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  • 1
    Publication Date: 2023-11-24
    Description: The Middle Miocene (15.99–11.65 Ma) of Europe witnessed major climatic, environmental, and vegetational change, yet we are lacking detailed reconstructions of Middle Miocene temperature and precipitation patterns over Europe. Here, we use a high‐resolution (∼0.75°) isotope‐enabled general circulation model (ECHAM5‐wiso) with time‐specific boundary conditions to investigate changes in temperature, precipitation, and δ〈sup〉18〈/sup〉O in precipitation (δ〈sup〉18〈/sup〉O〈sub〉p〈/sub〉). Experiments were designed with variable elevation configurations of the European Alps and different atmospheric CO〈sub〉2〈/sub〉 levels to examine the influence of Alpine elevation and global climate forcing on regional climate and δ〈sup〉18〈/sup〉Op patterns. Modeling results are in agreement with available paleobotanical temperature data and with low‐resolution Middle Miocene experiments of the Miocene Model Intercomparison Project (MioMIP1). However, simulated precipitation rates are 300–500 mm/yr lower in the Middle Miocene than for pre‐industrial times for central Europe. This result is consistent with precipitation estimates from herpetological fossil assemblages, but contradicts precipitation estimates from paleobotanical data. We attribute the Middle Miocene precipitation change in Europe to shifts in large‐scale pressure patterns in the North Atlantic and over Europe and associated changes in wind direction and humidity. We suggest that global climate forcing contributed to a maximum δ〈sup〉18〈/sup〉O〈sub〉p〈/sub〉 change of ∼2‰ over high elevation (Alps) and ∼1‰ over low elevation regions. In contrast, we observe a maximum modeled δ〈sup〉18〈/sup〉O〈sub〉p〈/sub〉 decrease of 8‰ across the Alpine orogen due to Alpine topography. However, the elevation‐δ〈sup〉18〈/sup〉O〈sub〉p〈/sub〉 lapse rate shallows in the Middle Miocene, leading to a possible underestimation of paleotopography when using present‐day δ〈sup〉18〈/sup〉O〈sub〉p〈/sub〉—elevation relationships data for stable isotope paleoaltimetry studies.
    Description: Key Points: A high‐resolution isotope‐enabled general circulation model is used to explore Middle Miocene climate and precipitation δ〈sup〉18〈/sup〉O across Europe. Middle Miocene bi‐directional precipitation change consistent with herpetological fossils and account for precipitation δ〈sup〉18〈/sup〉O variations. Global Miocene climate forcing contributed a max δ〈sup〉18〈/sup〉O change of ∼2‰ over the high Alpine elevation and to ∼1‰ over low elevation.
    Description: German research fondation
    Description: Alexander‐von‐Humboldt foundation, Feodor‐Lynen‐Fellowship
    Description: Alexander‐von‐Humboldt foundation, Humboldt Research Fellowship
    Description: Scientific Steering Committee
    Description: https://mpimet.mpg.de/fileadmin/projekte/ICON-ESM/mpi-m_sla_201202.pdf
    Description: https://gitlab.awi.de/mwerner/mpi-esm-wiso
    Description: https://zenodo.org/record/6308475#.Y0gmDSFS-2w
    Keywords: ddc:550.724 ; Europe ; Middle Miocene ; climate modeling ; stable water isotopes ; temperature ; precipitation ; paleoclimate ; paleoelevation ; Alps
    Language: English
    Type: doc-type:article
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  • 2
    Publication Date: 2023-11-24
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Uplift of the Tian Shan range modified regional climate during Cenozoic aridification in Central Asia. This study presents facies analyses and Neogene oxygen and carbon isotopic records from magnetostratigraphically dated terrestrial sedimentary sections on the southern side of the intermontane Issyk‐Kul basin in the Kyrgyz Tian Shan and 〈sup〉26〈/sup〉Al/〈sup〉10〈/sup〉Be isochron burial ages from the southern and eastern sides of the basin. The δ〈sup〉18〈/sup〉O and δ〈sup〉13〈/sup〉C data show a positive ca. 2‰ shift in values between ca. 8 and 7 Ma and a change from a negative to a positive trend. This change is attributed to the upwind growth of the Kyrgyz, Kungey and Trans Ili (Zaili) ranges, which diverted the westerlies, thereby changing the Issyk‐Kul basin from a windward to a leeward position, enhancing aridification and establishing the modern‐day spring and summer precipitation regime within the basin. Two 4 to 5 Ma 〈sup〉26〈/sup〉Al/〈sup〉10〈/sup〉Be isochron burial ages constrain the onset of Sharpyl Dak deposition on the eastern side of the basin; southward paleocurrent directions there suggest the eastward growth of the Kungey range in the Pliocene. Increased subsidence on the southern side of the basin and local tectonically induced river system reorganization led to the commencement of lake formation at ca. 5 Ma, followed by a ca. 2 Ma local depositional hiatus. The transition from sandstones of the Chu sedimentary group to conglomerates of the Sharpyl Dak group, marking a change from fluvial‐alluvial deposits to a proximal alluvial fan, is dated at 2.6–2.8 Ma by 〈sup〉26〈/sup〉Al/〈sup〉10〈/sup〉Be isochron burial dating on the southern side of the basin, driven either by tectonics or Northern Hemisphere glaciation. This study concludes that the late Miocene–Pliocene northward growth of Tian Shan significantly altered environmental conditions within the range, preventing the moisture‐bearing westerlies from reaching the intermontane Issyk‐Kul basin and promoting lake formation and expansion.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The late Miocene–Pliocene northward growth of Tian Shan created an orographic barrier that diverted the moisture‐bearing westerlies and enhanced aridification in the Issyk‐Kul basin. Reorganization of the river systems and enhanced subsidence led to the formation of an internally drained lake in Pliocene. The transition from sandstone to conglomerate (Sharpyl Dak group) deposition, linked to a change in climate and/or tectonic activity, occurred diachronously within the basin.〈boxed-text position="anchor" content-type="graphic" id="bre12751-blkfxd-0001" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:0950091X:bre12751:bre12751-toc-0001"〉 〈/graphic〉〈/boxed-text〉〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: University of Wollongong http://dx.doi.org/10.13039/501100001777
    Keywords: ddc:551 ; Cenozoic aridification ; Central Asia ; cosmogenic 26Al/10Be ; tectonic uplift ; westerlies ; δ18O and δ13C stable isotopes
    Language: English
    Type: doc-type:article
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 439 (2006), S. 670-671 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Is Everest now at its highest point, or was it once even loftier? What was the greatest height attained by the vast highlands of the Tibetan plateau, and when did this occur? As described elsewhere in this issue by Rowley and Currie (page 677), these questions can be tackled — if not ...
    Type of Medium: Electronic Resource
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  • 4
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    The Geological Society Publ. House
    In:  Bull., Polar Proj. OP-O3A4, The Nature and Tectonic Significance of Fault Zone Weakening, Bath, The Geological Society Publ. House, vol. 186, no. XVI:, pp. 305-332, (ISBN: 3-540-23712-7)
    Publication Date: 2001
    Keywords: Fault zone ; Rock mechanics ; Tectonics ; Fault plane solution, focal mechanism ; SAF ; Modelling ; Friction ; permeability ; Fluids ; Ocean Drilling Program ; Alpine ; Fault ; Rheology ; geometry ; melts ; Fracture ; Physical properties of rocks
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  • 5
    Publication Date: 2001-01-01
    Description: The rheology of crustal fault zones containing melts is governed primarily by two strain-dependent mechanical discontinuities: (1) a strength minimum parallel to mylonitic foliation just below the active brittle-viscous (b-v) transition; (2) the anatectic front, which marks the upper depth limit of anatectic flow. The mode of syntectonic melt segregation in fault zones is determined by the scale of strain localization and melt-space connectivity, to an extent dependent on strain, strain rate and melt fraction in the rock. Melt drains from the mylonitic wall rock into dilatant shear surfaces, which propagate sporadically as veins. Anatectic flow at natural strain rates therefore involves melt-assisted creep punctuated by melt-induced veining. On the crustal scale, dilatant shear surfaces and vein networks serve as conduits for the rapid, buoyancy-driven ascent of transiently overpressured melt from melt-source rocks at or just below the anatectic front to sinks higher in the crust. Strength estimates for natural rocks that experienced anatectic flow indicate that melts weaken the continental crust, particularly in depth intervals where they spread laterally beneath low-permeability layers or along active shear zones with a pronounced mylonitic foliation. However, acute weakening associated wit h strength drops of more than an order of magnitude occurs only during short periods (103-105 a) of crustal-scale veining. Cooling and crystallization at the end of these veining episodes is fast and hardens the crust to strengths at least as great as, and in some cases greater than, its pre-melting strength. Repeated melt-induced weakening then hardening of fault zones may be linked to other orogenic processes that occur episodically (shifting centres of clastic sedimentation and volcanism) and has implications for stress transmission across orogenic wedges and magmatic arcs.
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  • 6
    Publication Date: 2008-04-25
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 7
    Publication Date: 2018-12-10
    Description: New geochemical data from the Malawi Rift (Chiwondo Beds, Karonga Basin) fill a major spatial gap in our knowledge of hominin adaptations on a continental scale. Oxygen (δ18O), carbon (δ13C), and clumped (Δ47) isotope data on paleosols, hominins, and selected fauna elucidate an unexpected diversity in the Pleistocene hominin diet in the various habitats of the East African Rift System (EARS). Food sources of early Homo and Paranthropus thriving in relatively cool and wet wooded savanna ecosystems along the western shore of paleolake Malawi contained a large fraction of C3 plant material. Complementary water consumption reconstructions suggest that ca. 2.4 Ma, early Homo (Homo rudolfensis) and Paranthropus (Paranthropus boisei) remained rather stationary near freshwater sources along the lake margins. Time-equivalent Paranthropus aethiopicus from the Eastern Rift further north in the EARS consumed a higher fraction of C4 resources, an adaptation that grew more pronounced with increasing openness of the savanna setting after 2 Ma, while Homo maintained a high versatility. However, southern African Paranthropus robustus had, similar to the Malawi Rift individuals, C3-dominated feeding strategies throughout the Early Pleistocene. Collectively, the stable isotope and faunal data presented here document that early Homo and Paranthropus were dietary opportunists and able to cope with a wide range of paleohabitats, which clearly demonstrates their high behavioral flexibility in the African Early Pleistocene.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 8
    Publication Date: 2016-09-12
    Description: At global and regional scales, primary productivity strongly correlates with richness patterns of extant animals across space, suggesting that resource availability and climatic conditions drive patterns of diversity. However, the existence and consistency of such diversity–productivity relationships through geological history is unclear. Here we provide a comprehensive quantitative test of the diversity–productivity relationship for terrestrial large mammals through time across broad temporal and spatial scales. We combine 〉14,000 occurrences for 690 fossil genera through the Neogene (23–1.8 Mya) with regional estimates of primary productivity from fossil plant communities in North America and Europe. We show a significant positive diversity–productivity relationship through the 20-million-year record, providing evidence on unprecedented spatial and temporal scales that this relationship is a general pattern in the ecology and paleo-ecology of our planet. Further, we discover that genus richness today does not match the fossil relationship, suggesting that a combination of human impacts and Pleistocene climate variability has modified the 20-million-year ecological relationship by strongly reducing primary productivity and driving many mammalian species into decline or to extinction.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 9
    Publication Date: 2015-06-04
    Description: We present a new approach to identifying the source and age of paleofluids associated with low-temperature deformation in the brittle crust, using hydrogen isotopic compositions (δD) and 40 Ar/ 39 Ar geochronology of authigenic illite in clay gouge-bearing fault zones. The procedure involves grain size separation, polytype modeling, and isotopic analysis, creating a mixing line that is used to extrapolate to δD and age of pure authigenic and detrital material. We use this method on samples collected along the surface trace of today's North Anatolian Fault (NAF). δD values of the authigenic illite population, obtained by extrapolation, are -89±3‰, -90±2‰, and -97±2‰ (VSMOW) for samples KSL, RES4-1, and G1G2, respectively. These correspond to δD fluid values of -62‰ to -85‰ for the temperature range of 125°C ±25°, indistinguishable from present-day precipitation values. δD values of the detrital illite population are -45±13‰, -60±6‰, and -64±6‰ for samples KSL, G1G2, and RES4-1, respectively. Corresponding δD fluid values at 300°C are -26 to -45‰ and match values from adjacent metamorphic terranes. Corresponding clay gouge ages are 41.4 ±3.4 Ma (authigenic) and 95.8±7.7 Ma (detrital) for sample G2 and 24.6 ±1.6 Ma (authigenic) and 96.5±3.8 Ma (detrital) for sample RES4-1, demonstrating a long history of meteoric fluid infiltration in the area. We conclude that today's NAF incorporated pre-existing, weak clay-rich rocks that represent earlier mineralizing fluid events. The samples preserve at least three fluid flow pulses since the Eocene and indicate that meteoric fluid has been circulating in the upper crust in the North Anatolian Keirogen since that time. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
    Publication Date: 2013-02-01
    Description: Paleoelevation reconstructions of mountain belts and orogenic plateaus based on stable isotope climate and precipitation records benefit greatly from present-day calibrations that relate the fractionation of hydrogen (δD) and oxygen (δ18O) isotopes in precipitation to orographic rainfall. Here, we establish a first-order template of δD and δ18O of modern meteoric waters across the Central Anatolian Plateau (CAP) and its bordering Pontic and Taurus Mountains. We identify key regions in the plateau interior and along the plateau margins that have the potential to reliably record topography-related paleotemperature and paleoprecipitation changes as recovered from stable isotope paleosol, fossil teeth or lipid proxy data. Based on δD and δ18O data of more than 480 surface water samples from small catchments and springs, we characterize moisture sources affecting the net isotopic budget of precipitation over the CAP and analyze how orographic rainout and plateau aridity shape modern patterns of δD and δ18O in precipitation. The Taurus Mountains bordering the CAP to the south act as a major orographic barrier for transport of predominantly winter moisture and exhibit isotopic lapse rates of approximately −20‰/km for δD and −2.9‰/km for δ18O across an elevation range of nearly 3000 m. The Pontic Mountains at the northern margin of the CAP force perennial moisture to ascend and condensate revealing lapse rates of −19‰/km for δD and −2.6‰/km for δ18O. The difference in the predominant moisture source for the southern and northern margins of the CAP (North African versus Atlantic air masses) is manifested in systematic north-south differences in near-sea level meteoric water compositions of Δ(δDN-S) ∼20 permil and Δ(δ18ON-S) ∼3 permil in a swath across the central part of the plateau. Stable isotope data from the semi-arid plateau interior with rainfall as low as 300 to 500 mm/yr and mean summer temperatures attaining 23 °C, provide clear evidence for an evaporative regime that drastically affects surface water and runoff compositions and results in a local meteoric water line for the plateau interior that follows δD = 4.0 · δ18O − 29.3. Strongly evaporitic conditions contrast rainfall patterns along the plateau margins including their immediate leeward flanks where δD- and δ18O-elevation relationships are reliable predictors of modern topography.
    Print ISSN: 0002-9599
    Electronic ISSN: 1945-452X
    Topics: Geosciences
    Published by HighWire Press on behalf of The American Journal of Science.
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