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  • 1
    Call number: ZSP-166(57)
    In: Berichte aus dem MARUM und dem Fachbereich Geowissenschaften der Universität Bremen
    Type of Medium: Series available for loan
    Pages: 95 S. , zahlr. graph. Darst., Kt.
    Series Statement: Berichte aus dem Fachbereich Geowissenschaften der Universität Bremen 57
    Note: Zugl.: Bremen, Univ., Diss., 1994
    Location: Lower compact magazine
    Branch Library: GFZ Library
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  • 2
    Call number: ZSP-166(252)
    In: Berichte aus dem MARUM und dem Fachbereich Geowissenschaften der Universität Bremen
    Type of Medium: Series available for loan
    Pages: 151 S.
    Series Statement: Berichte aus dem Fachbereich Geowissenschaften der Universität Bremen 252
    Classification: D.3.
    Location: Lower compact magazine
    Branch Library: GFZ Library
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  • 3
    Call number: ZSP 16696-0535
    Pages: 97 S. : graph. Darst. ; Ill. : 29 cm
    ISSN: 0931-0800
    Series Statement: Berichte aus dem Fachbereich Geowissenschaften der Universität Bremen 57
    Branch Library: AWI Library
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  • 4
    Publication Date: 2014-06-27
    Description: The past climate evolution of southwestern Africa is poorly understood and interpretations of past hydrological changes are sometimes The past climate evolution of southwestern Africa is poorly understood and interpretations of past hydrological changes are sometimes contradictory. Here we present a record of leaf-wax δD and δ13C taken from a marine sediment core at 23°S off the coast of Namibia to reconstruct the hydrology and C3 versus C4 vegetation of southwestern Africa over the last 140 000 years (140 ka). We find lower leaf-wax δD and higher δ13C (more C4 grasses), which we interpret to indicate wetter Southern Hemisphere (SH) summer conditions and increased seasonality, during SH insolation maxima relative to minima and during the last glacial period relative to the Holocene and the last interglacial period. Nonetheless, the dominance of C4 grasses throughout the record indicates that the wet season remained brief and that this region has remained semi-arid. Our data suggest that past precipitation increases were derived from the tropics rather than from the winter westerlies. Comparison with a record from the Congo Basin indicates that hydroclimate in southwestern Africa has evolved in antiphase with that of central Africa over the last 140 ka.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Format: application/pdf
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  • 5
    Publication Date: 2016-02-01
    Description: Bulk organic parameters and stable and radiocarbon isotope compositions of organic carbon (δ13COC and Δ14COC) as well as various biomarkers (lignin phenols, plant waxes etc.) have been used to investigate the biogeochemical characteristics of organic carbon in the Amazon River system. However, the source, concentration and distribution pattern of lignin on the Amazon shelf and fan has not been assessed so far. In particular, the compound-specific stable carbon isotope compositions (δ13C) of lignin phenols have not been characterized in the Amazon River system. In order to study the distribution of lignin in the lower Amazon basin and its dispersal on the shelf and fan, we used riverbed sediments from the Amazon mainstream and its main tributaries and marine surface sediments on the Amazon shelf and fan. The samples were analyzed for particulate organic carbon content (POC), δ13COC, lignin phenol compositions and compound-specific δ13C of individual lignin phenols. The concentrations of aluminium and silicon (Al/Si) were used as a proxy for grain size[1]. The POC content in the main tributaries ranged from 0.13 to 3.99 wt-% and increased with Al/Si ratio in each tributary. δ13COC varied from -26.1‰ to -29.9‰ VPDB in riverbed sediments. Lignin content (represented by Λ8, sum of eight lignin phenols in OC, expressed as mg/100mg OC) ranged from 0.73 to 6.91 and is positively related with Al/Si ratio in the main tributaries except for the Xingu River, in which Λ8 decreased with Al/Si. Ratios of syringyl to vanillyl (S/V) and cinnamyl to vanillyl (C/V) varied from 0.70 to 1.51 and 0.08 to 0.47, respectively, suggesting that the dominant source of lignin is non-woody angiosperm tissue. The ratios of vanillic acid to vanillin (Ad/Al)v (0.26-0.71) and syringic acid to syringaldehyde (Ad/Al)s (0.15-0.57) indicated relatively fresh, non-degraded lignin. In marine sediments, the δ13COC ranged from -18.6‰ to -26.7‰ and is correlated with the Λ8 value (0.04-2.01). The decreasing Λ8 value along the coast from the Amazon River mouth towards the northwest implies that lignin is distributed by the North Brazil Current. A main plant source of non-woody angiosperm tissue was indicated by the S/V (0.59-1.62) and C/V (0.10-0.43) ratios on the marine samples. The agreement between riverbed and marine sediments suggests that processing of POC during transport from the basin to offshore does not change the plant source information of lignin. Highly degraded lignin on the Amazon fan and the southeast shelf is indicated by (Ad/Al)v (0.49-0.99). δ13C of lignin phenols of 9 marine sediments ranged from -28.6‰ to -33.3‰ and were consistently lower than δ13COC (-19.7‰ to -26.7‰). Depleted δ13C of lignin phenols indicate that the POC produced by the terrestrial biosphere is mainly derived from higher plants using C3 photosynthesis. References Bouchez, J., Galy, V., Hilton, R.G., Gaillardet, J., Moreira-Turcq, P., Pérez, M.A., France-Lanord, C., Maurice, L., 2014. Source, transport and fluxes of Amazon River particulate organic carbon: Insights from river sediment depth-profiles. Geochemica et Cosmochimica Acta 133, 280-298
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 6
    Publication Date: 2018-09-10
    Description: The temporal succession of changes in Amazonian hydroclimate during Heinrich Stadial 1 (HS1) (ca. 18–14.7 cal ka BP) is currently poorly resolved. Here we present HS1 records based on isotope, inorganic and organic geochemistry from a marine sediment core influenced by the Amazon River discharge. Our records offer a detailed reconstruction of the changes in Amazonian hydroclimate during HS1, integrated over the basin. We reconstructed surface water hydrography using stable oxygen isotopes (δ18O) and Mg/Ca-derived paleotemperatures from the planktonic foraminifera Globigerinoides ruber, as well as salinity changes based on stable hydrogen isotope (δD) of palmitic acid. We also analyzed branched and isoprenoid tetraether concentrations, and compared them to existing bulk sediment ln(Fe/Ca) data and vegetation reconstruction based on stable carbon isotopes from n-alkanes, in order to understand the relationship between continental precipitation, vegetation and sediment production. Our results indicate a two-phased HS1 (HS1a and HS1b). During HS1a (18–16.9 cal ka BP), a first sudden increase of sea surface temperatures (SST) in the western equatorial Atlantic correlated with the slowdown of the Atlantic Meridional Overturning Circulation (AMOC) and the associated southern hemisphere warming phase of the bipolar seesaw. This phase was also characterized by an increased delivery of terrestrial material. During HS1b (16.9–14.8 cal ka BP), a decrease in terrestrial input was, however, associated with a marked decline of seawater δ18O and palmitic acid δD. Both isotopic proxies independently indicate a drop in sea surface salinity (SSS). A number of records under the influence of the North Brazil Current, in contrast, indicate increases in SST and SSS resulting from a weakened AMOC during HS1. Our records thus suggest that the expected increase in SSS due to the AMOC slowdown was overridden by a two-phased positive precipitation anomaly in Amazonian hydroclimate.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 7
    Publication Date: 2017-06-18
    Description: We investigate the redistribution of terrigenous materials in the northeastern (NE) South American continental margin during slowdown events of the Atlantic Meridional Overturning Circulation (AMOC). The compilation of stratigraphic data from 108 marine sediment cores collected across the western tropical Atlantic shows an extreme rise in sedimentation rates off the Parnaíba River mouth (about 2◦S) during Heinrich Stadial 1 (HS1, 18–15 ka). Sediment core GeoB16206-1, raised offshore the Parnaíba River mouth, documents relatively constant 143 Nd/144 Nd values (expressed as εNd(0) ) throughout the last 30 ka. Whereas the homogeneous εNd(0) data support the input of fluvial sediments by the Parnaíba River from the same source area directly onshore, the increases in Fe/Ca, Al/Si and Rb/Sr during HS1 indicate a marked intensification of fluvial erosion in the Parnaíba River drainage basin. In contrast, the εNd(0) values from sediment core GeoB16224-1 collected off French Guiana (about 7◦N) suggest Amazon-sourced materials within the last 30 ka. We attribute the extremely high volume of terrigenous sediments deposited offshore the Parnaíba River mouth during HS1 to (i) an enhanced precipitation in the catchment region and (ii) a reduced North Brazil Current, which are both associated with a weakened AMOC.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 8
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Evidence for abrupt climate changes on millennial and shorter timescales is widespread in marine and terrestrial climate records. Rapid reorganization of ocean circulation is considered to exert some control over these changes, as are shifts in the concentrations of atmospheric greenhouse ...
    Type of Medium: Electronic Resource
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  • 9
    Publication Date: 2019-02-01
    Description: Changes in deep ocean ventilation are commonly invoked as the primary cause of lower glacial atmospheric CO2. The water mass structure of the glacial deep Atlantic Ocean and the mechanism by which it may have sequestered carbon remain elusive. Here we present neodymium isotope measurements from cores throughout the Atlantic that reveal glacial–interglacial changes in water mass distributions. These results demonstrate the sustained production of North Atlantic Deep Water under glacial conditions, indicating that southern-sourced waters were not as spatially extensive during the Last Glacial Maximum as previously believed. We demonstrate that the depleted glacial δ13C values in the deep Atlantic Ocean cannot be explained solely by water mass source changes. A greater amount of respired carbon, therefore, must have been stored in the abyssal Atlantic during the Last Glacial Maximum. We infer that this was achieved by a sluggish deep overturning cell, comprised of well-mixed northern- and southern-sourced waters.
    Type: Article , PeerReviewed
    Format: text
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  • 10
    Publication Date: 2019-02-01
    Description: Abundant hydroclimatic evidence from western Amazonia and the adjacent Andes documents wet conditions during Heinrich Stadial 1 (HS1, 18–15 ka), a cold period in the high latitudes of the North Atlantic. This precipitation anomaly was attributed to a strengthening of the South American summer monsoon due to a change in the Atlantic interhemispheric sea surface temperature (SST) gradient. However, the physical viability of this mechanism has never been rigorously tested. We address this issue by combining a thorough compilation of tropical South American paleorecords and a set of atmosphere model sensitivity experiments. Our results show that the Atlantic SST variations alone, although leading to dry conditions in northern South America and wet conditions in northeastern Brazil, cannot produce increased precipitation over western Amazonia and the adjacent Andes during HS1. Instead, an eastern equatorial Pacific SST increase (i.e., 0.5–1.5 °C), in response to the slowdown of the Atlantic Meridional Overturning Circulation during HS1, is crucial to generate the wet conditions in these regions. The mechanism works via anomalous low sea level pressure over the eastern equatorial Pacific, which promotes a regional easterly low-level wind anomaly and moisture recycling from central Amazonia towards the Andes.
    Type: Article , PeerReviewed
    Format: text
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