A Major reorganization of Asian climate
Clim.Past,4,153–174,2008
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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-
?rming 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
?rmly indicates the formation of inland deserts,which have
been constantly maintained during the past22Ma.
Grain-
Correspondence to:Z.T.Guo (ztguo@https://www.wendangku.net/doc/b111489912.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 signi?cantly 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 suf?cient to cause this major climate reorganization in Asia.
Published by Copernicus Publications on behalf of the European Geosciences Union.
n g tz e
R iv e r
Longitude( )
0 60Atacama
Sonoran
Namib
Sahara
Arabian
Gobi
Turkestan
Patagonia
Desert
Great sandy
monsoon
o Longitude( )
o )
(e d u t i t a L o )
(e d u t i t a L o Guo et al_Fig. 1
Fig.1.Sketch maps showing the modern environmental patterns of China and the world.(a)Modern environmental pattern in China and
the prevailing atmospheric circulations.The Loess Plateau is located in the middle reaches of the Yellow River,with the Tibetan Plateau to the Southwest,inland deserts to the North and Northwest.The subtropical and tropical regions in southern China are covered by so-called red earth (mainly soils formed under tropical and subtropical humid conditions).Dotted arrows indicate the southwest and southeast Asian summer monsoons,solid arrows indicate the Asian winter monsoon.(b)Distribution of the world drylands (modi?ed after Meigs,1953).Most of the subtropical zones are occupied by drylands with the exception of East Asia.
1Introduction
The modern environment in Asia is characterized by two prominent features:the moist southern part under the in-?uence of the southwest (South Asian)and southeast (East Asian)summer monsoons,the drylands in the central part beyond the monsoon in?uence (Wang,2006).These are clearly illustrated by the climate pattern in China (Fig.1a).In summer,the fronts of the summer monsoons penetrate north-wards into China and lead to abundant rainfall and high tem-perature.In winter,the region is mainly controlled by the northwesterly dry-cold winds,i.e.the Asia winter monsoon related to the Siberian high-pressure cell (Chen et al.,1991).Currently,precipitation in northern China is mostly brought by the southeast summer monsoon (Chen et al.,1991;Fu,2003).Although modern observations also indicate a contri-bution of the southwest summer monsoon to the precipitation in northern China (Chen et al.,1991;Wang,2006),the ef-fect is largely reduced by the barrier effect of the Himalayan-Tibetan complex.During the late Cenozoic,a large amount of eolian dust was transported from the inland deserts by win-ter monsoon winds to the middle reaches of the Yellow River,leading to the formation of the Loess Plateau (Liu,1985;An et al.,1990;Ding et al.,1995;Liu and Ding,1998;Guo et al.,2002).The western part of China is also in?uenced by the westerlies of the Northern Hemisphere (Wang,2006),but their contribution to regional rainfall is relatively small because of the long continental trajectory.
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105E
Guo et al_Fig. 2
110E
115E
Fig.2.The Loess Plateau in northern China relative to the inland deserts in northwestern China and various loess sites.The Plateau is delimited by the Liupan Mountains into the eastern and western parts.The right panel corresponds to an expanded part of the western Loess Plateau where the Miocene eolian deposits have been studied.
The very moist conditions in the subtropical zone in Asia,along with the presence of mid-latitude drylands,referred to here as the monsoon-dominated pattern (Guo,2003),are somewhat unusual compared to the widespread drylands in most subtropical regions (Fig.1b).These include the Aus-tralian and South American deserts in the Southern Hemi-sphere and the Sahara-Arabian deserts in the Northern Hemi-sphere.The causes of aridity for these two kinds of deserts are also very different.Except for the North American deserts that are primarily the result of rain-shadow develop-ment in the lee of mountains (Kutzbach et al.,1989),most low-latitude aridity results from subtropical high-pressure zones related to the descending branches of the Hadley Cells near the equator and the Ferrell Cells at mid-latitudes over both the hemispheres (Houghton,1984).The subsiding air of the subtropical highs adiabatically warms,causes the air to dry out,and inhibit condensation,leading to dry condi-tions on the underlying continents.
In contrast,aridity in Central and East Asia is essentially independent of the subtropical highs,and mainly related to the barrier and thermo-dynamic effects of the Himalayan-Tibetan complex,the Siberian high-pressure cell and the re-mote distance from the oceans (Kutzbach et al.,1989,1993;Ruddiman and Kutzbach,1989;Chen et al.,1991;Wang et al.,2006).Consequently,we discriminate between these two kinds of drylands as planetary and inland deserts.Be-cause subtropical high-pressure zones are a component of the planetary circulation system mainly forced by solar heating (Houghton,1984),we assume that they can be traced back to much earlier in Earth history.Consequently,the onset of planetary drylands should be primarily dependent on the tim-ing when a continent drifted to subtropical latitudes.On the contrary,the onset of inland-type deserts and monsoon-dominated climate in Asia is one of the most prominent changes in the climate system of the Cenozoic Era (Ruddiman and Kutzbach,1989).Since the late 1970’s,many numerical experiments have been conducted to address their causes.Invoked factors have focused on Tibetan up-lift and changes in land-sea distribution (Manabe and Terp-stra,1974;Ruddiman and Kutzbach,1989;Ruddiman et al.,1989;Kutzbach et al.,1989;1993;Prell and Kutzbach,1992;Ramstein et al.,1997;Fluteau et al.,1999;Abe et al.,2003;Zhang et al.,2007a,b).
Meanwhile,studies of geological records have led to ma-jor advances about the timing of these changes.On the southern side of the Himalayas,a record of planktonic foraminifera from the Arabian Sea that revealed strong up-welling since the late Miocene at ～8Ma was interpreted as an indication of the onset or strengthening of the Indian Ocean (South Asian)monsoon (Kroon et al.,1991).The expansion of plants that use C4photosynthesis at ～8Ma in South Asia may also be indicative of strengthening of South Asian monsoon (Quade et al.,1989).
On the northern side of the Himalayan-Tibetan complex,examination on the spatial distribution of geological indica-tors in China revealed a transformation of the dry areas in the Cenozoic from a roughly W-E zonal belt across China to a region restricted to northwestern China (Wang,1990).Later,six paleoenvironmental maps corresponding to the Pa-leocene,Eocene,Oligocene,Miocene,late Miocene-early Pliocene and Pliocene were compiled based on various ge-ological and biological indicators (Liu and Guo,1997).The results showed a roughly zonal climate pattern from the Pa-leocene to Oligocene,followed by a pattern similar to the present-day for later epochs,suggesting that the reorgani-zation occurred during the Oligocene or Miocene.Broadly similar results have been given by a detailed compilation of paleobotanical evidence (Sun and Wang,2005).Geologi-cal sequences from northern China also revealed more ac-curate age control on these changes.A pollen record from
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Clim.Past,4,153–174,2008
the Linxia basin showed a signi?cant increase in the contents of tree pollen,which was interpreted as an indication of the onset of Asian monsoon(Shi et al.,1999).
Recently,study of loess-soil sequences of Miocene ages (Guo et al.,2002)indicated that sizeable deserts in the Asian inlands and a monsoonal pattern had both been established by22Ma ago in the Loess Plateau region of eastern Asia. Correlative sequences with high-resolution magnetostrati-graphic time control show layered sequences of fully devel-oped soils indicative of south-to-north in?ow typical of wet summer monsoons,alternating with loess layers indicative of stronger north-to-south out?ow in dry winter monsoons. These alternations attest to cyclical changes of the summer and winter monsoons at the orbital scale(Guo et al.,2002). Despite these major advances,a number of questions re-main to be addressed.
1.Previous paleoenvironmental maps were mainly com-
piled in intervals of epochs,and hence have rather long time coverage(Liu and Guo,1997;Sun and Wang, 2005).Because dominant views about the timing of monsoon climate in Asia focused on the late Miocene (Quade et al.,1989;Kroon et al.,1991)or around the Oligocene-Miocene boundary(Liu and Guo,1997;
Sun and Wang,2005),a more detailed examination on the climate patterns within the Oligocene and Miocene would provide helpful insights about the timing of pat-tern changes.Over the past ten years,a signi?cant amount of new geological information has been ac-quired,providing the opportunity to reexamine the spa-tial patterns in greater detail.Although the climates in Asia in the Paleocene,Eocene and Oligocene are com-monly characterized by zonal patterns(Liu and Guo, 1997;Sun and Wang,2005),their link to Cenozoic global ice-volume and temperature changes as docu-mented by marineδ18O records(Zachos et al.,2001) also needs to be discussed.
2.Examination of temporal and spatial variations of the
Quaternary and Pliocene eolian deposits have provided
a signi?cant amount of information on monsoon and
dryland evolution in Asia during the past8Ma(e.g.Liu and Ding,1998;Miao et al.,2004).Their distribution in the Miocene remains unclear because of the insuf-?cient number of Miocene loess sections.Recently, several new sections at different localities have been dated and analyzed.These sections provide an op-portunity to further examine climate features prior to 8Ma.Moreover,speci?c features of monsoonal loess-soil sequences in China can be compared to those in non-monsoon zones such as Europe and North Amer-ica(Rousseau and Kukla,1994;Rousseau et al.,1998;
Berger,2003).
In Sect.2of this paper,we summarize Cenozoic changes of climate patterns using paleoenvironmental maps of ten time intervals based on new collection and re-examination of geological indicators from the literature.In Sect.3,we address the implications of the Miocene eolian deposits in northern China regarding the early stage of Asian inland de-serti?cation and monsoon climate.Other relevant geological records are reviewed in Sect.4.In Sect.5,we discuss the potential causes of this major change of Asian climate based on the insights from the Miocene loess-soil sequences,the available numerical experiments and tectonic studies.
2Cenozoic climate patterns in Asia
The data used to compile the paleoenvironmental maps were acquired mainly for studies of stratigraphy,paleontology, paleogeography and paleoclimate,for resource exploration and for geological mapping.The main sources are listed in the Supplementary Material https://www.wendangku.net/doc/b111489912.html,/4/153/ 2008/cp-4-153-2008-supplement.pdf.Among a larger num-ber of collected records,we have selected385for compiling the paleoenvironment maps based on reliability of chronol-ogy and clarity of environmental signi?cance.The chronolo-gies of157records are based on mammalian fossils,those of 146records on pollen chronology,and those of44records on other biochronological indicators(for example foraminifera, ostracoda).Isotope or magnetostratigraphic ages are avail-able for38records.
In China,calibrations of fossil chronology by isotopic and geomagnetic dating are only available for scattered sites. Most investigations used relative chronology assignments, which potentially have large uncertainties.We infer a poten-tial uncertainty of at least several million years for data with-out isotopic and geomagnetic age controls even with careful selection and examination.
These indicators are classi?ed into three groups(humid, semi-arid and arid)according to their environmental impli-cations.Indicators of humid conditions include coal,pollen and fossil assemblages typical of forest conditions.Arid in-dicators include saline and alkaline lake deposits,as well as pollen and fossils typical of deserts and desert-steppe envi-ronments.Pedogenic carbonates,pollen and fossil assem-blages typical of sparse forest-steppe and steppe are used as indicators of semi-arid environments.Because of the poten-tial uncertainty of environmental signi?cance for some mam-malian fossils,only carefully studied fauna with modern ana-logues are used for compiling the maps although most faunal data are useful for chronology.The maps compiled for the ten different intervals are shown in Figs.3and4.The data used in each map are listed in the Supplementary Material.
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2.1Paleogene climate patterns
The Paleocene data are rather sparse,probably due to tec-tonic changes and erosion,but they are abundant enough to show the dominance of arid and semi-arid conditions in large areas of China.Their spatial distribution de?nes a broad, roughly W-E dry belt across the country(Fig.3a).Only the southern-most Hainan Islands and northeastern China were dominated by more humid conditions.The Eocene data are signi?cantly more abundant,showing a pattern essentially similar to that of the Paleocene(Fig.3b).However,a north-wards migration of the southern boundary of the dry belt is evident.A further slight northwards retreat of this boundary is observed for the Oligocene,although the basic environ-mental pattern remained zonal(Fig.3c).
We further subdivided the Oligocene data into two groups, one corresponding to the early and mid-Oligocene(Fig.3d), and the other to the late Oligocene(Fig.3e).The data are suf-?cient to show a zonal climate pattern for the early and mid-Oligocene,but the pattern for the late Oligocene is hard to de?ne because of a lack of data in southern China,probably due to tectonic movements and large-scale erosion(Zhang and Guo,2005).In any case,the map for the late Oligocene does not clearly show a pattern different from that of the early and mid-Oligocene.
These?ve maps show that climate in Asia during most of the Paleogene was characterized by roughly W-E zonal patterns with dry conditions in southern China where humid conditions prevail today(Fig.1a).A dry belt existed from the western-most part to the eastern coasts at latitudes similar to the present-day drylands in North Africa(Fig.1b).The arid-ity was presumably caused by the subtropical high-pressure zone of the Northern Hemisphere,because of the lack of ev-idence of mountain ranges(and rain shadows)for the Paleo-gene.Thus,the zonal climate pattern is largely attributable to a planetary circulation system(Liu and Guo,1997;Sun and Wang,2005),rather than a monsoon-dominated regime. The broad dry zone with a northern boundary at higher latitudes has no modern analog,probably for two main rea-sons.First,the climate zones within each mapping inter-val would have experienced signi?cant short-term latitudi-nal oscillations caused by changes in global boundary condi-tions,leading to a broader distribution of the arid indicators. This possibility is supported by the scattered humid indica-tors within the dry belt(Fig.3).Second,the northeast trade winds had mostly a terrestrial origin,and would have broad-ened the zone with dry conditions.
The northward migration of the climate zones from the Paleocene to the Oligocene,including the dry belt,appears to be consistent with the Paleogene changes of the global boundary conditions as re?ected by marineδ18O records(Za-chos et al.,2001)(Fig.5a).The Paleocene Earth is com-monly considered ice-free.Glaciations may have started on Antarctica at～43Ma ago and then expanded in the early Oligocene at～34Ma(Miller et al.,1987;Zachos et al.,2001).Ice-volume on Antarctica during the early Oligocene glaciation may have reached～70%of the present-day vol-ume(Zachos et al.,1992).Although recent evidence of ice-rafting(Moran et al.,2006)revealed nearly synchronous bipolar cooling events during the Cenozoic,impermanent ice,probably mainly mountain and piedmont glaciers in the Northern Hemisphere,only appeared since the late Miocene,～10–6Ma(Lear et al.,2000).
These global scenarios in the Paleogene,characterized by great ice-sheets in Antarctica and ice-free or sporadic ice in Arctic,imply a much greater asymmetry of ice-conditions between the two hemispheres.Under the present-day global boundary conditions,the northern front of the southern hemi-spheric trade winds,i.e.the ITCZ,penetrates northwards to～22–24?N in summer and to～4?N in winter(Lezine et al.,2007)due to hemispheric asymmetry.The develop-ment of the Antarctic ice in the Eocene and early Oligocene (Zachos et al.,2001)would have forced global climate zones to migrate northwards,providing a likely explanation for the northward migration of the dry belt in Asia from the Pale-ocene to the Oligocene(Fig.3).
Although these interpretations remain hypothetical and need to be tested by climate models,a meridional shift of the atmospheric circulation induced by greater extents of sea ice over the Southern Atlantic and Southern Ocean has been demonstrated by the late Quaternary geological records(Iri-ono,2000;Markgraf et al.,2000;Stuut and Lamy,2004; Gersonde et al.,2005;Lambert et al.,2008).A climate model (Cox et al.,2008)shows that reduced aerosol pollution in the Northern Hemisphere also favors a northwards shift of the at-mospheric circulation.The much weaker dust intensity dur-ing the Paleogene,as evidenced by the lack of loess deposits in China and the low dust accumulation rates in the North Paci?c(Rea et al.,1985;Rea,1994),may also account for the northwards shift of the climate zones.
This explanation is also supported by the increased hu-midi?cation in the southern part of China from the Eocene to Oligocene(Fig.3),suggesting the existence of a circu-lation that brought moisture to the region.It might corre-spond to the so-called tropical monsoon(Chase et al.,2003) resulted from the penetration of Southern Hemisphere trade winds into the Northern Hemisphere,primarily driven by the seasonal oscillations of planetary circulations(Chase et al., 2003).
In summary,the climate in Asia in the Paleogene was dom-inated by a zonal pattern attributable to the planetary circula-tion system.Despite a possible monsoon regime in the trop-ical regions,its intensity was not strong enough to dominate the climate of the Asian continent.
2.2Neogene climate pattern
The Miocene climate patterns(Fig.4)are entirely differ-ent from those in the Paleogene(Fig.3).Indicators of arid conditions are mainly distributed in northwest China.
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(~65-56 Ma)
Humid belt
Arid/Semi-arid belt
Humid belt
(~56-34 Ma)
Early and Middle Oligocene
(~34-28 Ma)
Late Oligocene
(~28-24 Ma)
Oligocene
(~34-24 Ma)
Humid belt
Arid/Semi-arid belt
Humid belt
Humid belt
Arid/Semi-arid belt
Humid belt
Humid belt
Arid/Semi-arid belt
Humid belt
Arid Ind.Pollen Gypsum
Gyp./Salt Jarosite Arid Grassland Gyp./Mirabilite Humid Ind.Pollen Coal Forest Mammals
Boundary
Sub-Humid Pollen Carbonate Con.Wood-Steppe Mammals
Arid belt Semi-arid/Sub-humid
Terrestrial deposits in semi-arid/sub-humid belt
Terrestrial deposits in humid belt Volcanic rock Humid belt Terrestrial deposits in arid belt Marine deposits Lack of deposits or unclear
Molasses belt
(a)
(b)
(c)
(d)
(e)
Fig.3.Paleocene;(e)Late Oligocene.A Geological Survey (1999).
The middle semi-arid tions parts.This climate Earlier of climate changes in Asia,one in the early Miocene (Shi et al.,1999;Guo et al.,2002)and the other in the late Miocene (Quade et al.,1989;Kroon et al.,1991;An et al.,2001).To more accurately examine this problem,the Miocene data are separated into the early,middle and late Miocene parts (Fig.4b–d).Data for each interval are abun-dant enough to de?ne the climate patterns clearly.They show the existence of a pattern similar to the modern one since the early Miocene (Zhang and Guo,2005).The Pliocene pattern (Fig.4e)is also similar to the Miocene one,except that the far northeastern part is marked by semi-arid condi-tions,representing a slight humidi?cation compared to the late Miocene.
southwest of the strong in-monsoons.It diachronous at much higher latitudes indicates that the aridity was not caused by the subtropical high-pressure zone.Instead,the similar loca-tion to the present-day drylands indicates typical inland-type deserts.
In summary,the spatial distributions of the geological indicators clearly reveal that (1)the zonal climate pattern linked to the planetary circulation system was transformed to a monsoon-dominated pattern similar to the present-day one;(2)the low-latitude drylands related to the subtropical high-pressure zone disappeared while inland-type deserts at higher latitudes formed;and (3)both the humidi?cation in southwest and southeast China and the appearance of the northwest drylands were closely coupled,suggesting a joint change of circulation and aridity,and hence,dynamic links
Clim.Past,4,153–174,2008
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(~24-5.3 Ma)
(~24-16 Ma)
Late Miocene
(~11-5.3 Ma)
Pliocene
(~5.3-2.6 Ma)
Middle Miocene
(~16-11 Ma)
Humid belt Arid belt S e m i -a r i d S u b -h u m i d b e l t
Humid belt
Arid belt
S e m i -a r i d S u b -h u m i d b e l t
Humid belt
Arid belt S e m i -a r i d S u b -h u m i d b e l t
Humid belt
Arid belt
S e m i -a r i d S u b -h u m i d b e l t
Humid belt
Arid belt
S e m i -a r i d S u b -h u m i d b
e l t
Arid Ind.Pollen Gypsum
Gyp./Salt Salt Jarosite Arid Grassland Mud Crack Gyp./Mirabilite Humid Ind.Pollen Coal Forest Mammals
Boundary
Sub-Humid Pollen Carbonate Con.Wood-Steppe Mammals
Arid belt Semi-arid/Sub-humid
Terrestrial deposits in semi-arid/sub-humid belt
Terrestrial deposits in humid belt Volcanic rock Humid belt Terrestrial deposits in arid belt Marine deposits Lack of deposits or unclear
Molasses belt
(a)
(b)
(c)
(d)
(e)
Fig.4.Miocene;(b)(e)Pliocene.Data sources between by the ing the monsoons.
3Miocene loess-soil sequences as indications of mon-soon regime and inland-deserts Eolian dust deposits spread widely across the middle reaches of the Yellow River in the Loess Plateau (Liu,1985).The region is delimited by the Liupan Mountains into the east-ern and western parts,with the Asian inland deserts to the north and northwest,and the Himalayan-Tibetan Plateau to the southwest (Figs.1a and 2).Modern observations indi-cate that eolian dust is mainly derived from inland deserts and transported by the Asian winter monsoon (Liu,1985)while rainfall in the region is mainly brought by the south-east summer monsoon (An et al.,1990;Liu and Ding,1998)monsoon been identi?ed loess-Kukla et al.,Red-(2.6–8.0Ma)and only found in the eastern Loess Plateau (Sun et al.,1997;Ding et al.,1998;An et al.,2001;Guo et al.,2004),and the Miocene and Pliocene loess-soil sequences recently found in the western Loess Plateau with a combined time coverage from 22to 3.5Ma (Guo et al.,2002;Hao and Guo,2004,2007;Liu et al.,2005).These eolian formations provide a near continuous terrestrial record of paleoclimate for the past 22Ma.3.1
Onset of loess deposition roughly coupled with the changes of climate pattern
Miocene loess deposits were ?rstly found in the western Loess Plateau (Guo et al.,2002)near Qin’an (QA-I and QA-II sections),Gansu Province (Fig.2).Their eolian origin
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Marine O (%o )
18p CO 2 (ppmv)
p CO 2 (ppmv)
5
4
3
2
1
05101520
25
3035
40
4550
55
606570
1000
2000
3000
4000
A g e (M a
)1000
2000
δFig.5.Variations of global temperature/ice volume and proxy es-timates of the Cenozoic atmospheric concentration of CO 2.(a)Marine δ18O records of benthic foraminifera as an indication of global temperature and ice volumes (Zachos,et al.,2001);(b)Boron isotope-based estimates of atmospheric CO 2levels for the past 60Ma (Pearson and Palmer,2000);(c)Carbon isotope based estimates of Cenozoic atmospheric CO 2levels (Pagani et al.,2005).The shadowed band indicates the maximum and intermediate esti-mates and dashed line indicates the minimum estimates.
is attested by (1)the presence of several hundred paleosols and interbedded loess layers that were signi?cantly affected by pedogenesis,indicative of subaerial environments (Guo et al.,2002);(2)the ?ne silty texture throughout the ～16-Ma sequence with maximum grain-size mostly <120μm (Guo et al.,2002;Qiao et al.,2006);(3)the angular morphology of quartz grains typical of eolian dust deposits (Guo et al.,2002;Liu et al.,2006);(4)the similar geochemical properties to the Quaternary loess and to the average composition of the upper continental crust (Liang et al.,2006),a basic feature of loess deposits (Jahn et al.,2001);(5)the well-preserved,abundant and randomly distributed land snail fossils in both soil and loess layers,along with the lack of aquatic and amphibian species throughout the sequences (Li et al.,2006a,2006b);and (6)rock magnetic properties typical of eolian deposits (Hao et al.,2008).Spatial investigations showed that the Miocene eolian deposits mantle the highlands across a broad region of the western Loess Plateau (Yuan et al.,2007).We have dated ?ve Miocene loess-soil sections (Fig.2)using magnetostratigraphy.These include the QA-I (22-6.2Ma)and QA-II (21.6–7.4Ma)(Guo et al.,2002),QA-III (21.4–11.4Ma)(Hao and Guo,2007),QA-IV (Miziwan site,18.5–11.6Ma)(Liu et al.,2005)and ML-V (Gaojiazhuang site)in this study (Fig.6).The variable basal ages of the sections are related to their different topographic locations.A loess section near Xining containing a Miocene portion younger than 14Ma was also reported (Lu et al.,2004).These results provide several lines of new information about this unique terrestrial record.
1.These sections have stratigraphies and magnetic suscep-tibility time series that are spatially correlative (Guo et al.,2002;Liu et al.,2005;Hao and Guo,2007).This is clear in the correlations between ML-V and QA-I (Figs.6and 8),separated by ～75km.Such high spa-tial correlativity is characteristic of eolian deposits and also attests to the relative continuity of the sequences.
2.The spatial coverage of these sites,as well as our geomorphic investigations (Yuan et al.,2007),re-veals widespread Miocene eolian deposition in northern China,and their signi?cance for paleoclimate at larger regional scales.Miocene eolian dust input has also been identi?ed as the main source of ?ne-grained sediments in some ?uvial-lacustrine basins in the region (Garzione et al.,2005).Recently,a set of ?ne-grained sediments beneath a 15-Ma basalt sheet near Nanjing has been identi?ed as eolian deposits (Zhang et al.,2007)sug-gesting that the southern boundary of the Miocene eo-lian deposition might have reached as far south as the Yangtze River.
3.The lower boundaries of these sections indicate that loess deposition in northern China started at least in the early Miocene.The basal age of the QA-I section,～22Ma (Guo et al.,2002),still represents the oldest up to date.This is approximately consistent with the ma-jor change of climate patterns in Asia discussed above,con?rming a major reorganization of climate regime.3.2
Miocene loess as direct evidence of inland deserts in Asia
Loess deposits cover ～10%of the land surface and are found in variable environments (Liu,1985;Tsoar and Pye,1987;Pye,1995).Drylands are the most important dust sources and the resulted loess deposits are known as hot loess (Obruchev,1933,but see Liu,1985).In contrast,loess de-posits around glacial areas are referred to as cold loess ,with distributions spatially restricted to periglacial environments (Liu,1985).Loess deposits usually cover terraces of large rivers,mostly due to dust de?ation from ?ne-grained ?uvial materials during glacial periods (Qiao et al.,2003;Zoller et al.,2004;Johnson et al.,2007).Their distribution is clearly linked to river valleys.Loess deposits are also frequently found in coastal regions where dust was mostly derived from continental shelves exposed to wind erosion during the times of low sea level (Zhao,1996).Some loess deposits may re-sult from a mixture of sources,such as the unusually thick loess deposits on some river terraces in northern China (Jiang et al.,2004)where local ?uvial sources and remoter desert sources would have co-contributed.
Whatever the main sources of eolian dust,the formation of loess fundamentally requires (1)a sustained source of dust,
Clim.Past,4,153–174,2008
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Fig.6.34?24 N) Miocene latitudes are shown.1995) dates the phyllite and is at20–25cm stepwise thermal Magnetic
(2)
suitable
occurs in
1987;
monly
tion cover
?ated.An
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position
The
Central
tensive
The Miocene eolian deposits in northern China are un-doubtedly hot loess because of their wide distribution and nearly continuous temporal coverage.Their desert origin is also supported by the angular morphology of the quartz frac-tion extracted from these loess samples(Fig.7a and b).Scan-ning electronic microscope(SEM)observations show that a majority of quartz grains are?ner than100μm in diameter, mostly ranging from10to30μm.Most grains have irregu-lar and angular shapes and many are characterized by sharp edges and conchiform fractures.The angular grains resulted from mechanical collisions of eolian sandy grains,salt dis-
regions
dust
shapes
Miocene
the aver-
sedi-
such
tend to have more speci?c geochemical signatures.
Thus,the Miocene loess deposits in northern China pro-vide pertinent evidence on the following crucial features rel-ative to the Cenozoic history of Asian drying.
1.They indicate the existence of sizeable deserts in the
Asian inlands by22Ma ago as dust sources(Guo et al., 2002).Because the onset of loess deposition matches the reorganization of climate patterns,these deserts must be inland-type rather than planetary-type.These also indicate a joint change in inland aridity and the at-mospheric circulation.
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Fig.7.Quartz grain morphology of early Miocene loess samples and micromorphology of the early Miocene paleosols from QA-I.(a) Scanning electronic microscopic(SEM)picture of quartz grains in Miocene loess samples(QA-I,250m);(b)SEM picture of quartz grains in Miocene loess samples(QA-I,252.6m);(c)Clay coatings in an early Miocene soil(QA-I,253.1m,plain-polarized light);(d)Clay coatings and intercalations with high birefringence(QA-I,253.1m,cross-polarized light);(e)Clay illuvial features in the forms of intercalations within the groundmass(QA-I,214.8m,cross-polarized light);(f)Groundmass of an early Miocene soil showing the strong argilization (QA-I,211.8m,cross-polarized light).
2.The near-continuous development of eolian sequences
in northern China,from the early Miocene to the Holocene,implies that inland deserts have been con-stantly maintained over the past22Ma despite drastic changes in global climates during the Neogene and Qua-ternary(Miller et al.,1998;Zachos et al.,2001).
3.3Miocene dust transport and Asian winter monsoon
A large collection of observational evidence indicates that the Quaternary loess deposits in northern China were mainly transported by the northwest winds in the Asian winter mon-soon(Liu,1985;An et al.,1990;Ding et al.,1995;Liu and Ding,1998).This inference has been con?rmed by the spa-tial variations of eolian grain-size in the Loess Plateau re-gion,ranging from coarser in the northwestern part to?ner in the southeastern part(Liu,1985;Ding et al.,1995).Recent examination on the late Miocene-Pliocene Red-Earth(Miao et al.,2004)revealed a similar pattern of eolian grain-size, indicating a dominant role for the winter monsoon in dust transport since～8Ma ago.
The onset of eolian dust deposition by22Ma ago attests to the presence of a circulation suf?ciently energetic to carry eolian dust from the deserts to the Loess Plateau region(Guo et al.,2002).Several lines of evidence suggest that this
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circulation was also the winter monsoon.
1.Loess has been continuously deposited in the middle
reaches of the Yellow River since at least22Ma ago and the location of drylands in Asia(Fig.4)has been sim-ilar to the present-day(Fig.1).This evidence implies that the dust-carrying winds must have had a northern origin from the available dust sources,consistent with the modern trajectory of the Asian winter monsoon. 2.Although more sophisticated geochemical approaches
may discriminate among the relative contributions of different deserts to loess deposits(Chen et al.,2001;
Sun,2002),the similarity in the elemental geochemistry between the Miocene loess and those of the last8Ma (Guo et al.,2002;Liang et al.,2006)supports broadly comparable source areas and dust transporting trajecto-ries over the past22Ma,and hence the presence of the winter monsoon circulation.
To further address this issue,grain-size analyses were con-ducted on samples dating from15.4to11.1Ma at QA-I and ML-V(Gaojiazhang site),～75km south to QA-I(Fig.2). The analyses reveal similar trends of grain-size variations along the two sections,but signi?cantly?ner textures at the southern ML-V site(Fig.8).The average median grain-size at ML-V is～1μm?ner than for QA-I.These new data have three implications.
1.Similar to the magnetic susceptibility time series(Liu
et al.,2005;Hao and Guo,2007),grain-size variations in the Miocene loess-soil sequences are also spatially correlative,again characteristic of eolian deposits.
2.The grain-size gradients indicate that the source areas
lie to the north of the Loess Plateau,and thus in the inland deserts.
3.The patterns require north-to-south circulation(the
Asian winter monsoon).The establishment of northerly winds is regarded as the main criteria of the Asian mon-soon system(Liu and Yin,2002).Because of the close relationship of the winter monsoon with the Siberian high-pressure center,we believe that the Siberian High would have also formed or greatly intensi?ed by22Ma ago.
Unfortunately,available early Miocene sections are not ide-ally located for examining grain-size gradients prior to 15Ma.
3.4Early Miocene soils in loess as evidence of a monsoon
climate regime
Loess layers are deposited during relatively dry-cold periods while soils developed during more humid-warm intervals. Because soil formation requires a substantial amount of rain-fall,the numerous paleosols in the Miocene eolian sequences also imply the existence of other circulation branches able to bring moisture from the ocean to the south.Consequently, the alternations between loess and soil layers indicate cycli-cal orbital-scale occurrences of dry and humid conditions in northern China(Guo et al.,2002).
To further characterize the circulation characteristics,we examined properties of the early Miocene paleosols.Mi-cromorphology examination reveals abundant clay illuvial features(Fig.7)that are typical of Luvisols(FAO-Unesco, 1974)formed under humid forest environments(Fedoroff and Goldberg,1982).Their proportions of up to～30%are approximately comparable to those of the modern Luvisols in the south of the Yangtze River where annual rainfall is more than1000mm(Zhang et al.,1999).Moreover,a large fraction of the clay illuvial features are in the form of in-tercalations within the groundmass(Fig.7d–e).Such illu-vial features,commonly described as vertic due to alternative humidi?cation and shrinkage of soil pro?les(Hussein and Adey,1998;Cao and He,1999),are typical of soils formed under climates with contrasting seasons(Cao and He,1999). They suggest a strong seasonality in northern China since the early Miocene.
The intensity of clay illuviation of these early Miocene soils was much stronger compared to the most developed soil Quaternary S5-1soil(～0.5Ma in age)in the relatively humid southernmost Loess Plateau,for which clay illuvial features amount to～10%(Guo et al.,1998).Although the relative duration of the seasons may affect pedogene-sis,the substantially increased amount of illuvial features in the Miocene soils indicates much more abundant rainfall in northern China during the early Miocene than for the Qua-ternary.According to the climate patterns since the early Miocene(Fig.4),most of the moisture must have had a low-latitude origin in the summer monsoons.In view of the rather dry conditions in northwest China(Fig.4),the westerlies were unlikely to have provided a signi?cant moisture contri-bution,because of the extremely long continental trajectory from moisture sources.
Under a climate regime without seasonally alternating cir-culations,a soil largely represents a sedimentary hiatus(Fe-doroff and Goldberg,1982;Cremaschi et al.,1990),as is the case for most loess-soil sequences in non-monsoon regions. In these regions,soil develops on the parent loess deposited during a dry-cold period,such as late-glacial intervals just prior to the soil-forming interglacial period when dust de-position was negligible(Fedoroff and Goldberg,1982;Cre-maschi et al.,1990).In contrast,paleosols in the loess-soil sequences under a monsoonal climate regime have com-pletely different features resulting from interactions between summer and winter monsoons.In summer,the monsoonal rainfall associated with the high temperature favors pedoge-nesis,but eolian dust continues to be added to the soil sur-face in winter and early spring,although at lower intensi-ties than during typical loess deposition periods(Guo et al., 1991,1993).Thus,dust deposition and soil-formation under
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70
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68
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m Guo et al_Fig.8
4
8
12
16
23>)%( m 0
1
2
3
4
5
36>)%( m μμμhttps://www.wendangku.net/doc/b111489912.html,parison of grain-size changes between QA-I (blue lines)and ML-V (red lines).The ?ne dotted lines represent the data at 10cm intervals and the thick lines are 30-point moving averages.ML-V is adjusted to the QA-I depth using magnetic reversals as control points.The grain-size changes shown here correspond to the interval from 15.41to 11.12Ma.The intervals within ML-V without data correspond to two layers of water-reworked loess with some coarse sands derived from the upper slopes,for which sam-ples were not analyzed.The ?ner grain-size at the ML-V site in-dicates northern source locations and northerly dust-carrying winds during the Miocene.Grain-size of 787samples from QA-I and 868from ML-V were analyzed using a Malvern Mastersizer-2000laser particle analyzer with an analytical precision <1%.They were pre-treated with hydrogen peroxide to remove the organic matter,then with hydrochloric acid to remove the carbonates,and with sodium hexametaphosphate for dispersion.
a monsoonal climate regime are competing processes,and the presence of a soil implies that the latter process was pre-dominant (Porter,2001).These interactive processes lead to the formation of the so-called accretionary soils (Hovan and Rea,1991;Kemp,2001)that can be regarded as a strong evidence of a monsoonal climate regime.
Accretionary soils are characterized by speci?c features (Guo et al.,1991,1993),three of which allow quick discrim-ination from non-accretionary soils.First,eolian dust during the soil-forming intervals is usually signi?cantly ?ner due to the weakened winter monsoon and relatively smaller/remoter sources.This can be detected by examining the grain-size of the quartz fraction,which is highly resistant to weath-ering and hence independent of the effects of pedogenesis.The quartz fraction of an accretionary soil has ?ner grain-size than that of the underlying loess,while that of a non-accretionary soil has similar quartz grain-size to its parent loess.Second,because of the differences in dust grain-size between soil forming and loess deposition periods,the dust composition may also be different,as can be determined us-ing stable elements resistant to post-depositional pedogene-sis.Third,accretionary soils usually have highest chemical weathering intensity in the middle of their pro?les because of the intensi?ed dust deposition during the late stage of soil development,while non accretionary soils have strongest weathering at the top horizon (Duchaufour,1983).
To check if the soils in the Miocene loess sequences are accretionary soils,four kinds of analyses were conducted.First,microscopic observations show that the quartz fraction in soils are signi?cantly ?ner than in the underlying loess lay-ers indicating that the soils were not totally developed from the underlying loess.This conclusion is also con?rmed by grain-size analyses on the quartz fraction (Fig.9a).Second,chemical analyses show an unambiguous difference of chem-ical composition of the stable elements between the loess and soils that are not affected by the soil-forming processes,indi-cating a composition differences (Fig.9b).Finally,the chem-ical weathering pro?les of the soils show stronger weathering intensity in the middle of the pro?les (Fig.9c),followed by decreasing intensity to the top.These properties ?rmly de-?ne the accretionary nature of the paleosols in the Miocene loess deposits,indicating a monsoon climate regime.In summary,the properties of the Miocene loess-soil se-quences require the existence of a typical monsoonal climate in northern China.Still an open question is the relative con-tribution of moisture from the southeast and southwest sum-mer monsoons to the formation of the Luvisols in the Loess Plateau.Clari?cation of this question would require several suitably located Miocene loess-soil sections,but these are not yet available.Measurements on the oxygen isotope compo-sition of pedogenic carbonates would also be helpful.Al-though modern moisture in the Loess Plateau is mostly re-lated to the East Asian summer monsoon due to the elevated Tibetan Plateau to the southwest,a greater contribution from the southwest summer monsoon would be expected during times when the Himalayas and Tibetan Plateau were not as high as it is today,as might be the case for the early Miocene.The results of numerical experiments (Zhang et al.,2007a,b)appear to be supportive to this possibility.
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4Other records of the climate reorganization Although the onset of loess deposition is roughly consistent in time with the major reorganization of climate patterns,the
precise age of this change remains an open question,because the data used for spatial mapping are of coarse resolution and low chronological accuracy while the basal age of the loess sections may depend in part on the tectonic setting of the substrata(Guo,2003;Hao and Guo,2004).Also,whether or not this climatic reorganization represents a sudden change or stepwise changes need to be addressed.
During the past?ve years,we explored for older loess de-posits in the Loess Plateau,but did not?nd any.However, other kinds of records from surrounding regions may provide some insights to this issue.A pollen record from the nearby Linxia?uvial-lacustrine basin(Fig.10a)showed a drastic in-crease in the percentage of tree pollen near～22Ma(Shi et al.,1999).Because the site was located within the planetary-type dry belt during the Oligocene(Fig.3)and is presently within the monsoon zone,this vegetation shift would indi-cate humidi?cation of the region,and thus an enhanced in-?uence of the summer monsoon.Similar trends were shown by a slight decrease in the content of xerophytes at～23Ma (Fig.10b)in a core from the Qaidam basin(Wang et al., 1999)although the region is currently less in?uenced by the summer monsoons.In a carbon isotope record of terrestrial black carbon re?ective of vegetation changes in South China, the earliest highδ13C peaks appeared～20Ma ago and were interpreted as a support of early monsoon initiation(Jia et al., 2003).A prominent change in the mammalian and?oristic regions in China appears to have also occurred in the early Miocene(Song et al.,1983;Qiu and Li,2005).
A marine eolian record at the LL44-GPC3site from the North Paci?c(Rea et al.,1985;Rea,1994)shows lower rates of dust accumulation in the Paleogene and roughly doubled rates since～25Ma(Fig.10c).This transition,associated with mineralogy and chemistry changes,was interpreted as representing the time when the core site migrated north from the regime of trade winds to that dominated by eolian trans-port in the westerlies and the in?uence of Asian dust sources (Rea,1994).Recently,a comprehensive geochemical analy-sis shows a major increase in the delivery of Asian dust ma-terial since～20Ma(Fig.10d)at ODP site1215from the central Paci?c(Ziegler et al.,2007),which was interpreted as recording the development of East Asian monsoon and formation of Asian loess.
These lines of evidence,associated with the Miocene loess records(Guo et al.,2002),suggest that the major changes in the Asian climate regime occurred between25and22Ma ago,and most of them support an age close to22Ma.From these insights,we speculate that discovery of older loess-soil sections could yet be made in northern China but probably not more than a few million years older.
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Fig.9.Accretionary properties of the early Miocene paleosols.(a) Comparison of median grain-size(Md)and the proportions of the >32μm and>63μm fractions of quartz particles between soils and loess layers,showing the accretion of?ner eolian dust during soil-forming periods.30soil and30loess samples were analyzed along QA-I(totally253.1m in thickness).The quartz fraction was ex-tracted using the sodium pyrosulfate fusion-hydro?uorosilicic acid method(Xiao et al.,1995).X-Ray diffractions of the extracted fraction indicate a quartz purity of more than95%.Grain-size of the quartz samples was analyzed using a Malvern Mastersizer-2000 laser analyzer.(b)Variations of SiO2/Al2O3molecular ratio along an early Miocene portion of QA-I showing lower values in soils than in loess layers.Because this ratio has been shown to re?ect mainly the eolian grain-size prior to pedogenic affection(Peng and Guo, 2001;Guo et al.,2004),its lower values in soils indicate continu-ous dust deposition during the soil-forming periods,but with?ner grain sizes.Alternations between soil and loess layers are illus-trated by the?uctuations of magnetic susceptibility,higher in soils and lower in loess.SiO2and Al2O3contents were analyzed by X-Ray?uorescence using a Philips PW-1400unit with an analytical uncertainty of2%.(c)Variations of Fed/Fet ratio along two early Miocene portions at QA-I as examples show highest weathering at the middle of the soil pro?les.Fed/Fet is a chemical weathering in-dex(Duchaufour,1983)that measures the proportion of iron oxides and hydroxides liberated by chemical weathering from iron-bearing silicate minerals and has been successfully applied in the Quater-nary loess of China(Guo et al.,1996,2000).
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5Causes of climate reorganization
The new results therefore con?rm previous evidence that the climate in Asia experienced a transition from a zonal climate pattern to a monsoon-dominated one near the Oligocene/Miocene boundary,by22Ma ago.This reorgani-zation was marked by the joint onsets/strengthenings of the Asian summer and winter monsoon circulations and inland-type deserts.After this transition,the role of the summer Subtropical High was largely weakened,while that of the winter Siberian High was reinforced.The similarity of cli-mate patterns through the Neogene and Quaternary,and con-tinuous loess deposition over the past22Ma indicate that the monsoon-dominated climate and the inland deserts have constantly been maintained since their formation.
The causes of the Asian monsoons and inland deserti?ca-tion have been objectives of numerous studies.Earliest the-ories emphasized the role of land-sea thermal contrast and its link to monsoon phenomena(Halley,1986).However, these theories cannot explain the onset of a broad monsoon-dominated regime by the early Miocene.Normal seasonal oscillations of planetary circulations(Fl¨o hn,1956)such as the inter-tropical convergence zone(ITCZ)may explain the presence of monsoons in tropical regions,but not the deep penetration of the ITCZ and summer monsoons into eastern Asia since the early Miocene as indicated by the presence of well developed soils.
Although the Cenozoic global cooling trends had signi?-cant impacts on the Asian monsoon climate in the past6Ma (Ding et al.,1995;Guo et al.,2004),they are unlikely to account for the major reorganization of climate pattern by 22Ma ago because the most prominent changes in global ice-volume and temperature,as documented by the marineδ18O records(Miller et al.,1998;Zachos et al.,2001),are not cor-relative with the major changes in Asia(Fig.5a).Also,the consistently maintained monsoon-dominated climate pattern and inland deserts in the past22Ma,as evidenced by near-continuous eolian sequences in China and the paleoenviron-mental maps(Fig.4),indicate that ice volume changes had not rearranged the basic climate pattern in Asia.
Other possible factors include the decreasing atmospheric concentration of CO2,which would cause global cooling, and consequently intensify Asian aridity and the winter mon-soon.Proxy estimates(Perason and Palmer,2000;Pagani et al.,2005)suggested large CO2decreases at～50Ma,30Ma and24Ma(Fig.5b and c).Although the fall at～24Ma is close in time to the Asian climate change,changes in CO2 level are not likely by themselves be the main cause of the climate-pattern rearrangement.Consequently,regional fac-tors must have played a dominant role.
Climate model experiments have focused on two main factors:uplift of the Himalayan-Tibetan complex and re-treat of the Paratethys Sea,an epicontinental sea still largely opened during the Paleogene(Dercourt et al.,1993).Up-lift could shift the Asian climate from a zonal pattern to a non-zonal one(Manabe and Terpstra,1974).The grow-ing elevation(Kutzbach et al.,1989;1993;Ruddiman and Kutzbach,1989;Ruddiman et al.,1989;Abe et al.,2003) and expansion of Tibetan Plateau along its northern and east-ern margin(An et al.,2001)could lead to drying trends in the Asian inlands and enhance both the summer and winter monsoon circulations.The summer monsoon could be trig-gered when the Tibetan Plateau reached half its present-day elevation(Prell and Kutzbach,1992).This threshold of half-elevation also seems to apply to the winter monsoon circu-lation(Liu and Yin,2002).Continuing uplift and expansion would alter signi?cantly the thermally forced circulation and enhance continental-scale summer and winter monsoons and central Asian aridity(An et al.,2001).In northern China, the formation of the monsoon climate is mainly marked by the establishment of northerly winter winds,and uplift would have had a more signi?cant effect on the winter monsoon than for the summer monsoon(Liu and Yin,2002).
An alternative view invokes the impact of the Paratethys retreat(Ramstein et al.,1997;Fluteau et al.,1999)in intensi-fying the South Asian monsoon and shifting the central Asian climate from temperate to continental conditions.Shrinkage of this epicontinental sea could thus have played a major role in large-scale atmospheric changes along with plateau uplift (Fluteau et al.,1999).
Recently,we attempted to discriminate the effects of these two major factors,and to examine the potential roles of other tectonic changes,on the formation of the monsoon-dominated climate in Asia using a nine-layer AGCM(Zhang et al.,2006,2007a,b).Sensitivity experiments show that a progressively elevated Tibetan plateau intensi?es both the Asian summer and winter monsoons,increases the seasonal contrast of precipitation in the monsoon zone,and enhances aridity in northwestern China(Zhang et al.,2006,2007a,b). These?ndings con?rm earlier conclusions that uplift plays an important role in the formation and development of the Asian climate(Kutzbach et al.,1989;1993;Ruddiman and Kutzbach,1989;Ruddiman et al.,1989;An et al.,2001;Abe et al.,2003),and also explain the constant maintenance of the monsoon-dominated climate and inland deserts in Asia in the past22Ma.
Our experiments also revealed that a monsoon-dominated climate and inland deserts can be generated by a3000-m el-evated Tibetan Plateau under most of the Paratethys condi-tions except one in which the Paratethys Sea is connected with the Arctic Ocean(Zhang et al.,2007a,b).These ex-periments imply that once the Paratethys becomes discon-nected from the Arctic Ocean,a suf?ciently elevated Tibetan Plateau(～3000m)alone is able to cause formation of both a monsoon-dominated climate and inland deserts in Asia,re-gardless of the size of the Paratethys.The effects of the plateau are,however,largely weakened when the Paratethys is still connected with the Arctic Ocean.
Experiments with the Paratethys Sea also show that with-drawal of this epicontinental sea increases precipitation in
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LL44-GPC3 eolian MAR
-23-1 ODP Site 1215
0510152025
303540455055606570
A g e (M a )
Linxia Qaidam Basin Guo et al_Fig. 10Fig.10.Relevant geological records of Asian climate changes near the Miocene-Oligocene boundary.(a)Increase in the content of tree
pollen ～22Ma ago at Linxia (Shi et al.,1999);(b)Decrease in the content of xerophytic pollens in the Qaidan Basin at ～23Ma (Wang et
al.,1999);(c)Cenozoic variations of eolian mass accumulation rate (MAR)at Site LL44-GPC3from the North Paci?c (Rea et al.,1985);
(d)Estimated Asian eolian contribution at Site ODP 1215in the central Paci?c showing a large increase at ～20Ma (Ziegler et al.,2007).
the monsoon zone and decreases rainfall in northwest China (Zhang et al.,2007a,b).These results reinforce the earlier conclusion about the role of the Paratethys retreat (Ramstein et al.,1997;Fluteau et al.,1999),and meanwhile show that monsoon climate and inland deserts can be generated when the Paratethys retreats to the Turan Plate whatever the ele-vation of the Tibetan Plateau (1000–3000m).The results also suggest that widening of the South China Sea enhances the humidity contrast between southern and northern China (Zhang et al.,2007b).
The effects of Tibetan uplift and Paratethys retreat on the seasonal circulation patterns are somewhat similar for north-ern China (Fig.11).In summer,both factors deepen the Asian low pressure and cause south-to-north in?ow and bring moisture into China (Fig.11a and c).In winter,uplift in-tensi?es the Asian high-pressure and lead to northwesterly winds in northern China (Fig.11b).The Paratethys retreat leads to an anticyclonic anomaly circulation centered over Central Asia and a cyclonic anomaly circulation over Mon-golia (Fig.11d)in winter.The coupled anomalies inten-sify the northwest winter winds from the inland deserts to the Loess Plateau.Although the anomalies also cause a south-to-north winter ?ow over eastern China,it would be a moisture-depleted ?ow because of its terrestrial origin.Our results thus suggest different impacts of Tibetan uplift and Paratethys retreat on the winter circulations,but their com-mon effects are the intensi?cation of the Asian high-pressure and the formation of northwesterly winds in northern China that pick up eolian dust from the inland deserts and trans-port it to the southeast.These changes are mostly consistent with the seasonal circulation characteristics indicated by the Miocene loess-soil sequences and the Neogene environmen-tal maps (Fig.4).
As for the geological histories of the three invoked tectonic factors,there is a general consensus about the spreading of South China Sea,which was initiated during the Oligocene and reached a stable spreading state in the early Miocene (Briais et al.,1993;Li et al.,2005,2006c).This is broadly consistent with the onset of the monsoon-dominated climate.This factor would have enhanced the south-north contrast of humidity (Zhang et al.,2007b).The collision of India and Asia in South Tibet may have begun ～55Ma or 34Ma ago (Aitchison et al.,2007)while the subsequent uplift histo-ries of the Tibetan region remain highly controversial.Some views about major uplift focus on several boundaries,in-cluding the Eocene and Oligocene at ～45–30Ma (Chung et al.,1998;Guo et al.,2006;Rowley and Currie,2006;Wang et al.,2008),the late Oligocene or early Miocene at ～26–18Ma (Harrison et al.,1992;DeCelles et al.,2007),the mid-Miocene around 14Ma (Turner et al.,1993;Cole-man and Hodges,1995;Spicer et al.,2003),the late Miocene around 8Ma (Harrison et al.,1992;Valdiya,1999;Garzione et al.,2000;Clark et al.,2005;Molnar,2005)and the Plio-Pleistocene after 3–4Ma (Li and Fang,1999;Zheng et al.,2000).Because the Himalayan-Tibetan Plateau has undoubt-edly had a strong effect on moisture transport to the Asian
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Clim.Past,4,153–174,2008
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0.5Guo et al_Fig 11Fig.11.Effects of Tibetan Plateau uplift and Paratethys retreat on the summer and winter circulation patterns and precipitation ?elds in Asia (compiled from sensitivity experiments in Zhang et al.,2007b).(a)and (b)show the anomalies of sea-level pressure (color scale,hPa)and 850hPa wind circulations (stream lines)in summer and winter,respectively,corresponding to uplift of the Tibetan Plateau from half to full elevation.The gray shaded zone indicates the heightened area of the plateau.(c)and (d)show anomalies of sea-level pressure (color scale)and 850hPa wind circulations (stream lines)in summer and winter,respectively,corresponding to a retreat of the Paratethys Sea from south of Western Siberia to the Turan Plate.The gray shaded zone indicates the sea area that changed into land.(e)and (f)show the comparative precipitation ?elds under the combined boundary conditions of a low Tibetan Plateau and a large Paratethys Sea,and of a high Tibetan Plateau and a smaller Paratethys Sea,respectively.Color scale shows the elevation of topography with the sea areas in blue.White lines represent isohyets of annual precipitation.
interior,we believe that at least the southern margin of the plateau would have been suf?ciently elevated by 22Ma ago to act as a moisture barrier.This inference is strongly sup-ported by the deposition of debris in submarine fans in the Indian Ocean around this time (Corrigan and Crowley,1992;Clift,2006).
During an initial stage of the India and Asia collision,Paratethys would have already separated from the Arc-tic Ocean (Akhmet’ev et al.,2001;Akhmet’ev and Beni-amovski,2006)while the Tibetan Plateau remained low.Available data suggest shrinkage of this sea from a large extent during the Oligocene and Miocene (Dercourt et al.,1993;Pavelic et al.,2001;Akhmet’ev and Beniamovski,2006)to a smaller one during the Miocene (Dercourt et al.,1993).This withdrawal is broadly consistent in time with the suggested chronological ranges of Tibetan uplift and the onsets of monsoon dominant climate and inland deserts in Asia.
The fact that a monsoon-dominated climate and inland deserts were already formed by 22Ma ago provides an envi-ronmental clue for a further evaluation.It suggests that the tectonic conditions had evolved to a threshold by ～22Ma ago suf?cient to cause the climate reorganization.Since both Tibetan uplift and Paratethys retreat were linked with plate tectonics in the region,there is a strong possibility that these two factors evolved more or less synchronously.A large col-lection of data effectively demonstrates a peak range of re-gional tectonic changes around the early Miocene (Harrison et al.,1993;Hodell and Woodruff,1994;Ding and Zhong,1999;Pavelic et al.,2001;Ding et al.,2004;Guo et al.,
Clim.Past,4,153–174,2008
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2006).Consequently,the combined effect of Tibetan uplift and Paratethys shrinkage probably triggered the major cli-mate reorganization in Asia.
This combined effect is clear in our numerical experiments (Fig.11e and f).Under the conditions combining a low Ti-betan Plateau and a large Paratethys Sea(Fig.11e),a roughly zonal?eld of low precipitation occurs at lower latitudes in China,comparable to the zonal dry belt in the Paleogene (Fig.3).In contrast,the experiment with a high Tibetan Plateau and a smaller Paratethys Sea yield an arid zone at higher latitudes in northwestern China and increased rainfall in southern China(Fig.11f).These are comparable with the Neogene climate patterns(Fig.4).
The exact relationship of Asian climate change relative to tectonics remains to be determined because of uncer-tainties about the timing and extent of Tibetan uplift and Paratethys retreat,and the inability of models to simulate higher-resolution topography.An increasing amount of evi-dence suggests diachronous uplifts of the plateau(e.g.Chung et al.,1998;Wang et al.,2008)but detailed reconstructions are not yet possible.Models with higher resolution will also be necessary to investigate the effects of regional mountain ranges,such as the Liupan and Qinling Mountains,which were also likely uplifted during the Neogene.In addition, discriminating the effects of tectonics and global climate changes on the Asian paleoclimate remains an important is-sue.
Recently,paleo-altimeters based on stable-isotopic in-dices,such asδ18O of soil carbonate(DeCelles et al.,2006), 13C-18O bonds in carbonate minerals(Ghosh et al.,2006),
δ18O andδ2H of authigenic minerals(Rowley and Cur-rie,2006;Rowley and Garzione,2007),as well as paleo-botanical indicators(Lu et al.,2001;Spicer et al.,2003)have been developed to address the elevation history of moun-tains.Most of the results tend to suggest the existence of high-elevation parts of the Tibetan Plateau by or in the early Miocene(Spicer et al.,2003;DeCelles et al.,2006;Row-ley and Currie,2006;Rowley and Garzione,2007).How-ever,an elevation similar to the present-day one during the early Oligocene,as inferred by some studies(Chung et al., 1998;Rowley and Currie,2006;Rowley and Garzione,2007; Wang et al.,2008),may only be local in extent,because an extended plateau at this height would produce the monsoon-dominated climate pattern in Asia according to climate mod-els(Kutzbach et al.,1989;1993;Ruddiman and Kutzbach, 1989;Ruddiman et al.,1989;Abe et al.,2003;Zhang et al., 2007a,b),yet geological evidence clearly reveals a plane-tary climatic pattern in Asia during most of the Oligocene (Fig.3c).These results,associated with the model out-puts and geological records,likely support the notion of di-achronous uplifts of the plateau.
Chemical weathering of silicate materials is a process that consumes CO2(Raymo et al.,1988;Raymo and Ruddiman, 1992).Tectonic uplift may have major impacts on atmo-spheric CO2levels by accelerating chemical weathering and increasing the burial of organic matter(Raymo et al.,1988; Raymo and Ruddiman,1992;Derry and France-Lanord, 1996;Ruddiman et al.,1997).Consequently,reconstruction of the Cenozoic atmospheric CO2levels might be expected to provide helpful insights about the uplift history if other factors were secondary.Available proxy estimates based on marine boron-isotope(Pearson and Palmer,2000),marine carbon isotope(Pagani et al.,1999,2005)and paleobotan-ical evidence(Royer et al.,2001)consistently suggest a fall of the atmospheric CO2level near the Oligocene/Miocene boundary,followed by rather stable CO2levels during the Neogene.Whether these suggest an achieved state of ma-jor tectonic uplifts of global signi?cance by that time is a worthy question to consider in the future,as it appears to be coherent with the results of paleo-altimetry approaches for the Tibetan region(DeCelles et al.,2006;Rowley and Cur-rie,2006;Rowley and Garzione,2007).It should be noted, however,that proxy estimations of paleo-CO2level may be biased by other factors(ex.Lemarchand et al.,2000).Also, the rather stable and near present-day levels of CO2through the Neogene suggested by available estimates(Pagani et al., 1999,2005;Perason and Palmer,2000;Royer et al.,2001) face the question on explaining the ongoing global cooling since the early Neogene(Zachos et al.,2001).
6Conclusions
Based on a signi?cant amount of new data,we have exam-ined the spatial distribution of environmental indicators in ten Paleogene-Neogene time intervals,as well as the proper-ties of Miocene loess-soil sequences in northern China.The results led to the following conclusions.
1.Our geobiological data and map compilation con?rm
the earlier conclusion that the zonal climate pattern of the Paleogene was transformed into a monsoon-dominated pattern similar to the present-day one in the Neogene.These changes are marked by humidi?ca-tion in southwest and southeast China,disappearance of low-latitude aridity related to the subtropical high-pressure zone,and emergence of inland deserts at higher latitudes.Detailed mapping within the Oligocene and Miocene indicates that the reorganization was achieved by the early Miocene,matching the time of onset of widespread loess deposition in northern China.Al-though the basal ages of the loess sections do not nec-essarily provide the earliest age of this major climate transition,other terrestrial and marine records tend to suggest an age near the Oligocene-Miocene boundary, at25–22Ma.
2.The dated Miocene loess-soil sections in northern China
show spatially correlative stratigraphy and climate prox-ies,similar to younger eolian deposits in the region.
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The near-complete time coverage of Neogene and Pleis-tocene eolian deposits attest to the existence of inlands deserts in the Asian interior as persistent dust sources during the past22Ma despite major changes of global climate.Spatial gradients of eolian grain-size indicate
a source area lying north to the Loess Plateau in the in-
land deserts.They also provide evidence of strong dust-carrying circulation from the north in the Asian winter monsoon.
3.The well-developed Luvisols present since the early
Miocene indicate the existence of a circulation of oceanic origin that brought moisture to northern China, in the Asian summer monsoons.The intensity of these circulations was signi?cantly stronger than for the Qua-ternary.The accretionary properties of the soils attest to the presence of two seasonally alternating circulations, one from the oceans in the south carrying moisture and the other from the northern deserts carrying dust.These features rightly de?ne a full monsoonal(seasonally re-versing)climatic regime.
4.This major reorganization represents a fundamental
transformation from a planetary circulation system to a monsoon-dominated system.Following this transition, the effects of the subtropical high-pressure zone in gen-erating dry conditions at low latitudes weakened during the Neogene because of the strong in?uence of summer monsoons.In contrast,the effects of the winter Siberian High were reinforced.The roughly synchronous humid-i?cation in southwest and southeast China suggests a coupled strengthening of the southwest and southeast summer monsoon circulations,rather than largely di-achronous developments.In con?rming the roles of Ti-betan uplift and Paratethys shrinkage as suggested in previous studies,our recent numerical experiments and new geological data suggest a combined effect of these two factors with a contribution from the spreading and opening of the South China Sea.The loess record pro-vides a vital insight that these tectonic scenarios had evolved to a threshold by the early Miocene suf?cient to cause this major climate change in Asia. Acknowledgements.This work is supported by the National Project for Basic Research(2004CB720203),Chinese Academy of Sciences(Project KZCX2-YW-117)and National Natural Science Foundation of China(Project40730104).Sincerest thanks are extended to William Ruddiman,Gille Ramstein,Denis Rousseau and an anonymous reviewer for the highly constructive reviews and suggestions.
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大学文科专业介绍及就业介绍
大学文科专业介绍及就业介绍 汉语言文字学 专业概况：分为现代汉语和古代汉语两个大方向，主要研究从上古到现代的汉语的口语系统与文字系统的演变规律、结构特征和现实状况。 研究方向：汉语方言、汉语史、汉语词汇学、现代汉语语法修辞、汉字信息处理、对外汉语教学等。 就业前景：一般就职于高等院校、国家文化出版部门、中学、对外汉语培训机构等。 经济学 培养目标：毕业生能在综合经济管理部门、政策研究部门、金融机构和企业单位从事经济分析、预测、规划和经济管理实际工作。 主干课程：政治经济学（资、社）、西方经济学（微、宏）、会计学、统计学、货币银行学 就业方向：就业方向为政府经济管理部门，政策研究部门高校及金融、税务、证券、投资公司等单位。 法学 培养目标：培养能在律师、行政机关、检察机关、企事业单位和教学科研机构从事法律工作的复合型高级专门人才。
主干课程：法理学、中国法制史、宪法、行政法和行政诉讼法、民法、经济法、刑法、民事诉讼法、刑事诉讼法、国际法、国际私法。另设实践性教学环节，包括法律咨询、观摩审判、模拟审判，专业实习等。 就业方向：在法院、检察院等从事政法工作；在工商、税务、房地产、海关以及各类公司律师工作、在高等院校从事法律教育及法律研究工作。 国际政治 培养目标：本专业培养能在党政机关、企事业单位、高校和科研等部门从事外交和研究等方面的国际政治学高级专门人才。 主干课程：国际关系学、国际政治学概论、国际法、国际经济学、美国政治与外交、当代政府与公务员制度。 就业方向：毕业后主要在党政机关、企事业单位、高校和科研等部门从事外交、外事、对外宣传、教学和研究等方面的工作。 对外汉语 主干课程：现代汉语、古代汉语、文学概论、中国古代文学、中国文化概要、外国文化概要、英语听说、英语精读、英语写作 就业方向：在高等院校从事对外汉语教学和研究工作；在国家机关外事部门从事对外宣传等工作；在新闻、出版等部门从事创作等工作。 历史学
邻接表表示的图的基本操作的实现
邻接表表示的图的基本操作的实现 //采用邻接表完成无权无向及有向图的"建立、输出、深度遍历、广度遍历"操作 #include
typedef struct Headnode//头结点结构 { ElemType vertex;//顶点域vertex，存放顶点vi的信息 struct Tablenode *firstEdge;//vi的邻接表的头指针 }HeadNode; typedef struct Mgraph { struct Headnode vector[MAX_VERTEX_NUM]; //顶点向量 int vexnum; //图中当前顶点数 } MGraph; //队列初始化 Status InitLinkQueue(LinkQueue *Q) { QNode *p; p=(QNode*)malloc(sizeof(QNode));//开辟头结点空间 if(p!=NULL) { p->next=NULL; Q->front=Q->rear=p; return OK; } else return ERROR; } //链式队列的入队操作，在已知队列的队尾插入一个元素e，修改队尾指针rear。 Status InsertLinkQueue(LinkQueue *Q,ElemType e) { QNode *p;
Excel工作表的建立和编辑等基本操作
E x c e l工作表的建立和编辑 等基本操作 -标准化文件发布号：（9556-EUATWK-MWUB-WUNN-INNUL-DDQTY-KII
Excel工作表的建立和编辑等基本操作（2课时） 教学目的： 学习excel的使用，初步了解工作表的建立和编辑操作。 教学重点： 工作表的数据输入（包括不同文本、数值、日期等类型，有规律数据的输入，公式的编辑），工作表的格式设置（包括字体、对齐、边框和图案的设置）。 教学难点： 电子表格自动填充和公式编辑、函数应用。 上机任务 2
任务一：建立一个成绩表并简单设置格式 1、运行Excel，创建一个工作簿文件，文件命名为“学生成绩.xls”； 2、在sheet1中输入如下图所示的数据。注意，学号采用自动填充的功能快速输入； 3
3、在第1行上面插入一行，在A1单元格中输入标题“2009级学生入学成绩表”，将A1到I1单元格合并居中，设置标题为黑体、16号字、红色，单元格背景色为浅黄色； 4
4、在学号为“20080008”的记录前插入一行，任意输入数据。 5、删除学号为“20080006”的那一行。 6、将所有学号中的“2008”改为“2009”。 7、运用函数或公式计算出每个学生的“总分、平均分”，填入相应的单元格中。 8、分别在A11和A12单元格输入“最高分”、“最低分”，求出所有学生中各门课程的最高分和最低分，填入相应的单元格中。 9、设置表中各单元格水平居中对齐、垂直居中对齐。 10、设置第1行的行高为30，其余各行行高为16;列宽为“最适合的列宽”。 11、设置平均分列中的数值格式为保留2位小数位数。 5
大学专业介绍与就业方向(理科)
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算机技术等相关科学领域从事应用研究、技术开发以及教学和管理工作。 推荐院校：大学、清华大学、大学、大学、南开大学、大学、中国科学技术大学、大学。 4.应用化学 专业介绍：本专业以高分子材料、精细化工和计算机在化学化工中的应用技术为专业方向，培养具有可从事相关领域的科学研究，工业开发和管理知识的高级专门人才。 就业去向：主要到科研机构、高等学校及企事业单位等从事科学研究、教学及管理。 5.环境科学 专业介绍：本专业培养能在科研机构、高等院校、行政部门和企事业等单位从事科研、教学、规划与管理、环境评价和环境监测等工作的高级专业人才。 就业去向：主要到科研机构、高等学校、企业事业单位及行政部门等从事科研、教学、环境保护和环境管理等工作。 6.环境工程专业 专业介绍：本专业培养具备城市和城镇水、气、声、固体废物等污染防治和给排水工程，水污染控制规划和水资源保护等方面知识的环境工程学科高级工程技术人才。 就业去向：主要至政府部门、规划部门、经济管理部门、环保部门、设计单位、工矿企业、科研单位、学校等从事规划、设计、施工、管理、教育和研究开发方面的工作。
数据结构 图的基本操作实现
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输出： 第一行表示 A到B的旅游线路景点序列 第二行表示沿此线路，从A到B的旅游费用 设计要求： 1、上机前，认真学习教材，熟练掌握图的构造和遍历算法,图的存储结 构也可使用邻接矩阵等其他结构. 2、上机前，认真独立地写出本次程序清单，流程图。图的构造和遍历算法 分别参阅讲义和参考教材事例 图的存储结构定义参考教材 相关函数声明： 1、/* 输入图的顶点和边的信息,建立图*/ void CreateGraph(MGraph &G) 2、/* 深度优先搜索遍历图*/ void DFSTraverse(Graph G, int v) 3、/*广度优先搜索遍历图 */ void BFSTraverse(Graph G, int v)4、 4、/* 其他相关函数 */…… 三、实验步骤 ㈠、数据结构与核心算法的设计描述 ㈡、函数调用及主函数设计 （可用函数的调用关系图说明） ㈢程序调试及运行结果分析 ㈣实验总结 四、主要算法流程图及程序清单 1、主要算法流程图： 2、程序清单 （程序过长，可附主要部分）
关于锐捷路由器配置命令
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大学生专业选择与就业情况的调查报告
大学生专业选择与就业情况的调查报告 文件排版存档编号：[UYTR-OUPT28-KBNTL98-UYNN208]
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Photoshop基本操作介绍(图文介绍)
第一课：工具的使用 一、Photoshop 简介： Adobe 公司出品的Photoshop 是目前最广泛的图像处理软件，常用于广告、艺术、平面设计等创作。也广泛用于网页设计和三维效果图的后期处理，对于业余图像爱好者，也可将自己的照片扫描到计算机，做出精美的效果。总之，Photoshop 是一个功能强大、用途广泛的软件，总能做出惊心动魄的作品。 二、认识工具栏 1、 选框工具：用于选取需要的区域 ----选择一个像素的横向区域 ----选择一个像素的竖向区域
属性栏： 注：按shift 键+ 框选，可画出正方形或正圆形区域 2、 移动工具 ： -----用于移动图层或选区里的图像 3、套索工具： ----用于套索出选区 ----用于套索出多边形选区 ----可根据颜色的区别而自动产生套索选区 4、魔术棒工具： ----根据颜色相似原理，选择颜色相近的区域。 注：“容差”，定义可抹除的颜色范围，高容差会抹除范围更广的像素。 5、修复工具： 且是 ----类似于“仿制图工具”，但有智能修复功能。 ----用于大面积的修复 一新 ----用采样点的颜色替换原图像的颜色 注：Alt+鼠标单击，可拾取采样点。 6、仿制图章工具----仿制图章工具从图像中取样，然后您可将样本应用到其它图像或同一图像的其它部分。 ----仿制图章工具从图像中取样，然后将样本应用到其它图像或同 一图像的其它部分（按Alt键，拾取采样点）。 ----可先自定义一个图案，然后把图案复制到图像的其它区域或其它图像上。
三、小技巧： ①、取消选区：【Ctrl ＋D 】 ②、反选选区：【Shif+F7】 ③、复位调板：窗口—工作区—复位调板位置。 ④、ctrl+[+、-]=图像的缩放 ⑤空格键：抓手工具 ⑥Atl+Delete = 用前景色填充 Ctrl+Delete = 用背景色填充 第二课：工具的使用二 一、工具栏 自由变换工具：【 Ctrl ＋T 】 2、使用框选工具的时候，按【Shift 】后再框选，则框选出正圆或正方形。 按【Alt 】后再框选，则选区以鼠标点为中心
顺序表的建立及其基本操作技巧
山东师范大学 实验报告 课程：数据结构班级：2016级通信2班实验序号： 1 姓名：韩明达 学号: 201611030230 实验日期：9.17 题目: 顺序表的建立和运算 一、实验目的和要求 （1）熟悉C语言的上机环境，进一步掌握C语言的结构特点。 （2）掌握线性表的顺序存储结构的定义及基本运算 二、实验环境 Windows10，Visual Studio 2017 三、实验内容及实施 实验内容 1、建立一个顺序表，输入n个元素并输出； 2、查找线性表中的最大元素并输出； 3、在线性表的第i个元素前插入一个正整数x； 4、删除线性表中的第j个元素； 5、将线性表中的元素按升序排列； 【程序流程图】
【程序】 #include
图的基本操作(邻接表)
标头.h #include
无线网卡模拟AP功能设置指南
无线网卡模拟AP功能设置指南 本文适用于无线网卡：MW150U 4.0、MW150U 6.0、MW150UM 1.0、MW150US 1.0、MW300U 2.0、MW3030U1.0 无线AP可以为传统的有线局域网提供无线扩展接入，而一般的无线网卡只能作为客户端连接到无线AP。我司部分无线网卡具有模拟AP功能，不单可以作为无线客户端连接上无线网络，也可以切换为模拟AP，供其他无线客户端连接。其典型应用场景如下： 在没有无线路由器的情况下，电脑通过有线连接到宽带线路已经可以上网。电脑上安装具有模拟AP 功能的无线网卡，并设置共享可以访问互联网的网络连接，模拟AP与可以访问互联网的网络连接就虚拟出一个“无线路由器”。其他的无线设备如笔记本、手机、PAD等就可以无线连接上模拟AP共享上网了。 下面以MW300U为例介绍模拟AP功能以及虚拟无线路由器的设置方法，如下图所示。
步骤一安装无线网卡驱动和客户端软件，安装完成之后，如下图所示。 步骤二启用模拟AP功能。 1. 选择客户端软件中的“高级”选项。
2. SoftAP模式，选择“开”，提示“确认打开SoftAP模式”，点击“确认”。会显示“正在设置SoftAP模式，请稍后”，然后会提示“正在设置SoftAP模式成功”。 3. 配置模拟AP参数，如下图所示，本例中我们通过“本地连接”上网，配置完成之后点击“应用”。
Internet连接共享：当电脑上存在多个网络连接时，选择用于连接到互联网的网络连接，本例中以“本地连接”为例，选择本地连接对应的网卡作为“虚拟无线路由器”的WAN接口。 网络名称：网卡工作在SoftAP模式时发出来的无线网络名称（SSID），即无线设备搜索到模拟AP的无线网络名称。 安全模式：模拟AP的无线加密类型，推荐选择WPA2-PSK。 密码类型：无线网络的加密算法，推荐选择AES。 安全密钥：连接模拟AP时需要输入的无线网络密码。 IP地址：无线网卡的IP地址，在开启SoftAP模式时，自动生成，保持默认即可。 设置好上面的参数之后，点击“应用”。接着右键点击桌面“网上邻居”选择“属性”，打开“网络连接”，可以看到“本地连接”已经共享。 步骤三无线连接到SoftAP。电脑搜索无线网络，选中“SoftAP”，输入前面设置的“安全密钥”。
Excel工作表的建立和编辑等基本操作
Excel工作表的建立和编辑等基本操作（2课时） 教学目的： 学习excel的使用，初步了解工作表的建立和编辑操作。 教学重点： 工作表的数据输入（包括不同文本、数值、日期等类型，有规律数据的输入，公式的编辑），工作表的格式设置（包括字体、对齐、边框和图案的设置）。 教学难点： 电子表格自动填充和公式编辑、函数应用。 上机任务 1
任务一：建立一个成绩表并简单设置格式 1、运行Excel，创建一个工作簿文件，文件命名为“学生成绩.xls”； 2、在sheet1中输入如下图所示的数据。注意，学号采用自动填充的功能快速输入；2
3、在第1行上面插入一行，在A1单元格中输入标题“2009级学生入学成绩表”，将A1到I1单元格合并居中，设置标题为黑体、16号字、红色，单元格背景色为浅黄色； 4、在学号为“20080008”的记录前插入一行，任意输入数据。 3
5、删除学号为“20080006”的那一行。 6、将所有学号中的“2008”改为“2009”。 7、运用函数或公式计算出每个学生的“总分、平均分”，填入相应的单元格中。 8、分别在A11和A12单元格输入“最高分”、“最低分”，求出所有学生中各门课程的最高分和最低分，填入相应的单元格中。 9、设置表中各单元格水平居中对齐、垂直居中对齐。 10、设置第1行的行高为30，其余各行行高为16;列宽为“最适合的列宽”。 11、设置平均分列中的数值格式为保留2位小数位数。 12、为该表增加表格线（不包括标题行），内网格线为最细的实线，粉红色；外框线为最粗的实线，橙色。 4
13、将第2行的所有字符的字体设置为楷体、加粗，字号为14，颜色设置为红色，填充背景色为青绿色。 14、对“张三”插入批注，批注为“该生已转专业。” 15、把sheet1命名为“入学成绩表”； 16、保存文件并提交作业。 参考效果图如下： 5
大学理科专业介绍与就业方向
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注：按 shift 键 +框选，可画出正方形或正圆形区域 可根据颜色的区别而自动产生套索选区 根据颜色相似原理，选择颜色相近的区域。 5、 修复工具 ： 类似于“仿制图工具” ，但有智能修复功能。 用于大面积的修复 用采样点的颜色替换原图像的颜色 注： Alt+ 鼠标单击，可拾取采样点。 6、仿制图章工具 仿制图章工具从图像中取样， 然后您可将样本应用到其它图像或同一 图像的其它部分。 - 仿制图章工具从图像中取样，然后将样本应用到其它图像或同 一图像的其它部分（按 Alt 键，拾取采样点） 。 区域或其 它图像上。 2、 移动工具 ： 3、 套索工具 ： 用于移动图层或选区里的图像 - - 用于套索出选区 用于套索出多边形选 区 属性栏： 选区相交 单个选区 选区相加 选区相减 4、魔术棒工具 ，定义可抹除的颜色范围，高容差会抹除范围更广的像素。 且是 --------- -
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大学专业介绍及就业方向-土木建筑类大学专业解读
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设计题目：_______________ 指导教师：____________________________ 2013年12月30日
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