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  • 1
    Electronic Resource
    Electronic Resource
    Impacts of orbital forcing and atmospheric carbon dioxide on Miocene ice-sheet expansion (2005)
    [s.l.] : Nature Publishing Group
    Nature 438 (2005), S. 483-487 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The processes causing the middle Miocene global cooling, which marked the Earth's final transition into an ‘icehouse’ climate about 13.9 million years ago (Myr ago), remain enigmatic. Tectonically driven circulation changes and variations in atmospheric carbon dioxide levels ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature04123
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  • 2
    Electronic Resource
    Electronic Resource
    Late Cretaceous deep-water agglutinated foraminiferal assemblages from the North Atlantic and its marginal seas (1989)
    Springer
    International journal of earth sciences 78 (1989), S. 1121-1140 
    Details
    ISSN: 1437-3262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Abstract The stratigraphic and biogeographic distribution of more than 170 species of deep-water agglutinated benthic foraminifers (DWAF) from the North Atlantic and adjacent marginal seas has been compared with paleoenvironmental data (e.g. paleobathymetry, oxygenation of the bottom waters, amount of terrigenous input and substrate disturbance). Six general types of assemblages, in which deep water agglutinated taxa occur, are defined from the Turonian to Maastrichtian times: 1. High latitude slope assemblages 2. Low to mid latitude slope assemblages 3. Flysch-type assemblages 4. Deep water limestone assemblages (»Scaglia«-type) 5. Abyssal mixed calcareous-agglutinated assemblages 6. Abyssal purely agglutinated assemblages Latitudinal differences in faunal composition are observed, the most important of which is the lack or extreme paucity of calcareous forms in high latitude assemblages. East-to-west differences appear to be of comparatively minor importance. Most DWAF species occur in all studied regions and are thus considered as cosmopolitan. Biostratigraphic turnovers in the taxonomic content of assemblages are observed in the lowermost Turonian, mid- Campanian and in the upper Maastrichtian to lowermost Paleocene. These datum levels correspond to inter-regional and time-constant paleooceanographic events, which probably also affected the deep-water benthic biota. This allows us to use deep-water agglutinated foraminifers for biostratigraphy in the North Atlantic sequences deposited below CCD and to geographically extend the currently used zonal schemes which have been established in the Carpathian and Alpine areas.
    Abstract: Résumé La répartition stratigraphique et biogéographique de plus de cent soixante dix espèces de foraminifères benthiques agglutinants d'eaux profondes de l'Océan Atlantique Nord et des mers adjacentes a été examinée en fonction des paramètres du paléoenvironnement (paléobathymétrie, oxygénation et dynamique des eaux de fond, apports détritiques terrigènes). Sur une période s'étendant du Turonien au Maestrichtien, six types principaux d'associations, comprenant en tout ou partie des taxons agglutinants profonds, ont été définis: 1. associations de talus en haute latitude 2. associations de talus en basse latitude 3. associations de type flysch 4. associations de calcaires pélagiques (type »Scaglia«) 5. associations abyssales de type mixte avec foraminifères à test calcaire et foraminifères agglutinants 6. associations abyssales uniquement composées d'agglutinants. Des différences latitudinales sont apparues dans la composition faunique: la plus importante réside dans l'absence ou la très grande rareté des formes à test calcaire dans les associations de haute latitude. Des différences en longitude, d'est en ouest, apparaissent comparativement d'importance mineure. La plupart des espèces de foraminifères agglutinants d'eaux profondes se rencontrent dans toutes les régions étudiées et peuvent donc être considérées comme ubiquistes. De nettes coupures biostratigraphiques, fondées sur des renouvellements fauniques, sont décelées au Turonien basal, au Campanien moyen et au passage Meastrichtien supérieur-Paléocène basal. Ces niveaux repères correspondent à des événements paléo-océanographiques isochrones et d'extension supra-régionale, qui ont probablement affecté aussi les formes benthiques d'eaux profondes. Ceci nous incite à utiliser les foraminifères benthiques profonds pour la biostratigraphie des séries Nord-Atlantique déposées sous la CCD et par corrélation nous permet d'étendre géographiquement l'usage de zonations initialement définies dans le domaine alpino-carpathique.
    Notes: Zusammenfassung Die stratigraphische und biogeographische Verbreitung von mehr als 170 Arten sandschaliger benthischer Tiefwasser-Foraminiferen wurde im Nordatlantik und seinen Randmeeren untersucht. Hierbei wurden die in den einzelnen Untersuchungsgebieten unterschiedlichen Paläoenvironment- Bedingungen (Wassertiefe, Sauerstoffverhältnisse am Ozeanboden, detritischer Eintrag und Beeinträchtigung des Substrats durch Strömungs- und Sedimentationsprozesse) zu der jeweiligen taxonomischen Zusammensetzung der agglutinierenden Benthos-Fauna in Beziehung gesetzt. Für den Zeitraum vom Turon bis zum Maastricht ließen sich zwölf charakteristische Vergesellschaftungen agglutinierender Tiefwasser-Foraminiferen unterscheiden, die in sechs Hauptgruppen zusammengefaßt werden können: 1. Kontinentalhang-Vergesellschaftungen hoher Breiten 2. Kontinentalhang-Vergesellschaftungen niedriger bis mittlerer Breiten 3. Flysch-Vergesellschaftungen 4. Vergesellschaftungen pelagischer Kalke (»Scaglia«-Typ) 5. Abyssale gemischt kalkschalige und agglutinierende Benthos-Vergesellschaftungen 6. Abyssale rein agglutinierende Vergesellschaftungen Biogeographische Unterschiede in der Faunenzusammensetzung korrelieren vor allem mit der geographischen Breite, wobei besonders das Fehlen kalkschaliger Elemente in Faunen hoher Breiten auffällt. Ost-West-Unterschiede sind von geringerer Bedeutung, die Mehrzahl der Arten tritt in allen untersuchten Gebieten auf und kann als kosmopolitisch angesehen werden. Faunenschnitte können im basalen Turon, im mittleren Campan und an der Kreide/Tertiär-Grenze beobachtet werden. Diese Zeitabschnitte sind durch überregionale paläoozeanographische Events charakterisiert, die wahrscheinlich auch das Tiefsee-Benthos beeinflußt haben. Dieser Zusammenhang zwischen der Evolution agglutinierender Tiefsee- Foraminiferen und globalen, zeitkonstanten Events ermöglicht eine biostratigraphische Gliederung der Sub-CCD Serien des Nordatlantik mit Hilfe sandschaliger Foraminiferen, die sich weitgehend mit den Zonierungen, die in den Flyschzonen der Karpathen und Alpen entwickelt wurden, korrelieren läßt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01829336
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  • 3
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    Transient global cooling at the onset of early Aptian oceanic anoxic event (OAE) 1a (2011)
    Geological Society of America (GSA)
    Details
    Publication Date: 2011-04-01
    Description: The onset of the early Aptian oceanic anoxic event (OAE) 1a (ca. 120 Ma) coincided with a major perturbation of the carbon cycle, which is reflected in the sedimentary carbon isotope record. Triggering mechanisms, duration, and climatic repercussions of this episode of accelerated organic matter burial remain poorly constrained. Here, we present millennial-scale bulk rock carbon and oxygen isotope data from a marly subtropical intrashelf basin (La Bedoule, southeast France) with unusually high sedimentation rates, which track the onset of OAE1a in unprecedented resolution. Our record reveals that the negative, low-amplitude {delta}13C excursion preceding OAE1a lasted 〉100 k.y., implying that enhanced volcanic CO2 emission and/or pulsed methane dissociation over a prolonged time span were instrumental in triggering OAE1a. The main positive carbon isotope shift at the onset of OAE1a, previously regarded as continuous, occurred stepwise over an extended period of 〉300 k.y. Transient climate cooling during the initial {delta}13C increase probably reflects ephemeral high-latitude glaciation, triggered by changes in radiative forcing and drawdown of atmospheric CO2.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 4
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    Variations in sea surface hydrology in the southern Makassar Strait over the past 26kyr. (2016)
    PERGAMON-ELSEVIER SCIENCE LTD
    In:  EPIC3Quaternary Science Reviews, PERGAMON-ELSEVIER SCIENCE LTD, 154, pp. 143-156, ISSN: 0277-3791
    Details
    Publication Date: 2018-08-10
    Description: We present centennial-scale records of sea surface temperature and oxygen isotopes in a sediment core from Mandar Bay, offshore Sulawesi in the southern Makassar Strait, which provide new insights into the variability of Indonesian climate over the past 26 kyr. The age model for the core is constrained by 17 AMS radiocarbon ages, with a surface ocean reservoir age correction based on paired wood and foraminiferal samples. Small Holocene reservoir ages of 105 ± 180 years point to intense surface ocean-atmosphere interchange linked to increased monsoonal precipitation, whereas Last Glacial Maximum and deglacial reservoir ages are significantly higher. Mg/Ca derived sea surface temperature reconstructions based on Globigerinoides ruber (s. s., white) exhibit an extended plateau during the Antarctic Cold Reversal, suggesting an atmospheric connection to high-latitude Southern Hemisphere climate and a seasonal bias on G. ruber. This is in agreement with southern hemisphere sites along the track of the Indonesian Throughflow and in contrast to Northern Hemisphere records from the South China Sea, Sulu Sea and Western Pacific (off Mindanao), which exhibit warming during the Bølling-Allerød. Ice-volume corrected δ18O seawater (δ18Osw) increased during Heinrich Stadial 1 and the Younger Dryas, whereas the Bølling-Allerød is characterized by low δ18Osw. We attribute δ18Osw variability in the southern Makassar Strait during the Last Glacial Maximum and glacial termination to changes in provenance and seasonality of precipitation rather than to variability in the amount of local precipitation and runoff.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 5
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    Provenance and weathering of clays delivered to the Bay of Bengal during the middle Miocene: linkages to tectonics and monsoonal climate (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bretschneider, L., Hathorne, E. C., Huang, H., Luebbers, J., Kochhann, K. G. D., Holbourn, A., Kuhnt, W., Thiede, R., Gebregiorgis, D., Giosan, L., & Frank, M. Provenance and weathering of clays delivered to the Bay of Bengal during the middle Miocene: linkages to tectonics and monsoonal climate. Paleoceanography and Paleoclimatology, 36(2), (2021): e2020PA003917, https://doi.org/10.1029/2020PA003917.
    Description: Tectonics and regional monsoon strength control weathering and erosion regimes of the watersheds feeding into the Bay of Bengal, which are important contributors to global climate evolution via carbon cycle feedbacks. The detailed mechanisms controlling the input of terrigenous clay to the Bay of Bengal on tectonic to orbital timescales are, however, not yet well understood. We produced orbital‐scale resolution geochemical records for International Ocean Discovery Program Site U1443 (southern Bay of Bengal) across five key climatic intervals of the middle to late Miocene (15.8–9.5 Ma). Our new radiogenic Sr, Nd, and Pb isotope time series of clays transported to the Ninetyeast Ridge suggest that the individual contributions from different erosional sources overall remained remarkably consistent during the Miocene despite major tectonic reorganizations in the Himalayas. On orbital timescales, however, high‐resolution data from the five investigated intervals show marked fluctuations of all three isotope systems. Interestingly, the variability was much higher within the Miocene Climatic Optimum (around 16–15 Ma) and across the major global cooling (~13.9–13.8 Ma) until ~13.5 Ma, than during younger time intervals. This change is attributed to a major restriction on the supply of High Himalayan erosion products due to migration of the peak precipitation area toward the frontal domains of the Himalayas and the Indo‐Burman Ranges. The transient excursions of the radiogenic isotope signals on orbital timescales most likely reflect climatically driven shifts in monsoon strength.
    Description: This research used samples and data provided by the International Ocean Discovery Program and was funded by the German Research Foundation (DFG) (grants HA 5751/6‐1 and HA 5751/6‐2, KU 649/36‐1, and TH 1317‐8 and TH 1317‐9). Open access funding enabled and organized by Projekt DEAL.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 6
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    Enhanced late miocene chemical weathering and altered precipitation patterns in the watersheds of the Bay of Bengal recorded by detrital clay radiogenic isotopes (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bretschneider, L., Hathorne, E. C., Bolton, C. T., Gebregiorgis, D., Giosan, L., Gray, E., Huang, H., Holbourn, A., Kuhnt, W., & Frank, M. Enhanced late miocene chemical weathering and altered precipitation patterns in the watersheds of the Bay of Bengal recorded by detrital clay radiogenic isotopes. Paleoceanography and Paleoclimatology, 36(9), (2021): e2021PA004252, https://doi.org/10.1029/2021PA004252.
    Description: The late Miocene was a period of declining CO2 levels and extensive environmental changes, which likely had a large impact on monsoon strength as well as on the weathering and erosion intensity in the South Asian Monsoon domain. To improve our understanding of these feedback systems, detrital clays from the southern Bay of Bengal (International Ocean Discovery Program Site U1443) were analyzed for the radiogenic isotope compositions of Sr, Nd, and Pb to reconstruct changes in sediment provenance and weathering regime related to South Asian Monsoon rainfall from 9 to 5 Ma. The 100 kyr resolution late Miocene to earliest Pliocene record suggests overall low variability in the provenance of clays deposited on the Ninetyeast Ridge. However, at 7.3 Ma, Nd and Pb isotope compositions indicate a switch to an increased relative contribution from the Irrawaddy River (by ∼10%). This shift occurred during the global benthic δ13C decline, and we suggest that global cooling and increasing aridity resulted in an eastward shift of precipitation patterns leading to a more focused erosion of the Indo-Burman Ranges. Sr isotope compositions were decoupled from Nd and Pb isotope signatures and became more radiogenic between 6 and 5 Ma. Grassland expansion generating thick, easily weatherable soils may have led to an environment supporting intense chemical weathering, which is likely responsible for the elevated detrital clay 87Sr/86Sr ratios during this time. This change in Sr isotope signatures may also have contributed to the late Miocene increase of the global seawater Sr isotope composition.
    Description: This research used samples and data provided by the International Ocean Discovery Program and was funded by the German Research Foundation (DFG) (grants HA 5751/6-1 & -2). C. T. Bolton acknowledges funding from the French ANR project iMonsoon (ANR-16-CE01-0004-01) and IODP France. W. Kuhnt acknowledges funding from the DFG (grant Ku649/36-1).
    Keywords: Clay radiogenic isotopes ; Late Miocene ; South Asian Monsoon ; Chemical weathering
    Repository Name: Woods Hole Open Access Server
    Type: Article
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