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A Major reorganization of Asian climate

Clim.Past,4,153–174,2008

http://www.wendangku.net/doc/b9ae7a3a19e8b8f67c1cb9ff.html/4/153/2008/

©Author(s)2008.This work is distributed under the Creative Commons Attribution3.0

A Major reorganization of Asian climate

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Climate of the Past

A major reorganization of Asian climate by the early Miocene

Z.T.Guo1,B.Sun1,2,Z.S.Zhang1,3,S.Z.Peng1,G.Q.Xiao4,J.Y.Ge4,Q.Z.Hao1,Y.S.Qiao1,M.Y.Liang1,

J.F.Liu1,Q.Z.Yin1,and J.J.Wei1

1Key Laboratory of Cenozoic Geology and Environment,Institute of Geology and Geophysics,Chinese Academy of Sciences,P.O.Box9825,Beijing,100029,China

2Shandong Institute and Laboratory of Geological Sciences,Jinan,250013,China

3Nansen-Zhu International Research Center,Institute of Atmospheric Physics,Chinese Academy of Sciences,Beijing, 100029,China

4State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences,P.O. Box17,Xian,710075,China

Received:3April2008–Published in Clim.Past Discuss.:8May2008

Revised:29July2008–Accepted:29July2008–Published:18August2008

Abstract.The global climate system experienced a series

of drastic changes during the Cenozoic.In Asia,these in-

clude 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 per-

sist 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 con-

firming 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 deposi-

tion 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 dur-

ing 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 de-

termine the circulation characteristics with emphasis on the

early Miocene.Continuous eolian deposition in the mid-

dle reaches of the Yellow River since the early Miocene

firmly indicates the formation of inland deserts,which have

been constantly maintained during the past22Ma.

A Major reorganization of Asian climate

Grain-

Correspondence to:Z.T.Guo (ztguo@http://www.wendangku.net/doc/b9ae7a3a19e8b8f67c1cb9ff.html)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 co-existence of two kinds of circulations,one from the ocean carrying moisture and another from the inland deserts trans-porting dust.The formation of the early Miocene pale-osols resulted from interactive soil forming and dust deposi-tion 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 circula-tion 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 re-sponses,as well as the change from the“planetary”subtrop-ical 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 tec-tonic factors had evolved by the early Miocene to a threshold sufficient to cause this major climate reorganization in Asia.

Published by Copernicus Publications on behalf of the European Geosciences Union.