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  • 1
    Language: English
    In: Nature (London), 2007-01-04, Vol.445 (7123), p.74-77
    Description: The Asian-Australian monsoon is an important component of the Earth's climate system that influences the societal and economic activity of roughly half the world's population. The past strength of the rain-bearing East Asian summer monsoon can be reconstructed with archives such as cave deposits, but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct. Here we present high-resolution records of the magnetic properties and the titanium content of the sediments of Lake Huguang Maar in coastal southeast China over the past 16,000 years, which we use as proxies for the strength of the winter monsoon winds. We find evidence for stronger winter monsoon winds before the Bølling-Allerød warming, during the Younger Dryas episode and during the middle and late Holocene, when cave stalagmites suggest weaker summer monsoons. We conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone. Similar migrations of the intertropical convergence zone have been observed in Central America for the period ad 700 to 900 (refs 4-6), suggesting global climatic changes at that time. From the coincidence in timing, we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the Tang dynasty in China and the Classic Maya in Central America.
    Subject(s): Art and archaeology ; Asia ; China ; Climatology. Bioclimatology. Climate change ; Earth sciences ; Earth, ocean, space ; Exact sciences and technology ; External geophysics ; Meteorology ; Paleontology ; Paleontology: general ; Tang dynasty
    ISSN: 0028-0836
    E-ISSN: 1476-4687
    Source: Academic Search Ultimate
    Source: Nature Journals Online
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  • 2
    Language: English
    In: Nature geoscience, 2008-08, Vol.1 (8), p.520-523
    Description: The Younger Dryas cooling 12,700 years ago is one of the most abrupt climate changes observed in Northern Hemisphere palaeoclimate records. Annually laminated lake sediments are ideally suited to record the dynamics of such abrupt changes, as the seasonal deposition responds immediately to climate, and the varve counts provide an accurate estimate of the timing of the change. Here, we present sub-annual records of varve microfacies and geochemistry from Lake Meerfelder Maar in western Germany, providing one of the best dated records of this climate transition. Our data indicate an abrupt increase in storminess during the autumn to spring seasons, occurring from one year to the next at 12,679 yr BP, broadly coincident with other changes in this region. We suggest that this shift in wind strength represents an abrupt change in the North Atlantic westerlies towards a stronger and more zonal jet. Changes in meridional overturning circulation alone cannot fully explain the changes in European climate; we suggest the observed wind shift provides the mechanism for the strong temporal link between North Atlantic Ocean overturning circulation and European climate during deglaciation.
    ISSN: 1752-0894
    E-ISSN: 1752-0908
    Source: Nature Journals Online
    Source: Get It Now
    Source: ProQuest Central
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  • 3
    Language: English
    In: Nature (London), 1999-08-19, Vol.400 (6746), p.740-743
    Description: Oxygen-isotope records from Greenland ice cores, indicate numerous rapid climate fluctuations during the last glacial period. North Atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice-rafted debris. In contrast, very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents. Here we present high-resolution geochemical, physical and pollen data from lake sediments in Italy and from a Mediterranean sediment core, linked by a common tephrochronology. Our lacustrine sequence extends to the past 102,000 years. Many of its features correlate well with the Greenland ice-core records, demonstrating that the closely coupled ocean–atmosphere system of the Northern Hemisphere during the last glacial extended its influence at least as far as the central Mediterranean region. Numerous vegetation changes were rapid, frequently occurring in less than 200 years, showing that the terrestrial biosphere participated fully in last-glacial climate variability. Earlier than 65,000 years ago, our record shows more climate fluctuations than are apparent in the Greenland ice cores. Together, the multi-proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials, and provide a step towards determining the underlying mechanisms of the centennial–millennial-scale variability.
    Subject(s): Climate ; Deposition ; Earth sciences ; Earth, ocean, space ; Exact sciences and technology ; Fluctuation ; Freshwater ; Glacial epoch ; Glacial periods ; Lakes ; Marine ; Marine and continental quaternary ; Research ; Sea surface temperature ; Sediments ; Surficial geology
    ISSN: 0028-0836
    E-ISSN: 1476-4687
    Source: Academic Search Ultimate
    Source: Nature Journals Online
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  • 4
    Language: English
    In: Journal of paleolimnology, 2007-05-02, Vol.37 (4), p.517-528
    Description: Byline: Jens Mingram (1), Jorg F. W. Negendank (1), Achim Brauer (1), Dieter Berger (1), Andreas Hendrich (1), Michael Kohler (1), Hartmut Usinger (2) Keywords: Piston corers; Quaternary lake sediments; Coring equipment; Paleolimnology; Limnogeology We present a unique, versatile piston corer for recovering continuous lake and bog sediment sequences with superior accuracy and quality. The main components of the system and their function are described, with special focus on measures for obtaining long, continuous lake sediment sections up to a current maximum length of 95 m. Examples of lake sediment profiles obtained with this system from different climatic zones are presented. Author Affiliation: (1) GeoForschungsZentrum (GFZ) Potsdam, Telegrafenberg, D-14473, Potsdam, Germany (2) Universitat Kiel, Okologiezentrum, D-24098, Kiel, Germany Article History: Registration Date: 12/06/2006 Received Date: 14/02/2006 Accepted Date: 03/06/2006 Online Date: 26/08/2006
    Subject(s): Sediments (Geology)
    ISSN: 0921-2728
    E-ISSN: 1573-0417
    Source: Alma/SFX Local Collection
    Source: ProQuest Central
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  • 5
    Language: English
    In: Journal of Geophysical Research, 2008-11-04, Vol.113 (D21), p.D21101-n/a
    Description: We present a continuous record of fossil diatoms from Huguang Maar Lake (HML) in southeastern China, spanning the time interval 17,500 to 6000 calendar years (cal years) B.P. The seasonal change in relative abundance of the dominant diatom taxa, Aulacoseira and Cyclotella species, can be used as a proxy of the strength of winter monsoon winds (WMW), which is supported by the results of a sediment trap experiment in HML and by an extensive review of the literature on the autoecologies of these species. In the sediment, high C. stelligera abundance and high‐diatom concentration, which indicate warm conditions and low wind‐driven turbulence of the water column, characterize an interval equivalent to the Greenland Interstadial 1. This is followed by an interval with low‐diatom concentration and with assemblages dominated by Aulacoseira species, which suggests high wind‐driven turbulence and therefore strong WMW. This interval corresponds with the Greenland Stadial 1. During the early and middle Holocene, another two episodes with strong WMW are evident from the data between 10,000 and 8500 and between 7000 and 6000 cal years B.P. The diatom record implies that strong winter monsoon episodes not only occurred during the last glacial‐Holocene transition but also during the Holocene “thermal maximum.”
    Subject(s): Abrupt/rapid climate change ; Asian winter monsoon ; Atmospheric Composition and Structure ; Atmospheric Processes ; Biosphere/atmosphere interactions ; diatom ; Earth sciences ; Earth, ocean, space ; Exact sciences and technology ; Global Change ; Paleoclimatology ; Regional climate change ; the last glacial Holocene
    ISSN: 0148-0227
    E-ISSN: 2156-2202
    Source: Wiley Online Library All Backfiles
    Source: Alma/SFX Local Collection
    Source: Wiley-Blackwell Full Collection 2014
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  • 6
    Language: English
    In: Journal of geophysical research. Solid earth, 2013-06, Vol.118 (6), p.2648-2669
    Description: This study presents paleomagnetic data from 59 independent lava flows from the trans‐Mexican volcanic belt (TMVB) with ages from 6.4 Ma to recent, 52 being younger than 1 Ma, and 11 new 40Ar/39Ar age determinations. Most remanence carriers are Ti‐poor titanomagnetite of pseudosingle‐domain magnetic structure, nine lavas contain small amounts of titanomaghemite, and four lavas additional (titano‐) hematite. Paleosecular variation of lava flows younger than 1.7 Ma is consistent with latitude‐dependent Model G and also in agreement with other Pleistocene paleomagnetic data from the TMVB. The directional record of Brunhes and Matuyama Chrons lavas was correlated to the geomagnetic polarity timescale and there is evidence for at least four geomagnetic excursions. One lava flow dated at 592 ± 20 ka has a fully reversed paleodirection and most likely erupted during the Big Lost excursion. Another fully reversed flow, dated at 671 ± 12 ka, gives new volcanic evidence for the Delta/Stage 17 excursion. This excursion is supported by a reversed intermediate direction of another flow from a different volcanic field but of very close age of 673 ± 10 ka. From the Matuyama age lavas, one flow with normal polarity magnetization, dated at 949 ± 37 ka, could either be related to the Kamikatsura or the Santa Rosa excursion and a normal polarity flow, dated at 1628 ± 56 ka, could have been emplaced during the Gilsa excursion. The results presented here confirm in one case but disagree in four cases with results presented in two previous studies of the same lava flows and interpreted as geomagnetic excursions. Key Points Evidence for at least 4 geomagnetic excursions in 59 Brunhes‐Matuyama lava flows 11 new Ar‐Ar age determinations Results confirm in 1 but disagree in 4 cases with previously published data
    Subject(s): Age ; Age determination ; Belts ; Deltas ; excursions ; geochronology ; Geomagnetism ; Lava ; Magnetization ; Mexico ; paleomagnetism ; Polarity
    ISSN: 2169-9313
    E-ISSN: 2169-9356
    Source: Alma/SFX Local Collection
    Source: Wiley-Blackwell Full Collection 2014
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  • 7
    Language: English
    In: Nature (London), 2007-11-15, Vol.450 (7168), p.E8-E9
    Description: Replying to: De'er Zhang & Longhua Lu Nature 450, doi:10.1038/nature06338 (2007)Zhang and Lu argue that Chinese historical climate records contradict certain of our interpretations based on Lake Huguang Maar sediment records. Interpreting these records as an indicator for winter monsoon winds and Chinese cave records as an indicator for summer monsoon rainfall, we observed an inverse relationship between winter and summer monsoons on a millennial timescale over the past 16,000 yr. In sediments deposited during the period of Classical Chinese dynastic history, we found evidence for a temporal coincidence between winter monsoon strengthening and the terminations of important dynasties. Extrapolating the inverse monsoon relationship to these multidecadal timescales, we suggested that reduced summer rainfall contributed to dynastic terminations, including that of the Tang (ad 618-907). Zhang and Lu challenge the validity of the summer/winter monsoon relationship on the grounds that historical records indicate that relatively cold winters tended to be associated with relatively wet summers over the period they considered. They argue that the Tang dynasty decline was associated with cold winters, in agreement with our findings, but they find no evidence for rainfall changes having contributed to the decline of the Tang.
    ISSN: 0028-0836
    E-ISSN: 1476-4687
    Source: Academic Search Ultimate
    Source: Nature Journals Online
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  • 8
    Language: English
    In: Nature (London), 2007-11-15, Vol.450 (7168), p.E11-E11
    Description: Replying to: H. Zhou et al. Nature 450, doi: 10.1038/nature06408 (2007).Zhou et al. raise the possibility that the titanium (Ti) record at Lake Huguang Maar is controlled by local erosion and runoff to the lake, or through hydrological changes in the lake such as level fluctuations, rather than by changes in the inputs of airborne material. The authors come to this conclusion by considering the Ti record in isolation. They ignore the redox-sensitive parameters of the S-ratio, total organic-matter content, the Mn/Fe ratio, and magnetic susceptibility records. We believe that their case against our interpretation of the Ti record is weak, and that their interpretation can be ruled out if the other measurements are taken into account.
    ISSN: 0028-0836
    E-ISSN: 1476-4687
    Source: Academic Search Ultimate
    Source: Nature Journals Online
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  • 9
    Language: English
    In: Journal of Geophysical Research, 2003-08-15, Vol.108 (B8), p.2379-n/a
    Description: Detailed rock magnetic investigations, including the analysis of the laboratory installed magnetizations, the measurement of hysteresis parameters, and the high temperature‐dependency of the saturation magnetization, were carried out on sediments from Birkat Ram, Golan Heights, Israel. The 550 cm long composite profile, composed of three single cores, is supposed to span the Late Holocene, i.e., the last 4400 years, at least. Titanomagnetites in the pseudo single‐domain range were identified as the main magnetic carrier minerals in the homogenous sediments. The variations in concentration and grain size of the magnetic fraction are only partly reflected in the sediment lithology. The relative paleointensity was estimated by normalizing the intensity of the natural remanent magnetization (NRM) after demagnetization at 20 mT (JNRM(20 mT)) by different concentration parameters. The median destructive field of the NRM (MDFNRM) is coherent with the relative paleointensity estimates, indicating that a sedimentary effect has not sufficiently been removed by the normalization process. The morphologies of these estimates, however, correspond to the archeomagnetic records from Bulgaria and Greece. Therefore a second normalization, based on the linear relationship between the paleointensity estimates and the MDFNRM, was applied, resulting in an improvement of the records.
    Subject(s): Birkat Ram ; General or miscellaneous ; Geomagnetism and Paleomagnetism ; Instruments and techniques ; lacustrine sediments ; Late Holocene ; Near East ; Paleointensity ; relative paleointensity ; Rock and mineral magnetism ; rock magnetism
    ISSN: 0148-0227
    E-ISSN: 2156-2202
    Source: Wiley Online Library All Backfiles
    Source: Alma/SFX Local Collection
    Source: Wiley-Blackwell Full Collection 2014
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  • 10
    Language: English
    In: Geophysical journal international, 2007-03, Vol.168 (3), p.921-934
    Description: SUMMARY Laminated evaporitic sediments from the Dead Sea, Israel, were subjected to detailed rock magnetic investigations including the analysis of laboratory induced magnetizations and high temperature runs of the saturation magnetization. Ti‐magnetite and greigite were identified as the main magnetic carrier minerals. The variations in concentration, grain size and coercitivity depended parameters reflect the varying amount of greigite with respect to Ti‐magnetite. Samples with a high greigite concentration are characterized by S‐ratios close to 1 in combination with low JARM/JSIRM ratios. The results of a hierarchical agglomerative cluster analysis of the rock magnetic data presented in form of scatter plots allow for a qualitative identification of greigite‐indicative parameters/parameter ratios and thus semi‐quantitative estimation of the greigite content. The samples from the Dead Sea are distributed along a mixing line between the end members pure greigite and low Ti‐magnetite. Determination of hysteresis parameters revealed that the greigite dominated samples show SD‐behaviour whereas the Ti‐magnetites plot in the PSD‐range.
    Subject(s): Analysis ; Dead Sea ; greigite ; Israel ; lacustrine sediments ; Magnetism ; rock magnetism ; Sediments (Geology) ; Ti‐magnetite
    ISSN: 0956-540X
    E-ISSN: 1365-246X
    Source: Oxford Journals Current Collection
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