VARIATION OF THE MONSOON TROUGH INTENSITY IN THE SOUTH CHINA SEA AND WESTERN NORTH PACIFIC OCEAN

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A Single Species, Micromonas pusilla (Prasinophyceae), Dominates the Eukaryotic Picoplankton in the

A PPLIED AND E NVIRONMENTAL M ICROBIOLOGY,July2004,p.4064–4072Vol.70,No.7 0099-2240/04/$08.00ϩ0DOI:10.1128/AEM.70.7.4064–4072.2004Copyright©2004,American Society for Microbiology.All Rights Reserved.A Single Species,Micromonas pusilla(Prasinophyceae),Dominates theEukaryotic Picoplankton in the Western English ChannelFabrice Not,1Mikel Latasa,2Dominique Marie,1Thierry Cariou,1Daniel Vaulot,1*and Nathalie Simon1Station Biologique,UMR7127CNRS,INSU and Universite´Pierre et Marie Curie,29680Roscoff,France,1and Institut de Cie`ncies del Mar(C.S.I.C.),08003Barcelona,Spain2Received17September2003/Accepted11March2004The class Prasinophyceae(Chlorophyta)contains several photosynthetic picoeukaryotic species describedfrom cultured isolates.The ecology of these organisms and their contributions to the picoeukaryotic communityin aquatic ecosystems have received little consideration.We have designed and tested eight new18S ribosomalDNA oligonucleotide probes speciﬁc for different Prasinophyceae clades,genera,and ingﬂuorescentin situ hybridization associated with tyramide signal ampliﬁcation,these probes,along with more generalprobes,have been applied to samples from a marine coastal site off Roscoff(France)collected every2weeksbetween July2000and September2001.The abundance of eukaryotic picoplankton remained high(>103cellsml؊1)during the sampling period,with maxima in summer(up to2؋104cells ml؊1),and a single green algalspecies,Micromonas pusilla(Prasinophyceae),dominated the community all year round.Members of the orderPrasinococcales and the species Bathycoccus prasinos(Mamiellales)displayed sporadic occurrences,while theabundances of all other Prasinophyceae groups targeted remained negligible.Several studies have demonstrated the importance of eukaryotic picoplankton(cell size,0.2-to3-␮m)in terms of biomass and productivity in the euphotic zone of oceanic oligo-trophic waters(15),as well as in coastal waters(10).To date,only ϳ40species belonging to nine algal classes(Chlorophyceae,Pra-sinophyceae,Trebouxiophyceae,Prymnesiophyceae,Bolido-phyceae,Eustigmatophyceae,Pinguiophyceae,Bacillariophyceae, and Pelagophyceae)of photosynthetic picoplanktonic eukaryotes have been formerly described(41).However,phylogenetic anal-yses of sequences retrieved from natural samples in different oceanic regions have demonstrated much higher diversity,since many of these sequences do not correspond to any described taxa (19).The contributions of the different taxonomic groups to the picoplanktonic biomass,diversity,and ecology are poorly known because simple and reliable methods to detect and quantify such organisms in natural samples are lacking.Pigment signatures, scanning electron microscopy,and serial dilution cultures suggest that the classes Prasinophyceae(division Chlorophyta),Pelago-phyceae(division Heterokontophyta),and Prymnesiophyceae are major components of the picoplankton biomass in different ma-rine systems(20,35).Among these,the class Prasinophyceae contains several photosynthetic picoeukaryote species.This class is considered to be the most primitive in the green lineage and to have given rise to all other green algal classes,as well as to the land plants (34).Members are known to be common in temperate and cold regions and can occur as prominent constituents of ma-rine picoplankton(38).Within these organisms,genera such as Ostreococcus,Bathycoccus,and Micromonas have been de-scribed in coastal waters(4b,6).Micromonas pusilla(the only described species in the genus Micromonas)has been identiﬁed as a major component of the picoplanktonic community in several oceanic and coastal regions,such as the Mediterranean Sea(39),the Norwegian Sea(37),and central California wa-ters(35).However,the techniques used to establish these facts (microscopic identiﬁcation of cells presenting few morpholog-ical characteristics or serial dilution cultures)are time-consum-ing and incompatible with extensive ecological studies.In con-sequence,the precise distributions and the seasonal dynamics of an apparently very common picoplankter,such as M.pusilla, are poorly known.The aim of this work was to identify and study the seasonal variations of the dominant taxa in the picoeukaryote commu-nity at a coastal site of the western English Channel in the vicinity of a long-term oceanographic observation site(31). Oligonucleotide probes targeting18S rRNA coupled toﬂuo-rescent in situ hybridization associated with tyramide signal ampliﬁcation were used to detect the picoplanktonic taxa(22). Eight new oligonucleotide probes speciﬁc for Prasinophyceae were designed and validated on pure cultures.These probes,as well as more general probes targeting the Chlorobionta and the eukaryotes,allowed the study in detail of the dynamics of the dominant taxa along a seasonal time series between July 2000and September2001.MATERIALS AND METHODSCultures.Nineteen unialgal strains of picoeukaryotes belonging to different phylogenetic clades of the Prasinophyceae were selected(Table1).They were grown in Nalgene(Rochester,N.Y.)ﬂasks at20°C in K medium(11).In order to test the new probes designed in this study,cells were harvested during the mid-exponential growth phase.For each culture,4.5ml was harvested andﬁxed with paraformaldehyde(1%ﬁnal concentration)for1h.These cultures were ﬁltered on0.2-␮m-pore-size Anodiscﬁlters(Whatman International Ltd.,Maid-stone,England).Theﬁlters were dehydrated in an ethanol series(50,80,and 100%;3min each)and stored atϪ80°C until further hybridization tests were performed.*Corresponding author.Mailing address:Station Biologique,UMR 7127,CNRS et Universite´Pierre et Marie Curie,Place George Teis-sier,BP74,29682Roscoff Cedex,France.Phone:332-98-29-23-70. Fax:332-98-29-23-24.E-mail:vaulot@sb-roscoff.fr.4064Natural samples.Natural samples were collected twice a month between July 2000and September 2001at 0.5-m depth with 5-liter Niskin bottles off Roscoff,France,at the ASTAN station (48°46ЈN,3°57ЈW).The water was pre ﬁltered through a 200-␮m-pore-size mesh and further processed in the laboratory.Tem-perature,salinity,and concentrations of phosphate,nitrate,and ammonium were measured by standard oceanographic methods.For ﬂuorescent in situ hybridization (FISH),90ml of seawater was pre ﬁltered through 3-␮m-pore-size Nuclepore ﬁlters (Whatman International Ltd.)and ﬁxed with 10ml of 10%paraformaldehyde for 1h.Samples were then ﬁltered onto 0.2-␮m-pore-size Anodisc ﬁlters under a maximum pressure of 200mm Hg and dehydrated in an ethanol series (50,80,and 100%;3min each).The ﬁlters were stored at Ϫ80°C.For ﬂow cytometry analyses,1.5ml of pre ﬁltered (3-␮m pore size)samples was ﬁxed with a mixture of 1%paraformaldehyde and 0.1%glutaraldehyde (ﬁnal concentrations)and then deep frozen in liquid nitrogen and stored at Ϫ80°C.For high-performance liquid chromatography (HPLC)pigment measure-ments,the Ͻ200-␮m seawater fraction (1liter)was collected on a GF/F ﬁlter (Whatman International Ltd.).The 3-to 200-␮m fraction was collected on a 3-␮m-pore-size Nuclepore ﬁlter.Finally,the Ͻ3-␮m fraction was collected on a GF/F ﬁlter.The ﬁltrations were conducted under a pressure of 200mm Hg,and all of the ﬁlters were immediately deep frozen in liquid nitrogen and stored at Ϫ80°C.Flow cytometry.Total photosynthetic-cell counts were obtained from ﬁxed seawater samples using a FACSsort ﬂow cytometer (Becton Dickinson,San Jose ´,Calif.),as described previously (18).Photosynthetic picoeukaryotes were dis-criminated from cyanobacteria using Cytowin software (available from http://www.sb-roscoff.fr/Phyto/cyto.html).HPLC.Pigment analyses were performed using the method of Zapata et al.(43),with minor modi ﬁcations as described by Latasa et al.(14).The contribu-tions of different algal groups to the total chlorophyll a (Chl a )was estimated using CHEMTAX (17).While the contributions of the Mamiellales,Prasinococ-cales,and Pseudoscour ﬁeldiales,which possess prasinoxanthin,could be com-puted,those of the other clades (prasinoxanthinless Prasinophyceae)cannot be distinguished from those of other Chlorophyta.FISH associated with tyramide signal ampli ﬁcation.In situ hybridization with horseradish peroxidase-labeled probes,signal ampli ﬁcation,and target cell de-tection were performed as described previously by Not et al.(22).The only difference was the use of a more viscous antifading reagent,AF1(Citi ﬂuor Ltd.,London,United Kingdom),instead of AF3in order to preserve the hybridized slides longer (up to 2weeks in the dark at 4°C)without signi ﬁcant loss of ﬂuorescence.Epi ﬂuorescence microscopy and image acquisition.The hybridized cells were observed with an Olympus (Tokyo,Japan)BX 51epi ﬂuorescence microscope equipped with a mercury light source and an 100ϫUVFL (Olympus,Tokyo,Japan)objective.Excitation-emission ﬁlters were 360/420for DAPI (4Ј,6Ј-dia-midino-2-phenylindole)and 490/515for ﬂuorescein isothiocyanate.For each sample,10randomly chosen microscopic ﬁelds were counted by eye.For probes with broad taxonomic speci ﬁcity (e.g.,CHLO02),Ͼ500cells were counted.Because of the large number of hybridizations and the time required for each analysis,it was not possible to count replicates for each sample.However,for 33samples,three replicates (i.e.,three hybridizations with the same probe on three different ﬁlters)were analyzed,and the average error was 15%(range,2to 38%).Design of 18S rRNA oligonucleotide probes.The oligonucleotide probes (Ta-ble 2)were designed with ARB software (16)using a small-subunit rRNA database containing Ͼ30,000complete and partial sequences.In addition to published sequences,our database also contained unpublished partial eukaryote sequences retrieved from three coastal sites.Although the probes could have been designed based only on the public sequences,the additional sequencesTABLE 1.Origins and culture conditions of picoplankton strainsRCC a no.Genus and species Strain Light (␮E m Ϫ2s Ϫ1)Cell diameter (␮m)Origin116Ostreococcus tauri OTTH 05951000.8Thau Lagoon143Ostreococcus sp.EUM 13BBL 1000.8Tropical Atlantic Ocean 141Ostreococcus sp.EUM 16BBL 1000.8Tropical Atlantic Ocean 114M.pusilla CCMP b 4901002North Atlantic 299M.pusilla NOUM 171002Equatorial Paci ﬁc 372M.pusilla Naples 1002Gulf of Naples 373M.pusillaSkagerrak 1002Skagerrak 417Mantoniella squamata CCMP 4801003–5North Sea113 B.prasinos CCMP 18981002Mediterranean Sea 369Coccoid CCMP 12051002–6Sargasso Sea287Coccoid NOUM 15100 2.5Equatorial Paci ﬁc Ocean261P.marina TAK 9801404Takapoto Atoll (Paci ﬁc Ocean)370P.provasolii CCMP 12031002–4North Atlantic 135P.provasolii CCMP 11991002–4Gulf of Mexico 251Pycnococcus sp.ROS 94011002English Channel 253Pycnococcus sp.ROS 94041002English Channel 136P.capsulatus CCMP 14071003–6Sargasso Sea 134Prasinococcus MP 11941003–5Gulf of Mexico 137Prasinoderma MP 12201003–8Gulf of Mexicoa Roscoff Culture Collection (http://www.sb-roscoff.fr/Phyto/RCC/).bCCMP (Provasoli-Guillard National Center for Culture of Marine Phytoplankton,West Boothbay Harbor,Maine [/]).TABLE 2.Novel oligonucleotide probes targeting prasinophycean taxaProbe nameSequenceTarget groupPosition of 16S rRNA (Escherichia coli )Closest sequence not targetedTaxonomy No.of mismatchesPRAS015Ј-ACG GTC CCG AAG GGT TGG -3ЈPseudoscour ﬁeldiales clade V 193Tilletia caries2PRAS035Ј-GCC ACC AGT GCA CAC CGG -3ЈPrasinococcales620Friedmannia israeliensis 2PRAS045Ј-CGT AAG CCC GCT TTG AAC -3ЈMamiellales (except the genus Dolichomatix )651Choricystis minor 1PRAS055Ј-GCC AGA ACC ACG TCC TCG -3ЈClade VIIA,RCC 287,CCMP 1205651Pyramimonas olivacea 3PRAS065Ј-AAT CAA GAC GGA GCG CGT -3ЈEnvironmental clade VIIB 651Scutopus ventrolineatus 3MICRO015Ј-AAT GGA ACA CCG CCG GCG -3ЈM.pusilla 211Ostreococcus tauri 1BATHY015Ј-ACT CCA TGT CTC AGC GTT -3Ј B.prasinos 651Uncultivated bacteria3OSTREO015Ј-CCTCCTCACCAGGAAGCU -3ЈOstreococcus647Corynebacterium genitalium3V OL .70,2004PRASINOPHYCEAN PICOEUKARYOTES IN THE ENGLISH CHANNEL4065FIG.1.Phylogenetic tree of the Prasinophyceae obtained by the neighbor-joining method and based on analyses of complete 18S rRNA gene sequences.The speci ﬁcities of the different probes designed in this study are presented.The clades were named according to the system of Guillou et al.(8).The numbers on the branches correspond to bootstrap values (done on 1,000replicates).4066NOT ET AL.A PPL .E NVIRON .M ICROBIOL .allowed us to conﬁrm that the targeted regions were conserved on the corre-sponding sites of coastal representatives of taxa belonging to the clades targeted. When the probes were designed with the ARB Probe Design function,care was taken to maximize the number of mismatches to nontarget sequences and to position these mismatches near the center of the probe.The theoretical speci-ﬁcities of the new probes were checked using the Probe Match function of the ARB software.Oligonucleotide probes with a5Јamino link(C6)were purchased from MWG(Courtaboeuf,France).The probes were then labeled with horse-radish peroxidase(Roche Diagnostic Boehringer,Meylan,France)as described previously(40).The optimal formamide concentration was determined empiri-cally to be40%in the hybridization buffer,and speciﬁcity tests of the new probes were performed at this concentration.These probes are available in the rRNA probe database for protists and cyanobacteria(http://www.sb-roscoff.fr/Phyto /Databases/RNA_probes_introduction.php).Because probes with broad taxo-nomic speciﬁcity usually do not work equally well for all targeted organisms,the three probes EUK1209R,CHLO01,and NCHLO01were used in combination to estimate all eukaryotes(22).Finally,probe CHLO02,speciﬁc for the subregnum Chlorobionta(Chlorophyta and Streptophyta),was applied(30).To our knowl-edge,the division Streptophyta has no representative in the pelagic marine systems.Consequently,in this study,cells labeled by the probe CHLO02were considered to belong to the division Chlorophyta.Tree construction.PAUP*version4.0beta10(33)was used to perform phylogenetic analyses of complete18S rRNA sequences using neighbor-joining methods.Cyanophora paradoxa,Pavlova gyrans,Mesostigma viride,and Chara foetida were included in the analyses as an outgroup,and the tree was rooted with C.paradoxa.Bootstrapping(1,000replicates)allowed the evaluation of tree signiﬁcance.Trees were drawn using TreeView(Roderic Page,University of Glasgow,Glasgow,United Kingdom).RESULTSDesign and speciﬁcity tests of18S ribosomal DNA(rDNA) probes targeting Prasinophyceae.No unique characteristic ex-ists that unites all Prasinophyceae taxa to the exclusion of other Viridiplantae or members of other algal phyla(34).This is also supported by molecular phylogenies that show the paraphyletic structure of the class Prasinophyceae(21).Therefore,it is not possible to identify a single probe targeting all Prasinophyceae species.Based on comparative18S rRNA sequence analyses, we designed eight oligonucleotide probes(Fig.1).The probes PRAS01,PRAS03,PRAS04,PRAS05,and PRAS06are spe-ciﬁc,respectively,for the orders Pseudoscourﬁeldiales(clade V only);Prasinococcales(clade VI);Mamiellales(clade II, with the exception of Dolichomastix);clade VIIA,containing the coccoid strain CCMP1205;and clade VIIB,composed of sequences retrieved from the Paciﬁc Ocean.The probes OSTREO01,BATHY01,and MICRO01are speciﬁc for the genus Ostreococcus and the species Bathycoccus prasinos and M.pusilla,respectively(Table2).The speciﬁcities of the newly designed probes were evalu-ated by whole-cell hybridization of well-characterized refer-ence strains(Table3).Among the probes targeting Prasino-phyceae orders and clades(PRAS01to-06),only PRAS04 hybridized all,and only,target strains.Since no isolate of clade VIIB has yet been established in culture,positive controls could not be performed for PRAS06,but the probe did not show any nonspeciﬁc labeling with the strains tested.PRAS01, PRAS03,and PRAS05hybridized only target strains,but not all of them(Table3).We encountered two different problems. First,PRAS01conferred a goodﬂuorescence signal when hy-bridized with the two strains RCC261(Pseudoscourﬁeldia ma-rina)and RCC253(Pycnococcus sp.),but no signal was ob-served with the strain RCC135(Pycnococcus provasolii). Second,RCC369(CCMP1205)and RCC287,targeted by PRAS05,and Prasinoderma strain RCC137,targeted by PRAS03,presented a heterogeneous signal after hybridization: onlyϳ50%of the cells showed a positive signal.The problem encountered with these probes was also observed with the general Chlorophyta probe CHLO02with the same strains. The three genus-and species-speciﬁc probes(OSTREO01, BATHY01,and MICRO01)labeled all,and only,the taxa for which they were designed(Table4).Hydrological conditions at ASTAN station.Due to the strong tidal mixing,the coastal waters off Roscoff are perma-TABLE3.Speciﬁcity tests of the oligonucleotide probes for Prasinophyceae order level cladesSpecies RCC no.Speciﬁcity aPRAS01PRAS03PRAS04PRAS05PRAS06CHLO02M.pusilla114ϪϪ؉ϪϪ؉Ostreococcus tauri116ϪϪ؉ϪϪ؉Mantoniella squamata417ϪϪ؉ϪϪ؉B.prasinos113ϪϪ؉ϪϪ؉Coccoid strain369ϪϪϪ؎Ϫ؎Coccoid strain287ϪϪϪ؎Ϫ؎P.marina261؉ϪϪϪϪ؉P.provasolii135؊ϪϪϪϪ؊Pycnococcus sp.253؉ϪϪϪϪ؉Prasinoderma sp.137Ϫ؎ϪϪϪ؎Prasinococcus sp.134Ϫ؉ϪϪϪ؉P.capsulatus136Ϫ؉ϪϪϪ؉a Boldface indicates the theoretical speciﬁcity,whileϩandϪindicate the results of in situ hybridization tests(ϩ,brightﬂuorescent signal;Ϫ,no detectable ﬂuorescent signal;Ϯ,weakﬂuorescent signal).TABLE4.Speciﬁcities of oligonucleotide probes forMamiellales genera and speciesSpecies RCC no.Speciﬁcity aBATHY01OSTREO01MICRO01Ostreococcus tauri RCC116Ϫ؉ϪOstreococcus sp.RCC143Ϫ؉ϪOstreococcus sp.RCC141Ϫ؉ϪB.prasinos RCC113؉ϪϪM.pusilla RCC114ϪϪ؉M.pusilla RCC299ϪϪ؉M.pusilla RCC373ϪϪ؉M.pusilla RCC372ϪϪ؉a See Table3,footnote a,for explanation of symbols.V OL.70,2004PRASINOPHYCEAN PICOEUKARYOTES IN THE ENGLISH CHANNEL4067nently mixed all year round (32).During the sampling period,the temperature varied between 10.2(March 2001)and 16.6°C (August 2001).The nitrate and phosphate concentrations fol-lowed a similar pattern of variation,with minima in summer (0.4and 0.10␮M,respectively)and maxima in late fall and winter (15.3and 0.66␮M,respectively)(Fig.2).Photosynthetic pigments.During the period studied,Chl a concentrations in the 0.2-to 200-␮m fraction (total phyto-plankton)varied according to the classical pattern observed in this area,with minima in winter (0.2␮g liter Ϫ1)and maxima in summer (2.5␮g liter Ϫ1),corresponding to the diatom bloom (32).The 2001bloom occurred in late June (Fig.3A).Maxi-mum concentrations of picoplanktonic Chl a occurred later,at the end of July (753ng liter Ϫ1).Large phytoplankton (Ͼ3-␮m diameter)and picoplankton (Ͻ3-␮m diameter)contributed approximately equally to the Chl a biomass under nonbloom conditions.During bloom periods (July 2000and July 2001),large phytoplankton dominated the total Chl a biomass.Over-all,picophytoplankton made up 34%of the total Chl a throughout the study period.Within the picoplanktonic Chl a fraction,the contribution of the division Chlorophyta was almost always Ͼ25%(45%,on average)(Fig.3B),except at the end of May,when it plum-meted below 10%,although picoplanktonic Chl a decreased only slightly (Fig.3A).Within the Chlorophyta,the contri-butions of the Mamiellales,Prasinococcales,and some of the Pseudoscour ﬁeldiales (containing prasinoxanthin)to pico-planktonic Chl a ,as estimated by CHEMTAX,were signi ﬁcant all year round and largely dominant (Ͼ80and up to 100%)during spring and summer 2001.Overall composition of the picoeukaryotic community.The abundances of the photosynthetic picoeukaryotes determined by ﬂow cytometry varied between 1ϫ103and 2ϫ104cells ml Ϫ1.Maximum abundances were recorded in May and July 2001(Fig.4A).The abundance of picoeukaryotic cells de-tected by epi ﬂuorescence microscopy after in situ hybridization with a combination of the probes EUK1209R,CHLO01,and NCHLO01varied between 1.3ϫ103and 1.35ϫ104cells ml Ϫ1(Fig.4A).Cells belonging to the division Chlorophyta (tar-geted by CHLO02)dominated the picoeukaryotic community all year long (1ϫ103to 1.5ϫ104cells ml Ϫ1;85%,on average,of the total number of picoeukaryotes)(Fig.4A).Within the Chlorophyta,organisms belonging to the order Mamiellales (Prasinophyceae),targeted by the probe PRAS04,dominated year round (Fig.4B).Within the Mamiellales,M.pu-silla was the dominant species during the sampling period (75%of the cells detected by PRAS04,on average)(Fig.4C)and accounted for 45%of picoplanktonic eukaryotes.The sec-ond most abundant species detected was B.prasinos ,which accounted for 12%(range,1to 67%)of the Mamiellales and 8%of the picoplanktonic eukaryotes (Fig.4C).Cells belonging to the genus Ostreococcus were less abundant,with an average of 3%(range,0to 19%)of the Mamiellales and 1.4%of the eukaryotes (Fig.4C).The second most abundant clade within the division Chlo-rophyta was the order Prasinococcales,targeted by the probe PRAS03and accounting for an average of 3.4%(range,0to 34%)of the Chlorophyta cells (Fig.4B).Cells belonging to the other clades were detected at very low abundances all year long.Probes PRAS01,PRAS05,and PRAS06targeted an av-erage of 0.6,0.4,and 0.6%,respectively,of cells belonging to the division Chlorophyta (Fig.4B).Only 16%,on average,of the cells detected by the probe speci ﬁc for the division Chlo-rophyta were not targeted by the Prasinophyceae probes used in this study.Seasonal variation of picoeukaryotic community.The pico-eukaryotic community exhibited a marked seasonal cycle,with minima of abundance in early winter and maxima (ϳ10times the winter abundances)in midsummer.The patterns of abun-dance variation during the sampling period were similar for total picoplanktonic eukaryotes,photosynthetic picoeukary-otes,Chlorophyta,and Mamiellales and for the speciesM.FIG.2.Variations in temperature and phosphate and nitrate concentrations at the ASTAN station between July 2000and September 2001.4068NOT ET AL.A PPL .E NVIRON .M ICROBIOL .pusilla .On a smaller temporal scale,three major peaks of abundance were observed in 2001,in late spring and summer (mid-May,mid-June,and the end of July)(Fig.4A).For the Mamiellales and for M.pusilla ,an additional peak was ob-served in late August (Fig.4C).The other clades and genera detected in this study showed more sporadic proliferations throughout the year.The species B.prasinos was detected all year long but became more abundant during spring (1.8ϫ103cells ml Ϫ1in March 2001)(Fig.4C).The cells targeted by the probe PRAS03(order Prasinococcales)reached signi ﬁcant abundance in early fall (1.2ϫ103cells ml Ϫ1)and late spring (600cells ml Ϫ1).In fall 2000,they accounted for up to 34%of the cells targeted by the CHLO02probe (Fig.4B).Spectacular decreases in the cell abundances of all the taxa detected by our probes and in ﬂow cytometry counts were observed on May 30,2001.DISCUSSIONNew probes targeting Prasinophyceae.Phylogenetic analy-ses of 18S rDNAs recovered directly from samples collected in different oceanic regions have revealed an unsuspected diver-sity within eukaryotic picoplankton (20).In most gene libraries analyzed,including libraries constructed from samples col-lected in the western English Channel (26),prasinophycean sequences were well represented (42).The set of probes pre-sented in this study covers most known clades (Fig.1)and,compared to the few previously published probes for prasino-phycean taxa,have improved speci ﬁcities.Indeed,PRAS04has no mismatch with any Mamiellales sequence known to date,in contrast to PRAS02(2),which has one mismatch with B.pra-sinos .The probes Micro/Manto1and Micro/Manto2,designed in 1996(12)for Micromonas and Mantoniella ,presentmatchesFIG.3.(A)Variations in Chl a biomass as measured by HPLC (total Ͻ200-␮m and fraction Ͻ3-␮m)at the ASTAN station.(B)Contributions of the division Chlorophyta and of the orders Mamiellales,Prasinococcales,and Pseudoscour ﬁeldiales to the picoplankton fraction (Ͻ3-␮m diameter)according to the CHEMTAX algorithm applied to HPLC data.V OL .70,2004PRASINOPHYCEAN PICOEUKARYOTES IN THE ENGLISH CHANNEL 4069with the genus Ostreococcus and mismatches with some strains of Micromonas .They are therefore not speci ﬁc for their initial targets (data not shown).When tested against pure cultures,probes PRAS04,MICRO01,OSTREO01,and BATHY01showed perfect spec-i ﬁcity for their target strains and delivered a bright ﬂuorescent signal (Tables 3and 4).In contrast,we encountered hybrid-ization problems with some strain-probe combinations,i.e.,either cells showed no ﬂuorescent signal and a strong red ﬂuorescence under blue excitation or the ﬂuorescent signal was heterogeneous.Given that the corresponding sites on the 18S rRNA sequences of the strains tested showed 100%homology with the probes,the most likely hypothesis is that the probes did not penetrate into the cells.In fact,the redchlorophyllFIG.4.Abundances (number of cells ml Ϫ1)of photosynthetic picoplankton off Roscoff (western English Channel)between July 2000and September 2001.The average percentages over the time series of the different groups are represented in pie charts.(A)Picoeukaryotic photo-synthetic cells detected by ﬂow cytometry counts (Flow Cytometry);picoeukaryotic cells targeted by the mix of the general probes EUK1209R,CHLO01,and NCHLO01(EUK1209R ϩCHLO01ϩNCHLO01);and cells belonging to the division Chlorophyta detected by the probe CHLO02(CHLO02).(B)Cells targeted by the probe CHLO02and cells detected by the probes speci ﬁc for the clades PRAS01,PRAS03,PRAS04,PRAS05,and PRAS06.(C)Cells targeted by the probe speci ﬁc for Mamiellales (PRAS04)and cells detected by the probes (MICRO01,BATHY01,and OSTREO01)speci ﬁc for the species and genera.4070NOT ET AL.A PPL .E NVIRON .M ICROBIOL .ﬂuorescence remaining in these strains after ethanol treatmentsuggests that their cell walls are probably very thick and resis-tant,a fact previously established for P.provasolii and Prasi-noderma sp.(9),and therefore prevent probe penetration. Analysis of the picoeukaryotic community.The seasonal variation in microphytoplankton diversity and abundance intemperate sea waters has been well described.Off Roscoff,themicrophytoplankton bloom occurs in late spring(with cell den-sities up to3ϫ104cells literϪ1)and is characterized by thesuccession of a very limited number of diatom species(such asGuinardia delicatula)that occurs at low concentration outside this period(S.Ristori,unpublished data;32).The presentstudy indicates that the structure and dynamics of the pico-planktonic community are totally different from the classicalscheme observed for microphytoplankton.First,picophyto-plankton abundance remains high all year round(1ϫ103to2ϫ104cells mlϪ1).Hence,this size class contributes an average of50%of the total Chl a biomass under nonbloom conditions.Second,both FISH and chemotaxonomic analyses show thatgreen algae,and more precisely Prasinophyceae,dominate thecommunity(70%of the cells and35%of the total picoplank-tonic Chl a).Chlorophytes and Prasinophyceae have beenpreviously identiﬁed by chemotaxonomic analyses(i.e.,thepresence of Chl b)as major components of the nano-orpicoplankton size fractions in the English Channel(3),as wellas in other coastal systems,such as the Faroe-Shetland Chan-nel(20%of total Chl a)and the Galician coast(60%of totalChl a in winter)(24,25).Most interestingly,FISH data allowed us to establish unam-biguously that a single species,M.pusilla,is dominant all yearround and shapes the dynamics of the whole picophytoplank-ton ing published values of Chl a content percell for Micromonas(0.025pg cellϪ1)(5)and cell abundancesobtained by FISH,the contribution of Micromonas to the totalChl a can be estimated to range between2and50%(22%,onaverage)of the picoplanktonic Chl a.M.pusilla has alreadybeen detected in different polar and temperate marine systems,including coastal and open-ocean regions,such as the Norwe-gian coast(38),Bay of Biscay(1),Arctic Sea(36),Mediterra-nean Sea(44),and Skagerrak(13),with abundances rangingbetween1ϫ102and9ϫ103cells mlϪ1.The species has also been found to be present year round in the Skagerrak and North Sea(13)and to be abundant during winter-spring in the Mediterranean Sea(39)or spring and summer in the North Atlantic and North Sea(13).The contributions of other Mamiellales genera to the pico-planktonic community were less important.The contribution of the nonmotile picoplanktonic species B.prasinos,described from the Mediterranean Sea(6)and reported from the Atlan-tic and Paciﬁc Oceans(28)and Norwegian coastal waters (6),is much more sporadic:for example,in spring2001,it accounted for30%of picoeukaryote cells targeted.The genus Ostreococcus was detected,but always at low abundance,off Roscoff.Prior to this study,it had been found in abundance only in a somewhat atypical ecosystem,the Thau lagoon,a shallow ecosystem used intensively for oyster culture(4).The second most abundant group within the Prasinophyceae is the order Prasinococcales,which contains species such as Prasino-coccus capsulatus,which has been observed and is suspected to be signiﬁcant in the western Atlantic and the western Paciﬁc (27).The persistence of high abundances of picophytoplankton year round could be explained by the fact that picophytoplank-ton is controlled by small predators with short generation times (29)that prevent any sudden cell proliferation,even when conditions are optimal.This contrasts with what happens for diatoms controlled by copepods with long generation times and complex life cycles,which are able to reduce biomass only after a delay,allowing blooms to develop.The strong domi-nance of M.pusilla over other species all year in the system studied is very similar to what is observed for picophytoplank-tonic prokaryotes,among which single genera,such as Prochlo-rococcus and Synechococcus,dominate certain types of ecosys-tems(23).Micromonas may have a broad ability to respond to light and nutrient variations and thus,because of this large environmental spectrum,may be little affected by changes in the environment.However,during the seasonal series studied, a sharp decrease in abundance of picoeukaryotes(and M.pu-silla)was recorded at the end of May.This phenomenon was associated with a major peak in the ammonium concentration (data not shown).One explanation for this decrease could be that Micromonas was infected by viruses.Previous studies have suggested that viruses infecting M.pusilla have a profound impact on populations of the species in natural systems(44). Most surprising is the ability of Micromonas populations to recover rapidly to their initial levels only15days after the decrease.This upturn could be due to the proliferation of a different Micromonas genotype,resistant to the virus respon-sible for the decay.Indeed,a recent study based on the analysis of18S rDNA gene sequences demonstrated the presence of three clades within the species M.pusilla(8).Our results suggest that the taxonomic structure of the pi-coplanktonic communities is different from the structure of the microphytoplanktonic community,with one species(M.pu-silla)being dominant all year round off Roscoff.Hence,if the diatoms,dinoﬂagellates,and coccolithophorids(i.e.,Chl c-con-taining lineages)dominate the large eukaryotic phototrophic assemblages in the contemporary oceans(7),a few species of the green(Chl b-containing)lineage may dominate picoplank-ton and shape the marine microbial food webs.The next step will be to extend these observations to other coastal and oce-anic areas in order to determine how widespread M.pusilla dominance is and to understand the factors that regulate the diversity and abundance of picoeukaryotes.ACKNOWLEDGMENTSWe thank Isabelle Biegala and Carlos Pedro´s-Alio´for constructive discussions,Laure Guillou and Erwan Corre for help with phyloge-netic analyses,the MYSIS crew for efﬁcient assistance with sampling, and Florence Le Gall for help with phytoplankton cultures.This work was funded by the following programs:PICODIV,sup-ported by the European Union(EVK3-CT-1999-00021);PICMANCH, supported by the Re´gion Bretagne;and BIOSOPE,supported by PROOF(CNRS).F.N.was supported by a doctoral fellowship from the French Research Ministry.REFERENCES1.Ansotegui,A.,A.Sarobe,J.M.Trigueros,I.Urrutxurtu,and E.Orive.2003.Size distribution of algal pigments and phytoplankton assemblages in a coastal-estuarine environment:contribution of small eukaryotic algae.J.Plankton Res.25:341–355.V OL.70,2004PRASINOPHYCEAN PICOEUKARYOTES IN THE ENGLISH CHANNEL4071。

季风边缘区气候变化

Tracking millennial-scale climate change by analysis of the modern summer precipitation in the marginal regions of the Asian monsoonYu Li ⇑,Nai’ang Wang,Hongbao Chen,Zhuolun Li,Xuehua Zhou,Chengqi ZhangCollege of Earth and Environmental Sciences,Center for Hydrologic Cycle and Water Resources in Arid Region,Lanzhou University,Lanzhou 730000,Chinaa r t i c l e i n f o Article history:Received 14September 2011Received in revised form 13June 2012Accepted 4July 2012Available online 17July 2012Keywords:Millennial-scale HoloceneInterannual-scaleSummer precipitation Asian monsoon Westerly windsa b s t r a c tThe Asian summer monsoon and the westerly winds interact in the mid-latitude regions of East Asia,so that climate change there is inﬂuenced by the combined effect of the two climate systems.The Holocene millennial-scale Asian summer monsoon change shows the out-of-phase relationship with the moisture evolution in arid Central Asia.Although much research has been devoted to the long-term climate change,little work has been done on the mechanism.Summer precipitation,in the marginal regions of the Asian monsoon,is strongly affected by the monsoon and the westerly winds.The purpose of this paper is to examine the mechanism of the millennial-scale out-of-phase relationship by modern summer precipitation analysis in the northwest margin of the Asian monsoon (95–110°E,35–45°N).First,the method of Empirical Orthogonal Function (EOF)analysis was carried out to the 1960–2008summer rain-fall data from 64stations in that region;then the water vapor transportation and geopotential height ﬁeld data were studied,in order to explain and understand the factors that inﬂuence the summer precip-itation;lastly,the East Asian Summer Monsoon Index (EASMI),South Asian Summer Monsoon Index (SASMI),Summer Westerly Winds Index (SWI)were compared with the EOF time series.The results indi-cate the complicated interannual-scale interaction between the Asian summer monsoon and the westerly winds,which can result in the modern out-of-phase relationship in the study area.This study demon-strates that the interaction between the two climate systems can be considered as a factor for the millen-nial-scale out-of-phase relationship.Ó2012Elsevier Ltd.All rights reserved.1.IntroductionSince it is not possible to go back in time to see what climates were like,scientists use imprints created during past climate,known as proxies,to reconstruct paleoclimate (Ruddiman,2001).The processes of the modern climate system provide a scientiﬁc basis for understanding the evolution of paleoclimate (Cronin,2009).Past climate can be reconstructed using a combination of different types of proxy records.These records can then be inte-grated with observations of Earth’s modern climate and placed into a computer model to infer past as well as predict future climate.Study on the relationship between proxy indicators and modern climate is helpful to reconstruct the past climate conditions (Helle and Schleser,2004).Accordingly,several different methods have been developed for quantitative paleoclimatic reconstructions (Sheldon and Tabor,2009;Xu et al.,2010).Besides,understanding the processes governing modern climate variability and change provides signiﬁcant understanding of the climate changes over a variety of different timescales.The Asian monsoon system reaching from the western Arabian Sea through East Asia and North Australia,which can be divided into the East Asian monsoon system and South Asian (or Indian)monsoon system,is a dynamic component of the modern climate system (Webster et al.,1998;Wang and Lin,2002).Wang et al.(2005b)provided an overview of past and current paleomonsoon research on tectonic to interan-nual timescales,and emphasized the importance of modern mon-soonal climate research for interpreting paleoclimate change.Much attention has been focused on the links of monsoon systems across timescales (Wang et al.,2003,2010).While many studies have been published concerning the millennial-scale relationship between the Asian monsoon and the westerly winds,little infor-mation is available on interannual to interdecadal timescales (Chen et al.,2008,2010).In East Asia,the Asian summer monsoon and the westerly winds interact in the mid-latitude regions (Zhang and Lin,1992;Wang et al.,2005a ,Fig.1).Mid-latitude climates are dominated by the interaction of air masses,speciﬁcally cold air masses origi-nating in high latitudes and warm air masses originating in the sub-tropical Highs;therefore,the climates are commonly charac-terized by vigorous circulation (Aguado and Burt,2004;Barry et al.,2004).The interaction between the Asian summer monsoon and the westerly winds plays a critical role in East Asia climate changes over several different time scales.Precisely dated speleo-1367-9120/$-see front matter Ó2012Elsevier Ltd.All rights reserved./10.1016/j.jseaes.2012.07.001Corresponding author.Tel.:+869318912709;fax:+869318912712.E-mail address:liyu@ (Y.Li).them records have provided a continuous history of Holocene East Asian summer monsoon intensity (Fleitmann et al.,2003;Wang et al.,2005c ).The Holocene Asian summer monsoon variability re-ﬂected by d 18O from Qunf Cave (17°100N,after Fleitmann et al.(2003)),Dongge Cave (25°200N,after Wang et al.(2005c)and Dykoski et al.(2005)),Lianhua Cave (29°290N,after Cosford et al.(2008)),Heshang Cave (30°270N,after Hu et al.(2008)),Sanbao Cave (31°400N,after Dong et al.(2010))and Jiuxian Cave (33°340N,after Cai et al.(2010))shows a similar result (Figs.1and 2).Moreover,the evolution of the Holocene Asian summer monsoon reconstructed by lake records from the Qinghai-Tibet Plateau agrees with the result from the speleothem records (Gasse et al.,1991;Fleitmann et al.,2003;Shen et al.,2005;Wang et al.,2005c;Morrill et al.,2006;Liu et al.,2007).On the other hand,Chen et al.(2008)synthesized 11Holocene lake records from arid Central Asia to evaluate spatial and temporal patterns of moisture changes.Fig.3shows the synthesized moisture index and the Holocene lake records from Bosten Lake,Telmen Lake and Wulun-gu Lake (Fowell et al.,2003;Wünnemann et al.,2006;Chen et al.,2008;Liu et al.,2008).The Holocene moisture change in arid Cen-tral Asia is out-of-phase with the Asian summer monsoon evolu-tion (Fig.3).In addition,this out-of-phase relationship is also implied by the Holocene loess-paleosol records in East and Central Asia (Feng et al.,2011).Chen et al.(2008,2010)pointed out that the millennial-scale out-of-phase relationship can be related to the variability of the westerly winds.It is difﬁcult to verify the hypothesis with lack of modern climate research.Summer precip-itation,in the northwest margin of the Asian summer monsoon (95–110°E,35–45°N,Figs.1and 4),is directly inﬂuenced by the monsoon and the westerly winds.The objective of the present pa-per is to study the interaction between the Asian summer monsoon and the westerly winds through the research on summer precipita-tion and its relationship with the two climate systems.In the pres-ent investigation,we examined the 1960–2008summer rainfalldata from 64stations (95–110°E,35–45°N,Fig.4)by using Empir-ical Orthogonal Function (EOF)analysis.And then,the geopotential height ﬁeld and water vapor transportation data,East Asian Sum-mer Monsoon Index (EASMI),South Asian Summer Monsoon Index (SASMI),and Summer Westerly Winds Index (SWI)were used to study the interaction of the monsoon and the westerly winds and their impact on summer precipitation.2.Regional settingThe northwest margin of the Asian monsoon (95–110°E,35–45°N,Fig.4)is located in the transition zone of the Asian summer monsoon region,the arid region of Northwest China,and the Qing-hai-Tibet Plateau (Zhao,1983).The study area,varying in altitude from 1000m to 5000m above sea level,mainly comprises moun-tains,valleys,glaciers,deserts,oases,rivers,and lakes that reﬂect the characteristics of the transition zone.The Qilian Mountains,lo-cated in the middle of the study area,can reach an altitude of 5000m above sea level.The mean annual temperature in the mountain zone is 2–4°C and the annual precipitation is 200–700mm.To the north of the Qilian Mountains is the Tengger Des-ert;the annual mean temperature here is 6–8°C and the annual precipitation is 50–200mm.The annual potential evaporation ex-ceeds 2600mm in the desert (Chen and Qu,1992).The distribution of modern vegetation is strongly related to elevation:perennial snow and ice zone (>4500m);cushion-like vegetation zone (4500–3800m);meadow zone (3800–3500m);alpine shrub zone (3500–3100m);Picea and Sabina forest zone (3100–2500m);mountainous grassland zone (2500–2350m);desert grass zone (2350–2000m)and gobi-sand desert zone (<2000m)(Huang,1997).Rivers are mostly derived from the cold and humid moun-tain zone from 2000m to 5000m above sea level (Chen and Qu,1992).Water vapor,in the study area,is from the Asiansummer1.Map of East and Central Asia.The modern Asian summer monsoon limit is shown by a dashed line.Lines with arrows indicate the climate systems affecting East Central Asia,including East Asian summer monsoon,South Asia (or Indian)summer monsoon,Asian winter monsoon,and westerly winds.The black circles show caves mentioned in this research,including (a)Dongge Cave,(b)Lianhua Cave,(c)Heshang Cave,(d)Sanbao Cave,(e)Jiuxian Cave,(f)Qinghai Lake,(g)Bosten Lake,Wulungu Lake and (i)Telmen Lake.monsoon and the westerly winds (Wang et al.,2005a ).It is also conﬁrmed by an atmospheric general circulation model (GCM),as well as column integrated moisture source analysis (Numaguti,1999;Yoshimura et al.,2004).Fig.5a shows the summer vertically integrated atmospheric water vapor ﬂux that implies the interaction between the Asian summer monsoon and the westerly winds.A number of studies have been conducted on the summer precipitation in adjacent areas;however,little attention has been paid to the interaction between the Asian summer monsoon and the westerly winds and its effect on the summer precipitation (Wang et al.,2001;Feng and Hu,2004;Yatagai,2007).In this pa-per,we will attempt to show how the two climate systems affect the summer precipitation in the northwest margin of the Asian monsoon.3.Data and methods(1)Summer rainfall data were observed at 64weather stationsin the study area over the period 1960–2008(95–110°E,35–45°N,Figs.1and 4).The 2.5°Â2.5°resolution monthlymean water vapor and geopotential height ﬁeld data are from the NCEP/NCAR reanalysis to describe the atmosphere characteristics (Kalnay et al.,1996).(2)The dominant summer rainfall patterns and variability wereidentiﬁed using Empirical Orthogonal Function (EOF)analy-sis.North’s signiﬁcance test was used to determine the level of signiﬁcant (North et al.,1982).(3)East Asian Summer Monsoon Index (EASMI)and South AsianSummer Monsoon Index (SASMI)(Zeng et al.,1994;Li and Zeng,2002)were given byd ¼k V 1*ÀV m ;n *kk V *kÀ2;where V 1*and V m ;n *are the January climatological and monthly wind vectors at a point,respectively,(n ,year;m ,month),V *is the mean of January and July climatological wind vectors at the same point.The indices were calculated in the two key monsoon sectors:East Asian (10–40°N,110–Holocene speleothem records and Holocene Qinghai Lake record including d 18O (‰)from Qunf Cave (17°100N,after (25°200N,after Wang et al.(2005c)),d 18O (‰)of D4from Dongge Cave (25°200N,after Dykoski et al.(2005)),(2008)),d 18O (‰)from Heshang Cave (30°270N,after Hu et al.(2008)),d 18O (‰)of SB43from Sanbao Cave (31°400N,(31°400N,after Dong et al.(2010)),d 18O (‰)of cc996-1from Jiuxian Cave (33°340N,after Cai et al.(2010)),d 18(2010)),pollen concentration (grains/g)from Qinghai Lake (36°500N,after Shen et al.(2005)),d 18O (‰)of ostracode (2007))and summer insolation at 30°N (after Berger and Loutre (1991)).140°E)at 850hPa and South Asian (2.5–20°N,70–110°E)at 850hPa.(4)Westerly Index (WI)(Rossby,1939;Li et al.,2008)was givenbyI ¼35 À55¼1n X n k ¼1H k ð35 ÞÀ1n X n k ¼1H k ð55 Þ¼1n X n k ¼1D H k ;where H k is the 500-hPa height geopotential at latitude k and longitude n ,and I is the Westerly Index (WI)between 35°N and 55°N.(5)Water vapor ﬂux (Chen,1985;Simmonds et al.,1999)wasgiven byQ u ¼À1ZptpsqudpQ v ¼À1gZptpsq v dp ;where g is gravity acceleration,ps represents surface pres-sure,pt stands for top pressure,which is chosen as 300hPain this study,q is speciﬁc humidity,and Q u and Q v are water vapor ﬂuxes in the zonal and meridional directions,respec-tively (unit:kg m À1s À1).4.Results4.1.Temporal and spatial trends in the summer precipitation Fig.5b shows the spatial distribution of summer rainfall.Thesummer rainfall peaks in the eastern part of the study area,reach-ing a maximum of 310.7mm,while rainfall,in the western part,is generally low with a minimum of 22.6mm.The summer rainfall can reach 284.5mm in the northeast of the Qinghai-Tibet Plateau (37–38.5°N,99.5–102°E).As shown in Fig.5c,a remarkable increasing trend in summer rainfall was observed in most partsFig.4.Map of topography and 64meteorological stations in the study area.moisture indices in arid Central Asia,including moisture evolution trend from arid Central Asia (after Chen et al.(2008)),moisture index from Bosten Lake (after Wünnemann et al.(2006)and Chen et al.(2008)),Chen et al.(2008))and lake-level change from Wulungu Lake (Liu et al.,2008).of the study area from 1960to 2008.However,the summer rainfall in the southeast of the study area,the upper reaches of the Yellow River,exhibits a downward trend.Generally,the summer rainfall is relatively low from 1960to 1975,and relatively high from 1976to 1998;there is an increasing trend in summer rainfall since 1999(see Fig.5d).Nine years,1961,1964,1976,1979,1981,1988,1992,1994and 1996,with abnormally high summer rainfall are shown by summer rainfall anomalies in Fig.5d,while nine years,1962,1963,1965,1969,1971,1972,1974,1982and 1991,with abnormally low summer rainfall are shown in Fig.5d.4.2.EOF analysis of the summer precipitation,water vapor transportation and geopotential height ﬁeldKriging,an optimal method of spatial interpolation (Oliver and Webster,1990),was chosen to interpolate the normalized summer rainfall anomalies for establishing the summer rainfall ﬁeld.Empirical Orthogonal Function (EOF)analysis was applied to the summer rainfall ﬁeld,and the correlation matrix of the variables was used for computing the eigenvalues and eigenvectors of the EOFs.The ﬁrst three EOFs that account for 47.73%of total variance can pass the North’s signiﬁcance test.4.2.1.EOF1The ﬁrst EOF mode (EOF1)that shows positive values in most areas accounts for 26.66%of the total variance (Fig.6a).The rela-tively low values mainly appear in the west of the Qilian Moun-tains and the desert area.The EOF1time series indicates that the summer rainfall is relatively high in 1961,1964,1979,1994and 1996,and relatively low in 1962,1963,1965,1982and 1991(Fig.6b).The result is consistent with the summer rainfall anoma-lies from 1960to 2008(Fig.5d).Differences of water vapor ﬂux be-tween the 5years with the highest values of the EOF1time series and the 5years with the lowest values of the EOF1time series are signiﬁcant in the southeast of the study area,as Fig.6d shows.Fig.6c shows anomaly correlation between the 500hPa geopoten-tial height ﬁeld and the EOF1time series.There is a positive corre-lation between the intensity of the subtropical high and the EOF1time series.This means that EOF1of summer rainfall is strength-ened by the western Paciﬁc subtropical high whose intensity is al-ways related to the strength of the Asian summer monsoon (Sun et al.,2005).This 500hPa geopotential height ﬁeld between 50°N to 80°N and 40°E to 110°E is positively correlated with the EOF1time series that is negatively correlated with the 500hPa geopo-tential height ﬁeld between 50°N to 80°N and 110°E to 180°E.The result suggests the strong westerly winds can strengthen EOF1summer rainfall.Therefore,EOF1summer rainfall is inﬂu-enced by the combined effect of the western Paciﬁc subtropical high and the westerly winds.Differences of water vapor ﬂux,as shown in Fig.6d,indicate the Asian summer monsoon water vapor transportation play a more important role than the westerly winds.In the previous work it was proved that the water vapor from the westerly winds had little effect on summer precipitation in north-west China (Wang et al.,2005a;Li et al.,2008).Although EOF1summer rainfall is affected both by the westerly winds and the western Paciﬁc subtropical high,there is little water vapor contri-bution from the westerly winds.4.2.2.EOF2The second EOF mode (EOF2),accounting for 12.07%of the total variance,indicates the opposite trends between the upper reaches of the Yellow River and other areas,as shown in Fig.7a.Itsuggestssummer vertically integrated water vapor ﬂuxes (unit:kg m À1s À1,1960–2008)in the northwest margin of the Asian monsoon.Summer rainfall shown by Fig.5b,while the linear trend pattern (1960–2008)is represented by Fig.5c.An increasing trend is indicated in black,whereas a Fig.5d shows summer rainfall anomalies (1960–2008).that EOF2summer rainfall shows a negative correlation between the upper reaches of the Yellow River and other areas.The EOF2time series indicates that the summer rainfall is relatively high in 1979,1983,1993,1996and 2007,and relatively low in 1961,1962,1964,1978and 2001(Fig.7b).The 5years with the highest values of the EOF2time series and the 5years with the lowest val-ues of the EOF2time series are chosen to calculate differences of water vapor ﬂux (Fig.7d).Fig.7c shows anomaly correlation be-tween the 500hPa geopotential height ﬁeld and the EOF2time ser-ies.As can be seen in Fig.7c,positive values appear in mid-to-low latitudes and high values concentrating in India –the Bay of Bengal –South Peninsula –South China Sea,while the highest correlation coefﬁcient is 0.55in India and the Bay of Bengal.The correlation coefﬁcient also can reach 0.45in the northern Arabian Sea,which is signiﬁcant at the 0.05level.The low pressure system in India,the Bay of Bengal and the northern Arabian Sea is highly correlated with the Asian summer monsoon.It is likely that while the 500hPa geopotential height ﬁeld is low/high in those regions,the Asian summer monsoon is accompanied by high/low water vapor ﬂux.At the same time,EOF2summer rainfall over the upper reaches of the Yellow river is relatively high/low due to negative EOF2val-ues in that area.On the other hand,the western Paciﬁc subtropical high (between 30°N and 40°N)is positively correlated with EOF2summer rainfall over the upper reaches the Yellow River (see Fig.7c).It could be inferred that the western Paciﬁc subtropicalhigh could promote water vapor transportation in the southeast of the study area.As illustrated by Fig.7d,differences in water va-por ﬂux between the 5years with the highest and lowest values of the EOF2time series are mainly reﬂected in the southeast of the study area,the upper reaches of the Yellow River.It is conceivable that the negative correlation between the upper reaches of the Yel-low River and other areas in EOF2is related to the low pressure system and water vapor transportation in the low latitudes.4.2.3.EOF3The third EOF mode (EOF3),accounting for 9.00%of the total variance,shows the opposite trends between the southwest study area,where the high-altitude zones occupy most of the area,and other areas,as shown in Fig.8a.This indicates that EOF3summer rainfall shows a negative correlation between the two parts.Fig.8b shows the EOF3time series,and Fig.8c shows anomaly cor-relation between the 500hPa geopotential height ﬁeld and the EOF3time series.The 5years with the highest values of the EOF3time series (1962,1966,1968,1969and 1979)and the 5years with the lowest values of the EOF3time series (1961,1967,1976,1989and 1998)are chosen to calculate differences of water vapor ﬂux (Fig.8d).The 500hPa geopotential height ﬁeld in the high-latitude regions,concentrated in the Arctic Ocean,shows a positive correla-tion with the EOF3time series,while a positive correlation be-tween the 500hPa geopotential height ﬁeld and the EOF3time(a)shows the eigenvector spatial pattern of the ﬁrst mode (EOF1).Shaded areas indicate regions with negative values.Fig.6b shows the EOF1time series (the while the dashed line represents the 9-year Gaussian-type ﬁltered value.Fig.6c shows the correlation between the 500-hPa geopotential height anomalies and the series.Positive values are indicated by solid lines,and negative ones are dash lines.Shaded areas indicate regions with the correlation signiﬁcant at the 0.05level.the difference in vertically integrated water vapor ﬂuxes (unit:kg m À1s À1)between typical years.series appears in the mid-to-low latitudes.It is evident that EOF3summer rainfall in the southwest study area is positively related to the western Paciﬁc subtropical high,while the intensity of the westerly winds strengthened by the high-latitude ﬂows has a posi-tive correlation with EOF3summer rainfall in other areas.Differ-ences of water vapor ﬂux between the 5years with the highest and lowest EOF3time series reveals a considerably higher amount of water vapor input from the high-latitude regions (Fig.8d).It is different from EOF1and EOF2and suggests that EOF3summer rainfall is more related to water vapor transportation from the high latitudes.4.3.East Asian Summer Monsoon Index (EASMI),South Asian Summer Monsoon Index (SASMI)and Summer Westerly Index (SWI)EASMI,SASMI,SWI and the EOF time series,from 1960to 2008,are given in Fig.9,and their correlation coefﬁcients can be found in Table 1.It appears that the intensities of the East Asian summer monsoon,the South Asian summer monsoon and the summer wes-terly winds are correlated with each other,as shown in Table 1.However,they have different effects to the EOF time series.The EOF1time series is positively correlated with SWI,but negatively correlated with SASMI.On the contrary,the EOF2time series is negatively correlated with all three indices.Then,it seems that there is no obvious relationship between the EOF3time series and the three indices.As listed in Table 1,summer rainfall anom-alies are positively correlated with SWI,but negatively correlated with EASMI and SASMI;therefore,the summer monsoon system and the westerly winds have opposite effects to summer rainfall anomalies in the study area.5.DiscussionPrior work has documented the Holocene millennial-scale out-of-phase relationship between the Asian summer monsoon evolu-tion and the moisture change in arid Central Asia (Chen et al.,2008,2010;Feng et al.,2011).However,these studies focused on Holo-cene climate records in East and Central Asia which cannot provide physical mechanisms underpinning the out-of-phase relationship.In this study we tested the modern interaction between the Asian summer monsoon and the westerly winds using 1960–2008sum-mer rainfall data,East Asian Summer Monsoon Index (EASMI),South Asian Summer Monsoon Index (SASMI),and Summer Wes-terly Winds Index (SWI).Three types of interaction are recovered by EOF analysis in the northwest margin of the Asian summer monsoon.EOF1summer rainfall is inﬂuenced by the combined effect of the western Paciﬁc subtropical high and the westerly winds,while the EOF1time ser-ies is positively correlated with SWI,but negatively correlated with SASMI.Therefore,the South Asian summer monsoon and the wes-terly winds may have opposite effect on EOF1summer rainfall.EOF2summer rainfall shows a negative correlation betweentheshows the eigenvector spatial pattern of the second mode (EOF2).Shaded areas indicate regions with negative values.Fig.7b shows the EOF2time series while the dashed line represents the 9-year Gaussian-type ﬁltered value.Fig.7c shows the correlation between the 500-hPa geopotential height anomalies and series.Positive values are indicated by solid lines,and negative ones are dash lines.Shaded areas indicate regions with the correlation signiﬁcant at the 0.05level.difference in vertically integrated water vapor ﬂuxes (unit:kg m À1s À1)between typical years.(a)shows the eigenvector spatial pattern of the third mode(EOF3).Shaded areas indicate regions with negative values.Fig.8b shows the EOF3time series(the while the dashed line represents the9-year Gaussian-typeﬁltered value.Fig.8c shows the correlation between the500-hPa geopotential height anomalies and the series.Positive values are indicated by solid lines,and negative ones are dash lines.Shaded areas indicate regions with the correlation signiﬁcant at the0.05level.the difference in vertically integrated water vaporﬂuxes(unit:kg mÀ1sÀ1)between typical years.shows EOF1time series(EOF1-T),EOF2time series(EOF2-T),EOF3time series(EOF3-T),East Asian Summer Monsoon Index(EASMI),South Asian Summer Monsoon Winds Index(SWI)and summer rainfall anomalies(P)versus time(1960–2008).upper reaches of the Yellow River and other areas that is related to the northward anomalous water vapor transportation originated from the Asian summer monsoon.The EOF2time series is nega-tively correlated with EASMI,SASMI and SWI.As a result,summer rainfall in the upper reaches of the Yellow River is strengthened by the Asian summer monsoon.On the contrary,the intensity of the westerly winds is positively related to the summer rainfall in other areas.EOF3summer rainfall shows a negative correlation between the high-altitude zones and other areas.Water vapor transporta-tion from the high latitudes plays an important role in EOF3.There is no obvious relationship between the EOF3time series,EASMI, SASMI and SWI.In addition,the summer rainfall in the southeast of the study area exhibits a downward trend,while other areas indicate a remarkable increasing trend.Furthermore,summer rain-fall anomalies,in the study area,are positively correlated with SWI, but negatively correlated with EASMI and SASMI.These relation-ships jointly show the modern interaction between the Asian sum-mer monsoon and the westerly winds,which can be expressed as the modern out-of-phase relationship in the northwest margin of the Asian summer monsoon.Chen et al.(2008,2010)proposed that North Atlantic sea-sur-face temperatures(SSTs)and high-latitude air temperatures,as well as topography of the Qinghai-Tibet Plateau,affect the Holocene millennial-scale out-of-phase relationship.Holocene long-term climate model further conﬁrmed the impact from the westerly winds that can affect the millennial-scale out-of-phase relationship(Li and Morrill,2010;Jin et al.,2012).However, although the effect of westerly winds on the millennial-scale out-of-phase relationship was demonstrated,little attention has been paid to the interaction between the Asian summer monsoon and the westerly winds.Our results provide compelling evidence of the modern interaction between the two climate systems that also can trigger the modern out-of-phase relationship for summer rainfall in the marginal region of the Asian summer monsoon. However,some limitations are worth noting.Although the modern out-of-phase relationship was supported statistically,it is still un-clear whether the relationship appears in other regions and re-search,regarding the modern interaction between the Asian summer monsoon and the westerly winds,is needed.Future work should therefore include large-scale summer rainfall and climate model designed to evaluate the mechanism.6.ConclusionsIn summary,we have presented EOF analysis of the summer rainfall in the northwest margin of the Asian summer monsoon. Water vapor transportation,geopotential heightﬁeld,EASMI,SAS-MI and SWI have been considered for explaining the interaction between the Asian summer monsoon and the westerly winds and its impact on summer rainfall.There are four aspects that can be expressed regarding the modern out-of-phase relationship in the northwest margin of the Asian summer monsoon.First, the summer rainfall in the southeast of the study area shows the out-of-phase relationship with others areas.Second,the Asian summer monsoon and the westerly winds have opposite effects to the summer rainfall anomalies in the study area.Third,the EOF1time series has a positive correlation with Summer Westerly Winds Index,but is negatively correlated with South Asian Sum-mer Monsoon Index.Finally,there are out-of-phase relationships in EOF2and EOF3summer rainfall which are related to the inter-action between the Asian summer monsoon and the westerly winds.The modern out-of-phase relationship on summer rainfall provides clues for understanding the long-term climate change. AcknowledgementsI would like to express my sincere gratitude to the editor,Pro. Qinghai Xu and another anonymous reviewer who have put con-siderable time and effect into their comments on this paper.Spe-cial thanks should go to my advisor,Dr.Carrie Morrill,who works at University of Colorado and NOAA.I am deeply grateful of her help in completion of this research.I am also deeply in-debted to all the other professors in Lanzhou University for their help in scientiﬁc English writing.This study was supported by the National Natural Science Foundation of China(No.41001116). ReferencesAguado,E.,Burt,J.E.,2004.Understanding Weather and Climate,third ed.Prentice Hall,Upper Saddle River,New Jersey.Barry,R.G.,Chorley,R.J.,Yokoi,N.J.,2004.Atmosphere,Weather,and Climate, eighth ed.Routledge,London.Berger,A.,Loutre,M.F.,1991.Insolation values for the climate of the last10,000,000 years.Quaternary Science Reviews10,297–317.Cai,Y.,Tan,L.,Cheng,H.,An,Z.,Edwards,R.L.,Kelly,M.J.,Kong,X.,Wang,X.,2010.The variation of summer monsoon precipitation in central China since the last deglaciation.Earth and Planetary Science Letters291,21–31.Chen,T.,1985.Global water vaporﬂux and maintenance during FGGE.Monthly Weather Review113,1801–1819.Chen,L.H.,Qu,Y.G.,1992.Water-Land Resources and Reasonable Development and Utilization in the Hexi Region.Science Press,Beijing(in Chinese).Chen,F.H.,Yu,Z.C.,Yang,M.L.,Ito,E.,Wang,S.M.,Madsen,D.B.,Huang,X.Z.,Zhao,Y., Sato,T.,Birks,H.J.B.,Boomer,I.,Chen,J.H.,An,C.B.,Wünnemann,B.,2008.Holocene moisture evolution in arid central Asia and its out-of-phase relationship with Asian monsoon history.Quaternary Science Reviews27, 351–364.Chen,F.H.,Chen,J.,Holmes,J.,Boomer,I.,Austin,P.,Gates,J.B.,Wang,N.,Brooks,S.J., Zhang,J.,2010.Moisture changes over the last millennium in arid central Asia:a review,synthesis and comparison with monsoon region.Quaternary ScienceReviews29,1055–1068.Cosford,J.,Qing,H.R.,Eglington,B.,Mattey,D.,Yuan,D.X.,Zhang,M.L.,Cheng,H., 2008.East Asian monsoon variability since the Mid-Holocene recorded in a high-resolution,absolute-dated aragonite speleothem from eastern China.Earth and Planetary Science Letters275,296–307.Cronin,T.M.,2009.Paleoclimates:Understanding Climate Change Past and Present.Columbia University Press,New York.Dong,J.,Wang,Y.,Cheng,H.,Hardt,B.,Edwards,R.L.,Kong,X.,Wu,J.,Chen,S.,Liu,D.,Jiang,X.,Zhao,K.,2010.A high-resolution stalagmite record of the HoloceneEast Asian monsoon from Mt Shennongjia,central China.The Holocene20,257–264.Table1Correlation coefﬁcients(1960–2008)between EOF1time series(EOF1-T),EOF2time series(EOF2-T),EOF3time series(EOF3-T),East Asian Summer Monsoon Index(EASMI), South Asian Summer Monsoon Index(SASMI),Summer Westerly Winds Index(SWI)and summer rainfall anomalies(P).EASMI SASMI SWI P EOF1-T EOF2-T EOF3-TEASMI 1.000SASMI0.758** 1.000SWI0.407**0.396** 1.000PÀ0.158À0.1870.243 1.000EOF1-TÀ0.094À0.1110.315*0.982** 1.000EOF2-TÀ0.449**À0.549**À0.336*0.0790.002 1.000EOF3-TÀ0.0020.0760.038À0.1230.0000.009 1.000*Correlation is signiﬁcant at the0.05level.**Correlation is signiﬁcant at the0.01level.86Y.Li et al./Journal of Asian Earth Sciences58(2012)78–87。

2022年6月上饶市极端暴雨天气过程成因分析

Journal of Agricultural Catastrophology 2023, Vol.13 No.122022年6月上饶市极端暴雨天气过程成因分析洪俊，朱海燕*，周安平，项正鑫，赖诗琪上饶市气象局，江西上饶 334000摘要基于常规气象观测资料、ERA5 0.25°×0.25°再分析数据和雷达观测资料对2022年6月上饶市的一次极端暴雨过程进行天气学动力诊断和成因分析，结果表明：(1)此次持续性暴雨过程是南海季风暴发、西风带系统东移、东北冷涡后部偏弱的冷空气南下、副热带高压稳定维持共同作用的结果。

(2)江西东北部的对流层高层处于高空急流的入口区和低层辐合区叠加，上下抽吸作用加强了暖湿气流的垂直上升运动。

(3)冷暖气团长时间在赣东北对峙，是暴雨长时间在赣东北维持的原因，远高于大气可降水量的气候态(近5年)，为极端强降水提供了异常强盛的水汽条件。

关键词南海季风；日变化；极端强降水；低质心热带型降水中图分类号：P458.1+21.1 文献标识码：B 文章编号：2095–3305(2023)12–0166-04每年随着夏季风的向北推进，长江中下游地区就会出现持续性降雨，沿江各省逐渐进入汛期，对于汛期暴雨发生发展的成因，已有很多学者做过研究。

陶诗言[1]指出，夏季导致洪涝的暴雨是由稳定的西太平洋副热带高压、季风暴发向北推、西风带低槽共同作用的结果。

何立富等[2]认为低空急流对中尺度降水云团的发展起到重要作用。

徐双柱等[3]指出，强降水容易在多个大尺度系统交汇处触发，并指出干冷空气的影响和西南暖湿气流的增强对暴雨有增益作用。

张小玲等[4]根据梅雨锋暴雨活跃的不同区域、不同性质、不同尺度将我国梅雨锋暴雨概括为3种类型。

江晓燕等[5]指出，梅雨锋暴雨的中尺度对流系统与中尺度低空辐合和高空辐散场相伴随。

还有研究指出，西南急流增强和干冷空气活动对暴雨有加强作用[6-10]。

季风边缘区全新世水汽输送

The veriﬁcation of millennial-scale monsoon water vapor transport channel in northwestChinaYu Li ⇑,Chengqi Zhang,Yue WangKey Laboratory of Western China’s Environmental Systems (Ministry of Education),College of Earth and Environmental Sciences,Center for Hydrologic Cycle and Water Resources in Arid Region,Lanzhou University,Lanzhou,730000,Chinaa r t i c l e i n f o Article history:Received 24June 2015Received in revised form 1March 2016Accepted 3March 2016Available online 10March 2016This manuscript was handled by Geoff Syme,Editor-in-Chief Keywords:Asian summer monsoon Millennial-scaleWater vapor transport Climate simulations Isotopic datas u m m a r yLong-term changes of the Asian summer monsoon water vapor transport play a pivotal role in the vari-ability of monsoon precipitation.Paleo-climate simulations have shown that there is an important mon-soon vapor transport channel in western China.Previous studies mostly focused on the correlation between monsoon precipitation and intensity.Little research has been done on the veriﬁcation of the water vapor pared with speleothem and lacustrine systems,the hydrological cycle of land surface sediments is more directly related to the monsoon water vapor.In this study,we used carbonate d 18O and organic matter d 13C of the surface eolian sediments from the piedmont of the northern Qilian Mountains to verify the monsoon water vapor on the Holocene millennial-scale.Two surface sedimentary sections were selected to study paleo-monsoon water vapor transport.Proxy data,including carbonate d 18O and organic matter d 13C of surface eolian sediments,as well as total organic matter and carbonate content were obtained from the two eolian sections.We also synthesized transient simulations of the CCSM3and the Kiel climate models.The PMIP 3.0project and TRACE isotopic simulations were also com-pared with the reconstructed monsoon water vapor transport.Our ﬁndings indicate that the strength of the Holocene Asian summer monsoon is consistent with the water vapor transport in western China that has signiﬁcant impacts to long-term monsoon precipitation in northern China.This study veriﬁes a sig-niﬁcant millennial-scale correlation between the monsoon strength and monsoon water vapor transport intensity along the eastern Qinghai–Tibet Plateau.Ó2016Elsevier B.V.All rights reserved.1.IntroductionThe Asian summer monsoon system reaching from the western Arabian Sea through East Asia and North Australia is a dynamic component of the modern climate system and the monsoonal ﬂow that carries moist air from the Indian Ocean and Paciﬁc Ocean to East Asia affecting approximately one-third of the global popula-tion (Webster et al.,1998;Wang and Lin,2002).Modern variability of the Asian summer monsoon has substantial social and economic impacts,while it is still a challenge to predict the monsoon accu-rately due to lack of complete understanding about monsoon mechanisms (Trenberth et al.,2000;Wang and Ding,2008).Long-term records and simulations of monsoon processes can con-tribute to our understanding on monsoon dynamics.Many studies have been conducted on the millennial-scale Asian summer mon-soon reconstructions for the last twenty years (An et al.,2000;Herzschuh,2006;Chen et al.,2008).Since the early Holocene the Asian summer monsoon was strengthened by the increasing low-latitude solar insolation in the Northern Hemisphere,which has been widely reﬂected in the paleoclimate records in the typical monsoon domain (Morinaga et al.,1993;Fleitmann et al.,2003;Zhang et al.,2004,2006;Dykoski et al.,2005;Shen et al.,2005;Liu et al.,2007;Morrill et al.,2006;Li et al.,2009,2012a;Cai et al.,2010).At the same time,many Holocene Asian monsoon sim-ulations have been done focusing on the long-term driving mech-anisms of the monsoon precipitation and circulation (Kutzbach and Liu,1997;Joussaume et al.,1999;Li and Morrill,2010;Wang et al.,2010;Zheng et al.,2013;Jin et al.,2014;Li et al.,2014a;Liu et al.,2014).Although previous monsoon records and simulations have paid much attention to millennial-scale monsoon precipitation variabil-ity and regional responses to monsoon changes,few studies have shown a comprehensive understanding regarding the long-term monsoon water vapor transport process and its controlling factors./10.1016/j.jhydrol.2016.03.0060022-1694/Ó2016Elsevier B.V.All rights reserved.⇑Corresponding author at:Key Laboratory of Western China’s EnvironmentalSystems (Ministry of Education),College of Earth and Environmental Sciences,Center for Hydrologic Cycle and Water Resources in Arid Region,Lanzhou University,No 222Tianshui Road,Lanzhou City 730000,China.Tel.:+869318912709;fax:+869318912712.E-mail addresses:oscaryoulee@ ,liyu@ (Y.Li).In paleoclimatology and paleoceanography,d18O is a measure of the ratio of stable isotopes18O:16O,and it is commonly used as a measure of water vapor source in monsoonal Asian because today’s Asian summer monsoon rainfall is anomalously low in d18O while a higher proportion of monsoon rainfall in annual totals would result in more negative d18O(Cheng et al.,2009,2012;Liu et al.,2014).In addition to d18O,deuterium excess has become a key parameter in estimating vapor source regions(Pfahl and Sodemann,2014). Paleo-isotopic simulations have proved that the monsoon intensity is strongly correlated with negative d18O along the eastern margin of the Qinghai–Tibet Plateau that is key water vapor channel for northern China;by this way,monsoon rainfall was signiﬁcantly enhanced in northern China(LeGrande and Schmidt,2009; Pausata et al.,2011;Liu et al.,2014).Modern climate research has shown the correlation between monsoon intensity and precip-itation pattern in the monsoon water vapor transport channel(Li et al.,2012b).Fig.1shows JJA vertically integrated water vapor ﬂuxes(1960–2008)along the northwest margin of the Qinghai Tibet Plateau,which indicate modern monsoon water vapor trans-port channel clearly,and the result is consistent with previous atmospheric water vaporﬂux over China(Simmonds et al., 1999).The monthly water vapor and heightﬁeld data are based on the NCEP/NCAR reanalysis data(Kalnay et al.,1996).Although the monsoon water vapor transport channel has been veriﬁed by paleo-simulations and modern observations,little paleo-climatic evidence has been assembled to support the existence and vari-ability of the water vapor channel on the Holocene millennial-scale.Previous speleothem and lacustrine oxygen isotope records were widely obtained along the eastern margin of the Qinghai–Tibet Plateau;however,it is still controversial to explain the paleo-climatic signiﬁcance.Clemens et al.(2010)argued that the cave d18O cannot be interpreted as reﬂecting the Asian summer monsoon intensity due to complicated cave water cycle processes.2000;Ding and Zhang,2005);as a result,carbonate of surface sed-iments is an ideal material to reconstruct paleo-water vapor sources.The objective of the present paper is to develop a credible Holocene Asian summer monsoon water vapor transport indicator at the northern part of the monsoon vapor transport channel in the northeast of the Qinghai–Tibet Plateau,so as to verify the monsoon water vapor variability on the Holocene millennial-scale(Fig.1). Two surface sedimentary sections were selected to study paleo-monsoon water vapor transport.Both bulk organic matter and pol-len concentrates were used for the AMS14C dating and a compar-ison between them shows a reliable chronology.In this study, carbonate d18O and organic matter d13C of surface eolian sediments from the northern Qilian Mountains,as well as total organic matter and carbonate content,were used to reconstruct the water vapor transport history during the Holocene epoch.We also synthesized transient simulations of the Community Climate System Model version3(CCSM3)(Collins et al.,2006)and the Kiel climate model (Park et al.,2009).The PMIP3.0project and TRACE isotopic simu-lations were also used to compare with the reconstructed monsoon water vapor and effective moisture(the ratio of precipitation to potential evaporation)records.Ourﬁndings will address the con-trolling factors and mechanisms of the Holocene Asian summer monsoon water vapor transport channel.2.Regional settingIn the northeast of the Qinghai Tibet Plateau,there is a monsoon water vapor transport channel in the northwest margin of the Asian summer monsoon(95–110°E,35–45°N,Fig.1).The region is also located in the transition zone of the Asian summer monsoon region,the arid region of Northwest China,and the Qinghai–Tibet Plateau(Zhao,1983),which is sensitive to global climate change. Varying in altitude from1000m to5000m above sea level,theStudy area,the northeast of the Qinghai–Tibet Plateau,the Qilian Mountains and the Asian summer monsoon water vapor transport path in western China shows JJA vertically integrated water vaporﬂuxes(unit:kg mÀ1sÀ1,1960–2008)along the northwest margin of the Qinghai Tibet Plateau(Right),which monsoon water vapor transport channel.The broken line shows the general boundary of the monsoon water vapor and the water vapor from the westerly 274Y.Li et al./Journal of Hydrology536(2016)273–283Mountains,HCO 3Àand Ca2+are dominant ions of precipitation and the chemical composition of groundwater is consistent with that of precipitation with salinity of 0.3g/L.The contents of these ions,such as Cl À,SO 42À,Na +,Ca2+and Mg 2+,increase with the decreased altitude and precipitation,while the groundwater salinity increases accordingly (Ding and Zhang,2005).Fig.1shows the summer vertically integrated atmospheric water vapor ﬂux that implies the interaction between the Asian summer monsoon and the westerly winds (Zhao,1983;Li et al.,2012b ).The sampling site is at the northern piedmont of the Qilian Mountains,which are on the northwest margin of the vapor transport channel and sensitive to advancing and retreating of monsoon water vapor.(Fig.1,Chen and Qu,1992).The surrounding area of the sampling site is widely covered by surface eolian sediments that provide good materials to reconstruct past environmental changes.3.Materials,methods and simulations 3.1.Materials and methodsHuangyanghe(a)(Altitude:2447m,Depth: 3.20m,37°250N 102°360E)and Huangyanghe(b)(Altitude:2454m,Depth:3.20m,37°250N 102°360E)sections (Fig.2)are 1km apart and both situ-ated on the northern foothills of the Qilian Mountains.Study area is sensitive to the Asian summer monsoon water vapor transport according to modern water vapor ﬂux (Fig.1),where the annual precipitation is $500mm and the average annual temperature is $2°C.The two sections were sampled at 2cm interval,yielding 160samples each for analysis of total organic carbon (TOC),car-bonate content (CC)and grain-size.In total,133samples were obtained for analysis of carbonate d 18O and organic matter d 13C.Fig.2shows photos and lithology of the two sections.Bulk organic matter and pollen concentrates were selected for AMS 14C radio-carbon dating to establish chronologies for the Huangyanghe(a)and Huangyanghe(b)sections (Table 1).The AMS 14C dates were measured at the Dating Laboratory of Peking University.Pollen concentrates as materials for AMS 14C dating were extracted by treatment with acid and alkali,then sieving for enriching (Li2.Photos and lithology of the Huangyanghe(a)and Huangyanghe(b)sedimen-tary sections in the eastern Qilian Mountains and surrounding areas of the sections.Table 1Radiocarbon ages from the Huangyanghe surface sedimentary boratory number Depth (cm)Dating materials 14C age (yr BP)Calibrated 14C age (2r )(cal yr BP)Huangyanghe(a)BA121247100Organic matter 1165±251085BA111241152.5Organic matter 1970±251919BA121244176Organic matter3395±253644BA101282202.5Pollen concentrates 5540±256337BA121245226Organic matter 7235±358048BA121246250Organic matter8365±409397BA101283275Pollen concentrates 10,780±4012,661BA121243300Organic matter 9820±4511,231Huangyanghe(b)BA10127667.5Pollen concentrates 3505±253773BA12126090Organic matter 4600±355322BA121259100Organic matter 4765±255522BA111239112.5Organic matter 6095±306963BA121255130Organic matter 7435±358263BA121256140Organic matter 7315±308109BA121257160Organic matter 7425±308260BA121258180Organic matter 8610±309552BA121254200Organic matter 9260±3510,443BA111240215Organic matter 9695±4011,144BA121253230Organic matter9720±3511,176BA101279252.5Pollen concentrates 9785±4011,214BA121252260Organic matter 9875±4511,270BA121248270Organic matter10,310±4512,113BA101280292.5Pollen concentrates 10,635±3512,591BA121250310Organic matter 10,335±3512,170BA121251318Organic matter10,360±4012,222536(2016)273–283275et al.,2012c).Grain-size distribution of all samples was deter-mined by the Malvern Mastersizer2000particle analyzer that automatically yields the percentages of clay-,silt-and sand-size fractions,as well as median,mean and mode sample diameters. TOC was measured by Vario-III elemental analyzer;5g of sediment was pretreated with18%HCl for24h at room temperature to remove inorganic was measured by SK-2T04carbon-ate analyzer.The d13C value of organic matter is measured in Fujian Normal University by using a Finnigan-MAT253mass spectrome-ter,designed and produced by Thermo Electron Corporation,the USA.The samples are dried in oven under60°C,and then ground to about1.25mm in size.The pretreated samples are combusted with oxygen gas and converted to CO2gas in a high-vacuum sys-tem.The CO2gas is then puriﬁed collected and measured on the MAT-253mass spectrometer with carbon isotope error being less than0.1‰.All isotopic values are reported in the standard d-notation in permil relative to V-PDB.The d18O values of carbonate from samples were measured on a Finnigan-MAT252Mass Spec-trometer at the Stable Isotope Laboratory of Lanzhou Institute of Geology,Chinese Academy of Sciences(LIGCAS).Carbonate sam-ples were converted to CO2gas with100%phosphoric acid in vac-uum,at25°C for more than6h.CO2for isotopic analysis was puriﬁed cryogenically and then the analysis process was calibrated using the national standard material,and carbon isotopic ratio of carbonate was reported in the standard notation relative to the PDB standard.The measurement error was±0.2‰.Table1shows the AMS14C ages from bulk organic matter and pollen concen-trates.The two sections were well dated and mostly formed during the Holocene according to the twenty-ﬁve radiocarbon ages.The carbon reservoir effect is relatively weak in eolian sediments due to a low carbon exchange rate.Five pollen concentrates radiocar-bon dates are relatively consistent with bulk organic matter ages in the two sections.Radiocarbon ages(14C yr BP)were calibrated to calendar years(Cal yr BP)using the software of Calib6.11.Quan-titative relationships between calibrated ages and depths were established according to an interpolation.The average median, mean and mode grain-size are18.76l m,35.75l m and33.91l m at the Huangyanghe(a)section and21.77l m,38.22l m and 32.33l m at the Huangyanghe(b)section.The overall grain-size frequency distribution is similar for the two sections.The chi-squared test was performed on the two distributions,and the cor-responding conﬁdence level was95%.Fig.3shows the average grain-size frequency curves,which indicate that the peaks of grain-size frequency distribution are at28l m for the Huan-gyanghe(a)section and32l m for the Huangyanghe(b)section. The average clay,silt and sand contents are15.32%,73.51%and 11.17%at the Huangyanghe(a)section and13.09%,73.59%and 13.32%at the Huangyanghe(b)section(Fig.3).3.2.Paleo-climate and isotopic simulationsResults from two transient simulations were synthesized in this research.One of the transient experiment is the TRACE(Transient Climate Evolution)experiment of the last21ka,a state-of-art cou-pled ocean–atmosphere model,the Community Climate Model version3(CCSM3T31resolution)of the National Center for Atmo-spheric Research(hereafter TRACE simulation)(Liu et al.,2009). The simulation is forced by realistic external forcing of insolation, atmospheric greenhouse gases,and continental ice sheets(Fig.4) (Berger,1978;Joos and Spahni,2008;Liu et al.,2009,2014; Peltier,2004;Li and Morrill,2015).In the TRACE simulation,the Chinese monsoon wind index was calculated by Liu et al.(2014), measured as the averaged summer meridional surface wind in East China(V850JJA,110°E120°E;27°N37°N).The other is the coupled the Kiel Climate Model,a non-ﬂux-corrected coupled general cir-culation model(KCM;Park et al.,2009).The transient simulation was started from the last year of the1000-year equilibrium time-slice experiment H9K and is integrated under the orbital forc-ing for1000years after spin-up during the Holocene(9.5ka BP to 0ka BP)is achieved(Jin et al.,2014).In the Kiel Model,the Indian summer monsoon index(ISMI)was calculated by Jin et al.(2014), which is adapted from Goswami et al.(1999)as the difference of JJA meridional wind anomalies at850hPa and200hPa averaged over the ISM region.The EASMI was deﬁned as shear vorticity by Wang et al.(2008).The evolution of atmospheric water isotopes (d18O)was simulated by Liu et al.(2014)using the isotope-enabled atmospheric component model of the CCSM3CAM3(T31 resolution)that incorporates fractionation associated with surface evaporation and cloud processes(Noone and Sturm,2010).They performed23isotope snapshot sensitivity experiments in the last 21,000years using the CAM3set-up the same as in the TRACE experiment:21experiments are1000years apart.The Palaeocli-mate Modeling Intercomparison Project(PMIP)began in the early 1990s to provide an efﬁcient mechanism for coordinating palaeo-climate modeling activities(Joussaume et al.,1999).PMIP3is its newest version;within the framework of PMIP3,the mid-Holocene experiment is set up to examine the coupled model’s sensitivity to the changes of insolation(Wang et al.,2010;Zheng et al.,2013).The insolation pattern is standardized following Berger(1978),with an eccentricity of0.018682,an obliquity of 24.105and a longitude of perihelion of0.87(Fig.4).The green-house gases concentrations are set to the same as that in the pre-Industrial(PI)experiment,except that the CH4concentration reduces from760to650ppb.Other boundary conditions,such as the aerosols,solar constant,vegetation,ice sheets,topography and coastlines are prescribed as the same as in the PI experiments. Coupled GCMs from the PMIP3database accessed in this study include(BCC-CSM-1,CCSM4,CNRM-CM5,CSIRO-Mk3-6-0,FGOALS g2,FGOALS s2,FIO-ESM,IPSL-CM5A-LR,MPI-ESM-P,MRI-CGCM3) (Zheng et al.,2013;Liu et al.,2014).4.Results4.1.Carbonate d18O and organic matter d13CStable isotopes have been widely used in hydrology,meteorol-ogy,atmospheric physics and ecology,and they can be attributed to the recognition of empirical relation between d18O,precipitation and observed air temperature(Jones et al.,2005).Sensitivity of the d18O-temperature relationship could differ according to location changes in the world(Noone and Simmonds,2002;Brown and Simmonds,2004).In lacustrine carbonate minerals,d18O records can provide insights into past hydrological and climatic changes in East Asia(Wei and Gasse,1999;Yu et al.,2009).However,the fractionation of oxygen isotopes is controlled by different climate variables in different areas of East Asia due to the variability of cli-mate conditions in the region(Yu et al.,2009;Zhang et al.,2011). Speleothem oxygen isotope records from southern China are rela-tively consistent in showing millennial-scale climatic variability since the Last Glacial(Yuan et al.,2004;Cheng et al.,2009, 2012).However,the explanation of these proxies has remained a great controversy because of the complicated upstream depletion mechanism in China(Cheng et al.,2009;Clemens et al.,2010).As a result,cave d18O records cannot be directly used to reconstruct past water vapor transport channel in China pared with lacustrine and cave systems,carbonate d18O records from surface sedimentary system are more appropriate for paleo-vapor source reconstruction based on analysis of ions from modern precipitation in northwest China(Ding and Zhang,2005).From the Huan-gyanghe sedimentary section,carbonate d18O values(‰)range fromÀ9.117toÀ4.446and its range is relatively consistent with276Y.Li et al./Journal of Hydrology536(2016)273–283precipitation weighted Chinese annual d18O index in the snapshot simulations(TRACE model)(Fig.5).The average value of d18O(‰) isÀ6.978,which is also similar to the average value for the Holo-cene epoch simulated by TRACE model.The lowest value of d18O is reached at the depth of237cm and around11333cal yr BP from the Huangyanghe(b)section that is almost at the start point of the Holocene epoch showing the strengthening of the Asian sum-mer monsoon water vapor transport during the early Holocene, which is triggered by the increasing low-latitude solar insolation. Then,variability of the carbonate d18O value indicates an increas-ing trend from the early Holocene to late Holocene.The highest level of d18O values appears at around4000cal yr BP in the mid-to-late Holocene and its highest value isÀ4.446(‰).At the top of the section Huangyanghe(b)(above the depth of63cm),we canﬁnd d18O values are becoming lower even reaching the lowest value ofÀ7.757.The top sediments at Huangyanghe section are modern agriculture soils in the study area.Agricultural irrigation and farming have signiﬁcant impacts toward soil carbonate18O values;therefore,the top part of the sections cannot be used as materials to reconstruct millennial-scale water vapor transport.A linear regression was made using d18O values from early to late Holocene showing an obvious increasing trend in d18O values (Fig.6).Organic Carbon Isotope(d13C)is commonly used as an organic geochemical proxy,which can reﬂect primary productivity and vegetation types in a basin(Krishnamurthy and Bhattacharya, 1986;Meyers and Vergès,1999).Organic matter produced from atmospheric CO2by plants using the C3pathway has an averageLithology,grain-size and calibrated14C ages for the Huangyanghe(a)and Huangyanghe(b)sections.Green curves are from the Huangyanghe(a)section while from the Huangyanghe(b)section(Left).The average grain-size frequency distribution curves generally indicate the percentages of grain-size componentsPrescribed boundary conditions and forcings for the transient TRACE simulation.Orbital parameters were set according to Berger(1978),radiative forcing atmospheric greenhouse gases was from Joos and Spahni(2008),ice sheet area and height were set according to Peltier(2004).d13C(PDB)value of ca.À28‰(À34‰toÀ23‰),by those using the C4pathway ca.À14‰(À22‰toÀ6‰)and by those using CAM pathway betweenÀ20‰andÀ10‰(Bowen,1991).According to previous studies of organic geochemical proxies in this area,the d13C values from organic matter are always negatively correlated with TOC,C/N ratio and total pollen concentration;meanwhile, effective moisture is the main controlling factor for these organic geochemical proxies(Li et al.,2014b).Therefore,the d13C value isCarbonate d18O values,organic matter d13C values,total organic carbon and carbonate content from the Huangyanghe(a)and Huangyanghe(b)sections.Green the Huangyanghe(a)section while blue curves are from the Huangyanghe(b)section.(For interpretation of the references to color in thisﬁgure legend,theto the web version of this article.)6.A comparison of the reconstructed Holocene Asian summer monsoon proxies and simulated Holocene Asian summer monsoon indices and isotopic indicators: carbonate d18O values and organic matter d13C values from Huangyanghe sections;Holocene summer insolation at20°N(Berger,1978);precipitation weighted Chinese annual d18O index in the snapshot simulations(TRACE model,Liu et al.,2014);simulated Holocene Asian summer monsoon index from TRACE model(the averaged summer meridional surface wind in East China,Liu et al.(2014)(V850JJA,110°E120°E;27°N37°N));simulated Holocene Indian and East Asian summer monsoon indices from Kiel model(Jin et al.,2014);lacustrine carbonate d18O values from Qinghai Lake and Selin Co(Liu et al.,2007;Morinaga et al.,1993);cave speleothem d18O values records from Dongge Cave and Jiuxian Cave(Dykoski et al.,2005;Cai et al.,2010).Two linear regression lines for carbonate d18O values and organic matter d13C values from Huangyanghe sections were added for showing long-term trends.an ideal indicator showing the effective moisture change,the low d13C values always corresponding to high effective moisture.The organic matter d13C(‰)values range fromÀ23.687toÀ25.22at the Huangyanghe section,and its average value isÀ24.445.The lowest value of d13C(‰)(À25.22)appears at the depth of 277cm at Huangyanghe(b)section and around11,996cal yr BP (Fig.5).Based on the explanation of organic matter d13C values, the low values indicate relatively high effective moisture condi-tions.At the beginning of the Holocene epoch,the low d13C value is consistent with the negative d18O value showing the strong mon-soon water vapor transport in northwest China and its correspond-ing high effective moisture conditions.Although the d13C value ﬂuctuates severely since the early to late Holocene,there is also an increasing trend for its values.The highest value of d13C(‰) (À23.687)is at the depth of25cm from the Huangyanghe(b)sec-tion.A linear regression was also made according to variability of d13C values shown by Fig.6.It shows the increasing trend of the d13C value from early to late Holocene clearly.The d13C value is also becoming lower at the top of the section Huangyanghe(b),like the situation of the d18O value.Again,we think it can be related to modern agricultural irrigation and farming activities and cannot be related to natural effective moisture conditions.4.2.(TOC%)and(CC%)Percent TOC values reﬂect the amount of organic matter pro-duced within a basin,as well as terrestrial organic matter washed in from its watershed(Meyers and Vergès,1999).In the surface eolian sedimentary system,TOC and CC are impor-tant indicators for distinguishing loess and paleo-soils(Xiao et al.,2002;He et al.,2013).Paleo-soils are usually enriched with organic matter while soil formation is more mature in paleo-soils than that in is directly affected by carbonate leaching processes that can also be inﬂuenced by the phases of paleo-soil formation(Fang et al.,1999;He et al.,2013).A com-parison of the TOC and CC from the Huangyanghe(a)and(b) sections with the organic matter d13C values and the carbonate d18O values has been shown in Fig.5.Changing trends of proxy data,including TOC and CC,are relatively negatively correlated with each other.Since the high value of TOC shows a paleo-soil phase while the low value of CC indicates a strong leaching process.The average TOC and CC are 1.51%and4.46%for the Huangyanghe(a)section,and 1.14%and 5.87%for the Huan-gyanghe(b)section.Changes in TOC and CC are relatively consis-tent with variability of grain-size(Figs.3and5),showing a correlation between lithology and organic matter/carbonate. The high content of TOC and the low content of CC are always corresponding toﬁne particle sediments in grain-size from the early to late Holocene(Figs.3and5).At the Huangyanghe(a) section,the average TOC and CC are0.79%and 4.83%respec-tively below$183cm(5088cal yr BP).During this part,the color of lithology is relatively light and the content of paleo-soils is low.For the upper part of the section,the average TOC and CC are 2.05%and 4.18%showing the formation of soils.At the Huangyanghe(b)section,the average TOC and CC are0.69% and7.34%below$103cm($6089cal yr BP)while they are 2.09%and 2.84%for the upper part(Fig.5).Results from the two sections are similar.There is an abrupt increase of CC and TOC appearing at the top of the Huangyanghe(a)section,which may be related to modern agricultural irrigation and farming activities.As has been shown in Fig.5,changing trends of TOC and CC are generally showing the paleo-soil formation at the second part of the Holocene(after6000cal yr BP).However, the early-to-mid Holocene is characterized by strong monsoon water vapor transport and high effective moisture conditions according to the organic matter d13C values and the carbonate d18O values.This evidence demonstrates that water vapor and precipitation conditions are not the only factor affecting paleo-soil formation on the millennial-scale.The widely-distributed mid-Holocene paleo-soils can also support our idea that strong early Holocene Asian summer monsoon cannot maintain the paleo-soil formation in China(An et al.,2000;Herzschuh, 2006).The Holocene paleo-soil formation may be controlled by other climatic factors such as surface temperature and vegeta-tion condition,in addition to precipitation and moisture.n summer monsoon and d18O simulationsFig.6shows a comparison between the reconstructed Holocene monsoon water vapor transport intensity using the carbonate d18O values,effective moisture conditions using organic matter d13C val-ues,the simulated Holocene Asian summer monsoon indices using transient TRACE and KIEL simulations.They indicate a consistent changing trend,a strong early Holocene Asian summer monsoon and a strong monsoon water vapor transport in northwest China, and a generally smooth weakening tendency.The correspondence between the Asian summer monsoon winds and precipitation weighted Chinese annual d18O index in the snapshot simulations (TRACE model)is further seen in the consistent evolution between the isotopes and the monsoon wind index in TRACE(Fig.6).Gener-ally,the Asian summer monsoon winds calculated by the averaged summer meridional surface wind in East China(V850JJA) increased from the Last Deglaciation toward the early Holocene and then decreased in the Holocene,following the summer insola-tion.At the same time,precipitation weighted Chinese annual d18O index shows a positive trend from the early Holocene to late Holo-cene.These evolutionary features indicate that the Asian summer monsoon winds are negatively correlated with the precipitation weighted Chinese annual d18O,which is an important indicator for monsoon water vapor transport in China.As has been shown in Fig.6,the calculated Indian summer monsoon index during the Holocene is smoother than the Holocene East Asian summer monsoon index in the transient Kiel model,while the East Asian summer monsoon index shows large oscillations of multi-centennial variability,reﬂecting signiﬁcant regional differences of the Indian summer monsoon and East Asian summer monsoon.Fig.7shows the precipitation weighted summer(JJA)d18O dis-tribution difference between6ka and1ka in East Asia and the millennial-scale correlation between precipitation and d18O values. The6ka minus1ka summer(JJA)d18O distributionﬁgure indicates a strong negative region in western China that is also located in the eastern Qinghai–Tibet Plateau.That means an intensive mid-Holocene monsoon water vapor transport in the region,which is an important water vapor channel for monsoon precipitation in northern China.The arrow and the black point illustrate the aver-age water vapor channel and the study area in this research(Fig.7). In the millennial-scale correlationﬁgure,the relationship between monsoon water vapor transport and precipitation is more signiﬁ-cant along the water vapor channel in western China than in other regions.It further proves the paleo-climatic signiﬁcances of the water vapor channel and its impacts to northern China.However, it shows little correlation in eastern China due to the control of summer sub-tropical high in eastern China.Fig.8shows changes of summer precipitation(%)and850hPa meridional wind(m/s) of JJA in response to orbital forcing in the mid-Holocene(6k–0ka)for the ensemble mean of the PMIP3models with equal weight.Results show that the PMIP3model median captures well the large-scale characteristics of the mid-Holocene East Asian sum-mer monsoon,including the enhanced land-sea contrast during boreal summer and the strengthening of the East Asian summer monsoon circulation,featuring the stronger southerly winds pre-vailing over the eastern China(Fig.8).However,regarding theY.Li et al./Journal of Hydrology536(2016)273–283279。

Verifying a new proxy of the Holocene East Asian Winter Monsoon--Grain size of mud on the inner shel

Journal of China University of Geosciences. Vol. 18, Special Issue, p.333—336, Joune 2007 ISSN 1002-0705 Printed in ChinaVerifying a new proxy of the Holocene East Asian Winter Monsoon--Grain size of mud on the inner shelf of the East China SeaXiao Shangbin*, Tian Fang, Zhang GuodongChina Three Gorges University, Yichang 443002, ChinaWu Xiangyu, Chen Muhong, Xie Qiang, Yan WenSouth China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, ChinaYang XianghuaChina Geoscience University, Wuhan 430074, ChinaABSTRACT:Correlation of winter temperature between climate stations in China was analyzed in thispaper. Temperature and salinity changes at different sea water depths off the Zhejiang-Fujianprovinces also were analyzed, as was velocity of surface sea water in the same area (calculated fromwind field data from QuikScat Data). Grain size of the mud can be used as a good proxy to reconstructthe history of the EAWM because its sedimentation has been controlled by the winter coastal current,which resulted from the winter monsoon. In the past 400 years, the grain size of the terrigenous clasticcomponent of the mud in the region changed synchronously with winter temperature of East China.KEY WORDS: East Asian winter monsoon, winter temperature of China main land, mud, EastChina Sea, grain-sizeReconstructing the history of environmental changes over geological time is the basis for predicting future environmental changes. Grain size and magnetic susceptibility of the Chinese loess have been regarded as proxies of the EAWM and the East Asian Summer Monsoon (EASM), respectively, over long time scales (An et al., 1991; Stephen and An, 1995). However, using loess deposits to study climate changes at higher resolution (e.g., centennial or shorter time scales) is difficult because of the low sedimentation rate of this compound. To date, existing high-resolution records are limited mainly to the study of the EASM or to the total climate changes that occurred during the Holocene period, and most are land based. Recently, several researchers reconstructed high-resolution records of the Holocene EAWM using grain size of mud sediment as a proxy (Xiao et al., 2005a, 2005b, 2006; Xiang et al., 2005, 2006). These records were established based on the following hypothesis: The winter currents flow more rapidly when the winter monsoon strengthens, which results in deposition of coarser suspended sediment; at the same time, a big temperature-lowering event occurs on land (and vice versa). In this paper, the correlation between the winter temperature on China’s mainland and the velocity of the winter ECS Coastal Current (ECSCC) was ─────────This research was sponsored by Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences (No. MSGL0507) and Doctoral Foundationof China Three Gorges University (No. 603117).*Corresponding author email: shangbinx@ under varying winter monsoon analyzed strengths to verify this hypothesis.REGIONAL SETTINGA major feature of the ECSCC is its seasonally changingflow path. It flows northward in summer due to the southeast monsoon and southward in winter due to the prevailing north wind. The mud on the inner shelf of the ECS, which has been accumulating since ~7.6 ka BP (Cal. age), is derived mainlyfrom suspended sediments from the Yangtze River that is transported southward by the winter coastal current (Qin et al., 1987; Su et al., 1989; Guo et al., 1999; Sun et al., 2000). The Yangtze River discharges 4.8×108 t/a (Milliman and Meade, 1983), which results in a high sedimentation rate of mud on the inner shelf. For example, the sedimentation rate of Core DD2was more than 100 cm/ka during the last 2 ka (Xiao et al., 2005a). So high sedimentation rate makes it possible to reconstruct high-resolution records (several years) of palaeoenvironmental changes by extracting the right information from the mud.Materials and MethodsTemperature data from China’s mainland were downloaded from the Shared Data Web of the Chinese Meteorology Administration (), and temperature and salinity data of sea water off the Zhejiang-Fujian provinces were downloaded from the Shared Data Center of Chinese Marine Science334(/).Wind field data are from QuikScat Data to calculate the velocity of the winter ECSCC, and have a spatial resolution of× of month’s data. High temporal and spatialresolution is the strong point of QuickScat data; they are the most complete and advanced of modern remote sensing data. Creditability of the data is well verified (Xie et al., 2003). Data from January from 2000 to 2005 were used in this study.°25.0°25.0Because a current at the sea surface results mainly from wind effects, its velocity of orientation U (latitude) and V (longitude) can be calculated from wind data by using Ekman theory with z = 0 (i.e., surface Ekman effect) when the velocity of two points is analyzed. Wind drives sea current when the winter monsoon bursts, and the surface sea current deflects 45° to the right (in the Northern Hemisphere) due to the Coriolis force and frictional force. The following equation is used to calculate the surface current velocity with sea surface wind stress:u (0)= (τx +τy )/(2ρ*A z *a ); v (0)= (τy -τx )/(2ρ*A z *a );Az 2/f a =;where u (0) and v (0) are the vector components at orientations U and V of surface current velocity; τx and τy are vector components at orientations latitude and longitude of sea surface wind stress; A z (vertical eddy diffusivity) is vertical vorticitydiffusivity, which is valued at 0.001 due to surface flow lying in the mixed layer; f is the parameter of the Coriolis force; andρ is the density of sea water.RELATION BETWEEN THE TEMPERATURE OF CHINA’S MAINLAND AND THE SURFACE VELOCITY OF SEA WATER OFF THE ZHEJIANG-FUJIAN PROVINCESData collected at 8 climate stations between December and February from 1952 to 2001 were used in this study. Table 1 lists correlation coefficients between these stations and shows good correlation of winter temperature (Table 1) and synchronous changes between these stations.Table1 Correlation coefficient between winter temperature of some China climate stations drawn from 50 years’ dataDT YA BX YZ XY YC GL XZ DT 1.00.810.750.85 0.75 0.70 0.690.86YA ** 1.000.540.80 0.69 0.63 0.670.80BX **** 1.0 0.61 0.61 0.58 0.530.67YZ **** ** 1.0 0.73 0.75 0.750.95XY **** ** ** 1.0 0.92 0.810.83YC **** ** ** ** 1.0 0.900.80GL **** ** ** ** ** 1.0 0.73XZ**** ** ** ** ** ** 1.0**: Correlation is significant at the 0.01 level (2-tailed). DT-Datong, YA-Yan’an, BX-Benxi, YZ-Yanzhou, XY-Xinyang,YC-Yichang, GL-Guilin, XZ-XuzhouTable 2 Changes of temperature and salinity of sea water off Zhejiang-Fujian provincesOct.-Mar.Jan.-Feb.Jan.-Feb. of Areaa ATemperature(℃) Salinity(‰) Temperature(℃) Salinity(‰) Temperature(℃) Salinity(‰) 25.3-11.6 34.87-32.81 21.4-11.60 34.87-32.91 20.03-15.57 34.67-33.31Temperature and salinity data of sea water off the Zhejiang-Fujian provinces collected between October and March from 1933 to 1993 were analyzed in this study (particularly for Area A. Figure 1) between January and February. The salinity of sea water off the Zhejiang-Fujian provinceschanged little during winter (Table 2), which corresponds to little fresh water input from rivers. For example, less than 30% of the runoff from the Yangtze River occurs from November to April (Hori et al., 2001). Changes in sea water temperature were relatively big and varied with season and distance from the coast. It changed about 5°C in January–February. Even so, it did not have a big effect on sea water density; thus, the influence of temperature and salinity on sea water density can be ignored at the same site and in the same season.Winter temperature changes of China’s mainland show a coincident and synchronous trend on an annual scale and are well correlated (Table 1). Yichang station was selected as a representative climate station because it was highly correlated with other stations and is centrally located in China. The sites atFig. 1 Sites for temperature and salinity analysis of seawater off the Zhejiang-Fujian provinces. The rectangle marked with shadow is Area A.335which cores DD2 (122º37.92´E, 29º34.92´N) (Xiao et al., 2005a) and PC-6 (122º34.02´E, 28º58.06´N) (Xiao et al., 2006, 2005b) were taken and three other sites were selected at random for the correlation analysis of sea surface current velocity and the temperature at the Yichang station. Data from January for 2000–2005 were analyzed. Current velocity and temperature were correlated (Table 3); the lower the temperature of China’s mainland, the greater the velocity of the surface coastal current.Table 3 Correlation coefficient between the temperature of Yichang station and the velocity of surface sea water offZhejiang-Fujian provinces in Jan. YC DD2 PC-6 B C D YC 1 -0.835 -0.837 -0.946 -0.957 -0.921DD2 *1 0.997 0.927 0.904 0.966PC-6 * **1 0.928 0.901 0.967B ** ** ** 1 0.989 0.975C ** * * ** 1 0.977D ** ** ** ** ** 1 ** and *: Correlation is significant at the 0.01 and 0.05 level(2-tailed).RELATION BETWEEN WINTER HALF-YEAR TEMPERATURE OF EAST CHINA AND GRAIN SIZE OF MUD ON THE INNER SHELF OF THE EAST CHINA SEAHydrodynamic conditions and sedimentary environmentscontrol sedimentation of terrigenous clastic sediments. The main hydrodynamic conditions that control mud deposition are velocityof the winter coastal current and density of the sea water(buoyancy). On the inner shelf of the ECS, sea water densitychanges little at the same site and in the same season, leavingcurrent velocity as the crucial factor affecting grain size of muddeposited in the area. Thus, by determining the grain size thatcorresponds to deposition by the winter coastal current andextracting this subpopulation from the terrigenous clasticcomponent of the mud with rational mathematical methods, thehistory of the temperature of China’s mainland and the EAWM can be reconstructed during the same time associated with exact age dating. Figure 2 shows the comparison between the mean grain size of Core DD2 corresponding to the EAWM(Xiao et al., 2005a) and the winter half-year temperature of East China (Ge et al., 2003).The mean grain size of Core DD2 clearly increased when thewinter half-year temperature of East China decreased; the twoparameters change in synchrony.CONCLUSIONSThe following conclusions can be drawn based on the analysis of temperature data from Chinese climate stations, temperature and salinity data of seaFig. 2 Comparison between temperature fluctuation of East China (dash-dotted line) (Ge et al., 2003) and mean grain size of Core DD2 (real line) (Xiao et al., 2005a).water, and wind field data off the Zhejiang-Fujian provinces: (1) Winter temperature of China’s monsoon region changes synchronously on an annual scale. (2) The temperature and salinity of sea water off the Zhejiang-Fujian provinces change little at the same site and in the same season, and the hydrodynamic conditions in the area are determined mainly by the velocity of the winter coastal current. (3) Very good correlation exists between the velocity of surface sea water in the mud area on the inner shelf of the ECS and temperature of China’s mainland in winter. The grain size of the terrigenous clastic component of the mud can be used as a good proxy for the EAWM, which is useful for reconstructing the temperaturehistory of China’s mainland and the evolution of the EAWM.REFERENCES CITEDAn Z.S., Kukla G., Porter S.C., et al., 1991 MagneticSusceptibility Evidence of Monsoon Variation on The Loess Plateau Of Central China During the Last 130,000 Years. Quaternary Research , 36: 29-36. Ge, Q., Zheng J., Fang X. , et al., 2003. Winter Half-Year Temperature Reconstruction for the Middle and Lower Reaches of the Yellow River and Yangtze River, China,during the Past 2000 Years. The Holocene , 13(6): 933-940.Guo, Z.G., Yang, Z.S., Lei, K. et al., 1999, SeasonalVariation of the Sedimentary Dynamic Processed for theMud Area in the Northern East China Sea. Jouranl ofOcean University of Qingdao , 29(3): 507-513. (in Chinese with English abstract) Hori K., Cheng X., Wang P., et al., 2001. Sedimentary Facies and Holocene Progradation Rates of the Changjiang(Yangtze) Delta, China. Geomorphology, 41(2): 233-248.Milliman J.D., Meade R.H., 1983. World-Wide Delivery of River Sediment to the Oceans. Journal of Geology, 91: 1-21. Qin, Y.S., Zhao, Y.Y., Chen, L.R., et al., 1987, Geology of the East China Sea. Science Press, Beijing. 7. (in Chinese)Stephen C.P., An Z.S., 1995. Correlation between ClimateEvents in the North Atlantic and China during the LastGlaciation. Nature, 375: 305-308.Su, J., 2001, A Review of Circulation Dynamics of the CoastalOceans near China: Acta Oceanonlogica Sinica, 23(4):3361-16. (in Chinese with English abstract)Su, Y.S., Li, F.Q., Ma, H.L. , et al., 1989, Formation and Seasonal Changes of the NorthernBottom Cold Water in the East China Sea: Oceanologia et Limnologia Sinica, 19(1): 1-14 (in Chinese with English Abstract)Sun, X.G., Fang, M., Huang, W., 2000, Spatial and Temporal Variations in Suspended Particulate Matter Transport on the Yellow and East China Sea shelf . Oceanologia et Limnologia Sinica, 31(6): 581-587. (in Chinese with English Abstract)Xiang R., Yang Z.S., Saito Y., et al., 2006. East Asia Winter Monsoon Changes Inferred from Environmentally Sensitive Grain-size Component Records during the Last 2300 Years in Mud Area Southwest off Cheju Island, ECS. Science in China (D), 36(7) : 654-662 (in Chinese)X i a n g R.,Ya n g Z.S.,G u o Z.G.,e t a l.,2005.Paleoenvironmental Implicantions of Grain-zise Component Variations in the Mud Area Southwest off ChejuI s l a n d,E C S.E a r t h S c i e n c e—J o u r n a l o f C h i n a University of Geosciences, 30(5): 582-588. (in Chinese with English Abstract)Xiao, S.B., Li, A.C., Chen, M.H. , et al., 2005b, Recent 8 ka Mud Records of the East Asian Winter Monsoon from the Inner Shelf of the East China Sea. Earth Science—Journal of China University of Geosciences, 30(5): 573-581. (in Chinese with English abstract)Xiao, S.B., Li, A.C., Jiang, F.Q., et al., 2005a. Recent 2000- Year Geological Records of Mud in the Inner Shelf of the East China Sea and their Climatic Implications. Chinese Science Bulletin, 50(5): 466-471.Xiao, S.B., Li, A.C., Liu J. P., et al., 2006. Coherence between Solar Variability and the East Asian Monsoon during the Past 8 kaB. Palaeogeography, Palaeoclimatology, Palaeoecology, 237: 293- 304.Xie S.P., Xie Q., Wang D., 2003. Summer Upwelling in the South China Sea and its Role in Regional Climate Variations. J. Geophys. Res., 108(C8), 3261。

(福建专用)高考英语一轮作业手册(6) Unit 1 Cultural relics(含解析) 新人教版必修2

课时作业(六) [必修2 Unit 1 Cultural relics](限时：35分钟)Ⅰ.单项填空1．He didn't put the things________they belonged，for________he got his punishment.A．which；that B．what；thisC．that；whose D．where；which2．As far as I'm concerned，there is no point ________with him. He will never change his mind.A．argued B．arguingC．to argue D．for arguing3．It is reported that there was an air crash in Cuba. Nobody on board________it with all the passengers and the crew killed.A．avoided B．escapedC．missed D．survived4．Although he had taken a lot of medicine，his health________poor.A．proved B．remainedC．maintained D．lasted5．There is________to ask him for advice，because he has never done this kind of work before.A．no need B．no timeC．no point D．no doubt6．Although the Eiffel Tower ________ to last for 20 years, it is still standing today.A．has designed B．had designedC．is designed D．was designed7．Normally you could stay with us, but our house ________ at the moment.A．is decorated B．was decoratedC．is being decorated D．was being decorated8．The toddler who miraculously ________ a fall from her 10thfloor home in Hangzhou, east China, ________ recovering quickly.A．is survived; is B．are survived; areC．survived; is D．being survived; are9．[2012·江苏卷] There is little doubt in your mind that he is innocent, ________？A．is there B．isn' t thereC．is he D．isn' t he10．Like most simple puzzles, it is easily________， but putting it back together is something else.A．taken apart B．built upC．set off D．dealt with11．—What do you think of his talk on Information Technology?—Oh, excellent. It's worth ________．A．listening to B．being listened toC．listening of D．to be listened to12．In April，thousands of holidaymakers remained ________ abroad due to the volcanic ash cloud.A．sticking B．stuckC．to be stuck D．to have stuck13．We give dogs time，space and love we can spare，and________，dogs give us their all.A．in all B．in factC．in short D．in return14．In the 1990's，many welleducated young people went to Hainan Island ________ jobs.A．in favour of B．in memory ofC．in honour of D．in search of15．—So you gave her your phone?—________．She said she'd return it to me when she could afford her own.A．My pleasure B．Not exactlyC．No wonder D．All rightⅡ.完形填空What do Chinese college graduates have in common with ants? The recent __16__ Ant Tribes about the life of some young people __17__ flock to Beijing after leaving university，__18__ the graduates，like ants，as smart but __19__ as individuals, drawing strength from living together in communities.The book，which is based __20__ two years of interviews with about 600 lowincome college graduates in Beijing，__21__ in midSeptember，about a month ahead of an announcement by the Ministry of Human Resources and Social Security that 74% of the 6.11 million new graduates from universities and colleges had been __22__ by Sept.1.The book's chief editor，Lian Si，tells that piece of statistic says __23__ about the real situation for many of these graduates.“I am always __24__ how many of these employed college graduates are leading a happy life”，Lian said.“I hope this book could offer a window on these graduates，whose stories are __25__ k nown.”The __26__ of the book is several socalled settlement villages for college students on the outskirts(市郊) of Beijing，where a large __27__ of college graduates live.Most of these graduates work for __28__ or mediumsized businesses，__29__ less than 2，000 yuan a month.They live together because it's __30__：the rent in these communities is only around 350 yuan a month.Many of them travel several hours a day for shortterm jobs or job interviews.Tangjialing，a small __31__ 20 kilometers from Tian'anmen Square，has around 3，000 __32__ villagers，but has become a home for more than 50，000 migrants，most of whom __33__ from universities or colleges all over the country.Lian describes the students' __34__ as five or sixstorey buildings built by local farmers with 12 roomson each floor and two or three people crowded together in each room of about 10 square meters.Up to 70 or 80 people __35__ the same toilet and kitchen.16．A.film B．story C．book D．magazine17．A.who B．what C．which D．whose18．A.describes B．tellsC．shows D．gives19．A.necessary B．meaninglessC．important D．strong20．A.in B．on C．at D．for21．A.came up B．came onC．came along D．came out22．A.fired B．interviewedC．employed D．trained23．A.much B．little C．some D．more24．A.wondering B．realizingC．studying D．confusing25．A.seldom B．well C．always D．never26．A.environment B．settingC．range D．coverage27．A.deal B．plenty C．amount D．number28．A.small B．big C．famous D．unknown29．A.earning B．spendingC．shopping D．paying30．A.expensive B．comfortableC．cheap D．convenient31．A.city B．townC．community D．village32．A.original B．youngC．rich D．poor33．A.suffer B．differ C．graduate D．suffer34．A.lives B．dormitoriesC．buildings D．restaurants35．A.share B．borrow C．build D．cleanⅢ.阅读理解A severe heatwave sweeping India, with temperatures of almost 44℃， the highest in 52 years, has killed at least 80 people this month, officials said on Sunday. The hot weather, which officials said would continue over northern, northwestern and central India in the next 48 hours, also may have some impact on wheat production, exporters and flourmill associations said.New Delhi recorded a maximum temperature of 43.7 ℃ on Saturday, indicating a hot summer in the next two months in the nation's capital and other parts of northernand eastern India.The highest temperature in the past 24 hours was 47℃ at Ganganagar city, in Rajasthan state.Summer temperatures have been 4℃～6℃ above normal over most parts of northern and central India since March, weather officials said.In the eastern state of Orissa, authorities have decided to shut down schools from next Tuesday, advancing the annual summer holiday.Authorities said they were investigating reports of 53 deaths from various parts of the state.“District collectors have been asked to investigate and submit reports on other deaths”， Bhimsen Gochhayat, a government official said. Other deaths were reported from northern state of Uttar Pradesh and central Madhya Pradesh states.India is expected to produce about 82 million tons of wheat in 2009～2010, but there could be a shortage of 1 million—1.5 million tons due to the heatwave, said Veena Sharma, Secretary General of the Roller Flour Millers Federation of India. “Most of the harvesting is over, but there definitely will be a slight shortage of 1 million—1.5 million tons due to the extreme weather conditions”，she told Reuters.India is relying on an abundant wheat crop to make up for a 14.2% drop in rice output, the major summersown grain, marred by the worst monsoon(季风) in 37 years last year. Weather officials said with summer temperatures in India set to remain above average, there were hopes of heavy rain at the start of the monsoon that would help early sowing of rice, soybeans and lentils.36．The purpose of the passage is ________．A．to tell a piece of news of a heatwaveB．to record the highest temperature in IndiaC．to report the deaths in the heatwaveD．to inform people of a drop of rice output37．Which of the following is TRUE according to the passage?A．The highest temperature in the history of India is 44℃.B．Schools were closed because of the hot weather throughout India.C．India is expected to produce about 82 million tons of rice in 2009～2010.D．India has a good harvest of wheat while the rice output is decreasing.38．The underlined word “marred” in the last paragraph probably means “________”．A．dropped B．damagedC．blown D．followed39．What is the main idea of the passage?A．A severe heatwave would continue over India.B．At least 80% people were killed in the disaster this month.C．A severe heatwave swept India with a great loss.D．A slight shortage of 1 million—1.5 million tons of wheat is due to the heatwave.Ⅳ.短文填词When you visit London, one of the first things you will see is Big Ben, the famous clock which can be 40.________ all over the world on the B B C. 41.________ the Houses of Parliament had not been 42.b________ down in the great fire of 1834, the great clock would never have been built. Big Ben takes 43.i________ name from Sir Benjamin Hall who was responsible 44.________ the making of the clock. It is not only of great size, but is extremely accurate as well. 45.________ (官员) from Greenwich Observatoryhave the clock 46.c________ twice a day. Big Ben has rarely gone wrong. Once, however, it 47.________ (不能) to give the 48.c________ time. A painter who had been working on the tower hung a pot of paint on one of the 49.________ (指针) and slowed it down!参考答案课时作业(六)Ⅰ.1.D 第一个空考查belong的用法，belong为不及物动词，故应用where引导地点状语从句；第二个空考查定语从句，which引导定语从句，作介词for的宾语。

南极的气候特征英语作文

南极的气候特征英语作文Title: Climate Features of Antarctica。

Antarctica, the southernmost continent on Earth, is renowned for its extreme climate conditions. Its unique geographical position, coupled with various atmospheric phenomena, contributes to its distinct climate features. In this essay, we will delve into the climate characteristics of Antarctica.Firstly, Antarctica is widely known for its frigid temperatures. The continent holds the record for the lowest temperature ever recorded on Earth, reaching a bone-chilling -89.2 degrees Celsius (-128.6 degrees Fahrenheit). This extreme cold is primarily attributed to its high latitude and the presence of the Antarctic ice sheet, which reflects sunlight away, resulting in minimal warming of the surface.Secondly, Antarctica experiences drastic seasonalvariations in daylight due to its location near the South Pole. During the austral summer, which spans from December to February, the continent experiences continuous daylight for several months, known as the "midnight sun" phenomenon. Conversely, during the austral winter, from June to August, Antarctica plunges into darkness for months, with the sun barely rising above the horizon. These prolonged periods of daylight and darkness significantly influence thecontinent's climate and ecosystem.Thirdly, Antarctica is characterized by strong winds, particularly along its coastlines. The infamous katabatic winds, generated by the flow of cold, dense air from the interior ice sheet towards the coast, can reach speeds exceeding 200 kilometers per hour (124 miles per hour). These powerful winds contribute to the formation of massive icebergs and shape the unique landscape of the Antarctic region.Moreover, Antarctica is one of the driest continents on Earth in terms of precipitation. Most of the interior receives very little snowfall, with the majority ofprecipitation occurring along the coastal regions. The cold temperatures cause the air to hold minimal moisture, resulting in limited cloud formation and precipitation. However, Antarctica's coastal areas may experiencesignificant snowfall and blizzards, further adding to the continent's icy landscape.Additionally, Antarctica plays a crucial role in regulating global climate patterns through its vast ice sheets and surrounding ocean currents. The Antarctic ice sheet, comprising approximately 90% of the world's ice and 70% of its freshwater, helps maintain the Earth's energy balance by reflecting sunlight back into space. Furthermore, the cold, dense waters surrounding Antarctica drive ocean currents that influence climate systems worldwide, such as the Antarctic Circumpolar Current.In conclusion, Antarctica's climate is characterized by extreme cold, seasonal variations in daylight, strong winds, minimal precipitation, and significant ice cover. These unique climate features make Antarctica a challenging yet fascinating environment to study. Understanding theintricacies of Antarctica's climate is crucial for unraveling its role in the Earth's climate system and predicting future climate changes on a global scale.。

散度高原季风指数相关英文文献

散度高原季风指数相关英文文献The Loess Plateau is an area in northwest China that is characterized by its unique geographical and climatic features. The region is known for its high altitude andarid climate, which makes it susceptible to the effects of the East Asian monsoon. In recent years, researchers have become increasingly interested in studying the relationship between the Loess Plateau and the East Asian monsoon, and one of the key indicators used in these studies is the plateau's monsoon climate index.The monsoon climate index is a measure of the strength and variability of the monsoon in a particular region. It takes into account factors such as precipitation, temperature, and wind patterns to assess the overall impact of the monsoon on the local climate. In the case of the Loess Plateau, the monsoon climate index is particularly important because of the region's vulnerability to drought and desertification. By understanding the patterns and trends of the monsoon, researchers and policymakers can better predict and mitigate the potential impacts of climate change on the plateau.One of the most widely used monsoon climate indices is the Monsoon Trough Index (MTI), which is based on the position and intensity of the monsoon trough. The MTI is calculated using data from weather stations and satellite observations, and it provides a comprehensive picture of the monsoon's influence on a given area. In the case of the Loess Plateau, the MTI can help researchers understand how the monsoon affects the region's precipitation patterns, which in turn can inform strategies for water resource management and agricultural development.In addition to the MTI, researchers also use the Palmer Drought Severity Index (PDSI) to assess the impact of the monsoon on the Loess Plateau. The PDSI takes into account factors such as temperature, precipitation, and soil moisture to determine the severity of drought conditions in a given area. By combining the MTI and the PDSI, researchers can gain a more comprehensive understanding of how the monsoon influences the climate of the Loess Plateau and how it may change in the future.Overall, the study of the monsoon climate index in the context of the Loess Plateau is an important area ofresearch with implications for both scientificunderstanding and practical applications. By better understanding the relationship between the plateau and the East Asian monsoon, researchers can contribute to effortsto mitigate the impacts of climate change and promote sustainable development in the region.散度高原是中国西北部的一个地区，以其独特的地理和气候特征而闻名。

215494098_全球各主要季风区湿季和干季降雨变化趋势、变率和偏度特征的对比

农业灾害研究 2023,13(4)全球各主要季风区湿季和干季降雨变化趋势、变率和偏度特征的对比骆鉴洲，翁锦文，骆蔚健，王磊广东海洋大学海洋与气象学院，广东湛江 524088摘要对比了1979—2020年全球8个主要季风区湿季和干季降雨的长期变化趋势、变率和偏度特征。

主要结果如下：（1）在长期变化趋势方面，东亚、西北太平洋和北非季风的湿季降雨以及印度季风的干季降雨呈现显著的增加趋势，而北美和南美季风的干季降雨和南美季风的湿季降雨呈现显著的下降趋势。

东亚和北非季风（南美季风）的湿季—干季降雨差值呈现显著的增加（下降）趋势。

（2）在变率方面，北美和北非季风湿季和干季降雨的方差在2000—2020年（P2时期）要小于1979—1999年（P1时期）；南非和澳洲季风湿季和干季降雨的方差在P2时期要大于P1时期；东亚、西北太平洋和南美季风降雨方差的变化在湿季和干季存在不一致性，湿季（干季）降雨的方差在P2时期增加（减小）。

（3）在偏度方面，东亚、印度、澳洲和南非季风干季降雨和东亚季风湿季降雨的偏度值在P2时期增加；而西北太平洋季风干季降雨和北非季风湿季降雨的偏度值在P2时期减小。

关键词全球季风；季风降雨；变化趋势；偏度；方差中图分类号：P467 文献标识码：B 文章编号：2095–3305(2023)04–0129-03全球各主要季风区湿季和干季降雨的变异与农业生产活动息息相关。

全球季风区降雨的变异受到了广泛关注[1-7]。

围绕全球季风降雨变异的特征、机制和预报等方面的研究具有重要的现实与科学意义。

全球包括多个不同的季风区，这些不同季风区降雨的变异主周期，以及与El Niño-Southern Oscillation (ENSO)之间的关系等方面均存在区域差异性[8-9]。

本研究将对比全球各主要季风区湿季和干季降雨在长期变化趋势、变率和偏度特征等方面可能存在的区域差异。

1 数据和方法本研究使用的降雨数据来自全球GPCP降水数据[10]，数据的时间范围为1979—2020年。

气候现象英语作文高中

气候现象英语作文高中The Enigma of the Monsoon: A Climate PhenomenonThe monsoon, a unique climate phenomenon, holds a fascinating position in the global weather patterns. It is a seasonal reversal of wind direction that brings about dramatic changes in weather conditions, often resulting in extreme climatic events.The monsoon typically occurs in tropical and subtropical regions, and it is marked by a shift in wind direction from inland to coastal areas, bringing with it heavy rainfall and significant temperature changes. This reversal in wind direction is driven by the difference in heating rates between land and water masses, which creates pressure gradients that direct the flow of air.The most famous monsoon systems are the Asian monsoon and the Indian monsoon, which bring life-giving rains to vast regions of Asia. These monsoons are responsible for the unique agricultural cycles of these regions, supporting a diverse array of crops and ecosystems. However, they are also known for their unpredictability, often resulting in flooding and droughts that can wreak havoc on human settlements and natural habitats.The monsoon's impact on the environment is profound. It not only shapes the landscapes of the regions it affects, but also influences the distribution of biodiversity and the patterns of human settlement. The regular cycles of the monsoon have also been a key factor in the historical development and cultural identities of many regions.In recent years, climate change has posed a significant threat to the stability of monsoon systems. Global warming has altered the patterns of rainfall and temperature, making the monsoons more unpredictable and extreme. This, in turn, has had profound implications for agriculture, water resources, and human settlements in monsoon-dependent regions.In summary, the monsoon is a remarkable climate phenomenon that continues to fascinate and challenge scientists and communities alike. Its complexity and unpredictability highlight the need for a deeper understanding of its mechanisms and a more nuanced approach to managing its impacts in the face of climate change.。

介绍季风气候英语作文

介绍季风气候英语作文英文回答：I would like to introduce the monsoon climate. The monsoon climate is a type of climate that is characterized by a seasonal reversal of wind direction. This reversal of wind direction brings about significant changes in precipitation patterns, temperature, and humidity.For example, in South Asia, the monsoon seasontypically occurs from June to September. During this time, warm, moist air from the Indian Ocean is carried inland by the southwest monsoon winds, bringing heavy rainfall to the region. This rainfall is crucial for agriculture and helps to sustain the livelihoods of millions of people in the region.On the other hand, during the dry season, which occurs from October to May, the northeast monsoon winds bring dry air from the continent, resulting in little to no rainfall.This can lead to drought conditions and water shortages, which can have a significant impact on agriculture and the economy.Overall, the monsoon climate plays a crucial role in shaping the environment and livelihoods of people inregions where it occurs.中文回答：我想介绍一下季风气候。

中国气候的英语作文

China is a vast country with a diverse range of climates due to its extensive geographical span.The climate in China varies significantly from north to south and east to west,influenced by factors such as latitude,altitude,and proximity to the ocean.Here is an essay on the climate of China,highlighting its main features and the implications for the countrys environment and people.Title:The Diverse Climate of ChinaChina,with its vast territory,is home to a multitude of climates that contribute to its rich natural landscapes and cultural diversity.The countrys climate can be broadly categorized into several types,each with its own distinct characteristics and influences on the local environment and inhabitants.Tropical Monsoon ClimateIn the southernmost regions of China,such as Hainan Island and the southern parts of Guangdong and Guangxi,the climate is characterized as a tropical monsoon.This climate is marked by high temperatures and heavy rainfall,particularly during the summer months.The warm and humid conditions are conducive to the growth of tropical crops like rice,tea,and rubber,and support a rich biodiversity in the regions forests.Subtropical Monsoon ClimateMoving northward,the eastern coastal regions of China,including the Yangtze River Delta and the southeastern provinces,experience a subtropical monsoon climate.This climate is characterized by hot,humid summers and mild,dry winters.The distinct seasons allow for a variety of agricultural activities,with rice,wheat,and a variety of fruits and vegetables being cultivated throughout the year.Temperate Monsoon ClimateIn the northern parts of China,such as the North China Plain and the Northeast,the climate is temperate monsoon.The summers are warm and rainy,while the winters are cold and dry.This climate is suitable for crops like wheat,corn,and soybeans,and the region is known for its fertile soil and productive agricultural lands.Continental ClimateIn the far northwest of China,the climate is predominantly continental,with extreme temperature variations between summer and winter.This region,which includes Xinjiang and Inner Mongolia,experiences hot summers and bitterly cold winters.The dry conditions are ideal for pastoralism,with livestock farming being a significant economic activity in these areas.Alpine ClimateThe highaltitude regions of China,such as Tibet and the western parts of Sichuan,have an alpine climate.The climate is characterized by low temperatures,high levels of precipitation,and a short growing season.The harsh conditions have led to the development of unique agricultural practices,such as terrace farming and the cultivation of hardy crops like barley and potatoes.Impact on Agriculture and SocietyThe diverse climate of China has a profound impact on its agriculture,with different regions being suited to the cultivation of various crops.This diversity has also shaped the countrys culinary traditions,with regional cuisines reflecting the local climate and available ingredients.Moreover,the climate influences the lifestyle and culture of the Chinese people.For example,the hot and humid summers in the south have led to the development of cooling practices such as airdrying foods and the use of cooling herbs in cooking.In contrast,the cold winters in the north have given rise to the tradition of eating hot pot and other warming foods.ConclusionChinas climate is a complex tapestry,woven with threads of tropical,subtropical, temperate,continental,and alpine conditions.This diversity not only enriches the countrys natural landscape but also shapes its agricultural practices,culinary traditions, and cultural identity.Understanding the climate of China is essential for appreciating the complexity and beauty of this ancient civilization.。

关于墨西哥的天气英语作文

Mexico,a country located in North America,is known for its diverse climate due to its varied geography.The weather in Mexico can be quite different depending on the region you are in.Heres an overview of the weather patterns you might expect:1.Tropical Climate:Coastal areas along the Gulf of Mexico and the Pacific Ocean experience a tropical climate.This region is characterized by high temperatures and humidity throughout the year,with an average temperature ranging from25to30degrees Celsius77to86degrees Fahrenheit.The rainy season typically occurs from June to October,with occasional hurricanes.2.Arid Climate:The northern regions of Mexico,particularly the areas surrounding the Chihuahuan Desert,have an arid climate.These areas experience hot summers with temperatures that can exceed40degrees Celsius104degrees Fahrenheit and cool winters with temperatures dropping to around0degrees Celsius32degrees Fahrenheit.Rainfall is scarce,making the region quite dry.3.Temperate Climate:The central highlands of Mexico,including the capital city of Mexico City,have a temperate climate.The weather here is mild with less humidity. Summers are warm with temperatures around25degrees Celsius77degrees Fahrenheit, while winters can be cool with temperatures dropping to around10degrees Celsius50 degrees Fahrenheit.Rainfall is moderate and evenly distributed throughout the year.4.Cold Climate:The highest elevations in Mexico,such as the Sierra Madre mountain ranges,experience a cold climate.These areas have lower temperatures,especially during the night,and can receive snowfall during the winter months.The average temperature can drop to below freezing,especially at higher altitudes.5.Marine West Coast Climate:The Pacific coast of Mexico has a marine west coast climate,with mild temperatures and high humidity.The weather is generally pleasant with average temperatures around20to25degrees Celsius68to77degrees Fahrenheit. The rainy season here is similar to the tropical areas,occurring from June to October.6.Monsoon Influence:Some parts of Mexico,particularly the southern regions,are influenced by the monsoon,which brings heavy rainfall during the summer months.This can lead to flooding in some areas.In conclusion,Mexicos weather is as diverse as its landscapes,offering a range of climates from tropical to arid,temperate to cold.Whether you prefer the heat of the tropics or the coolness of the highlands,Mexico has a climate to suit every preference.Just remember to check the local weather forecast before you travel to ensure you are prepared for the conditions you will encounter.。

海盐季风的英语

海盐季风的英语The monsoon season in Haiyan is a time of transformation and renewal. It is a period when the coastal town experiences a dramatic shift in weather patterns, bringing with it a change in the atmosphere and the landscape.As the summer months approach, Haiyan is graced by the warm and gentle breezes of the monsoon winds. These winds, originating from the Indian Ocean, carry with them the life-giving rains that nourish the land and its inhabitants. The air becomes heavy with moisture, and the skies are often overcast, signaling the arrival of the rainy season.The monsoon rains are a blessing for Haiyan, as they replenish the water sources and ensure a bountiful harvestfor the local farmers. The rice paddies, a staple of the region's agriculture, thrive under the nourishing showers, and the lush greenery becomes a testament to the monsoon's generosity.However, the monsoon also brings challenges. The heavy rains can sometimes lead to flooding, and the strong winds can disrupt daily life. Yet, the people of Haiyan areresilient and have learned to adapt to the whims of the monsoon. They prepare their homes and fields, ensuring that they are ready to face whatever the season may bring.Despite the challenges, the monsoon season is a time ofcelebration in Haiyan. It is a reminder of the cycle of life and the importance of embracing change. The people come together to celebrate the arrival of the monsoon with traditional festivals and ceremonies, expressing their gratitude for the life-sustaining rains.As the monsoon winds gradually recede, they leave behind a refreshed and revitalized Haiyan. The town emerges from the monsoon with a renewed sense of vitality, ready to face the challenges and opportunities of the coming months.In conclusion, the monsoon season in Haiyan is a time of both challenge and opportunity. It is a testament to the resilience and adaptability of the people who call this coastal town home, and a reminder of the power and beauty of nature's cycles.。

Monsoon Meteorology

Fig 6-28 in Ramage
•India IND •West Africa WAFR •East Africa EAFR •Southeast Asia SEASIA •Australia AUS
Where don’t monsoons happen?
• South America
– 1. Cold upwelling means that the land is ALWAYS warmer than the surrounding oceans.
• South America
– 3. In the NH, SAMER doesn’t extend to regions of subsidence (which favor heat low formation).
Where don’t monsoons happen?
• Mexico, SW US
Heat Lows
500mb 700mb 850mb 1000mb
Polar Highs
500mb 700mb 850mb 1000mb
Polar Highs
500mb 700mb 850mb 1000mb
Polar Highs
500mb 700mb 850mb 1000mb
Polar Highs
Monsoon Regions
The prevailing wind needs to be reasonably robust.
Monsoon Regions
Monsoons are NOT just a shift in the storm track, bringing sequences of highs and lows.

热带季风及其特点英文作文

热带季风及其特点英文作文英文：Tropical monsoon is a weather phenomenon characterized by seasonal reversal of winds accompanied by corresponding changes in precipitation. It has distinct features that influence the climate of regions where it occurs. 。

During summer, warm air rises over land, creating an area of low pressure, while cooler air from the ocean flows towards the land, creating a moisture-laden wind. This convergence of winds brings heavy rainfall, often resulting in floods and lush vegetation growth. In contrast, during winter, the situation reverses. Cooler, denser air over the land creates a high-pressure zone, causing winds to blow from land to sea. This period is usually dry, with little to no rainfall.One of the key characteristics of tropical monsoon climates is their seasonality. Regions experiencing thisclimate type typically have a distinct wet and dry season. For example, in parts of Southeast Asia, such as Thailand and Vietnam, the wet season usually occurs from May to October, while the dry season spans from November to April. This seasonal variation greatly influences various aspects of life, including agriculture, tourism, and daily activities.Moreover, tropical monsoon climates often exhibit high humidity levels, especially during the wet season. The combination of heat and moisture creates a humid and uncomfortable environment, which can be challenging for both locals and visitors. However, this high humidity also supports diverse ecosystems, contributing to the richness of biodiversity in these regions.In terms of agriculture, the seasonal rainfall patterns of tropical monsoon climates play a crucial role. Farmers rely on the onset of the monsoon rains to cultivate crops, and the timing and amount of rainfall directly impact crop yields. For instance, in India, the arrival of the southwest monsoon is eagerly awaited as it marks thebeginning of the planting season for crops like rice, sugarcane, and cotton.Overall, tropical monsoon climates are characterized by their distinct wet and dry seasons, high humidity levels, and significant influence on agriculture and daily life.中文：热带季风是一种季节性风向逆转伴随着相应降水变化的气象现象。

回南天英文介绍

回南天英文介绍In the southern regions of China, a unique meteorological phenomenon known as "HuiNanTian" occurs during the transition from winter to spring. Also known as the "return of southern moisture," HuiNanTian is marked by a significant increase in humidity, often accompanied by foggy, overcast skies. This article aims to introduce this fascinating climatic event, exploring its causes, characteristics, and impacts on daily life.1. Causes of HuiNanTianHuiNanTian results from the complex interaction of several meteorological factors. Firstly, as the winter monsoon weakens and the spring monsoon begins to strengthen, the airflow over the southern regions of China becomes less directed and more turbulent. This allows moisture-rich air from the South China Sea to easily penetrate inland, leading to an increase in humidity levels.Secondly, during this period, the temperature difference between the land and the sea is significant. The relatively warm sea surface temperature leads to the evaporation of water into the atmosphere, further contributing to the humidity increase.Lastly, the presence of mountains and other geographical features in the southern regions of China can also affect the airflow and humidity levels, often causing the phenomenon to be more pronounced in specific areas.2. Characteristics of HuiNanTianHuiNanTian is typically characterized by high humidity levels, often exceeding 90%. This leads to foggy, overcast skies and a feeling of dampness in the air. The temperature during this period is generally mild, with daytime highs in the low to mid-teens Celsius and nighttime lows just above freezing.Another distinctive feature of HuiNanTian is the presence of "dew" or "hoarfrost" on surfaces such as grass, trees, and buildings. This is caused by the condensation of water vapor on cooler surfaces as the humidity levels rise.3. Impacts on Daily LifeHuiNanTian has both positive and negative impacts on daily life in southern China. On the one hand, the increase in humidity levels can be beneficial for agricultural activities, especially for crops that require high moisture content. The mild temperatures during this period are also ideal for outdoor activities such as hiking and picnicking.However, the high humidity can also lead to uncomfortable conditions for residents, causing their bodies to feel sticky and unrefreshing. It can also lead to increased mold growth and the spread of diseases such as flu and colds. Furthermore, the foggy weather can affect visibility and road safety, necessitating caution when driving or walking outdoors.ConclusionHuiNanTian is a unique meteorological phenomenon that occurs during the transition from winter to spring in the southern regions of China. Caused by a combination of meteorological factors and geographical features, it is characterized by high humidity levels and foggy skies. While it brings some benefits to agricultural activities and outdoor pursuits, it also poses challenges to residents in terms of discomfort and health concerns. Understanding and adapting to this climatic event is essential for maintaining a comfortable and healthy lifestyle in southern China during this period.。

(整理)英语科普小知识南北半球气温差异导致热带降水模式改变

One often ignored consequence of global climate change is that the Northern Hemisphere is becoming warmer than the Southern Hemisphere, which could significantly altertropical precipitation（降水，沉淀） patterns, according to a new study by climatologists from the University of California, Berkeley, and the University of Washington, Seattle. Such a shift could increase or decrease seasonal rainfall in areas such as the Amazon, sub-Saharan Africa or East Asia, leaving some areas wetter and some drier than today."A key finding is a tendency to shift tropical rainfall northward, which could mean increases in monsoon weather systems in Asia or shifts of the wet season from south to north in Africa and South America," said UC Berkeley graduate student Andrew R. Friedman, who led the analysis."Tropical rainfall likes the warmer hemisphere," summed up John Chiang, UC Berkeley associate professor of geography and a member of the Berkeley Atmospheric Sciences Center. "As a result, tropical rainfall cares a lot about the temperature difference between the two hemispheres."Chiang and Friedman, along with University of Washington colleagues Dargan M. W. Frierson and graduate student Yen-Ting Hwang, report their findings in a paper now accepted by the Journal of Climate, a publication of the American Meteorological Society. It will appear in an upcoming issue.Generally, rainfall patterns fall into bands at specific latitudes, such as the Intertropical Convergence Zone. The researchers say that a warmer northern hemisphere causes atmospheric overturning to weaken in the north and strengthen in the south, shifting rain bands northward.The regions most affected by this shift are likely to be on the bands' north and south edges, Frierson said."It really is these borderline regions that will be most affected, which, not coincidentally, are some of the most vulnerable places: areas like the Sahel where rainfall is variable from year to year and the people tend to be dependent on subsistence agriculture," said Frierson, associate professor of atmospheric sciences. "We are making major climate changes to the planet and to expect that rainfall patterns would stay the same is verynaïve."一个经常被忽略的全球气候变化的后果是，北半球比南半球，这可能显着改变热带降水（降水，沉淀）模式，根据一项新的研究由大学加州大学伯克利分校的气候学家温暖，西雅图华盛顿大学的。

听力精听笔记

Official 33 Set 1 University's Policies Regarding Dorm Rooms Maintenance n.维修electric heaters 电热器went out ,out 熄灭Sofa n.沙发kept up 吵醒，跟上Custodian n. 管理人Weird a.奇怪的fill out this form 填好这个表格Crew n. 工作人员Seriously ad. 认真的说take off 起飞，脱掉，突然离开Official 11 Set 4 To Join the Interview CommitteeThat's why I want to talk to you 那是我为什么要和你谈话的原因Hire v.应聘hiring process 应聘流程but what's that got to do with me? 但是那和我有什么关系呢？Qualified a. 有资格的a committee of professors and students 一个教授和学生的委员会give a talk 做一次演讲academic interests 学术兴趣-- 学术领域Make sense 合理a student representative 一个学生代表grad school application 研究生学校申请a schedule of the applicant's visits 一个申请者的日程表what time the talk is 演讲的时间the formal discussion 正式的讨论right after. 之后It's going to be a tough decision. 这将是一个艰难的决定is interested in 对...感兴趣the copy of the schedule 日程表的复印件Official 12 Set 4 A Problem of the TA's PayrollPaycheck n.薪水That's odd那很奇怪Payroll 工资总额at the end of August 在八月底two pay periods 两个支付周期There was a problem in processing some of the graduate students' payroll paper work, ‘cause their computer program crashed 崩溃after all the information was processed 处理, and some people’s information couldn’t be retrieved.恢复Fax n.传真fill out those forms 填写这些表格And then what? ...well... what I really need to know is... how long till I get some money? I'm already a month behind on my bills and my tuition's due soonIt should. I will double-check 核实with the payroll departmentIs there any way I could get paid 领工资sooner?based on past experiences, you shouldn't count on it 基于以前的工作经验，有不应该期望它I know it's not your fault, and that you're doing everything you can.我知道这不是你的错，有在尽力帮助我Official 02 Set 6 Bode's LawMultiplying v.乘Decimal n. 十进位From prep. 到，离，从the distance of the planets from the Sun 行星到太阳的距离Tantalizingly ad. 诱人地，令人着急地tantalizingly close 很接近The next planet out 下一个行星出现The next planet out, Uranus - after Saturn. And look, Uranus fits in the next spot in the pattern pretty nicely, um, not perfectly, but close.the missing object 丢失的天体Validity a.合法性有效性Ceres n. 谷神星star-like appearance 星型特征Greek n. 希腊文too faint to be a planet 作为一个行星太暗Form v. 形成That's how the asteroid belt was discovered. 这是小行星带如何发现的Official 03 Set 6 SpectroscopySpectroscopy n.光谱学Balloon n.气球Emitted v.发出Before we get into讲到that, though, it’s probably a good thing to back up 补充背景知识，-支持a bit.crystal prisma continuous band of rainbow colors 一个连续的彩虹颜色的色带Anyone wanna take a stab at尝试the scientific term for visible light Uranium n.Stab 动词刺伤spreads away发出from its sourcea beam of sunlight 一束光the colors bleed into相互融合each other,Violet n. 紫色Magnified v.放大spreading out 发出kinda randomly placed 有点随机排列break it up 分开stands for 代表Patterns n.方案，图案spectral patterns=spectrograph 光谱图案Well, a kind of spectroscopic library of elements一套各元素的光谱集合was compiled using flame tests火焰测试a chemical fingerprint 化学印记in a pure gas flame 在纯气焰中chemical makeup 化学组成be familiar with熟悉the Greek word for sun, by chance偶然Official 05 Set 3 Moon Landingpinpoint the moon's age. 准确测出月球的年龄on the far side of the moon 在月球的远边color-coated 着色的lunar missions 月球任务topographical map 地形图Purples=violet 紫色Depth n. 深度we especially want to know if是否any of the mantle, the layer beneath the crust, was exposed by the impact.planet formation 行星形成later meteor showers 后来的流星雨was more reflective than expectedby inference 据推测Perpetually ad.永久地in shadow 在阴影处primitive life 原始的生命Astronauts n.宇航员It could also be broken down into被分解成its component parts - oxygen and hydrogena self-sustaining moon base 一个自给自足的月球基地a mining camp perhaps or a departure point for further space explorationOfficial 01 Set 3 Uranium-Lead DatingDating techniques 年代测定法Grand Canyon 大峡谷a vast desert 一个大沙漠flattened out 变平conventional wisdom 传统的观点Refinements 改良Uranium-Lead Dating 铀-铅测定法That's really eye-opening news 瞠目结舌的how did that sand end up so far west? 沙子是如何移动到西边的呢？grain type within sandstone 砂砾内部的纹理类型You can do other things too, like look at the wind or water that brought the grains to their location and figure out which way it was flowing测出它的流向grains of Zircon 锆石的纹理dating purposes 年代测定的目的starts off 开始于Crystallizes v.使结晶，使凝结Once you do that, you can compare the age of the Zircon in the sandstone in your sample to the age of the Zircon in the mountains.an increasingly popular dating method 一个越来越受欢迎的年代测定方法joined together and only split apart relatively recently 始合近分more conclusively 根具有决定性Official 04 Set 5 Moving Rocksyou need to know about more than just rocks and the structure of solid matter.不仅仅long trails 长长的痕迹But nobody has been able to figure out how they are moving because no one has ever seen it happen. 知道tyre tracks 轮胎痕迹a bulldozer 推土机Most of the rocks move in the same direction as the dominant wind pattern from southwest to northeast. 盛行风的主要模式How can that be ？那怎么可能？One team of scientists flooded an area of the desert with water, then try to establish how much wind force would be necessary to move the rocks Ever! Not on this planet.多大的风力It's possible that rain on the desert floor could turn to thin sheets of ice when temperatures drop at night.embedded in 嵌入Tilting v. 倾斜Shifting v.移动Vibrate v. 震动why don't scientists just set up video cameras to record what actually happens?So why can't researchers just live there for a while until they observe the rocks' moving?Official 06 Set 6 Climate Change in Sahara DesertNARRATOR：Listen to part of a lecture in an earth science class.MALE PROFESSOR：We're really just now beginning to understand how quickly drastic climate change can take place.We can see past occurrences of climate change that took place over just a few hundred years.Take uh... the Sahara Desert in Northern Africa.The Sahara was really different 6,000 years ago.I mean, you wouldn't call it a tropical paradise n. 天堂or anything, uh... or maybe you would if you think about how today in some parts of the Sahara it... it only rains about once a century.Um... but basically, you had greenery名词，绿色植被and you had water. And what I find particularly interesting and amazing really, what really indicates how un-desert-like the Sahara was thousands of years ago was something painted on the rock, pre-historic art, hippopotamuses名词，河马.As you know hippos need a lot of water and hence? Hence what? FEMALE STUDENT：They need to live near a large source of water year round.MALE PROFESSOR：That's right.MALE STUDENT：But how is that proved that the Sahara used to be a lot wetter?I mean the people who painted those hippos, well, couldn't they have seen them on their travels?MALE PROFESSOR：Okay, in principle they could, Karl. But the rock paintings aren't the only evidence.Beneath the Sahara are huge aquifers,名词，含水层basically a sea of fresh water that's perhaps a million years old, filtered through 动词，过滤rock layers.And... er... and then there is fossilized pollen 花粉化石, from low shrubs and grasses that once grew in the Sahara.In fact these plants still grow, er... but hundreds of miles away, in more vegetated areas.Anyway, it's this fossilized pollen along with the aquifers and the rock paintings—these three things are all evidence that the Sahara was once much greener than it is today, that there were hippos and probably elephants大象and giraffes 长颈鹿and so on.MALE STUDENT：So what happened?MALE PROFESSOR：How did it happen?Well now we're so used to hearing about how human activities are affecting the climate, right; but that takes the focus away将注意力转移到from the natural variations in the earth climate, like the Ice Age, right? The planet was practically covered in ice just a few thousand years ago. Now as far as the Sahara goes, there is some recent literature that points to the migration of the monsoon 名词，季风in that area.FEMALE STUDENT & MALE STUDENT：[audible] “huh?”MALE PROFESSOR：What do I mean?Okay, a monsoon is a seasonal wind that can bring in a large amount of rainfall 名词，降雨量.Now if the monsoon migrates, well, that means that the rains move to another area, right?So what caused the monsoon to migrate?Well, the answer is: the dynamics of earth's motions地球运动的动力学the same thing that caused the Ice Age by the way.[slowly, wanting every word to sink in] The earth's not always the same distance from the sun, and it's not always tilting toward the sun at the same angle.There are slight variations in these two parameters名词，参数.They're gradual variations but their effects can be pretty abrupt形容词，突然的, and can cause the climate to change in just a few hundred years. FEMALE STUDENT：That's abrupt?MALE PROFESSOR：Well, yeah, considering that other climate shifts take thousands of years, this one is pretty abrupt.So these changes in the planet's motions, they caused the climate to change; but it was also compounded.[key point] What the Sahara experienced was um... sort of runaway drying effect.As I said the monsoon migrated south—there was less rain in the Sahara.The land started to get drier, which in turn caused huge decrease in the amount of vegetation, because vegetation doesn't grow as well in dry soil, right?And then, less vegetation means the soil can't hold water as well—the soil loses its ability to retain water when it does rain.So then you have less moisture to help clouds form, nothing to evaporate for cloud formation.And then the cycle continues—less rain, drier soil, less vegetation, fewer clouds, less rain etc. etc.. etcetera[ɪt'sɛtərə]MALE STUDENT：But, what about the people who made the rock paintings?MALE PROFESSOR：Good question. Well, no one really knows.But there might be some connections to ancient Egypt.At about the same time that the Sahara was becoming a desert... hmm... 5,000 years ago, Egypt really began to flourish out in the Nile River valley.And that's not that far away.So it's only logical to hypothesize that a lot of these people migrated to the Nile valley when they realized that this was more than a temporary drought.And some people take this a step further--and that's okay, that'sscience--and they hypothesize that this migration actually provided an important impetus in the development of ancient Egypt.[intrigued, not skeptical] Well, we'll stay tuned on that.Official 09 Set 3 Shrubs in TundraCelsius n.摄氏度flat land 平坦地面Thaws v. 融化Permafrost v.永冻层being low to the ground protects them from the cold and windshrub-free tundra 无灌木苔原how can increased temperatures in the winter and spring increased shrub growth in the summer?Active a.活跃的what’s responsible for the growth of shrubs in the summer =result in what about run-off in the spring, when the snow finally melts?insulating effect of snow 雪的隔热效果Prairie 草原semiarid grassland and tall grass prairies.半干旱草地和草丛平原Official 10 Set 5 Phosphorus CycleScarcity v.稀缺性The rocks get broken down into smaller and smaller particles as they’re weathered侵蚀，风化的mined rocks 矿石We call all of this the land phase of the Phosphorus cycle 陆地P循环阶段empty into 倾泻gets absorbed 被吸收excessive fertilizers 过多的肥料getting clogged with organisms 被有机物所堵塞Several current studies are looking at these effects, and I really do hope we can find the way to deal with this issue before these ecosystems areadversely affected 不利的影响interrupt the normal process is fishing 捕鱼业gets mixed into ocean sediments 混合all over again 再次submerged rock 海底岩石It can move from the land or from the oceans to the atomosphere and vice versa 反之亦然Official 11 Set 5 Landscape & Climateand so forth 等等citrus industry 柑橘类工业Crops n.庄稼A bad bout of cold weather, a long spell of frosts could ruin a farmer's entire crop 一个坏天气these citric growers 这些柑橘的种植者marshy, swampy 沼泽的Farmers moved south. But the land was not suitable for farmingyou have to drain the water from the land 此句but为线索词，divert the water sources such as rivers.转移，转到Susceptible 易受影响的And what I, another think is that the loss of the wetlands has created the situation where the local temperatures in the area are now slightly different, slightly colder than they were 100 years ago, before the wetlands were drained.And freezing causes frosts, which kill crops 霜personally subscribe to 从个人角度Official 05 Set 5 SpectroscopyBe coming out 出来Spectroscopy is the study of the interaction between matter and light spectral signature 物与光的相互作用in a lot of different disciplines 学科Curator n.馆长，管理人Original a.原始的Canvas n. 画布Brushstrokes n 绘画的技巧Pigments n. 颜料Paints n.绘画颜料Varnishes n.涂清漆的面an infrared microscope 红外显微镜ultraviolet light 紫外线ow spectroscopy has a very distinct advantage over previous methods of analyzing artworks because it’s not invasive侵略性的—you don’t have to remove big chips of paint to do your analysis, which is what other methods require.Then, if we want to undo复原，解开some bad restoration attempts, we can determine what kind of process we can use to remove them—to dissolve溶解the paint and uncover去除the originalDeteriorated 变坏，恶化Official 21 Set 3 Software Developmentsoftware engineering 软件工程Cycle n.循环，周期the software development cycle 软件发展周期Ah, uh, th-the quality of a software product often relies heavily on how well it's been tested. Liz? 严重依赖just a quick thing 仅仅是一个小小的问题the computer's circuits 计算机回路a five-centimeter-long moth 一个5cm长的蛾子Debugged n. 调试Embarrassing 尴尬的different mentalities 不同的心态a bit of friction 一点儿小摩擦a couple of years ago 两三年前Fixed 修理，修复，固定should be fixed 应该被修复the conflict 冲突Literally-the testers and the developers sat on opposite sides of the table 准确的说the developers were very defensive about the feedback 对保守putting up walls 对立的局势So we were being proactive and effective So为线索词Official 43 Set 6 Electromagnetic Waveselectromagnetic wavesradio wavessound wavesSound waves are mechanical in natureinterplanetary spaceoscillations of the electromagnetichousehold or car radioConvert v.a pulse of radio waves every time it flashesbecause lightning strikes Earth constantlyhear the crackling from stormssunset or sunrisenatural waveguides,that's used to guide and direct waves.Some really interesting ones are called "whistlers."Whistlers come from lightning-generated radio waves that leave Earth's atmosphere and travel into Earth's magnetosphere before bouncing back down.a chirpy soundFeatures of different types of electromagnetic radiationOfficial 07 Set 3 Bats' Use of UltrasoundPara.1NARRATOR：Listen to part of a lecture in a biology class.Para.2FEMALE PROFESSOR：So, that is how elephant uses infrasound n.次声波.Now, let's talk about the other end of the acoustical spectrum声谱—sound that is too high for humans to hear--Ultrasound n.超声波Para.3Ultrasound is used by many animals that detect—and, some of them, send out发出—very high-frequency sounds.So, what's a good example? Yes, Carol.Para.4FEMALE STUDENT：[matter-of-factly, stating the obvious] Well, bats—since they are all blind a.blaɪnd 看不见的，瞎的, bats have to use sound for, you know, to keep from flying into 防止撞到things.Para.5FEMALE PROFESSOR：That's echolocation.Echolocation is pretty self-explanatory a.不言自明的: Using echoes—reflectedsound waves—to locate things…As Carol said, bats use it for navigation and orientation… and what else? Mike? Para.6MALE STUDENT：Well, finding food is always important—and I guess not becomingfood for other animals.Para.7FEMALE PROFESSOR：[light laugh]Right, on both counts.Avoiding other predators—and locating prey—uh, typically insects that fly around at night.Now, before I go on, let me just respond to something Carol was saying—this idea that bats are blind…Actually, there are some species of bats, the ones that don't use echolocation that do rely on their vision for navigation, but it is true that for many bats,their vision is too weak to count on.Para.8OK, so quick summary of how echolocation works.The bat emits these ultrasonic pulses超声波脉冲—very high-pitched高分贝soundwaves that we can’t hear—and then: they analyze the echoes—how the waves bounce back.Here, let me finish this diagram I started before the class.So the bat sends out these pulses, very focused bursts of sound, and echoes bounce back.You know, I don't think I need to draw in the echoes, your reading assignment for the next class—it has diagram shows this very clearly—so anyway as I was saying…Para.9By analyzing these echoes, the bat can determine, say, if there is wall in a cave that needs to avoid, and how far away it is.Another thing it uses the ultrasound to detect, is the size and shape of objects.For example, one echo they quickly identified is one they associate with moth 与有关（系）, which is common prey for a bat, particularly a moth beating its wings. However, moth happened to have major advantage over most other insects比大多数昆虫有很大的优势: they can detect ultrasound; this means that when the batapproaches, the moth can detect the bat's presence.So, it has time to escape to safety, or else they can just remain motionless. Since, when they stop beating their wings, they will be much harder for the bat todistinguish from辨别, oh a leaf or some other object.Para.10Now, we have tended to underestimate just how sophisticated the abilities ofanimals that use ultrasound are.In fact, we kind of assume 推断，假定that they were filtering a lot out—uh, the way asophisticated radar system can ignore echoes from stationary objects on the ground.information about, um, hillsor buildings that it doesn’t need…But bats, we thought they were filtering out this kind of information, because they simply couldn't analyze it.But, it looks as if we were wrong.Recently, there was this experiment with trees and a specific species of bats—a bat called the lesser spear-nosed bat.Para.11Now, a tree should be a huge and acoustical challenge for bat, right? I mean it got all kinds of surfaces with different shapes and angles n.角度.So, well, the echoes from a tree are going to be a mass of chaotic acoustic reflections, right? Not like the echo from a moth.So, we thought, for a long time, that bats stopped their evaluation at simply “that’s a tree.”Yet, it turns out that-that bats, or at least this particular species, can not only tell that it’s a tree, but can also distinguish between, say, a pine tree and a deciduoustree—like, a maple n 枫树., or an oak tree: just by their leaves—an-and when I say “leaves,” I mean pine needles 松针, too.Any ideas on how it would know that?Para.12MALE STUDENT：Well, like with the moth, could it be their shape?Para.13FEMALE PROFESSOR：You are on the right track痕迹，轨迹表示你的思路很对.It’s actually the echo of f all the leaves—as a whole—that matters.Now, think: A pine tree—with all those little, densely packed needles… those produce a large number of faint reflections in wh-what’s called a-a “smooth a. 光滑的” echo—the waveform is very even a. 均匀的…But an oak which has fewer but bigger leaves with stronger reflections, produces jagged wave 锯齿状的声波form, or what we called a rough echo.And these bats can distinguish between the two, and not just with trees, but with any echo that comes in a smooth or rough shape.Official 10 Set 2 WhalesPara.1NARRATOR：Listen to part of a lecture in a Marine Biology Class. Para.2FEMALE PROFESSOR：We know whales are mammals and that they evolved from land creatures.So the mystery is figuring out how they became ocean dwellers. Because until recently there was no fossil record of what we call "the missing link", that is evidence of species that show the transition between land-dwelling mammals and today's whales.Fortunately, some recent fossil discoveries have made the picture a little bit clearer.Para.3For example, a few years back in Pakistan, they found a skull of awolf-like creature.It's about fifty million years old.Scientists had seen this wolf-like creature before, but this skull was different.The ear area of the skull had characteristics seen only in aquatic mammals, specifically whales.Para.4Err, well, then also in Pakistan they found a fossil of another creature, which we call Ambulocetus natans.That's a mouthful,eh?The name Ambulocetus natans comes from Latin of course, and means "walking whale that swims".It clearly had four limbs that could have been used for walking.It also had a long thin tail, typical of mammals, something we don't see in today's whales.But it also had a long skeletal structure, and that long skeletal structure suggests that it was aquatic.Para.5And very recently, in Egypt, they found skeleton of Basilosaurus. Basilosaurus was a creature that we've already known about for over a hundred years.And it has been linked to modern whales because of its long whale-like body.But this new fossil find showed a full set of leg bones, something we didn't have before.The legs were too small to be useful.They weren't even connected to its pelvis and couldn't have supported its weight.But it clearly shows Basilosaurus’s evolution from land creatures.So that's a giant step in the right direction.Even better, it establishes Ambulocetus as a clear link between thewolf-like creature and Basilosaurus.Para.6Now these discoveries don't completely solve the mystery.I mean, Ambulocetus is a mammal that shows a sort of bridge between walking on land and swimming.But it also is very different from the whales we know today.So, really we are working with just a few pieces of a big puzzle.Para.7Emm, a related debate involved some recent DNA studies. Remember, DNA is the genetic code for any organism, and when the DNA from two different species is similar, it suggests that those two species are related.And when we compared some whale's DNA with DNA from some other species, we got quite a surprise.The DNA suggests that whales are descendants of the hippopotamus. Yes the hippopotamus! Well, that came as a bit of shock.I mean that a four-legged land and river dweller could be the evolutionary source of a completely aquatic creature up to twenty five times its size. Unfortunately, this revelation about the hippopotamus apparently contradicts the fossil record, which suggests that the hippopotamus is only a very distant relative of the whale, not an ancestor.And of course as I mentioned that the whales are descendant not from hippos but from that distant wolf-like creature.Para.8So we have contradictory evidence.And more research might just raise more questions and create more controversies.At any rate, we have a choice.We can believe the molecular data, the DNA, or we can believe the skeleton trail.But unfortunately, probably not both.Para.9Um, and there have been some other interesting findings from DNA research.For a long time, we assumed that all whales that had teeth, including sperm whales and killer whales were closely related to one another, and the same for the toothless whales, like the bule whale and other baleen whales.We assumed that they be closely related.But recent DNA studies suggest that's not the case at all.The sperm whale is actually closely related to the baleen whale, and it's only distantly related to the toothed-whales.So that was the real surprise to all of us.Official 14 Set 3 MicroclimateNARRATOR：Listen to part of a lecture in a biology class.Para.2FEMALE PROFESSOR：Almost all animals have some way of regulating their body temperature; otherwise, they wouldn’t survive extreme hot or cold conditions.Sweating, panting n.喘气, swimming to cooler or warmer water, ducking into躲进somewhere cool like a burrow n.地洞or a hole under a rock ... these are just a few.And that spot is colder or warmer than the surrounding environment because it's a microclimate.A microclimate is a group of climate conditions that affect a localized area, weather features like temperature, wind, moisture and so on.And when I say localized, I mean really localized, because microclimates can be, as the name suggests, pretty small, even less than a square meter小于1平方米.And microclimates are affected by a huge number of other variables … obviously weather conditions in the surrounding area are a factor.But other aspects of the location like... um... the elevation of the land, the plant life nearby and so on, have a substantial effect on在重大的影响microclimates.And, of course, the human development in the area... um... a road will affect a nearby microclimate.It's also interesting to note that microclimates that are near each other can have very different conditions.In the forest for example, there can be a number of very different microclimates close to each other because of all the variables I just mentioned.Para.3MALE STUDENT：So how does a hole in the ground, a burrow, stay cool in a hot climate?Para.4FEMALE PROFESSOR：Well, since cold air sinks动词，下降, and these spots are shaded, they are usually much cooler than the surrounding area.And these spots are so important because many animals rely on microclimates to regulate their body temperature.Once they get there, their body temperatures decrease very very quickly. The trip to the burrow prevents the squirrel from getting too hot.Para.5MALE STUDENT：But squirrels are mammals right? I thought mammals regulated their temperature internally 副词，内部地…Para.6FEMALE PROFESSOR：Mammals do have the ability to regulate their body temperature … but not all can do it to the same degree, or even the same way.Like when you walk outside on a hot day, you perspire and your body cools itself down, a classic example of how a mammal regulates its own body temperature.But one challenge that squirrels face, well, many small mammals do, is that because of their size, sweating=panting流汗would make them lose too much moisture 名词，水分，湿气，降雨量; they dehydrate.But on the other hand, their small size allows them to fit into适合very tiny spaces.So for small mammals, microclimates can make a big difference有很重大的意义—they rely on 依赖，依靠microclimates for survival.Para.7MALE STUDENT：行动物—they can't control their own body temperature, so I can imagine the effect a microclimate would have on them.Para.8FEMALE PROFESSOR：Yes. Many reptiles and insects rely on microclimates to control their body temperature.A lot of reptiles use burr ows … or stay under rocks to cool down降温. Of course, with reptiles, it's a balancing act.Staying in the heat for too long can lead to problems, but staying in the cold can do the same.So reptiles have to be really precise about真正精确把握where they spend their time, even how they position their bodies.And when I say they are precise, I mean it—some snakes will search out a place under rocks of a specific thickness, because too thin a rock doesn’t keep them cool enough and too thick a rock will cause them to get too cold.That level of precision is critical to the snake for maintaining its body temperature.And even microscopic organisms rely on microclimates for survival. Para.9。

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