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Datasets with PANGAEA technical keyword @ORFOISatPorosity

Mostrando recursos 1 - 20 de 2.235

  1. Alkenone analyses of sediment cores from the western Arabian Sea

    Budziak, Dörte
    Records of total organic carbon (TOC) and C37 alkenones were used as indicators for past primary productivity in the western and eastern Arabian Sea. Data from GeoB 3005, an open ocean site in the western Arabian Sea upwelling area, are compared with similar records of GeoB 3007 from the Owen Ridge, Ocean Drilling Program (ODP) Site 723 from the continental margin off Oman and MD 900963 from the eastern Arabian Sea. TOC/C37 alkenone records together with other proxies used to reconstruct upwelling intensity, indicate periods of high productivity in tune with precessional forcing all over the Arabian Sea. Based on...

  2. Geochemistry, fluxes and nitrogen isotopic composition data of traps LP1 and EBC2-1 and cores GeoB4242-4 and Geo4301-1

    Freudenthal, Tim; Neuer, Susanne; Meggers, Helge; Davenport, Robert; Wefer, Gerold
    We compare total and biogenic particle fluxes and stable nitrogen isotope ratios (d15N) at three mooring sites along a productivity gradient in the Canary Islands region with surface sediment accumulation rates and sedimentary d15N. Higher particle fluxes and sediment accumulation rates, and lower d15N were observed in the upwelling influenced eastern boundary region (EBC) compared to the oligotrophic sites north of Gran Canaria [European Station for Time-Series in the Ocean, Canary Islands (ESTOC]] and north of La Palma (LP). The impact of organic matter degradation and lateral particle advection on sediment accumulation was quantified with respect to the multi-year flux...

  3. Geochemistry and soil characteristics of sediment core GeoB4234

    Freudenthal, Tim; Wagner, Thomas; Wenzhöfer, Frank; Zabel, Matthias; Wefer, Gerold
    Stable isotopes of sedimentary nitrogen and organic carbon are widely used as proxy variables for biogeochemical parameters and processes in the water column. In order to investigate alterations of the primary isotopic signal by sedimentary diagenetic processes, we determined concentrations and isotopic compositions of inorganic nitrogen (IN), organic nitrogen (ON), total nitrogen (TN), and total organic carbon (TOC) on one short core recovered from sediments of the eastern subtropical Atlantic, between the Canary Islands and the Moroccan coast. Changes with depth in concentration and isotopic composition of the different fractions were related to early diagenetic conditions indicated by pore water...

  4. Alkenone and foraminifera records from sediment samples off Namibia

    Mollenhauer, Gesine; Eglinton, Timothy I; Ohkouchi, Naohiko; Schneider, Ralph R; Müller, Peter J; Grootes, Pieter Meiert; Rullkötter, Jürgen
    Radiocarbon stratigraphy is an essential tool for high resolution paleoceanographic studies. Age models based on radiocarbon ages of foraminifera are commonly applied to a wide range of geochemical studies, including the investigation of temporal leads and lags. The critical assumption is that temporal coupling between foraminifera and other sediment constituents, including specific molecular organic compounds (biomarkers) of marine phytoplankton, e.g. alkenones, is maintained in the sediments. To test this critical assumption in the Benguela upwelling area, we have determined radiocarbon ages of total C37-C39 alkenones in 20 samples from two gravity cores and three multicorer cores. The cores were retrieved from...

  5. Long time-series benthic observation at station DYFAMED

    Guidi-Guilvard, Laurence D
    In 1990, a benthic component to the DYFAMED (dynamics of fluxes in the Mediterranean) program, the DYFAMED-BENTHOS survey, was established to investigate the possible coupling of benthic to pelagic processes at a permanent station in >2700 m water depth, 52 km off Nice, France. Surface sediment was first sampled at different periods of the year to assess the importance of the biological compartment (particularly metazoan meiofauna) and its relation to seasonally varying particulate matter input to the sea floor (estimated by measuring surface sediment particle size and porosity, as well as chloroplastic pigments, organic carbon, nitrogen and calcium carbonate contents). Beginning in...

  6. Oxygen microprofiles and porewater chemistry in sediments of the Skagerrak

    Bakker, Joop F; Helder, Wim
    Sediment porewater oxygen profiles were measured with micro and needle electrodes in sediment cores of 27 stations in the Skagerrak (northeastern North Sea). Oxygen penetration depth ranged from 3 to 20 mm depth. Fluxes estimated from the oxygen gradients varied from 3 to 18 mmol m**-2 d**-1. Oxygen penetration and flux depend on water depth, but possibly more on the hydrological conditions, related to the import of fresh organic matter by primary production in the water column. Oxygen fluxes were not related to the total organic carbon (TOC) content of the sediments. Stations in the eastern part of the Skagerrak...

  7. Benthic oxygen flixes on the Washington shelf and slope

    Archer, David E; Devol, Alan H
    Benthic oxygen fluxes calculated from in situ microelectrode profiles arc compared with benthic flux chamber O2 uptake measurements on a transect of eight stations across the continental shelf and three stations on the slope of Washington State. Station depths ranged from 40 to 630 m and bottom-water oxygen concentrations were 127-38 µM. The fluxes measured by the two methods were similar on the slope, but on the shelf, the chamber flux exceeded the microelectrode flux by as much as a factor of 3-4. We attribute this difference to pore-water irrigation, a process which apparently accounts for the oxidation of a...

  8. Mineralogical and chemical investigation of biogenic siliceous Antarctic deep-ses sediments

    Bohrmann, Gerhard; Abelmann, Andrea; Gersonde, Rainer; Kuhn, Gerhard
    The formation of marine opal-CT nodules or layers as early diagenetic deposits has been documented only in Antarctic deep-sea sediments. In contrast, porcellanites and cherts in land sections and Deep Sea Drilling Project and Ocean Drilling Program drill sites are usually found in sediment sections of Miocene age and older. During R.V. Polarstem cruises ANT-IX/3 and 4, young porcellanites were recovered for the first time in contact with their host sediment in two cores from the Atlantic sector of the southern ocean. Chemical and mineralogical studies of these deposits and their surrounding sediments have increased knowledge about very early chert...

  9. Sedimentology and geochemistry of the Iberian margin

    Thomson, John; Nixon, S; Summerhayes, Colin P; Schönfeld, Joachim; Zahn, Rainer; Grootes, Pieter Meiert
    The Portuguese margin is well-suited for studies of the contrasts in North Atlantic circulation during glacial and interglacial times because of its rapid sediment accumulation rate. This paper reports a (230Thexcess)0-based study of sediment accumulation over the past 140 ky, a period which includes the last two glacial/interglacial transitions, in two cores at 2.4 and 3.5 km water depth on a slope transect at 40°N. Although the independently-determined mean sediment accumulation fluxes over the past 140 ky are unequivocally high with means of 13.2 and 10.5 g cm**-2 ky**-1 in the two cores, conventional application of the (230Thexcess)0 method yields...

  10. Physical properties of ODP Leg 178 sites

    Volpi, Valentina; Camerlenghi, Angelo; Moerz, Tobias; Corubolo, P; Rebesco, Michele; Tinivella, Umberta
    We have reanalyzed the porosity, bulk density, and seismic velocity information collected from continental rise Sites 1095, 1096, and 1101 during the drilling of Ocean Drilling Program (ODP) Leg 178 (Fig. F1). The purpose is to provide a comprehensive composite digital set of data readily available for future studies aimed at well-seismic correlation. The work originates from the occurrence of overlapping sets of physical parameters and acoustic velocity collected by different methods (downhole logging, core logging, laboratory determination, and derivation from seismic data) and from different holes at the same site. These data do not always provide the same information...

  11. Geochemistry of sediments from the upwelling off Morocco

    Freudenthal, Tim; Meggers, Helge; Henderiks, Jorijntje; Kuhlmann, Holger; Moreno, Ana; Wefer, Gerold
    The high-productive upwelling area off Morocco is part of one of the four major trade-wind driven continental margin upwelling zones in the world oceans. While coastal upwelling occurs mostly on the shelf, biogenic particles derived from upwelling are deposited mostly at the upper continental slope. Nutrient-rich coastal water is transported within the Cape Ghir filament region at 30°N up to several hundreds of kilometers offshore. Both upwelling intensity and filament activity are dependent on the strength of the summer Trades. This study is aimed to reconstruct changes in trade wind intensity over the last 250,000 years by the analysis of...

  12. Organic carbon and biomarker record from the Laptev Sea continental margin

    Stein, Ruediger; Fahl, Kirsten; Niessen, Frank; Siebold, Martina
    In order to understand the processes controlling organic carbon deposition (i.e., primary productivity vs. terrigenous supply) and their paleoceanographic significance, three sediment cores (PS2471, PS2474. and PS2476) from the Laptev Sea continental margin were investigated for their content and composition of organic carbon. The characterization of organic matter indudes the determination of buk parameters (hydrogen index values and C/N ratios) and the analysis of specific biomarkers (n-alaknes, fatty acids, alkenones, and pigments). Total organic carbon (TOC) values vary between 0.3 and 2%. In general, the organic matter from the Laptev Sea continental margin is dominated by terrigenous matter throughout. However. significant...

  13. Biomass and bioturbation in surface sediments of the Arctic Ocean

    Clough, Lisa; Ambrose jr, William G; Cochran, James R; Barnes, C; Renaud, Paul E; Aller, Robert C.
    Little is known about the benthic communities of the Arctic Ocean's slope and abyssal plains. Here we report on benthic data collected from box cores along a transect from Alaska to the Barents Abyssal Plain during the Arctic Ocean Section of 1994. We determined: (1) density and biomass of the polychaetes, foraminifera and total infauna; (2) concentrations of potential sources of food (pigment concentration and percent organic carbon) in the sediments; (3) surficial particle mixing depths and rates using downcore 210Pb profiles; and (4) surficial porewater irrigation using NaBr as an inert tracer. Metazoan density and biomass vary by almost...

  14. Carbon and Lead chemistry of sediments from the Middle Atlantic Bight

    Anderson, Robert F; Rowe, Gilbert T; Kemp, P F; Trumbore, S; Biscaye, Pierre Eginton
    A mass budget was constructed for organic carbon on the upper slope of the Middle Atlantic Bight, a region thought to serve as a depocenter for fine-grained material exported from the adjacent shelf. Various components of the budget are internally consistent, and observed differences can be attributed to natural spatial variability or to the different time scales over which measurements were made. The flux of organic carbon to the sediments in the core of the depocenter zone, at a water depth of 1000 m, was measured with sediment traps to be 65 mg C m**-2 day**-1, of which 6-24 mg...

  15. Sedimentology, organic geochemistry, and stable isotopes of core PS2138-1

    Knies, Jochen; Stein, Ruediger
    We studied variations in terrigenous (TOM) and marine organic matter (MOM) input in a sediment core on the northern Barents Sea margin over the last 30 ka. Using a multiproxy approach, we reconstructed processes controlling organic carbon deposition and investigated their paleoceanographic significance in the North Atlantic-Arctic Gateways. Variations in paleo-surface-water productivity are not documented in amount and composition of organic carbon. The highest level of MOM was deposited during 25-23 ka as a result of scavenging on fine-grained, reworked, and TOM-rich material released by the retreating Svalbard/Barents Sea ice sheet during the late Weichselian. A second peak of MOM...

  16. Opal and barium records of six sediment cores for the last 400 ka

    Bonn, Wolfgang J; Gingele, Franz; Grobe, Hannes; Mackensen, Andreas; Fütterer, Dieter K
    Records of biogenic opal and barium were measured in sediment cores at the Antarctic continental margin in the area of the Weddell, Lazarev and Cosmonaut seas. These records provide a qualitative and quantitative tool to estimate changes in palaeoproductivity over the last 400 ka. The stratigraphy of the investigated cores is calibrated to a lithostratigraphy, adjusted to a stable isotope record from the eastern Weddell Sea, which is supported by a Th-dating method. We present evidence that interglacial productivity along the Antarctic continental margin is twice as high compared to subantarctic sites near South Orkney. A glacial/interglacial pattern with high...

  17. Sedimentology of cores from the shelf of Lazarev Sea, East Antarctica

    Gingele, Franz; Kuhn, Gerhard; Maus, B; Melles, Martin; Schöne, Tilo
    Distinct facies types, classified in radiocarbon-dated sediments from the shelf of the Lazarev Sea, East Antarctica, reveal a detailed history of processes that have controlled sedimentation during the deglaciation over the last 10,000 yr. The ice retreat on this part of the Antarctic shelf started 9500 yr BP, marked by the deposition of laminated sediments, deposited from a floating ice shelf. These laminites, which occur on top of diamictons laid down from a grounded ice sheet, are the basal sediments of the postglacial sequence. The intensity of the Antarctic Coastal Current (ACC), directed by shelf morphology, controlled sedimentation of the...

  18. Organic carbon and opal in deep sea sediments of the southern and eastern Weddell Sea

    Schlüter, Michael
    During the ANT V14 (1986187) and ANT V113 (1987188) cruises of R.V. Polarstern sedirnents from the eastern, southern and central Weddell Sea were sarnpled with a boxcorer andlor a multicorer. The 24 sampling locations are distributed over the whole depth range, from shelf to pelagic environments. Porewater concentrations of aluminium, fluoride, manganese, nitrate, nitrite, oxygen and silicate, the pH and the alkalinity were measured. Of the sediment the opal, calcium carbonate and organic carbon content were quantified. The 210Pb-profile was measured for three sedirnent cores. This investigation deals with the estimation of the amounts of opal and organic carbon (Corg) that...

  19. Accumulation of organic carbon in the Laptev Sea

    Stein, Ruediger; Fahl, Kirsten
    Composition and accumulation rates of organic carbon in Holocene sediments provided data to calculate an organic carbon budget for the Laptev Sea continental margin. Mean Holocene accumulation rates in the inner Laptev Sea vary between 0.14 and 2.7 g C cm**2/ky; maximum values occur close to the Lena River delta. Seawards, the mean accumulation rates decrease from 0.43 to 0.02 g C cm**2/ky. The organic matter is predominantly of terrigenous origin. About 0.9*10**6 t/year of organic carbon are buried in the Laptev Sea, and 0.25*10**6 t/year on the continental slope. Between about 8.5 and 9 ka, major changes in supply...

  20. Sediment record of the last 1.8 Ma in the Amundsen Sea

    Hillenbrand, Claus-Dieter; Fütterer, Dieter K; Grobe, Hannes; Frederichs, Thomas
    Records of glaciomarine deposition recovered from the West Antarctic continental margin in the Amundsen Sea allow the reconstruction of the behaviour of the West Antarctic Ice Sheet (WAIS) in response to the natural climatic changes of the last 1.8 million years. Contents of gravel-sized and lithogenic components represent the input and redeposition of glaciogenic debris, whereas variations in the proportions of the calcareous sediment fraction reflect palaeoproductivity changes. All proxies, which are regarded as sensitive to a WAIS collapse, changed markedly during the global climatic cycles, but do not confirm a complete disintegration of the WAIS during the Pleistocene.

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