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| Titel |
A major reorganization of Asian climate by the early Miocene |
| VerfasserIn |
Z. T. Guo, B. Sun, Z. S. Zhang, S. Z. Peng, G. Q. Xiao, J. Y. Ge, Q. Z. Hao, Y. S. Qiao, M. Y. Liang, J. F. Liu, Q. Z. Yin, J. J. Wei |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 4, no. 3 ; Nr. 4, no. 3 (2008-08-18), S.153-174 |
| Datensatznummer |
250001739
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| Publikation (Nr.) |
 copernicus.org/cp-4-153-2008.pdf |
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| Zusammenfassung |
The global climate system experienced a series of drastic changes during the
Cenozoic. In Asia, these include the climate transformation from a zonal
pattern to a monsoon-dominated pattern, the disappearance of typical subtropical aridity, and the
onset of inland deserts. Despite major advances in the last two decades in characterizing
and understanding these climate phenomena, disagreements persist relative to
the timing, behaviors and underlying causes.
This paper addresses these issues mainly based on two lines of evidence.
First, we compiled newly collected data from geological indicators of the
Cenozoic environment in China as paleoenvironmental maps of ten intervals.
In confirming the earlier observation that a zonal climate pattern was
transformed into a monsoonal one, the maps within the Miocene indicate that
this change was achieved by the early Miocene, roughly consistent with the
onset of loess deposition in China. Although a monsoon-like regime would
have existed in the Eocene, it was restricted to tropical-subtropical
regions. The latitudinal oscillations of the climate zones during the
Paleogene are likely attributable to the imbalance in evolution of polar
ice-sheets between the two hemispheres.
Secondly, we examine the relevant depositional and soil forming processes of
the Miocene loess-soil sequences to determine the circulation
characteristics with emphasis on the early Miocene. Continuous eolian
deposition in the middle reaches of the Yellow River since the early Miocene
firmly indicates the formation of inland deserts, which have been constantly
maintained during the past 22 Ma. Grain-size gradients between loess
sections indicate northerly dust-carrying winds from northern sources, a
clear indication of an Asian winter monsoon system. Meanwhile,
well-developed Luvisols show evidence that moisture from the oceans reached
northern China. This evidence shows the coexistence of two kinds of
circulations, one from the ocean carrying moisture and another from the
inland deserts transporting dust. The formation of the early Miocene
paleosols resulted from interactive soil forming and dust deposition
processes in these two seasonally alternating monsoonal circulations. The
much stronger development of the early Miocene soils compared to those in
the Quaternary loess indicates that summer monsoons were either
significantly stronger, more persistent through the year, or both.
These lines of evidence indicate a joint change in circulation and inland
aridity by the early Miocene and suggest a dynamic linkage of them. Our
recent sensitivity tests with a general circulation model, along with
relevant geological data, suggest that the onset of these contrasting
wet/dry responses, as well as the change from the "planetary" subtropical
aridity pattern to the "inland" aridity pattern, resulted from the combined
effects of Tibetan uplift and withdrawal of the Paratethys seaway in central
Asia, as suggested by earlier experiments. The spreading of South China Sea
also helped to enhance the south-north contrast of humidity. The Miocene
loess record provides a vital insight that these tectonic factors had
evolved by the early Miocene to a threshold sufficient to cause this major
climate reorganization in Asia. |
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