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| Titel |
Three exceptionally strong East-Asian summer monsoon events during glacial times in the past 470 kyr |
| VerfasserIn |
D.-D. Rousseau, N. Wu, Y. Pei, F. Li |
| 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 ; 5, no. 2 ; Nr. 5, no. 2 (2009-04-23), S.157-169 |
| Datensatznummer |
250002394
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| Publikation (Nr.) |
 copernicus.org/cp-5-157-2009.pdf |
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| Zusammenfassung |
| Chinese loess sequences are interpreted as a reliable record of the
past variation of the East Asian monsoon regime through the alternation of
loess and paleosols units, dominated by the winter and summer monsoon,
respectively. Different proxies have been used to describe this system,
mostly geophysical, geochemical or sedimentological. Terrestrial mollusks
are also a reliable proxy of past environmental conditions and are often
preserved in large numbers in loess deposits. The analysis of the mollusk
remains in the Luochuan sequence, comprising L5 loess to S0 soil, i.e. the
last 500 ka, shows that for almost all identified species, the abundance is
higher at the base of the interval (L5 to L4) than in the younger deposits.
Using the present ecological requirements of the identified mollusk species
in the Luochuan sequence allows the definition of two main mollusk groups
varying during the last 500 kyr. The cold-aridiphilous individuals indicate
the so-called Asian winter monsoon regime and predominantly occur during
glacials, when dust is deposited. The thermal-humidiphilous mollusks are
prevalent during interglacial or interstadial conditions of the Asian summer
monsoon, when soil formation takes place. In the sequence, three events with
exceptionally high abundance of the Asian summer monsoon indicators are
recorded during the L5, L4 and L2 glacial intervals, i.e., at about 470, 360
and 170 kyr, respectively. The L5 and L4 events appear to be the strongest
(high counts). Similar variations have also been identified in the Xifeng
sequence, distant enough from Luochuan, but also in Lake Baikal further
North, to suggest that this phenomenon is regional rather than local. The
indicators of the summer monsoon within the glacial intervals imply a
strengthened East-Asian monsoon interpreted as corresponding to marine
isotope stages 12, 10 and 6, respectively. The L5 and L2 summer monsoons are
coeval with Mediterranean sapropels S12 and S6, which characterize a strong
African summer monsoon with relatively low surface water salinity in the
Indian Ocean. Changes in the precipitation regime could correspond to a
response to a particular astronomical configuration (low obliquity, low
precession, summer solstice at perihelion) leading to an increased summer
insolation gradient between the tropics and the high latitudes and resulting
in enhanced atmospheric water transport from the tropics to the African and
Asian continents. However, other climate drivers such as reorganization of
marine and atmospheric circulations, tectonic, and the extent of the Northern
Hemisphere ice sheet are also discussed. |
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