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Datasets with PANGAEA technical keyword @ORFOISatBENGAL

Mostrando recursos 1 - 20 de 5.587

  1. Stable oxygen isotope in opal and seawater

    Anders, Tania-Maria
    Sauerstoff-Isotopenuntersuchungen wurden an frischem Diatomeenopal aus der obersten Wassersäule, Diatomeen aus Kulturen, sowie an sedimentärem Diatomeenopal durchgeführt, um die Anwendbarkeit von d18O-Signalen aus marinen Diatomeen für paläozeanographische Fragestellungen zu untersuchen. Diatomeenopal ist, besonders aus Sedimentproben, schwierig anzureichern. Physikalische und chemische Verfahren müssen mehrfach angewendet werden, um Proben zu erhalten, die den für Sauerstoff-Isotopenmessungen erforderlichen Reinheitsgrad aufweisen. Die Ausgangskonzentration an Diatomeen im Probenmaterial wirkt sich hierbei erheblich auf den Erfolg der Reinigung aus. Verläßliche und reproduzierbare d18O-Werte können nur an sehr reinen Diatomeenproben bestimmt werden. Mittels mikroskopischer Untersuchungen (Durchlichtmikroskopie, Rasterelektronenrnikroskopie), Röntgendiffraktametrie und geochernischer Analysen am ICP-MS können z.T. Art und Menge von Verunreinigungen...

  2. Pteropoda abundances in multinet samples

    Schiebel, Ralf
    The vertical flux and sedimentation rate of planktic foraminiferal tests are quantified and a global planktic foraminiferal CaCO3 budget is presented. Test and calcite flux rates are calculated according to the distribution of species obtained from multinet and sediment trap samples. Modern planktic foraminiferal population dynamics are discussed as a prerequisite for the quantification of the calcite budget, highlighting the importance of ecological, autecological (e.g., reproduction), and biogeochemical conditions that determine the presence or absence of species. To complete the open-marine, particulate CaCO3 inventory, the contribution of coccolithophores, pteropods, and calcareous dinophytes is discussed. Based on the studied regions, the...

  3. A review of Si particle fluxes in the modern ocean

    Ragueneau, Olivier; Tréguer, Paul; Leynaert, Aude; Anderson, Robert F; Brzezinski, Mark A; DeMaster, David J; Dugdale, Richard; Dymond, Jack R; Fischer, Gerhard; Francois, Roger; Heinze, Christoph; Maier-Reimer, Ernst; Martin-Jézéquel, Véronique; Nelson, David M; Quéguiner, Bernard
    Due to the major role played by diatoms in the biological pump of CO2, and to the presence of silica-rich sediments in areas that play a major role in air-sea CO2 exchange (e.g. the Southern Ocean and the Equatorial Pacific), opal has a strong potential as a proxy for paleoproductivity reconstructions. However, because of spatial variations in the biogenic silica preservation, and in the degree of coupling between the marine Si and C biogeochemical cycles, paleoreconstructions are not straitghtforward. A better calibration of this proxy in the modern ocean is required, which needs a good understanding of the mechanisms that...

  4. Physical oceanography during POLARSTERN cruise ANT-XVII/4

    Kuhn, Gerhard; Usbeck, Regina

  5. Pigments of sediment cores of the Northwest European Continental Margin

    Pfannkuche, Olaf; Soltwedel, Thomas
    In the context of the European OMEX Programme this investigation focused on gradients in the biomass and activity of the small benthic size spectrum along a transect across the Goban Spur from the outer Celtic Sea into Porcupine Abyssal Plain. The effects of food pulses (seasonal, episodic) on this part of the benthic size spectrum were investigated. Sediments sampled during eight expeditions at different seasons covering a range from 200 m to 4800 m water depth were assayed with biochemical bulk measurements: determinations of chloroplastic pigment equivalents (CPE), the sum of chlorophyll a and its breakdown products, provide information concerning...

  6. Calcareous dinoflagellate cycst in the mid-Cenomanian Boreal realm

    Wendler, Jens E; Gräfe, Kai-Uwe; Willems, Helmut
    A transect from the bathyal to proximal shelf facies of the Boreal Realm was investigated to compare spatial and temporal distribution changes of calcareous dinoflagellate cysts (c-dinocysts) throughout the mid-Cenomanian in order to gain information on the ecology of these organisms. Pithonelloideae dominated the cyst assemblages to more than 95% on the shelf, a prevalence that can be observed throughout most of the Upper Cretaceous. The affinity of this group with the dinoflagellates, which is still controversially discussed, can be confirmed, based on evidence from morphological features and distribution patterns. The consistent prevalence of Pithonella sphaerica and P. ovalis in...

  7. Global compilation of benthic data sets I

    Seiter, Katherina; Hensen, Christian; Schröter, Jürgen; Zabel, Matthias
    Approaches to quantify the organic carbon accumulation on a global scale generally do not consider the small-scale variability of sedimentary and oceanographic boundary conditions along continental margins. In this study, we present a new approach to regionalize the total organic carbon (TOC) content in surface sediments (<5 cm sediment depth). It is based on a compilation of more than 5500 single measurements from various sources. Global TOC distribution was determined by the application of a combined qualitative and quantitative-geostatistical method. Overall, 33 benthic TOC-based provinces were defined and used to process the global distribution pattern of the TOC content in...

  8. Global data compilation of benthic data sets II

    Seiter, Katherina; Hensen, Christian; Zabel, Matthias
    In this study we present a global distribution pattern and budget of the minimum flux of particulate organic carbon to the sea floor (J POC alpha). The estimations are based on regionally specific correlations between the diffusive oxygen flux across the sediment-water interface, the total organic carbon content in surface sediments, and the oxygen concentration in bottom waters. For this, we modified the principal equation of Cai and Reimers [1995] as a basic monod reaction rate, applied within 11 regions where in situ measurements of diffusive oxygen uptake exist. By application of the resulting transfer functions to other regions with...

  9. Planktic foraminiferal populations and test flux in the eastern North Atlantic Ocean

    Schiebel, Ralf; Hemleben, Christoph
    Planktic foraminiferal assemblages vary in response to seasonal fluctuations of hydrographic properties, between water masses, and after periodical changes and episodic events (e.g. reproduction, storms). Distinct annual variability of the planktic foraminiferal flux is also known from sediment trap data. In this paper we discuss the short-term impacts on interannual flux rates based on data from opening-closing net hauls obtained between the ocean surface and 500 m water depth. Data were recorded during April, May, June, and August at around 47°N, 20°W (BIOTRANS) in 1988, 1989, 1990, 1992, 1993, and during May 1989 and 1992 at 57°N, 20-22°W. Species assemblages...

  10. Planktic foraminiferal populations and test flux in the eastern North Atlantic Ocean

    Schiebel, Ralf; Hemleben, Christoph
    Planktic foraminiferal assemblages vary in response to seasonal fluctuations of hydrographic properties, between water masses, and after periodical changes and episodic events (e.g. reproduction, storms). Distinct annual variability of the planktic foraminiferal flux is also known from sediment trap data. In this paper we discuss the short-term impacts on interannual flux rates based on data from opening-closing net hauls obtained between the ocean surface and 500 m water depth. Data were recorded during April, May, June, and August at around 47°N, 20°W (BIOTRANS) in 1988, 1989, 1990, 1992, 1993, and during May 1989 and 1992 at 57°N, 20-22°W. Species assemblages...

  11. Stable isotope record of Cibicidoides spp. from early and middle Miocene sediments

    Wright, James D; Miller, Kenneth G; Fairbanks, Richard G
    The middle Miocene delta18O increase represents a fundamental change in the ocean-atmosphere system which, like late Pleistocene climates, may be related to deepwater circulation patterns. There has been some debate concerning the early to early middle Miocene deepwater circulation patterns. Specifically, recent discussions have focused on the relative roles of Northern Component Water (NCW) production and warm, saline deep water originating in the eastern Tethys. Our time series and time slice reconstructions indicate that NCW and Tethyan outflow water, two relatively warm deepwater masses, were produced from ~20 to 16 Ma. NCW was produced again from 12.5 to 10.5 Ma....

  12. Ge/Si record of marine biogenic opal

    Shemesh, Aldo; Mortlock, Richard A; Froelich, Philip N
    We have determined germanium/silicon ratios in purified diatoms and radiolarians from siliceous sediments in Holocene core tops, one late Pleistocene piston core, and four high-latitude Southern Ocean Deep Sea Drilling Project (DSDP) sites ranging in age from Holocene to Oligocene. High-latitude Holocene diatoms in the 10- to 38-µm size fraction ([Ge/Si]opal = 0.693 +/- 0.039 * 10**-6) faithfully record the present oceanic ratio ([Ge/Si]seawater = 0.699 +/- 0.004 * 10**-6). This confirms that diatoms from siliceous oozes are monitors of seawater Ge/Si and may record past changes in rates of delivery of weathering products to the sea from continental and...

  13. Upper Eocene to Oligocene strontium, carbon and oxygen isotope record of DSDP holes

    Miller, Kenneth G; Feigenson, Mark D; Kent, Dennis V; Olsson, Richard K
    We improved upper Eocene to Oligocene deep-sea chronostratigraphic control by integrating isotope (87Sr/86Sr, delta18O, delta13C) stratigraphy and magnetostratigraphy. Most previous attempts to establish the timing of isotope fluctuations have relied upon biostratigraphic age estimates which have uncertainties of 0.5 to over 4.0 m.y. Deep Sea Drilling Project (DSDP) Site 522 contains the best available upper Eocene to Oligocene magnetostratigraphic record which allows first-order correlations of isotope records (87Sr/86Sr, delta18O, delta13C) to the Geomagnetic Polarity Time Scale (GPTS). Empirical calibrations between the 87Sr/86Sr of foraminifera and magnetochronology at Site 522 allow more precise correlation of ,unknown' samples with the GPTS. For...

  14. Comparison of glacial/interglacial carbonate concentrations in Atlantic sediments

    Balsam, William L; McCoy, F M J
    To assess the regional effects of glaciation on sedimentation in the Atlantic Ocean we compare sediment types, distributions, and rates between Recent (core top) and last glacial maximum (LGM: ~18,000 years B.P.) stratigraphic levels. Based upon smear slides and carbonate analyses in 178 cores we find that glacial age carbonate content is generally lower than Recent. During both the Recent and LGM, carbonate content shows an east/west asymmetry with western basins exhibiting lower carbonate values. Input of ice-rafted detritus into the North Atlantic during LGM time interrupts this topographic control on carbonate distribution considerably farther south than at present; in...

  15. Calcium carbonate global LGM Burial rate data

    Catubig, Nina R; Archer, David E; Francois, Roger; deMenocal, Peter B; Howard, William R; Yu, Ein-Fen
    Global databases of calcium carbonate concentrations and mass accumulation rates in Holocene and last glacial maximum sediments were used to estimate the deep-sea sedimentary calcium carbonate burial rate during these two time intervals. Sparse calcite mass accumulation rate data were extrapolated across regions of varying calcium carbonate concentration using a gridded map of calcium carbonate concentrations and the assumption that accumulation of noncarbonate material is uncorrelated with calcite concentration within some geographical region. Mean noncarbonate accumulation rates were estimated within each of nine regions, determined by the distribution and nature of the accumulation rate data. For core-top sediments the regions...

  16. Age determination of North Atlantic sediment cores

    Bard, Édouard; Fairbanks, Richard G; Maurice, Pierre; Duprat, Josette M; Moyes, Jean; Duplessy, Jean-Claude
    Coupled measurements of delta18O and accelerator mass spectrometry (AMS) 14C in a particular species of planktonic foraminifera may be used to calculate sea-level estimates for the last deglaciation. Of critical importance for this type of study is a knowledge of the seasonality of foraminiferal growth, which can be provided by delta18O measurements of modern shells (core tops, plankton tows). Isotopic (delta18O, AMS-14C dating) and faunal records (transfer function sea surface temperature) were obtained from two cores in the North Atlantic at about 37°N. The locations were chosen to obtain high sedimentation rate records removed from the major ice-melt discharge areas...

  17. Age determinations on sediment cores from the North Atlantic

    Bond, Gerard C; Heinrich, Hartmut; Broecker, Wallace S; Labeyrie, Laurent D; McManus, Jerry F; Andrews, John T; Huson, S; Jantschik, Ruediger; Clasen, Silke; Simet, Christine; Tedesco, Kathy; Klas, Mieczyslawa; Bonani, Georges; Ivy, Susan
    Sediments in the North Atlantic ocean contain as eries of layers that are rich in ice-rafted debris and unusally poor in foraminifera. Here we present evidence that the most recent six of the 'Heinrich layers', deposited between 14,000 and 70,000 years ago, record marked decreases in sea surface temperature and salinity, decreases in the flux of planktonic forminifera to the sediments, and short-lived, massive discharges of icebergs originating in eastern Canada. The path of the icebergs, clearly marked by the presence of ice-rafted detrital carbonate, can be traced for more than 3,000 km - a remarkable distance, attesting to extreme...

  18. Particle flux in the NE Atlantic as recorded by sediment traps

    Lampitt, Richard Stephen; Bett, Brian J; Kiriakoulakis, Kostas; Popova, E E; Ragueneau, Olivier; Vangriesheim, Annick; Wolff, George A
    Downward particle flux was measured using sediment traps at various depths over the Porcupine Abyssal Plain (water depth ab. 4850 m) for prolonged periods from 1989 to 1999. A strong seasonal pattern of flux was evident reaching a maximum in mid-summer. The composition of the material changed with depth, reflecting the processes of remineralisation and dissolution as the material sank through the water column. However, there was surprisingly little seasonal variation in its composition to reflect changes in the biology of the euphotic zone. Currents at the site have a strong tidal component with speeds almost always less than 15...

  19. Biogenic silica and silicic acid benthic fluxes of a North-eastern Atlantic Abyssal Locality

    Ragueneau, Olivier; Gallinari, Morgane; Corrin, Lydie; Grandel, Sibylle; Hall, Per; Hauvespre, Anne; Lampitt, Richard Stephen; Rickert, Dirk; Ståhl, Henrik; Tengberg, Anders; Witbaard, Rob
    Within the framework of the EU-funded BENGAL programme, the effects of seasonality on biogenic silica early diagenesis have been studied at the Porcupine Abyssal Plain (PAP), an abyssal locality located in the northeast Atlantic Ocean. Nine cruises were carried out between August 1996 and August 1998. Silicic acid (DSi) increased downward from 46.2 to 213 µM (mean of 27 profiles). Biogenic silica (BSi) decreased from ca. 2% near the sediment-water interface to <1% at depth. Benthic silicic acid fluxes as measured from benthic chambers were close to those estimated from non-linear DSi porewater gradients. Some 90% of the dissolution occurred...

  20. Size distribution of Holocene planktic foraminifer assemblages

    Schmidt, Daniela N; Renaud, Sabrina; Bollmann, Jörg; Schiebel, Ralf; Thierstein, Hans R
    The size of any organism is influenced by the surrounding ecological conditions. In this study, we investigate the effects of such factors on the size spectra of planktic foraminiferal assemblages from Holocene surface sediments. We analyzed assemblages from 69 Holocene samples, which cover the major physical and chemical gradients of the oceans. On a global scale, the range of sizes in assemblages triples from the poles to the tropics. This general temperature-related size increase is interrupted by smaller sizes at temperatures characteristic of the polar and subtropical fronts, at 2°C and 17°C, respectively, as well as in upwelling areas. On...

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