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Datasets of project "South Atlantic in Late Quaternary: Reconstruction of Budget and Currents"

Mostrando recursos 1 - 20 de 1.066

  1. Cadmium analytical results from sediment and foraminifera shells

    Boyle, Edwards A; Rosenthal, Yair
    There has been a major contradiction between benthic foraminiferal Cd/Ca and d13C data concerning the labile nutrient chemistry of the Southern Ocean during the Last Glacial Maximum (LGM). Cd data indicates that LGM South Atlantic nutrient concentrations were as low as they are today, indicative of a persistent influx of nutrient-depleted North Atlantic Deep Water (NADW). d13C data indicates that LGM South Atlantic nutrient concentrations were much higher than at present (even higher than anywhere else in the ocean at that time), and these data have been interpreted as signifying the complete shutdown ofthe export of NADW into the global...

  2. Table 2. Bulk sedimentary Cd content for sediment core RC13-228

    Boyle, Edwards A; Rosenthal, Yair

  3. Table 1. Comparison of samples cleaned by old and new methods for various cores

    Boyle, Edwards A; Rosenthal, Yair

  4. Table 2. 14C AMS datings for sediment core T89-24

    Jansen, J H Fred; Ufkes, Els; Schneider, Ralph R
    Planktic foraminifera data from three cores of the Angola-Zaire margin are used to reconstruct palaeopositions of the Angola-Benguela Front (ABF) between the warm Angola Current and cold Benguela Current for the last 180,000 years. Strong northward shifts occurred in stages 4 and 3.3-3.1, but not in stages 6 and 2. The Benguela Current did not penetrate into the Gulf of Guinea. The southernmost positions, not far from the present one, were occupied in stages 5.5 and 1, but also in stage 6.3. The record of the shifts contains significant variance in the 23 ky**-1 orbital frequency band and there are...

  5. Oxygen and silica flux from 9 multicorer profiles

    Holstein, Jan M; Hensen, Christian
    Pore water profiles from 24 stations in the South Atlantic (located in the Guinea, Angola, Cape, Guyana, and Argentine basins) show good correlations of oxygen and silicon, suggesting microbially mediated dissolution of biogenic silica. We used simple analytical transport and reaction models to show the tight coupling of the reconstructed process kinetics of aerobic respiration and silicon regeneration. A generic transport and reaction model successfully reproduced the majority of Si pore water profiles from aerobic respiration rates, confirming that the dissolution of biogenic silica (BSi) occurs proportionally to O2 consumption. Possibly limited to well-oxygenated sediments poor in BSi, benthic Si...

  6. Calculated oxygen and silicon benthic fluxes in sediments of the South Atlantic

    Holstein, Jan M; Hensen, Christian

  7. Biogenic silica depth profiles in sediments of the South Atlantic

    Holstein, Jan M; Hensen, Christian

  8. Stable isotopes of foraminifers, mineralogy and ages of sediment core GeoB1523-1

    Rühlemann, Carsten; Diekmann, Bernhard; Mulitza, Stefan; Frank, Martin
    Today the western tropical Atlantic is the most important passage for cross-equatorial transfer of heat in the form of warm surface water flowing from the South into the North Atlantic. Circulation changes north of South America may thus have influenced the global thermohaline circulation system and high northern latitude climate. Here we reconstruct late Quaternary variations of western equatorial Atlantic surface circulation and Amazon lowland climate obtained from a multiproxy sediment record from Ceará Rise. Variations in the illite/smectite ratio suggest drier climatic conditions in the Amazon Basin during glacials relative to interglacials. The 230Thex-normalized fluxes and the 13C/12C record...

  9. Benthic foraminifera in South Atlantic Ocean surface sediments

    Schumacher, Stefanie
    Benthic foraminiferal assemblages were analyzed on forty-eight surfacesediment samples which were taken with a multiple corer from the southern South Atlantic Ocean and the northern Angola-Basin. The short cores were split into 1-cm-thick slices down to 15 cm sediment depth. Live (with Rose Bengal stained) and dead faunas were counted separately. The data were used to calculate numerical faunal characteristics like standing stocks, benthic foraminifera accumulation rates, diversity, average living depth, and habitat depth. Additionally the live and dead faunas were grouped into a number of principal faunal endmembers by Q-mode principal component analysis. Faunal composition, numerical faunal characteristics, and...

  10. (Fig. 16) Grain-sizes of magnetosomes from sediment core GeoB1713-5

    Frederichs, Thomas; Schmidt, Andrea

  11. (Fig. 15a) Hysteresis loops to maximum fields of 0.3 T for samples from sediment core GeoB1713-5

    Frederichs, Thomas; Schmidt, Andrea

  12. Geochemistry of sediment cores GeoB4901-3 and GeoB4901-8 from the southern flank of the Niger Fan

    Zabel, Matthias; Schneider, Ralph R; Wagner, Thomas; Adegbie, Adesina T; de Vries, Uwe; Kolonic, Sadat
    Time series of terrigenous source elements (Al, K, Ti, Zr) from core GeoB4901-8 recovered from the deep-sea fan of the Niger River record variations in riverine sediment discharge over the past 245,000 yr. Although the flux rates of all the elements depend on physical erosion, which is mainly controlled by the extent of vegetation coverage in central Africa, element/Al ratios reflect conditions for chemical weathering in the river basin. Maximum sediment input to the ocean occurs during cold and arid periods, when precipitation intensity and associated freshwater runoff are reduced. High carbonate contents during the same periods indicate that the...

  13. Hydrochemistry measured on water bottle samples during POLARSTERN cruise ANT-VIII/2

    Mackensen, Andreas; Hubberten, Hans-Wolfgang; Scheele, Norbert; Schlitzer, Reiner
    On a section between 72°S and 42°S and a transect between 60°E and 10°E through the Weddell Sea and the southernmost eastern Atlantic Ocean, the water column was sampled on 72 stations, and the stable carbon isotopic composition of total dissolved inorganic carbon (delta13C(SumCO2)) as well as the stable oxygen isotopic composition of seawater (delta18O) was determined. These data were compared with potential temperature, salinity, dissolved oxygen and phosphate data from the same stations. The observed delta13C(SumCO2)/PO4[3-] relationship in the deep Weddell Sea strongly differs from the global Redfield-driven deep water relationship. We attribute this to enhanced thermodynamic fractionation at...

  14. Alkenone data of sediment traps off Cape Blanc, NW Africa

    Müller, Peter J; Fischer, Gerhard
    We analysed long-chain alkenones in sinking particles and surface sediments from the filamentous upwelling region off Cape Blanc, NW Africa, to evaluate the transfer of surface water signals into the geological record. Our study is based on time-series sediment trap records from 730 m (1990-1991) to 2195-3562 m depth (1988-1991). Alkenone fluxes showed considerable interannual variations and no consistent seasonality. The average flux of C37 and C38 alkenones to the deep traps was 1.9 µg/m**2/d from March 1988 to October 1990 and sevenfold higher in the subsequent year. Alkenone fluxes to the shallower traps were on average twice as high...

  15. Biogenic flux and primary production of sediment traps in the Atlantic and the Southern Ocean

    Fischer, Gerhard; Ratmeyer, Volker; Wefer, Gerold
    Fluxes of organic carbon normalised to a depth of 1000 m from 18 sites in the Atlantic and the Southern Ocean are presented, comprising nine biogeochemical provinces as defined by Longhurst et al. (1995. Journal of Plankton Research 17, 1245-1271). For comparison with primary production, we used a recent compilation of primary production values derived from CZCS data (Antoine et al., 1996. Global Biogeochemical Cycles 10, 57-69). In most cases, the seasonal patterns stood reasonably well in accordance with the carbon fluxes. Particularly, organic carbon flux records from two coastal sites off northwest and southwest Africa displayed a more distinct...

  16. Age determination of Southeast Atlantic sediment cores

    Versteegh, Gerard J M; Schefuß, Enno; Dupont, Lydie M; Marret, Fabienne; Sinninghe Damsté, Jaap S; Jansen, J H Fred
    Angola Basin and Cape Basin (southeast Atlantic) surface sediments and sediment cores show that maxima in the abundance of taraxerol (relative to other land-derived lipids) covary with maxima in the relative abundance of pollen from the mangrove tree genus Rhizophora and that in the surface sediments offshore maxima in the relative abundance of taraxerol occur at latitudes with abundant coastal mangrove forests. Together with the observation that Rhizophora mangle and Rhizophora racemosa leaves are extraordinarily rich in taraxerol, this strongly indicates that taraxerol can be used as a lipid biomarker for mangrove input to the SE Atlantic. The proxy-environment relations...

  17. Stable isotope record of planktonic foraminifera of the South Atlantic

    Wefer, Gerold; Berger, Wolfgang H; Bickert, Torsten; Donner, Barbara; Fischer, Gerhard; Kemle-von Mücke, Sylvia; Pätzold, Jürgen; Meinecke, Gerrit; Müller, Peter J; Mulitza, Stefan; Niebler, Hans-Stefan; Schmidt, Heike; Schneider, Ralph R; Segl, Monika
    The central problem of late Quaternary circulation in the South Atlantic is its role in transfer of heat to the North Atlantic, as this modifies amplitude, and perhaps phase, of glacialinterglacial fluctuations. Here we attempt to define the problem and establish ways to attack it. We identify several crucial elements in the dynamics of heat export: (1) warm-water pile-up (and lack thereof) in the Western equatorial Atlantic, (2) general spin-up (or spin-down) of central gyre, tied to SE trades, (3) opening and closing of Cape Valve (Agulhas retroflection), (4) deepwater E-W asymmetry. Means for reconstruction are biogeography, stable isotopes, and...

  18. Physical properties of sediment cores of the Bengal Fan

    Weber, Michael E; Niessen, Frank; Kuhn, Gerhard; Wiedicke-Hombach, Michael
    We examined geophysical data from a Multi-Sensor Core Logger (MSCL), a logging device providing continuous measurements of gamma-ray attenuation, p-wave travel time, and magnetic susceptibility on marine sediment cores. In the first part we focused on the gamma-ray system and compared two different calibration methods. From the gamma-ray attenuation, we calculated densities and porosities by incorporating mass weighted attenuation coefficients. The application of an iteration method reduces the error of the density and porosity estimates compared to GRAPE data. In addition, we derived equations to calculate water content and dry bulk density from gamma-ray attenuation measurements. Comparison with physical properties...

  19. Sea-surface reconstruction of the east-equatorial South Atlantic

    Schneider, Ralph R; Müller, Peter J; Ruhland, Götz; Meinecke, Gerrit; Schmidt, Heike; Wefer, Gerold
    In order to reconstruct Late Quatemary variations of surface oceanography in the eastequatorial South Atlantic, time series of sea-surface temperatures (SST) and paleoproductivity were established from cores recovered in the Guinea and Angola Basins, and at the Walvis Ridge. These records, based on sedimentary alkenone and organic carbon concentrations, reveal that during the last 350,000 years surface circulation and productivity changes in the east-equatorial South Atlantic were highiy sensitive to climate forcing at 23- and 100-kyr periodicities. Covarying SST and paleoproductivity changes at the equator and at the Walvis Ridge appear to be driven by variations in zonal trade-wind intensity,...

  20. Distribution of coccoliths in surface sediments of the south-eastern South Atlantic Ocean

    Boeckel, Babette; Baumann, Karl-Heinz
    Recent coccoliths from 52 surface sediment samples recovered from the south-eastern South Atlantic were examined qualitatively and quantitatively in order to assess the controlling mechanisms for their distribution patterns, such as ecological and preservational factors, and their role as carbonate producers. Total coccolith abundances range from 0.2 to 39.9 coccoliths*10**9/ g sediment. Four assemblages can be delineated by their coccolith content characterising the northern Benguela, the middle to southern Benguela, the Walvis Ridge and the deeper water. Distinctions are based on multivariate ordination techniques applied on the relative abundances of the most abundant taxa, Emiliania huxleyi, Calcidiscus leptoporus, Gephyrocapsa spp.,...

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