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  • 2005-2009  (5)
  • 1990-1994
  • 1960-1964
  • 2007  (5)
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  • 2005-2009  (5)
  • 1990-1994
  • 1960-1964
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  • 1
    Publikationsdatum: 2020-02-12
    Beschreibung: 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.
    Schlagwort(e): 550 - Earth sciences
    Materialart: info:eu-repo/semantics/article
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    Publikationsdatum: 2020-02-12
    Beschreibung: 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.
    Schlagwort(e): 550 - Earth sciences
    Materialart: info:eu-repo/semantics/article
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    Publikationsdatum: 2020-02-12
    Schlagwort(e): 550 - Earth sciences
    Materialart: info:eu-repo/semantics/conferenceObject
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 4
    Publikationsdatum: 2020-02-12
    Beschreibung: 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.
    Schlagwort(e): 550 - Earth sciences
    Materialart: info:eu-repo/semantics/article
    Format: application/pdf
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 5
    Publikationsdatum: 2020-02-12
    Beschreibung: For the last deglaciation and Termination V (the initiation of MIS 11 at around 430 ka) we report high-resolution sedimentary nitrogen isotope (δ 15N) records from Cariaco Basin in the Caribbean Sea. During both terminations the previously reported interglacial decrease in δ 15N clearly lags local changes such as water column anoxia as well as global increases in denitrification by several thousand years. On top of the glacial-interglacial change, several δ 15N peaks were observed during the last deglaciation. The deglacial signal in Cariaco Basin can be best explained as a combination of (1) local variations in suboxia and water column denitrification as the reason for the millennial-scale peaks, (2) a deglacial maximum in mean ocean nitrate δ 15N, and (3) increasing N2 fixation in response to globally increased denitrification causing the overall deglacial δ 15N decrease. In the Holocene, much of the decrease in δ 15N occurred between 6 and 3 ka, coinciding with an expected precession-modulated increase in African dust transport to the tropical North Atlantic and the Caribbean. This begs the hypothesis that N2 fixation in this region increased in response to interglacial maxima in denitrification elsewhere but that this response strengthened with increased mid-Holocene iron input. It remains to be seen whether the data for MIS 11 support this interpretation.
    Schlagwort(e): 550 - Earth sciences
    Materialart: info:eu-repo/semantics/article
    Format: application/pdf
    Standort Signatur Einschränkungen Verfügbarkeit
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