hitherto a major unknown. The proxy is based on Similarity Maximum Modern-Analog Technique (SIMMAX) estimates of threshold temperatures near the sea surface (SST). Today, almost 100% of all sites with SST 〉2.5°C during summer, 〉0.4° for winters 1978–1987, and 〉0.75°C for Little Ice Age winters lie seaward of the sea ice margin. When applied to 〉60 sediment records of the Last Glacial Maximum, this proxy shows that peak glacial sea ice was far more restricted than in the “classic” CLIMAP Project Members [1981] reconstruction. During glacial summer, sea ice only covered the Arctic Ocean and western Fram Strait. The northern North Atlantic and Nordic Seas were largely ice-free and thus formed a high-latitude moisture source for the continued buildup of continental ice sheets. In contrast, sea ice spread far south across the Iceland Faeroe Ridge during glacial winter, with an inferred patch of sea ice also in the central east Atlantic, near the center of the Azores High. A broad ice-free channel extended from 50° to 60°N, forming an ideal site for large-scale convection of glacial upper North Atlantic Deep Water. The extreme seasonality in glacial sea ice formation and melt in the Nordic Seas implies a major consumption of the regional energy income.
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  • 59
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    Unbekannt
    AMS (American Meteorological Society)
    In:  Journal of Climate, 16 (20). pp. 3371-3382.
    Publikationsdatum: 2017-07-20
    Beschreibung: Recent observational studies have shown that the centers of action of interannual variability of the North Atlantic Oscillation (NAO) were located farther eastward during winters of the period 1978–97 compared to previous decades of the twentieth century. In this study, which focuses on the winter season (December–March), new diagnostics characterizing this shift are presented. Further, the importance of this shift for NAO-related interannual climate variability in the North Atlantic region is discussed. It is shown that an NAO-related eastward shift in variability can be found for a wide range of different parameters like the number of deep cyclones, near-surface air temperature, and turbulent surface heat flux throughout the North Atlantic region. By using a near-surface air temperature dataset that is homogenous with respect to the kind of observations used, it is shown that the eastward shift is not an artifact of changes in observational practices that took place around the late 1970s. Finally, an EOF-based Monte Carlo test is developed to quantify the probability of changes in the spatial structure of interannual NAO variability for a relatively short (20 yr) time series given multivariate “white noise.” It is estimated that the likelihood for differences in the spatial structure of the NAO between two independent 20-yr periods, which are similar (as measured by the angle and pattern correlation between two NAO patterns) to the observed differences, to occur just by chance is about 18%. From the above results it is argued that care has to be taken when conclusions about long-term properties of NAO-related climate variability are being drawn from relatively short recent observational data (e.g., 1978–97).
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  • 60
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    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 30 (2). p. 1050.
    Publikationsdatum: 2018-02-20
    Beschreibung: A high-resolution model of the North Atlantic Ocean is used to examine the potential of chlorofluorocarbon (CFC) inventories for calculating the rate of Labrador Sea Water (LSW) formation. While the simulated CFC-11 inventory and its geographical distribution in 1997 is fairly similar to observations, the model indicates pronounced variations in the history of CFC uptake, reflecting pulsations in LSW renewal in response to changes in wintertime atmospheric conditions. The LSW formation rate based on the volume of newly homogenized water during a winter season varies between 0 Sv and 11 Sv, and it is correlated (with a lag of 1 year) with the North Atlantic Oscillation (NAO) Index. The CFC-based estimate of the mean LSW formation rate is 3.5–4.4 Sv, approximately representing the mean volumetric formation rate (4.3 Sv) for the period 1970–1997.
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  • 61
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    AGU (American Geophysical Union)
    In:  In: The North Atlantic Oscillation: Climate Significance and Environmental Impact. , ed. by Hurrell, J. W., Kushnir, Y., Ottersen, G. and Visbeck, M. Geophysical Monograph Series, 134 . AGU (American Geophysical Union), Washington, DC, pp. 113-146.
    Publikationsdatum: 2012-03-13
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  • 62
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    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 30 (17).
    Publikationsdatum: 2014-02-04
    Beschreibung: Concentrations of dissolved iron (DFe, 0.2μm) were determined at two stations in the Biscay Abyssal Plain (North East Atlantic) in March 2002. DFe concentrations in the surface layer (0.23–0.34 nM) were typical of winter conditions in this area. At 1000 m, DFe concentrations increased to 0.62–0.86 nM. This feature is consistent with the production of DFe by remineralization of the biogenic material. However, at this depth, Mediterranean Outflow Water (MOW) could be an additional source of DFe. Below 2500 m, DFe concentrations were constant (0.75 ± 0.04 nM). An interesting feature of the profiles was the intermediate maximum of DFe (1.19–1.12 nM) around 2000 m, associated with the Labrador Sea Water (LSW). We suggest that the iron enrichment of LSW occurred when this water mass reached the continental margin, likely in the vicinity of the Goban plateau. Vertical distributions were highly dependent on water masses encountered.
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  • 63
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    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Atmospheres, 108 (D14). p. 4407.
    Publikationsdatum: 2019-03-06
    Beschreibung: We present the Met Office Hadley Centre's sea ice and sea surface temperature (SST) data set, HadISST1, and the nighttime marine air temperature (NMAT) data set, HadMAT1. HadISST1 replaces the global sea ice and sea surface temperature (GISST) data sets and is a unique combination of monthly globally complete fields of SST and sea ice concentration on a 1° latitude‐longitude grid from 1871. The companion HadMAT1 runs monthly from 1856 on a 5° latitude‐longitude grid and incorporates new corrections for the effect on NMAT of increasing deck (and hence measurement) heights. HadISST1 and HadMAT1 temperatures are reconstructed using a two‐stage reduced‐space optimal interpolation procedure, followed by superposition of quality‐improved gridded observations onto the reconstructions to restore local detail. The sea ice fields are made more homogeneous by compensating satellite microwave‐based sea ice concentrations for the impact of surface melt effects on retrievals in the Arctic and for algorithm deficiencies in the Antarctic and by making the historical in situ concentrations consistent with the satellite data. SSTs near sea ice are estimated using statistical relationships between SST and sea ice concentration. HadISST1 compares well with other published analyses, capturing trends in global, hemispheric, and regional SST well, containing SST fields with more uniform variance through time and better month‐to‐month persistence than those in GISST. HadMAT1 is more consistent with SST and with collocated land surface air temperatures than previous NMAT data sets.
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  • 64
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    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 108 (B10). p. 2491.
    Publikationsdatum: 2018-05-30
    Beschreibung: The shallow seismogenic portion of subduction zones generates damaging large and great earthquakes. This study provides structural constraints on the seismogenic zone of the Middle America Trench offshore central Costa Rica and insights into the physical and mechanical characteristics controlling seismogenesis. We have located ~300 events that occurred following the MW 6.9, 20 August 1999, Quepos, Costa Rica, underthrusting earthquake using a three-dimensional velocity model and arrival time data recorded by a temporary local network of land and ocean bottom seismometers. We use aftershock locations to define the geometry and characteristics of the seismogenic zone in this region. These events define a plane dipping at 19° that marks the interface between the Cocos Plate and the Panama Block. The majority of aftershocks occur below 10 km and above 30 km depth below sea level, corresponding to 30–35 km and 95 km from the trench axis, respectively. Relative event relocation produces a seismicity pattern similar to that obtained using absolute locations, increasing confidence in the geometry of the seismogenic zone. The aftershock locations spatially correlate with the downdip extension of the oceanic Quepos Plateau and reflect the structure of the main shock rupture asperity. This strengthens an earlier argument that the 1999 Quepos earthquake ruptured specific bathymetric highs on the downgoing plate. We believe that subduction of this highly disrupted seafloor has established a set of conditions which presently limit the seismogenic zone to be between 10 and 35 km below sea level.
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  • 65
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    AGU (American Geophysical Union)
    In:  Eos, Transactions American Geophysical Union, 84 (21). pp. 197-204.
    Publikationsdatum: 2017-02-14
    Beschreibung: Recent measurements and model studies have consistently identified a decreasing trend in the concentration of dissolved O2 in the ocean over the last several decades. This trend has important implications for our understanding of anthropogenic climate change. First, the observed oceanic oxygen changes may be a signal of the beginning of a reorganization of large-scale ocean circulation in response to anthropogenic radiative forcing. Second, the repartitioning of oxygen between the ocean and the atmosphere requires a revision of the current atmospheric carbon budget and the estimates of the terrestrial and oceanic carbon sinks as calculated by the Intergovernmental Panel on Climate Change (IPCC) from measurements of atmospheric O2/N2.
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  • 66
    Publikationsdatum: 2017-01-23
    Beschreibung: The isotopic composition of Nd in present-day deep waters of the central and northeastern Atlantic Ocean is thought to fingerprint mixing of North Atlantic Deep Water with Antarctic Bottom Water. The central Atlantic Romanche and Vema Fracture Zones are considered the most important pathways for deep water exchange between the western and eastern Atlantic basins today. We present new Nd isotope records of the deepwater evolution in the fracture zones obtained from ferromanganese crusts, which are inconsistent with simple water mass mixing alone prior to 3 Ma and require additional inputs from other sources. The new Pb isotope time series from the fracture zones are inexplicable by simple mixing of North Atlantic Deep Water and Antarctic Bottom Water for the entire past 33 Myr. The distinct and relatively invariable Nd and Pb isotope records of deep waters in the fracture zones appear instead to have been controlled to a large extent by contributions from Saharan dust and the Orinoco/Amazon Rivers. Thus the previously observed similarity of Nd and Pb isotope time series from the western and eastern North Atlantic basins is better explainable by direct supply of Labrador Seawater to the eastern basin via a northern pathway rather than by advection of North Atlantic Deep Water via the Romanche and Vema Fracture Zones.
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  • 67
    Publikationsdatum: 2019-09-23
    Beschreibung: The paleoclimatology and paleoceanology of the Late Jurassic and Early Cretaceous are of special interest because this was a time when large amounts of marine organic matter were deposited in sediments that have subsequently become petroleum source rocks. However, because of the lack of outcrops, most studies have concentrated on low latitudes, in particular the Tethys and the “Boreal Realm,” where information has been based largely on material from northwest Germany, the North Sea, and England. These areas were all south of 40°N latitude during the Late Jurassic and Early Cretaceous. We have studied sediment samples of Kimmeridgian (∼154 Ma) to Barremian (∼121 Ma) age from cores taken at sites offshore mid-Norway and in the Barents Sea that lay in a narrow seaway connecting the Tethys with the northern polar ocean. During the Late Jurassic-Early Cretaceous these sites had paleolatitudes of 42–67°N. The Late Jurassic-Early Cretaceous sequences at these sites reflect the global sea-level rise during the Volgian-Hauterivian and a climatic shift from warm humid conditions in Volgian times to arid cold climates in the early Hauterivian. The sediments indicate orbital control of climate, reflected in fluctuations in the clastic influx and variations in carbonate and organic matter production. Trace element concentrations in the Volgian-Berriasian sediments suggest that the central part of the Greenland-Norwegian Seaway might have had suboxic bottom water beneath an oxic water column. Both marine and terrigenous organic matter are present in the seaway sediments. The Volgian-Berriasian strata have unusually high contents of organic carbon and are the source rocks for petroleum and gas fields in the region. The accumulation of organic carbon is attributed to restricted conditions in the seaway during this time of low sea level. It might be that the Greenland-Norwegian segment was the deepest part of the transcontinental seaway, bounded at both ends by relatively shallow swells. The decline in organic matter content of the sediments in the Valanginian-Hauterivian indicates greater ventilation and more active flow through the seaway as the sea level rose. The same benthic foraminifera assemblages are encountered throughout the seaway. Endemic assemblages of arenaceous foraminifera in the Volgian-Berriasian give way to more diverse and cosmopolitan Valanginian-Hauterivian benthic communities that include calcareous species. The foraminiferal assemblages also suggest low oxygen content bottom waters during the earlier Cretaceous, changing to more fully oxygenated conditions later. The calcareous nannoplankton, particularly Crucibiscutum salebrosum, which is rare at low latitudes and abundant in high latitudes, reflect the meridional thermal gradient. They indicate that the Greenland-Norwegian segment of the seaway was north of a subtropical frontal zone that acted as a barrier between the Tethyan and Boreal Realms. This implies the existence of stable climatic belts during the early Valanginian and Hauterivian, significant meridional temperature gradients, and moderate “ice house” conditions.
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  • 68
    Publikationsdatum: 2017-05-10
    Beschreibung: We investigate aragonitic skeletons of the Caribbean sclerosponge Ceratoporella nicholsoni from Jamaica, 20 m below sea level (mbsl), and Pedro Bank, 125 mbsl. We use d18O and Sr/Ca ratios as temperature proxies to reconstruct the Caribbean mixed layer and thermocline temperature history since 1400 A.D. with a decadal time resolution. Our age models are based on U/Th dating and locating of the radiocarbon bomb spike. The modern temperature difference between the two sites is used to tentatively calibrate the C. nicholsoni Sr/Ca thermometer. The resulting calibration points to a temperature sensitivity of Sr/Ca in C. nicholsoni aragonite of about -0.1 mmol/mol/K. Our Sr/Ca records reveal a pronounced warming from the early 19th to the late 20th century, both at 20 and 125 mbsl. Two temperature minima in the shallow water record during the late 17th and early 19th century correspond to the Maunder and Dalton sunspot minima, respectively. Another major cooling occurred in the late 16th century and is not correlatable with a sunspot minimum. The temperature contrast between the two sites decreased from the 14th century to a minimum in the late 17th century and subsequently increased to modern values in the early 19th century. This is interpreted as a long-term deepening and subsequent shoaling of the Caribbean thermocline. The major trends of the Sr/Ca records are reproduced in both specimens but hardly reflected in the d18O records.
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  • 69
    Publikationsdatum: 2018-02-20
    Beschreibung: The total of 13 existing cross-equatorial shipboard current profiling sections taken during the WOCE period between 1990 and 2002 along 35°W are used to determine the mean meridional structure of the zonal top-to-bottom circulation between the Brazilian coast, near 5°S, and 5°N and to estimate mean transports of the individual identified shallow, intermediate and deep current branches. One of the results is that, on the equator, a mean westward Equatorial Intermediate Current below the Equatorial Undercurrent exists.
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  • 70
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    Unbekannt
    AMS (American Meteorological Society)
    In:  Journal of Climate, 16 . pp. 1094-1098.
    Publikationsdatum: 2018-07-24
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  • 71
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    Unbekannt
    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 33 (12). pp. 2719-2737.
    Publikationsdatum: 2018-04-10
    Beschreibung: A new type of ocean general circulation model with simplified physics is described and tested for various simple wind-driven circulation problems. The model consists of the vorticity balance of the depth-averaged flow and a hierarchy of equations for “vertical moments” of density and baroclinic velocity. The first vertical density moment is the (vertically integrated) potential energy, which is used to describe the predominant link between the barotropic and the baroclinic oceanic flow in the presence of sloping topography. Tendency equations for the vertical moments of density and baroclinic velocity and an appropriate truncation of the coupled hierarchy of moments are derived that, together with the barotropic vorticity balance, yield a closed set of equations describing the barotropic–baroclinic interaction (BARBI) model of the oceanic circulation. Idealized companion experiments with a numerical implementation of the BARBI model and a primitive equation model indicate that wave propagation properties and baroclinic adjustments are correctly represented in BARBI in midlatitudes as well as in equatorial latitudes. Furthermore, a set of experiments with a realistic application to the Atlantic/Southern Ocean system reproduces important aspects that have been previously reported by studies of gyre circulations and circumpolar currents using full primitive equation models
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  • 72
    Publikationsdatum: 2019-09-23
    Beschreibung: At least since the middle Miocene (∼16 Ma), subduction erosion has been the dominant process controlling the tectonic evolution of the Pacific margin of Costa Rica. Ocean Drilling Program Site 1042 recovered 16.5 Ma nearshore sediment at ∼3.9 km depth, ∼7 km landward of the trench axis. The overlying Miocene to Quaternary sediment contains benthic foraminifera documenting margin subsidence from upper bathyal (∼200 m) to abyssal (∼2000 m) depth. The rate of subsidence was low during the early to middle Miocene but increased sharply in the late Miocene-early Pliocene (5–6.5 Ma) and at the Pliocene-Pleistocene boundary (2.4 Ma). Foraminifera data, bedding dip, and the geometry of slope sediment indicate that tilting of the forearc occurred coincident with the onset of rapid late Miocene subsidence. Seismic images show that normal faulting is widespread across the continental slope; however, extension by faulting only accounts for a minor amount of the post-6.5 Ma subsidence. Basal tectonic erosion is invoked to explain the subsidence. The short-term rate of removal of rock from the forearc is about 107–123 km3 Myr−1 km−1. Mass removal is a nonsteady state process affecting the chemical balance of the arc: the ocean sediment input, with the short-term erosion rate, is a factor of 10 smaller than the eroded mass input. The low 10Be concentration in the volcanic arc of Costa Rica could be explained by dilution with eroded material. The late Miocene onset of rapid subsidence is coeval with the arrival of the Cocos Ridge at the subduction zone. The underthrusting of thick and thermally younger ocean crust decreased the subduction angle of the slab along a large segment of the margin and changed the dynamic equilibrium of the margin taper. This process may have induced the increase in the rate of subduction erosion and thus the recycling of crustal material to the mantle.
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  • 73
    Publikationsdatum: 2019-09-23
    Beschreibung: We report Sr, Nd and Pb isotopic compositions of sediments and variably altered igneous rocks from ODP Site 801 (Marianas) and ODP Site 1149 (Izu-Bonin). These Sites provide the most complete drilled ocean crust sections located in front of the Mariana and Izu-Bonin trenches and characterize the unmodified isotopic input into these subduction zones. The subducted ocean crust belongs to the oldest (130–167 Ma) in situ Pacific Ocean crust and thus has end-member character with respect to alteration and sediment load. The lithostratigraphic division of sedimentary units at Site 1149 into clays, cherts, lower clays and carbonates with clay is reflected on isotope correlation diagrams. The Pb isotope data of the sediments show much greater variation than previously reported from this region. Particularly noteworthy are zeolite-bearing clays and clay bearing carbonates from the lower Units that have Pb isotopic compositions identical to the Izu Volcanic Front. The basaltic basement samples display variable 87Sr/86Sr ratios at near constant 143Nd/144Nd ratios, indicating mixing with seawater derived Sr. Most basaltic samples from Site 1149 and 801 exhibit highly variable 206Pb/204Pb (17.88–20.00) at near constant 207Pb/204Pb and 208Pb/204Pb ratios. Three samples from Site 801 display the most extreme 206Pb/204Pb (23.70–26.86) and 207Pb/204Pb (15.73–15.83) ratios ever measured in altered MORB reflecting an increase of 238U/204Pb ratios (μ), most likely through addition of seawater derived U. Initial Pb isotopes of most samples overlap with the age corrected field of the Pacific MORB source, thus the increase in μ took place shortly after formation of the crust in most samples. According to our new isotope data the radiogenic end-member of the Izu arc volcanic rocks could either represent Pb from the lower sediment column released from the slab by delayed dewatering or an integrated slab fluid in which 90–95% of the Pb comes from the basaltic crust and 5–10% of the Pb from the sediments. The Pb isotope systematics of the Mariana arc output suggest two component mixing. Both components appear to be input derived with the radiogenic component represented by average Site 801 sediment and the unradiogenic component generated by mixing of ∼80% unaltered crust with ∼20% highly altered crust.
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  • 74
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    Unbekannt
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 30 . pp. 1085-1088.
    Publikationsdatum: 2018-02-20
    Beschreibung: Normalization to a constant salinity (S) is widely used for the adjustment of marine inorganic carbon chemistry data such as total alkalinity (AT) and total dissolved inorganic carbon (CT). This procedure traces back to the earliest studies in marine chemistry, but ignores the influence of riverine input of alkalinity and of dissolution of biogenic carbonates in the ocean. We tested different adjustment possibilities for AT and conclude that in most parts of the surface ocean the normalization concept does not reflect relationships which represent reality. In this paper, we propose a salinity adjustment based on a constant and region-specific term for S = 0, which expresses river run off, upwelling from below the lysocline, calcification, and lateral sea surface water exchange. One application of the normalization concept is its extension to AT and also CT predictions and implementation in models. We give a brief discussion on the usage of such extensions.
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  • 75
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    Unbekannt
    AGU (American Geophysical Union)
    In:  In: Earth's Climate and Orbital Eccentricity: The Marine Isotope Stage 11 Question. , ed. by Droxler, A. W., Poore, R. Z. and Burckle, L. H. Geophysical Monograph, 137 . AGU (American Geophysical Union), Washington, D.C., pp. 87-102. ISBN 9780875909967
    Publikationsdatum: 2019-08-29
    Materialart: Book chapter , PeerReviewed
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  • 76
    facet.materialart.
    Unbekannt
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 30 (12). p. 1643.
    Publikationsdatum: 2018-02-20
    Beschreibung: Submersible investigations of the Cascadia accretionary complex have identified localized venting of methane gas bubbles in association with gas hydrate occurrence. Acoustic profiles of these bubble plumes in the water column in the vicinity of Hydrate Ridge offshore Oregon provide new constraints on the spatial distribution of these gas vents and the fate of the gas in the water column. The gas vent sites remained active over the span of two years, but varied dramatically on time scales of a few hours. All plumes emanated from local topographic highs near the summit of ridge structures. The acoustic images of the bubble plumes in the water column disappear at water depths between 500 to 460 m, independent of the seafloor depth. This coincides with the predicted depth of the gas hydrate stability boundary of 510 to 490 m, suggesting that the presence of a hydrate skin on the bubble surface prevents them from rapid dissolution. The upper limit of the acoustic bubble plumes at 460 m suggests that dissolution of the residual bubbles is relatively rapid above the hydrate stability zone.
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  • 77
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    Unbekannt
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 31 (L04303).
    Publikationsdatum: 2018-02-20
    Beschreibung: We use a global coupled atmosphere-ocean sea-ice model of intermediate complexity to demonstrate that wind-forcing is a crucial element to sustain meridional overturning flow in the Atlantic. Neglecting wind-stress in our multi-century-long simulations leads to a complete shutdown of the conveyor belt circulation. This result may have tremendous impacts for an assessment of the sensitivity of 2-d climate models which typically do not capture wind-driven gyres. It is argued that wind effects may be a key element in determining the fate and length of a collapsed THC state. Possible paleo implications will be discussed.
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  • 78
    facet.materialart.
    Unbekannt
    AGU (American Geophysical Union)
    In:  Paleoceanography, 18 (2). p. 1027.
    Publikationsdatum: 2017-05-10
    Beschreibung: Diatom assemblages were employed to study temporal changes of Siberian river runoff on the Laptev Sea shelf. Using a correlation between freshwater diatoms (%) in core-top sediments and summer surface water salinities from the inner Kara Sea, salinity conditions were reconstructed for a site northeast of the Lena River Delta (present water depth 32 m) since 9 calendar years (cal) ka. The reconstruction indicate a strong, near-coastal, and river-influenced environment at the site until about 8.6 cal ka. Corroborated by comparison with other proxy records from further to the east, surface salinities increased from 9 to 14 until about 7.4 cal ka, owing to ongoing global sea level rise and synchronous southward shift of the coastline. Although riverine water became less influential at the site since then, salinities still varied between 12.5 and 15, particularly during the last 3.5 kyr. These more recent salinity fluctuations agree well with reconstructions from just north of the Lena Delta, emphasizing the strong linkage between shelf hydrography and riverine discharge patterns in Arctic Siberia.
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  • 79
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    Unbekannt
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 30 (23). p. 2204.
    Publikationsdatum: 2019-09-23
    Beschreibung: In the subtropics, estimates of upper-ocean nitrate supply by turbulent mixing have been found insufficent to balance estimated nutrient loss through organic-matter export. Most mixing-rate estimates as well as numerical turbulence closure schemes commonly employed in numerical models have, however, neglected salt-finger induced mixing. Here we examine the potential contribution of salt-finger induced mixing to nutrient fluxes. Our model results suggest that salt-fingering instabilities generate substantial nutrient fluxes (on average 0.03 mol N m−2 yr−1) which are of similar magnitude as fluxes associated with mechanically induced turbulence or with mesoscale eddies. Because salt-fingering activity depends on the proportion of temperature versus salinity effects on stratification rather than on the stability of stratification itself, its sensitivity to climate change will differ from that of “ordinary” mixing processes and needs to be considered in the context of global change.
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  • 80
    facet.materialart.
    Unbekannt
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 108 (B8). p. 2372.
    Publikationsdatum: 2018-04-25
    Beschreibung: Depth migration of seismic reflection profiles across the Mediterranean Ridge accretionary complex between the African and Eurasian blocks illustrates profound variations in the geometry and internal structure along strike. Structural interpretations of four cross sections, together with bathymetric and acoustic surface information and drilling data, are used to volumetrically balance the amount of subduction versus accretion with time. Results suggest the existence of three distinct scenarios, with a jump in décollement in the west, intense backthrusting in the central part between Libya and Crete, and transcurrent tectonism in the east. The onset of accretion coincides with exhumation of thrust sheets (∼19 Ma), followed by rapid sediment accretion with thick, evaporite-bearing incoming successions facilitating outward growth of the wedge. The minimum rate of accretion (20–25% of the total sediment supply) is observed in the central portion where the ridge suffers maximum deformation. Here the indenting leading edge of the African Plate apparently forces the sediment into subduction, or local underplating. In contrast, an estimated 40–60% of the available sedimentary input was accreted in the western domain where collision is less accentuated. The results support the hypothesis that highly destructive forearc collisional events, like slab break off and exhumation of thrust sheets, can be followed by periods of accretion and continuous growth of accretionary wedges.
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  • 81
    facet.materialart.
    Unbekannt
    AGU (American Geophysical Union)
    In:  Paleoceanography, 18 (2). p. 1036.
    Publikationsdatum: 2017-05-10
    Beschreibung: A multiparameter-based interpretation of sediment records from the northeast Atlantic and the western Nordic seas suggests that during the last 500,000 years only in marine isotopes stage (MIS) 11, 5e, and 1 were there somewhat comparable interglacial boundary conditions in both regions, i.e., strongly reduced occurrence of iceberg-rafted debris (IRD) and high carbonate bioproductivity. Although the northeast Atlantic experienced such conditions during all peak interglaciations, with the exception of MIS 7, planktic foraminiferal δ18O from this region would still indicate that significantly colder sea surface temperatures (SST) prevailed during MIS 11 than during MIS 9, 5e, and 1. This assumption is corroborated by a continuous input of IRD into the western Nordic seas during MIS 11, implying a much steeper SST gradient between the polar and subpolar region and an overall reduced thermohaline activity in the polar latitudes. The iceberg proxy also reveals that maximum IRD discharge always happened during the final phase of glaciation and into early deglaciation (terminations). As these IRD records from the two regions are characterized by a high time coherency, it is concluded that short-term variability is a persistent feature of the glacial climate system.
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  • 82
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    Unbekannt
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 30 (9). pp. 1473-1476.
    Publikationsdatum: 2018-02-20
    Beschreibung: North Atlantic/Arctic ocean and sea ice variability for the period 1948–2001 is studied using a global Ocean General Circulation Model coupled to a dynamic/thermodynamic sea ice model forced by daily NCEP/NCAR reanalysis data [Kalnay et al., 1996]. Variability of Arctic sea ice properties is analysed, in particular the formation and propagation of sea ice thickness anomalies that are communicated via Fram Strait into the North Atlantic. These export events led to the Great Salinity Anomalies (GSA) of the 1970s, 1980s and 1990s in the Labrador Sea (LS). All GSAs were found to be remotely excited in the Arctic, rather than by local atmospheric forcing over the LS. Sea ice and fresh water exports through the Canadian Archipelago (CAA) are found to be only of minor importance, except for the 1990s GSA. Part of the anomalies are tracked to the Newfoundland Basin, where they enter the North Atlantic Current. The experiments indicate only a minor impact of a single GSA event on the strength of the North Atlantic Thermohaline Circulation (THC).
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  • 83
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    Unbekannt
    AMS (American Meteorological Society)
    In:  Journal of Climate, - (16). pp. 443-460.
    Publikationsdatum: 2020-08-04
    Beschreibung: A simple stochastic atmosphere model is coupled to a realistic model of the North Atlantic Ocean. A north–south SST dipole, with its zero line centered along the subpolar front, influences the atmosphere model, which in turn forces the ocean model by surface fluxes related to the North Atlantic Oscillation. The coupled system exhibits a damped decadal oscillation associated with the adjustment through the ocean model to the changing surface forcing. The oscillation consists of a fast wind-driven, positive feedback of the ocean and a delayed negative feedback orchestrated by overturning circulation anomalies. The positive feedback turns out to be necessary to distinguish the coupled oscillation from that in a model without any influence from the ocean to the atmosphere. Using a novel diagnosing technique, it is possible to rule out the importance of baroclinic wave processes for determining the period of the oscillation, and to show the important role played by anomalous geostrophic advection in sustaining the oscillation.
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  • 84
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    Unbekannt
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 30 (2). n/a-n/a.
    Publikationsdatum: 2016-03-30
    Beschreibung: The marine production, cycling, and air-sea gas exchange of nitrous oxide (N2O) are simulated in a coupled climate-biogeochemical model of reduced complexity. The model gives a good representation of the large-scale features of the observed oceanic N2O distribution and emissions to the atmosphere. The transient behavior of the model is tested for the Younger Dryas (Y-D) cold period (12,700–11,550 BP), which is simulated by releasing a freshwater pulse into the North Atlantic, causing a temporary collapse of the model's Atlantic thermohaline circulation (THC). A temporary drop in atmospheric N2O of about 10 ppb results, while ice-core measurements show a total drop of 25 to 30 ppb. This suggests that terrestrial changes have also contributed to the observed variations. The main cause of the modeled reduction in atmospheric N2O is increased oceanic storage in the short-term and a reduction of new production in the long-term due to increased stratification.
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  • 85
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    Unbekannt
    AGU (American Geophysical Union)
    In:  In: Inside the Subduction Factory. , ed. by Eiler, J. Geophysical Monograph Series, 138 . AGU (American Geophysical Union), Washington, D.C., pp. 223-276. ISBN 0-87590-997-3
    Publikationsdatum: 2018-10-08
    Materialart: Book chapter , NonPeerReviewed
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  • 86
    Publikationsdatum: 2022-03-04
    Beschreibung: Subduction erosion is commonly associated with strong interplate coupling and a consequent abrasion of the upper plate. Northern Chile is an often cited example of a strongly coupled erosional margin. Its crystalline basement is inferred to form a strong upper plate, the trench axis contains little detectable sediment, and the subducting lower plate has a high‐relief horst‐graben topography. With little water‐rich sediment to reduce interplate friction, the high relief of an igneous ocean crust thrust beneath continental basement should generate high friction interplate abrasion. However, a prestack depth‐migrated seismic record images slope debris that collects in a frontal prism. This debris, including ∼30% pore fluid, fills subducting grabens and is subsequently incorporated into an ∼1.5‐km‐thick interplate reflective layer. The subduction zone thrust passes through the upper part of this layer. Interplate seismicity and taper analyses indicate basal friction at levels that are common in sedimented convergent margins. The continued growth of lower plate grabens after subduction probably accommodates upper plate material, a process that erodes the upper plate. Erosion is aided by weakening of the upper plate rock framework beneath the continental slope. This erosion undermines the upper plate and tips it seaward thereby steepening the continental slope which induces midslope gravity tectonics. Despite sediment starvation, a frontal prism constructed of remolded slope debris elevates pore pressure to reduce interplate friction. Coeval erosion and prism building control the size of the frontal prism. Processes other than high friction abrasion best explain subduction erosion along northern Chile.
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  • 87
    Publikationsdatum: 2022-03-07
    Beschreibung: The Musicians Seamount Province is a group of volcanic elongated ridges (VERs) and single seamounts located north of the Hawaiian Chain. A 327° trending seamount chain defines the western part of the province and has been interpreted as the expression of a Cretaceous hot spot beneath the northward moving Pacific Plate. To the east, elongated E-W striking ridges dominate the morphology. In 1999, wide-angle seismic data were collected across two 400 km long VERs. We present tomographic images of the volcanic edifices, which indicate that crustal thickening occurs in oceanic layer 2 rather than in layer 3. This extrusive style of volcanism appears to strongly contrast with the formation processes of aseismic ridges, where crustal thickening is mostly accommodated by intrusive underplating. High-resolution bathymetry was also collected, which yields a detailed image of the morphology of the VERs. From the occurrence of flat-top guyots and from the unique geomorphologic setting, two independent age constraints for the Pacific crust during the Cretaceous “quiet” zone are obtained, allowing a tectonic reconstruction for the formation of the Musicians VERs. Hot spot-ridge interaction leads to asthenosphere channeling from the plume to the nearby spreading center over a maximum distance of 400 km. The Musicians VERs were formed by mainly extrusive volcanism on top of this melt-generating channel. The proposed formation model may be applicable to a number of observed volcanic ridges in the Pacific, including the Tuamotu Isles, the eastern portion of the Foundation chain, and the western termination of the Salas y Gomez seamount chain.
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  • 88
    Publikationsdatum: 2022-03-07
    Beschreibung: Abundant grabens transect the volcano Alba Patera. Their complex geometry and formation mechanisms are still poorly understood. Tectonic processes and magmatic intrusions are responsible for these long surface features. Cross-cutting relationships of the grabens show radial fractures that were formed during early stages and were progressively overprinted by concentric fractures on the mid and upper flanks of the volcano. Two modeling methods are used to understand the formation of the observed structures and to evaluate their implications for hidden subvolcanic processes. Surface deformation and fault arrangements predicted in finite element models are compared to the graben systems observed in Viking images. The orientation and position of the concentric grabens are found to be best reproduced by local crustal subsidence, superimposed on a regional NW-SE oriented extension with decreasing magnitude from south to north. In analogue sandbox models we also simulate surface structures of arrangements that almost perfectly mimic the observed lineaments on Alba Patera. Formation of the grabens spans a period on the order of a billion years, suggesting long-term geodynamic processes to be responsible for the subsidence of the central Alba Patera area. The progressive change toward higher concentricity is likely resultant from an increase in density in the crust by accumulation of intrusive material and cooling, thus causing subsidence of the region above this volcanic root.
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  • 89
    Publikationsdatum: 2022-03-10
    Beschreibung: Group and phase velocities of fundamental mode Rayleigh waves, in the period range of 10 to 70 s, are obtained for southern and northern Tibet. Significant variations in crustal velocity structure are found. The group velocity minimum for Tibet occurs at ∼33 s and the minimum is ∼0.12 km/s lower for southern Tibet than for northern Tibet. At periods greater than 50 s, however, group velocities are up to 0.2 km/s faster in southern Tibet. The group and phase velocities are inverted for layered S wave models. The dispersion observations in southern Tibet can only be fit with a low‐velocity layer in the middle crust. In contrast, the velocity models for northern Tibet do not require any low‐velocity zone in the crust. The S wave velocity of the lower crust of southern Tibet is ∼0.2 km/s faster than the lower crust of northern Tibet. In southern Tibet the sub‐Moho velocity increases with a positive gradient that is similar to a shield, while there is no velocity gradient beneath northern Tibet. The high‐velocity lower crust of southern Tibet is consistent with the underthrusting of Indian continental lithosphere. The most plausible explanation of the mid‐crustal low velocity zone is the presence of crustal melt resulting from H2O‐saturated melting of the interplate shear zone between the underthrusting Indian crust and overflowing Asian crust. The lack of a pronounced crustal low‐velocity zone in northern Tibet is an indication of a relatively dry crust. The low S wave velocity in the lower crust of northern Tibet is interpreted to be due to a combination of compositional differences, high temperatures, presumably caused by a high mantle heat flux, and possibly small amounts of partial melt. Combined with all available observations in Tibet, the new surface wave results are consistent with a hot and weak upper mantle beneath northern Tibet.
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  • 90
    Publikationsdatum: 2022-03-10
    Beschreibung: We have studied a nonvolcanic margin, the West Iberia margin, to understand how the mechanisms of thinning evolve with increasing extension. We present a coincident prestack depth‐migrated seismic section and a wide‐angle profile across a Mesozoic abandoned rift, the Galicia Interior Basin (GIB). The data show that the basin is asymmetric, with major faults dipping to the east. The velocity structure at both basin flanks is different, suggesting that the basin formed along a Paleozoic terrain boundary. The ratios of upper to lower crustal thickness and tectonic structure are used to infer the mechanisms of extension. At the rift flanks (stretching factor, β ≤ 2) the ratio is fairly constant, indicating that stretching of upper and lower crust was uniform. Toward the center of the basin (β ∼ 3.5–5.5), fault‐block size decreases as the crust thins and faults reach progressively deeper crustal levels, indicating a switch from ductile to brittle behavior of the lower crust. At β ≥ 3.5, faults exhume lower crustal rocks to shallow levels, creating an excess of lower crust within their footwalls. We infer that initially, extension occurred by large‐scale uniform pure shear but as extension increased, it switched to simple shear along deep penetrating faults as most of the crust was brittle. The predominant brittle deformation might have driven small‐scale flow (≤40 km) of the deepest crust to accommodate fault offsets, resulting in a smooth Moho topography. The GIB might provide a type example of nonvolcanic rifting of cold and thin crust.
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  • 91
    Publikationsdatum: 2022-03-10
    Beschreibung: The Cocos and Malpelo Volcanic Ridges are blocks of thickened oceanic crust thought to be the result of the interaction between the Galapagos hot spot and the Cocos‐Nazca Spreading Center during the last 20 m.y. In this work we investigate the seismic structure of these two aseismic ridges along three wide‐angle transects acquired during the Panama basin and Galapagos plume—New Investigations of Intraplate magmatism (PAGANINI)‐1999 experiment. A two‐dimensional velocity field with the Moho geometry is obtained using joint refraction/reflection travel time tomography, and the uncertainty and robustness of the results are estimated by performing a Monte Carlo‐type analysis. Our results show that the maximum crustal thickness along these profiles ranges from ∼16.5 km (southern Cocos) to ∼19 km (northern Cocos and Malpelo). Oceanic layer 2 thickness is quite uniform regardless of total crustal thickness variations; crustal thickening is mainly accommodated by layer 3. These observations are shown to be consistent with gravity data. The variation of layer 3 velocities is similar along all profiles, being lower where crust is thicker. This leads to an overall anticorrelation between crustal thickness and bulk lower crustal velocity. Since this anticorrelation is contrary to crustal thickening resulting from passive upwelling of abnormally hot mantle, it is necessary to consider active upwelling components and/or some compositional heterogeneities in the mantle source. The NW limit of the Malpelo Ridge shows a dramatic crustal thinning and displays high lower crustal velocities and a poorly defined crust‐mantle boundary, suggesting that differential motion along the Coiba transform fault probably separated Regina and Malpelo Ridges.
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  • 92
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    Unbekannt
    Kluwer
    In:  Fossil and recent biofilms. A natural history of life on Earth
    Publikationsdatum: 2022-03-21
    Materialart: info:eu-repo/semantics/bookPart
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  • 93
    Publikationsdatum: 2023-09-19
    Beschreibung: During Meteor cruise 55 a strong undersaturation of surface seawater with respect to atmospheric CO2 was found in the Amazon River plume which is advected into the surface circulation of the tropical Atlantic. A conservative estimate of the plume-related CO2 sink in the tropical Atlantic yields a net air-sea flux of 0.014 ± 0.005 Pg C yr−1. The corresponding average CO2 flux density of 1.35 mmol m−2 d−1 is of similar magnitude but opposite sign as found elsewhere in the slightly supersaturated tropical Atlantic illustrating the significant impact of the Amazon on the biogeochemistry of large ocean areas. The dramatic change of the CO2 saturation state from highly supersaturated river waters to markedly undersaturated surface waters in the plume can be explained by a combination of the effects of CO2 outgassing from river water, of mixing between river and ocean water on the CO2 system properties, and of strong biological carbon drawdown in the plume.
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