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  • 1
    Language: English
    In: Palaeogeography, Palaeoclimatology, Palaeoecology, Jan 1, 2013, Vol.369, p.430(22)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.palaeo.2012.11.009 Byline: Christian Zeeden, Frederik Hilgen, Thomas Westerhold, Lucas Lourens, Ursula Rohl, Torsten Bickert Keywords: Miocene; Stratigraphy; ODP Site 926; Splice; Astronomical tuning Abstract: The distinctly cyclic sediments recovered during ODP Leg 154 played an important role in constructing the astronomical time scale and associated astro(bio)chronology for the Miocene, and in deciphering ocean-climate history. The accuracy of the timescale critically depends on the reliability of the shipboard splice used for the tuning and on the tuning itself. New high-resolution colour- and magnetic susceptibility core scanning data supplemented with limited XRF-data allow improvement of the stratigraphy. The revised composite record results in an improved astronomical age model for ODP Site 926 between 5 and 14.4Ma. The new age model is confirmed by results of complex amplitude demodulation of the precession and obliquity related cycle patterns. Different values for tidal dissipation are applied to improve the fit between the sedimentary cycle patterns and the astronomical solution. Due to the improved stratigraphy and tuning, supported by the results of amplitude demodulation, the revised time scale yields more reliable age estimates for planktic foraminiferal and calcareous nannofossil events. The results of this study highlight the importance of stratigraphy for timescale construction. Article History: Received 27 January 2012; Revised 7 November 2012; Accepted 9 November 2012
    ISSN: 0031-0182
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Palaeogeography, Palaeoclimatology, Palaeoecology, 01 May 2015, Vol.425, pp.67-75
    Description: We provide a new multivariate calibration-function based on South Atlantic modern assemblages of planktonic foraminifera and atlas water column parameters from the Antarctic Circumpolar Current to the Subtropical Gyre and tropical warm waters (i.e., 60°S to 0°S). Therefore, we used a dataset with the abundance pattern of 35 taxonomic groups of planktonic foraminifera in 141 surface sediment samples. Five factors were taken into consideration for the analysis, which account for 93% of the total variance of the original data representing the regional main oceanographic fronts. The new calibration-function F141-35-5 enables the reconstruction of Late Quaternary summer and winter sea-surface temperatures with a statistical error of ~ 0.5°C. Our function was verified by its application to a sediment core extracted from the western South Atlantic. The downcore reconstruction shows negative anomalies in sea-surface temperatures during the early–mid Holocene and temperatures within the range of modern values during the late Holocene. This pattern is consistent with available reconstructions.
    Keywords: Planktonic Foraminifera ; Sea-Surface Temperature ; Multivariate Correlation-Function ; Quaternary ; Western South Atlantic ; Geology
    ISSN: 0031-0182
    E-ISSN: 1872-616X
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  • 3
    Language: English
    In: Palaeogeography Palaeoclimatology Palaeoecology, 2013, Vol.369, pp.430-0182
    Description: The distinctly cyclic sediments recovered during ODP Leg 154 played an important role in constructing the astronomical time scale and associated astro(bio)chronology for the Miocene, and in deciphering ocean–climate history. The accuracy of the timescale critically depends on the reliability of the shipboard splice used for the tuning and on the tuning itself. New high-resolution colour- and magnetic susceptibility core scanning data supplemented with limited XRF-data allow improvement of the stratigraphy. The revised composite record results in an improved astronomical agemodel for ODP Site 926 between 5 and 14.4 Ma. The newagemodel is confirmed by results of complex amplitude demodulation of the precession and obliquity related cycle patterns. Different values for tidal dissipation are applied to improve the fit between the sedimentary cycle patterns and the astronomical solution. Due to the improved stratigraphy and tuning, supported by the results of amplitude demodulation, the revised time scale yields more reliable age estimates for planktic foraminiferal and calcareous nannofossil events. The results of this study highlight the importance of stratigraphy for timescale construction.
    Keywords: Miocene ; Stratigraphy ; Odp Site 926 ; Splice ; Astronomical Tuning
    ISSN: 0031-0182
    Source: NARCIS (National Academic Research and Collaborations Information System)
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  • 4
    Language: English
    In: Palaeogeography, Palaeoclimatology, Palaeoecology, 01 January 2013, Vol.369, pp.430-451
    Description: The distinctly cyclic sediments recovered during ODP Leg 154 played an important role in constructing the astronomical time scale and associated astro(bio)chronology for the Miocene, and in deciphering ocean–climate history. The accuracy of the timescale critically depends on the reliability of the shipboard splice used for the tuning and on the tuning itself. New high-resolution colour- and magnetic susceptibility core scanning data supplemented with limited XRF-data allow improvement of the stratigraphy. The revised composite record results in an improved astronomical age model for ODP Site 926 between 5 and 14.4 Ma. The new age model is confirmed by results of complex amplitude demodulation of the precession and obliquity related cycle patterns. Different values for tidal dissipation are applied to improve the fit between the sedimentary cycle patterns and the astronomical solution. Due to the improved stratigraphy and tuning, supported by the results of amplitude demodulation, the revised time scale yields more reliable age estimates for planktic foraminiferal and calcareous nannofossil events. The results of this study highlight the importance of stratigraphy for timescale construction. ► The stratigraphy of ODP Site 926 is improved. ► The orbitally tuned age model of ODP Site 926 is improved. ► The new age model is used to improve the calcareous plankton biochronology.
    Keywords: Miocene ; Stratigraphy ; Odp Site 926 ; Splice ; Astronomical Tuning ; Geology
    ISSN: 0031-0182
    E-ISSN: 1872-616X
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  • 5
    Language: English
    In: Marine Geology, Sept 1, 2013, Vol.343, p.39(8)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.margeo.2013.06.010 Byline: Inga V. Preiss-Daimler, Rudiger Henrich, Torsten Bickert Abstract: In many palaeoceanographic studies low carbonate contents in Neogene deep-sea sediments are interpreted as dissolution events related to prominent shifts in intermediate and deep-water circulation. In the middle to late Miocene such carbonate crash events were a widespread phenomenon throughout the world's ocean basins. However, low carbonate contents may also derive from terrigenous dilution and carbonate production changes in surface waters as shown for late Miocene records of the South Atlantic (Diester-Haass et al., 2004; Westerhold et al., 2005). In order to contribute to solve this question we investigated the youngest of the Miocene crash events (10.5Ma to 9.0Ma) at a prominent key location of global deep water circulation, i.e. the Equatorial Atlantic Ceara Rise depth transect (ODP Sites 926, 927 and 928). By analysing different carbonate preservation proxies like carbonate content, silt grain size parameters, sand content, fragmentation index and mass accumulation rates we were able to quantify dissolution, dilution and production, and to assess previous conflicting interpretations. Critical evaluation of the different dissolution proxies and comparison to former studies revealed that silt preservation proxies do not entirely reproduce the depth dependant dissolution in the Miocene sediments, as indicated by foraminifer fragmentation. In the investigated late Miocene time slice three minima of carbonate accumulation were detected. The predominant control on these events changed from dissolution of carbonate to lowered production. The last event at 9.6Ma is accompanied by an increased preservation but reduced carbonate accumulation. During this time the first prominent pulses of Northern Component Water (NCW) occurred, sourced most probably from the Labrador Sea. This may be understood as a first short term precursor of long time persistent and much stronger NCW production that is characteristic for younger periods and marks the turnover to the modern type of basin-to-basin fractionation between the Atlantic and Pacific. Furthermore, preservation trends of Caribbean and Ceara Rise records were in phase in contrast to former hypotheses that suggested antithetical preservation during carbonate crash events. The similarity of the preservation records in the studied ocean basins in conjunction with the inconsistency in timing of the CC-events and proposed NCW estimates indicates that changes in the carbon cycle other than dissolution controlled the CC events prior to ~9.9Ma. Article History: Received 8 March 2011; Revised 17 May 2013; Accepted 14 June 2013 Article Note: (miscellaneous) Communicated by G.J. de Lange
    Keywords: Water Circulation -- Analysis ; Carbonates -- Analysis ; Carbon Cycle -- Analysis ; Terrigenous Sediments -- Analysis
    ISSN: 0025-3227
    Source: Cengage Learning, Inc.
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  • 6
    Language: English
    In: Earth and Planetary Science Letters, 2009, Vol.284(3), pp.630-638
    Description: The middle Miocene climate approximately 14 Ma ago was characterized by the glaciation of Antarctica, deep-ocean cooling and variations in the global carbon cycle. Although the Southern Ocean underwent significant oceanographic changes, there is limited information on their spatial extent and timing. However, such knowledge is crucial for understanding the role of the Southern Ocean and the Antarctic Circumpolar Current (ACC) for Antarctic glaciation and the coupling between the ocean and continental climate. We have reconstructed surface temperatures and seawater oxygen isotopes at Ocean Drilling Program (ODP) Site 1092 in the Polar Frontal Zone of the Atlantic sector of the Southern Ocean from foraminiferal oxygen isotopes ( O) and magnesium to calcium ratios (Mg/Ca). Sea surface cooling by ~ 4 °C and freshening indicated by the ~ 1‰ reduction of seawater O ( O ) at 14.2 Ma precede the major step in Antarctic ice sheet growth at 13.8–13.9 Ma. This pattern qualitatively mirrors previous findings from the Pacific sector, and we interpret the surface hydrographic changes to reflect the circum-Antarctic northward shift of the Southern Ocean fronts and specifically at Site 1092 the passage of the Subantarctic Front. The magnitude of change in reconstructed O requires a O : salinity gradient significantly higher than the modern value (~ 0.52‰) and it possibly exceeded 1.1‰. This implies the Polar Frontal Zone was influenced by freshwater derived from Antarctica, which in turn confirms higher than modern continental precipitation. The latter has previously been suggested to have contributed to Antarctic glaciation.
    Keywords: Middle Miocene ; Southern Ocean ; Mg/Ca ; Stable Isotopes ; Subantarctic Front ; Geology ; Physics
    ISSN: 0012-821X
    E-ISSN: 1385-013X
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  • 7
    In: Paleoceanography, September 2011, Vol.26(3), pp.n/a-n/a
    Description: The glacial marine isotope stage 14 (MIS 14) appears in many climate records as an unusually warm glacial. During this period an almost monospecific, up to 1.5 m thick, laminated layer of the giant diatom has been deposited below the South Atlantic Subtropical Gyre. This oligotrophic region is today less favorable for diatom growth with sediments typically consisting of calcareous nannofossil oozes. We have reconstructed temperatures and the stable oxygen isotopic compositions of sea surface and thermocline water (O) from planktonic foraminiferal ( and ) Mg/Ca and stable oxygen isotopes to test whether perturbations in surface ocean conditions contributed to the deposition of the diatom layer at ∼530 kyr B.P. Temperatures and O values reconstructed from this diatom ooze interval are highly variable, with maxima similar to interglacial values. Since the area of the oozes resembles the region where Agulhas rings are present, we interpret these hydrographic changes to reflect the varying influence of warm and saline water of Indian Ocean origin that entered the Subtropical Gyre trapped in Agulhas rings. The formation of the oozes is associated with a period of maximum Agulhas leakage and a maximum frequency of Agulhas ring formation caused by a termination‐type position of the Subtropical Front during the unusual warm MIS 14. The input of silica through the Agulhas rings enabled the shift in primary production from calcareous nannoplankton to diatoms, leading to the deposition of the massive diatom oozes. Maximum Agulhas leakage caused massive South Atlantic Ethmodiscus oozes Agulhas rings were favorable environment for buoyant giant diatom E. rex Agulhas rings led to shift from calcareous nannoplankton to diatom production
    Keywords: Agulhas ; Ethmodiscus ; Mis 14 ; South Atlantic ; Subtropical Gyre
    ISSN: 0883-8305
    E-ISSN: 1944-9186
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  • 8
    Language: English
    In: Marine Geology, 01 September 2013, Vol.343, pp.39-46
    Description: In many palaeoceanographic studies low carbonate contents in Neogene deep-sea sediments are interpreted as dissolution events related to prominent shifts in intermediate and deep-water circulation. In the middle to late Miocene such carbonate crash events were a widespread phenomenon throughout the world's ocean basins. However, low carbonate contents may also derive from terrigenous dilution and carbonate production changes in surface waters as shown for late Miocene records of the South Atlantic ( ). In order to contribute to solve this question we investigated the youngest of the Miocene crash events (10.5 Ma to 9.0 Ma) at a prominent key location of global deep water circulation, i.e. the Equatorial Atlantic Ceará Rise depth transect (ODP Sites 926, 927 and 928). By analysing different carbonate preservation proxies like carbonate content, silt grain size parameters, sand content, fragmentation index and mass accumulation rates we were able to quantify dissolution, dilution and production, and to assess previous conflicting interpretations. Critical evaluation of the different dissolution proxies and comparison to former studies revealed that silt preservation proxies do not entirely reproduce the depth dependant dissolution in the Miocene sediments, as indicated by foraminifer fragmentation. In the investigated late Miocene time slice three minima of carbonate accumulation were detected. The predominant control on these events changed from dissolution of carbonate to lowered production. The last event at 9.6 Ma is accompanied by an increased preservation but reduced carbonate accumulation. During this time the first prominent pulses of Northern Component Water (NCW) occurred, sourced most probably from the Labrador Sea. This may be understood as a first short term precursor of long time persistent and much stronger NCW production that is characteristic for younger periods and marks the turnover to the modern type of basin-to-basin fractionation between the Atlantic and Pacific. Furthermore, preservation trends of Caribbean and Ceará Rise records were in phase in contrast to former hypotheses that suggested antithetical preservation during carbonate crash events. The similarity of the preservation records in the studied ocean basins in conjunction with the inconsistency in timing of the CC-events and proposed NCW estimates indicates that changes in the carbon cycle other than dissolution controlled the CC events prior to ~ 9.9 Ma.
    Keywords: Carbonate Crash Events ; Miocene ; Silt Grain Size Distribution ; Carbonate Mass Accumulation ; Atlantic ; Caribbean ; Oceanography ; Geology
    ISSN: 0025-3227
    E-ISSN: 1872-6151
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  • 9
    In: Reviews of Geophysics, September 2014, Vol.52(3), pp.333-374
    Description: The climate during the Cenozoic era changed in several steps from ice‐free poles and warm conditions to ice‐covered poles and cold conditions. Since the 1950s, a body of information on ice volume and temperature changes has been built up predominantly on the basis of measurements of the oxygen isotopic composition of shells of benthic foraminifera collected from marine sediment cores. The statistical methodology of time series analysis has also evolved, allowing more information to be extracted from these records. Here we provide a comprehensive view of Cenozoic climate evolution by means of a coherent and systematic application of time series analytical tools to each record from a compilation spanning the interval from 4 to 61 Myr ago. We quantitatively describe several prominent features of the oxygen isotope record, taking into account the various sources of uncertainty (including measurement, proxy noise, and dating errors). The estimated transition times and amplitudes allow us to assess causal climatological‐tectonic influences on the following known features of the Cenozoic oxygen isotopic record: Paleocene‐Eocene Thermal Maximum, Eocene‐Oligocene Transition, Oligocene‐Miocene Boundary, and the Middle Miocene Climate Optimum. We further describe and causally interpret the following features: Paleocene‐Eocene warming trend, the two‐step, long‐term Eocene cooling, and the changes within the most recent interval (Miocene‐Pliocene). We review the scope and methods of constructing Cenozoic stacks of benthic oxygen isotope records and present two new latitudinal stacks, which capture besides global ice volume also bottom water temperatures at low (less than 30°) and high latitudes. This review concludes with an identification of future directions for data collection, statistical method development, and climate modeling. We provide a comprehensive, quantitative view of Cenozoic climate evolution
    Keywords: Climate ; Cenozoic ; Oxygen Isotopes ; Time Series Analysis
    ISSN: 8755-1209
    E-ISSN: 1944-9208
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  • 10
    Language: English
    In: Journal of Marine Science and Engineering, 01 November 2015, Vol.3(4), pp.1311-1333
    Description: We examine the role of the vegetation cover and the associated hydrological cycle on the deep ocean circulation during the Late Miocene (~10 million years ago). In our simulations, an open Central American gateway and exchange with fresh Pacific waters leads to a weak and shallow thermohaline...
    Keywords: Ocean Circulation ; Late Miocene ; Hydrological Cycle ; Central American Gateway ; Oceanography
    E-ISSN: 2077-1312
    Source: Directory of Open Access Journals (DOAJ)
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