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  • 1
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    High- and low-latitude forcing of the Nile River regime during the Holocene inferred from laminated sediments of the Nile deep-sea fan (2013)
    Elsevier
    In:  Earth and Planetary Science Letters, 364 . pp. 98-110.
    Details
    Publikationsdatum: 2019-09-23
    Beschreibung: Sediments deposited on deep-sea fans are an excellent geological archive to reconstruct past changes in fluvial discharge. Here we present a reconstruction of changes in the regime of the Nile River during the Holocene obtained using bulk elemental composition, grain-size analyses and radiogenic strontium (Sr) and neodymium (Nd) isotopes from a sediment core collected on the Nile deep-sea fan. This 6-m long core was retrieved at View the MathML source water-depth and is characterized by the presence of a 5-m thick section of finely laminated sediments, which were deposited between 9.5 and 7.3 ka BP and correspond to the African Humid Period (AHP). The data show distinct changes in eolian dust inputs as well as variations in discharge of the Blue Nile and White Nile. Sedimentation was mainly controlled by changes in fluvial discharge during the Holocene, which was predominantly forced by low-latitude summer insolation and by the location of the eastern African Rain Belt. The changes in relative contribution from the Blue Nile and White Nile followed changes in low-latitude spring/autumn insolation, which highlights the role of changes in seasonality of the precipitation on the Nile River regime. The relative intensity of the Blue Nile discharge was enhanced during the early and late Holocene at times of higher spring insolation (with massive erosion and runoff during the AHP at times of high summer insolation), while it was reduced between 8 and 4 ka at times of high autumn insolation. The gradual insolation-paced changes in fluvial regime were interrupted by a short-term arid event at 8.5–7.3 ka BP (also associated with rejuvenation of bottom-water ventilation above the Nile fan), which was likely related to northern hemisphere cooling events. Another arid event at 4.5–3.7 ka BP occurred as the apex of a gradually drier phase in NE Africa and marks the end of the AHP.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.epsl.2013.01.009
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  • 2
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    Asynchronous Changes in Vegetation, Runoff and Erosion in the Nile River Watershed during the Holocene (2014)
    Public Library of Science
    In:  PLoS ONE, 9 (12). e115958.
    Details
    Publikationsdatum: 2017-06-22
    Beschreibung: The termination of the African Humid Period in northeastern Africa during the early Holocene was marked by the southward migration of the rain belt and the disappearance of the Green Sahara. This interval of drastic environmental changes was also marked by the initiation of food production by North African huntergatherer populations and thus provides critical information on human-environment relationships. However, existing records of regional climatic and environmental changes exhibit large differences in timing and modes of the wet/dry transition at the end of the African Humid Period. Here we present independent records of changes in river runoff, vegetation and erosion in the Nile River watershed during the Holocene obtained from a unique sedimentary sequence on the Nile River fan using organic and inorganic proxy data. This high-resolution reconstruction allows to examine the phase relationship between the changes of these three parameters and provides a detailed picture of the environmental conditions during the Paleolithic/Neolithic transition. The data show that river runoff decreased gradually during the wet/arid transition at the end of the AHP whereas rapid shifts of vegetation and erosion occurred earlier between 8.7 and ,6 ka BP. These asynchronous changes are compared to other regional records and provide new insights into the threshold responses of the environment to climatic changes. Our record demonstrates that the degradation of the environment in northeastern Africa was more abrupt and occurred earlier than previously thought and may have accelerated the process of domestication in order to secure sustainable food resources for the Neolithic African populations.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1371/journal.pone.0115958
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  • 3
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    Influence of diagenesis on the stable isotopic composition of biogenic carbonates from the Gulf of Tehuantepec oxygen minimum zone (2012)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 13 (4). Q04003.
    Details
    Publikationsdatum: 2019-09-23
    Beschreibung: In order to evaluate the influence of diagenetic and post-sampling processes on the stable oxygen and carbon isotope compositions of biogenic carbonates, we conducted a multiproxy study of organic-rich sediments from the eastern Pacific oxygen minimum zone. Core MD02-2520, which was retrieved from the Gulf of Tehuantepec (Mexico), has seasonal laminations and covers the last 40 kyr. Together with the presence of gypsum crystals and inorganic calcite aggregates, the occurrence of large excursions in the stable oxygen and carbon isotope records of both planktonic and benthic foraminifera (as large as +3‰ in d18O and -5‰ in d13C) point to significant secondary transformations. Storage-related gypsum precipitation was ruled out since it implies sulfide reoxidation by oxygen that triggers biogenic calcite dissolution, which proved to be of minor importance here. Instead, precipitation of authigenic calcite during early diagenesis appears to be the most likely process responsible for the observed isotopic excursions. The d13C composition for inorganic calcite aggregates (-5 to -7‰) suggests a major contribution from anaerobic oxidation of organic matter. The d34S composition for gypsum crystals (-10 to +15‰) suggests a major contribution from anaerobic reoxidation of authigenic sulfides, potentially involving reactions with metal oxides and sulfur disproportionation. A minor part of the gypsum might possibly have formed as a result of local pore water salinity increases induced by gas hydrate formation.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2011GC003800
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  • 4
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    Runoff and precipitation dynamics in the Blue and White Nile catchments during the mid-Holocene: A data-model comparison (2015)
    Elsevier
    In:  Quaternary Science Reviews, 130 . pp. 222-230.
    Details
    Publikationsdatum: 2017-04-11
    Beschreibung: The Blue Nile is the major contributor of freshwater and sediments to the modern-day main Nile River and exerts a key control on seasonal flooding in the Nile valley. Recent studies have postulated that the relative contribution from the Blue Nile to the main Nile runoff might have been reduced during the mid-Holocene, at a time when higher boreal summer insolation stimulated enhanced precipitation in North Africa. Whether the decrease in the relative contribution from the Blue Nile resulted from a decrease in precipitation over the catchment, from an increase in White Nile runoff or from a combination of both is still a matter of debate. By comparing regional proxy-records with the output from a global atmospheric model zoomed on Africa, we propose that the reduced contribution from the Blue Nile at 6 ka originated from both a higher White Nile runoff and a lower Blue Nile runoff. Enhanced African and Indian monsoons at 6 ka induced a northern shift of the Intertropical Convergence Zone and an eastward shift of the Congo Air Boundary. Such an atmospheric configuration led to a negative anomaly of summer precipitation over the Blue Nile catchment that likely resulted in a reduction in the Blue Nile runoff. By contrast, a sustained positive anomaly of precipitation over the White Nile catchment during both summer and autumn most likely induced a higher main Nile runoff during the mid-Holocene. Using the model output, we propose a first synoptic view on regional rainfall dynamics that permits to reconcile contrasting proxy records.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.quascirev.2015.07.014
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  • 5
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    Response of vegetation and erosion dynamics to changes in precipitation in the Nile River drainage basin during the African Humid Period (2011)
    In:  [Talk] In: Goldschmidt Conference 2011, 14.-19.08.2011, Prague, Czech Republic .
    Details
    Publikationsdatum: 2019-09-23
    Materialart: Conference or Workshop Item , NonPeerReviewed
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  • 6
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    Data inventory of the varve database (VARDA): Sediment profiles, chronologies, radiocarbon dates, tephra layers and varve thickness data (2019)
    GFZ Data Services
    In:  GFZ Data Services .
    Details
    Publikationsdatum: 2020-05-13
    Beschreibung: The data collection presented here is the data inventory of the VARved sediments DAtabase (VARDA) in version 1.1. VARDA is freely accessible and was created to assess outputs from climate models with high-resolution terrestrial palaeoclimatic proxies. All data were collected as raw data from freely available online sources, either from online data repositories (Pangaea, NOAA, and Neotoma) or data archives within the supplementary materials section of online publications. The current data collection consists of meta information and datasets from 95 lake archives. The data is stored in JSON and CSV format. All datasets are stored as individual files (JSON and CSV). Each dataset consists of samples for either i) chronologies; ii) radiocarbon data; iii) tephra layer; or iv) varve thickness data. Meta-information for each dataset is summarized in one csv and seven JSON files. Additional paleoclimate proxy data will be provided in forthcoming updates of VARDA. The data collection of VARDA Version 1.1 is provided as an archive (.tar.gz) with the following files/folders. Overview lists with categories, cores, countries, datasets, lakes and publications included in VARDA. Each item in the lists is cross-referenced with the other files via its $ref property which includes the corresponding list index or the dataset's UUID (from the VARDA database). The data points themselves are provided in the "records" folder and named with each dataset's UUID respectively. For more information on the data structure please read the "index.html" file included in the archive and available on the DOI landing page.
    Materialart: Other , NonPeerReviewed
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  • 7
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    Active mud volcanoes on the upper slope of the western Nile deep-sea fan - first results from the P362/2 cruise of R/V Poseidon (2010)
    Springer
    In:  Geo-Marine Letters, 30 (3/4). pp. 169-186.
    Details
    Publikationsdatum: 2017-05-19
    Beschreibung: In February 2008, cruise P362/2 was undertaken aboard R/V Poseidon to the Giza and North Alex mud volcanoes (MVs) on the upper slope of the western Nile deep-sea fan. Emitted fluids were strongly depleted in chloride and rich in hydrocarbons, predominantly of thermogenic origin. In-situ sediment temperature measurements indicate extremely high and moderate levels of activity for the North Alex MV and Giza MV, respectively, and suggest rapid changes from dormant to active stages. Both the physical properties of core sediments (e.g., color and magnetic susceptibility), and their assemblages of micro- and nannofossils point to different sources for the two mud volcanoes. Biostratigraphic dating suggests source depths of 2,100–2,450 mbsf for the Giza MV and 1,150–1,550 mbsf for the North Alex MV. Very high temperatures of up to 70°C in shallow sediments at the North Alex MV can be explained only if the fluid source were warmer and deeper than the sediment source.
    Materialart: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1007/s00367-010-0192-0
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  • 8
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    Nature and origin of fine laminated sediments from the western Nile Delta: high resolution elemental content and lithology (2009)
    In:  [Poster] In: EGU General Assembly, 20.04.-24.04, Vienna, Austria .
    Details
    Publikationsdatum: 2012-07-06
    Materialart: Conference or Workshop Item , NonPeerReviewed
    Format: text
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  • 9
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    Deep water formation in the Bering Sea? Insights from Nd isotopes fo Site U1341 (Bowers Ridge, IODP 323) (2012)
    In:  [Poster] In: Gemeinsames IODP/ICDP Kolloquium 2012, 07.03.-09.03.2012, Kiel .
    Details
    Publikationsdatum: 2012-04-12
    Materialart: Conference or Workshop Item , NonPeerReviewed
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  • 10
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    Formation and preservation of greigite (Fe〈sub〉3〈/sub〉S〈sub〉4〈/sub〉) in sediments from the Santa Barbara Basin: implications for paleoenvironmental changes during the past 35 ka (2009)
    AGU (American Geophysical Union)
    In:  Paleoceanography, 24 (PA2224).
    Details
    Publikationsdatum: 2017-05-10
    Beschreibung: Diagenetic processes are known to modify sedimentary records, but they can also reveal important paleoenvironmental changes. Here we investigate variations in sedimentary iron diagenesis and depositional environments for the last 35 ka by analyzing the rock magnetic and geochemical properties of two sediment cores collected in the Santa Barbara Basin (California). In organic-rich sediments, early diagenesis often leads to partial dissolution of detrital iron oxides and stepwise formation of authigenic pyrite (FeS2). The pyritization process takes place following several geochemical pathways, sometimes involving intermediate iron sulfide species such as greigite (Fe3S4). Sedimentary conditions in the basin appear to have recurrently favored preservation of greigite (identified by its magnetic properties) and inhibited its complete transformation into pyrite. The Holocene interval contains a series of centimeter-thick greigite-bearing layers that are associated with large flood deposits, which are known in the basin as ‘‘gray layers.’’ We propose that greigite preservation was enabled in these sediments by their relative enrichment in reactive iron over organic matter and/or hydrogen sulfide (because of their high ratio of terrigenous over organic material), which limited pyritization reactions. Within the glacial deposits, formation and preservation of meter-thick greigite layers occurred in terrigenous-rich and organic-poor sedimentary layers and is proposed to result from a similar diagenetic process to that in the Holocene greigite-bearing layers (dominance of reactive iron over organic matter and/or HS�). The terrigenous enrichments in the glacial greigite-bearing layers are probably related to climatic or sea level changes because they occur at times of massive iceberg releases in the North Atlantic, the so-called Heinrich events.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2008PA001719
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